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Quick-N-Save #2 - 2 - 12 March 2018 2057 El Dorado Street Stockton, San Joaquin County Significant petroleum hydrocarbons concentrations were reported in off-site downgradient borings CPT-3 and CPT-4, with the highest detections, including 1,500 micrograms per liter (ug/L) total petroleum hydrocarbons as gasoline (TPHg) and 240 ug/L benzene, reported in CPT-4 at 94 feet below ground surface (bgs). As such, it appears that additional downgradient assessment is needed to define the extent of hydrocarbon impact to groundwater. By 29 May 2018, please submit a Work Plan for additional delineation of the downgradient extent of groundwater impact. In the Assessment Report Stratus states that the Site is exempt from Petroleum Vapor Intrusion criteria as it is an active petroleum fueling facility. Central Valley Water Board staff concurs. Stratus states that, while limited soil samples have been collected above 10 feet bgs since termination of soil vapor extraction (SVE) remediation, detected petroleum hydrocarbons in the two on-site WOT borings were below LTCP Table thresholds. While this is true, historical maximum petroleum hydrocarbon detections in soil are below both residential and commercial thresholds established in Table 1 of the LCTP (Table 2 below). Table 2 - Shallow Soil Results & LT Depth (ft bgs) No. of Samples Max Benzene (mg/kg) Max Ethylbenzene (mg/kg) Max Naphthalene (mg/kg) Max PAHs (mg/kg) All ND 0-5 8 <0.005 <0.005 <0.04 5-10 _ 7 <0.005 <0.005 <0.04 All ND LTCP Residential Thresholds 0-5 ft 1.9 21 9.7 0.063 5-10 ft 2.8 32 9.7 NA LTCP Commercial Thresholds 0-5 ft 8.2 89 45 0.68 5-10 ft 12 134 45 NA LTCP Util. Worker Thresholds 14 314 219 4.5 — • • s=po yaroma y rocar ons; ft bgsfeetbelow ground surface; mg/kg=milligrams per kilogram; ND=not detected above laboratory reporting limits; mg/kg=milligrams per kilogram In the Assessment Report, Stratus states that all contaminants at the Site appear to have originated from UST operations consisting only of petroleum product storage. Based on current and historical soil sampling in the vicinity of the former waste oil tank (WOT; Table 3 below), Central Valley Water Board staff concurs with Stratus's conclusion. Table 3 - Waste Oil Tank Shallow Soil Res I Depth GRO DRO ORO BTEX Oxygenates VOCs ..d VI SVOCs PAHs PCBs1 4 <1 17 490 All ND All ND All ND All ND All ND All ND 6 <1 <5 39 All ND All ND All ND All ND All ND All ND URO=gasoline range organics; -diesel range organics; ORO=oil range organics; BTEX=benzene, toluene, ethylbenzene, xylenes; Oxygenates=methyl tert butyl ether (MTBE), tert butyl alcohol (TBA), ethyl tert butyl ether (ETBE), ten amyl methyl ether (TAME), di-isopropyl ether (DIPE); VOCs=volatile organic compounds; SVOCs=semi- volatile organic compounds; PAHs=polycyclic aromatic hydrocarbons; PCBs=polychlorinated biphenyls 1=PCB analysis performed in 2001 6. In the Assessment Report, Stratus states that the Site meets seven of the eight General Criteria of the LTCP. Stratus indicates that secondary source has not been removed to the extent practicable, and recommends groundwater remediation to address residual petroleum hydrocarbons at the Site. Central Valley Water Board staff concurs with