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Ongoing natural attenuation to concentrations below EPA Tap Water and Tier 1 <br />Groundwater ESLs with soil vapors below applicable screening levels. If groundwater and <br />soil vapor data are below applicable levels, Kleinfelder will recommend no further action. <br />Ongoing natural attenuation to concentrations above EPA Tap Water and Tier 1 <br />Groundwater ELSs with soil vapors below applicable screening levels. If Kleinfelder finds <br />that the average groundwater concentration is above applicable levels but soil vapor <br />concentrations are below levels, Kleinfelder will recommend no further action and will <br />petition for closure under low threat criteria. <br />Concentrations that do not indicate natural attenuation and/or soil vapor concentrations <br />above applicable screening levels. If Kleinfelder does not find evidence of natural <br />attenuation in these data, or if soil vapor concentrations are above applicable levels, <br />Kleinfelder will use PSGS data to conduct a soil removal action and then petition for <br />closure under low threat criteria. <br />OPERABLE UNIT 6 <br />OU 6 Description <br />OU 6 Corresponds to Sub-Recommendation 12.4, which concerns an above-ground gasoline <br />convault. The Phase I identified potential for soil contamination via leaks/spills of petroleum- <br />related compounds. Phase ll samples were collected and analyzed for petroleum-related <br />compounds. <br />Petroleum: Existing Data <br />Two soil samples were analyzed for BTEX (EPA 5030/8020), MtBE (EPA 5030/8020M), and <br />TPHg (EPA 5030/8020) (Table OU6-P, soil samples 12-17 and 12-18). These analyses yielded <br />12 results, of which all are ND. Laboratory reporting limits are not tabulated. <br />Petroleum: Recommendations <br />While OU 6 soil results are all ND, there are not enough soil results for OU 6 to strongly indicate <br />a statistical distribution constrained well below reporting limits. We therefore recommend <br />tabulating OU 6 soil reporting limits and evaluating them against Protection of Groundwater SSLs. <br />It is anticipated that this exercise demonstrate that reporting limits typically only marginally exceed <br />Protection of Groundwater SSLs. This should provide the Board the data it needs to demonstrate <br />due diligence in concluding that these data warrant no further action, even if some reporting limits <br />exceed Protection of Groundwater SSLs. <br />20173951.001A/SAC17R68420 Page 12 of 26 November 2, 2017 <br />© 2017 Kleinfelder www.kleinfelder.com <br />KLEINFELDER 2882 Prospect Park Dr., Suite 200, Rancho Cordova, CA 95670 pJ 916.366-1701 f I 916.366-7013