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J cadepa's Car Wash (Pacific Avenue) Problem Assessment Report and Corrective Action Plan 'I Page 4 1 On September 20 . break through on the second carbon unit effluent was measured by PID at 2 parts per million by volume . The carbon in the first vessel was replace and the piping rerouted so the new carbon is in the second vessel in series . The system was restarted on September 30, 2002 . In the Report — Soil and Groundwater Investigation, dated June 12, 1998, Condor recommended additional soil and groundwater investigation to further characterize the extent of contamination at the site. Condor performed additional groundwater investicyation at the site consisting of three CPT borings, 'I hydropunch sampling, and the installation of three soil borings and four monitor wells . Details of the investigation are presented in the Additional Soil and Groundwater Investigation Report dated January 21 , 2002 . Twelve monitor wells, MW- 1 through MW- 12d, were surveyed as part of the investigation . The new survey identified errors in the previously reported elevations of monitor wells MW-6 and MW-7. The new survey elevations for these wells are higher than previously reported, and consequently, the groundwater elevation contours for the site no longer indicated a groundwater mound in the vicinity of well MW-2 . The task of surveying the monitor wells was sufficient to complete fire Groundwater Mounding Study Report dated February 13 , 2002 . Soil samples were collected immediately above the groundwater in selected wells and soil borings during the investigation described in the January 21 , 2002 report. The purpose of those soil samples was to evaluate existing vadose zone contamination _ No contaminants were detected in the vadose zone. In August 2001 , Condor conducted a sensitive receptor survey within a 2,000-foot radius of the site to identify potential areas of groundwater recharge or discharge (surface water bodies), schools, and potential water well users that could be impacted by migration Of groundwater from the site. The results of the sensitive receptor survey are included in the Quarterly Groundwater Monitoring (Third Quarter 2001) and Sensitive Receptor Survey Report, dated August 16, 2001 . The results indicated the presence of several domestic and municipal wells, two schools, three child-care facilities, and three leaking underground storage tank (LUST) sites within the study area. No actively pumped drinking water wells were identified within 500 feet of the site, however. Condor performed quarterly monitoring at the site on January 10, 2002 and April 10, 2002 . Laboratory analytical results of the groundwater samples indicated concentrations of petroleum hydrocarbon constituents that were consistent with historical data. The analytical results also indicated substantial declines in contaminant concentration in monitor wells MW- 1l and MW-12d compared to the initial sampling results. 4.0 HYDROGEOLOGY The car wash site is situated on fine-grained flood plain deposits overlying distal alluvial fan deposits sloping westward from the eastern part of San Joaquin County. The upper part (�50 to 60 feet) of the section underlying the site is made up of flood-stage, overbank deposits consisting mostly of clay, clay- rich silt, and silt. Following retreat of the flood waters, the muds and silts dry out and desiccation cracks form . Abundant vegetation may also cover the flood plain . Interbedded with the overbank deposits are less abundant clayey-, silty-, and poorly-sorted sands that may have originated as channel or natural levee deposits . The interbedded sandy deposits appear to be thin and may be discontinuous . Generalized geological sections have been constructed from the boring logs for the site monitor wells and soil borings . The sections are shown in Figures 3 , 4, and 5 . In general, black to gray organic clay is present from the surface to about eight feet. Beneath the clay to a depth of about 50 to 60 feet are silt deposits with interbedded and discontinuous lenses of clayey to silty sand . Root molds and carbonate A % 4) CONDOR