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Site Background Canepa's Car Wash,Park Street Page 2 of 5 contaminant concentration with depth, with a benzene concentration of 17,000 µg/L at 74 to 78 feet bgs and 150 µg/L at the refusal depth of 107 feet bgs The results of the deepest groundwater samples collected from the hydropunch borings associated with the CPT borings indicated that the vertical extent of petroleum hydrocarbon contamination was not fully characterized No soil horizon was encountered during the investigation that apparently had substantially impeded the vertical movement of gasoline contamination Laboratory analytical results from hydropunch groundwater samples indicated that shallow groundwater northeast of the site was not impacted by gasoline constituents at or above the laboratory reported detection limits Results of the groundwater samples collected north of the site indicated that the shallow groundwater immediately north of the site was impacted by moderate and low concentrations of gasoline constituents Results of the groundwater samples collected wells screened below the water table indicated that the lateral and vertical extent of groundwater contamination was not fully investigated north of the site The highest concentrations of gasoline constituents were detected in the shallow groundwater sample collected near the former location of the USTs with benzene at 15,000 pg/L MTBE iso-concentration contours constructed with the shallow groundwater data from the investigation indicated a low concentration MTBE plume The plume was apparently from an off-site source located southwest of the site and not from the former USTs at the site The low concentrations of benzene detected may also have been from an off-site source located southwest of the site based on the distribution of the benzene contamination in that area Based on the results of the March 2002 investigation, Condor recommended additional groundwater investigation at the site to further evaluate the vertical distribution of the contaminant plume Condor prepared the Work Plan for Additional Soil and Groundwater Investigation by Cone Penetrometer Testing (CPT), dated November 1, 2002 The work described included additional CPT borings, discrete depth sampling, and monitor well installation to further evaluate the lateral and vertical extent of gasoline contamination at and near the site Quarterly groundwater monitoring activities were conducted on October 17, 2002 The laboratory analytical results for the groundwater samples collected from monitor wells (MW) MW-1,MW-4,MW-6, and MW-7 indicated that benzene, toluene, ethyl benzene, and total xylenes (BTTX) were not detected at or above laboratory reported detection limits, but were detected in MW-2 and MW-5 Benzene was detected in the groundwater samples collected from MW-3 Total petroleum hydrocarbons quantified as gasoline (TPH-G) were detected in the groundwater samples collected from MW-2, MW-3, MW-4, MW- 5, and MW-7 MTBE was detected in the groundwater samples collected from MW-1, MW-3, MW-4, MW-6, and MW-7 The concentration of benzene in monitor well MW-2 generally has an inverse relationship with groundwater elevation In contrast, benzene concentrations in MW-5 have generally increased as the groundwater elevation has increased Concentrations of MTBE in monitor well MW-6 have ranged from < 0 5 to 21 pg/L over time, with an general trend of increasing concentration since April 2001 Low concentrations of MTBE have been sporadically present in groundwater samples collected from monitor well MW-3 Concentrations of MTBE slightly above the laboratory detection limit historically appeared first in monitor well MW-4, followed by MW-1, and most recently MW-7, which are located on the western extent of the site It is possible that the low concentrations of MTBE represent background concentrations since they are at the up-gradient extent of the site