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LEEDSHILL HERKENNOFF, INC excavation. As mentioned in section 5.1, 0.3 ppm is the accepted minimum detection limit for BTX&E in the general risk appraisal . Since the collected soil samples have residual levels less than 0.3 ppm, the general risk worksheets are not necessary. The results show that these residual hydrocarbon levels can be left in place without posing a threat to the groundwater resources in the area. Therefore, based on the LUFT Manual leaching potential analysis and general risk appraisal , LH proposes that the BCA drums and existing soil stockpile be used as backfill material for the current open excavation. 5.3 EVALUATION OF GROUNDWATER The LUFT Manual does not specify maximum allowable hydrocarbon concentrations in groundwater. Therefore, for illustrative purposes only, LH will compare the analytical results from the monitoring wells to established California drinking water standards. Department of Health Services (DOHS) has established maximum concentration levels (MCL) for specific organic and inorganic chemicals (Title 22, Section 64445 of the California Administrative Code) . Three gasoline constituents are on the list of regulated chemicals: benzene(MCL=1.0 ppb), ethylbenzene (MCL=680 ppb) and xylenes(MCL=1750 ppb) , An MCL is a legally enforceable maximum level ; therefore, water to be provided for public consumption cannot contain concentration levels in excess of the established MCL. DOHS has also established action levels for a much broader list of chemicals These suggested action levels are to be used for guidance purposes only, and are not legally enforceable maximum concentration levels. The action level for Toluene 7s 100 ppb Water samples collected from all five monitoring wells showed detectable levels of petroleum hydrocarbon constituents Levels detected in MW1 are below all of the above MCL and action levels. Levels detected in MW3 and MW4 only exceed MCL levels for benzene. Samples collected from MW2 and MW5 indicate gasoline constituents to excess of all of the above MCL and action levels In general , these levels are several orders of magnitude greater than the regulatory guidelines. As discussed in Section 4.3, Groundwater Flow, flow is eastward across the site. Since MW5 is in the far northeast corner of the site, and does contain detectable levels of BTX&E and TPH, there is a concern regarding offsite release of these constituents. -2a-