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Site Assessment Work Plan 1022 Frontage Road, Ripon, California CONESTOGA-ROVERS March 7, 2008 &ASSOCIATES bgs and petroleum hydrocarbons were detected in all three samples. In boring B-18 TPHd and TPHg groundwater concentrations increased with depth, low BTEX concentrations were detected in all three samples,and MTBE concentrations were lower in the two samples collected below the 30 ft bgs sample. September 2005:In September 2005,Cambria conducted a SVE and a SVE/AS test using well EW-1 as a vapor extraction well,well AS-1 as an air sparge well,and wells MW-2,MW-7,MW-9,and MW-10 as observation wells. The effective radius of vacuum influence was determined to be approximately 75 feet for both SVE and combined SVE/AS. The maximum flow rates of 125 cfin and 158 cfm were observed during the SVE and SVE/AS constant vacuum tests, respectively. The maximum hydrocarbon mass removal rates of 22.73 pounds per day(lbs/day) and 39.77 lbs/day were observed during the SVE and SVE/AS constant vacuum tests,respectively. Approximately 11 pounds of hydrocarbons were removed during the two days of the feasibility testing. It was concluded that SVE/AS would be an effective remedial option for petroleum hydrocarbons detected in and above the shallow aquifer. February/March 2007:In February and March 2007,Conestoga-Rovers&Associates(CRA)advanced 10 direct push borings and collected 28 soil samples and 10 grab groundwater samples,advanced 3 cone ,l 1 penetration test (CPT) borings and collected 9 depth-discreet hydropunch® groundwater samples,and 3 evaluated historical supply well construction and pumping records Sampling results from the geoprobe drilling indicated that dissolved-phase TPHd concentrations likely extend southeast of the former USTs beneath the tire shop/truck wash,but that there appears to have been a second diesel release in the vicinity of diesel pump station and MW-6."Groundwater results from the CPT drilling indicated no significant c ncentrations of dissolved-phase TPHd,TPHmo,TPHg,and MTBE beneath the former USTs at or below ��✓1�p1 40 ft bgs, and that low dissolved-phase MTBE concentrations had migrated vertically and laterally in a '✓westerly direction. Based on the low dissolved-phase MTBE concentrations,intervening low permeability q'S clay layers,the deep well screen intervals and proximity to the site, it was concluded that MTBE did not pose a significant threat to the municipal supply well. There was insufficient data to conclude whether groundwater pumping from nearby supply well or private domestic wells had affected the fluctuating r groundwater table and the vertical contaminant distribution at the site. March 2005 to present: Since March 2005, groundwater sampling has been conducted by Cambria or CRA on monitoring wells MW-1 through MW-3, MW-6 through MW-10,and commercial supply well DW-1. Wells MW-4 and MW-5 were sampled annually after April 2006.All groundwater monitoring and analytical data, for wells gauged and sampled, were submitted to the GeoTracker database. 6 Worldwide Engineering,Environmental,Construction,and IT Services