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ATC Associates Inc. 1 1 17 Lone Palm Avenue,Suite B Modesto,California 95351 209-579-2221 ASS O C T ATE 5 I N C . Fax:209-579-2225 SITE LOCATION The site is located at 7675 West Eleventh Street, between MacArthur Drive and Chrisman Road in Tracy, California. The site location is shown on Figure 1. The surrounding site vicinity is primarily a commercial and industrial area. The property is owned by Dr. A.R. Glover and is operated as a lumberyard. BACKGROUND On October 15, 1986, two 500-gallon gasoline underground storage tanks (USTs) were removed from the site. During the UST removal, petroleum product was noted in the southern UST excavation (Figure 2). Soil samples were collected from two feet below the bottom of the USTs, and petroleum constituents and lead were detected in the soil samples. 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 down gradient of the former gasoline UST locations. On September 24 and October 2, 1996, Smith Technology conducted an additional subsurface investigation at the site. 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 on 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 the monitoring well installation, soil samples were collected from the borings. On March 11, 1999, ATC developed and collected groundwater samples from monitoring wells MW-4, MW-5, and MW-6. Analytical results of the soil and Page 2 IV, w:\17861\WP for Additional Subsurface Investigation VLTC x Soil Vapor Study,and Modeling L