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OPERABLE UNIT 10 Description OU 10 Corresponds to Sub-Recommendation 17.1, which concerns a solvent washdown pad. The Phase I identified potential for soil contamination via leaks/spills/improper disposal of petroleum- or solvent-related compounds. Phase II samples were collected and analyzed for petroleum- and solvent-related compounds. Petroleum/Solvents: Existing Data Six soil samples were collected and analyzed for TPEH, Fuel Fingerprint (EPA 8015M), VOCs by GCMS with TICs (EPA 8240), and BTEX (EPA 8260) (Table 10-P, soil samples 14-1 through 14- 6). These analyses yielded 230 results, of which all are ND. Most laboratory reporting limits are not tabulated. BTEX and TPH reporting limits, however, are tabulated. Most of these limits are all below Industrial Thresholds, but TPHueh, TPH-JP4, TPHg, MtBE, Benzene, and Ethylbenzene reporting limits are above Protection of Groundwater SSLs. In addition, OU 10 is located in the same area as OU 2. The two Hydropunch samples collected for OU 2 are therefore relevant to OU 10 (Table 0U2-P, Hydropunch samples 11-2-HP and 11- 7-HP). Both Hydropunch samples were analyzed for organic lead, TPHg, and purgeable hydrocarbons. One was also sampled for VOCs and EDB. These analyses yielded 57 results. All were ND. Reporting limits were tabulated for organic lead, TPHg, purgeable hydrocarbons, and BTEX. All are below associated Tier 1 and EPA Tap Water ESLs, except for benzene, for which the reporting limit of 0.5 ug/L exceeds the Tier 1 and EPA Tap Water ESLs of 0.46 ug/L, and organic lead, for which the reporting limit of 0.15 ug/L exceeds the EPA Tap Water ESL of 0.0013 ug/L. Petroleum/Solvents: Recommendations Because OU 2 and OU 10 are located in the same area and were investigated for similar petroleum- and solvent-related compounds, these data can be combined into a single dataset, which yields 342 soil results, of which all are ND except for except for two xylenes concentrations of 0.0056 and 0.0065 mg/kg detected at OU 2. While many reporting limits are not tabulated, these data strongly indicate that there are no petroleum-related issues at OU 10. Potential concentrations would be expected to be normally distributed. Such a distribution resulting in only 2 detections out of 342 soil results and 0 detections out of 57 groundwater results would have to fall well below reporting limits. Kleinfelder therefore recommends spot-checking the reporting limits to confirm they are reasonably low and therefore constrain potential concentration distributions as expected. Moreover, OU 2 Hydropunch data provide direct evidence of groundwater conditions. These data are all ND. While VOC reporting limits are not tabulated, BTEX are, and they are generally below associated groundwater ESLs. This indicates that groundwater is effectively protected, no matter the soil data reporting limits. Kleinfelder therefore recommends that evaluation of spot-checked soil reporting limits be conducted with the context that direct groundwater data strongly indicate that groundwater has been protected. 20173951.001A/SAC17R68420 Page 19 of 26 November 2, 2017 © 2017 Kleinfelder www.kleinfelder.com KLEINFELDER 2882 Prospect Park Dr., Suite 200, Rancho Cordova, CA 95670 p I 916.366-1701 f I 916.366-7013