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1 detected above laboratory reporting limits in any of the confirmation soil samples submitted for analysis Total lead was detected in 12 soil samples collected during the tank and product line removal activities in June 1992 at depths ranging from 5 to 16 feet bgs at concentrations ranging from 3 0 to 5 3 mg/kg These values were compared to Environmental Protection Agency (EPA) Region IX Preliminary Remediation Goals (PRGs) PRGs are tools for evaluating and cleaning up impacted sites They are nsk-based concentrations derived from standardized equations, combining exposure information assumptions and EPA toxicity data The PRGs contained in the EPA Region IX PRG Table are generic and are calculated without site-specific information The lead PRG for residential soil is 400 mg/kg, which is well above the maximum concentration of total lead detected onsite of 5 3 mg/kg (EPA 1999) 4 2.2 Groundwater Characterization During the quarterly groundwater sampling program, which began in 1991, liquid-phase hydrocarbons have never been observed at the site As presented in Section 2 3, and graphically in Figure 2, the average groundwater flow direction at the site over time is to the south 80 degrees east with a magnitude of 0 003 Based on the average values, the onsite and offsite wells are properly located to provide an accurate assessment of groundwater quality over time ' The most recent (30 July 2000)groundwater monitoring and sampling event results are presented in Figure 10, and in Table 6 Cumulative data are presented in Table 1 BTEX and TPH-g were not detected above reported detection limits during this event MTBE was detected in wells MW6 and VEW2 at 6 and 21 pg/L (EPA Method 8260B), respectively As presented in Table 1, samples from well MW6 have been analyzed for MTBE during 15 quarterly events since 1996, and MTBE has only been detected one other time, at 12 gg/L The analytical results for grab groundwater samples collected from the onsite confirmation borings on 26-27 August 1999 are summarized in Table 4 Benzene and oxygenates other than MTBE were not detected above reported detection limits in any of these grab groundwater samples Sample SB7W contained 3,930 ug/L TPH-g, but no detectable benzene As part of the overall assessment of data quality, hydrographs (Appendix B) were prepared to assess if rising groundwater elevations at the site affected the concentrations in groundwater at the site A review of these hydrographs does not reveal a correlation between rising groundwater elevations and groundwater concentrations Additionally, the time penod during which the top of the screened interval of these wells became submerged is not accompanied by a reduction in ' hydrocarbon or oxygenate concentrations, which indicates that the groundwater samples collected over time are representative of the site conditions 4,3 STABILITY OF DISSOLVED HYDROCARBONS Hydrographs, which are presented in Appendix B, were prepared to allow for an assessment of concentrations of TPH-g, benzene, and MTBE over time A review of these hydrographs demonstrates gradual changes in concentrations over time rather than erratic ones The stability f lYrn�eFt5�70137}Mas[erl5VplClosurel IOM0137crtext doc 11