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Shall Sarvlea Station(WIC No,204-7624-2408) <br /> 4446 Perahinp Avenue,Stockton,California <br /> The soils beneath the former tanks were vented during vapor extraction performed at <br /> the site from December 1991 to February 1992. Air monitoring data indicated <br /> petroleum hydrocarbons in concentrations of up to 6,500 parts-per-million-volume <br /> were removed from soil. Groundwater samples collected from MW-4 following vapor <br /> extraction have contained very low concentrations of hydrocarbons when detected. <br /> The letter dated February 24, 1993, from the SJCEHD to Shell, stated an additional <br /> monitoring well should be constructed unless a site history dating back to 1964 <br /> reveals pristine conditions regarding tank integrity, fuel reconciliation, etc. A search <br /> of records on file with Shell did not indicate any repairs, other than routine <br /> maintenance, were made to the former tank system. <br /> Aegis and Shell question the validity of the sample collected in February 1993, from <br /> Exxon's well MW-8. The sample collected may not have been representative of actual <br /> groundwater conditions due to: a) the shallow penetration of MW-8 into the saturated <br /> zone, and b) the limited purging capability from the well. The well had not been <br /> sampled since May 1991 , and contained less than a 2 foot water column. <br /> It remains the opinion of Aegis and Shell that sufficient data does not exist to warrant <br /> the drilling and installation of an additional monitoring well. This opinion is based on <br /> the following: <br /> • All sampling and subsurface investigations have been conducted <br /> according to the "Tri-Regional" guidelines and with the guidance and <br /> concurrence of the SJCEHD; <br /> • The monitoring well network on site appears appropriate for monitoring <br /> the "most probable source" of hydrocarbons, as requested by the <br /> SJCEHD; <br /> • Hydrocarbons were removed from the former tank area by vapor <br /> extraction in 1991 and 1992; <br /> • Maintenance and reconciliation records on file with Shell do no indicate <br /> any fuel releases occurred from the former steel UST system; and, <br /> • The historic groundwater sampling data from the Shell site do not <br /> indicate an on site source of hydrocarbons. <br /> It should also be pointed out that no petroleum hydrocarbons have been indicated <br /> above the respective detection limits in wells MW-1 , MW-2, and MW-3 since <br /> October 1991 . <br /> 89-0182.L7R <br />