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despite samples being collected from two separate areas to assess potential for two separate means of potential contamination. This indicates OU 1 metal concentrations represent natural background concentrations. Moreover, additional sampling was conducted during installation of monitoring well MW-13 (Table OU11-M, soil sample MW-13), which was located approximately 30 feet northwest of an OU 11 rail spur (Figure OU11-1). Soil samples were collected at depths of 10 and 15 feet bgs and analyzed for CAM 17 metals. Most results are ND, except for barium, chromium, copper, nickel, vanadium, and zinc. Concentrations are similar to OU 1 and OU 7 concentrations. These data further indicate that OU 1 and OU 7 metal concentration represent natural background conditions. Metals: Recommendations Kleinfelder recommends assessing OU 7 data against the natural background conditions evaluation recommended for OU 1. It is anticipated that OU 7 metal concentrations will fall within natural background concentrations and therefore no further action will be recommended. Kleinfelder also recommends that distinguishing chromium results and report chromium III and VI, as per the Board's request. Based on existing total chromium data, it is anticipated that chromium (VI) concentrations should not exceed ESLs. OU 7: Work Plan Background metal sampling is included in the OU 1 work plan. No additional sampling is therefore required for OU 7. Existing Phase II OU 7 data will be evaluated against background data conducted for OU 1. OPERABLE UNIT 8 Description OU 8 Corresponds to Sub-Recommendation 13.1, which concerns slab/factory drains. The Phase I identified potential for soil contamination via improper disposal of petroleum- or solvent-related compounds. Phase II samples were collected and analyzed for petroleum- and solvent-related compounds (Figure 0U8-1). Petroleum/Solvents: Existing Data Ten soil samples were collected and analyzed for TEPH, Fuel Fingerprint (EPA 8015M), VOCs by GCMS (EPA 8240), and semi-VOCs (EPA 8270) (Table 0U8-P, soil samples 13-16 through 13-19). These analyses yielded 459 results, of which most are ND. TPHueh, however, was detected at concentrations of up to 4,800 mg/kg at 10 feet and 1,600 mg/kg at 20 feet, exceeding the Protection of Groundwater SSL of 1.5 mg/kg and Industrial Threshold of 440 mg/kg, and a petroleum odor was noted during exploration. Most laboratory reporting limits are not tabulated. Those that are tabulated are generally below Industrial Thresholds and above Protection of Groundwater SSLs. Monitoring wells MW-16, MW-17, MW-18, MW-19, MW-20, and MW-21 were installed to monitor potential groundwater issues associated with OU 8. MW-18 was located within about 10 feet down gradient of soil samples noted above. MW-17 was located within about 50 down/cross gradient. MW-19 was located about 200 feet cross gradient and MW-20 was located about 200 feet up/cross gradient. MW-21 appears to have been located somewhere offsite. 20173951.001A/SAC17R68420 Page 14 of 26 November 2,2017 0 2017 Kleinfelder www.kleinfelder.com KLEINFELDER 2882 Prospect Park Dr., Suite 200, Rancho Cordova, CA 95670 p 916.366-1701 f I 916.366-7013