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31 October 1996 AGE-NC Project No. 95-0190 Page 5 of 7 monitoring wells MW-2 and MW-5, at maximum concentrations"of 250 ppb. Further, BTE&X compounds were detected in the same monitoring well samples at a maximum concentration of 1.1 ppb(xylenes in MW_4 on 31 October 1996).Neither TPI-I-g nor BTE&X were detected in any other groundwater samples from the site in 1995 or 1996. Additionally, during the 1995 sampling event, matrix interference from the HVOCs compound 1,2-dichloropropane was noted in the laboratory report,again indicating that the majority_ of gasoline detected was actually the HVOC compound 1,2- dichloropropane. 3.5. STOCKPILED SOIL SAMPLING On 17 May 1996, representatives of AGE collected soil samples from the soil stockpiled on-site from the excavation of the USTs. The PHS-EHD observed the sampling. Soil was collected in a metric soil sampler, loaded with a pre-cleaned brass sleeve. The ends of the recovered brass sleeve were covered with teflon plastic,capped and sealed with tape.',Twosamples were collected and sent under chain-of-custody to McCampbell Analytical Inc. (MAIL'in Pacheco, California. The samples were composited by MAI and Nvere analyzed for TPH-g and BTE&X.Petroleum hydrocarbons were not detected in.the soil analyzed. The Aiialytical results of all soil samples are summarized in Table LM ,,, 1. A copy of the laboratory report .(MAI laboratory numbers 65271) and chain-of-custody are included.in Appendix E. 4.0. DISCUSSION The results of site investigations and ground water monitoring events presented above show that petroleum hydrocarbons,presumably released from the two removed 1,000-gallon USTs, impacted the soil in the area around the former USTs. The impacted soil apparently caused some impact on �-' ground water on the site. The consistent ground water flow direction toward the northeast could make it possible for a narrow hydrocarbon-impacted plume of ground water to pass largely undetected between MW-1.and MW-2, an area where no ground water analytical data is available. However,with the low groundwater gradient on site(approximately 0.018 foot/foot,or 1.04°),AGE believes that a significant plume of hydrocarbon-impacted water would spread out to such an extent that MW-2 would detect much higher TPH-g and BTE&X concentrations than has been detected if a significant ground water plume was migrating with the ground water. � The TPH-g encountered,in MW-5 appears to be a matrix effect produced in the water samples by the presence of the HVOC compound 1,2- dichloropropane."What TPH-g may actually be in the sample is not likely to have originated from the two former .1,000-gallon,USTs as MW-5 is a significant distance from the former tanks and is up-gradient and cross-gradient from the former tank pit.