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' Quik Stop Market No. 132 January 6, 1993 Project No. F7132.34 Page 7 downgradient from previous excavation activities at this site and the presence of low concentrations of these compounds is not unexpected. ' TPHG, toluene, ethylbenzene, and total xylenes were detected in the groundwater sample from MW-5. As can be seen in Table 2, MW-5 has had a history of detectable TPHG and BTEX constituents since installation. However, as these compounds have not been detected in downgradient wells MW-6 and MW-7 it appears that the compounds are limited in extent and appear to be restricted to the area around MW-5. This information would suggest that petroleum hydrocarbon compounds are trapped in isolated pore spaces in the vadose zone and aquifer soil matrix and will gradually be released. This can result in low concentrations of these compounds which may be detected over a long period of time. As observed, these concentration levels have been decreasing with time and may be expected to continue to decrease. ' Groundwater samples from MW-6 and MW-7 were also tested for the presence of fecal coliform as required by the SJCPHS. No fecal coliform was detected. At the present time, annual testing for fecal coliform is required by the SJCPHS due to the initial, one ' time detection of fecal coliform in MW-2 reported in April of 1991. Subsequent analysis for fecal coliform conducted in July 1991, September 1991, March 1992, and ' September 1992 (see Table 2) have not detected the presence of fecal coliform in this well. It may be that the initial sample was inadvertently contaminated during sampling or laboratory analysis. These wells were installed to help determine the extent of petroleum hydrocarbons. The wells were installed in locations based on the estimated extent of a possible petroleum hydrocarbon plume and not the location of sanitary sewer lines. Since all wells have laboratory data indicating that fecal coliform is not present and fecal coliform detection was not the purpose of the well or the responsibility of Quik Stop Markets, RESNA recommends that analysis for fecal coliform be discontinued at this site. RECOMMENDATION SUMMARY ' - On the basis of an established history of nondetectable concentrations of TPHG and BTEX (eight consecutive quarters), in groundwater samples from monitoring wells MW-3, and MW-4 RESNA recommends that sampling and analysis be discontinued ' in these two wells. Quarterly measurement of groundwater elevations will continue. • On the basis of laboratory data indicating that fecal coliform is not present, is ' beyond the scope of this investigation and is not the responsibility of Quik Stop Markets, RESNA recommends that sampling and analysis of groundwater samples for fecal coliform be discontinued. • RESNA recommends that quarterly sampling and analysis for TPHG and BTEX and measurement of groundwater elevations will be continued in wells MW-1 R, MW-2, and MW-5 and that wells MW-6 and MW-7 be added to the array of wells being monitored.