Addressing Nitrate
in California’s Drinking Water
With a Focus on Tulare Lake Basin and Salinas Valley Groundwater
Report for the State Water Resources Control Board Report to the Legislature

California Nitrate Project,
Implementation of Senate Bill X2 1
Center for Watershed Sciences
University of California, Davis
http://groundwaternitrate.ucdavis.edu

Prepared for the California State Water Resources Control Board

 The health of our waters
is the principal measure
of how we live on the land.

?Luna Leopold

Addressing Nitrate in California’s Drinking Water
With a Focus on Tulare Lake Basin and Salinas Valley Groundwater
Report for the State Water Resources Control Board Report to the Legislature
This Report and its associated eight Technical Reports were prepared by
Thomas Harter and Jay R. Lund
(Principal Investigators)
Jeannie Darby, Graham E. Fogg, Richard Howitt,
Katrina K. Jessoe, G. Stuart Pettygrove,
James F. Quinn, and Joshua H. Viers
(Co-Investigators)

Dylan B. Boyle, Holly E. Canada, Nicole
DeLaMora, Kristin N. Dzurella, Anna FryjoffHung, Allan D. Hollander, Kristin L. Honeycutt,
Marion W. Jenkins, Vivian B. Jensen, Aaron M.
King, George Kourakos, Daniel Liptzin, Elena M.
Lopez, Megan M. Mayzelle, Alison McNally, Josue
Medellin-Azuara, and Todd S. Rosenstock
With project management support from
Cathryn Lawrence and Danielle V. Dolan

Center for Watershed Sciences • University of California, Davis
Groundwater Nitrate Project, Implementation of Senate Bill X2 1
Prepared for California State Water Resources Control Board • January 2012
http://groundwaternitrate.ucdavis.edu

 Copyright ©2012 The Regents of the University of California
All rights reserved
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Suggested citation: Harter, T., J. R. Lund, J. Darby, G. E.
Fogg, R. Howitt, K. K. Jessoe, G. S. Pettygrove, J. F. Quinn,
J. H. Viers, D. B. Boyle, H. E. Canada, N. DeLaMora, K. N.
Dzurella, A. Fryjoff-Hung, A. D. Hollander, K. L. Honeycutt,
M. W. Jenkins, V. B. Jensen, A. M. King, G. Kourakos, D.
Liptzin, E. M. Lopez, M. M. Mayzelle, A. McNally, J. MedellinAzuara, and T. S. Rosenstock. 2012. Addressing Nitrate in
California's Drinking Water with a Focus on Tulare Lake Basin
and Salinas Valley Groundwater. Report for the State Water
Resources Control Board Report to the Legislature. Center
for Watershed Sciences, University of California, Davis. 78 p.
http://groundwaternitrate.ucdavis.edu.

 Contents
List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  vi
Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Acronyms and Abbreviations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  viii

Executive Summary.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 1
Key Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Summary of Key Findings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Findings: Sources of Nitrate Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Findings: Reducing Nitrate Pollution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Findings: Groundwater Nitrate Pollution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Findings: Groundwater Remediation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Findings: Safe Drinking Water Supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Findings: Regulatory, Funding, and Policy Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Promising Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Safe Drinking Water Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Source Reduction Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Monitoring and Assessment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Funding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1 Introduction .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 9
2 Sources of Groundwater Nitrate .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 15
2.1 Nitrogen Cycle: Basic Concepts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2 Sources of Nitrate Discharge to Groundwater. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Natural Nitrate Sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Human Nitrate Sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Groundwater Nitrate Contributions by Source Category. . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Agricultural Sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Urban and Domestic Sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
General Sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.3 Reducing Nitrate Source Emissions to Groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Reducing Nitrate Loading from Irrigated Cropland and Livestock Operations. . . . . . . . . . . 29
Reducing Nitrate Leaching from Municipal Wastewater Treatment
and Food Processing Plants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Reducing Nitrate Contributions from Leaking Sewer Pipes and Septic Systems. . . . . . . . . . 34
Reducing Nitrate Leaching from Turfgrass in Urban Areas. . . . . . . . . . . . . . . . . . . . . . . . . . 34
Reducing Nitrate Transfer and Loading from Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

 

Addressing Nitrate in California’s Drinking Water 

iii

 3 Impact: Groundwater Nitrate Occurrence.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 35
3.1 Current Groundwater Quality Status. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.2 Cleanup of Groundwater: Groundwater Remediation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.3 Existing Regulatory and Funding Programs for Nitrate Groundwater Contamination. . . . . . . 39
The Dutch Experience. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

4 Impact: Drinking Water Contamination .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 47
4.1 Susceptible Populations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.2 Alternative Water Supply and Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Community Public Water System Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Self-Supplied Households and Local Small Water System Options. . . . . . . . . . . . . . . . . . . . 54
Treatment to Remove Nitrate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Consolidation and Regionalization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.3 Comparison and Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Options for Small Community Public Water Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Options for Self-Supplied Households and Local Small Water Systems. . . . . . . . . . . . . . . . 60
4.4 Cost of Providing Safe Drinking Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

5 Policy Options for Nitrate Source Reduction and Funding. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 63
5.1 Nitrate Source Reduction Policy Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Major Findings: Future Source Reduction Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.2 Funding Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Major Findings: Future Funding Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Payment for Ecosystem Services in New York City. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

6 Promising Solutions.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 67
6.1 Areas of Promising Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Safe Drinking Water Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Source Reduction Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Monitoring and Assessment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Funding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
6.2 Developing an Effective Solution Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Options without Tax Legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Options Requiring Tax or Fee Legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
6.3 Getting Organized. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Informational Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Task Forces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
6.4 Dilemmas for State Action. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

7 Conclusions.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 73
Literature Cited.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 75

iv 

Addressing Nitrate in California’s Drinking Water

 Tables
Table ES-1. Performance of state and agency actions for nitrate groundwater contamination. . . . . . . . 8
Table 1.  

Major sources of groundwater nitrate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Table 2.  

Major nitrogen fluxes to and from cropland. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Table 3.  

Total nitrogen discharge to land and average total nitrogen
concentration in discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Table 4. 

Measures for improving nitrogen use efficiency and decreasing nitrate leaching. . . . . . . 30

Table 5.  

Effect of nitrate load reduction on applied water, revenues,
crop area, and nitrogen application. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Table 6.  

Total number of wells and samples, location, nitrate concentration,
and MCL exceedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Table 7.  

Total groundwater and remediation volume by sub-basin. . . . . . . . . . . . . . . . . . . . . . 41

Table 8a.   Programs and statutes for reducing nitrate contamination in groundwater . . . . . . . . . 42
Table 8b.   Current planning and regulatory programs regarding nitrate in groundwater . . . . . . . 43
Table 9.  

Existing funding sources for safe drinking water . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Table 10.   Number of years until community public water supply sources exceed nitrate MCL. . . . . . 52
Table 11.   Options for community public water systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Table 12.   Options for self-supplied households and local small water systems. . . . . . . . . . . . . . 55
Table 13.   Influence of nitrate concentration on treatment selection. . . . . . . . . . . . . . . . . . . . . . 58
Table 14.   Safe drinking water option costs for household and small water systems . . . . . . . . . . 60
Table 15.   Least cost of short-term alternative water supply for
community public water systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Table 16.   Least cost of long-term alternative water supply for
community public water systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Table 17.   Regulatory options to reduce nitrate contamination to groundwater. . . . . . . . . . . . . . 63
Table 18.   Future state funding options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Table 19.   Performance of state and agency actions for nitrate groundwater contamination . . . . . . 68

 

Addressing Nitrate in California’s Drinking Water 

v

 Figures
Figure ES-1.  Estimated groundwater nitrate loading from major sources. . . . . . . . . . . . . . . . . . . . 3
Figure ES-2.  Overview of cropland input and output. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Figure 1.  

Maximum of raw water nitrate levels in public water systems, 2006–2010. . . . . . .  10

Figure 2.  

Tulare Lake Basin and Salinas Valley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  13

Figure 3.  

Overview of cropland input and output. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  19

Figure 4.  

Current typical fertilization rate for irrigated agricultural cropland. . . . . . . . . . . . .  20

Figure 5.  

Estimated current average nitrogen uptake in harvested crop materials. . . . . . . . . .  22

Figure 6.  

Estimated historical agricultural development . . . . . . . . . . . . . . . . . . . . . . . . . . . .  23

Figure 7.  

Nitrogen applied, nitrogen harvested, and suggested nitrogen
application reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  25

Figure 8.  

Septic-derived nitrate leaching rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  28

Figure 9.  

Overall hazard index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  31

Figure 10.   Decrease in net farm income as a function of nitrogen
efficiency improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  33
Figure 11.   Mean of the time-average nitrate concentration in wells, 2000–2009 . . . . . . . . . . .  38
Figure 12.   Maximum nitrate concentrations, 2000–2009 . . . . . . . . . . . . . . . . . . . . . . . . . . . .  39
Figure 13.   Five-year moving average of wells exceeding the MCL in any given year. . . . . . . . .  40
Figure 14.   Public water system size distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  48
Figure 15.   Estimated locations of unregulated and unmonitored small water systems . . . . . . .  48
Figure 16.   Susceptible populations based on estimated vulnerability and water quality . . . . . . .  49
Figure 17.   Small water systems located near wells with nitrate greater than the MCL. . . . . . . .  50
Figure 18.   Relationship between disadvantaged communities and delivered
water quality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  51
Figure 19.   California drinking water systems treating or blending for nitrate. . . . . . . . . . . . . .  56
Figure 20.   Study area systems treating or blending for nitrate. . . . . . . . . . . . . . . . . . . . . . . . .  57
Figure 21.   Minimum distance from a small water system to a larger system. . . . . . . . . . . . . . .  59
Figure 22.   Lowest-cost alternative supply for community public small water systems. . . . . . . . .  61

vi 

Addressing Nitrate in California’s Drinking Water

 Acknowledgments
Preparation of this Report would not have been
possible without assistance from many people
contributing in many different ways: Staff members
from local, state, and federal agencies and from
non-governmental organizations, consultants, and
academic colleagues were involved in collecting,
organizing, and providing data; exchanging information and ideas; providing technical support and
assistance; and reviewing drafts of the Technical
Reports. Many students and UC Davis staff other
than the authors helped with data entry, literature
research, informal surveys, and report preparation.
We particularly thank the following persons
for their support of this project: Ben Aldridge,
Charles Andrews, Adam Asquith, Denise Atkins,
Amadou Ba, Lisa Babcock, Keith Backman, Carolina
Balazs, Jennifer Baldwin, Tom Barcellos, Stephen
Barnett, Robert H. Beede, Ken Belitz, Daniel Benas,
Jamie Bledsoe, Tim Borel, Tony Boren, John Borkovich, Paul Boyer, Scott Bradford, Beverly Briano, Jess
Brown, Susan Brownstein, Karen Burow, Jim Butler,
Michael Cahn, Kristine Cai, Mary Madison Campbell, Maria de la Paz Carpio-Obeso, Eugene Cassady,
Thomas Chamberlain, Antoine Champetier de Ribes,
Paul Charpentier, Anthony Chavarria, Kathy Chung,
Jennifer Clary, Dennis Clifford, Ron Cole, Tom Coleman, Carol Collar, Paul Collins, Rob Coman, Marc
Commandatore, David Cory, Leslie Cotham, Vern
Crawford, Pamela Creedon, David Crohn, Debbie
Davis, Kevin Day, Michelle De Haan, Susana Deanda,
Ria DeBiase, Jesse Dhaliwal, John Dickey, John
Diener, Danielle V. Dolan, Paige Dulberg, Murray
Einarson, Erik Ekdahl, Brad Esser, Joe Fabry, Bart
Faris, Claudia Faunt, Bret Ferguson, Laurel Firestone, Chione Flegal, Robert Flynn, Lauren Fondahl,
Wayne Fox, Ryan Fox, Carol Frate, Rob Gailey,
James Giannopoulos, Craig Gorman, Lynn Gorman,
Kelly Granger, Sarge Green, David Greenwood, Nick

 

Groenenberg, Amrith Gunasekara, Ellen Hanak, Elise
Harrington, Tim Hartz, Tom Haslebacher, Charles
Hemans, Samantha Hendricks, Tarrah Henrie,
Charles Hewitt, Mike Hickey, Cheryl Higgins, Glenn
Holder, Gerald Horner, Clay Houchin, Ceil Howe
III, Allen Ishida, Chris Johnson, Tim Johnson,
Joel Jones, Gary Jorgensen, Stephen Kafka, Mary
Kaneshiro, Matthew Keeling, Sally Keldgord, Dennis
Keller, Parry Klassen, Ralf Kunkel, William LaBarge,
Tess Lake, Matt Landon, Michael Larkin, Sarah
Laybourne, Armando Leal, Lauren Ledesma, France
Lemieux, Michelle LeStrange, John Letey, Harold
Leverenz, Betsy Lichti, Carl Lischeske, Katherine
Lockhart, Karl Longley, Michael Louie, Jerry Lowry,
Mark Lubell, Patrick Maloney, Elizabeth Martinez,
Marsha Campbell Mathews, Megan Mayzelle, Joe
McGahan, Mike McGinnis, Chiara McKenney, Zachary Meyers, Gretchen Miller, Eli Moore, Jean Moran,
Shannon Mueller, Erin Mustain, Rob Neenan, Dick
Newton, Mart Noel, Ben Nydam, Gavin O’Leary,
Tricia Orlando, David Orth, Eric Overeem, Doug
Parker, Tim Parker, Doug Patterson, Sam Perry, Joe
Prado, Kurt Quade, Jose Antonio Ramirez, Solana
Rice, Clay Rodgers, Michael Rosberg, Jim Ross, Lisa
Ross, Omid Rowhani, Yoram Rubin, Victor Rubin,
Joseph Rust, Blake Sanden, Cheryl Sandoval, Sandra
Schubert, Kurt Schwabe, Seth Scott, Alan Scroggs,
Chad Seidel, Eric Senter, Ann Senuta, David Sholes,
Richard Smith, Rosa Staggs, Scott Stoddard, Daniel
Sumner, Michael Tharp, Sonja Thiede, Kathy Thomasberg, Larry Tokiwa, Thomas Tomich, Andrew Tran,
Thomas Travagli, Kaomine Vang, Leah Walker, Jo
Anna Walker, Emily Wallace, Robin Walton, Greg
Wegis, Frank Wendland, Dennis Westcot, Jim White,
Blake Wilbur, Joel Wiley, Jeff Witte, Craig Wolff,
Steve Wright, Xiaoming Yang, and Janice Zinky.
This work was funded by the State Water
Resources Control Board under agreement number
09-122-250.

Addressing Nitrate in California’s Drinking Water 

vii

 Acronyms and Abbreviations

viii 

AB

Assembly Bill

ac

Acre (about 0.4 hectares)

AF

Acre-foot (about 1,233 cubic meters)

AMBAG

Association of Monterey Bay Area Governments

AQUA

Association of People United for Water

ARRA

American Recovery and Reinvestment Act

AWP

Agricultural Waiver Program

BD

Biological Denitrification

BMP

Best Management Practices

CAA

Cleanup and Abatement Account

CalEPA

California Environmental Protection Agency

CAL FAC

California Food and Agriculture Code

CalNRA

California Natural Resources Agency

CCR

California Code of Regulations

CCR

Consumer Confidence Report

CDBG

Community Development Block Grant

CDFA

California Department of Food and Agriculture

CDPH

California Department of Public Health

CoBank

Cooperative Bank

CPWS

Community Public Water System

CRWA

California Rural Water Association

CV-SALTS

Central Valley Salinity Alternative for Long-Term Sustainability

CVSC

Central Valley Salinity Coalition

CWA

Clean Water Act

CWC

Community Water Center

CWSRF

Clean Water State Revolving Fund

DAC

Disadvantaged Communities

DPEIR

Draft Program Environmental Impact Report (of the Central Valley ILRP)

DPR

California Department of Pesticide Regulation

DWR

California Department of Water Resources

DWSAP

Drinking Water Source Assessment and Protection

DWSRF

Drinking Water State Revolving Fund

EDA

U.S. Economic Development Administration

Addressing Nitrate in California’s Drinking Water

  

EDR

Electrodialysis Reversal

ERG

Expense Reimbursement Grant Program

ERP-ETT

Enforcement Response Policy and Enforcement Targeting Tool

FFLDERS

Feed, Fertilizer, Livestock, Drugs, and Egg Regulatory Services

FMIP

Fertilizing Materials Inspection Program

FP

Food Processors

FREP

Fertilizer Research and Education Program

GAMA

Groundwater Ambient Monitoring and Assessment

Gg

Gigagram (1 million kilograms, about 1,100 tons)

ha

Hectare (about 2.5 acres)

HAC

Housing Assistance Council

HSNC

Historical Significant Non-Compliers

HUD

U.S. Department of Housing and Urban Development

I-Bank

California Infrastructure and Economic Development Bank

ILRP

Irrigated Lands Regulatory Program

IRWM

Integrated Regional Water Management

ISRF

Infrastructure State Revolving Fund

IX

Ion Exchange

KCWA

Kern County Water Agency

kg

Kilogram (about 2.2 pounds)

L

Liter (about 1.06 liquid quarts)

lb

Pound (about 0.45 kilogram)

LLNL

Lawrence Livermore National Lab

MCL

Maximum Contaminant Level

MCWRA

Monterey County Water Resources Agency

mg

Milligram (about 0.00003 ounce)

MHI

Median Household Income

MUN

Municipal or domestic water supply (beneficial use)

NDWC

National Drinking Water Clearinghouse

NMP

Nutrient Management Plan

NPDES

National Pollutant Discharge Elimination System

NRWA

National Rural Water Association

NUE

Nitrogen Use Efficiency

NWG

Nitrate Working Group

Addressing Nitrate in California’s Drinking Water 

ix

 x 

O&M

Operations and Maintenance

OW

EPA’s Office of Water

PES

Payment for Ecosystem Services

PHG

Public Health Goal

PNB

Partial Nutrient Balance

POE

Point-of-Entry (for household water treatment)

Porter-Cologne

Porter-Cologne Water Quality Control Act (California Water Code § 13000 et seq.)

POU

Point-of-Use (for household water treatment)

PPL

Project Priority List

PWS

Public Water System

RCAC

Rural Community Assistance Corporation

RCAP

Rural Community Assistance and Partnership

RO

Reverse Osmosis

RUS

Rural Utilities Service

SB

Senate Bill

SDAC

Severely Disadvantaged Communities

SDWA

Safe Drinking Water Act

SDWSRF

Safe Drinking Water State Revolving Fund

SEP

Supplement Environmental Program

SHE

Self-Help Enterprises

SRF

State Revolving Fund

SSWS

State Small Water System

SV

Salinas Valley

t

Ton (U.S. short ton, about 907 kilograms)

TLB

Tulare Lake Basin

U.S. EPA

United States Environmental Protection Agency

U.S.C.

United States Code

USDA

United States Department of Agriculture

USGS

U.S. Geological Survey

WARMF

Watershed Analysis Risk Management Framework

WDR

Waste Discharge Requirements

WEP

Water Environmental Program

WMP

Waste Management Plan

WWTP

Wastewater Treatment Plant

Addressing Nitrate in California’s Drinking Water

  

Addressing Nitrate in California?s Drinking Water Executive Summary 1

Executive Summary
In 2008, Senate Bill SBX2 1 (Perata) was signed into law
(Water Code Section 83002.5), requiring the State Water
Resources Control Board (State Water Board), in consultation
with other agencies, to prepare a Report to the Legislature to
“improve understanding of the causes of [nitrate] groundwater contamination, identify potential remediation solutions
and funding sources to recover costs expended by the State…
to clean up or treat groundwater, and ensure the provision of
safe drinking water to all communities.” The University of
California prepared this Report under contract with the State
Water Board as it prepares its Report to the Legislature.
This executive summary focuses on major findings
and promising actions. Details can be found in the Main
Report and eight accompanying Technical Reports.

Key Issues
Groundwater is essential to California, and nitrate is one
of the state’s most widespread groundwater contaminants.
Nitrate in groundwater is principally a by-product of nitrogen use, a key input to agricultural production. However,
too much intake of nitrate through drinking water can harm
human health.
California’s governments, communities, and agricultural industry have struggled over nitrate contamination
for decades. The California Department of Public Health
(CDPH) has set the maximum contaminant level (MCL)
for nitrate in drinking water at 45 milligrams per liter (as
nitrate). Nitrate concentrations in public drinking water
supplies exceeding the MCL require water system actions to
provide safe drinking water.
For this study, the four-county Tulare Lake Basin and
the Monterey County portion of the Salinas Valley are
examined. About 2.6 million people in these regions rely
on groundwater for drinking water. The study area includes
four of the nation’s five counties with the largest agricultural
production. It represents about 40% of California’s irrigated
cropland (including 80 different crops) and over half of
California’s dairy herd. Many communities in the area are
among the poorest in California and have limited economic
means or technical capacity to maintain safe drinking water
given threats from nitrate and other contaminants.

2 

Summary of Key Findings
1  Nitrate problems will likely worsen for several

decades. For more than half a century, nitrate from
fertilizer and animal waste have infiltrated into Tulare Lake Basin and Salinas Valley aquifers. Most
nitrate in drinking water wells today was applied to
the surface decades ago.

2  Agricultural fertilizers and animal wastes applied

to cropland are by far the largest regional sources
of nitrate in groundwater. Other sources can be locally relevant.

3   Nitrate loading reductions are possible, some at

modest cost. Large reductions of nitrate loads to
groundwater can have substantial economic cost.

4   Direct remediation to remove nitrate from large

groundwater basins is extremely costly and not
technically feasible. Instead, “pump-and-fertilize”
and improved groundwater recharge management
are less costly long-term alternatives.

5   Drinking water supply actions such as blending,

treatment, and alternative water supplies are most
cost-effective. Blending will become less available in
many cases as nitrate pollution continues to spread.

6   Many small communities cannot afford safe drink-

ing water treatment and supply actions. High fixed
costs affect small systems disproportionately.

7   The most promising revenue source is a fee on

nitrogen fertilizer use in these basins. A nitrogen
fertilizer use fee could compensate affected small
communities for mitigation expenses and effects of
nitrate pollution.

8  Inconsistency and inaccessibility of data prevent

effective and continuous assessment. A statewide
effort is needed to integrate diverse water-related
data collection activities by many state and local
agencies.

Addressing Nitrate in California’s Drinking Water / Executive Summary 

 Nitrate in groundwater poses two major problems
and risks:
•  Public health concerns for those exposed to nitrate
contamination in drinking water; in California’s Tulare
Lake Basin and Salinas Valley, roughly 254,000 people
are currently at risk for nitrate contamination of their
drinking water. Of these, 220,000 are connected to
community public (>14 connections) or state small
water systems (5–14 connections), and 34,000 are
served by private domestic wells or other systems
smaller than the threshold for state or county regulation and which are largely unmonitored.
•  Financial costs of nitrate contamination include
additional drinking water treatment, new wells,
monitoring, or other safe drinking water actions; over
1.3 million people are financially susceptible because
nitrate in raw source water exceeds the MCL, requiring
actions by drinking water systems. Nitrate contamination of drinking water sources will continue to increase
as nitrogen from fertilizer, manure, and other sources
applied in the last half century continues to percolate
downward and flow toward drinking water wells.

Findings: Sources of Nitrate Pollution

Findings: Reducing Nitrate Pollution
Options for reducing nitrate pollution were identified for all
sources. For cropland, where less than 40% of applied nitrogen is removed by crop harvest, 10 management measures
(and 50 practices and technologies to achieve these management objectives) were reviewed that can reduce—but not
eliminate—nitrate leaching to groundwater. These fall into
four categories:
1.  Design and operate irrigation and drainage systems to
reduce deep percolation.
2.  Manage crop plants to capture more nitrogen and decrease deep percolation.
3.  Manage nitrogen fertilizer and manure to increase crop
nitrogen use efficiency.
4.  Improve storage and handling of fertilizers and manure
to decrease off-target discharge.

WWTP-FP 3.2
Lagoons 0.2
Corrals 0.5

Septic 2.3
Urban 0.9

Within the study area, human-generated nitrate sources to
groundwater include (Figure ES-1):
•  cropland (96% of total), where nitrogen applied to crops,
but not removed by harvest, air emission, or runoff, is
leached from the root zone to groundwater. Nitrogen intentionally or incidentally applied to cropland includes
synthetic fertilizer (54%), animal manure (33%), irrigation source water (8%), atmospheric deposition (3%),
and wastewater treatment and food processing facility
effluent and associated solids (2%) (Figure ES-2);
•  percolation of wastewater treatment plant (WWTP)
and food processing (FP) wastes (1.5% of total);
•  leachate from septic system drainfields (1% of total);

Cropland 200

•  urban parks, lawns, golf courses, and leaky sewer
systems (less than 1% of total); and
•  recharge from animal corrals and manure storage
lagoons (less than 1% of total);
•  downward migration of nitrate-contaminated water
via wells (less than 1% of total).

 

Figure ES-1. Estimated groundwater nitrate loading from major
sources within the Tulare Lake Basin and Salinas Valley, in Gg
nitrogen per year (1 Gg = 1,100 t).

Addressing Nitrate in California’s Drinking Water / Executive Summary 

3

 Cropland Nitrogen Inputs

Irrigation water 29

Atmospheric
losses 38

Atmospheric deposition 12

Synthetic fertilizer 204

Runoff 18

Leaching to groundwater 195

Land-applied biosolids 4.8
Land-applied liquids,
WWTP-FP 3.4
Land-applied manure from
CAFOs other than dairy 0.9

Land-applied dairy manure 127

Harvest 130

Cropland Nitrogen Outputs

Note: No mass balance was performed on 0.17 million ha (0.4 million ac) of nitrogen-fixing alfalfa, which is estimated to contribute an
additional 5 Gg N/yr to groundwater. Groundwater nitrate loading from all non-cropland sources is about 8 Gg N/yr.

Figure ES-2. Overview of cropland input and output (Gg N/yr) in the study area (Tulare Lake Basin and Salinas Valley) in 2005. The left
half of the pie chart represents total nitrogen inputs to 1.27 million ha (3.12 million ac) of cropland, not including alfalfa. The right half
of the pie chart represents total nitrogen outputs with leaching to groundwater estimated by difference between the known inputs and
the known outputs. Source: Viers et al. 2012.

4 

Addressing Nitrate in California’s Drinking Water / Executive Summary 

 Some of the needed improvements in nitrogen use
efficiency by crops will require increased operating costs,
capital improvements, and education. For some cropland,
the high economic costs of nitrate source reduction sufficient
to prevent groundwater degradation will likely hinder strict
compliance with the state’s current anti-degradation policy
for groundwater (State Water Board Resolution 68-16).

Findings: Groundwater Nitrate Pollution
Groundwater nitrate data were assembled from nearly two
dozen agencies and other sources (100,000 samples from
nearly 20,000 wells). Of the 20,000 wells, 2,500 are frequently
sampled public water supply wells (over 60,000 samples). In
these public supply wells, about 1 in 10 raw water samples
exceed the nitrate MCL. Apart from the recently established
Central Valley dairy regulatory program in the Tulare Lake
Basin, there are no existing regular well sampling programs
for domestic and other private wells.
The largest percentages of groundwater nitrate MCL
exceedances are in the eastern Tulare Lake Basin and in the
northern, eastern, and central Salinas Valley, where about
one-third of tested domestic and irrigation wells exceed the
MCL. These same areas have seen a significant increase in
nitrate concentrations over the past half century, although
local conditions and short-term trends vary widely.
Travel times of nitrate from source to wells range from a
few years to decades in domestic wells, and from years to many
decades and even centuries in deeper production wells. This
means that nitrate source reduction actions made today may
not affect sources of drinking water for years to many decades.

Findings: Groundwater Remediation
Groundwater remediation is the cleanup of contaminated
groundwater to within regulatory limits. Traditional pumpand-treat and in-place approaches to remediation, common
for localized industrial contamination plumes, would cost
billions of dollars over many decades to remove nitrate from
groundwater in the Tulare Lake Basin and Salinas Valley.
Timely cleanup of basin-scale nitrate contamination is not
technically feasible.
Instead, long-term remediation by “pump-and-fertilize” would use existing agricultural wells to gradually remove
nitrate-contaminated groundwater and treat the water by
ensuring nitrate uptake by crops through appropriate nutrient and irrigation water management. Improved groundwater recharge management would provide clean groundwater
recharge to mix with irrigation water recharge and partially
mitigate nitrate levels in groundwater regionally.

 

Removal or reduction of contamination sources must
accompany any successful remediation effort. Combining
“pump-and-fertilize” with improved groundwater recharge
management is more technically feasible and cost-effective.

Findings: Safe Drinking Water Supply
Nitrate contamination is widespread and increasing.
Groundwater data show that 57% of the current population
in the study area use a community public water system with
recorded raw (untreated) nitrate concentrations that have
exceeded the MCL at least once between 2006 and 2010.
Continued basin-wide trends in nitrate groundwater concentration may raise the affected population to nearly 80% by
2050. Most of this population is protected by water system
treatment, or alternative wells, at additional cost. But about
10% of the current population is at risk of nitrate contamination in their delivered drinking water, primarily in small
systems and self-supplied households.
No single solution will fit every community affected by
nitrate in groundwater. Each affected water system requires
individual engineering and financial analyses.
Communities served by small systems vulnerable to
nitrate contamination can (a) consolidate with a larger system
that can provide safe drinking water to more customers; (b)
consolidate with nearby small systems into a new single
larger system that has a larger ratepayer base and economies
of scale; (c) treat the contaminated water source; (d) switch
to surface water; (e) use interim bottled water or point-ofuse treatment until an approved long-term solution can be
implemented; (f) drill a new well; or (g) blend contaminated
wells with cleaner sources, at least temporarily.
There is significant engineering and economic potential for consolidating some systems. Consolidation can often
permanently address nitrate problems, as well as many other
problems faced by small water systems.
Solutions for self-supplied households (domestic well)
or local small water systems (2–4 connections) affected by
nitrate contamination are point-of-use (POU) or point-of-entry
(POE) treatment and drilling a new or deeper well, albeit with
no guarantee for safe drinking water.
Additional costs for safe drinking water solutions to
nitrate contamination in the Tulare Lake Basin and Salinas
Valley are roughly $20 and $36 million per year for the
short- and long-term solutions, respectively. About $17 to
$34 million per year will be needed to provide safe drinking
water for 85 identified community public and state small
water systems in the study area that exceed the nitrate drinking water MCL (serving an estimated 220,000 people). The
annualized cost of providing nitrate-compliant drinking water

Addressing Nitrate in California’s Drinking Water / Executive Summary 

5

 to an estimated 10,000 affected rural households (34,000
people) using private domestic wells or local small water
systems is estimated to be at least $2.5 million for point-of-use
treatment for drinking use only. The total cost for alternative
solutions translates to $80 to $142 per affected person per
year, $5 to $9 per irrigated acre per year, or $100 to $180 per
ton of fertilizer nitrogen applied in these groundwater basins.

Findings: Regulatory, Funding,
and Policy Options
To date, regulatory actions have been insufficient to control
nitrate contamination of groundwater. Many options exist to
regulate nitrate loading to groundwater, with no ideal solution.
Nitrate source reductions will improve drinking water quality
only after years to decades. Fertilizer regulations have lower
monitoring and enforcement costs and information requirements than do nitrate leachate regulations, but they achieve
nitrate reduction targets less directly. Costs to farmers can be
lower with fertilizer fees or market-based regulations than
with technology mandates or prescriptive standards. Marketbased approaches may also encourage the development and
adoption of new technologies to reduce fertilizer use.
Current funding programs cannot ensure safe drinking water in the Salinas Valley and Tulare Lake Basin. Small
water system costs are high, and some of these systems
already face chronic financial problems. Most current state
funding for nitrate contamination problems is short term.
Little funding is provided for regionalization and consolidation of drinking water systems. Policy options exist for
long-term funding of safe drinking water, but all existing
and potential options will require someone to bear the costs.

Promising Actions
Addressing groundwater nitrate contamination requires
actions in four areas: (a) safe drinking water actions for
affected areas, (b) reducing sources of nitrate contamination
to groundwater, (c) monitoring and assessment of groundwater and drinking water, and (d) revenues to help fund
solutions. Promising actions for legislative and state agency
consideration in these areas appear below (see also Table
ES-1). Starred (*) actions do not appear to require legislative
action, but might benefit from it.

Safe Drinking Water Actions (D)
Safe drinking water actions are the most effective and
economical short- and long-term approach to address
nitrate contamination problems in the Tulare Lake Basin
and Salinas Valley. These actions apply especially to small
and self-supplied household water systems, which face the

6 

greatest financial and public health problems from nitrate
groundwater contamination.
D1: Point-of-Use (POU) Treatment Option. CDPH reports
on how to make economical household and point-of-use
treatment for nitrate contamination an available and permanent solution for small water systems.*
D2: Small Water System Task Force. CalEPA and CDPH
convene an independently led Task Force on Small Water
Systems that would report on problems and solutions of
small water and wastewater systems statewide as well as the
efficacy of various state, county, and federal programs to aid
small water and wastewater systems. Many nitrate contamination problems are symptomatic of the broad problems of
small water and wastewater systems.*
D3: Regional Consolidation. CDPH and counties provide
more legal, technical, and funding support for preparing
consolidation of small water systems with nearby larger
systems and creating new, regional safe drinking water solutions for groups of small water systems, where cost-effective.*
D4: Domestic Well Testing. In areas identified as being
at risk for nitrate contamination by the California Water
Boards, as a public health requirement, CDPH (a) mandates
periodic nitrate testing for private domestic wells and local
and state small systems and (b) requires disclosure of recent
well tests for nitrate contamination on sales of residential
property. County health departments also might impose
such requirements.
D5: Stable Small System Funds. CDPH receives more
stable funding to help support capital and operation and
maintenance costs for new, cost-effective and sustainable
safe drinking water solutions, particularly for disadvantaged
communities (DACs).

Source Reduction Actions (S)
Reducing nitrate loading to groundwater is possible, sometimes
at a modest expense. But nitrate source reduction works slowly
and cannot effectively restore all affected aquifers to drinking
water quality. Within the framework of Porter-Cologne, unless
groundwater were to be de-designated as a drinking water
source, reduction of nitrate loading to groundwater is required
to improve long-term water quality. The following options
seem most promising to reduce nitrate loading.
S1: Education and Research. California Department of Food
and Agriculture (CDFA), in cooperation with the University
of California and other organizations, develops and delivers a comprehensive educational and technical program to
help farmers improve efficiency in nitrogen use (including
manure) and reduce nitrate loading to groundwater. This

Addressing Nitrate in California’s Drinking Water / Executive Summary 

 could include a groundwater nitrate–focused element for the
existing CDFA Fertilizer Research and Education Program,
including “pump-and-fertilize” remediation and improved
recharge options for groundwater cleanup.*
S2: Nitrogen Mass Accounting Task Force. CalEPA establishes a Task Force, including CDFA, to explore nitrogen mass
balance accounting methods for regulating agricultural land
uses in areas at risk for nitrate contamination, and to compare
three long-term nitrogen source control approaches: (a) a cap
and trade system; (b) farm-level nutrient management plans,
standards, and penalties; and (c) nitrogen fertilizer fees.*
S3: Fertilizer Excise Fee. Significantly raising the cost of
commercial fertilizer through a fee or excise tax would fund
safe drinking water actions and monitoring and give further
incentive to farmers for reducing nitrate contamination. An
equivalent fee or excise tax could be considered for organic
fertilizer sources (manure, green waste, wastewater effluent,
biosolids, etc.).
S4: Higher Fertilizer Fee in Areas at Risk. Areas declared
to be at risk for nitrate contamination might be authorized
to maintain a higher set of excise fees on nitrogen fertilizer
applications (including synthetic fertilizer, manure, waste
effluent, biosolids, and organic amendments), perhaps as
part of a local safe drinking water compensation agreement.

Monitoring and Assessment (M)
Monitoring and assessment is needed to better assess the
evolving nitrate pollution problem and the effectiveness of
safe drinking water and nitrate source loading reduction
actions. Such activities should be integrated with other state
agricultural, environmental, and land use management;
groundwater data; and assessment programs (source loading
reduction actions)—along with other drinking water, treatment, and wastewater management programs (safe drinking
water actions).
M1: Define Areas at Risk. Regional Water Boards designate
areas where groundwater sources of drinking water are at risk
of being contaminated by nitrate.*
M2: Monitor at-Risk Population. CDPH and the State Water
Board, in coordination with DWR and CDFA, issue a report
every 5 years to identify populations at risk of contaminated
drinking water and to monitor long-term trends of the state’s
success in providing safe drinking water as a supplement to
the California Water Plan Update.*
M3: Learn from Department of Pesticide Regulation
Programs. CalEPA and CDFA examine successful DPR data
collection, analysis, education, and enforcement programs
for lessons in managing nitrogen and other agricultural

 

contaminants, and consider expanding or building upon the
existing DPR program to include comprehensive nitrogen use
reporting to support nitrate discharge management.*
M4: Groundwater Data Task Force. CalEPA , in coordination with CalNRA and CDPH, convenes an independently led
State Groundwater Data Task Force to examine the efficacy of
current state and local efforts to collect, maintain, report, and
use groundwater data for California’s groundwater quality
and quantity problems.
M5: Groundwater Task Force. CalEPA, CalNRA, and CDPH
maintain a joint, permanent, and independently led State
Groundwater Task Force to periodically assess and coordinate state technical and regulatory groundwater programs in
terms of effectiveness at addressing California’s groundwater
quality and quantity problems. These reports would be
incorporated into each California Water Plan Update.*

Funding (F)
Little effective action can occur without funding. Four
funding options seem most promising, individually or in
combination. State funding from fees on nitrogen or water
use, which directly affect nitrate groundwater contamination,
seem particularly promising and appropriate.
F1: Mill Fee. Increase the mill assessment rate on nitrogen
fertilizer to the full authorized amount (CAL. FAC Code Section
14611). This would raise roughly $1 million/year statewide
and is authorized for fertilizer use research and education.*
F2: Local Compensation Agreements. Regional Water
Boards can require and arrange for local compensation of
affected drinking water users under Porter-Cologne Act Water
Code Section 13304. Strengthening existing authority, the
Legislature could require that a Regional Water Board finding
that an area is at risk of groundwater nitrate contamination
for drinking water be accompanied by a cleanup and abatement order requiring overlying, current sources of nitrate to
financially support safe drinking water actions acceptable to
the local County Health Department. This might take the
form of a local “liability district.”*
F3: Fertilizer Excise Fee. Introduce a substantial fee on
nitrogen fertilizer sales or use, statewide or regionally, to fund
safe drinking water actions, nitrate source load reduction
efforts, and nitrate monitoring and assessment programs.
F4: Water Use Fee. A more comprehensive statewide fee
on water use could support many beneficial activities. Some
of such revenues could fund management and safe drinking water actions in areas affected by nitrate contamination,
including short-term emergency drinking water measures for
disadvantaged communities.

Addressing Nitrate in California’s Drinking Water / Executive Summary 

7

 Table ES-1. Likely performance of promising state and agency actions for nitrate groundwater contamination.

Action

Safe Drinking Water

Groundwater
Degradation

Economic Cost

No Legislation Required
Safe Drinking Water Actions
D1: Point-of-Use Treatment Option for Small Systems +
D2: Small Water Systems Task Force +
D3: Regionalization and Consolidation of Small Systems +

♦♦

low

♦

low

♦♦

low

Source Reduction Actions
S1: Nitrogen/Nitrate Education and Research +

♦♦♦

low–moderate

♦♦

low

♦♦♦

♦♦♦

low

♦

♦

low

♦♦

low

S2: Nitrogen Accounting Task Force +

Monitoring and Assessment
M1: Regional Boards Define Areas at Risk +
M2: CDPH Monitors At-Risk Population +
M3: Implement Nitrogen Use Reporting +
M4: Groundwater Data Task Force +

♦

♦

low

M5: Groundwater Task Force +

♦

♦

low

♦♦♦

low

♦

moderate

Funding
F1: Nitrogen Fertilizer Mill Fee
F2: Local Compensation Agreements for Water +

♦♦

New Legislation Required
D4: Domestic Well Testing *
D5: Stable Small System Funds

♦♦

low

♦

moderate

Non-tax legislation could also strengthen and augment existing authority.

Fiscal Legislation Required
Source Reduction
S3: Fertilizer Excise Fee

♦♦

♦

moderate

♦

♦

moderate

F3: Fertilizer Excise Fee

♦♦

♦♦

moderate

F4: Water Use Fee

♦♦

♦♦

moderate

S4: Higher Fertilizer Fee in Areas at Risk

Funding Options

♦ Helpful
♦♦ Effective
♦♦♦ Essential
+ Legislation would strengthen.
* County health departments may have authority; CDPH requires legislation.

8 

Addressing Nitrate in California’s Drinking Water / Executive Summary 

 1 Introduction
The development of California’s tremendous economy has not
been without environmental costs. Since early in the twentieth
century, nitrate from agricultural and urban activities has slowly
infiltrated into groundwater. Nitrate has accumulated and spread
and will continue to make its way into drinking water supplies.
The time lag between the application of nitrogen to the landscape
and its withdrawal at household and community public water
supply wells, after percolating through soils and groundwater,
commonly extends over decades.
This Report is an overview of groundwater contamination by nitrate in the Tulare Lake Basin and Salinas Valley.
We examine the extent, causes, consequences, and costs
of this contamination, as well as how it will likely develop
over time. We also examine management and policy actions
available for this problem, including possible nitrate source
reduction, provisions for safe drinking water, monitoring and
assessment, and aquifer remediation actions. The costs and
institutional complexities of these options, and how they
might be funded, also are addressed.
Addressing nitrate contamination problems in the
Tulare Lake Basin and Salinas Valley will require decades
to resolve, driven by the pace of groundwater flow and the
response times of humans and institutions on the surface.
Nitrate in drinking water today is a legacy contaminant, but
years and decades from now the nitrate in drinking water
will be from today’s discharges. Assistance and management
to improve drinking water supplies in response to nitrate
contamination is a central and urgent policy issue for the
State of California. Another major policy issue is the inevitability of widespread groundwater degradation for decades to
come, despite even heroic (and ultimately expensive) efforts
to reduce nitrate loading into aquifers. This introduction
attempts to put the issue in a larger context.
Groundwater is essential to California. Groundwater is vital for California’s agricultural, industrial, urban,
and drinking water uses. Depending on drought conditions,
groundwater provides between one-third and nearly one-half
of the state’s water supplies. As a source of drinking water,
groundwater serves people from highly dispersed rural
communities to densely populated cities. More than 85%

 

of community public water systems in California (serving
30 million residents) rely on groundwater for at least part
of their drinking water supply. In addition, approximately 2
million residents rely on groundwater from either a private
domestic well or a smaller water system not regulated by the
state (State Water Board 2011). Intensive agricultural production, population growth, and—indirectly—partial restoration
of environmental instream flows have led to groundwater
overdraft (Hanak et al. 2011). More protective health-based
water quality standards for naturally occurring water quality
constituents and groundwater contamination from urban and
agricultural activities pose serious challenges to managing the
state’s drinking water supply.
Nitrate is one of California’s most widespread
groundwater contaminants. Nitrate is among the most
frequently detected contaminants in groundwater systems
around the world, including the extensively tapped aquifers in
California’s Central Valley and Salinas Valley (Figure 1) (Spalding and Exner 1993; Burow et al. 2010; Dubrovsky et al. 2010;
MCWRA 2010; Sutton et al. 2011). Nitrate contamination
poses an environmental health risk because many rural areas
obtain drinking water from wells that are often shallow and
vulnerable to contamination (Guillette and Edwards 2005; Fan
and Steinberg 1996).
High levels of nitrate affect human health. Infants
who drink water (often mixed with baby formula) containing
nitrate in excess of the maximum contaminant level (MCL)
for drinking water may quickly become seriously ill and, if
untreated, may die because high nitrate levels can decrease the
capacity of an infant’s blood to carry oxygen (methemoglobinemia, or “blue baby syndrome”). High nitrate levels may also
affect pregnant women and adults with hereditary cytochrome
b5 reductase deficiency. In addition, nitrate and nitrite ingestion in humans has been linked to goitrogenic (anti-thyroid)
actions on the thyroid gland (similar to perchlorate), fatigue
and reduced cognitive functioning due to chronic hypoxia,
maternal reproductive complications including spontaneous
abortion, and a variety of carcinogenic outcomes deriving
from N-nitrosamines formed via gastric nitrate conversion in
the presence of amines (Ward et al. 2005).

Addressing Nitrate in California’s Drinking Water / Introduction 

9

 Nitrate is part of the natural nitrogen cycle in the
environment. Groundwater nitrate is part of the global
nitrogen cycle. Like other key elements essential for life,
nitrogen flows through the environment in a dynamic cycle
that supports organisms ranging from microbes to plants to
animals. Plants require nitrogen for growth, and scarcity of
fixed soil nitrogen often limits plant growth. Specialized microorganisms can fix atmospheric elemental nitrogen and make it
available for plants to use for photosynthesis and growth. The
natural nitrogen cycle is a dynamic balance between elemental
nitrogen in the atmosphere and reactive forms of nitrogen
moving through the soil-plant-animal-water-atmosphere cycle
of ecosystems globally. Production of synthetic nitrogen fertilizer has disrupted this balance.

Nitrogen is key to global food production. Modern
agricultural practices, using synthetically produced nitrogen
fertilizer, have supplied the nitrogen uses of plants to increase
food, fiber, feed, and fuel production for consumption by
humans and livestock. Agricultural production is driven by
continued global growth in population and wealth, which
increases demand for agricultural products, particularly highvalue agricultural products such as those produced in California. Global food, feed, and fiber demands are anticipated
to increase by over 70% over the next 40 years (Tilman et al.
2002; De Fraiture et al. 2010).

Figure 1. Maximum reported raw-level nitrate concentration in community public water systems and state-documented state small water
systems, 2006–2010. Source: CDPH PICME WQM Database (see Honeycutt et al. 2011).

10 

Addressing Nitrate in California’s Drinking Water / Introduction

 Intensive agriculture and human activities have
increased nitrate concentrations in the environment.
Greater use of nitrogen-based fertilizers, soil amendments
such as manure, and nitrogen-fixing cover crops add nitrogen
to deficient soils and dramatically raise crop yields. Technological advances in agriculture, manufacturing, and urban
practices have increased levels of reactive forms of nitrogen,
including nitrate, released into the atmosphere, into surface
water, and into groundwater. The nearly 10-fold increase of
reactive nitrogen creation related to human activities over the
past 100 years (Galloway and Cowling 2002) has caused a
wide range of adverse ecological and environmental impacts
(Davidson et al. 2012).
The most remarkable impacts globally include the leaching of nitrate to groundwater; the eutrophication of surface
waters and resultant marine “dead zones”; atmospheric deposition that acidifies ecosystems; and the emission of nitrogen
oxides (NOx) that deplete stratospheric ozone (Keeney and
Hatfield 2007; Beever et al. 2007; Foley et al. 2005). These
widespread environmental changes also can threaten human
health (Galloway et al. 2008; Guillette and Edwards 2005;
Galloway et al. 2004; Townsend et al. 2003; Vitousek et al.
1997; Fan and Steinberg 1996; Jordan and Weller 1996).
California has decentralized regulatory responsibility for groundwater nitrate contamination. Nitrate contamination of groundwater affects two state agencies most directly.
Sources of groundwater nitrate are regulated under California’s
Porter-Cologne Water Quality Control Act (Porter-Cologne)
administered through the State Water Resources Control
Board (State Water Board) and the Regional Water Quality
Control Boards (Regional Water Boards). State Water Board
Resolution 88-63 designates drinking water as a beneficial use
in nearly all of California’s major aquifers. Under the PorterCologne Act, dischargers to groundwater are responsible, first,
for preventing adverse effects on groundwater as a source of
drinking water, and second, for cleaning up groundwater
when it becomes contaminated.
Drinking water in public water systems (systems with
at least 15 connections or serving at least 25 people for 60
or more days per year) is regulated by CDPH under the
federal Safe Drinking Water Act of 1972 (SWDA). CDPH
has set the nitrate MCL in drinking water at 45 mg/L (10

 

mg/L as nitrate-N). If nitrate levels in public drinking water
supplies exceed the MCL standard, mitigation measures must
be employed by water purveyors to provide a safe supply of
drinking water to the population at risk.
The California Department of Food and Agriculture
(CDFA) and the Department of Water Resources (DWR) also
have roles in nitrate management. The DWR is charged with
statewide planning and funding efforts for water supply and
water quality protection, including the funding of Integrated
Regional Water Management Plans and DWR’s management
of urban and agricultural water use efficiency. CDFA collects
data, funds research, and promotes education regarding the
use of nitrogen fertilizers and other nutrients in agriculture.
SBX2 1 Nitrate in Groundwater Report to Legislature. In 2008, the California legislature enacted Senate
Bill SBX2 1 (Perata), which created California Water Code
Section 83002.5. The bill requires the State Water Board
to prepare a Report to the Legislature (within 2 years
of receiving funding) to “improve understanding of the
causes of [nitrate] groundwater contamination, identify potential remediation solutions and funding sources
to recover costs expended by the state for the purposes of
this section to clean up or treat groundwater, and ensure
the provision of safe drinking water to all communities.”
Specifically, the bill directs the State Water Board to
identify sources, by category of discharger, of groundwater contamination due to nitrate in the pilot project
basins; to estimate proportionate contributions to
groundwater contamination by source and category of
discharger; to identify and analyze options within the
board’s current authority to reduce current nitrate levels
and prevent continuing nitrate contamination of these
basins and estimate the costs associated with exercising existing authority; to identify methods and costs
associated with the treatment of nitrate contaminated
groundwater for use as drinking water; to identify
methods and costs to provide an alternative water
supply to groundwater reliant communities in each pilot
project basin; to identify all potential funding sources to
provide resources for the cleanup of nitrate, groundwater
treatment for nitrate, and the provision of alternative
drinking water supply, including, but not limited to,
State bond funding, federal funds, water rates, and fees
or fines on polluters; and to develop recommendations
for developing a groundwater cleanup program for the
Central Valley Water Quality Control Region and the
Central Coast Water Quality Control Region based upon
pilot project results.

Addressing Nitrate in California’s Drinking Water / Introduction 

11

 The bill designates the groundwater basins of the
Tulare Lake Basin region and the Monterey County portion of
the Salinas Valley as the selected pilot project areas. In June
2010, the State Water Board contracted with the University
of California, Davis, to prepare this Report for the Board as
background for its Report to the Legislature.
Project area is relevant to all of California. The
project area encompasses all DWR Bulletin 118 designated
groundwater sub-basins of the Salinas River watershed that
are fully contained within Monterey County, and the Pleasant
Valley, Westside, Tulare Lake Bed, Kern, Tule River, Kaweah
River, and Kings River groundwater sub-basins of the Tulare
Lake Basin. The study area—2.3 million ha (5.7 million ac) in
size—is home to approximately 2.65 million people, almost
all of whom rely on groundwater as a source of drinking water.
The study area includes four of the nation’s five counties with
the largest agricultural production; 1.5 million ha (3.7 million
ac) of irrigated cropland, representing about 40% of California’s irrigated cropland; and more than half of California’s dairy
herd. More than 80 different crops are grown in the study
area (Figure 2). This is also one of California’s poorest regions:
many census blocks with significant population belong to the
category of severely disadvantaged communities (less than
60% of the state’s median household income), and many of
the remaining populated areas are disadvantaged communities (less than 80% of the state’s median household income).
These communities have little economic means and technical
capacity to maintain safe public drinking water systems given
contamination from nitrate and other contaminants in their
drinking water sources.
Report excludes assessment of public health standards for nitrate. Public health and appropriateness of the
drinking water limits are prescribed by CDPH and by U.S.
EPA under SDWA. The scope of SBX2 1 precluded a review of
the public health aspects or a review of the appropriateness of
the nitrate MCL, although this is recognized as an important
and complex aspect of the nitrate contamination issue (Ward
et al. 2005).

12 

“Report for the State Water Resources Control
Board Report to the Legislature” and supporting Technical Reports. This Report for the State Water Board Report
to the Legislature (“Report”) has been provided in fulfillment
of the University of California, Davis, contract with the State
Water Board. This Report provides an overview of the goals
of the research, methods, and key findings of our work, and
is supported by eight related Technical Reports (Harter et
al. 2012; Viers et al. 2012; Dzurella et al. 2012; Boyle et al.
2012; King et al. 2012; Jensen et al. 2012; Honeycutt et al.
2012; and Canada et al. 2012). The Technical Reports provide
detailed information on research methods, research results,
data summaries, and accompanying research analyses that are
important for evaluating our results and findings and for applying our approach and results to other groundwater basins.
The Report takes a broad yet quantitative view of the
groundwater nitrate problem and solutions for this area and
reflects collaboration among a diverse, interdisciplinary team
of experts. In its assessment, the Report spans institutional
and governmental boundaries. The Report quantifies the
diverse range of sources of groundwater nitrate. It reviews
the current groundwater quality status in the project area by
compiling and analyzing all available data from a variety of
institutions. It then identifies source reduction, groundwater
remediation, drinking water treatment, and alternative drinking water supply alternatives, along with the costs of these
options. Descriptions and summaries are also included of
current and potential future funding options and regulatory
measures to control source loading and provide safe drinking water, along with their advantages, disadvantages, and
potential effectiveness.
This set of Reports is the latest in a series of reports on
nitrate contamination in groundwater beginning in the 1970s
(Schmidt 1972; Report to Legislature 1988; Dubrovsky et al.
2010; U.S. EPA 2011). This Report has some of the same
conclusions as previous reports but takes a much broader
perspective, contains more analysis, and perhaps provides a
wider range of promising actions.

Addressing Nitrate in California’s Drinking Water / Introduction

 Figure 2. The Tulare Lake Basin (TLB) and Salinas Valley (SV) are the focus of this study. The study area represents 40% of California’s
diverse irrigated agriculture and more than half of its confined animal farming industry. It is home to 2.6 million people, with a significant
rural population in economically disadvantaged communities. Source: Viers et al. 2012.

 

Addressing Nitrate in California’s Drinking Water / Introduction 

13

 Source: Dubrovsky et al. 2010.

14 

Addressing Nitrate in California’s Drinking Water / Introduction

 2 Sources of Groundwater Nitrate
2.1 Nitrogen Cycle: Basic Concepts
Nitrogen is an essential element for all living organisms.
Nitrogen cycles through the atmosphere, hydrosphere, and
biosphere. The dominant gas (78%) in the atmosphere is highly
stable (inert) N2 gas. Biological nitrogen fixation transforms
N2 gas into ammonia (NH3), which is rapidly converted to the
forms of nitrogen needed for plant growth. Nitrogen fixation
is performed only by specialized soil and aquatic microbes.
Other living organisms cannot use inert atmospheric N2
directly but rely on accumulated soil organic matter, plants,
animals, and microbial communities for nitrogen.
Soil nitrogen is most abundant in the organic form
(Norg). Mineralization is a suite of processes performed by soil
microbes that converts organic nitrogen to inorganic forms of
nitrogen. The rates of mineralization depend on the environmental conditions such as temperature, moisture, pH, and
oxygen content, as well as the type of organic matter available.
The first product of mineralization is ammonium (NH4+ ), but
under aerobic conditions, microbes can convert ammonium
(NH4+ ) first to nitrite (NO2–) and then to nitrate (NO3–). Most
plants use nitrate or ammonium as their preferred source
of nitrogen (White 2006). Immobilization is the reverse of
mineralization in that soil ammonium and nitrate are taken
up by soil organisms and plants and converted into Norg.
The ultimate fate of “reactive” nitrogen (organic nitrogen, ammonium, nitrate, ammonia, nitrous oxide, etc.) is to
return back to the atmosphere as N2. For nitrate, this is a
microbially mediated process (“denitrification”) that requires
an anoxic (i.e., oxygen-free) environment.
Groundwater is becoming a growing component of
the global nitrogen cycle because of the increased nitrogen
inflows and because of long groundwater residence times.
Nitrate does not significantly adhere to or react with sediments or other geologic materials, and it moves with groundwater flow. Other forms of reactive nitrogen in groundwater
are less significant and much less mobile: ammonia occurs
under some groundwater conditions, but it is subject to
sorption and rapidly converts to nitrate under oxidizing
conditions. Dissolved organic nitrogen (DON) concentrations are generally much less than those of nitrate, except
near wastewater sources, due to the high adsorption of DON
to aquifer materials.

 

Groundwater nitrate inputs may come from natural,
urban, industrial, and agricultural sources. Groundwater
nitrate outputs occur through wells or via discharge to
springs, streams, and wetlands. Discharge to surface water
sometimes involves denitrification or reduction of nitrate to
ammonium when oxygen-depleted conditions exist beneath
wetlands and in the soils immediately below streams.

2.2 Sources of Nitrate Discharge
to Groundwater
Nitrogen enters groundwater at varying concentrations and
in varying forms (organic nitrogen, ammonium, nitrate)
with practically all sources of recharge: diffuse recharge from
precipitation and irrigation; focused recharge from streams,
rivers, and lakes; focused recharge from recharge basins and
storage lagoons; and focused recharge from septic system
drainfields. Across major groundwater basins in California,
diffuse recharge from irrigation, stream recharge, and intentional recharge are the major contributors to groundwater.
Since groundwater is an important reservoir for long-term
water storage, recharge is extremely important and desirable
in many areas. Controlling nitrate in recharge and managing
recharge are therefore key to nitrate source control.
Current groundwater nitrate, its spatial distribution,
and its changes over time are the result of recent as well as
historical nitrate loading. To understand current and future
groundwater conditions requires knowledge of historical, current, and anticipated changes in land use patterns,
recharge rates, and nitrate loading rates (Viers et al. 2012).

Natural Nitrate Sources
Nitrate occurs naturally in many groundwaters but at levels far
below the MCL for drinking water (Mueller and Helsel 1996).
The main potential sources of naturally occurring nitrate are
bedrock nitrogen and nitrogen leached from natural soils.
Surface water nitrate concentrations can be elevated in areas
with significant bedrock nitrogen (Holloway et al. 1998), but
they are not high enough to be a drinking water concern.
During the early twentieth century, conversion of the study
area’s semiarid and arid natural landscape to irrigated agriculture may have mobilized two additional, naturally occurring
sources of nitrate. First, nitrate was released from drained

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate 15

 wetlands at the time of land conversion due to increased
microbial activity in agricultural soils; stable organic forms
of nitrogen that had accumulated in soils over millennia
were converted to mobile nitrate. Second, nitrate salts that
had accumulated over thousands of years in the unsaturated
zone below the grassland and desert soil root zone due to
lack of significant natural recharge were mobilized by irrigation (Dyer 1965; Stadler et al. 2008; Walvoord et al. 2003).
However, the magnitude of these sources (Scanlon 2008) is
considered to have negligible effects on regional groundwater
nitrate given the magnitude of human sources.

Human Nitrate Sources
Anthropogenic groundwater nitrate sources in the study area
include agricultural cropland, animal corrals, animal manure
storage lagoons, wastewater percolation basins at municipal
wastewater treatment plants (WWTPs) and food processors
(FPs), septic system drainfields (onsite sewage systems), leaky
urban sewer lines, lawns, parks, golf courses, and dry wells
or percolation basins that collect and recharge stormwater
runoff. Incidental leakage of nitrate may also occur directly
via poorly constructed wells. Croplands receive nitrogen from
multiple inputs: synthetic fertilizer, animal manure, WWTP
and FP effluent, WWTP biosolids, atmospheric deposition,
and nitrate in irrigation water sources.
Source categories. For this Report, we estimated
the groundwater nitrate contributions for 58 individual
agricultural cropland categories, for animal corrals, for
manure lagoons, for each individual WWTP and FP within
the study area, for dairies and other animal farming operations, for septic system drainfields, and for urban sources.
Contributions from dry wells and incidental leakage through
existing wells were estimated at the basin scale. Groundwater
nitrate contributions were estimated for five time periods,
each consisting of 5 years: 1943–1947 (“1945”), 1958–1962
(“1960”), 1973–1977 (“1975”), 1988–1992 (“1990”), and
2003–2007 (“2005”); the latter is considered to be current.
Future year 2050 loading was estimated based on anticipated
land use changes (primarily urbanization). These categorical
or individual estimates of nitrate leaching lead to maps that

show nitrate discharge at a resolution of 0.25 ha (less than
1 ac) for the entire study area and its changes over a period of
105 years (1945–2050) (Viers et al. 2012; Boyle et al. 2012).
Separately, we also aggregated nitrate loads to
groundwater
•  by crop categories (e.g., olives, persimmons, lettuce,
strawberries) and crop groups (e.g., “subtropicals,”
“vegetables and berries”) averaged or summed over the
entire study area;
•  by county, totaled across all cropland, all WWTPs and
FPs, all dairies, all septic drains, and all municipal
areas; and
•  summed or averaged for the study area.
Higher levels of aggregation provide more accurate
estimates but are less descriptive of actual conditions at any
given location. Aggregated totals are most useful for policy
and planning.
We report nitrate loading to groundwater in two ways:
•  Total annual nitrate leached to groundwater, measured
in gigagrams of nitrate-nitrogen per year (Gg N/yr).1 As
a practical measure, 1 gigagram is roughly equivalent
to $1 million of nitrogen fertilizer at 2011 prices.
•  Intensity of the nitrate leaching to groundwater, measured in kilograms of nitrate-nitrogen per ha of use per
year (kg N/ha/yr) [lb per acre per year, lb/ac/yr], which
represents the intensity of the source at its location
(field, pond, corral, census block, city) and its potential
for local groundwater pollution.
How much nitrate loading to groundwater is acceptable? To provide a broad reference point of what the source
loading numbers mean with respect to potential groundwater
pollution, it is useful to introduce an operational benchmark that indicates whether nitrate leached in recharge to
groundwater exceeds the nitrate drinking water standard.
This operational benchmark considers that nearly all relevant
anthropogenic nitrate sources provide significant groundwater recharge and therefore remain essentially undiluted when

One gigagram is equal to 1 million kilograms (kg), 1,000 metric tons, 2.2 million pounds (lb), or 1,100 tons (t). In this report, nitrogen application to land refers
to total nitrogen (organic nitrogen, ammonium-nitrogen, and nitrate-nitrogen). For consistency and comparison, total nitrate loading and the intensity of nitrate
loading from the root zone to groundwater are also provided in units of nitrogen, not as nitrate. However, concentrations of nitrate in groundwater or leachate
are always stated as nitrate (MCL: 45 mg/L) unless noted otherwise.

1 

16 

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate

 reaching groundwater. Our benchmark for “low” intensity
versus “high” intensity of nitrate leaching is 35 kg N/ha/yr
(31 lb N/ac/yr).2 Aggregated across the 1.5 million ha (3.7
million ac) of cropland, the benchmark for total annual nitrate
loading in the study area is 50 Gg N/yr (55,000 t N/yr). Total
nitrate loading to groundwater above this benchmark indicates a high potential for regional groundwater degradation.
Estimating nitrate loading by source category. We
used two methods to assess nitrate loading:
•  a mass balance approach was used to estimate nitrate
loading from all categories of cropland except alfalfa;
•  alfalfa cropland and nitrate sources other than cropland
were assessed by reviewing permit records, literature
sources, and by conducting surveys to estimate groundwater nitrate loading (Viers et al. 2012).

Groundwater Nitrate Contributions by Source Category
Cropland is by far the largest nitrate source, contributing
an estimated 96% of all nitrate leached to groundwater
(Table 1). The total nitrate leached to groundwater (200
Gg N/yr [220,000 t N/yr]) is four times the benchmark
amount, which suggests large and widespread degradation of
groundwater quality. Wastewater treatment plants and food
processor waste percolation basins are also substantial, highintensity sources.3 Septic systems, manure storage lagoons,
and corrals are relatively small sources basin-wide, but since
their discharge intensity significantly exceeds the operational
benchmark of 35 kg N/ha/yr (31 lb N/ac/yr), these source
categories can be locally important. The magnitude and
intensity of urban sources (other than septic systems) does not
suggest widespread impact to groundwater (Viers et al. 2012).
The following sections provide further detail on these sources.
Agricultural Sources
Cropland sources: Overview. The five counties in the
study area include 1.5 million ha (3.7 million ac) of cropland,
about 40% of California’s irrigated cropland. Agricultural
production involves many crops and significant year-to-year

changes in crops grown and crop yields. The dominant crop
groups in the project area include subtropical crops (citrus
and olives), tree fruits and nuts, field crops including corn
and cotton, grain crops, alfalfa, vegetables and strawberries,
and grapes (see Figure 2). The study area also supports
1 million dairy cows. These produce one-tenth of the nation’s
milk supply as well as large amounts of manure.
Cropland sources: Alfalfa. The mass balance approach
is not applied to alfalfa because it does not receive significant
amounts of fertilizer, yet alfalfa fixes large amounts of nitrogen
from the atmosphere. Little is known about nitrate leaching
from alfalfa; we used a reported value of 30 kg N/ha/yr (27 lb
N/ac/yr) (Viers et al. 2012). In total, 170,000 ha (420,000 ac)
of alfalfa fields are estimated to contribute about 5 Gg N/yr
(5,500 t N/yr) in the study area. Alfalfa harvest exceeds 400 kg
N/ha/yr (360 lb N/ac/yr), or 74 Gg N/yr (82,000 t N/yr), in
the study area.
Cropland sources other than alfalfa. Unlike other
groundwater nitrate source categories, cropland has many
sources of nitrogen application, all of which can contribute
to nitrate leaching. Principally, crops are managed for optimal harvest. Synthetic nitrogen is the fertilizer of choice to
achieve this goal, except in alfalfa. Other sources of nitrogen
are also applied to cropland, providing additional fertilizer,
serving as soil amendments, or providing a means of waste
disposal. These additional nitrogen sources include animal
manure and effluent and biosolids from WWTPs, FPs, and
other urban sources. Often do they replace synthetic fertilizer
as the main source of nitrogen for a crop. Atmospheric deposition of nitrogen and nitrate in irrigation water are mostly
incidental but ubiquitous.
For the mass balance analysis, external nitrogen inputs
to cropland are considered to be balanced over the long
run (5 years and more) by nitrogen leaving the field in crop
harvest, atmospheric losses (volatilization, denitrification),
runoff to streams, or groundwater leaching. Hence, cropland
nitrate leaching to groundwater is estimated by summing
nitrogen inputs to a field (fertilizer, effluent, biosolids,

A typical groundwater recharge rate in the study area is roughly 300 mm/yr (1 AF/ac/yr). If that recharge contains nitrate at the MCL, the annual nitrate loading
rate is 30 kg N/ha/yr (27 lb N/ac/yr). We allow an additional 5 kg N/ha/yr (4.5 lb N/ac/yr) to account for potential denitrification in the deep vadose zone or in
shallow groundwater.

2 

The benchmark of 35 kg N/ha (31 lb N/ac) is not adequate for percolation basins, as their recharge rate is much more than 1 AF/ac. Instead, we consider
actual average concentration (by county) of nitrogen in FP and WWTP discharges to percolation basins, which range from 2 to 10 times the MCL and 1 to 2
times the MCL, respectively (Viers et al. 2012).

3 

 

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate 17

 manure, atmospheric deposition, irrigation water) and then
subtracting the three other nitrogen outputs (harvest, atmospheric losses, and runoff).
In total, the 1.27 million ha (3.1 million ac) of cropland,
not including 0.17 million ha (0.4 million ac) of alfalfa, receive
380 Gg N/yr (419,000 t N/yr) from all sources. Synthetic fertilizer, at 204 Gg N/yr (225,000 t N/yr), is more than half of these

inputs (Figure 3). Manure applied on dairy forages or exported
for cropland applications off-dairy (but not leaving the study
area) is one-third of all nitrogen inputs. Atmospheric deposition
and nitrate-nitrogen in groundwater used as irrigation water are
approximately one-tenth of all nitrogen input. Urban effluent
and biosolids application are small portions of the overall
nitrogen input in the study area, but they are locally significant.

Table 1. Major sources of groundwater nitrate, their estimated total contribution in the study area, their percent of total contribution, and their estimated average local intensity, which indicates local pollution potential (actual total nitrate loading from these
source categories is very likely within the range provided in parentheses)

Total Nitrate Loading
to Groundwater
Gg N/yr*
(range)
[1,000 t N/yr (range)]

Percent Contribution to
Total Nitrate Leaching
in the Study Area

Average Intensity of Nitrate
Loading to Groundwater
kg N/ha/yr
[lb N/ac/yr]

195 (135–255)
[215 (150–280)]

93.7%

154
[137]

Alfalfa cropland

5 (<1–10)
[5 (<1–10)]

2.4%

30
[27]

Animal corrals

1.5 (0.5–8)
[1.7 (0.5–9)]

0.7%

183
[163]

Manure storage lagoons

0.23 (0.2–2)
[0.25 (0.2–2)]

0.1%

183
[163]

WWTP and FP†
percolation basins

3.2 (2–4)
[3.5 (2–4)]

1.5%

1,200‡
[1,070]

Septic systems

2.3 (1–4)
[2.5 (1–4)]

1.1%

<10 – > 50
[<8.8 – >45]

0.88 (0.1–2)
[0.97 (0.1–2)]

0.5%

10
[8.8]

< 0.4
[<0.4]

—

§

Cropland

Urban (leaky sewers, lawns,
parks, golf courses)
Surface leakage to wells
Source: Viers et al. 2012.

*At 2011 prices, 1 Gg N (1,100 t N) is roughly equivalent to $1 million in fertilizer nitrogen.
WWTP = wastewater treatment plant; FP = food processor.
The benchmark of 35 kg N/ha/yr does not apply to WWTP and FP percolation basins, which may recharge significantly more water than
other sources. Their nitrate loading may be high even if nitrate concentrations are below the MCL (Viers et al. 2012).
§
Surface leakage through improperly constructed wells is based on hypothetical estimates and represents an upper limit.
†
‡

18 

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate

 Cropland Nitrogen Inputs

Irrigation water 29
Atmospheric deposition 12

Synthetic fertilizer 204

Atmospheric
losses 38

Runoff 18

Leaching to groundwater 195

Land-applied biosolids 4.8
Land-applied liquids,
WWTP-FP 3.4
Land-applied manure from
CAFOs other than dairy 0.9

Land-applied dairy manure 127

Harvest 130

Cropland Nitrogen Outputs

Note: No mass balance was performed on 0.17 million ha (0.4 million ac) of nitrogen-fixing alfalfa, which is estimated to contribute an
additional 5 Gg N/yr to groundwater. Groundwater nitrate loading from all non-cropland sources is about 8 Gg N/yr.

Figure 3. Overview of cropland input and output (Gg N/yr) in the study area (Tulare Lake Basin and Salinas Valley) in 2005. The left half
of the pie chart represents total nitrogen inputs to 1.27 million ha (3.12 million ac) of cropland, not including alfalfa. The right half of the
pie chart represents total nitrogen outputs with leaching to groundwater estimated by difference between the known inputs and the known
outputs. Source: Viers et al. 2012.

 

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate 19

 On the output side, the total nitrate leaching to groundwater from cropland, not including alfalfa, comprises 195
Gg N/yr (215,000 t N/yr) and is by far the largest nitrogen
flux from cropland, much larger than the harvested nitrogen
at 130 Gg N/yr (143,000 t N/yr). The nitrogen leached to
groundwater nearly matches the amount of synthetic fertilizer applied to the same cropland, suggesting large system
surpluses of nitrogen use on cropland. Other outputs are
small: atmospheric losses are assumed to be one-tenth of the
inputs (Viers et al. 2012), and runoff is assumed to be 14 kg
N/ha/yr (12.5 lb N/ac/yr) (Beaulac and Reckhow 1982).
Applying the benchmark of 50 Gg N/yr (55,000 t N/yr),
groundwater leaching losses would need to be reduced by 150
Gg N/year (165,000 t N/yr) or more area-wide to avoid further
large-scale groundwater degradation. Figure 3 suggests three

major options to reduce nitrate loading to groundwater from
cropland: develop techniques to make manure a useful and
widely used fertilizer and reduce synthetic fertilizer application in the study area by as much as 75%; drastically reduce
the use of manure in the study area; or significantly increase
the agricultural output (harvest) without increasing the
nitrogen input. Nitrate source reduction efforts will involve a
combination of these options (see Section 2.3).
The following sections further discuss individual inputs
and outputs that control agricultural cropland nitrate leaching.
Cropland inputs: Synthetic fertilizer (204 Gg N/yr
[225,000 t N/yr]). Synthetic fertilizer application rates are
estimated by first establishing a typical nitrogen application
rate for each crop, derived from the literature, United States
Department of Agriculture (USDA) Chemical Usage Reports,

Figure 4. Current typical annual fertilization rates (1 kg/ha/yr = 1.1 lb/ac/yr) in irrigated agricultural cropland of the study area derived from the
literature, USDA Chemical Usage Reports, and agricultural cost and return studies for each of 58 crop categories (does not include excess manure
applications). Rates account for multi-cropping in some vegetable crops and double-cropping of corn and winter grain. Source: Viers et al. 2012.

20 

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate

 and UC Davis ARE agricultural cost and return studies for
each of 58 crop categories within 10 crop groups (Figure 4).
In a second step, we assess whether some of the typical nitrogen application rate is met by other sources such as effluent,
biosolids, and manure. The procedure varies with crop type,
location, and aggregation level. Fertilizer needs not met
by effluent, biosolids, or manure (see below) are assumed
to be met by synthetic fertilizer, providing an estimate of
synthetic fertilizer use at local (Figure 4), crop (see Figure 7),
county (see Table 2), and study area (see Figure 3) levels. The
magnitude of total estimated synthetic fertilizer use (204 Gg
N/yr [225,000 t N/yr]) in the study area, on about 40% of
California’s irrigated land, is consistent with statewide average
recorded sales of synthetic fertilizer used on cropland of 466
Gg N/yr (514,000 t N/yr) (D. Liptzin, pers. comm., 2012).
Cropland inputs: Animal manure (land-applied:
128 Gg N/yr [141,000 t N/yr]; corral and lagoon loading
directly to groundwater: 1.7 Gg N/yr [1,900 t N/yr]). The
Tulare Lake Basin houses 1 million adult dairy cows and their
support stock (more than half of California’s dairy herd),
10,000 hogs and pigs, and 15 million poultry animals. Dairy
cattle are by far the largest source of land-applied manure
nitrogen in the area (127 Gg N/yr [140,000 t N/yr]; see
Figure 3). Manure is collected in dry and liquid forms, recycled
within the animal housing area for bedding (dry manure) and
as flushwater (freestall dairies), and ultimately applied to the
land. Manure is applied in solid and liquid forms, typically
on forage crops (e.g., summer corn, winter grain) managed
by the dairy farm, or is exported to nearby farms (mostly as
manure solids) and used as soil amendment. The amount of
land-applied manure nitrogen is estimated based on: recently
published studies of dairy cow, swine, and poultry excretion rates; animal numbers reported by the Regional Water
Board and the USDA Agricultural Census; and an estimated
38% atmospheric nitrogen loss in dairy facilities before land
application of the manure. Manure not exported from dairy
farms is applied to portions of 130,000 ha (320,000 ac) of
dairy cropland. Exported manure nitrogen is largely applied
within the study area, mostly within the county of origin, on
cropland nearby dairies.
Direct leaching to groundwater from animal corrals and
manure lagoons is about 1.5 Gg N/yr (1,700 t N/yr) and 0.2
Gg N/yr (220 t N/yr), respectively (see Table 1).

 

Cropland inputs: Irrigation water (29 Gg N/yr
[32,000 t N/yr]). Irrigation water is also a source of nitrogen
applied to crops. Surface irrigation water is generally very low
in nitrate. Nitrate in groundwater used as irrigation water is a
significant source of nitrogen but varies widely with location
and time. We used average nitrate concentrations measured
in wells and basin-wide estimates of agricultural groundwater
pumping (Faunt 2009) to estimate the total nitrogen application to agricultural lands from irrigation water, in the range of
20 Gg N/yr ( 22,000 t N/yr) to 33.4 Gg N/yr (36,800 t N/yr).
Cropland and general landscape inputs: Aerial
deposition (12 Gg N/yr [13,000 t N/yr]). Nitrogen emissions to the atmosphere as NOx from fossil fuel combustion
and ammonia from manure at confined animal feeding operations undergo transformations in the atmosphere before being
redeposited, often far from the source of emissions. Nitrogen
deposition estimates at broader spatial scales are typically
based on modeled data. Nitrogen deposition in urban and
natural areas was assumed to be retained with the ecosystem
(Vitousek and Howarth 1991). In cropland, nitrogen deposition was included in the nitrogen mass balance. For the Salinas
Valley, average aerial deposition is 5.6 kg N/ha/yr (0.6 Gg N/
yr) (5.0 lb N/ac [660 t N/yr]). The Tulare Lake Basin receives
among the highest levels in the state, averaging 9.8 kg N/ha/yr
(11.3 Gg N/yr) (8.7 lb N/ac/yr [12,500 t N/yr]).
Cropland output: Harvested nitrogen (130 Gg N/
yr [143,000 t N/yr]). The nitrogen harvested is the largest
independently estimated nitrogen output flow from cropland.
Historical and current annual County Agricultural Commissioner reports provide annual harvested acreage and yields for
major crops. From the reported harvest, we estimate the nitrogen removed. For each of 58 crop categories, the study area
total harvest nitrogen and total acreage used to estimate the
rate of nitrogen harvested (Figure 5). All crops combined (not
including alfalfa) contain a total of 130 Gg N/yr (143,000 t N/
yr), with cotton (21 Gg N/yr [23,000 t N/yr]), field crops (28 Gg
N/yr [31,000 t N/yr]), grain and hay crops (30 Gg N/yr [33,000
t N/yr]), and vegetable crops (30 Gg N/yr [30,000 t N/yr])
making up 85% of harvested nitrogen. Tree fruits, nuts, grapes,
and subtropical crops constitute the remainder of the nitrogen
export from cropland.

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate 21

 Historical Development of Fertilizer Use, Manure
Production, Harvested Nitrogen, and Estimated Nitrate
Leaching to Groundwater. Current and near-future groundwater nitrate conditions are mostly the result of past agricultural practices. So the historical development of nitrogen
fluxes to and from cropland provides significant insight in
the relationship between past agricultural practices, their
estimated groundwater impacts, and current as well as anticipated groundwater quality. Two major inventions effectively
doubled the farmland in production from the 1940s to the
1960s: the introduction of the turbine pump in the 1930s,

allowing access to groundwater for irrigation in a region with
very limited surface water supplies, and the invention and
commercialization of the Haber-Bosch process, which made
synthetic fertilizer widely and cheaply available by the 1940s.
The amount of cropland (not including alfalfa) in the
study area nearly doubled in less than 20 years, from 0.6 million
ha (1.5 million ac) in the mid-1940s to nearly 1.0 million ha
(2.5 million ac) in 1960 (not including alfalfa) (Figure 6).
Further increases occurred until the 1970s, to 1.3 million ha
(3.2 million ac), but the extent of farmland has been relatively
stable for the past 30 years.

Figure 5. Current annual nitrogen removal rate in harvested materials (1 kg/ha/yr = 1.1 lb/ac/yr) derived from county reports of harvested
area and harvested tonnage for each of 58 crop categories. Rates account for multi-cropping in some vegetable crops and double-cropping of
corn and winter grain. Source: Viers et al. 2012.

22 

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate

 In contrast, the harvested nitrogen has consistently
increased throughout the past 60 years (see Figure 6). From
1945 to 1975, total harvested nitrogen increased twice as fast
as farmland expansion, quadrupling from 20 Gg N/yr (22,000 t
N/yr) to 80 Gg N/yr (88,000 t N/yr). Without further increases
in farmland, harvests and harvested nitrogen increased by
more than 60% in the second 30-year period, from the mid1970s to the mid-2000s.
Synthetic fertilizer inputs also increased from the 1940s
to the 1980s but have since leveled off. Between 1990 and
2005, the gap between synthetic nitrogen fertilizer applied
and harvested nitrogen has significantly decreased.4

In contrast, dairy manure applied to land has increased
exponentially, effectively doubling every 15 years (see Figure 6),
from 8 Gg N/yr (9,000 t N/yr) in 1945 to 16 Gg N/yr (18,000 t
N/yr) in 1960, 32 Gg N/yr (35,000 t N/yr) in 1975, 56 Gg N/yr
(62,000 t N/yr) in 1990, and 127 Gg N/yr (140,000 t N/yr) in
2005, an overall 16-fold increase in manure nitrogen output.
The increase in manure nitrogen is a result of increasing herd
size (7-fold) and increasing milk production per cow (3-fold)
and is slowed only by the increased nitrogen-use efficiency of
milk production.
Until the 1960s, most dairy animals in the region were
only partly confined, often grazing on irrigated pasture with

Cropland area
Manure N and fertilizer N
Fertilizer N
400

1.6

Manure N

300

1.2

200

0.8

100

0.4

0

0
1940

1950

1960

1970

1980

1990

2000

2010

Year
Figure 6. Estimated historical agricultural development in the study area (not including alfalfa): total harvested area, total harvested nitrogen in fertilized crops, fertilizer applied to cropland (5-year average), manure applied to cropland (5-year average), and sum of manure and
fertilizer applied to cropland (5-year average). Not shown: In the study area, harvested alfalfa area grew from 0.12 million ha (0.3 million ac)
in the 1940s to 0.2 million ha (0.5 million ac) around 1960, then leveled off to current levels of 0.17 million ha (0.42 million ac). Since the
1960s, nitrogen removal in alfalfa harvest has varied from 50 to 80 Gg N/yr. Note: 0.4 million ha = 1 million ac. Source: Viers et al. 2012.
4 

 

Fertilizer application rates and statewide fertilizer sales have grown little since the late 1980s.

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate 23

Million/ha

Gg N/year = million $
equivalent fertilizer value/year

Harvest N

 limited feed imports. Manure from dairy livestock generally matched the nitrogen needs of dairy pastures. Since the
1970s, dairies in the Tulare Lake Basin have operated mostly
as confined animal facilities, growing alfalfa, corn, and grain
feed on-site, importing additional feed, and housing the
animals in corrals and freestalls. The growth in the dairy
industry has created a nitrogen excess pool that remains unabsorbed by crops (see Figure 6). Much of the nitrogen excess
is a recent phenomenon (see Figure 6). With groundwater
quality impacts delayed by decades in many production wells
(see Section 3), the recent increase in land applied manure
nitrogen is only now beginning to affect water quality in wells
of the Tulare Lake Basin, with much of the impact yet to come.
Groundwater loading from irrigated agriculture,
by crop group and by county. Significant differences exist
in groundwater loading intensity between crop groups.5
The intensity of groundwater loading is least in vineyards
(less than 35 kg N/ha/yr [31 lb N/ac/yr]), followed by rice
and subtropical tree crops (about 60 kg N/ha/yr [54 lb N/
ac/yr]), tree fruits, nuts, and cotton (90–100 kg N/ha/
yr [80–90 lb N/ac/yr]), vegetables and berry crops (over
150 kg N/ha/yr [130 lb N/ac/yr]), which includes some
vegetables being cropped twice per year), field crops (about
480 kg N/ha/yr [430 lb N/ac/yr]), and grain and hay crops
(about 200 kg N/ha/yr [180 lb N/ac/yr]). Manure applications constitute the source of nearly all of the nitrate leaching
from these latter two crops. Without manure, field crops
leach less than 35 kg N/ha/yr (31 lb N/ac/yr), and grain and
hay crops leach 50 kg N/ha/yr (45 lb N/ac/yr). Figure 7 shows
the rate of reduction (in kg N/ha/crop) that would be needed,
on average across each crop group, to reduce groundwater
nitrate leaching to benchmark levels.
At the county level, we aggregate cropland area, fertilizer applications (by crop category), manure output from
individual dairies, effluent and biosolid land applications
from individual facilities, and crop category–specific harvest.

Differences in cropping patterns between counties and the
absence or presence of dairy facilities within counties drive
county-by-county differences in total groundwater loading
and in the average intensity of groundwater loading (Table 2).
Fresno County, which has fewer mature dairy cows (133,000)
than Kings (180,000), Tulare (546,000), or Kern (164,000)
Counties and also has large areas of vineyards (see Figure 2),
has the lowest average groundwater loading intensity (103 kg
N/ha/yr [103 lb N/ac/yr]). Monterey County is dominated by
vegetable and berry crops (high intensity) and grape vineyards
(low intensity).
Urban and Domestic Sources
Urban and domestic sources: Overview. Urban
nitrate loading to groundwater is divided into four categories:
nitrate leaching from turf, nitrate from leaky sewer systems,
groundwater nitrate contributions from WWTPs and FPs,
and groundwater nitrate from septic systems. For all these
systems, groundwater nitrate loading is estimated based on
either actual data or reported data of typical nitrate leaching.
Urban and domestic sources: Wastewater treatment
plants and food processors (11.4 Gg N/yr [12,600 t/yr]:
3.2 Gg N/yr [3,500 t/yr] to percolation ponds, 3.4 Gg N/
yr [3,800 t/yr] in effluent applications to cropland, and
4.8 Gg N/yr [5,300 t/yr] in WWTP biosolids applications
to cropland). The study area has roughly 2 million people on
sewer systems that collect and treat raw sewage in WWTPs.
In addition, many of the 132 food processors within the study
area generate organic waste that is rich in nitrogen (Table
3). Potential sources of groundwater nitrate contamination
from these facilities include effluent that is land applied on
cropland or recharged directly to groundwater via percolation basins, along with waste solids and biosolids that are
land applied. Typically, WWTP influent contains from 20
mg N/L to 100 mg N/L total dissolved nitrogen (organic
N, ammonium N, nitrate-N), of which little is removed in
standard treatment (some WWTPs add treatment beyond

Aggregated estimates were obtained from study area-wide totals for harvested area (by crop group), for typical nitrogen application, and for harvested
nitrogen. The following averages were assumed: irrigation water nitrogen (24 kg N/ha/yr [21 lb N/ac/yr]), atmospheric nitrogen losses (10% of all N inputs),
and runoff (14 kg N/ha/yr [12.5 lb N/ac/yr]). Most manure is likely land-applied to field crops, particularly corn, and to grain and hay crops. Little is known
about the actual distribution prior to 2007 and the amount of synthetic fertilizer applied on fields receiving manure. As an illustrative scenario, we assume
that two-thirds of dairy manure is applied to field crops and one-third of dairy manure is applied to grain and hay crops. In field crops, 50% of crop nitrogen
requirements are assumed to be met with synthetic fertilizer, and in grain and hay crops 90% of their crop nitrogen requirements are assumed to be met
by synthetic fertilizer. These are simplifying assumptions that neglect the nonuniform distribution of manure on field and grain crops between on-dairy,
near-dairy, and away-from-dairy regions. However, corn constitutes most (106,000 ha [262,000 ac]) of the 130,000 ha (321,000 ac) in field crops, with at
least 40,000 ha (99,000 ac) grown directly on dairies. Grain crops are harvested from 220,000 ha (544,000 ac). For further detail, see Viers et al. 2012.

5 

24 

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate

 760
N applied

720

N harvested

680

N applied: estimated average
reduction needed

640

400

N rate (kg/ha/crop)

360

443

320
280
240

167

200
160

64

51

66

23

120

24

80

59

0

40

Tree fruit

Subtropical

Vegetables and berries

Crop group

Rice

Nuts

Grapes

Grain and hay

Field crops

Cotton

0

Figure 7. Nitrogen application reduction needed to reduce groundwater nitrate loading to less than 35 kg N/ha/crop, compared with average
nitrogen applied (synthetic fertilizer and manure) and nitrogen harvested (all units in kg N/ha/crop). Rates are given per crop, and the required reduction does not account for double-cropping. Some vegetables and some field crops are harvested more than once per year. In that
case, additional reductions in fertilizer applications would be necessary to reduce nitrate loading to less than 35 kg N/ha. Large reductions
needed in field crops and grain and hay crops are due to the operational assumption that manure generated in the study area is applied to
only these crop groups. Typical amounts of synthetic fertilizer applied (“N applied”) to these crops, without excess manure, are 220 kg N/ha/
crop for field crops and 190 kg N/ha/crop for grain and hay crops. Thus, without excess manure, average field crops and grain and hay crops
may require relatively small reductions in nitrogen application. Source: Viers et al. 2012.

 

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate 25

 Table 2. Major nitrogen fluxes to and from cropland in the study area, by county (not including alfalfa)

Synthetic
Manure
Fertilizer
Application
Application
Gg N/yr
Gg N/yr
[1,000 t
[1,000 t
N/yr]
N/yr]

Land
Applied
Effluent
and
Biosolids,
Gg N/yr
[1,000 t
N/yr]

Harvest
Gg N/yr
[1,000 t
N/yr]

PNB*
%

PNB0
%

†

Groundwater Groundwater
Loading
Loading
Gg N/yr
Intensity
[1,000 t
kg N/ha/yr
N/yr]
[lb N/ac/yr]

By County
Fresno

62.1
[68.3]

16.6
[18.3]

0.8
[0.88]

35.5
[39.1]

44.7

54.4

42.4
[46.7]

103
[92]

Kern

50.3
[55.4]

20.4
[22.5]

4.6
[5.0]

29.6
[32.6]

39.3

56.4

42.8
[47.2]

141
[123]

Kings

27.5
[30.3]

22.0
[24.3]

1.9
[2.1]

19.6
[21.6]

38.1

62.7

29.2
[32.2]

179
[160]

Tulare

36.0
[39.7]

67.3
[74.2]

0.7
[0.77]

32.7
[36.0]

31.4

72.5

65.1
[71.8]

236
[210]

Monterey

28.1
[30.9]

1.4
[1.54]

0.1
[0.11]

12.4
[13.6]

41.9

43.5

15.6
[17.2]

138
[123]

TLB

176
[194]

127
[140]

8.1
[8.9]

118
[130]

37.8

60.5

179
[197]

155
[138]

SV

28
[30.8]

1
[1.1]

0.1
[0.11]

12
[13]

41.9

43.5

16
[18]

138
[123]

Overall

204
[225]

128
[141]

8.2
[9]

130
[143]

38.2

58.3

195
[215]

154
[137]

By Basin

Source: Viers et al. 2012.
Manure applications include non-dairy manure nitrogen (0.9 Gg N/yr [(990 t N/yr)] for the entire study area). Groundwater loading
accounts for atmospheric deposition (9.8 and 5.6 kg N/ha/yr [(8.7 and 5 t N/yr)] in TLB and SV, respectively), atmospheric losses (10% of
all inputs), irrigation water quality (22.8 kg N/ha/yr [20 lb N/ac/yr]), and runoff (14 kg N/ha/yr [12.5 lb N/ac/yr]) to and from agricultural
cropland, in addition to fertilizer and manure application, and harvested nitrogen. Synthetic fertilizer application on field crops is assumed
to meet 50% of typical application rates; on grain and hay crops, 90% of typical applications, with the remainder met by manure.
* PNB = partial nutrient balance, here defined as Harvest N divided by (Synthetic + Manure + Effluent + Biosolids Fertilizer N).
†

PNB0 = hypothetical PNB, if no manure/effluent/biosolids overage was applied above typical fertilizer rates.

26 

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate

 conventional processes to remove nutrients including nitrate
and other forms of nitrogen). Across the study area, WWTP
effluent nitrogen levels average 16 mg N/L. Within the study
area, 40 WWTPs treat 90% of the urban sewage. FP effluent
nitrogen levels to percolation basins and irrigated agriculture
average 42 mg N/L and 69 mg N/L, respectively.
Urban and domestic sources: Septic systems (2.3
Gg N/yr [2,500 t N/yr]). Crites and Tchobanoglous (1998)
estimated that the daily nitrogen excretion per adult is 13.3 g.

Approximately 15% of that nitrogen is assumed to either stay
in the septic tank, volatilize from the tank, or volatilize from
the septic leachfield (Siegrist et al. 2000). Based on census
data, the number of people on septic systems in the study
areas is about 509,000 for the Tulare Lake Basin and 48,300 for
Salinas Valley. Total nitrate loading from septic leaching is 2.1
Gg N/yr (2,300 t N/yr) in the Tulare Lake Basin and 0.2 Gg N/
yr (220 t N/yr) in the Salinas Valley. The distribution of septic
systems varies greatly. The highest density of septic systems is

Table 3. Total nitrogen discharge to land application and average total nitrogen concentration (as nitrate-N, MCL: 10 mg N/L) in
discharge to percolation basins from WWTPs and FPs, based on our surveys of WWTPs and the FP survey of Rubin et al. (2007)

Biosolids
Gg N/yr
[1,000 t N/yr]

WWTP
Land Application
Gg N/yr
[1,000 t N/yr]

WWTP
Percolation
Concentration
mg N/L

FP
Land Application
Gg N/yr
[1,000 t N/yr]

FP
Percolation
Concentration
mg N/L

0.006
[0.006]

0.40
[0.40]

18.5

0.42
[0.46]

56.2

Kern

3.1
[3.4]

0.92
[0.92]

17.7

0.56
[0.62]

43.9

Kings

1.6
[1.7]

0.09
[0.09]

11.2

0.26
[0.29]

2.1

Tulare

0.038
[0.044]

0.50
[0.50]

14.9

0.13
[0.14]

34.2

0
[0]

0.09
[0.09]

13.9

0.05
[0.05]

22.1

4.8
[5.3]

1.9
[2.1]

16.3

1.37
[1.51]

43.3

0
[0]

0.09
[0.09]

13.9

0.05
[0.05]

22.1

4.8
[5.3]

2.0
[2.2]

16

1.4
[1.5]

42

By County
Fresno

Monterey
By Basin
Tulare Lake Basin

Salinas Valley

Overall

 

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate 27

 in peri-urban (rural sub-urban) areas near cities but outside
the service areas of the wastewater systems that serve those
cities (Figure 8). In the Tulare Lake Basin and Salinas Valley,
7.9% and 12.6%, respectively, of the land area exceeds the
EPA-recommended threshold of 40 septic systems per square
mile (0.154 systems per ha). Nearly 1.5% of the study area has
a septic system density of over 256 systems per square mile (1
system/ha, or 1 system/2.5 ac). In those areas, groundwater
leaching can significantly exceed our operational benchmark
rate of 35 kg N/ha/yr (31 lb N/ac/yr).

Urban and domestic sources: Fertilizer and leaky
sewer lines (0.88 Gg N/yr [970 t N/yr]). Fertilizer is used
in urban areas for lawns, parks, and recreational facilities
such as sports fields and golf courses. These land uses differ
in their recommended fertilizer use, and there is almost
no evidence of actual fertilization rates. Based on the most
comprehensive survey of turfgrass leaching, only about 2% of
applied nitrogen fertilizer was found to leach below the rooting zone (Petrovic 1990). For our nitrogen flow calculations,
we assume a net groundwater loss of 10 kg N/ha/yr (8.9 lb
N/ac/yr) from lawns and golf courses in urban areas (0.35 Gg
N/yr [380 t N/yr]).

Figure 8. Septic-derived nitrate leaching rates within the study area. Source: Viers et al. 2012.

28 

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate

 Sewer systems in urban areas can be a locally significant source of nitrogen. We use both reported sewer nitrogen
flows and per capita nitrogen excretion rates to obtain total
nitrogen losses via leaky sewer lines in urban areas. Nationally, estimated municipal sewer system leakage rates range
from 1% to 25% of the total sewage generated. Given that
much of the urban area within the study region is relatively
young, we consider that the leakage rate is low, roughly 5%
or less (0.53 Gg N/yr).

average annual nitrate loading estimates for specific categories
are based on many assumptions and are based on (limited)
data with varying degrees of accuracy; the numbers given
represent a best, albeit rough, approximation of the actual
nitrate loading from specific sources. These estimates have
inherent uncertainty. Very likely, though, the actual groundwater nitrate loading from source categories falls within the
ranges shown in Table 1.

General Sources
General sources: Wells, dry wells, and abandoned
wells (<0.4 Gg N/yr [<440 t N/yr]). Wells contribute to
groundwater nitrate pollution through several potential pathways. Lack of or poor construction of the seal between the
well casing and the borehole wall can lead to rapid transport
of nitrate-laden irrigation water from the surface into the
aquifer. In an inactive or abandoned production well, long
well screens (several hundred feet) extending from relatively
shallow depth to greater depth, traversing multiple aquifers,
may cause water from nitrate-contaminated shallow aquifer
layers to pollute deeper aquifer layers, at least in the vicinity
of wells. Dry wells, which are large-diameter gravel-filled
open wells, were historically designed to capture stormwater
runoff or irrigation tailwater for rapid recharge to groundwater. Abandoned wells also allow surface water leakage to
groundwater (spills) and cross-aquifer contamination. Lack
of backflow prevention devices can lead to direct introduction of fertilizer chemicals into the aquifer via a supply well.
Few data are available on these types of nitrate transfer in
the Tulare Lake Basin or Salinas Valley. In a worst-case situation, as much as 0.4 Gg N/yr (440 t N/yr) may leak from
the surface to groundwater via improperly constructed,
abandoned, or dry wells, and as much as 6.7 Gg N/yr (7,400
t N/yr) are transferred within wells from shallow to deeper
aquifers. Actual leakage rates are likely much lower than
these worst-case estimates.
Groundwater Nitrate Loading: Uncertainty. The
analyses above provide specific numbers for the average
amount and intensity of nitrate loading from various categories of sources. However, discharges of nitrate to groundwater
may vary widely between individual fields, farms, or facilities of the same category due to differences in operations,
management practices, and environmental conditions. Also,

2.3 Reducing Nitrate Source Emissions
to Groundwater

 

Although reduction of anthropogenic loading of nitrate to
groundwater aquifers will not reduce well contamination in
the short term (due to long travel times), reduction efforts
are essential for any long-term improvement of drinking
water sources. Technologies for reducing nitrate contributions to groundwater involve (a) reducing nitrogen quantity
discharged or applied to the land and (b) controlling the
quantity of water applied to land, which carries nitrate to
groundwater (Dzurella et al. 2012).
Many source control methods require changes in land
management practices and upgrading of infrastructure. Costs
for mitigation or abatement vary widely and can be difficult
to estimate. In particular, the quantity of nitrate leached
from irrigated fields (the largest source) is determined by a
complex interaction of nitrogen cycle processes, soil properties, and farm management decisions. Only broad estimates
of the cost of mitigation per unit of decrease in the nitrate
load are possible.

Reducing Nitrate Loading from Irrigated
Cropland and Livestock Operations
Reduction of nitrate leaching from cropland, livestock, and
poultry operations can come from changes in farm management that improve crop nitrogen use efficiency and proper
storage and handling of manure and fertilizer. A common
measure of cropland nitrogen use efficiency is the partial
nitrogen balance (PNB), which is the ratio of harvested nitrogen to applied (synthetic, manure, or other organic) fertilizer
nitrogen (Table 2).
We reviewed technical and scientific literature to
compile a list of practices known or theorized to improve
crop nitrogen use efficiency. Crop-specific expert panels

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate 29

 reviewed and revised this list of practices. Input from these
panel members also helped to estimate the current extent of
use of each practice in the study area and to identify barriers
to expanded adoption.
PNB can be increased by optimizing the timing and
application rates of fertilizer nitrogen, animal manure, and
irrigation water to better match crop needs, and to a lesser
extent by modifying crop rotation. Improving the storage and
handling of manure, livestock facility wastewater, and fertilizer also helps reduce nitrate leaching. A suite of improved
management practices is generally required to reduce nitrate
leachate most effectively, and these must be chosen locally
for each unique field situation. No single set of management
practices will be effective in protecting groundwater quality
everywhere. The best approach depends on the crop grown,

soil characteristics of the field, and other specific factors. As
summarized in Table 4, ten key farm management measures
for increasing crop nitrogen use efficiency (and PNB) are
identified and reviewed (Dzurella et al. 2012).
Although PNBs as low as 33% have been reported, a
recent EPA report estimated that with the adoption of best
management practices, PNB could increase by up to 25% of
current average values (U.S. EPA 2011). Improvements in
PNB are possible, but a practical upper limit is about 80%
crop recovery of applied nitrogen (U.S. EPA 2011; Raun and
Schepers 2008). This limit is due to the unpredictability of
rainfall, the difficulty in predicting the rate of mineralization
of organic nitrogen in the soil, spatial variability and nonuniformity in soil properties, and the need to leach salts from
the soil.

Table 4. Management measures for improving nitrogen use efficiency and decreasing nitrate leaching from agriculture
(local conditions determine which specific practices will be most effective and appropriate)

Basic Principle

Design and operate irrigation
and drainage systems to decrease
deep percolation.

Manage crop plants to capture more
N and decrease deep percolation.

Manage N fertilizer and manure to
increase crop N use efficiency.

Improve storage and handling of
fertilizer materials and manure to
decrease off-target discharges.

Management Measure

MM 1. Perform irrigation system evaluation and monitoring.

3

MM 2. Improve irrigation scheduling.

4

MM 3. Improve surface gravity system design and operation.

6

MM 4. Improve sprinkler system design and operation.

5

MM 5. Improve microirrigation system design and operation.

2

MM 6. Make other irrigation infrastructure improvements.

2

MM 7. Modify crop rotation.

4

MM 8. Improve rate, timing, placement of N fertilizers.

9

MM 9. Improve rate, timing, placement of animal manure applications.

6
9

MM 10. Avoid fertilizer material and manure spills during transport,
storage, and application.

Source: Dzurella et al. 2012.

30 

Number of
Recommended
Practices

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate

Total: 50

 Based on expert panel commentary, several farm
management practices that reduce nitrate leaching have been
widely adopted in recent years in the study area, representing
a positive change from past practices that have contributed
to current groundwater nitrate concentrations. High PNB can
sometimes increase yields and decrease costs to the producer
(by decreasing costs for fertilizer and water). Alas, field data
that document improvements in nitrate leaching from these
actions are largely unavailable.
Significant barriers to increased adoption of improved
practices exist. These include higher operating or capital
costs, risks to crop quality or yield, conflicting farm logistics,
and constraints from land tenure. Lack of access to adequate
education, extension, and outreach activities is another

primary barrier, especially for the adoption of many of the
currently underused practices, highlighting the importance
of efforts such as those offered by the University of California Cooperative Extension. The future success of leaching
reductions through improved crop and livestock facility
management will require a significant investment in cropspecific research that links specific management practices
with groundwater nitrate contamination. Additional investments in farmer (and farm labor) education and extension
opportunities are needed, as well as increased support for
farm infrastructure improvements. Monitoring and assessment programs need to be developed to evaluate management practices being implemented and their relative efficacy.

Figure 9. Overall nitrate hazard index calculated for the study area fields. Index values over 20 indicate increased potential for nitrate leaching from the crop root zone, benefiting most from implementation of improved management practices. Comparison between values in the
higher-risk categories is not necessarily an indication of further risk differentiation, but it may indicate that multiple variables are involved in
risk. Less-vulnerable areas still require vigilance in exercising good farm management practices. Source: Dzurella et al. 2012.

 

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate 31

 To establish the areas that would benefit most from
improved management practices, we conducted a vulnerability assessment. Management-specific vulnerability was
mapped using the UC Nitrate Hazard Index (Wu et al. 2005),
which calculates the potential of nitrate leaching as a function of the crop grown, the irrigation system type in use, and
the soil characteristics of each individual field. Based on this
information, approximately 52% of irrigated cropland in the
Salinas Valley and 35% of such land in the Tulare Lake Basin
would most benefit from broad implementation of improved
management practices (Figure 9).
A maximum net benefit modeling approach was developed to estimate relative costs of policies to improve PNB while
maintaining constant crop yields for selected crop groups in
the study area. Net revenue losses from limiting nitrate load to

groundwater increase at an increasing rate (Table 5 and Figure
10). Our modeling results, although preliminary due to the
lack of data on the cost of improving nitrogen use efficiency,
suggest that reductions of 25% in total nitrate load to groundwater from crops will slightly increase production costs but
are unlikely to affect total irrigated crop area, as summarized
in Table 5. Smaller reductions (<10%) can be achieved at low
costs, assuming adequate farmer education is in place (see
Figure 10).
Greater reductions in total nitrate loading (>50%) are
much more costly to implement, as capital and management
investments in efficient use of nitrogen are required. Achieving such high load reductions may ultimately shift cropping
toward more profitable and nitrogen-efficient crops or
fallowing, as lower-value field crops and low-PNB crops lose

Table 5. Summary of how two groundwater nitrate load reduction scenarios may affect total applied water, annual net revenues,
total crop area, and nitrogen applications, according to our estimative models for each basin*

Region

Applied Water
km3/yr
[million AF/yr]

Net Revenues
$M/yr
(2008)

Irrigated Land
1,000 ha
[ac]

Applied Nitrogen
Gg N/yr (%)
[1,000 t/yr]

base load

10.5
[8.5]

4,415 (0%)

1,293
[3,194]

200 (0%)
[221]

25% load reduction

10.0
[8.1]

4,259 (–3.5%)

1,240
[3,064]

181 (–9%)
[199]

50% load reduction

7.9
[6.4]

3,783 (–14%)

952
[2,352]

135 (–32%)
[149]

base load

0.37
[0.30]

309 (0%)

92
[227]

18 (0%)
[19]

25% load reduction

0.33
[0.27]

285 (–7.5%)

83
[205]

15 (–16%)
[16]

50% load reduction

0.25
[0.20]

239 (–22%)

62
[153]

10 (–46%)
[11]

Scenario

Tulare Lake
Basin

Salinas Valley

Source: Dzurella et al. 2012.
* Irrigated land area and applied nitrogen in base load vary slightly from those reported in Section 2.2 due to land use data being based
on Figure 2 (derived from DWR data) instead of County Agricultural Commissioner Reports (Figure 6).

32 

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate

 favor economically. The average net revenue loss of reducing
nitrate loading to groundwater is estimated to be $16 per
kilogram of nitrogen at this 50% reduction level. Modeling
a 7.5% sales fee on nitrogen fertilizer indicated an estimated
reduction in total applied nitrogen by roughly 1.6%, with a
0.6% loss in net farm revenues.
Agricultural source reduction: Promising actions.
Expanded efforts to promote nitrogen-efficient practices
are needed. Educational and outreach activities could assist
farmers in applying best management practices (BMPs) and
nutrient management. Research should focus on demonstrating the value of practices on PNB and on adapting
practices to local conditions for crop rotations and soils with

the greatest risk of nitrate leaching. This especially includes
row crops receiving high rates of nitrogen and/or manure
that are surface- or sprinkler-irrigated. Research on the costs
of increasing nitrogen use efficiency in crops would greatly
benefit the capacity to estimate the economic costs of reductions in agricultural nitrate loading to groundwater. Research
and education programs are needed to promote conversion of
solid and liquid dairy manure into forms that meet food safety
and production requirements for a wider range of crops.
We suggest that a working group develop crop-specific
technical standards on nitrogen mass balance metrics for
regulatory and assessment purposes. This nitrogen-driven
metric would reduce the need for more expensive direct
measurement of nitrate leaching to groundwater. Such

25%
Tulare Lake Basin

Salinas Valley

Percent reduction in net revenues

20%

15%

10%

5%

0%
0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

Percent reduction in nitrate load to groundwater
Figure 10. Percent reduction in net revenues estimated from different levels of reduction in nitrate loading to groundwater.
Source: Dzurella et al. 2012.

 

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate 33

 metrics would also serve as a starting point to assist farmers
in assessing their crop nitrogen use efficiency and be useful
for nitrogen management. Finally, we recommend that a task
force review and further develop methods to identify croplands most in need of improved management practices. Such
a method should include consideration of soil characteristics
(as in the UC Nitrate Hazard Index), as well as possible monitoring requirements.

Reducing Nitrate Leaching from Municipal Wastewater Treatment and Food Processing Plants
Implementation of nitrogen control options for WWTP and
FP sources is feasible and useful. Nitrogen removal from
wastewater can be accomplished using a variety of technologies and configurations; both biological and physical or
chemical processes are effective. The selection of the most
appropriate treatment option depends on many factors.
Estimated capital costs for nutrient removal from all
wastewater (FPs and WWTPs) for facilities categorized as
“at-risk” range from $70 to $266 million. Cropland application of wastewater treatment and food processing effluents
can reduce direct groundwater contamination and total
fertilizer application requirements of such fields, as the water
and nutrients are effectively treated and recycled. These
wastes should be managed in an agronomic manner rather
than applied to land for disposal or land treatment purposes
so that the nutrients are included in the overall nitrogen
management plan for the receiving crops.
Optimizing wastewater treatment plant and food
processing plant operations is another way to reduce nitrogen
and total discharge volume. Facility process modifications
may be sufficient in some cases. Groundwater monitoring is required for many facilities, but the data are largely
unavailable since they are not in a digital format. To improve
monitoring, enforcement, and abatement efforts related to
these facilities, groundwater data need to be more centrally
managed and organized digitally.

Reducing Nitrate Contributions from Leaking
Sewer Pipes and Septic Systems
Retrofitting of septic system components and sewer pipes is
the main way to diminish loading from these sources. Replacing aging sewer system infrastructure and ensuring proper
maintenance are required to reduce risks to human health;
such infrastructure upgrades also reduce nitrate leaching.

34 

Loading from septic systems, significant locally, can
be reduced significantly by two approaches where connection to a sewer system is not possible. Source separation
technology can reduce nitrate loading to wastewater treatment systems by about 50%. Costs include separating toilets
($300–$1,100), dual plumbing systems ($2,000–$15,000),
storage tank costs, and maintenance, pumping, heating, and
transport costs (where applicable). Post-septic tank biological nitrification and denitrification treatment reduces nitrate
concentrations below levels achieved via source separation
technology but does not result in a reusable resource. Wood
chip bioreactors have reduced influent nitrate by 74% to
91%, with costs ranging from $10,000 to $20,000 to retrofit
existing septic systems.

Reducing Nitrate Leaching from Turfgrass
in Urban Areas
Nitrate leaching from urban turfgrass, including golf courses,
is often negligible due to the dense plant canopy and perennial growth habit of turf, which results in continuous plant
nitrogen uptake over a large portion of the year. However,
poor management can lead to a discontinuous canopy and
weed presence, wherein nitrate leaching risk increases, especially if the turf is grown on permeable soils, is overirrigated,
or is fertilized at high rates during dormant periods. The
UCCE and UC IPM publish guidelines on proper fertilizer use
in turfgrass. The knowledge and willingness of homeowners
and groundskeepers to apply guidelines depend on funding
for outreach efforts.

Reducing Nitrate Transfer and Loading from Wells
Backflow prevention devices should be required on agricultural and other wells used to mix fertilizer with water.
Furthermore, local or state programs and associated funding
to identify and properly destroy abandoned and dry wells
are needed to prevent them from becoming nitrate transfer
conduits. However, many well owners may not be able to
afford the high costs of retrofitting long-screened wells to seal
contaminated groundwater layers. As such, enforcement of
proper well construction standards for future wells may be
more feasible. Expenditures on retrofitting of existing dry
and abandoned wells should be based on the contamination
risks of individual wells. The nitrate contamination potential
of wells needs to be identified as a basis for developing and
enforcing improved, appropriate well construction standards
that avoid the large-scale transfer of nitrate to deep groundwater in all newly constructed wells.

Addressing Nitrate in California’s Drinking Water / Sources of Groundwater Nitrate

 3 Impact: Groundwater Nitrate Occurrence
3.1 Current Groundwater Quality Status
We assembled groundwater quality data from nearly two
dozen local, state, and federal agencies and other sources into
a dataset, here referred to as the (Central) California SpatioTemporal Information on Nitrate in Groundwater (CASTING) dataset (see Table 6 for information about data sources,
Boyle et al. 2012). The dataset combines nitrate concentrations from 16,709 individual samples taken at 1,890 wells in
the Salinas Valley and from 83,375 individual samples taken
at 17,205 wells in the Tulare Lake Basin collected from the
1940s to 2011, a total of 100,084 samples from 19,095 wells.
Almost 70% of these samples were collected from 2000 to
2010; only 15% of the samples were collected prior to 1990.
Half of all wells sampled had no recorded samples prior to
2000 (Boyle et al. 2012).
Of the nearly 20,000 wells, 2,500 are frequently
sampled public water supply wells (over 60,000 samples).
Apart from the recently established Central Valley dairy regulatory program, which now monitors about 4,000 domestic
and irrigation wells in the Tulare Lake Basin, there are no
existing regular well sampling programs for domestic and
other private wells.
From 2000 to 2011, the median nitrate concentration
in the Tulare Lake Basin and Salinas Valley public water
supply well samples was 23 mg/L and 21 mg/L,6 respectively,
and in all reported non-public well samples, 23 mg/L and 20
mg/L, respectively. In public supply wells, about one in ten
raw water samples exceeds the nitrate MCL. Nitrate concentrations in wells vary widely with location and well depth.
More domestic wells and unregulated small system wells
have high nitrate concentrations due to their shallow depth
(Table 6). Highest nitrate concentrations are found in wells of
the alluvial fans in the eastern Tulare Lake Basin and in wells
of unconfined to semi-confined aquifers in the northern,
eastern, and central Salinas Valley (Figure 11). In the Kings,
Kaweah, and Tule River groundwater sub-basins of Fresno
and Kings County, and in the Eastside and Forebay sub-basins

6 

 

of Monterey County, one-third of domestic or irrigation wells
exceed the nitrate MCL. Consistent with these findings, the
maximum nitrate level, measured in any given land section
(1 square mile) for which nitrate data exist between 2000 and
2009, exceeds the MCL across wide portions of these areas
(Figure 12). Low nitrate concentrations tend to occur in the
deeper, confined aquifer in the western and central Tulare
Lake Basin (Boyle et al. 2012).
Nitrate levels have not always been this high. While no
significant trend is observed in some areas with low nitrate
(e.g., areas of the western TLB), USGS research indicates
significant long-term increases in the higher-nitrate areas of
the Tulare Lake Basin (Burow et al. 2008), which is consistent
with the CASTING dataset. Average nitrate concentrations
in public supply wells of the Tulare Lake Basin and Salinas
Valley have increased by 2.5 mg/L (±0.9 mg/L) per decade
over the past three decades. Average trends of similar magnitude are observed in private wells. As a result, the number
of wells with nitrate above background levels ( > 9 mg/L) has
steadily increased over the past half century from one-third of
wells in the 1950s to nearly two-thirds of wells in the 2000s
(Figure 13). Due to the large increase in the number of wells
tested across agencies and programs, the overall fraction of
sampled wells exceeding the MCL grew significantly in the
2000s (Boyle et al. 2012).
The increase in groundwater nitrate concentration
measured in domestic wells, irrigation wells, and public
supply wells lags significantly behind the actual time of
nitrate discharge from the land surface. The lag is due, first,
to travel time between the land surface or bottom of the root
zone and the water table, which ranges from less than 1 year
in areas with shallow water table (<3 m [10 ft]) to several
years or even decades where the water table is deep (>20 m
[70 ft]). High water recharge rates shorten travel time to a
deep water table, but in irrigated areas with high irrigation
efficiency and low recharge rates, the transfer to a deep water
table may take many decades.

Unless noted otherwise, nitrate concentration is given in mg/L as nitrate (MCL = 45 mg/L).

Addressing Nitrate in California’s Drinking Water / Groundwater Nitrate Occurrence 35

 Once nitrate is recharged to groundwater, additional
travel times to shallow domestic wells are from a few years to
several decades and one to several decades and even centuries
for deeper production wells.

3.2 Cleanup of Groundwater:
Groundwater Remediation
Groundwater remediation is the cleanup of contaminated
groundwater to levels that comply with regulatory limits. In

the pump-and-treat (PAT) approach, groundwater is extracted
from wells, treated on the surface, and returned to the aquifer
by injection wells or surface spreading basins. In-situ treatment approaches create subsurface conditions that aid degradation of contaminants underground. In-situ remediation is
not appropriate for contaminants spread over large regions or
resistant to degradation. Both remediation methods typically
also require removal or reduction of contamination sources
and long-term groundwater monitoring.

Table 6. Data sources with the total number of samples recorded, total number of sampled wells, location of wells, type of wells,
and for the last decade (2000–2010) in the Tulare Lake Basin and Salinas Valley: Number of wells measured, median nitrate
concentration, and percentage of MCL exceedance for the Tulare Lake Basin and the Salinas Valley*

Years 2000–2010
Total #
of Wells

Total
# of
Samples

CDPH

2,421

CVRWB
DAIRY

6,459

Data
Source†

# of
Wells
TLB

# of
Wells
SV

TLB
Median
mg/L
nitrate

SV
Median
mg/L
nitrate

TLB %
> MCL

SV %
> MCL

public supply
wells

1,769

327

12

8

6%

5%

dairies in TLB

domestic,
irrigation, and
monitoring wells

6,459

—

22

—

31%

—

domestic wells

71

—

40

—

45%

—

Location
of Wells

Type of
Wells

62,153

throughout
study area

11,300

DPR

71

814

eastern
Fresno
and Tulare
Counties

DWR

26

44

Westlands
Water District

irrigation wells

28

—

1

—

0%

—

irrigation,
domestic, and
public supply
wells

—

—

—

—

—

—

DWR
Bulletin
130

685

2,862

throughout
study area

ENVMON

537

2,601

throughout
study area

monitoring wells

357

180

—

27

52%

44%

2,860

4,946

throughout
study area

—

—

—

—

—

—

—

Fresno
County

368

369

Fresno
County

domestic wells

349

—

18

—

15%

—

GAMA

141

141

Tulare County

domestic wells

141

—

38

—

43%

—

Kern
County

2,893

3,825

Kern County

Irrigation,
domestic wells

361

—

5

—

7%

—

EPA

Continued on next page

36 

Addressing Nitrate in California’s Drinking Water / Groundwater Nitrate Occurrence

 Groundwater remediation is difficult and expensive
(NRC 1994, 2000). Groundwater remediation is done only
very locally (less than 1 km2 [< 0.5 mi2] to often less than 2 ha
[<5 ac]). Cleanup of contaminants over a wide region is not
feasible, and would require many decades and considerable
expense. The success rate for cleanup of widespread groundwater contaminants is very disappointing (NRC 1994, 2000).
Because of the difficulty and poor success rates of
plume remediation, an approach known as monitored natural
attenuation (MNA) has become popular. MNA involves
letting natural biochemical transformations and dispersion
reduce and dilute contamination below cleanup goals, while

monitoring to confirm whether MNA is adequately protecting
groundwater quality. However, this approach is effective only
for contaminants that transform to relatively harmless byproducts. The combination of circumstances that would favor
denitrification of nitrate is generally lacking in California’s
alluvial aquifer systems (Fogg et al. 1998; Boyle et al. 2012),
so MNA does not seem to be an effective way of remediating
nitrate-contaminated groundwater in the study area.
The total estimated volume of groundwater exceeding
the nitrate MCL in the Tulare Lake Basin and Salinas Valley
is 39.7 km3 (32.2 million acre-feet, AF) and 4.2 km3 (3.4
million AF), respectively, more than the total groundwater

Table 6. Continued

Years 2000–2010
Total #
of Wells

Total
# of
Samples

Monterey
County,
Reports

239

Monterey
County,
Geospatial
Monterey
County,
Scanned

Data
Source†

# of
Wells
TLB

# of
Wells
SV

TLB
Median
mg/L
nitrate

SV
Median
mg/L
nitrate

TLB %
> MCL

SV %
> MCL

monitoring,
irrigation wells

—

98

—

14

—

36%

Monterey
County

local small
systems wells

—

431

—

18

—

15%

Monterey
County

local small
systems wells

—

427

—

17

—

14%

—

miscellaneous

76

4

35

0

36%

0%

444

Tulare County

domestic wells

438

—

22

—

27%

—

77

Westlands
Water District

irrigation wells

31

—

4

—

0%

—

Location
of Wells

Type of
Wells

1,018

Monterey
County

388

1,574

452

5,674

1,028

2,151

Tulare
County

444

Westlands
Water
District

48

NWIS

Source: Boyle et al. 2012.
* Median and percent MCL exceedance were computed based on the annual mean nitrate concentration at each well for which data were
available.
† Data sources: CDPH: public supply well database; CVRWB Dairy: Central Valley RWB Dairy General Order; DWR Bulletin 130: data
reports from the 1960–1970s, 1985; ENVMON: SWRCB Geotracker environmental monitoring wells with nitrate data (does not include
data from the CVRWB dairy dataset); EPA: STORET dataset; Fresno County: Public Health Department; GAMA: SWRCB domestic well
survey; Kern County: Water Agency; Monterey County, Reports: data published in reports by MCWRA; Monterey County, Geospatial:
Health Department geospatial database; Monterey County, Scanned: Health Department scanned paper records; NWIS: USGS National
Water Information System; Tulare County: Health and Human Services; Westlands Water District: district dataset. Some smaller datasets
are not listed. Individual wells that are known to be monitored by multiple sources are here associated only with the data source reporting
the first water quality record.

 

Addressing Nitrate in California’s Drinking Water / Groundwater Nitrate Occurrence 37

 pumped from the project area aquifers between 2005 and
2010 (Table 7). This is a basin-scale groundwater cleanup
problem. Annual costs of traditional remediation would be
on the order of $13 to $30 billion (Dzurella et al. 2012; King
et al. 2012). This explains why no attempt at remediation
of a contaminated groundwater basin on the scale of the
Tulare Lake Basin or Salinas Valley has ever been undertaken.
Except for cleanup of hot-spot sites, traditional remediation
for nitrate is not a promising option.
A more promising remediation approach is what
we refer to as “pump-and-fertilize” (PAF) (Dzurella et al.
2012; King et al. 2012). This approach uses existing agricultural wells to remove nitrate-contaminated groundwater
and “treat” the water by ensuring nitrate uptake into crops
through proper nutrient management. A disadvantage of PAF

is that many irrigation wells are drilled deep to maximize the
pumping rate, but most high levels of nitrate contamination
are seen at shallower depths. Shallower nitrate-contaminated
groundwater is en route toward the deep intake screens of
many of the irrigation wells (Viers et al. 2012). One option
is to drill intermediate-depth irrigation wells to intercept
contaminated groundwater before it penetrates farther into
the deeper subsurface. The cost, energy, and management
requirements of this approach would need to be carefully
evaluated, as it requires the drilling and operation of many
shallower wells with smaller capture zones and smaller
pumping rates at each well. At a regional or sub-regional
scale, it may be an innovative alternative, although decades of
PAF operations would be needed together with large reductions in nitrate leachate from the surface.

Figure 11. Mean of the time-average nitrate concentration (mg/L) in each well belonging within a square mile land section, 2000–2009.
Some areas in the TLB are larger than 1 square mile. Source: Boyle et al. 2012.

38 

Addressing Nitrate in California’s Drinking Water / Groundwater Nitrate Occurrence

 Groundwater recharge operations could be managed
to improve groundwater quality if the recharged water is
of good quality and relatively low in nitrate (remediation
by dilution). By introducing as much clean recharge water
as possible, the long-term effects of contaminated agricultural recharge can be partially mitigated. But the large
water volumes already affected would require decades of
management.
Pump-and-fertilize along with improved groundwater recharge management are technically feasible, less
costly alternatives than pump-and-treat and could help place
regional groundwater quality on a more sustainable path.
These alternatives should be accompanied by remediation of
local nitrate contamination hot spots and long-term groundwater quality monitoring to track benefits of the strategy (for
details, see King et al. 2012).

3.3 Existing Regulatory and
Funding Programs for Nitrate
Groundwater Contamination
Many regulatory and planning programs in the study area
provide regulatory structure or technical and managerial
support to water systems, communities, farmers, dairies, and
others who deal with nitrate contamination in groundwater.
Statutes also provide a regulatory framework for nitrate
contamination of groundwater and drinking water. In the
study area, there are several federal programs/statutes (Table
8a and Table 8b, blue), State programs/statutes (purple),
and nongovernmental programs/agencies (orange) relevant
to nitrate contamination and its effects on drinking water.
Current regulatory/planning programs and statutes that have
the ability to reduce groundwater nitrate contamination

Figure 12. Maximum nitrate concentration (mg/L) measured at any time during 2000–2009 within a 1-square-mile land section. Some areas
in the TLB are larger than 1 square mile. Source: Boyle et al. 2012.

 

Addressing Nitrate in California’s Drinking Water / Groundwater Nitrate Occurrence 39

 are summarized in Table 8a. These programs/statutes have
components that target nitrate source reduction or groundwater remediation. While providing a framework to address
the groundwater nitrate issue, these programs have not been
effective at preventing substantial nitrate contamination of
groundwater used in drinking water supplies. Table 8b is a
summary of current programs and statutes related to groundwater nitrate and drinking water. These provide for data
collection, information, and education on nitrate sources and
groundwater nitrate. Some of these programs regulate nitrate
in drinking water.
In addition, several state, federal, and local agencies,
as well as nongovernmental organizations, have established

funding programs related to nitrate contamination in Cali­
fornia’s groundwater. A summary of existing funding sources
to address problems related to nitrate in drinking water is
shown in Table 9. In general, these programs are structured
to provide assistance for activities related to alternative water
supplies and nitrate load reduction. The State of California
has eighteen relevant funding programs, administered by
four agencies (Table 9, purple); the federal government
manages an additional three funding programs (blue). Three
large nongovernmental drinking water funding programs in
the study area are highlighted in orange in Table 9. For a
more detailed review, see Canada et al. (2012).

70%

7,000
Percent of wells above natural background

60%

6,000

50%

5,000
Number of wells tested
4,000

40%
Percent of wells above half nitrate MCL
30%

3,000

20%

2,000
Percent of wells above nitrate MCL
1,000

10%

0

0%
1950

1960

1970

1980

1990

2000

2010

Figure 13. Five-year moving average of the percentage of wells for which the average annual measured concentration exceeded 9 mg/L
(background), 22.5 mg/L (half of the MCL), and 45 mg/L (MCL) in any given year. Since the 1990s, an increasing number of wells other
than public supply wells have been tested. In 2007, Central Valley dairies began testing their domestic and irrigation wells on an annual
basis. Source: Boyle et al. 2012.

40 

Addressing Nitrate in California’s Drinking Water / Groundwater Nitrate Occurrence

 Table 7. Total groundwater volume* and estimated remediation volume by sub-basin

Total Groundwater Volume
in Study Area
km3
[million AF]

Remediation Volume
> MCL
km3
(% of total)

Remediation Volume
> MCL
million AF
(% of total)

5-22.06–Madera

1.48
[1.2]

0.15 (10%)

0.12 (10%)

5-22.07–Delta-Mendota

3.21
[2.6]

0.16 (5%)

0.13 (5%)

5-22.08–Kings

115
[93]

12.75 (11%)

10.34 (11%)

5-22.09–Westside

64
[52]

1.67 (3%)

1.35 (3%)

5-22.10–Pleasant Valley

4.9
[4.0]

1.11 (23%)

0.90 (23%)

5-22.11–Kaweah

42
[34]

9.12 (21%)

7.39 (21%)

5-22.12–Tulare Lake

46
[37]

4.65 (10%)

3.77 (10%)

5-22.13–Tule

41
[33]

4.29 (11%)

3.48 (11%)

5-22.14–Kern

49
[40]

5.81 (12%)

4.71 (12%)

TLB TOTAL

366
[297]

39.7 (11%)

32.2 (11%)

3-4.01–180/400 Foot Aquifer

8.46
[6.86]

0.91 (11%)

0.74 (11%)

3-4.02–Eastside

3.16
[2.56]

1.23 (39%)

1.00 (39%)

3-4.04–Forebay

5.59
[4.53]

1.37 (25%)

1.11 (25%)

3-4.05–Upper Valley

3.03
[2.46]

0.56 (19%)

0.45 (19%)

3-4.08–Seaside

0.78
[0.63]

0.07 (10%)

0.06 (10%)

3-4.09–Langley

0.44
[0.36†]

3-4.10–Corral de Tierra

0.60
[0.49‡]

0.002 (0.5%)

SV TOTAL

22.1
[17.9]

4.19 (19%)

Study Area Total

315
[255]

43.9 (11%)

Sub-Basin

Tulare Lake Basin

Salinas Valley

0.04 (9%)

0.03 (9%)
0.002 (0.5%)
3.4 (19%)

35.6 (11%)

Source: King et al. 2012.
* Source: DWR 2010.

 

†

Storage; actual groundwater volume not listed.

‡

Source: Montgomery Watson Americas 1997, not listed in DWR Bulletin 118.

Addressing Nitrate in California’s Drinking Water / Groundwater Nitrate Occurrence 41

 Table 8a. Summary of programs and statutes for reducing nitrate contamination in groundwater

Agency

Program/Statute
(year created/passed)

Goal/Purpose

U.S. Environmental
Protection Agency
(U.S. EPA)

Supplemental Environmental Programs
(SEP) (1998)

Environmentally beneficial project that a violator of environmental laws may choose
to perform (under an enforcement settlement) in addition to the actions required by
law to correct the violation.

Porter-Cologne Water Quality Control Act
(1969)

Grants the State Water Board authority over state water quality policy and aims to
regulate activities in California to achieve the highest reasonable water quality.

Recycled Water Policy (2009)

Resolution No. 2009-0011: Calls for development of salt and nutrient management
plans and promotes recharge of clean storm water.

Cleanup and Abatement Order (CAO)

CA Water Code § 13304: Allows the Regional Water Board to issue a directive to a
polluter to require clean up of waste discharged into waters of the state.

Irrigated Lands Regulatory Program (ILRP)
(2004, draft in 2011)

General Conditional Waiver of Waste Discharge Requirements, 3-Tiered Agricultural
Regulatory Program (2004): Groundwater quality monitoring required to different degrees
based on discharger’s tier. Draft (2001) requires Tier 3 dischargers with high nitrate loading
to meet specified Nitrogen Mass Balance Ratios or implement a solution that leads to an
equivalent nitrate load reduction.

Irrigated Lands Regulatory Program (ILRP)
(2003, draft in 2011)

Conditional Wavier of Waste Discharge Requirements of Discharges from Irrigated Lands:
Interim program to regulate irrigated lands. Does not address groundwater.
Recommended ILRP Framework (2011): Development of new monitoring and
regulatory requirements (includes groundwater).

CV-SALTS (2006)

Planning effort to develop and implement a basin plan amendment for comprehensive
salinity and nitrate management.

Dairy Program (2007)

Waste Discharge Requirements General Order for Existing Milk Cow Dairies: Confined
animal facilities must comply with set statewide water quality regulations, and existing
milk cow dairies must conduct nutrient and groundwater monitoring plans.

State Water
Resources Control
Board (State Water
Board)

Regional Water
Quality Control
Boards
Central Coast
Regional Water
Quality Control
Board

Central Valley
Regional Water
Quality Control
Board

California
Feed, Fertilizer, Livestock, Drugs, Egg
Department of Food
Quality Control Regulatory Services
and Agriculture
(FFLDERS)
(CDFA)

42 

Manages licenses, registration and inspection fees, and a mill fee levied on fertilizer
sales, to fund research and educational projects that improve fertilizer practices and
decrease environmental impacts from fertilizer use.

Addressing Nitrate in California’s Drinking Water / Groundwater Nitrate Occurrence

 Table 8b. Summary of programs and statutes related to groundwater nitrate and drinking water (data collection, information,
education, or regulation of drinking water)

Agency

Goal/Purpose

Safe Drinking Water Act (SDWA)
(1974, 1986, 1996)

Mandates EPA to set the drinking water standards and to work with states, localities, and water
systems to ensure that standards are met.

Phase II Rule (1992)

Established federal maximum contaminant level (MCL) for nitrate in public water systems.

Enforcement Response Policy—
Enforcement Targeting Tool

Focuses on high-priority systems with health-based violations or with monitoring or reporting
violations that can mask acute health-based violations.

Rural Utilities Service: National
Drinking Water Clearinghouse
(1977)

Provides technical assistance and educational materials to small and rural drinking water systems.

22 CCR § 64431

Established state maximum contaminant level (MCL) for nitrate in public water systems.

Drinking Water Source Assessment
and Protection (DWSAP)

Evaluation of possible contaminating activities surrounding groundwater and surface water
sources for drinking water.

Expense Reimbursement Grant
Program (EPG)

Education, training, and certification for small water system (serving < 3,301 people) operators.

Groundwater Ambient Monitoring
and Assessment (GAMA)

Improves statewide groundwater monitoring and increases availability of groundwater quality
information. Funded by Prop 50 and special fund fees.

Assembly Bill 3030

(1993)

Permits local agencies to adopt programs to manage groundwater and requires all water suppliers
overlying useable groundwater basins to develop groundwater management plans that include
technical means for monitoring and improving groundwater quality.

Kern County Water
Agency (KCWA)

(1961)

Collects, interprets, and distributes groundwater quality data in Kern County.

U.S. Environmental
Protection Agency
(U.S. EPA)

U.S. Department of
Agriculture (USDA)

California Department
of Public Health
(CDPH)

 

Program/Statute
(year created/passed)

Monterey County
Health Department

Implements a tiered, regular nitrate sampling program based on increasing nitrate concentration
for local small water systems and for state small water systems.

Southern San Joaquin
(2002)
Valley Water Quality
Coalition

Protects and preserves water quality in the Tulare Lake Basin through surface water quality
monitoring and dissemination of collected data. Particular focus is on agricultural discharge areas.
Does not currently focus on groundwater.

Tulare County Water
Commission

(2007)

Discusses water issues impacting Tulare County and advises the Tulare County Board of Supervisors.
Special focus on nitrate in groundwater and improving drinking water in small communities.

Monterey County
Water Resources
Agency (MCWRA)

(1947)

Provides water quality management and protection through groundwater quality monitoring
(including nitrate levels) and research and outreach efforts to growers to improve fertilizer
management and reduce nitrate leaching.

The Waterkeeper
Alliance

Monterey Coastkeeper
(2007)

Collaborates with the State Water Board to ensure effective monitoring requirements for agricultural
runoff and more stringent waste discharge requirements for other nitrate sources.

Rural Community
Assistance
Partnership (RCAP)

(1979)

Uses publications, training, conferences, and technical assistance to help communities of less than
10,000 people access safe drinking water, treat and dispose of wastewater, finance infrastructure
projects, understand regulations, and manage water facilities.

National Rural Water
Association (NRWA)

(1976)

Offers drinking water system technical advice (operation, management, finance, and governance)
and advocates for small/rural systems to ensure regulations are appropriate.

California Rural Water
Association

(1990)

Provides online classes, onsite training, low-cost educational publications, and other forms of
technical advice for rural water and wastewater systems.

Self-Help Enterprises
(SHE)

Community Development Program
(1965)

Provides technical advice and some seed money to small/rural/poor communities for the planning
studies and funding applications associated with drinking water system projects.

Community Water
Center

Association of People United for
Water (AGUA) (2006)

Advocates for regional solutions to chronic local water problems in the San Joaquin Valley. Focused
on securing safe drinking water, particularly from nitrate-impacted sources.

Addressing Nitrate in California’s Drinking Water / Groundwater Nitrate Occurrence 43

 Table 9. Summary of existing funding sources for water quality investigations and safe drinking water

Agency

California Department
of Public Health
(CDPH)

State Water Resources
Control Board
(State Water Board)

Program (year passed or created)

Funding Provided (in millions of dollars)

Safe Drinking Water State
Revolving Fund (SDWSRF) (1996)
(grants and loans)

Generally $100–$150: Low-interest loans and some grants to support
water systems with technical, managerial, and financial development
and infrastructure improvements.

Proposition 84 (2006)
(grants)
(fully allocated)

$180: Small community improvements.
$60: Protection and reduction of contamination of groundwater sources.
$10: Emergency and urgent projects.

Proposition 50 (2002)
(grants)
(fully allocated)

$50: Water security for drinking water systems.
$69: Community treatment facilities and monitoring programs.
$105: Matching funds for federal grants for public water system
infrastructure improvements.

Clean Water State Revolving Fund (CWSRF)
(1987)
(loans)

$200–$300 per year: Water quality protection projects, wastewater
treatment, nonpoint source contamination control, and watershed
management.

Small Community Wastewater Grants (2004,
amended 2007)
(grants)

$86 (fees on the CWSRF): Loan forgiveness to small disadvantaged
communities and grants to nonprofits that provide technical assistance
and training to these communities in wastewater management and
preparation of project applications.

Proposition 50 (2002)
(grants) (fully allocated)

$100: Drinking water source protection, water contamination prevention,
and water quality blending and exchange projects.

Agricultural Drainage Program (1986)
(loans) (fully allocated)

$30: Addressing treatment, storage, conveyance or disposal of
agricultural drainage.

Dairy Water Quality Grant Program (2005)
(grants) (fully allocated)

$5 (Prop 50): Regional and on-farm dairy projects to address dairy water
quality impacts.

Nonpoint Source Implementation Program
(2005)
(grants)

$5.5 per year: Projects that reduce or prevent nonpoint source
contamination to ground and surface waters.

Cleanup and Abatement Account (2009)

$9 in 2010: Clean up or abate a condition of contamination affecting
water quality.

Integrated Regional Water Management (IRWM)
(2002)
(grants) (fully allocated)

$380 (Prop 50): Planning ($15) and implementation ($365) projects related
to protecting and improving water quality, and other projects to ensure
sustainable water use.

continued on next page

44 

Addressing Nitrate in California’s Drinking Water / Groundwater Nitrate Occurrence

 Table 9. Continued

Agency

Program (year passed or created)

Funding Provided (in millions of dollars)

Integrated Regional Water Management (IRWM)
(2002)
(grants)

$500 remaining (Prop 84): Regional water planning
and implementation.

Local Groundwater Assistance Grant
(2008)
(grants)

$4.7 anticipated for 2011–2012 (Prop 84): Groundwater studies,
monitoring and management activities.

Proposition 82 (1988)
(loans)

$22: New local water supply feasibility and construction loans.

Water Use Efficiency Grant Program
(2001)
(grants)

$15 in 2011 (Prop 50): Water use efficiency projects for agriculture,
such as: wellhead rehabilitation, water and wastewater treatment,
conjunctive use, water storage tanks.

Agricultural Water Conservation Loan Program
(2003)
(loans)

$28 (Prop 13): Agricultural water conservation projects, such as: lining
ditches, tailwater or spill recovery systems, and water use measurement.

Infrastructure Rehabilitation Construction Grants
(2001) (grants) (fully allocated)

$57 (Prop 13): Drinking water infrastructure rehabilitation and
construction projects in poor communities.

California Infrastructure
and Economic
Development Bank
(I-Bank)

Infrastructure State Revolving Fund (ISRF)
(1994)
(loans)

$0.25 to $10 per project: Construction or repair of publicly owned water
supply, treatment, and distribution systems.

U.S. Department of
Agriculture (USDA)

Rural Utilities Service—Water and
Environmental Programs (RUS WEPs)
(loans and grants)

$15.5: Development and rehabilitation of community public water
systems (less than 10,000 people), including: emergency community
water assistance grants, predevelopment planning grants, technical
assistance, guaranteed loans, and a household well water program.

U.S. Department
of Housing and
Development (HUD)

Community Development Block Grant (CDBG)
(grants)

$500 in 2010 for CA: Community development projects: feasibility
studies, final plans and specs, site acquisition and construction, and
grant administration.

U.S. Department of
Commerce

Economic Development Administration (EDA)
(grants)

Grants up to 50% of project costs: supports economic development,
planning, and technical assistance for public works projects.

Rural Community
Assistance Corporation
(RCAC)

Drinking Water Technical Assistance and
Training Services Project (loans)

$1.2 per year: Administers funds from the US EPA Office of Groundwater
& Drinking Water for infrastructure projects, including water.

The Housing
Assistance Council
(HAC)

Small Water/Wastewater Fund (loans)

Up to $0.25 per project: Loans for land acquisition, site development,
and construction.

Cooperative Bank
(CoBank)

Water and Wastewater Loan
(loans)

$1 per project: Water and wastewater infrastructure, system
improvements, water right purchases, and system acquisitions.
$0.05–$0.5 per project: Construction costs.

California Department
of Water Resources
(DWR)

Source: Canada et al. 2012.

 

Addressing Nitrate in California’s Drinking Water / Groundwater Nitrate Occurrence 45

 The Dutch Experience
In response to increasingly intensive animal production and a growing awareness of its effects on nitrate
concentrations in surface water and groundwater,
the European Council Nitrate Directive (ND) (Council
Directive 91/67/EEC) was established in 1991 as
part of the European Union (EU) Water Framework.
The ND imposes a performance standard of 50
mg/L nitrate on effluent, groundwater, and surface
water quality levels within all EU countries. Furthermore, each country is required to establish nitrate
contamination reduction plans, monitor program
effectiveness, and regularly report their findings to
the European Council (EC) (EU Publications Office).
Compliance with the ND is costly in terms of time,
expertise, and money; however, countries that do
not meet ND standards face large fines from the EC.
While the ND does very little in the way of explicitly
specifying how countries should act in efforts to
comply with these requirements, plans that do
not propose to regulate manure application at ND
standards (i.e., land application rates in the range of
170–210 kg N/ha) have been historically rejected.
As an agricultural hotspot, The Netherlands has
struggled to meet the ND requisites. To fulfill the
obligatory ND requirements (Ondersteijn 2002), the
Dutch government first created the Mineral Accounting System (MINAS) in 1998 (Henkens and Van
Keulen 2001). MINAS was a farm-gate policy created
to ensure the balance of nitrogen and phosphorus
inputs (fertilizer and feed) and outputs (products
and manure) on individual farms via balance sheets
(Oenema et al. 2005). MINAS resembled a farm-gate
performance standard that was enforced by a penalty tax for excess nitrogen and phosphorus inputs:
farms consuming more nitrogen or phosphorus than
could be accounted for via harvest outputs would
be fined per kilogram of nitrogen or phosphorus lost
to the environment. As of 2003, fines of € 2.27/kg N
($1.40/lb N) were enforced, more than seven times
the cost of nitrogen fertilizer at the time. MINAS was

46 

popular for its simplicity, and was well supported
by government aid. RIVM (Netherland’s National
Institute for Public Health and the Environment),
which monitors nitrogen and phosphorus soil and
water concentrations nationally, reports that nitrogen surpluses in agricultural areas fell substantially
beginning in 1998 as a result of its implementation.
Nevertheless, the EU declared the Dutch MINAS
policy noncompliant with ND requirements, stating
that the policy did not directly regulate water nitrate
concentrations (Henkens and Van Keulen 2001).
In response to the EU’s rejection of MINAS, the Netherlands implemented an additional policy in 2002:
the Mineral Transfer Agreement System (MTAS).
MTAS was a cap-and-trade system that prescribed
manure (not inorganic fertilizer) application rates (as
per ND objectives) and allowed farmers to purchase
surplus application rights from those farmers applying manure to their land below legal limits. Rather
than repealing MINAS, however, the Dutch increased
enforceable fines under MINAS to serve as a safety
net under the newly implemented MTAS (Ondersteijn
2002). Following the enactment of MTAS, water
nitrate levels continued to fall at pre-MTAS rates
(Henkens and Van Keulen 2001; Ondersteijn 2002;
Berentsen and Tiessink 2003; Helming and Reinhard
2009), suggesting that the implementation of MTAS
in addition to MINAS had little or no additional effect.
Given the apparent futility of MTAS, and following the
repeated rejection of MINAS by the European court
of justice in 2003, both MTAS and MINAS were abandoned by the Dutch government by 2006. The two
competing regulations were replaced by a composite
policy that enforces nitrogen as well as phosphorus
application standards for both manure and inorganic
fertilizer, thereby satisfying both ND standards and
the unique challenges encountered in Dutch territory,
while minimizing administrative and economic costs.
The composite policy remains in effect to date.

Addressing Nitrate in California’s Drinking Water / Groundwater Nitrate Occurrence

 4 Impact: Drinking Water Contamination
About 2.6 million people in the Tulare Lake Basin and Salinas
Valley rely on groundwater for drinking water. This section
estimates the population susceptible to nitrate contamination
of groundwater, identifies safe drinking water actions available
and the most promising options to address nitrate groundwater contamination, and estimates the total cost of nitrate
contamination to communities and households in these areas.
This discussion summarizes more detailed examinations by
Jensen et al. (2012) and Honeycutt et al. (2012).

4.1 Susceptible Populations
Groundwater nitrate contamination brings two forms
of susceptibility: public health risks and the economic costs
of avoiding such risks through treatment, source reduction,
remediation, or alternative water supplies. California’s Tulare
Lake Basin and Salinas Valley are particularly susceptible to
public health and financial risks from nitrate contamination
for the following reasons (Honeycutt et al. 2012).
•  Communities in this region are unusually dependent
on groundwater. Less than 3% of the area’s population
is served by surface water alone.
•  These areas have more and larger nitrate contamination
sources than most other parts of California (Viers et al.
2012).
•  Of the region’s 402 community public and
state-documented state small water systems, 275 are
very small (15–500 connections) and 58 are small
(501–3,300 connections) (Figure 14). Small and very
small systems are about 81% of Tulare Lake Basin water
systems (serving 89,125 people, 4% of the population)
and about 89% of the Salinas Valley water systems
(serving 23,215 people, 6% of the population).
•  Many of these small systems rely on a single well,
without emergency alternatives when contamination is
detected. These small water systems are inherently less
reliable and face higher per capita expenses to address
nitrate contamination of groundwater.
•  Roughly 10.5% and 2.6% of the populations of Tulare
Lake Basin and Salinas Valley, respectively, use unregulated, unmonitored domestic wells, serving 245,000
people from 74,000 wells (Figure 15).

 

•  The area has many poor communities that cannot
afford drinking water treatment or capital-intensive
alternative water supplies. Over 17% of the Tulare Lake
Basin and 10% of the Monterey County population
lives in poverty.
We estimated the population of these basins that is
susceptible to significant financial cost and public health
concerns from nitrate contamination in groundwater (Honeycutt et al. 2012). The drinking water source (groundwater well
or surface water), history of nitrate contamination, size, and
potential for contamination were considered for each water
system and self-supplied rural household well location in this
region. “Vulnerability” describes the intrinsic potential for
a system to deliver drinking water to users with high nitrate
levels based on the type of system and based on the number
of water sources within the system. Vulnerability is scored
as follows:
•  Lower vulnerability is assigned to community public
water systems (water systems with >15 connections)
having more than one water source (i.e., more than one
well), regardless of whether they treat their water to
remove nitrate.
•  Higher vulnerability is assigned to all other water
systems: community public water systems with a single
source (one well) and state small (5–14 connections),
local small (2–4 connections), and household selfsupplied water systems (domestic well).
•  No vulnerability to nitrate groundwater contamination
is assigned to water systems solely supplied by surface
water.
Susceptible water users could be harmed by consuming drinking water containing contaminants or by the costs
for avoiding such contamination. We define “susceptible
population” as those
•  served by a water system with multiple sources (wells)
that has reported at least one delivered water nitrate
MCL exceedance in the past 5 years, or
•  served by a water system with a single source (well)
that has reported at least one raw water nitrate MCL
exceedance in the past 5 years, or

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination 47

 4
2

Size (population)

Very large (100,000+)
Large (10,001–100,000+)

Tulare Lake Basin
31

5

Medium (3,301–10,000)

19

7

Small (501–3,300)

Salinas Valley

47

11

Very small (15 – 500)

180

95
0

20

40

60

80

100

120

140

160

180

200

Number of systems
Figure 14. Community public and state-documented state small water systems of the Tulare Lake
Basin and Salinas Valley. Source: CDPH 2010.

Figure 15. Estimated locations of the area’s roughly 400 regulated community public and state-documented state small water systems and of
74,000 unregulated self-supplied water systems. Source: Honeycutt et al. 2012; CDPH PICME 2010.

48 

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination

 •  relying on domestic wells or local small water systems
(fewer than 5 connections) in an area where shallow
groundwater (< 300 feet) has exceeded the nitrate MCL
in the past (1989–2010), based on data from the UC
Davis CASTING dataset (Boyle et al. 2012) or
•  served by a water system lacking nitrate water quality
data.
Figure 16 shows how these categorizations were used
to classify populations and water systems. Of the 2.6 million
people in the Tulare Lake Basin and Salinas Valley, 254,000
people have drinking water supplies susceptible to significant
nitrate contamination. Of these, about 220,000 are connected
to 85 community public or state small water systems with

high or unknown susceptibility. For the majority of these
systems, treatment will be expensive due to their small size
(lack of economies of scale).
About 34,000 people are served by about 10,000 selfsupplied household wells or local small water system wells
at high risk for nitrate contamination given the known raw
water quality exceedances in nearby wells (Figure 17). These
systems are currently not regulated by the state or counties,
and little public monitoring data exist for them.
Nine of 105 single-source small water systems in
the study area exceeded the nitrate MCL at least once
since 2006 and are not currently treating their water
(CDPH 2010). Currently, 13 groundwater-supplied

Total Study Area
2,647,200 people

Higher Vulnerability

Household SelfSupplied or Local
Water System
245,500 people
~74,400 systems

Community Public
or State Small
Water System with
Only 1 Well
8,800 people
105 systems

High Likelihood of
NO3 in Groundwater
(Nearby NO3 MCL
Exceedances)

Low Likelihood of
NO3 in Groundwater
(No Nearby NO3 MCL
Exceedances)

3,400–37,500 people
34 CPWS/SSWS
0–10,000 private or
local small systems

5,400–217,200 people
71 CPWS/SSWS
0–59,800 private or
local small systems

Lower Vulnerability

No Vulnerability

Community Public
Water with > 1 Well

Only Surface
Water Sources

2,339,400 people
264 systems

64,500 people
32 systems

Treating or
Blending for NO3

Not Treating or
Blending for NO3

325,000 people
13 systems

2,014,400 people
251 systems

NO3 MCL
Exceedances

No NO3 MCL
Exceedances

670,000 people
39 systems

1,665,500 people
212 systems

No NO3 Data
3,900 people
13 systems

457,500 people
1 system

High Susceptibility

Low Susceptibility

212,500 –250,000 people
72 CPWS/SSWS
10,000 private or local small systems

2,123,000 –2,340,200 people
284 CPWS/SSWS
59,800 private or local small systems

Unknown Susceptibility
3,900 people
13 systems

Figure 16. Classification of susceptible populations based on estimated vulnerability and water quality data for the study area. Due to different sources of data, the summation of the top row does not equal the total study area population. All population and connection information
is approximate. CPWS: community public water system; SSWS: state small water system. Source: Honeycutt et al. 2012.
 

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination 49

 community public water systems and state small water systems
treat for nitrate: 8 treat by blending and 5 by treatment processes
(4 by ion exchange [IX] and 1 by reverse osmosis [RO]).
About 45% of the multiple-source systems that have
delivered water exceeding the nitrate MCL serve severely
disadvantaged and disadvantaged communities (SDACs and
DACs) (Figure 18). DACs that are unincorporated, known
as DUCs, often lack central water and sewer services. These
DUCs are highly susceptible to nitrate contamination because
they may lack a safe water source and are less financially able
to resort to alternatives if their water source becomes contaminated. Since these areas have a large concentration of families
with low incomes, community solutions to nitrate treatment
or alternative water supply also might be difficult.

Over 2 million people in the study area are not classified
as susceptible to a public health risk for nitrate contamination
today. However, more than half of the study area population
is considered to be at financial risk from nitrate contamination, having to potentially pay higher costs for treatment and
monitoring because of regional groundwater contamination:
A total of 1.3 million people (57%) in the area are served by
community public water systems or state small water systems
in which raw water sources have exceeded the nitrate MCL
at least once between 2006 and 2010 (Figure 1 and Table
10). This includes over 457,000 people in the City of Fresno,
which has nitrate exceedances in some wells but is taking
measures to avoid this contamination, including significant
expansion of surface water use.

Figure 17. Household self-supplied and local small water systems located near wells having a maximum nitrate concentration value greater
than the MCL. Source: 1989–2010 CASTING Database: GAMA, DWR, SWB, CDPH-CADWSAP, USGS, County Officials, Land Use Parcel
Codes and DWR Land Use (see Honeycutt et al. 2012).

50 

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination

 Severely disadvantaged communities (SDACs) are particularly vulnerable to financial costs. Of 51 community public
water systems (serving about 714,000 people) in the study area
with a raw source exceeding the nitrate MCL, most systems (40,
serving about 379,000 people) are in a DAC. Thirteen of the 40
exceeding systems are in unincorporated areas (serving about
167,000 people), and 27 are in incorporated communities
(serving about 212,000 people). They often cannot afford or
organize and maintain capital-intensive solutions.
As past and current nitrogen applications migrate
downward and through aquifers in the Tulare Lake Basin and
Salinas Valley, populations susceptible to the costs and public
health risks of nitrate contamination are likely to increase.
Assuming unchanging and unabated basin-wide trends in

CPWS raw nitrate groundwater levels since 1970, the financially susceptible population is estimated to increase from
57% currently to almost 80% or 1.9 million people by 2050
(not accounting for population growth, Table 10).

4.2 Alternative Water Supply
and Treatment
Source reduction and aquifer remediation are insufficient to
address drinking water nitrate contamination in the short- or
near-term. In these cases, local water system authorities and
users must select from a variety of treatment and alternative
supply options. These options are summarized for community public water systems in Table 11 and for self-supplied

Figure 18. DACs, SDACs, and delivered water quality in multiple-source community public water systems. Source: CDPH PICME WQM
2006–2010; U.S. Census Bureau 2000, 2001 (see Honeycutt et al. 2012).

 

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination 51

 households and local small water systems in Table 12. This
section further outlines these options (for details, see Honeycutt et al. 2012, and Jensen et al. 2012).

Community Public Water System Options
Each water system is unique, despite having many common
problems and characteristics. No single solution will fit every
community affected by nitrate in groundwater; each water
system requires individual engineering and financial analysis.
The uniqueness of individual water systems is multiplied by the large number of small water systems in the Tulare
Lake Basin and Salinas Valley. Small water systems have
fewer and more expensive options per capita than do larger
systems. They lack economies of scale and have fewer staff
resources. Small water and wastewater systems also typically
have disproportionately greater water quality and reliability
problems and higher costs per capita (NRC 1997).
The options available for community public water
systems faced with problems from nitrate contamination
are summarized in Table 11. Blending is the most common
approach to nitrate contamination for larger community public
water systems with more than one water source. Water from
the contaminated well is reduced, eliminated, or mixed with
water from a safer water source. Eight community public water
systems in the Tulare Lake Basin and Salinas Valley currently
blend sources to comply with the nitrate MCL.7

Drilling a deeper or a new well is another common
response to nitrate groundwater contamination. This approach
can be cost-effective, but it is often only a temporary solution
when nitrate contamination continues to spread locally and to
deeper aquifers.
Treatment of community public water supplies is often
explored and sometimes employed. A variety of treatment
options are available (Jensen et al. 2012). Ion exchange and
reverse osmosis are used for community public water system
treatment in the basins. Additional treatment options, such
as biological denitrification, may become economical and
accepted in time (Jensen et al. 2012). However, treatment is
expensive, especially for small systems. Under some circumstances, only a portion of extracted water is treated for nitrate
because regulations can be met by blending treated water
with water not treated for nitrate.
Management of waste concentrate or brine, by-products
of ion exchange and reverse osmosis treatments, can also be
costly. Options include discharge to a sewer or septic system,
waste volume reduction using drying beds, trucking or
piping for off-site disposal, deep well injection, and advanced
treatment (Jensen et al. 2012).
Connecting to a larger system with reliable good-quality
water can often solve many problems of small water systems,
including nitrate contamination. This provides economies
of scale in costs and greater access to expertise for resolving
water system problems. However, connecting a small, often

Table 10. Estimated number of years until community public water supply (CPWS) sources exceed the nitrate MCL, and total
affected population (not accounting for population growth)

Time for Maximum
Recorded Raw Nitrate Level
to Reach the MCL

Total Number of Affected
CPWSs*

Total Affected Population*

Percent of Total CPWSs
Population (study area)

0 years (2010)

77

1,363,700

57%

25 years (2035)

114

1,836,700

76%

40 years (2050)

127

1,903,300

79%

Source: Honeycutt et al. 2012.
* Based on raw water quality, not delivered quality susceptibility.
Jensen et al. (2012) found a total of 23 water systems, including all types of water systems, in the study area that treat or blend to address the nitrate problem
(10 blending systems, 10 IX systems, and 3 RO systems).

7 

52 

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination

 Table 11. Options for community public water systems

Option

Advantages

Disadvantages
•  Capital investment for accessing an alternative source.

Blending

•  Simple nontreatment alternative.

•  Relies on availability and consistency of low-nitrate source.

•  Cost-effective, given suitable wells.

•  Monitoring requirements.
•  Rising nitrate levels may preclude ability to blend.
•  Potential decrease in source capacity.
•  Capital and operational costs increase with depth.

Drilling a deeper
or new well

•  Potentially more reliable water supply.
•  Cheaper than bottled water for
households using more than 8 gal/day.

•  Potentially only a temporary quick fix; longevity depends
on local hydrogeologic conditions and land use.
•  Risk of encountering other water quality concerns at greater depths
(i.e., arsenic, manganese).
•  Pipeline costs if source area is far from original source.

Community treatment
(IX, RO and EDR)

Piped connection to an
existing system

•  Multiple contaminant removal.
•  Feasible, safe supply.

•  Disposal of waste residuals (i.e., brine waste).
•  High maintenance and/or energy demands.
•  Resin or membrane susceptibility.
•  Capital cost of pipe installation.

•  Safe, reliable water supply.

•  Connection fee.
•  Water rights purchase (surface water).
•  Capital cost of pipe installation.

Piped connection to
a new system

•  Safe, reliable water supply.

Regionalization and
consolidation

•  Often lower costs.

•  High capital and O&M costs.

•  Community-wide distribution.

•  Temporary “emergency” solution.

•  No start-up capital cost.

•  Not approved for new water systems.

Trucked water

•  High treatment system capital and O&M costs.
•  Water rights purchase (surface water).

•  Socially and politically difficult, extreme option.

Relocate households

•  Safe, reliable water supply.

•  Loss of property value and jobs.
•  Social, familial dislocation.

Well water quality testing
(already in place)

Dual system

•  Water quality awareness.
•  Beneficial to blending.

•  Hybrid of options.
•  Treating only potable.

•  Possible consumption of contaminated source.
•  Cost of contaminated supply plus cost for POU system or
trucked/bottled water, or capital dual plumbing costs.

Source: Honeycutt et al. 2012.
 

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination 53

 substandard system to a larger system often involves substantial initial capital costs to make the connection and to upgrade
the smaller distribution system. Establishing connections also
can pose institutional challenges (such as water rights and
governance) and financial risks to the larger system.
Connecting several smaller systems into a new larger
water system has many of the same advantages and costs of
connecting small systems to an existing larger system. Establishing a new system also requires additional start-up costs
for infrastructure and institutional development.
Institutional consolidation of several small systems
avoids the costs of hydraulically connecting small systems,
and it can provide a higher level of staff expertise and administrative economies of scale. This is attractive when systems are
too small to merit full-time, trained staff and too scattered to
economically connect their distribution systems and sources.
Trucking uncontaminated water to supply small communities allows the servicing of small scattered water systems,
usually at a high cost. Trucking in water is generally seen as
a temporary or emergency solution while a more permanent
high-quality drinking water source is being developed.
Relocating households to a different area with betterquality water is an extreme approach that might be suitable
if a small community is unviable for a variety of reasons and
can not attract additional customer investments. Relocating
households is likely to be accompanied by a loss of property
values and local jobs, as well as social dislocation.
Two ancillary options that can supplement some of the
above options are well water quality testing and the development of dual plumbing systems. Well water testing programs
provide better and more timely information for awareness of
nitrate contamination and can also provide useful information
for blending. Dual plumbing systems separate potable from
nonpotable water distribution systems, allowing a smaller
quantity of contaminated water to be treated or conveyed
from a higher-quality source for potable water uses.
The least expensive option is usually to stop using a
nitrate-contaminated well and switch to another existing
well, if a safer well is available. Similarly, many systems with
more than one well blend water from a low-nitrate source or
well with more contaminated supplies.

Self-Supplied Households and Local Small Water
System Options
There are approximately 74,000 self-supplied households
and local small water systems in the Tulare Lake Basin and

54 

Salinas Valley. Their nitrate contamination response options
are summarized in Table 12 and discussed below.
Water supply options for self-supplied households and
local small water systems are are similar to the options available to community public water systems, but are are similar
to the options available to community public water systems,
but are applied at a much smaller scale.
Drilling a deeper or new well can provide a reliable
supply where better water quality exists. This option is
costly, deeper wells can be accompanied by additional forms
of contamination (such as arsenic), and new wells might
provide only temporary relief if the nitrate plume is spreading
deeper into the aquifer.
Treatment of household water supplies for nitrate is
typically by reverse osmosis (RO). RO has advantages including the ability to remove multiple contaminants (where nitrate
is not the only concern). However, household treatment does
require some costs as well as additional burdens for maintenance, inspection, and operation of equipment. Treatment
can be either point-of-entry (treating all household water
use) or point-of-use (treating only potable water at household taps, usually the kitchen). As with centralized nitrate
treatment, RO units create a concentrate or brine waste that
requires disposal. Dilute waste streams, characteristic of RO,
can sometimes be used for irrigation.
Connection to a larger system with more reliable water
quality is a promising solution where a larger system is
nearby. Such a connection often has a high cost, but it may
provide a net economic benefit from lower long-term costs
and delegation of many water quality concerns to qualified
entities.
Trucking in water to the household or local small water
system can be convenient and requires little start-up cost,
but it is often expensive and is commonly considered to be a
temporary solution. Bottled water use is similar to trucking in
water, but it often entails a greater cost.
Households or local small water systems can relocate
to avoid water quality problems, but this typically would
involve some loss of property value. If the household or business is prosperous, relocation is unlikely. Poorer households
are likely to feel any resultant loss of jobs or social dislocation
more acutely.
Well water testing can better inform self-supplied users
of their risks from nitrate contamination. These tests are not
expensive. Dual plumbing systems can help reduce the amount

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination

 of water that is trucked in or treated, but it imposes additional
costs and some risk of cross-connection of contaminated and
safe water supplies.

Treatment to Remove Nitrate
Contaminated groundwater can be treated at a community
treatment plant for all users, at the point-of entry-to residential
or commercial buildings, or at the point of potable drinking
water use (such as the kitchen sink). A variety of treatment

options are available (Jensen et al. 2012). Ion exchange and
reverse osmosis are used for community public water system
treatment (Figures 19 and 20). RO is often used for pointof-use treatment in households and businesses. Additional
treatment options, such as biological denitrification, may
become economical and accepted (see Jensen et al. 2012).
The effectiveness of treatment technologies across nitrate
concentrations is summarized in Table 13.

Table 12. Options for self-supplied households and local small water systems

Option

Advantages

Disadvantages
•  Potential decrease in source capacity.
•  Capital and operational costs increase with depth.

Drilling a deeper
or new well

•  Potentially more reliable water supply.
•  Cheaper than bottled water for households
using more than 8 gal/day.

•  Potentially only a temporary quick fix; the nitrate plume follows
groundwater movement.
•  Risk of encountering other water quality concerns at greater depths
(i.e., arsenic, manganese).
•  Pipeline costs required if source area is far from original source.

Household treatment
(RO)

•  Multiple contaminant removal.

Regionalization and
consolidation

•  Cheaper treatment costs on a
customer basis.

•  High capital and O&M costs.

•  Community-wide distribution.

•  Temporary “emergency” solution.

•  No start-up capital cost.

•  Extra potable water storage required if a small community.

•  Nitrate-free water supply.

•  Inconvenience, monthly expenditure.

•  No start-up cost.

•  Temporary solution.

Trucked water

Bottled water

•  Low-nitrate water supply.

•  Unless instructed, risk of improper handling or maintenance
of equipment.

•  Unpleasant, extreme option.

Relocate households

•  Safe, reliable water supply.

•  Loss of property value and jobs.
•  Social, familial dislocation.

Well water quality
testing

Dual system

•  Water quality awareness.
•  Beneficial to blending.

•  Hybrid of options.
•  Treating only potable.

•  Possible consumption of contaminated source.
•  Cost of contaminated supply plus cost for community treatment of
potable supply and dual plumbing costs.

Source: Honeycutt et al. 2012.
 

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination 55

 Treatment Type
IX = Ion exchange

RO = Reverse osmosis

BD = Biological denitrification
BD/RO
5%

IX/RO

5%

2%

19%
69%

Figure 19. California drinking water systems treating or blending for nitrate, 2010. Source: Jensen et al. 2012.

56 

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination

 However, treatment is expensive, especially for small
systems. The development of treatment alternatives requires
local engineering and development to accommodate local
conditions. Nitrate contamination can be accompanied
by other forms of groundwater contamination, including
arsenic, magnesium, or pesticides, and treatment must
accommodate the spectrum of water quality concerns as well
as local water chemistry and distribution system conditions.
Statewide, over 50% of nitrate treating systems utilize blending. Approximately 70% are using IX, and about 20% are
using RO (Figure 19). In the Tulare Lake Basin and the Salinas
Valley (Figure 20), 23 systems (of all types) were found to be
treating and/or blending to address the nitrate problem (10
blending systems, 10 IX systems, and 3 RO systems).

Consolidation and Regionalization
Consolidation or regionalization of small systems is often
suggested for addressing nitrate contamination and many other

problems of small water systems. Although small systems are
theoretically accountable and responsive to local customers,
they often have diminished financial and technical resources
that limit their ability to respond effectively or economically.
Where a small system is near a larger system with superior water
quality, connecting and consolidating these systems can provide
a long-term remedy for the smaller system. Figure 21 shows the
proximity of small systems (<10,000 people) in the Tulare Lake
Basin and Salinas Valley to larger systems. Many small systems
are reasonably close to potential long-term solutions.
However, the larger system may be concerned with
financial and administrative burdens that may arise from
upgrading the smaller system. Commonly, a smaller system
must pay for the costs of connecting to a larger system as well
as any distribution system upgrades needed to make the two
systems compatible. This system upgrade burden on the financially weaker partner can require external financial assistance.

Figure 20. Utilities treating or blending for nitrate in the Salinas Valley and Tulare Lake Basin, 2010. Source: Jensen et al. 2012.
 

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination 57

 Many small systems are far from a larger system. For
these cases, physical connection with a larger system is less
financially attractive. However, even where systems remain
hydraulically separated, consolidated operations, maintenance, and administration can sometimes have sufficient
advantages to overcome financial barriers.

4.3 Comparison and Discussion
Economically promising and appropriate treatment and
alternative water supply options have been identified
(Honeycutt et al. 2012). These promising options give indications for state policy, and their costs are used to help estimate
the overall cost of nitrate groundwater contamination in the
Tulare Lake Basin and Salinas Valley.

Options for Small Community Public Water Systems
Estimated costs of options for community public water systems
are compared in Table 14. Promising options for communities
at risk of nitrate groundwater contamination are:
•  Consolidation to a larger system that can provide
safe drinking water to more customers. Although

this option is viable for only a moderate number of
systems, consolidation or regionalization of water systems can benefit a larger proportion of the vulnerable
population and can help resolve many other long-term
problems of small systems.
•  Consolidation of nearby small systems into a larger
system with a larger rate payer base and economies of
scale. Even where small systems cannot economically
connect to a large system, some opportunities exist to
connect some small systems or to jointly manage several
small systems to improve their overall financial condition.
•  Ion exchange treatment, which is usually the most
economical community treatment for groundwater
contaminated by nitrate.
•  Interim point-of-use treatment or use of bottled
water until a more long-term and sustainable solution
can be evaluated and implemented.
•  Blending of contaminated wells, albeit temporarily if
local nitrate contamination is expanding.

Table 13. Influence of nitrate concentration on treatment selection

Practical Nitrate
Range

Option

Considerations

10–30% above MCL

blend

Depends on capacity and nitrate level of blending sources.

Up to 2× MCL

ion exchange

Depends on regeneration efficiency and costs of disposal and salt usage. Brine treatment, reuse, and
recycling can improve feasibility at higher nitrate levels.

Up to many × MCL

reverse osmosis

Depends on availability of waste discharge options, energy use for pumping, and number of stages. May be
more cost-effective than IX for addressing very high nitrate levels.

Up to many × MCL

biological
denitrification

Depends on the supply of electron donor and optimal conditions for denitrifiers. Ability to operate in a startstop mode has not yet been demonstrated in full-scale application; difficult to implement for single well
systems. May be more cost-effective than IX for addressing high nitrate levels.

Source: Contact with vendors and environmental engineering consultants; Jensen et al. 2012.

58 

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination

 A preliminary analysis was conducted to identify the
short-term lowest-cost option for susceptible water systems in
the project area to respond to nitrate contamination (Honeycutt et al. 2012). Results from this preliminary analysis, with
and without point-of-use treatment for state small water
systems, are summarized in Table 15 and Figure 22 (excluding POU). Due to public health and reliability concerns,
point-of-use treatment is currently only allowed by CDPH as
an interim action for very small water systems (serving <200
connections) facing nitrate pollution. In either case, drilling
a new well appears to be the most economical solution for
larger systems serving most of the susceptible population.
In the long term, expanding nitrate contamination might
reduce the viability of this option. If permanently allowed,

point-of-use treatment for individual households would be
economically preferred for most very small systems. Regionalization by connecting to a nearby larger system is attractive
for a substantial minority of systems and about 10% of the
susceptible population. The expense of groundwater treatment makes it relatively rare, but it remains important when
other options are unavailable. Connection to surface water
facilities was generally not found to be economical due to the
high cost of surface water treatment facilities.
If expanding nitrate contamination precludes sustainable use of new wells, costs increase greatly for community
public water systems to respond to nitrate contamination
(Table 16). In this most constrained case, connecting to
nearby larger systems (regionalization) is more common,

300

250

Number of systems

Study area

Tulare Lake Basin

Salinas Valley

200

150

100

50

0
0

4

8

12

16

20

24

28

32

36

40

44

Distance from a small system (<10,000 people)
to a larger system (>10,000 people) (miles)
Figure 21. Cumulative distribution of the minimum distance from a small system (<10,000 people) to a larger system (>10,000 people)
for the study area. Source: Honeycutt et al. 2012.

 

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination 59

 Options for Self-Supplied Households and Local
Small Water Systems

groundwater community treatment is common for small
systems, and several of the largest systems (serving most of
the susceptible population) switch to surface water treatment. The total estimated cost of alternative water supplies
for susceptible community water systems more than doubles
under this sustainable long-term scenario.

Self-supplied and local small water systems have a smaller
range of options (see Table 14). Point-of-use treatment is often
the least-expensive option. Drilling a new well is sometimes
more economical, where water use is greater and future nitrate
contamination is less problematic.

Table 14. Safe drinking water option costs for self-supplied household and small community public water systems

Estimated Annual Cost Range ($/year)
Option
Self-Supplied Household

Small Water System (1,000 households)

N/A

$85,000–$150,000

Drill deeper well

$860–$3,300

$80,000–$100,000

Drill a new well

$2,100–$3,100

$40,000–$290,000

Community supply treatment

N/A

$135,000–$1,090,000

Household supply treatment

$250–$360

$223,000

$52,400–$185,500

$59,700–$192,800

Trucked water

$950

$350,000

Bottled water

$1,339

$1.34 M

Relocate Households

$15,090

$15.1 M

Well water quality testing

$15–$50

N/A

Dual distribution system

$575–$1,580

$260,000–$900,000

Improve Existing Water Source
Blending

Alternative Supplies
Piped connection to an existing system

Ancillary Activities

Source: Honeycutt et al. 2012.

60 

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination

 Table 15. Estimated cost of the lowest-cost short-term alternative water supply option for susceptible community public water
systems and state small water systems based on system size and proximity to a larger system

Option

Number of Susceptible
Water Systems

Population

Total Cost ($/year)

Including POU

Excluding
POU

Including POU

Excluding
POU

Including POU

Excluding
POU

Drill new well

10

63

184,100

191,700

$10,144,000

$14,500,000

POU device for potable use

70

——

10,500

——

$1,320,000

——

Pipeline to a nearby large
system (10,000+ system)

5

13

25,300

27,300

$865,000

$1,463,000

Groundwater treatment
facility

0

9

0

900

$0

$450,000

Surface water treatment

0

0

0

0

$0

$0

Total

85

85

219,900

219,900

$12,329,000

$16,413,000

Source: Honeycutt et al. 2012.

Figure 22. Lowest-cost alternative supply option (excluding POU systems) based on a high estimate of option costs for susceptible community public water systems and state small water systems (multiple source CPWS or SSWSs exceeding the nitrate MCL; or single-source
CPWS or SSWSs exceeding the nitrate MCL at least once from 2006–2010; or those having no data). Source: Honeycutt et al. 2012.
 

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination 61

 4.4 Cost of Providing Safe
Drinking Water

costs could be lower if a manufacturing discount for bulk
purchase of POU/POE systems were available. The lowest-cost
POU option is used for all domestic well and local small water
systems in the study area, estimated for both the short and
long term. This does not include the cost of monitoring, public
awareness, or regulatory programs to identify and reach out to
this currently unregulated and unmonitored population.
The short-term cost to fund alternative water supplies
for the highly susceptible nitrate-affected population amounts
to $60 to $80 per susceptible person per year, $4 to $5 per
irrigated acre per year for the 4 million acres of agriculture
in these basins, or $75 to $100 per ton of fertilizer nitrogen
(assuming about 200,000 tons of fertilizer nitrogen is applied
in the study area). Allowing for only long-term, more viable,
and sustainable alternative drinking water solutions for the
affected population, the total cost amounts to $142 per
susceptible person per year, $9 per irrigated acre per year, or
$180 per ton of fertilizer in the long term.

Roughly $12 to $17 million per year in additional costs
in the near term will be needed to provide safe drinking
water for people on community systems in the Tulare Lake
Basin and Salinas Valley affected by nitrate contamination of
groundwater (see Table 15). These costs are for 85 susceptible systems currently serving roughly 220,000 people. To
provide safe drinking water for long-term solutions for these
85 systems will cost roughly $34 million per year if new
wells are no longer sufficient. As additional systems become
affected by nitrate contamination, these costs could increase.
The annualized additional cost of providing nitratecompliant drinking water to the estimated 34,000 people
(10,000 rural households) using domestic wells or local
small water systems that are highly susceptible to current or
future nitrate contamination is at least $2.5 million per year
for point-of-use treatment for drinking purposes only. These

Table 16. Estimated cost of the lowest-cost long-term alternative water supply options for susceptible community public
water systems and state small water systems based on system size and proximity to a larger system

Number of Susceptible
CPWSs/SSWSs

Population

Total Cost ($/year)

Pipeline to a nearby system (10,000+ system)

29

36,600

$5,592,000

Groundwater treatment facility

51

8,000

$6,344,000

Surface water treatment facility

5

175,300

$21,532,000

Total

85

219,900

$33,468,000

Option

Source: Honeycutt et al. 2012.

62 

Addressing Nitrate in California’s Drinking Water / Drinking Water Contamination

 5 Policy Options for Nitrate Source Reduction and Funding
This section summarizes a range of policy options for reducing nitrate sources of contamination to groundwater and
funding for resolving the problems of nitrate contamination.
These options are drawn from the more detailed and extensive examination in Canada et al. (2012). Promising actions
on future nitrate source reduction and funding options are
discussed in Section 6.

5.1 Nitrate Source Reduction
Policy Options
A wide range of policy options are available to reduce nitrate
contamination to groundwater over time. We use four criteria
for evaluating broad classes of regulatory options: the costs
incurred by dischargers to reduce nitrate loading to achieve
a nitrate standard (abatement costs), the costs of monitoring
and enforcement, the information requirements, and the
potential for raising revenues (for funding drinking water
actions and other purposes related to nitrate contamination). These results are summarized in Table 17 and further
described by Canada et al. (2012).
Specific technology mandates on farmers and agriculture will result in high per-unit costs for reducing nitrate
contamination. Farming practices vary tremendously, even
within these basins, so specific technology standards would
be unlikely to be broadly effective or economical. Less-specific

performance standards would provide more flexibility but
still do not account for the variation in costs across farms.
Nitrate or nitrogen fees or cap-and-trade approaches give
farmers more flexibility to respond to required reductions in
nitrate loading, thereby reducing the costs of nitrate abatement. If these actions are monitored and enforced based on
nitrate leaching rates, much more costly and extensive on-site
monitoring would be needed, whereas enforcement and
accounting of fertilizer application requirements would be
much less burdensome. Reducing nitrate leachate by imposing fees on nitrate or nitrogen has an added advantage of raising funds that may be used to compensate affected drinking
water users. A cap-and-trade approach can also raise funds if
nitrogen use permits are auctioned.
Hybrid options are also available to regulate nitrate. For
nearly 15 years, the Netherlands has used a hybrid approach
to manage nitrate (Kruitwagen et al. 2009; Ondersteijn et al.
2002). Under this system, agricultural sources are regulated
using a performance standard combined with a fertilizer fee.
(see “The Dutch Experience,” p. 46). Hybrid regulations
might be practical for managing nitrate leachate.
Information disclosure would have dischargers of
nitrate or users of nitrogen make such information public.
Water systems could also face more stringent water quality
consumer reporting rules. Such disclosures should provide
some motivation to reduce nitrate discharges.

Table 17. Summary of regulatory options to reduce nitrate contamination to groundwater

Regulatory Option

Abatement
Costs

Monitoring and
Enforcement Costs

Information
Requirements

Technology mandate

high

Performance standard

medium

Fee

low

Cap and trade

low

Information disclosure

medium

low

low

no (unless fines)

Liability rules

—

high

high

yes

Payment for water quality

low

low (if payment
made to farmers)
high (if payment
made to state)

high

yes (if payment
made to state)

De-designation of beneficial use

low

high

medium

no

Revenue Raising
no (unless fines)

Fertilizer application: low
Nitrate leachate: high

no (unless fines)
yes
yes (if permits auctioned)

Source: Canada et al. 2012.
 

Addressing Nitrate in California’s Drinking Water / Policy Options 63

 Liability rules would make nitrate dischargers liable to
users of drinking water and other groundwater users for the
costs imposed by their discharges. If liability is established in
courts, the costs could be quite high and may not necessarily
result in much discharge reduction. Porter-Cologne Act Water
Code Section 13304 might provide a useful framework.
Having water users or the state pay nitrate dischargers
to reduce their dischargers (“payment for water quality”) also
has high transaction costs, without immediate effect to drinking water quality. But nitrate dischargers might find this an
attractive long-term or preventive solution.
De-designating groundwater for drinking water use
would shift all drinking water burdens to local water users.
This would be administratively and politically awkward,
acknowledging a permanent degradation to groundwater quality without compensating drinking water users.

Major Findings: Future Source Reduction Options
1.  Many options exist to regulate nitrate in groundwater,
but there is no ideal solution. The costs of regulatory
options vary greatly, and while no option is perfect, some
seem preferable to others.
2.  Regulating fertilizer application has lower monitoring
and enforcement costs and information requirements
than does regulating nitrate leachate, but it may be
less effective in achieving nitrate reduction targets.
While the regulation of fertilizer application is easier to
implement and enforce than the regulation of nitrate
leachate, fertilizer regulation does not guarantee that water
quality standards will be met. Due to nonuniform mixing,
transport, and dispersion of nitrate in groundwater, it is
difficult to quantify the impact of a unit of fertilizer on
nitrate contamination of drinking water over time.
3.  Costs to farmers for reducing nitrate contamination
can be lower with market-based regulations (fertilizer
fees or cap-and-trade programs) than with technology
mandates or prescriptive standards because of the additional flexibility farmers have in complying with
market-based regulations. Market-based instruments also
encourage the development and adoption of new technologies to reduce fertilizer use, but they may lead to the formation of contamination hot spots.

64 

4.  Well-defined and enforceable regulatory requirements
are needed for liability rules to work. In California,
all groundwater is considered to be suitable, or potentially suitable, for municipal or domestic water supply and
should be so designated by the Porter-Cologne Section
13304 which gives the California Water Boards authority
to force polluters to pay for alternative water supplies for
affected users of public water systems and private wells.
Legislation might be useful to solidify Regional Board
authority to apply this provision broadly.

5.2 Funding Options
Existing funding to address the costs of drinking water
actions for communities and systems affected by nitrate
contamination appears to be inadequate for many systems
and largely requires drinking water users to bear the costs
of groundwater contamination by others. The cost of nitrate
contamination is felt disproportionately for small water
systems (Honeycutt et al. 2012; Canada et al. 2012). Funding
is also sparse for monitoring and for broad understanding of
groundwater nitrate.
Many state, federal, and local programs exist to help
fund local communities responding to nitrate contamination
of their groundwater supplies, as discussed in Section 3 and
Canada et al. (2012) and summarized in Table 9. Although
current programs provide useful resources, they have been
insufficient in addressing problems of nitrate groundwater
contamination, particularly for smaller and poorer communities, who have less technical, managerial, and financial
capacity for safe drinking water infrastructure and who are
often ill-equipped for formal funding program applications.
A wide range of options is available to improve funding
for drinking water supplies in areas affected by groundwater
nitrate contamination, in addition to funding for nitrate
source reduction and groundwater remediation activities.
These options include state funding options summarized
in Table 18 as well as traditional local water utility and tax
options for funding water systems. These funding alternatives are addressed in greater depth by Canada et al. (2012).
That examination and analysis led to the following findings
for state funding and the promising options that are stated in
Section 6.1(F).

Addressing Nitrate in California’s Drinking Water / Policy Options

 Major Findings: Future Funding Options
1.  Many options exist to raise funds for safe drinking water
and nitrate source reduction actions, but but all require
that someone bear the cost, and many are awkward or
insufficient. Water use fees, groundwater pumping fees,
bottled water fees, crop fees, and fertilizer fees are a few of

the many potential sources for funding safe drinking water
and source reduction actions.
2.  Some funding options give polluters a useful price
signal. Fertilizer (or nitrate leachate) fees and auctioned
permits induce emitters to reduce fertilizer or nitrate use.
Farmers do not pay sales tax on fertilizer in California.

Table 18. Summary of future state funding options

Option

Incentive
to Reduce
Nitrate

Who Pays

Example

Crop tax

no

producers and consumers
of food

State Sales Tax Rate for Soft Drinks: The State of Maryland charges
a 6% sales tax for soft drinks.

Fixed fee on
drinking water
agricultural water

no
no

drinking water users
agricultural users

Federal Communications Commission Universal Service Fee: A
fixed fee placed on monthly phone bill to assure universal access to
telecommunications for low-income and high-cost rural populations.

Volumetric fee on
drinking water
agricultural water

no
low

drinking water users
agricultural users

Gas Public Purpose Program Surcharge: A volumetric fee on gas bills in
California to fund assistance programs for low-income gas customers,
energy efficiency programs, and public-interest research.

Groundwater
pumping fee

medium

agricultural groundwater users

Pajaro Valley Groundwater Pumping Fee: A per-acre-foot charge to secure
financing for debt stabilization and to address groundwater overdraft.

Fee on bottled water

no

consumers of bottled water

California Redemption Value: A refundable fee placed on recyclable
bottles at the point of sale.

Agricultural
property tax

no

agricultural property owners

CA State Property Tax: A statewide ad valorem tax equal to a
percentage of the purchase price is collected from all properties
in the state, with some exceptions.

Fertilizer tax

high

consumers of fertilizer

Mill Assessment Program: The state imposes a fee of 2.1 cents per
dollar on pesticide sales at the point of first sale into the state.

Nitrate leachate tax

highest

nitrate emitters

Duty on Wastewater: In the Netherlands, a tax of approximately $3.60
is imposed on each kilogram of nitrate in wastewater.

Cap and trade with
auctioned permits

high/
highest

consumers of fertilizer
and nitrate emitters

Title IV of the Clean Air Act Amendments: Established a tradable
permit approach to control sulfur dioxide emissions. A small portion
of permits sold in an auction.

Source: Canada et al. 2012.

 

Addressing Nitrate in California’s Drinking Water / Policy Options 65

 Payment for Ecosystem Services in New York City
Currently, New York City participates in a payment
for ecosystem services program for watershed
protection. Under the U.S. Safe Drinking Water Act
(SDWA), the city was required to meet the state
water quality standards by either constructing a
water filtration plant at an estimated cost of $6
billion in capital and $300 million in annual operating
costs (Postel and Thompson 2005) or implementing a much less expensive watershed protection
program. New York successfully requested a waiver
from the SDWA filtration requirement and negotiated an agreement with upstream landowners and
communities within the Catskill-Delaware watershed
to establish a watershed protection plan. In 1997, a
memorandum of agreement (MOA) was signed by
state and federal officials, environmental organizations, and 70 watershed towns and villages to invest
$1.5 billion over ten years to restore and protect the
watershed (Postel and Thompson 2005). Program
financing comes from bonds issued by the city and
increases in residential water bills.
The program’s fundamental activities include land
acquisition; a program to manage and reduce agricultural runoff; a program for better forestry management; a program for enhanced stream management

66 

to reduce erosion and habitat degradation; improvements for wastewater infrastructure in the watershed;
construction of an ultraviolet disinfection plant; and
new regulation and enforcement of mechanisms to
ensure continued water quality protection within the
watershed (Postel and Thompson 2004). As of 2004,
New York City has put $1 billion into the watershed
protection program (Ward 2004). The negotiated
partnership creates a watershed that provides
high-quality drinking water, provides landowners with
additional income, and improves recreational usage
for nearby communities.
In this instance, negotiation or payment for ecosystem services led to the provision of safe drinking
water at a lower cost than the default water filtration
plant. By linking the ecosystem service providers
with the beneficiaries, New York City successfully
executed a comprehensive watershed protection
program that delivers safe drinking water at a relatively low cost. New York City’s watershed protection
program is an example of a payment for ecosystem
services program that guarantees the supply of highquality drinking water and is financed via residential
water bills and city bonds.

Addressing Nitrate in California’s Drinking Water / Policy Options

 6 Promising Solutions
Many options are available to address the problems of drinking water quality, aquifer degradation, and economic costs
from nitrate contamination of groundwater and its regulation.
Of the many options available, some are more promising
than others. But even among these promising options, major
policy choices must be made.

6.1 Areas of Promising Action
Addressing groundwater nitrate contamination requires actions
in four areas: (a) safe drinking water actions for affected areas,
(b) reducing sources of nitrate contamination to groundwater,
(c) monitoring and assessment of groundwater and drinking
water, and (d) revenues to help fund solutions. Promising
actions for legislative and state agency consideration in these
areas appear below. Starred (*) actions do not appear to require
legislative action, but might benefit from it. All actions are
compared in Table 19.

D4: Domestic Well Testing. In areas identified as being at risk
for nitrate contamination by the California Water Boards, as a
public health requirement, CDPH (a) mandates periodic nitrate
testing for private domestic wells and local and state small systems and (b) requires disclosure of recent well tests for nitrate
contamination on sales of residential property. County health
departments also might impose such requirements.
D5: Stable Small System Funds. CDPH receives more stable
funding to help support capital and operation and maintenance
costs for new, cost-effective, and sustainable safe drinking
water solutions, particularly for disadvantaged communities.

Source Reduction Actions (S)

Safe Drinking Water Actions (D)
Safe drinking water actions are the most effective and
economical short- and long-term approach to address nitrate
contamination problems in the Tulare Lake Basin and Salinas
Valley. These actions apply especially to small and selfsupplied household water systems, which face the greatest
financial and public health problems from nitrate groundwater contamination.
D1: Point-of-Use (POU) Treatment. CDPH reports on how
to make economical household and point-of-use treatment
for nitrate contamination an available and permanent solution for small water systems.*
D2: Small Water System Task Force. CalEPA and CDPH
convene an independently led Task Force on Small Water
Systems that would report on problems and solutions of small
water and wastewater systems statewide as well as the efficacy
of various state, county, and federal programs to aid small
water and wastewater systems. Many nitrate contamination
problems are symptomatic of the broad problems of small
water and wastewater systems.*

 

D3: Regional Consolidation. CDPH and counties provide
more legal, technical, and funding support for preparing consolidation of small water systems with nearby larger systems
and creating new, regional safe drinking water solutions for
groups of small water systems, where cost-effective.*

Reducing nitrate loading to groundwater is possible,
sometimes at a modest expense. But nitrate source reduction works slowly and cannot effectively restore all affected
aquifers to drinking water quality. Within the framework of
Porter-Cologne, unless groundwater were to be de-designated
as a drinking water source, reduction of nitrate loading to
groundwater is required to improve long-term water quality.
The following options seem most promising to reduce nitrate
loading.
S1: Education and Research. California Department of
Food and Agriculture (CDFA), in cooperation with the University of California and other organizations, develops and
delivers a comprehensive educational and technical program
to help farmers improve efficiency in nitrogen use (including
manure) and reduce nitrate loading to groundwater. This
could include a groundwater nitrate–focused element for the
existing CDFA Fertilizer Research and Education Program
(FREP), including “pump-and-fertilize” remediation and
improved recharge options for groundwater cleanup.*

Addressing Nitrate in California’s Drinking Water / Promising Solutions 67

 Table 19. Likely performance of promising state and agency actions for nitrate groundwater contamination

Action

Safe Drinking Water

Groundwater
Degradation

Economic Cost

No Legislation Required
Safe Drinking Water Actions
D1: Point-of-Use Treatment Option for Small Systems +
D2: Small Water Systems Task Force +
D3: Regionalization and Consolidation of Small Systems +

♦♦

low

♦

low

♦♦

low

Source Reduction Actions
S1: Nitrogen/Nitrate Education and Research +

♦♦♦

low–moderate

♦♦

low

♦♦♦

♦♦♦

low

♦

♦

low

♦♦

low

S2: Nitrogen Accounting Task Force +

Monitoring and Assessment
M1: Regional Boards Define Areas at Risk +
M2: CDPH Monitors At-Risk Population +
M3: Implement Nitrogen Use Reporting +
M4: Groundwater Data Task Force +

♦

♦

low

M5: Groundwater Task Force +

♦

♦

low

♦♦♦

low

♦

moderate

Funding
F1: Nitrogen Fertilizer Mill Fee
F2: Local Compensation Agreements for Water +

♦♦

New Legislation Required
D4: Domestic Well Testing *
D5: Stable Small System Funds

♦♦

low

♦

moderate

Non-tax legislation could also strengthen and augment existing authority.

Fiscal Legislation Required
Source Reduction
S3: Fertilizer Excise Fee

♦♦

♦

low

♦

♦

moderate

F3: Fertilizer Excise Fee

♦♦

♦♦

moderate

F4: Water Use Fee

♦♦

♦♦

moderate

S4: Higher Fertilizer Fee in Areas at Risk

Funding Options

♦ Helpful
♦♦ Effective
♦♦♦ Essential
+ Legislation would strengthen.
* County health departments may have authority; CDPH requires legislation.

68 

Addressing Nitrate in California’s Drinking Water / Promising Solutions

 S2: Nitrogen Mass Accounting Task Force. CalEPA establishes a Task Force, including CDFA, to explore nitrogen mass
balance accounting methods for regulating agricultural land
uses in areas at risk for nitrate contamination, and to compare
three long-term nitrogen source control approaches: (a) a capand-trade system; (b) farm-level nutrient management plans,
standards, and penalties; and (c) nitrogen fertilizer fees.*
S3: Fertilizer Excise Fee. Significantly raising the cost of
commercial fertilizer through a fee or excise tax would fund
safe drinking water actions and monitoring and give further
incentive to farmers for reducing nitrate contamination. An
equivalent fee or excise tax could be considered for organic
fertilizer sources (manure, green waste, wastewater effluent,
biosolids, etc.).
S4: Higher Fertilizer Fee in Areas at Risk. Areas declared
to be at risk for nitrate contamination might be authorized
to maintain a higher set of excise fees on nitrogen fertilizer
applications (including synthetic fertilizer, manure, waste effluent, biosolids, and organic amendments), perhaps as part
of a local safe drinking water compensation agreement.

Monitoring and Assessment (M)
Monitoring and assessment is needed to better assess the
evolving nitrate pollution problem and the effectiveness of
safe drinking water and nitrate source loading reduction
actions. Such activities should be integrated with other state
agricultural, environmental, and land use management,
groundwater data, and assessment programs (source loading
reduction actions), along with other drinking water, treatment, and wastewater management programs (safe drinking
water actions).
M1: Define Areas at Risk. Regional Water Boards designate
areas where groundwater sources of drinking water are at risk
of being contaminated by nitrate.*
M2: Monitor at-Risk Population. CDPH and the State Water
Board, in coordination with DWR and CDFA, issue a report
every 5 years to identify populations at risk of contaminated
drinking water and to monitor long-term trends of the state’s
success in providing safe drinking water as a supplement to
the California Water Plan Update.*
M3: Learn from Department of Pesticide Regulation
Programs. CalEPA and CDFA examine successful DPR data
collection, analysis, education, and enforcement programs

 

for lessons in managing nitrogen and other agricultural
contaminants, and consider expanding or building upon the
existing DPR program to include comprehensive nitrogen use
reporting to support nitrate discharge management.*
M4: Groundwater Data Task Force. CalEPA, in coordination with CalNRA and CDPH, convenes an independently led
State Groundwater Data Task Force to examine the efficacy of
current state and local efforts to collect, maintain, report, and
use groundwater data for California’s groundwater quality
and quantity problems.*
M5: Groundwater Task Force. CalEPA, CalNRA, and CDPH
maintain a joint, permanent, and independently led State
Groundwater Task Force to periodically assess and coordinate state technical and regulatory groundwater programs in
terms of effectiveness at addressing California’s groundwater
quality and quantity problems. These reports would be incorporated into each California Water Plan Update.*

Funding (F)
Little effective action can occur without funding. Four funding options seem most promising, individually or in combination. State funding from fees on nitrogen or water use, which
directly affect nitrate groundwater contamination, seem
particularly promising and appropriate.
F1: Mill Fee. Increase the mill assessment rate on nitrogen
fertilizer to the full authorized amount (CAL. FAC Code Section 14611). This would raise about $1 million/year statewide
and is authorized for fertilizer use research and education.*
F2: Local Compensation Agreements. Regional Water
Boards can require and arrange for local compensation of
affected drinking water users under Porter-Cologne Section
13304. Strengthening existing authority, the Legislature
could require that a Regional Water Board finding that an
area is at risk of groundwater nitrate contamination for drinking water be accompanied by a cleanup and abatement order
requiring overlying, current sources of nitrate to financially
support safe drinking water actions acceptable to the local
County Health Department. This might take the form of a
local “liability district.”*
F3: Fertilizer Excise Fee. Introduce a substantial fee on
nitrogen fertilizer sales or use, statewide or regionally, to fund
safe drinking water actions, nitrate source load reduction efforts, and nitrate monitoring and assessment programs.

Addressing Nitrate in California’s Drinking Water / Promising Solutions 69

 F4: Water Use Fee. A more comprehensive statewide fee
on water use could support many beneficial activities. Some
of such revenues could fund management and safe drinking water actions in areas affected by nitrate contamination,
including short-term emergency drinking water measures for
disadvantaged communities.

6.2 Developing an Effective
Solution Strategy
Table 19 summarizes the required implementation levels and
likely performance of promising actions identified above.
Much can be done under existing authority and by existing
agencies, although additional legislation could strengthen,
augment, and further support these capabilities. While these
actions include many helpful and effective solutions, none
alone are sufficient to address the problems of groundwater
nitrate contamination and the resulting drinking water problems. The most effective results will arise through a synergistic
combination of major policy direction, legislation, and appropriate blends of of these identified actions.

Options without Fiscal Legislation
Without fiscal (tax, fee) legislation, there are several options to
address drinking water or groundwater degradation, though
each has a separate suite of choices. The most essential is
having the Water Boards formally declare areas at risk for
nitrate contamination. Such a declaration (M1) might entail
a series of complementary actions, such as requiring domestic well testing in at-risk areas (D3), monitoring of at-risk
populations (M2), and formation of a local compensation
agreement or liability district for at-risk areas under Water
Code Section 13304 (F2). Perhaps greater education and
outreach to farmers in at-risk areas would also occur, along
with discharger fees to fund safe drinking water actions to
reduce nitrate discharges.
Porter-Cologne Act, Water Code Section 13304, states
that “a cleanup and abatement order issued by the State
Water Board or a regional Water Board may require the
provision of, or payment for, uninterrupted replacement
water service, which may include wellhead treatment, to each
affected public water supplier or private well owner.” This
provides authority for the California Water Boards to require
landowners contributing to nitrate in groundwater drinking
water supplies to fund drinking water actions for affected
public water supplies and private wells.

70 

Using this authority, when a Regional Water Board
establishes that an area is at risk for nitrate contamination
of groundwater, it could simultaneously issue a cleanup and
abatement order initiating a process for overlying landowners and contributors of nitrate to groundwater in that area
to respond with an area drinking water compensation plan.
This process might involve requiring overlying landowners to support drinking water actions that comply with
public health requirements established by the local County
Health Department, including:
•  an initial date by which groups of overlying landowners would submit a proposed area drinking water
compensation plan for actions, implementation, and
funding to the County Health Department;
•  an intermediate date by which the appropriate Regional
Water Board and County Health Department would
approve such a plan, or one of their own, for overlying
landowners to support drinking water actions; and
•  a date by which any overlying landowner not complying
with the area drinking water compensation plan would
be required to cease and desist applications of nitrogen
to overlying land exceeding a standard established by
the Regional Water Board to protect drinking water
users from nitrate pollution. This condition would apply to all overlying landowners if no alternative local
compensation agreement drinking water action plan
had been approved.
CDPH could issue suitable guidance to County Health
Departments on establishing public health requirements.
County Health Departments would need to be empowered to collect fees from landowners pursuant to a drinking
water action plan under a cleanup and abatement order. These
fees would include the cost to the County Health Department
of overseeing the drinking water action plan. Fees could be
collected as part of annual county property tax assessments.
This approach would provide a relatively organized and
efficient means for landowners contributing nitrate to a
contaminated aquifer to help decrease the additional costs
incurred by drinking water users from nitrate contamination.
To protect public health, requiring testing of domestic
wells in areas declared to be at risk of nitrate contamination
seems prudent and in the public interest. Legislation seems
needed to require such testing (perhaps periodically or on
property sale), although perhaps this can be done by county

Addressing Nitrate in California’s Drinking Water / Promising Solutions

 ordinance or administratively as a requirement to receive
compensation under Water Code Section 13304.

Options Requiring Fiscal Legislation
Raising additional revenue to address nitrate issues seems to
likely require legislation. The only exception is raising the
small mill fee on fertilizer to its full authorized limit, which
is approved for funding nitrogen use education and research
activities.
Among these funding options, perhaps the most promising is to establish a statewide fee on the sale of nitrogen fertilizers, or a more administratively awkward fee on nitrogen use
only in designated drinking water contamination risk areas.
Such fees would act as both funding sources for safe drinking water actions and as an incentive to reduce nitrogen use,
thereby somewhat reducing nitrate loading to groundwater.
Partial rebates on these fees could be arranged for farmers
who are involved in local area drinking water compensation
plans or who have agreed to enforceable reductions in nitrate
loads to groundwater.

6.3 Getting Organized
Many promising options are organizational. The management
of nitrate groundwater contamination and its drinking water
consequences is currently divided among several state agencies, each with historically derived authorities, purposes, and
funding, as summarized in Section 3. In particular, the State
and Regional Water Boards have the greatest authority under
California’s Porter-Cologne Act for groundwater quality. The
California Department of Public Health and County Health
Departments have authority over drinking water quality and
public health. The California Department of Food and Agriculture has the greatest authority over fertilizer management and
agricultural activities. The Department of Pesticide Regulation
has no authority or direct interest in nitrate problems, but it
has a successful, modern, integrated program for pesticide
management, which may serve as a model for other forms
of contamination, including nitrate. California’s Department
of Water Resources has overall water planning responsibility
for the state, including oversight and funding authority for
Integrated Regional Water Management Plans, and the State
Water Board regulates water rights. The nitrate issues of the
Tulare Lake Basin and Salinas Valley overlap several agencies.
As environmental problems evolve beyond the origins of these

 

agencies, there is often a need to evolve and coordinate the
actions of different state and local agencies.
Nitrate contamination of groundwater is just one
example of groundwater quality (and quantity) issues that
many state agencies have in common. Each of the above agencies has its own groundwater monitoring, data, management,
and often funding programs for groundwater overall or for
individual groundwater quality or quantity concerns. Each of
these agencies is facing, or will soon face, a range of similar and
related groundwater problems regarding nitrate, pesticides,
salts, and groundwater recharge and overdraft quantities.

Informational Actions
To help prepare the state to better address these problems, we
propose several informational actions. Many informational
actions could be triggered by requiring each of the California Water Boards to declare areas at risk of drinking water
contamination from nitrate in groundwater (promising action
M1). This finding is purely technical and seems well within
the means of the Regional Water Boards, perhaps with some
coordination from the State Water Board. A declaration of
an area being at risk for nitrate groundwater contamination
could also trigger several other informational actions. To
protect public health, households and other very small water
systems would be required to test drinking water wells for
nitrate concentration upon sale and periodically thereafter
(D4). Populations depending on groundwater in at-risk areas
would also be reported to DWR for inclusion in state water
planning efforts (M2). The “area at risk” designation could
also serve to prioritize or trigger other funding, fee, education, monitoring, or regulatory actions.

Task Forces
We also propose four independently led task forces consisting of a core of agencies with overlapping interests. Having
independent leadership would provide some assurance that
each task force views the subject problem from more than
just a collection of pre-existing agency perspectives.
•  A task force on small water systems would seek to
develop a common state policy for the problems of
small water and wastewater systems in California. Small
systems have inherent problems with higher costs, more
precarious finance, and fewer technical and managerial
resources, as they lack economies of scale. CDPH has
long recognized these problems on the water supply side,

Addressing Nitrate in California’s Drinking Water / Promising Solutions 71

 but there are likely to be benefits from addressing these
local water and wastewater utility problems together.
•  A task force on nitrogen mass accounting would explore
the technical, economic, and institutional issues of having farms account for nitrogen and nitrate fluxes as a
basis for regulation or fees. Currently, such detailed accounting is done for pesticides, air emissions, and dairy
nitrogen, and it is being contemplated for salts and irrigation water. Having widespread and relatively detailed
accounting for nitrogen would allow for some forms of
economic management, such as cap and trade, and could
also potentially support various educational and regulatory means of reducing nitrate loads to groundwater. This
leads to a larger strategic question of whether the range
of environmental emissions from agriculture should be
accounted for separately by different agencies, gathered
together in a single agency, or coordinated among separate agencies. Having a fragmented accounting system
seems likely to increase costs and the regulatory burden,
while reducing overall insight and understanding of
environmental and agricultural problems. Accounting
systems can be costly and time consuming for agencies
and nitrogen users to administer.
•  Two groundwater task forces are proposed. The first
is in regard to groundwater data. A major difficulty
in preparing this Report has been the fragmentation
of groundwater data within and between agencies, as
well as the lack of general access to groundwater data.
Groundwater has become such an important issue that
most agencies have their own groundwater activities. It
is now critical that the state has a coherent and more
forward-looking policy and technical capability for the
collection and management of groundwater data. This
issue seems sufficiently complex to call for a separate
groundwater data task force.
•  The many state interests and agencies involved with
groundwater issues also seem to call for a periodic assessment of how effective these distributed programs are in
practically addressing California’s groundwater problems.
This second independent groundwater task force would
periodically review and report on the effectiveness of state
groundwater activities to each California Water Plan.

72 

6.4 Dilemmas for State Action
Groundwater nitrate contamination poses several overarching dilemmas and challenges for state policy, which will likely
require broader discussions.
Local, statewide, or no compensation for pollution. In
practice, the costs of pollution of drinking water sources are
often borne by drinking water users. Some aspects of state
policy (Water Code Section 13304) allow for fairly direct compensation for such costs. And general state support for water
treatment also helps cover such costs. State general funds seem
unlikely to be able to provide substantial support in the future,
and many local communities, particularly small systems, are
unlikely to have financial resources to cover such costs. Can
the state establish a reasonable, relatively low-cost means to
assess non-point source polluters for the drinking water (and
perhaps other) costs entailed?
Degradation of groundwater. Current state law and policy
does not allow degradation of groundwater quality to levels
above water quality objectives defined in the applicable Basin
Plan. However, no technological and institutional strategy
has been found to economically reduce all nitrate discharges
to levels that prevent further groundwater degradation. More
modest approaches to reducing nitrate loads are likely to be
economical. However, these more moderate reductions in
nitrate loads would typically reduce the rate of groundwater
degradation, but they would not always prevent degradation,
particularly in the short term. If degradation is practically
inevitable for some sources, how should state policy best
oversee and regulate degradation?
Policy and policy implementation for environmental effects
of land use. Both agriculture and urban land uses now face a
host of environmental issues overseen by separate agencies and
programs. The environmental causes and effects of nitrate contamination alone, for example, involve a diverse array of state
agencies and programs. However, these same land uses also
imply environmental impacts via pesticides, salinity, water use,
air pollution, surface runoff, and endangered species. Many
of these regulated (or potentially regulated) aspects interact
environmentally, or their solutions have interactive effects and
costs for land management. Is there a more effective and efficient policy approach to managing the environmental effects
of land uses than mostly independent agencies and programs
for each impact?

Addressing Nitrate in California’s Drinking Water / Promising Solutions

 7 Conclusions
1. Nitrate problems will likely worsen for decades. For
more than half a century, nitrate from fertilizer and animal
waste have infiltrated into Tulare Lake Basin and Salinas
Valley aquifers. Nitrate will spread and increase nitrate
concentrations in many areas for decades to come, even
if the amount of nitrate loading is significantly reduced.
Most nitrate in drinking water wells today was applied to
the surface decades ago.
2. Agricultural fertilizers and animal waste applied to
cropland are the two largest regional sources of nitrate
in groundwater. Although discharges from wastewater
treatment plants, food processors, and septic tanks also
contribute nitrate to groundwater and can be locally
important, almost all of the regional groundwater nitrate
contamination in the Tulare Lake Basin and Salinas Valley
is from agricultural fertilizers and confined animal waste.
3.  Nitrate loading reductions are possible, some at modest
cost. Large reductions of nitrate loads to groundwater
can come at substantial economic cost. Farm management is improving, but further improvements are necessary.
While some are immediately achievable at modest cost, significant barriers exist, including logistical constraints and
inadequate education. The cost of reducing nitrate loads
to groundwater can be considerable for large reductions,
especially on crops that require a substantial (much greater
than 25%) decrease in nitrogen application from today’s
agronomically accepted, typical rates. Such dramatic reductions in fertilization rates without crop yield improvements
can decrease net revenues by possibly several hundred
million dollars per year within the study area.
4. Direct remediation to remove nitrate from large
groundwater basins is extremely costly and not technically feasible. The volume of nitrate-contaminated
groundwater is far larger than for urban contamination
plumes. Standard pump-and-treat remediation to treat
the groundwater underlying the Salinas Valley and Tulare
Lake Basin would cost tens of billions of dollars. Instead,
“pump-and-fertilize” and improved groundwater recharge
management are less-costly long-term alternatives.

 

5.  Drinking water supply actions, such as blending, treatment, and alternative water supplies, are most costeffective. Blending will become less available in many
cases as nitrate pollution continues to spread. Regardless of actions taken to reduce long-term nitrate loading to
groundwater, many local communities in the Tulare Lake
Basin and Salinas Valley will need to blend contaminated
groundwater with cleaner water sources, treat contaminated
well sources, or develop and employ safe alternative water
supplies. Blending will become less available as an option
in many cases as nitrate pollution continues to spread. The
cost of alternative supplies and treatment for these basins is
estimated at roughly $20 million to $36 million per year for
the next 20 years or more.
6.  Many small communities cannot afford safe drinking
water treatment and supply actions. High fixed costs
affect small systems disproportionately. Many small
rural water systems and rural households affected by
groundwater nitrate pollution are at or below the poverty
level. Treatment and alternative supplies for small systems
are more costly, as they lack economies of scale. Adherence to nitrate drinking water safety standards without
substantial external funding or access to much less expensive treatment technology will potentially bankrupt many
of these small systems and households.
7.  The most promising revenue source is a fee on nitrogen
fertilizer use in these basins. A nitrogen fertilizer use
fee could compensate affected small communities for
mitigation expenses and effects of nitrate pollution.
Under Water Code Section 13304, California Water
Boards could also mandate that nitrate dischargers
pay for alternative safe drinking water supplies. Either
mechanism would provide funds for small communities
affected by nitrate pollution, allowing them to develop
treatment or alternative water supplies that reduce the
cost and effect of nitrate pollution over time.

Addressing Nitrate in California’s Drinking Water / Conclusions 73

 8.  Inconsistency and inaccessibility of data from multiple
sources prevent effective and continuous assessment.
A statewide effort is needed to integrate diverse waterrelated data collection activities by various state and
local agencies. Throughout this study, we often faced
insurmountable difficulties in gaining access to data already
collected on groundwater and groundwater contamination
by numerous local, state, and federal agencies. Inconsistencies in record keeping, labeling, and naming of well records

74 

make it difficult to combine information on the same well
that exist in different databases or that were collected by
different agencies. A statewide effort is needed to integrate
diverse water-related data collection activities of various
state and local agencies with a wide range of jurisdictions.
Comprehensive integration, facilitation of data entry, and
creation of clear protocols for providing confidentiality as
needed are key characteristics of such an integrated database structure.

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78 

Addressing Nitrate in California’s Drinking Water / Literature Cited

 The Tulare Lake Basin and the Salinas Valley, with 2.6
million inhabitants and home to nearly half of California’s
agricultural production, are the focus of this report. Nearly
one in ten people in these two regions are currently at risk for
nitrate contamination of their drinking water. Water systems
providing water for half of these regions’ population have
encountered excessive nitrate levels in production wells at
least once over the last five years.
An independent team of scientists at The University of California, Davis, was contracted by the State Water Resources
Control Board to examine this problem. Working in consultation with an Interagency Task Force representing many
state and local agencies, the authors undertake a uniquely
broad and comprehensive assessment of the wide spectrum
of technical, scientific, management, economic, planning,
policy, and regulatory issues related to addressing nitrate in
groundwater and drinking water for the Tulare Lake Basin
and Salinas Valley.

This report identifies, describes, and quantifies past and
current sources of nitrate, details the extent of groundwater
nitrate contamination, and provides a comprehensive,
up-to-date guide to the many options available to address the
problems of drinking water quality, aquifer degradation, and
economic costs from nitrate contamination of groundwater
and its regulation. The report concludes by outlining promising actions in four key areas: safe drinking water actions for
affected areas; reducing sources of nitrate contamination to
groundwater; monitoring and assessment of groundwater
and drinking water; and revenues to help fund solutions. Even
among these promising options, major policy choices must be
made. The research compiled in this report provides a foundation for informed discussion among the many stakeholders
and the public about these policy choices.
The Center for Watershed Sciences at the University of
California, Davis, brings a wide range of experts together
to examine California’s major water issues and problems.
Its activities range from scientific and analytical modeling
studies to major works on urgent problems. More about the
Center can be found at watershed.ucdavis.edu.

Center for Watershed Sciences
University of California, Davis
http://groundwaternitrate.ucdavis.edu