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e W w - Mr. Clint Rodgers February 22, 1991 Page 2 GROUNDWATER SAMPLING AND AFIALYSES Following monitoring on January 9, 1991,b%e three wells were purged by hand bailing to allow for the coCection of representative groundwater samples. Standard Operating Procedure SOP 9 describes the Groundwater Technology purging and sampling procedure(Appendix A). Wells were purged with a clean polyvinyl-chloride (PVC),hand-held bailer until three well volumes of water had been removed. None of the wells bailed dry. The purged water from all wells was put into 55-gallon steel drums, labeled,and stared on the north side of the site pending proper disposal. After allowing the water to recover to at least 80 percent of the original levels,groundwater samples were collected in accordartcs with Groundwater Technology SOPS 9, 10,and 12(Appendix A). The samples were placed in acidified 413-milliliter(ml)glass vials which were capped with Teflon'septa lids so that no air was trapped Inside. The samplo vials were then labeled and placed In an insulated cooler for transportation to Superior Analytical Laboratory, Inc.,a State of California-certified laboratory In Martinez,California Proper Chain-of-Custody Manifest documentation,as descrW in SOP 11,was maintained with the samples,and a copy of the manifest is Included in this report(Appendix A). All groundwater samples we;a analyzed for the presence of benzene,toluene,ethylbenzene,and xylenes (BT©(),and for total petroleum hydrocarbons(iPH)-as-gasoline using modified U.S.Envirmmuntal Protection Agency(EPA)Methods 5030/8o20/8o15. Additionally,the groundwater samplo collected from monitoring well MW-1,which is adjacent to the location of the former waste-oil tank,also was anaiy:ed for volatile organics using EPA Method 8240. No volatile organics were detected?.t the Method Detection Limit(MDL). Analytical results for benzene and TPH-as-gasoline are presented on Figure 4 and summarized in Table 2. The laboratory report L enclosed.n Appendix A. Analytical results Indicate that groundwater samples from monitoring wells MW-1 and MW-3 contained detectable concentration&of TPH-as-gasoline(180 parts per billion(ppb)and 380 ppb, respectively. A concentration of 18 ppb benzene was detected In the sample from monitoring well MW- 3. No detectable amounts of TPH-4x ga5aline or BTEC compounds were found In the sample from monitoring well MW-2. In summary,groundwater elevations in the three monitoring wells have decreased an average of approximately 3 feet from August 1990 to January 1991. Additionally,the groundwater gradient has changed from northwest to northeast,and flattened from 0.02 to 0.002 across the site. These effects may be due to changes In groundwater well pumpage In the Stockton area Concentrations of TPH-as-gasoline were detected in samples from two monitoring wells.MW-1 and MW-3. The next round of mnitoring and sampling fur this site is scheduled for April 1991. Additional well installation 1s delayed pending the result of the planned n BAT-probe study at Chevron Service Statlo -- -- - -- - No.9-4275. #GROulvowa.TER - TECHNOLOCY,INC. ;r