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i Additional soil and Groundwater Investigation Report Canepa's Car Wash(Pacific Avenue) - January 21,2002 Page 9 5.0 SUMMARY/DISCUSSION OF RESULTS lCondor personnel conducted soil and groundwater investigation activities from September 26, 2001 through October 26, 2001 at the site. CPT logs and direct push (hydropunch) water samples were collected from three site locations. Monitor wells MW-9 through MW-12d were drilled, constructed, developed, surveyed and sampled. In addition, soil samples were collected from soil borings SB-2 through SB-4 and the borehole for MW-11. The results of the soil sampling indicate that very little gasoline contamination remains in the site vadose zone in the locations sampled. This is consistent with recent results of the soil vapor extraction influent Isampling at the site. The results of the hydropunch groundwater sampling indicate that groundwater contamination is not present at or above the laboratory reported detection limits at the depths sampled in the locations of the I CPT-2 and CPT-3 clusters. These results suggest that the vertical extent of contamination has been adequately investigated in the northwest and northeasfportions of the site. The results of the groundwater sample collected at 100 to 110 feet bgs in the center of the contaminant plume (CPT-1 cluster) indicate that further monitoring of this horizon is necessary. MW-12d was installed to serve this purpose. The results of the groundwater sample collected from MW-12d serve as preliminary confirmation of the results of the hydropunch sample collected from 100 to 1 I0 feet bgs. However, additional sampling of MW-12d is necessary to establish typical groundwater quality there because the initial sampling results from the well may reflect some temporary, limited movement of contamination from upper horizons during the construction of the well. Development of the well may have been inadequate to remove the remnant contamination from above because of the lack of productivity of the well (only a limited amount lie of groundwater could be removed from the well during development). The results of the deepest groundwater sample collected in the location of the CPT-1 cluster(from 120 to 125 feet bgs) indicate that this deeper horizon was not impacted with gasoline constituents. Therefore, the vertical extent of contamination in this location (in the center of the contaminant plume) appears to be adequately investigated. I The results of the groundwater samples collected from MW-9 and MW-10 indicate that the shallowest groundwater in those locations is not impacted at or above the laboratory reported detection limits. The results of the groundwater sample collected from MW-11 indicate that groundwater in that location is Impacted with relatively low concentrations of gasoline constituents. The results of the new monitor well Isampling need to be confirmed during subsequent quarterly monitoring events. The contamination present in the location of MW-11 (based on the initial sampling event) is at significantly lower concentrations than has historically been present in groundwater samples collected Frnm MW-1 and 1V W— 11 -7� PVPn thnucrh MW-1 l is in c-Ime, proximity to MW-1 and MW-2. This is probably because the MW-11 well screen intersects the current water table and the MW-I and MW-2 well screens do not. The shallow water table groundwater in the location of MW-11 currently resides in a I soil horizon that was previously remediated by the site SVE system at a time when the groundwater was substantially deeper and the soil there was exposed to the SVE well screens. MW-1 and MW-2, however, are currently screened in groundwater that is in contact with relatively unremediated soil and are therefore exhibiting higher contaminant concentrations. 0 In addition to the soil and groundwater data collected, a new monitor well survey was conducted at the 1 site to comply with new electronic deliverable format (EDF) requirements. The results of the n V* NCI-6� Ii 41 CONDOR