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c ATC Associates Inc. 1117 Lone Palm Avenue, Suite B Modesto,California 95351 209-579-2221 Fax:209-579-2225 A S S O C I A T E S I N C. On July 18, 1995, Smith Technology supervised the installation of three groundwater monitoring wells, MW-1, MW-2, and MW-3 (Figure 2). During installation of the monitoring wells, soil samples were collected from the borings. On July 21, 1995, Smith Technology developed and sampled monitoring wells MW-1, MW-2 and MW-3. Analytical results of the soil and groundwater samples collected indicated elevated concentrations of petroleum hydrocarbons were present in the soil and groundwater downgradient of the former gasoline UST locations. On September 24 and October 2, 1996, Smith Technology conducted an additional subsurface investigation at the site. A total of nine soil borings were advanced to depths up to 15 feet below ground surface. Soil, soil vapor, and groundwater samples were collected from the borings. Analytical results of the soil and groundwater samples indicated the general extent of total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and xylenes (BTEX), and methyl tertiary butyl ether (MTBE) in soil and groundwater under the site. Analytical results for geochemical parameters in soil and groundwater indicated bioremediation is occurring in the plume of petroleum hydrocarbons in groundwater beneath the site. Analytical �-' results of soil vapor samples indicated the availability of oxygen, carbon dioxide, nitrogen and methane in the vadose zone. Also, results of laboratory geophysical testing of soil samples from the site indicated that the potential receptor on-site, the water supply well, would not be affected by the plume of petroleum hydrocarbons in groundwater within the next 20 years, in the worst case. On March 9, 1999, ATC supervised the installation of three groundwater monitoring wells, MW- 4, MW-5, and MW-6 (Figure 2). During installation of the monitoring wells, soil samples were collected from the borings. On March 11, 1999, ATC developed and sampled monitoring wells MW-4, MW-5, and MW-6. Analytical results of the soil and groundwater samples collected at the site indicated the lateral extent of impacted soil and groundwater had been defined. Refer to ATC's Summary Report Additional Subsurface Investigation, 7675 West Eleventh Street, Tracy, California, dated May 12, 1999, for additional information. Based on historical data and a verbal discussion with Mr. Ron Rowe of the SJCEHD, ATC submitted a closure report request dated June 27, 2000. The SJCEHD did not formally respond to the report but instead requested that ATC perform another monitoring event. In a letter dated October 2, 2001, Ms. Dot Lofstom of the SJCEHD requested computer modeling of the groundwater plume be conducted. ATC evaluated contaminant migration potential of affected soil and groundwater at the site using the EPA's BIOSCREEN (v.1.4) software program. The results of the computer modeling indicated the petroleum impacted soil and groundwater at the site do not appear to be an immediate and significant threat to human health or the environment. The s:\Environmental\17861keports\4gm(1005.doc 2 ATC Associates Inc.