Response to Comments Document: Review Analysis of Gamma Survey and Ra-226 Soil Concentration Data at the Treasure Island Site-Wide Background Areas and the Area 7 Background Reference Area, a memorandum with attachments dated April 23, 2012 Comment No. Section, Figure, Table Response Comments Commellts made by CDPH (06/06/12) General The Environmental Management Branch (EMB) ofthe CDPH utilized Title 17 of the California Code of Regulations, Section 30256 and bases its recommendation regarding radiological unrestricted release in part on a comparison of the distribution of measurements at a surveyed and sampled site to the distribution of measurements in relevant background distributions, Therefore, the type of measurements and distribution analysis applied to this background data set are relevant and EMB will expect to see comparison of these background distributions to final status survey measurements in reports aimed at supporting unrestricted release of sites with soil sampling and surveys, All Treasure Island (TI) Work Plans are in agreement with the EMB comment. In every Work Plan it states that unrestricted release of soil is based on gamma spectroscopy of soil samples, Every soil samples must report Ra-226 concentration less than the release criterion of 1,0 pCi/g above established background to be considered for unrestricted release, Excavated soil is placed on laydown pads in 6-inch layers and a gamma walk over survey (GWS) is performed over 100 percent of the surface soiL Excavation floors and sidewalls also receive gamma surveys over 100 percent of their surfaces, These gamma surveys are perfonned to identitY potential Ra-226 commodities and small areas of elevated Ra-226 soil concentrations exceeding the release criterion, If a gamma survey count rate exceeds the background reference area derived investigation level (IL) additional investigation is performed e.g. gamma static survey and biased soil sampling. If count rates do not exceed investigation levels the gamma survey count rate distributions are still compared to gamma survey count rates of the background reference area and appropriate systematic soil sampling is conducted, Gamma surveys of surface soil using portable instruments, by their very nature, cannot be quantitative. Therefore, the decision that a survey unit may be ready for unrestricted release is based only on gamma spectroscopy of soil samples. 2 51131'109120112 General This background study deals only with Ra-226 as a contaminant of concern, However, other isotopes have been identified in historical documents as being present or used at Treasure Island (TI), One example is Cs-137.1t has not been agreed upon by EMB that the only isotope of concern is Ra-226, Therefore, samples from sites and from the background study should be counted long enough to quantitatively determine Cs-137 and, if there are any, other gamma 1014 The off-site radioanalytical laboratory reports natural gamma emitting radionuclide concentrations and Cs-137 even if the concentration is less than the minimum detectable concentration (MDC), In addition, the laboratory report lists gamma energy peaks and the potential radionuclide associated with each peak. All gamma energy peaks are listed. Comment No. Section, Figure, Table Comments Response Comments made by CDPH (06/06/12) emitters of concern, 3 4 5 $lmw09l2fJ112 Section I.l General Section 1.2, pages 2 and 3 Over 200 surface soil samples have been collected from TI and analyzed at the off-site certified lab, The concentration of all gamma-emitting radionuclides except Ra-226 are in the range found in soil samples collected from non-impacted, undisturbed, background concentrations, The maximum Cs- 137 concentration in a TI soil samples is 0,104 pCi/g ? 0,12 pCi/g, The minimum detectable concentrations for Cs-137 in soil samples ranged from 0,05 to 0,13 pCi/g, N9t one soil sample collected from TI has a positive Cs-137 concentration; even at the 95% confidence leveL Section 1,1 points out that the range ofRa-226 concentrations in the study is within the range of concentrations for undisturbed background locations in San Francisco based on the cited McArthur and Miller study from 1989, The range ofRa-226 concentration is also similar to the range ofRa-226 concentrations in undisturbed soil at McClellan AFB as reported in their final Reference Area Study performed a few years ago, A better comparison would be the background reference area and import fill data set reported in the Hunters Point Shipyard (HPS) report dated July 8,201 I titled Survey Unit Project Reports Abstract for SanitalY Sewer and Storm Drain Removal Conducted After JanualY I, 2011, The HPS study includes three data sets with mean values ranging from OAO to 0,63 pCi/g and all three data sets were analyzed by the same laboratory using the same method used for this Treasure Island background study, The HPS study also reminds us that the background distribution may vary from site to site, Thank you for the comment Unlike Hunter's Point, TI is manmade, Material used in building TI was collected from the San Francisco bay, tunnel and roadway construction sites outside San Francisco, and fill from multiple undocumented locations, In addition, construction and development of the land by civilian and Navy agencies has disturbed the surface soil significantly over the previous 60 years, Soil samples with the Ra-226 exceeding twice the mean Ra-226 concentrations at Hunters Point have been analyzed and the Ra-226 and decay products are in secular equilibrium with the U-234, The range in Ra-226 concentrations in Hunter's Point soil is likely to be more restrictive than the soil used to build Treasure Island, In addition, the background reference area radio nuclide concentrations vary significantly from soil sample to soil sample because the soil at Treasure Island has been disturbed, It is reasonable to believe that the concentration of natural occurring radionuclides in the TI soil more closely follow the broad distributions reported in San Francisco/OaklandlSan Mateo/Contra Costa counties than in anyone single location, This report indicates that comparison of cumulative probability distributions is a useful approach and EMB will expect to see cumulative probability distributions for future measurements made at sites where radiological unrestricted release is being considered, The comment is noted, Section 1,2 on Pages 2 and 3 of the subject memorandum report indicate that static gamma measurements correlate much better with Ac-228 concentrations (a thorium daughter) than with Ra-226 TI Work Plans require static gamma survey measurements at biased locations where the count rate from the GWS exceeds the investigation level (lL), The IL is defined as the mean plus three 20f4 Comment No. Section, Figure, Table Comments Response concentrations. This indicates that gamma measurements are not a strong indicator of Ra-226 concentration at near background levels. Therefore, one would expect to base conclusions regarding Ra-226 levels on sample data and to use the gamma scanning and static measurements to determine where some biased sample locations may be needed. Generally, one would want to collect samples at sites where the cumulative probability curve for gamma indicated multiple components of a distribution instead of a single normal distribution. standard deviation ofthe mean GWS count rate acquired at the background reference area. Soil samples are collected from locations where the static gamma survey count rates exceed its IL and analyzed using gamma spectroscopy. In addition, soil samples are collected from systematic locations based on a random starting point using the equations and methodology in Section 5.5.2.2 through 5.5.2.5 ofMARSSIM. The cumulative or normal probability plots for Ra-226 concentrations shown in the report compare well as indicated in the report and these plots provide a useful visual method of comparison Ra-226 data from different sites. EMB expect to see cumulative probability plots in final status survey reports that may be compared to the ones in this report for background soil distributions at Treasure Island Final status survey reports and remedial action completion reports will include nonnal probability plots of the Ra-226 concentrations along with comparison to the Ra-226 concentrations in the soil samples collected from a background reference area. Please note that Treasure Island is man-made and has been significantly disturbed. The soil and its radio nuclide concentrations are not homogeneous. .. Attachment I, Page AI-7, Section 1.1.2, is about Ra-226 concentrations, however, the example calculations shown under Equations I and 2 on this page are count data instead ofRa-226 concentrations. The count examples on Page A I - 7 appear to be discussed in Section 1.2.2 in the second paragraph of Page A I-B. The third paragraph in Section 1.2.2 starts out referring to "Figure I" but it appears that it should refer to "Figure 4" on the same page. The examples on Page A 1-7 need to be corrected and the existing examples on that page appear to belong on Page A-I3. The examples, call-out to figures, and text on pages A 1-7 and A 113 have been corrected. Section 1.2 points out that static survey count rate data should be symmetrical and have a good fit to a normal distribution and goes on to point out specific criteria or characteristics of this type of distribution. These distributions characteristics refer to a background distribution. Since EMB looks at distributions of measurements relative to background distributions, the distribution characteristics The comparison of the static survey count rate data distributions will be included in final status survey reports and remedial action completion reports. However, the decision as to whether or not a site is suitable for unrestricted release is based solely on the Ra-226 concentrations in soil samples. Portable survey instrument count rates cannot be quantitative. During characterization and Comments made by CDPH (06/06/12) 6 7 S Sflaw09l20112 General Attachment I, Page AI-7, Section 1.1.2 Section 1.2 3014 Cumulative probability curves are used to analyze GWS and gamma static survey data. Analysis of gamma survey count rate distributions to date demonstrate that 2 3 components sometimes occur but the components are typically in the low count rate range. Comment No. Section, Figure, Table Comments Response Commellts made by CDPH (06/06/12) covered in Section 1.2 should be included in final status survey reports for surveys conducted at sites that may be suitable for unrestricted release. 9 10 Shaw09!20112 General General remediation activities the comparisons are performed in order to define locations that may require additional excavation of soil due to the potential for Ra-226 concentrations that exceed the 99.7'h percentile of its concentration in background reference area soil. It is not clear how this background data will be reported, reference or used in final status survey reports for comparison site survey data. Laboratory reports for sample analysis will need to be included when the background data is used or referenced in final status survey reports. Are there plans to add that laboratory data and produce a revised background survey report including both the asphalt and soil sample data. It is agreed, and all TI Work Plans state that the decision as to whether or not a survey unit or site is suitable for free release is solely based on the Ra-226 concentrations in soil samples collected from that survey unit/site. The unrestricted release criterion is I pCi/g above the mean Ra-226 concentration in soil samples collected from the background reference area. Every soil sample collected during the Final Status Survey must have a Ra-226 concentration less than this criterion. The GWS and static survey results are used during characterization and remediation activities to direct excavation activities and for making preliminary waste characterization decisions. Using investigation levels such as the ones derived in this report for gamma measurements may be useful at the time of initial surveys at a site. However, since gross gamma measurements do not correlate well with Ra-226 concentrations at near background levels, it is the sample analysis results that are most important. And it is important to ensure that samples have been collected at least at some locations exceeding any gamma investigation levels and at some locations that have gamma measurements that appear to be part of different distribution components. This indicates the needed capability to view the distribution of gamma scanning results before selecting biased static gamma measurement locations and biased sampling locations. It is agreed. All TI Work Plans state that radiological unrestricted 4014 released ofland will be based on the Ra-226 concentration in soil samples. The soil samples will be collected at both systematic locations having a random starting point and at biased locations where the static gamma survey exceeds the IL. Additional biased soil samples may be collected at locations where the static gamma survey count rate may not exceed the IL but where GWS and or static gamma count rate distributions indicate high count rates that represent different distribution components.