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PREVIOUS ENVIRONMENTAL INVESTIGATIONS AND CORRECTIVE ACTIONS UNDERGROUND STORAGE TANK REMOVALS AND SOIL EXCAVATION (1999 — 2000) An unauthorized fuel release was initially discovered in October 1999 during the removal of one 12,000 gallon gasoline UST, two 4,000 gallon gasoline USTs and one 2,000 gallon diesel UST. In conjunction with the UST removals, approximately 150 cubic yads (yds3) of TPH impacted soil were removed. A total of nine soil samples were collected from beneath the USTs and an additional six soil samples were collected beneath the fuel dispensers. Total petroleum hydrocarbons as gasoline (TPHg), benzene and ethylbenzene were detected at maximum concentrations of 3,849 milligrams per kilogram (mg/kg), 65 mg/kg and 2,930 mg/kg, respectively, from the base of the UST cavity. Petroleum hydrocarbon compounds were not detected in soil samples collected from beneath the dispensers (AGE, 2000). Laboratory analytical results for the collected soils samples are further summarized in Table 1. In April 2000 an additional 175 yds3 of TPH impacted soils were excavated from the UST cavity. TPHg, benzene and ethylbenzene were detected in post excavation soil samples at concentrations of 12,000 mg/kg, 1,800 mg/kg and 58 mg/kg, respectively (AGE, 2000). Laboratory analytical results for soil samples collected following the additional soil removal are further summarized in Table 1. Dispenser and post excavation soil sample locations and the approximate limits of the soil over excavation are shown on a site plan figure prepared by Advance GeoEnvironmental, Inc. (AGE) presented in Appendix B. PRELIMINARY SITE ASSESSMENT (2003) In August 2003, direct-push continuous-core soil borings B 1 through B4 were advanced to depths of 50 feet bgs at the approximate locations shown on Figure 2. Groundwater was encountered in each boring at approximately 40 feet bgs. Selected soil samples collected between 15 and 50 feet bgs from each boring were submitted for laboratory analysis. Additionally, a groundwater grab sample was collected from each soil boring (AGE, 2003). TPHg, benzene and ethylbenzene were detected in soil samples at maximum concentrations of 21,000 mg/kg, 27 mg/kg and 270 mg/kg, respectively. Laboratory analytical results for soil samples collected are further summarized in Table 1. TPHg, benzene, ethylbenzene and methyl tert-butyl ether (MTBE) were detected in the groundwater grab samples at maximum concentrations of I10,000 micrograms per liter (ug/1), 13,000 ug/l, 3,800 ug/1 and 45,000 ug/l, respectively (AGE, 2003). Laboratory analytical results for the groundwater grab samples are further summarized in Table 2. GROUNDWATER MONITORING WELL INSTALLATIONS (2004) In March 2004, groundwater monitoring wells MW-1 through MW-4 were installed at the Site, at the approximate locations shown on Figure 2. Wells were drilled to depths ranging between 45 and 55 feet bgs, and were constructed with 2-inch diameter schedule 40 PVC casing with 20 FREY Environmental,Inc. 3 Project No. 1095-01