YERINGTON PAIUTE TRIBE 17l Campbell Lane Yerington, NV 89447 Phone: (775) 783?0200 Fax: (775) 463-2416 Tribal Chairman Laurie A. Thom November 20, 2019 Vice-Chairman Ginny Hatch Member LeAnna Blue Horse Greg LOVBIO Member Administrator Elwood Emm NV Division of Environmental Protection Member 901 S. Stewart Street. Ste. 4001 Loretta Johnson Carson City. NV 89701 Member Michelle Keats Member Rli: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 Anaconda Copper Mine Site Albert Roberts Deputy Administrator Mr. Lovato: Vinton Hawley Secretary of Record Please ?nd attached our comments regarding the Revised Draft Remedial Deseree Landa Investigation Report Site-Wide Operable Unit (2019 R1) Anaconda Copper Mine Site, Lyon County, Nevada. We look forward to meeting with BP, BLM and NDEP regarding the comments and reviewing a revised document in the near future. Our review of the document found it to be incomplete. Please consider this another request for those necessary technical meetings regarding these issues. Sincerely, ass-?Z Laurie A Thom. Chair an Yerington Paiute Tribe C: Harold Ball. USEPA Dave Davies, BLM Gerry Emm, BIA Tashina Jim, WRPT ?This Agency is an Equal Opportunity Provider and Employer? Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 RI) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 Overview Review of this document is inhibited by inappropriate and problematic references. In addition, NDEP and BP have failed to meet the request by the Tribe for technical meetings needed to manage the dramatic change in hydrologic conceptual model proposed since the introduction of the 2018 geothermal and plume stability documents. The combination of poor-quality editing for this document, incorrect assumptions regarding mine history and other issues will require a major revision and review; the document is incomplete at best. This review should be considered incomplete; a more complete review can be conducted once the document is revised to the standard required for the intended site decision. In the absence ofa dramatic increase in the resources available to the Tribe, it is important to remind the lead regulatory agency(s) and responsible party that the Tribe?s role in the process to review, not author the site documents. Page 1 Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 RI) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November l9, 20I9 Comments 1. Section 3.2.4 5 Redox preserved soil samples from ?ve near evaporation ponds and four borings/wells located in agricultural areas north of the Site. What is meant by the term "opportunisticall)-' collected? samples? Was there a design in the consideration and location of soil samples of for Oxidation-Reduction Potential (ORP) measurements? 2. Section 3.2.4. The ?eld and laboratory measurement of the ORP in a water or soil sample is complex. in light ol?thc attached article abstract by Lindberg and Runnels (1984). and some ofthe challenges in ORP measurement (not calibrated measurement but checked against a knoun standard(s): electrode poisoning. aqueous disequilibrium. mixed redox potentials)?please describe how reliable or uncertain RI sample ORP values are: and the uncertainty ofmodelling code results with respect to geotliennal mineral saturation results. The follow reference should be considered: spun -- 0 Ground Water Redox Reactions: An Analysis of 0 Equilibrium State Applied to Eh Measurements and fin-chemical Modeling 0 [m ml. ?Ill 9 Ian-h rill-mm mammal-summer mmhmumm 3. Section 5 1 17}. The three major sources ofcontaminants of interest (COls) are Mine-In?uenced Water (MIW). Agriculture. and Geologic Materials including geothermal alteration zones. Arimetco facilities 122) are discussed. but there are statements regarding the need for possible further investigation of process ?uids spill areas and their potential to impact groundwater quality. Are anv further investigations planned for Arimetco process fluid spill areas? Page 2 Document: Revised Draft Remedial investigation Report Site-Wide Operable Unit (2019 R1) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 4. Section 5.2.2 126). The RI directs the reader to Appendix M. Section 5 for further information about agriculture in?uence on groundwater quality. and it should note this refers to the Final Plume Stability Technical Memorandum. 5. Section 5.23 130). The describes geologic sources (mineralization and hydrothermal alteration) under a structural step-over fault setting as an alternate source of natural COls following the methodology of Faults et a1 (2011). The reference is incorrect and not included in the References section. The correct author is Jim Faulds and it should be correctly referenced in the text and References Section 9. 6. Section 5.2.3. This section brie?y describes how enrichment and depletion of trace elements occurs in a geothermal system. What geothermal minerals would incorporate or bind the trace elements in the mineral structures? 7. Section 5.2.3 132). How does modelling con?rm geothermal water types without some manner of independent last paragraph. last veri?cation or results credibility testing? sentence. 8. Section 5.3 (p.133). The reference to Figure 5-1 appears to be incorrect. The "Figures Section 5" starts with Figure 5- la and does not appear to support the statements in this section. 9. Section 5.4.2 146). The discussion of the extent ofthe plume of contaminated groundwater caused by agricultural irrigation. leaching. and recharge as presented in Figure 5-14 (5-l9a to 5-l9g): Shouldn?t an area around be included in the agriculture impacted water plume map since the Final Plume Stability Technical Memorandum speci?cally cited as the classic example ofan agriculture impacted well? 10. Section 5.4.3 152). The summary description of the Exploratory Data Analysis (BSA) and Mulitivariable Statistical Analysis (MSA) are inadequately summarized and described for the main body of an R1. The Rl brief description ofthe three major water types identified by the Final Geothermal Technical Memorandum (GTM) in Appendix is an oversimpli?cation of the MSA complexities and analysis contained in the GTM. The RI should include information from the GTM Executive Summary to more fully describe the MSA section. 11. Section 5.4.3 and Appendix MSA and cluster analysis. The development of [8 water types by cluster analysis is not completely clear in the Final GTM report. Doesn?t the operator ofthe cluster analysis have to provide an initial number of clusters to start the analysis leading to the results that there are 18 distinct water types encompassed in the Page 3 Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 RI) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19. 2019 three major nater types? Please provide a more quanti?ed explanation of the steps in the MSA cluster analysis that clearly shous hon l8 nater types were developed in the statistical analysis. 12. Section 5.4.3 and The Appendix report determination that there are 18 chemical distinct water types in the Appendix MSA and cluster analysis. Anaconda Copper Mine Site Study Area is complex and seems to imply that mixing ofthese distinct water zones does not occur very much il'at all. How is this possible given that the RI describes hon the agricultural production well pumping near the ACMS exerts a strong in?uence on the groundwater flows and direction?? 13 Section 5.4.3 and Appendix N. The Final GTM describes hon relic geothermal mineralization and hydrothermal alteration impacted bedrock and alluvial materials along the Sales Fault north of the ACMS. Since there it as very limited soil and-'or rock testing for speci?c geothermal minerals and alteration, is there not a data gap in the R1 database for this component? Should there be some limited sampling and analysis of bedrock alluvial materials for the minerals or textural alteration evidence using Scanning Electron Microscopy (SEM) or X-Ray Diffraction (XRD) to con?rm the geothermal mineralization and subsequent aqueous equilibrium modelling? 14. Section 5.4.4 This section states: A quantia?e-quantiie (Q-Q) piot of the sulfur isotopic data is shown in the upper panel of Figure 5 - 16. The data do not piot aiong a straight line. and there are muitiple in?ection points indicating the presence ofnmitipie populations within the data set. Figure 5-16 is entitled ?Extent ofEievated Nitrate in the Shaiiow Zone from Agricuttural Activities North of Site.? The referenced ?gure may be 5-18 but the issue with references requires revision. 15. Section 5.4.4 This section discusses the application of a 0-0 plot to determining relationships within the sulfur isotope data. The method should be better described, ?statisticatpiots of the sni?ir isotopic data generated in Pro UCL is not a reference for a method. There are a variety of methods and formulas for this application. the one used here should be clearly stated and referenced. The sections also discusses "multiple inflection points? as the indication for ?presence of multiple populations." Lacking reference for what is a signi?cant in?ection point. i.e. not utilizing Page: Document: Reviewer: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 R1) Anaconda Copper Mine Site Yerington Paiute Tribe Date: November 19, 2019 con?dence bands, creates a question regarding this interpretation. Confidence bands or other discussions of signi?cance are needed. There is one notable inflection that will likely be found signi?cant with further evaluation. There are two notable sources of sulfur that were used at the mine as discussed in a previous comment set generated for the BGWQ (Brown and Caldwell, 2015) by the Yerington Paiute Tribe November ll, 20l6, Section and 3.2: The document states highly positive 63"Ssrn signature of 7. was observed in shallow groundwater immediately don-'ngradient of the IT. Pond at well suggesting a release of a dt?'erent source ofsulfitr at the location than what was used during early processing operations at the Site (Page 59 Section 5.5.2). This would suggest that the built of the plume may align with the J. 93 marimum value but the leading edge. material released during that ?early processing operations at the site may not. in addition, the leading edge of the plume could have a larger proportion of naturally occurring sulfate which may mask the 5345'.er signature. in this case. the monitoring wells on the south side of the Reservation generah'y are below the 4.93960 standard (MlV's l-l. i5 and while others more to the north (MW l2) do not. This provides an indication that the leading edge of the plume may be impacting groundwater at the Reservation. This topic is also com?ounded in the document. last paragraph that states. 6345304 values in the NSA groundwater are within or above the range of 63 45st): values in background groundwater. even in the presence of elevated sulfate and uranium concentrations above MCLs seems to contradict the context of the paragraph that the groundwater in the NSA does not have characteristics consistent with impacts from the Site sources. Following the conceptual model used in this study. that the edge of the plume reflects the earliest part of the operation. then the use of 63 ?San signature will be confounded by the first mine waste introduced into the aquifer which. follou-?ing ARC 's theory, is the edge of the plume. In reality, the edge of the plume is iltelv farther north than this approach can detect resulting in the ?mired Page 5 Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 RI) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November I9, 2019 results at l?Pi? monitoring wells other words. the higher signature initiai waste is masking the inter iower 634.5304 signature anitr at the edge ofthe phime. Adding this caveat wili improve the resolution of the actuai phtme size. and ?liiows other iines of evidence presented in this review. This supports the large inflection (the statement of ?multiple in?ections" requires the use of con?dence bands) but counters the argument that the earliest releases are from Leviathan Mine Sulfur. The oldest releases from Anaconda Mine were not from Leviathan subsequently, this process is only applicable to ?nding releases associated with that product and not the plume edge. This is further complicated by the use of non-Levaithan Mine sulfur after according the site history (U.S. EPA. 20l0): in [962. Anaconda ceased mining sui?tr ore from the Leviathan .liine in Aipine County. Cah'fornia. the purpose of generating acid. Foiiowing ciosure of Leviathan Mine. acquiring sui?ir from outside sources was required. i't'istoricatr correspondence indicate that iiqnid srtifur was being purchased?'om severai suppiiers, transported by railcar to H?abuska station. and hauled to the Site. where Anaconda then continued generating acid at the piant. So, for Operations from I953 - I962. sulfur from Leviathan mine was used. From 1962 until operations ceased in 2000. a ?variety of other sources? were used. Therefore, the presence of sulfur associated with Leviathan mine would indicate but the absence of the Leviathan signature would not indicate the sulfur was not from the mine. This results in a need to correct this section and other conclusions based on the assumption. The statistics are useful but are overstated and in need of further modification for both applications and significance (con?dence bands}. Page ll Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 R1) Anaeon da Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 16: __Section 7.0 185) This section states: Groundwater quaiity in the A1524 has been impacted by agrictdturai activities rather than mining activities (BC 26? 6b) based on nndtipie tines of evidence including groundwater ?ow patterns. ciremicai distributions, groundwater age estimates. hydroiogic tracers. and sui?rr isotopes. These agriculturai practices have resuited in concentrations ofsui?ate and uranium that are elevated above background vaiues under ii {(13 and or exhibit increasing trends Where the results in NBA rely on the analysis based on groundwater age. hydrologic tracers and sulfur isotopes. the same parameters presented in the BGQA (Brown and Caldwell. 2015) that show a very different interpretation ofthe plume. It would appear that the use of these methods is inconsistent. Those methods also indicate a much larger MIW area (Brown and Caldwell. 2015) than what is presented in this document. The result is a need to revise the approach and use of the sulfur isotope data to more closely match the data from the site. values underneath the evaporation pond that do not follow the Leviathan sulfur theory. and the site history. the other sulfuric acid sources used for the majority of the mines operation. Follou ing this correction. the approach to determining the plume will require revision. Page i Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 R1) Anaconda C0pper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 17. The Tribe provided comments on the DRAFT Identi?cation and Geochemical Characterization of a Geothermal System in Mason Valley, Nevada (October 2018). These comments are included as Appendix 1 and are applicable to Appendix ofthe Rl. Despite request, the technical review and discussion of the document has been inadequate; many of the Tribe?s comments remain unaddressed. 18. The Tribe provided comments on the DRAFT Evaluation of Plume Stability, Anaconda Copper Mine Site, Lyon County, Nevada (May 7, 2018) in June of 20 8. The Tribe did not receive a response regarding these comments from NDEP or BP. These comments are included as Appendix 1 and are applicable to Appendix ofthe RI. Despite request, the technical review and discussion ofthe document has been inadequate; many ofthe Tribe?s comments remain unaddressed. References Brown and Caldwell. (20 5). Background Groundwater Quality Assessment Revision 3. La Palma, CA: Atlantic Rich?eld Company (BP). LI .8. EPA. (2010). Historical Summary Report. Anaconda-Yeringron Mine Sire, Yerington, NV. Page 8 Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 RI) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 Attachment 1 Document: DRAFT Identi?cation and Geochemical Characterization of a Geothermal System in Mason Valley, Nevada (October 20l 8) Reviewer: Yerington Paiute Tribe Review provided November 28, 2018 Introduction This report was produced by BP without the participation of stakeholders and at least some regulatory agencies. The conclusions are contrary to the previous analysis provide by BP and disregard the current understanding ofthe site conceptual model. The entire effort appears to be outside the more practical processes found to be effective for this type of analysis and lacking in both peer review and planning. The theory itself is suspect but the delay this type of effort can cause to real efforts to address the contaminated aquifer are obvious. The inability of the current lead regulatory agency, NDEP, to control this type of process manipulation and keep the site on a path that will reduce the risk to the community and environment is cause to request the return to EPA lead. General Comments I. NDEP failed to notify participating Tribes, stakeholders and other regulatory agencies that there was a need for a study to determine the extent of elevated trace element concentrations in Operable Unit I groundwater at the Anaconda Copper Mine Site (ACMS) proposed to be attributable to a geothermal system and altered minerals in the aqueous and-"or solid phases. This leaves all parties at a disadvantage; BP is making technical decisions outside of peer or regulatory review and then NDEP is not permitting appropriate review ofthese major changes in the conceptual site model. 2. This document disregards all previous discussions and interpretations of aquifer conditions. The responsible party is actually disagreeing with their own, previous interpretation of site conditions. In the ?Background Groundwater Quality Assessment - Revision 2? (July 2, 20l5) report, a word search for the term ?geothermal? does not find a single entry. There is no attempt by BP or NDEP to describe the need to revisit background concentrations using a suspect geothermal system concept and more modelling. The 2015 BGQA report describes key well locations that were sampled to define background values for various parameters including trace elements for the three study areas (See Tables and 6-3). The methodology to determine background concentrations in 2015 did not include geothermal system components in the groundwater characterization. 3. The GUI monitoring system, including over 300 monitoring wells and hundreds of thousands of data collection events, was designed and implemented without a consideration for the processes introduced in this document. In the absence of any Attachment 1 Page 9 Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 R1) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 planning for this type of analysis, a regional event that according to this document, was known prior to the planning process for this site, what are the limits to forcing this monitoring system into the new role? What additional regulatory review is required to push the monitoring system into this new unanticipated role? General Comments (Continued) 4. The arrival of the DRAFT Geothermal-Geochemical report is unexpected and creates a dilemma for key stakeholders in the ACMS process because there is no attempt to demonstrate how this new document and information ?ts into the er'FS ROD process. We cannot say how the current process under state deferral is proceeding because there have been no Technical Group meetings since NDEP took over as the lead regulatory agency in 2017. 5. The DRAFT Geothermal-Geochemical report does not make an attempt to compare to and reconcile with the 2015 BGQA report data regarding trace element background concentrations and the interpretations about the extent and location of mine-impacted water to date. The DRAFT Geothermal?Geochemical report provides a suspect alternative interpretation and location for the extent of mine-impacted water (See Figure 7-5). How will the new information be reconciled with previous information and interpretations about the geochemical characteristics of OLI-I groundwater in the three study areas (SERA, SWRA, 6. Section 5.1 Study Area Water Types describes three major types of groundwater and the characteristics used to select "a few? representative groundwater samples to indicate geothermal background, regional background, and mine-influenced water to help the reader identify differences in data chemistry in piper diagrams and X-Y plots. The locations of wells for the three types of water data are shown in Figure 5-1, but there is no description of the methodology used to select wells. The methodology seems arbitrary or biased toward embracing the geothermal concept as the correct approach. Mixed Groundwater well locations are not shown? Without actual discussion and analysis of this process, it has to be taken at face value; cherry picked data used to support a predetermined outcome. 7. Figures 5-2 (Piper diagram of four groundwater types) and 5-3 (X-Y plot of Cl vs. TDS of four groundwater types) emphasizes the three (or four) groundwater types: Geothermal Background; Regional Background; Mine-Influenced. The fourth water type, Mixed Groundwater, is present as numerous sample points in both Figures show, but this water type is not discussed or given any context in this report. Why? Attachment 1 Page 10 Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 R1) Anaconda C0pper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 General Comments (Continued) 8. In Section 5.3 key geochemical indicator parameters associated with geothermal activity were identi?ed as: TDSMo, and based on the work of Zehner, 2006 and Bamford, and other elements associated with copper hydrothermal system alteration mineral assemblages. Uranium is usually not one of the kev indicator parameters for a geothermal system, but in the case of the Yerington deposit it is a unique, enriched element. Given the importance of uranium as a primary C01 in the groundwater system the explanation ofthe uranium mineral coffinite that is altered to haiweeite as a reduced groundwater becomes more oxidized the geochemical discussion and explanation are inadequately described. Why are there no roll-front type uranium deposits in the alluvial sand deposits along the thermal zones associated with the Yerington deposit that are in contact with oxidized groundwater from the ?Eastern Zone?? 9. In Section 5.4 the de?nition ofthree major mineralogic zones associated with the geothermal system is based primarily on mineral assemblages that are chemically unique to each zone. Mineral saturation indices were calculated for data points in each ofthe three areas to define a geochemical spatial distribution of minerals that indicate a relationship to a geothermal feature or characteristic chemical attribute. The geochemical modelling is used to show the potential relationship to the geothermal feature, but how will this modeled information be validated? Will there be soil and rock samples collected and analyzed with SEM or other methods to help validate the predicted mineral assemblages? 10. In Sections 5 and 6 the report explains there are three (fourJ major water types as depicted in Figures 5-2 and 5-3: 1) Mine-Influenced Groundwater; 2) Regional Background Groundwater; 3) Geothermal Background Groundwater; and 4) Mixed Groundwater. At the bottom of page 22 in Section 5.4, it appears that the Geothermal Background Groundwater type is TDS normalized and rede?ned to represent three major mineralogic zones: 1) Geothermal Core; 2) Western Zone; and Eastern Zone? Are the locations of these geothermal zones-areas de?ned on a map somewhere? The methodology to explain the process followed is not very clear. I 1. In Section 6, although the statistics indicate mineral assemblage clusters that agree with the geochemical signatures of groundwater, the earlier explanation of the groundwater types was in question; the statistics do not clarify the issue of Mixed Groundwater and its role in this alternative interpretation of the extent of mine-influenced water. Attachment 1 I Page 11 Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 RI) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 Attachment 2 Document: DRAFT Evaluation of Plume Stability, Anaconda Copper Mine Site, Lyon County, Nevada (May 7, 2018) Reviewer: Yerington Paiute Tribe June 21, 2018 Comment No. 1. Data density varies across creating data gaps in critical areas. The size of at approximately 10 square miles of area is so large that the density of data points (monitoring wells and-"or private wells) is lacking resulting in a higher level of uncertainty regarding the character of the groundwater system with respect to the presence or absence of contaminant sources from the mine. natural, and-?or agricultural practices. The southeastern and southwestern parts of are adequately characterized with monitoring wells and media sampling to identify sources of Contaminants of Interest (COls), but as one moves into the northern part of the data density is much less due to the absence of wells and media sampling. The leading edge of the northern extent of Mine impacted Water (MIW) is not necessarily a uniform front of all COls in a line or similar position, but more ofa zone of mixing and hydrologic ?uctuation clue to local and seasonal agricultural pumping and recharge along the plume edge. Some potential sources of ?015 tn the groundwater system in the northern are conceptually viable, but uranium is complex and not all potential sources have been fully characterized. See Figure for a map of the size nfthe boundary encompassed by (Figure from the Groundwater Geochemical Characterization Data Summary Report, DSR Revision 1, li20l5). ARC stated in their June 27, 2017 response to EPA that further sampling to determine agricultural signature (andlor inputs) to the groundwater system is not necessary (See Figure 2). This assumes a static system, an incorrect assumption when surface supply changes (diminishes by climatic drought) and more utilization of groundwater are expected. This will create a need for identi?cation of agricultural signatures in the NSA as the plume of MIW would likely move further north due to increased downgradient pumping. RE COMMENDA TION additional data is needed in sections of including on the Reservation. Expansion ofrlre monitoring system will also be required as response actions are planned. Comment No. 2. Concerns about the level of uncertainty with interpretation and monitoring in the NSA may not be adequate to support the RI. is subdivided into three smaller study areas with two areas, the South West Recharge Area (SWRA) and the South East Recharge Area (SERA) Attachment 2 Page 12 Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 R1) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 hosting monitoring well networks designed to characterize the nature and extent of Mine Impacted Water (MIW). The third study area, the North Study Area (NSA) has approximately [3 well clusters and 8 single wells. The NSA background wells BEW- 59D3) were constructed to determine the Shallow zone and D3 zone water composition in?ows to the NSA. No in?ow into the Intermediate zone was investigated. The NSA monitoring well network is not designed to monitor the presence or absence of MIW although it is used for this function with a lower level ofcertainty than the SWRA and SERA networks. The NSA was designed to monitor agricultural inputs to the groundwater system up gradient of the NSA and beyond the furthest northern extent ofthe MIW plume. Unfortunately, not all the hydrologic source term inputs from natural (soil leachate and Walker River water) and-"or agricultural practices (soil amendments, fertilizer) that could introduce uranium (U), sulfate nitrate (N03), bicarbonate (HCOs) to groundwater in the NSA have been adequately characterized. BP has stated that NSA sampling is not necessary according to ARC June 20I 7 responses to EPA March 2017 comments regarding OU-7 (Wabuska Drain) that is beyond the scope and intent of the RI (see Figure 2 attached with yellow highlight of ARC response). Depth pro?le characterization data was collected during the installation of some ofthe NSA well clusters, but the well density and level of sampling data indicate private agricultural and tribal land areas beyond the northern most plume extent lack data north of BW-I 0). Comment No. 3. Mason Valley Agriculture Input to Walker River is not adequately characterized. The Remedial Investigation (and Plume Stability Report) cite published literature on the Walker River natural uranium content (Benson and Leach, I980, Reference No. I). Analog studies are cited to interpret the increased uranium levels in NSA wells beyond as attributed to complexation with increased HC03 from crop root reSpiration and irrigated soil leaching of natural uranium (Jurgens et al, 2010, Reference No. 2). Approximately four samples of Walker River water in the Smith Valley-Mason Valley reach (60-100 km from Walker Lake) were sampled in June and August I975 for uranium and other indicator parameters like sodium and chloride. The June river water was 2.6 higher in (up to 6.3 ppb), and the August river water was 7 higher (up to 15 ppb). The increases are attributed to agricultural practices and evaporation in irrigation return water to the Walker River that leach and concentrate ions like sodium, chloride, and uranium. Benson and Leach considered phosphate fertilizer application as a potential source of uranium, but calculations of the amount of fertilizer needed to account for the observed increases were unreasonable so they considered two other possible sources. First, the Pleistocene lake sediments in the Mason Valley are uraniferous and a source of mobile uranium under oxygenated conditions created by oxygen-rich irrigation waters that release precipitated or sorbed forms of as oxygenated and complexable form. Second, the other possible mobile source they considered are the uranium minerals associated with the Yerington copper deposit. At the time (I975) it was not possible to clearly determine if either Attachment 2 Page 13 Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 R1) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 potential source is responsible for the observed increases in Walker River dissolved levels. The clear identi?cation of uranium sources attributed agricultural practices and irrigation water return flow to the Walker River remains unknown in parts of the NSA. The total amount of uranium observed in groundwater in the NSA includes a contribution from these potential sources: I) naturally uraniferous Walker River source water upgradient ofthe East and West Fork con?uence; 2) naturally uraniferous Pleistocene sediments in the Mason Valley; 3) uranium-bearing phosphate fertilizer application from agriculture; 4) Yerington copper mine deposit uranium minerals; and 5) anthropogenic uranium in groundwater at north end ofmine south of Luzier Lane. In the RI Appendix 01 Hydrologic Tracer Supplemental Information report, samples of soil, soil amendment, and fertilizer being used at the Hunewill Ranch were tested for values of 6348 and 5130 isotopes (see Table C-4). The level of uranium appears low in the River until the con?uence, but from there down the sources, forms, and mechanisms of C01 inputs to surface water become more complex. The natural background of uranium in soil in major growing areas ofthe NSA (1.83 ppm?) should be characterized to help de?ne that contribution to the total observed uranium in some groundwater. There needs to be testing of fertilizer samples used by growers in the NSA for sulfur and oxygen isotopes for characterizing the isotopic input from this source compared to the +4.9 to +6.6 per mil] 5348 range that identi?es the presence or absence ofMlW. The uranium mass level and isotopic composition of fertilizer should also be tested to identify the Activity Ratio ofmUsz (AR) that is also used to de?ne the extent of MIW. An example of the water quality impact from uranium ph05phate fertilizer in surface run off from an agricultural area that was investigated using uranium and sulfur isotopes is found in Zielinski, Orem, Simmons, and Bohlen, 2006 (Reference No. 3). In an article by Vitoria, Otero, Soler, and Canals (2004, Reference No. 4) that studied the isotopic composition of fertilizer (N, S, O, C, and Sr); the isotopic composition of sulfur in fertilizers comes from two major sources, sulfuric acid and marine evaporites. Usually metal sul?des, sulfates, sulfurous gases, and native sulfur are the raw materials used in the production of sulfuric acid. The sulfuric acid will inherit the isotopic signature of the source materials and so does the fertilizer which can display a range of534S values that are mostly positive but variable. Given that the sulfur isotopic identi?er of MIW is between the +4.9 to -6.6 per mill 5348 range, will this isotopic identi?er range be a reliable indicator over a long time (3-20 years?) despite applications ofan additional source of sulfur? Some ofthe sulfur isotopic results of fertilizer analysis are presented in Figure 4 from Reference No. 4. Attachment 2 Page 14 Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 R1) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 RE COMMENDA HON-determine if sources ofcontaminants-isotopic identifiers of MI W, and alternative sources (Walker River, soil, fertilizers, soil water) have been adequately sampled and characterized in the NSA to an acceptable level of certainty to ensure credible interpretation of the groundwater composition and mechanisms in the NSA. Comment No. 4. Although the example of the dramatic increase in uranium at well is well substantiated by the data, the amount of increase in such a short period of time by such a simple mechanism as leaching of infiltration water from a storage pond and adjacent field seems surprisingly high. Concentrations of $04 and dramatically increased in less than one year from 5 ug/L to 180 (Oct 2016 to Feb 2017) along with concentrations ofalkalinity, nitrate, and calcium. Many laboratory controlled leaching experiments on soil material cannot produce such high concentrations of uranium in the leachate in a similar fashion. Since the 180 ug-"L is 6 times above the 30 ugl standard for drinking water and it is now rendered unfit for public consumption, is this a point source pollutant discharge that needs to be regulated? Is this the potential concentration of uranium that could be in groundwater from all parts ofthe With so much potential uranium contamination to groundwater in the NSA, con?rmation ofthe natural level of uranium in soil in surface irrigation recharge areas needs to be established. Recommendation - Establish the natural concentration of uranium in the soil and groundwater in the MSA so in places like the location one can be sure the elevated uranium is from natural sources because this well is also located along the northern edge- mixing zone of the MI plume and agriculture-impacted groundwater. Comment No. 5. In the Draft May 2018 Plume Stability report - Limitations of BCLs for De?ning Mining Impacts This section seemed to imply that there is complexity and a lack of clear identification with respect to sources of COls to groundwater. proper accounting would demonstrate the significant impacts natural inputs and agricultural activities have had on groundwater in the area.? This seems to imply that ARC still has the desire to revisit the BGQA values that are used to de?ne MIW because EPA had them remove naturally mineralized bedrock inputs and agricultural inputs to the data set. These smaller inputs would bump up the BGQA values to higher levels and potentially raise the as-yet-to-be determined cleanup standards for The Draft Plume Stability report ?proper accounting? term seems to imply that more characterization work is needed in the NSA and other areas where agricultural practices have a greater impact on groundwater composition than the MIW. Attachment 2 Page 15 Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 RI) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 Comment No. 6. The EPA comment and idea ofeolian transport of dust from the mine as a source of ?015 were discounted by ARC in their June 27, 2017 response as negligible (See Figure No. 3 attached). Conceptually the idea of eolian transport of dust that later infiltrates to groundwater has merit because it has occurred elsewhere in the Southwestern north of Tuba City, AZ (Reference No. 5). The residents around the north end of the Anaconda Site recall and have photographs of the ?pink dust? that used to blow offthe evaporation ponds. Could some ofthis dust have landed in certain areas more than others where oxygenated surface irrigation water quickly incorporated the C015 into the recharge to groundwater? Seems like if dust from the Anaconda Mine was ?xed to iron oxide and may be chemically a different form in the soil andr?or groundwater some further sampling could rule out this potential source of ?015 once and for all. In Reference No. 5, Johnson and Wirt studied the potential sources of uranium in shallow groundwater in an arid part of the Black Mesa Plateau near Tuba City where elevated uranium was measured in wells near a closed uranium mill. The Chinle Formation (Group) surface exposures west and southwest of Tuba City appeared to be the source of uranium in groundwater and not groundwater from the nearby closed mill. The well with the highest concentration of uranium in this study (I75 appears to have a signi?cant contribution of uranium that was deposited by wind and quickly incorporated in recharge due to the high level of oxygen in the meteoric surface water. Again, one comes back to the need to clearly identify sources of ?015 with greater certainty in the NSA so as to rule out mine dust as a potential source of COls to groundwater. References l. Benson, L. V. and Leach, D. L., 1980. Uranium transport in the Walker River Basin, California and Nevada. Journal of Geochemical Exploration, Vol. I l, 1979, p. 227-248. 2. Jugens, B. C., Fram, M.S., Belitz,K., Burow, K. R. and Landon, M. K., 2010. Effects of Groundwater Development on Uranium: Central Valley, California, USA. Ground Water, Vol. 48 (6), P. 913-928. 3. Vitora, L., Otero, N., Soler, A., and Canals, A., 2004. Fertilizer characterization: isotopic data (N, S, 0, C, and Sr). Environmental Science and Technology, 38, p. 3254-3262. 4. Zielinkski, R. A., Orem, W. H., Simmons, K. R., and Bohlen, P. J., 2006. Fertilizer- derived uranium and sulfur in rangeland soil and runoff: a case study in central Florida. Journal of Water, Air, and Soil Pollution, No. 176, p. 163-183. Attachment 2 Page 16 Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 R1) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 5. Johnson, R. H. and Wirt, L., 2009. Geochemical analysis of rock, sediment, and water from the region in and around the Tuba City land?ll, Tuba City, Arizona. US. Geological Survey, Open File Report, 2009?1020. Attachment 2 . Page 17 Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 RI) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 Figures nah?,- Figure l. Map ofOU-l area, Mason Valley, Nevada. EPA Comment 13. Section 2.1, Potential Background Soils subsection, last paragraph (11.5): This paragraph discmses the data some ofpotential use in supporting development ofan "agriculmral signature" in the Phase 1 OUJ Study Area. No flu-then work IS provided in the document for developing such a signature, though analyses were shown in the Jammy 31 meeting regarding agrtculttn'al impacts north of Lun'er. Dewlopment of such a Signature, to the exteiu data currently allows. world be of constdetable utility to the project. Such an ?agncultural Signature? could be based on an of locally used agriculml chenucals and could offer a hypothetical ?typical? agrtcultm?al return water characterization. The would need to he time-based as the type of agricultural chemicals may have changed over the years. A?er identi?cation of the types and sources of agricultural chemicals rs complete, an of their composmons and typical addihoolapplication rates would be needed. Lastly, an analysu'. of the emuotunental fate and namport characteristics of each chemical would be needed This information could then he med to better developltef'uie the agricultural Signature and help distinguish none impacts from agnculnn'al activities. Work with EPA to dengn such a task. ARC Response to Comment 13: At the March 26, 2015 00-7 technical meeting, EPA 's contractor stated that background in?uences?om agriatlnue would be "comoluted and that the program needs to keep the "bigpt'cntre in mind During the meeting there was ?consensus that assessing background on agricultural land would be di?icult, and would be dependent of crop practices, amendments. irrigation unter source, etc. tree meeting notes page 5, item 209M). ARC agrees. As noted in the retpmue to comment 7, at the January 20} 7 Wabash: Drain Phase Orerriew Presentation and meeting. ARCJtated that quann?cation of agricultural sow-res and contributions are not thepriman'focus oftlteRI and demonstrated that agriculntral in?uences were observed in the data north of Luzter tone. The data provided in the Technical Memorandum and ?trther presented at the January 20! 7 meeting con?nn the assumption made by all parties during Riplanniug meetings that agnculmral activities unlueuce the current Wabtuka Drain. Further sampling to develop a specr?c agriculntral signanu-e it' 11-0: necessao- ., Figure 2. Snippet of ARC 27Jun2018 response stating further sampling of agricultural signatures is not necessary. Attachment 2 Page 18 Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 RI) Anaconda Copper Mine Site Document: Reviewer: Yerington Paiute Tribe Date: November 19, 2019 Pri'nitiw Mantle Value i no -. Fertilizers I Urbandatargenn a may i . narrator ammo Tu'tlary aural-r sultan I I - - coerce dc MmEnpontoo . Kurokc Macmillan Volcanic tic-ted Massive SullidoDopotib IborimPyriticBolt I Western8?5 values oIsome major sulfur reservoirs and selected materials {data from tel: 34. 15, 38. arid Soler et al. Wished data?. Fertilizer values correspond to the compiled data or Figire 2; rectangles most at the data; dots represent single values. Present day .0 seawater supi- in I FD +30 +40 rear FIGURE 3. Sulfate isompic cornposition ot sortie selected nnterials [data from tel: 14. 15. 38, 47. 49?51. and Solar at al. Mlislied data?. Fertilizer talus correspond to the con'piled data of Figaro 2; 80% at them plot within the dashed line. Figure 3. Sulfur isotopic data from the study cited in Reference No. 3, Vitora et al., 2004. Attachment 2 Page 19 Document: Revised Draft Remedial Investigation Report Site-Wide Operable Unit (2019 R1) Anaconda Copper Mine Site Reviewer: Yerington Paiute Tribe Date: November 19, 2019 ARC Response to Comment The trends observed in bachgroundsamples. both within tlLe \er-tiglsoilprg?leu and located near the mine Site, suggest that any aerial deposition ofmine? sourced material in the Plane area is minimal: ARCobset'red in the Phase 1 analysis that l) background sample results are not systematicalh elevated in the O-OJfoot sampling interml that might be indicative of aerial deposition: and 2) background sample results ?om the BLM triangle in closer Inorimity to the Site are not gaternaticolly higher than background sample results?mher anay?'om the Site .F'tmhetrnore. when comparing the distributions ofbachgmund sample results to results for other subsets of the data lie, all samples. historical drain alignment. current drain alignment). ue?nd that with the etception of sulfate and nitrate. the bachgroundsample results are not comparable to results for the current and historical drain alignments south ofLuzier Lane. which have been identi?ed as mine-impactai with values one to two orders of magnitude higher than background for some COls. For these reasons, ARC concluded that aerial deposition ofmine-sourced material in the area. imitating the BLM oiangle. is negligible?r the purpose of characterising mine haste associated with the current and historical Wabusha Drain alignments. The last column in Table 2 included Isith the comments is labeled UCL-Fitll Dept and values in this column correspond to the 8612: reported in the Technical Memorandum. it is unparant to -ote that the BCLs reported in the Technical Manoramhtm (Section 6. l. 2. Table 6-2 and Table 6-3) are based on the Chebyshev Upper hediction Limit and not the Chebysher Upper Con?dence Louis (UCLJ. The depth-speci?c Cheb?hev UCL talues in Table 2. based an ARC is of these values. are calculated using the Chebphev UCL The UCL is a statistic based on the mean of the sample population. whereas the 0T1. is a statistic based on an upper percentile 90th percentile ?it the 9096 Chebysher UPLJ of the sample population data set. The comparison of UCLs to UPLs is not rahd because they represent completely di?'erent characteristics ofa dataset and are intended?sr dt??erent uses. EPA 's guidance i20l5l prescribes methods for I: alculation of UCLs. which may be used to estimate aposure point concentrations in a risk assessment or may be used when comparing with the UCL of another dataset tor other estimate ofa mean concentration). The UCL is not intended for use in comparing with individual site obsersatians (EPA. As described by EPA UPLs "are computed based upon background data sets. and point-by-point onst'te observations are compared with those limits. also prescribes use of upper tolerance limits (fins). upper simultaneous limits (URLs). and upper pmenules in de?ning comparisons. EPA ?s guidance is clear- that UCLs should not be used in point-by-point comparisons as presented in EPA 's comment #l2. Table 2: "it is re-emphasized that only mter'ages should be compared nith averages or UCLs. and indn'idual site observations should be compared with UPlls. upper percenttla. am. or USLs. ARC attributes the dt??erence in the and ?ill-depllt Bots. and the resulting increase in number erceedances in Table 2 to the diy?erent statistic (Le. vs. used and improper comparison of individual samples to the UCL. ARC 's preliminary analysis ofdepth-spea?c 909i theirs-shes UPlls in comparison to the ?tll-depth 90% Chebyshev UPLs presented in the Technical Memorandum shows that the resulting depth-specy?ic (0-2feey BCLs are generally similar to thejitll-depth BCLs. but?with higher many duals-res. As discussed above with regard to the patentialfor near-staface e?'ects in bachgrotmd sample areas ?om alleged aerial dispersion ofcontarnmants. there are notastanaticalh- higher or lower commutation; in near-surface body-moat gametes to sugest that near-surface BCLs willptowde additional clop?cationfor chamctertation efforts; ARC agrees with the statement in corrunent that "our study area is Iery?at so sediment transport utthin the streambed iseli'may be minimal and that there a. likely a strong in?uence ?om nearby surface soils on drain sediment. However. ARC does not want to exclude the potennalfor deepa soils to In?uence drain sedirnent?om historical and conternpomn? soil exca'lmions (eg, agricnlno'al drain and road construction) and raising leg. agricultural and groding?eldsl or from percolation through the radase :one before reaching tributary drains. For these reasons and the existing analssis in the Technical Memorandum. ARC elects to retain ?rll-depth BCLs at this time. ARC Response to Comment The trends alum-ed in background santoles. both uithin the rental soil pro?les and ligated near the mine Sits sages: that any aerial deposition cy'mlne- the Phase area is mintmah ARC observed in the Phase analpis that I) baclground sample results are not systematically elevated in the 0.0.5 foot sampling internal that might be indicative of aerial deposition; and Ill background sample results ?ont the triangle in closer proximity to the Site are not sisternaticallv higher than bockgrowrd sample results ?ather amty?'om the Site. Furthermore. when comparing the distributions qt? background sample results to results for other subsets of the data tie . all samples. historical drain alignment, current drain alignment). we?nd that with the exception of sulfate and nitrate. the bachgrormd sample results are not comparable to results for the current and historical drain alignments south Lane which have been identi?ed as mine-impacted with solues one to two orders of magnitude higher than background for some C?Ols. For these reasons. ARC concluded that aerial deposition ofmine-sourced material in the area. including the BLM triangle. is negligible the purpose mine smste ossoctated with the current and historical trabuska Drain alignments The last column in Table 2 included with the comments is labeled "Chebyshe?r rm.- Deptlr and values in this coltonn correspond to the BCLs reported in the Technical Memorandum. It is important to note that the 30!: reported in the Technical Manorandum (Section l.2_ Table ti 2 anti Table at!) are based on the C?hebysher Upper Prediction Limit (UPL) and not the Chebishev Lpper Con?dence Limit The depth-specific Chelnshev UCL mines in Table 2. based on ARC is reproduction of these values, are calculated using the Cheb) sher UCL The UCL is a statistic based on the mean of the sample population. whereas the UH. is a statistic based on an upper percentile leg. 90th percentile Jibr the 90% UPI.) of the sample population data set. The comparison of to UPI: is not valid because they represent completel} dt?'erent characteristics ofa dataset and are intended for di?'erent uses. EPA ?s Prob?CL guidance r20l5)prescnbes methods for calculation ofL'CLs. which may be used to estimate exposure point concentrations in a risk assessment or ma}r be used when comparing with the UCL of another dataset (or other estimate ofo mean concentration). The UCL is not intended for use In comparing with individual site obsen'atiotts (EPA. 2W5). As described by EPA URLs ?are computed based upon background data sets. and point-by?point onsite obsenations are compared uith those limits. use of upper tolerance limits (UTIs), upper s-multaneous limits (USle. and upper percentiles in de?ning comparisons. EPA 's guidance (2015) is clear that UCLs should not be used in point-b1 -point comparisons as presented in EPA 's comment #12. Table 2: ?it is re-ernphastetl that only aver-ages should be compared with averages or UCLs. and mils-idual site observations should be compared with UPLs. upper percentiles. U715. or D'Sls. ARC attributes the dm?'rence in the depth-speci?c and ?ll-depth BCLs. and the resulting increase in number of?C?L atceadances in Table 2 to the dt?'erent statistic ti.e.. 1's. UPI.) used and improper comparison ofindn ldual samples to the UCL ARC ?s preliminary analssis ofdepuh-speci?c 909$ Chebysher in comparison to the ?rlhdepth 00% UPLs presented in the Technical Mernorandtun shows that the resulting depth-speci?c {o-Z?et} BCLs are generally similar to the BCLs. but with higher RClIsfor many anal-Wes. As discussed above with regard to the potennolfor n?rmaface tfects tn bockrotmd sautple oreas?-om alleged aerial dispersion ofcontamutaiti. there are not systauaticolly higher or lower_concena'ations in neat-surface background samples to suggest that near-surface BCIs will provide additional clari?cation for chgacterizat?ion ARC agrees With the statement in this comment that "our study area is reo'?at so sediment transport within the streornbed itseli'may be minimal and that there is likely a strong in?uence ?om nearby surface soils on drain sediment. Harmer. ARC does not want to exclude the potential for deeper soils to in?uence drain sediment ?om historical and contemporary soil ercmations ag?culntral drain and road construction) and raising agriculao'al tilling and grading ?elds) or ?oat percolation through the \adose zone before reaching tributary drains. For these reasons and the misting analtst?s in the Technical Memorandum. ARC elects to retain ?tll-depth BCLs at this time. Figure 4. Snippet of ARC 27lun2018 response discounting eolian transport and deposition of mine dust. Attachment 2 Page 20