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7 <br />November 21, 2011 <br />Cardno ERI 2789C.R02 Former Mobil Service Station 99CAS, Stockton, California <br />Hydrocarbons in Groundwater <br />Concentrations of TPHd, TPHg, MTBE, BTEX, and TBA were reported in select grab groundwater samples <br />collected during this investigation. Concentrations of EDB, 1,2 -DCA, TAME, DIPE, ETBE, and ethanol were not <br />reported in the samples. <br />Maximum concentrations of TPHd, TPHg, and benzene were reported at 92,000 pg/L, 42,000,000 pg/L, and <br />30,000 pg/L, respectively, in the groundwater samples collected from boring AS3. Concentrations reported in <br />samples collected in the vicinity of the former USTs (from borings SVE2, AS3, AS4, and AS6) were one order of <br />magnitude larger than concentrations reported in samples collected in the vicinity of the northern former <br />dispenser (from borings SVE1 and SVE5). Select groundwater analytical results are illustrated on Plate 4. <br />CONCLUSIONS <br />During this investigation, sediment observed was consistent with observations made during previous site <br />investigations and maximum petroleum hydrocarbons in soil and groundwater were present beneath the former <br />USTs. <br />RECOMMENDATIONS <br />Cardno ERI recommends connecting the wells to the remediation system once system installation is complete. <br />Cardno ERI will submit a system start-up report under separate cover. <br />CONTACT INFORMATION <br />The responsible party contact is Ms. Jennifer C. Sedlachek, ExxonMobil Environmental Services, <br />4096 Piedmont Avenue #194, Oakland, California, 94611. The consultant contact is Mr. Greg A. Gurss, Cardno <br />ERI, 601 N. McDowell Boulevard, Petaluma, California, 94954. The agency contact is Mr. James Barton P.G., <br />California Regional Water Quality Control Board, Central Valley Region, 11020 Sun Center Drive #200, Rancho <br />Cordova, California, 95670-6114. <br />LIMITATIONS <br />For any documents cited that were not generated by Cardno ERI, the data taken from those documents is used <br />"as is" and is assumed to be accurate. Cardno ERI does not guarantee the accuracy of this data and makes no <br />warranties for the referenced work performed nor the inferences or conclusions stated in these documents. <br />