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REVISED ADDITIONAL ASSESSMENT WORKPLAN JAY'S MINI-MART,STOCKTON SEPTEMBER 2003 Site History In 1997,three gasoline dispensing UST's were removed. Soil samples collected up to 24 feet bgs at the base of the former UST's excavation reported high concentrations of total petroleum hydrocarbons, as gasoline (TPH G), TPH, as diesel (TPH D), benzene,toluene, ethylbenzene, total xylenes, (BTEX) and fuel oxygenates. One soil sample was reported to contain methyl tertiary butyl ether(MTBE) at a concentration of 0.650 mg/kg. Based on the soil data, the Central Valley Regional Water Quality Control Board (Regional Board) required drilling of a single soil boring and the collection of soil and groundwater samples for laboratory analyses. On August 11, 2000 John P. Cummings&Associates(JPCA) attempted to drill a soil boring with a push rig, but encountered refusal at 25-feet bgs. On September 7, 2000 JPCA completed the soil boring to 53-feet bgs using a rotary auger drill rig. MTBE and tertiary Butanol were detected in soil at concentrations of up to 210 mg/kg and 1,800 mg/kg, respectively, at depths of between 30 and 40 feet bgs. TPH G, toluene, and MTBE were reported in groundwater at 800 µg/1, 18 µg/1, and 10 µg/1, respectively. On December 23, 1999 the County directed that an additional site investigation be conducted to assess the impact of petroleum constituents, including MTBE, in groundwater at the site. GHH assumed environmental consulting responsibilities for the site in March 2002, and prepared an Additional Assessment Workplan in May 2002. This workplan was approved by the County. On May 22-23, 2003,three borings (SB-2 through SB-4)were completed on-site to determine if there were soil and/or groundwater impacts near the former UST, dispensers, and fuel lines. Low levels of petroleum hydrocarbons, MTBE, and 1,2-dichloroethane(1,2-DCA)were detected. Soil sample analytical results are summarized in Table 1 and on Figure 3. Groundwater sample analytical results are summarized in Table 2 and on Figure 4. GHH prepared an Additional Assessment Report(AAR) dated June 2003. Objective The objective of this workplan is to present a scope of work that will evaluate the extent of impacted soil and groundwater in the area surrounding soil borings B-1, SB-2, SB-3 and SB-4, as shown on Figures 3, and 4 and reported in AAR. This workplan proposes to drill three monitoring wells to approximately 65-feet bgs to define subsurface conditions. Soil and groundwater samples will be collected and analyzed for TPH G, TPH D, BTEX, 1,2- dichloroethane (1,2-DCA), ethylene dibromide(EDB), and fuel oxygenates. 2