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Mr. Brendan Kenny Central Valley Regional Water Quality Control Board November 23, 2020 Page 2 The WET method applies to only select laboratory analytical methods proposed for the soil samples in the Work Plan and additional analyses requested in Comment 2 below.The WET method for soil samples will be applied to the following U.S. Environmental Protection Agency(EPA) analytical methods contained in the Work Plan and described in Comment 2: • EPA 8081A (organochlorine pesticides) • EPA 8141A (organophosphorus pesticides) • EPA 8151A (herbicides) • EPA 6010 (Title 22 metals) • EPA 3060/7199 (hexavalent chromium) The additional cost to analyze the samples for STLCs in addition to Total Threshold Limit Concentrations (TTLC) as originally proposed in the Work Plan is significant.To reduce costs, it is proposed that a two- step process of sample collection be used to minimize the number of soluble analyses performed as these analyses may be redundant since several of the classes of constituents are not known to be present in the vicinity of the pond. The proposed two-step process is as follows: • An initial round of sampling will be conducted at three boring locations (B-1, B-5, and B-8) as shown on Figure 3 excerpted from the Work Plan, which is provided in Appendix A. Based on its configuration, it is believed that the Southwest Pond was previously used as a settling pond. These boring locations were selected to represent the starting, middle, and end points of the settling area. Soil samples from these borings will be analyzed using total and soluble methods to obtain TTLC and STLC results. • The second round of sampling will be conducted at the remaining base, sidewall, and surface locations (B-2 through B-4, B-6, B-7, SW-1, SW-2, SS-1, SS-2, and BG-1) described in the Work Plan. The analyses described in the Work Plan will be conducted on all the samples collected during the second round of sampling.Additionally, if the results of the samples collected from the initial three borings indicate an analyte was detected in any of the samples for either total or soluble analyses, then the analysis will be repeated for all the samples collected in the second round of sampling. The proposed sample analysis for the first and second rounds of sampling are summarized in Table 1. 2) Because the Southwest Pond was operated when the Occidental Chemical Company operated the site, in addition to the proposed constituents in the workplan, soil samples should be analyzed for all constituents in Table 2 of Monitoring and Reporting Program R5-2075-0870 for the former Occidental Chemical Corporation. As described in the response to Comment 1, all the samples collected in the initial round of sampling will be analyzed for constituents described in Table 2 of Monitoring and Reporting Program R5-2015-0810 (MRP). The constituents and associated analytical methods described in Table 2 of the MRP are summarized in Table 2 (attached). Samples collected in the second round of sampling may also be