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WIN +r r '-' .. ....� _ w r. MEN Mr.Clint Rodgers ,«. February 22, 1991 Page 2 GROUNDWATER SAMPLING AND ANALYSES Following monitoring on January s, 1991,the three wells were purged by hand bailing to allow for the collection 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 s 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 stored on the north side of the site pending proper i disposal. 1 After allowing the water to recover to at least 80 percent of the original levels,groundwater samples were collected In accordance with Groundwater Technology SOk 9, 10,and 12(Appendix A). The samples were placed in acidified 40-milliliter(mQ glass vials which were capped with TefianR septa lids so that no air was trapped Inside. The sample vials were then labeled and placed In an Insulated cooler for transportation to Superior Analytical Laboratory,Inc.,a State of Caiifomla-c erfified laboratory In f Martinez,California Proper Chain-of-Custody Manifest documentation,as described In SOP 11,was maintained with the samples,and a copy of the manifest is Included In this report(Appendix A). 3 All groundwater samples were analyzed for the presence of benzene,toluene,ethylbenzene,and xylenes F (BTEC,and for total petroleum hydrocarbons(TP!-1)-as-Baso}ine using modified U.S.Environmental Protection Agency(EPA)Methods 5030/8020/8015. Additionally,the groundwater sample collected ' from monitoring well MW-1,which Is ed)acent to the location of the former waste-oil tank,also was analyzed for volatile organics using EPA Method 8240. Na volatile organics were detected at the Method Detection Limit(MDL). Analytical results for benzene and Teri-as-gasoline are presented on Figure 4 and summarized in Table 2 The laboratory report Is enclosed In Appendix A. $; Analytical results Indicate that groundwater samples from monitoring wells MW-1 and MW-3 contained detectable concentrations of TPH-as-gasoline (180 parts per billion Ippb)and 380 ppb, respectiv*). A concentration of 18 ppb benzene was detected In the sample from monitoring well Mw- 3. No detectable amounts of TPHi-as-gasollne or BTEX compounds were found In the sample from k monitoring well MW-2. In summary,groundwater elevatlons 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-11 and MW-3- The W 3.The next round of monitoring and sampling for this site Is scheduled for April 1991. Addltlonal well Installation Is delayed pending the result of the planned BAT probe study at Chevron Service Station No.9-4275. GROUNDWATER TECHNOLOGY.INC.