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Im. <br /> v <br /> CHAPTER 5 <br /> "W SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS <br /> Summary <br /> Purgeable halocarbon (EPA Method 8010) constituents in the soil <br /> 6.0 were below California Regional Water Quality Control Board, Central <br /> Valley Region (Regional Board) designated levels. With the exception <br /> of soil sample ATR-4B, benzene, toluene, and xylene (BTX) (EPA Method <br /> 8020) were below Regional Board designated levels. Dissolved BTX in <br /> groundwater in wells ATR-3 and ATR-4 exceeded California Department <br /> of Health Services (DHS) designated levels. Dissolved total lead and <br /> 1,2-Dichloroethane in wells ATR-2 and ATR-3 exceed Regional Board <br /> Primary Drinking Water Standards (MCL) . No floating hydrocarbon <br /> product was found on the groundwater surface. <br /> LM Conclusions <br /> The soils at the locations of wells ATR-1, ATR--2, ATR-3, and <br /> ATR--4 do not contain significant levels of hydrocarbons. Therefore, <br /> excavation, on-site soil aeration, soil venting, off-site soil <br /> treatment, and landfilling are unnecessary. <br /> L" Groundwater results show concentration of BTX in monitoring wells <br /> ATR-3 and ATR-4 above action levels. BTX levels in downgradient <br /> monitoring wells ATR-1 and ATR-2 are insignificant or non- <br /> detectable. Therefore, it is unlikely the plume has moved off <br /> site. From the levels detected and the fact the tanks and lines <br /> appear to be structurally sound, it is thought the contamination is a <br /> result of overfilling the tanks. <br /> It is unlikely that the nearby municipal well would be affected <br /> by the hydrocarbon levels in groundwater beneath ARCO Petroleum <br /> +r Products Company (ARCO) Service Station 2093. There are no known <br /> downgradient municipal wells. The nearest municipal well is approxi-- <br /> mately 3/4-mile upgradient and probably draws from a deeper aquifer . <br /> Recommendations <br /> Hydrocarbon levels present do not warrant cleanup at this time. <br /> To detect whether the plume moves off site and to document the <br /> natural degradation of the dissolved constituents, BC recommends <br /> continued monitoring and sampling. We suggest monitoring water level <br /> 16a changes and gradient changes, and sampling for BTX (EPA Method <br /> 8020) . Such monitoring and sampling should be done on a quarterly <br /> basis . <br /> LN <br /> BROWN AND CALDWELL <br /> C CdNSULfING ENGINEERS <br /> Lo <br />