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Fourth Quarter 1998 Status Report - Former Discovery Chevrolet December 8, 1998 the gasoline USTs to the dispenser,located inside the service bays,was left in place beneath the concrete apron outside the shop building. Petroleum hydrocarbons were detected in all soil samples collected during the UST removal. Soil samples collected from the gasoline UST excavation contained Total Petroleum Hydrocarbons as gasoline (TPHg) at concentrations ranging from 920 to 4,400 part per million (ppm). Benzene was detected in all these soil samples at concentrations ranging from 5.9 to 39 ppm. Total lead was detected in two of these soil samples at concentrations of 19 and 4.0 ppm. TPHg and benzene were detected in the soil sample collected beneath the product dispenser at concentrations of 21 and 0.88 ppm,respectively.TPHg,Total Petroleum Hydrocarbons as Diesel (TPHd), and benzene were detected in the soil sample from the waste oil excavation at concentrations of 31,270 and 0.18 ppm,respectively. Tetrachlororoethene(72 parts per billion, or ppb), lead (7.8 ppm), and chromium (9.2 ppm) were also detected in this sample. Based on results of soil sample analyses from the UST removal, GSI performed a preliminary site assessment to further evaluate hydrocarbons in the soil and to evaluate whether hydrocarbons had impacted groundwater beneath the site. Three on-site groundwater monitoring wells were installed at the locations shown on the Site Plan(Figure 2) in September 1994. One soil sample from approximately 10 bgs in each soil boring was submitted for analysis. TPHg were detected in the soil sample from boring MW-1 (340 ppm) and MW-2 (240 ppm). The benzene concentrations in these samples were 3.9 and 2.4 ppm, respectively. Petroleum hydrocarbons were not detected in the soil sample from boring MW-3. Groundwater in the newly installed wells was measured between 9.97 and 10.49 feet bgs, and appeared to flow north-northeast at a gradient of 0.003. Floating product was not observed in the monitoring wells. TPHg was detected in the groundwater sample collected from well MW-1 (640 parts per billion,or ppb)and MW-2 (7,200 ppb). The benzene concentrations in these samples were 35 and 370 ppb, respectively. Petroleum hydrocarbons were not detected in the groundwater sample collected from well MW-3. Results of that investigation were reported in GSI Report No. 8146.701-1, Preliminary Environmental Investigation Report, dated December 7, 1994. Depth-to- groundwater and chemical analytical data are summarized in Table 1. Quarterly monitoring and sampling of the monitoring wells begin in March 1995. Historically, depth to groundwater has fluctuated between 9.25 and 11.53 feet bgs. Groundwater appears to flow toward the north-northwest at a gradient of approximately 0.003 to 0.005. Floating product has not been observed in the monitoring wells. TPHg, BTEX, or Oil and Grease have not been detected in well MW-3. TPHg or benzene have never been detected in well MW-5. TPHg concentrations in wells MW-1 and MW-2 have ranged from <50 to 17,000 ppb, and benzene concentrations have ranged from 1.1 to 3,100 ppb. TPHg(415 ppb)and benzene(1.1 ppb)were detected only once in well MW-4 (April, 1997), and have never been detected in well MW-5- Historical quarterly groundwater monitoring and chemical analytical data are summarized in Table 1. 948146.05-8 2