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i Work P1anAdditional Site Assessment Jimco Truck Plaza C A M B R I A 1022 Frontage Road Ripon, California J P/'— May 18, 2005 site. As such,defining the lateral extent of the dissolved-phase contaminantsputhwest of the USTs will complete the delineation of the dissolved-phase plume related to the former USTs. 4.2 VerticalExtent of Contamination Soil Contamination: The release of fuel from the former.UST system is presumed to have occurred prior to September 1998, whereupon the USTs and its associated fuel dispensers and piping were removed from the site. As noted previously in Section 2.4,groundwater levels have dropped over 10 feet since 1998. The steady drop in groundwater levels at the site has effectively left the majority of impacted soil above the current groundwater table. Soil beneath the former USTs has been p ,�' investigated to 40`feet bgs. Soil data from soil boring B17 indicates that impacted soil is present primarily at 20 ft bgs and does not appear to extend to 40 ft bgs. The vertical extent of impacted soil appears to be adequately characterized �tl5 Groundwater Contamination:A water-bearing zone consisting of poorly graded sand appears to exist from approximately 20 to 30 ft bgs beneath the former USTs. Hydrocarbons and fuel oxygenates have been detected within the water-bearing zone in wells screened from 10 to 30 ft bgs. TPHg, ethylbenze, xylenes and MTBE were detected at approximately 42 feet bgs in a grab groundwater sample collected from boring B 17. Due to the potential for cross contamination during the groundwater sampling method and the lack of any detected concentrations in soil at 40 ft bgs, the presence of impacted groundwater at 42 to 46 ft bgs remains uncertain. The vertical extent of any impacted groundwater is adequate and likely attenuates quickly with depth, consistent with the soil "! sample results. " 5.0 PROPOSED SCOPE OF WORK k The objectives of the proposed scope of work are to assess the lateral extent of impacted groundwater 0t(J, �`-ywest of wells MW-8 and MW-9,and to assess the vertical extent of impacted groundwater in the ,, M ,I vicinity of the USTs as requested by San Joaquin County Environmental Health. To meet these GVA objectives, Cambria will conduct the following: • Install one groundwater monitoring well(MW-.10) in the southwest corner of the property. • Collect depth discrete groundwater samples from a soil boring in the vicinity of the former USTs. The locations of the proposed well and boring are shown on Figure 4. 6