SITE INFORMATION AND CORRESPONDENCE FILE 1

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07/ 16/ 1999 14 : 04 209- 579 -2225 MODESTO ATC PAGE 04 C/A • i i O C 1 A T E 8 I N C . In March 1989, hydrocarbon impacted soil was detected to the east of the restaurant building during a geotechnical investigation by Klemfelder, Inc. In April 1989, two shallow borings were advanced and soil samples were collected from depths of 3 to 5 feet below ground surface (bgs), and grab groundwater samples were also collected from the borings. Elevated concentrations of total petroleum hydrocarbons and benzene were detected in soil and groundwater. On August 19, 1989, diesel fuel was discovered leaking from a product line between the buildings and the back side of the levee. The diesel fuel line was purged, capped, and removed. A new diesel fuel line and gasoline fuel fine were installed and placed above ground. Approximately 40 cubic yards of petroleum affected peat were excavated and removed by Falcon Energy, and replaced with sandy loam backfill. In order to assess the potential presence of hydrocarbons at the site a soil vapor survey was performed in March 1990. Soil vapor samples were collected from 29 locations at approximate depths of 18 to 22 inches bgs. Low levels of volatile organic compounds (VOCs) were detected in the soil vapor on-site during the survey. In October 1990, RESNA Industries Inc. (RESNA) hand augured 19 shallow soil borings to help determine the extent of petroleum hydrocarbons in soil in the vicinity of the product line leak. Soil samples were collected at approximately 4 feet bgs and screened for possible volatile organic vapors using a photoicnization detector (PID). PID readings ranged from 0 to 1 ,032 ppm. In March and April 1991 , to provide additional information regarding subsurface conditions at j the site, RESNA supervised the drilling of five borings to be completed as groundwater monitoring wells MW- 1 through MW-5 (Figure 2). Petroleum hydrocarbon constituents were only detected in the soil sample collected from 2.5 feet bgs in boring MW-2. Analytical results of groundwater samples indicated that wells MW-3. MW-4, and MW-5 contained detectable petroleum hydrocarbons. Quarterly monitoring and sampling of the groundwater monitoring wells on site was initiated in October1991 . In July 1991 , RESNA personnel witnessed the removal of the 2,000-gallon regular gasoline UST and the associated product line. No holes were observed in the UST. Soil samples were collected beneath the UST and product line and contained only toluene at 0.045 parts per million (PPM)• In September 1993 , RESNA supervised the advancement of a boring to be completed as groundwater monitoring well MW-6. Soil encountered during drilling was monitored for organic vapors using a PID. No evidence of soil contamination was noted. Analytical results of groundwater samples indicated only toluene was detected, at a concentration of 38 parts per billion (ppb). In August 1995, due to infiltration of organic debris in groundwater monitoring well MW-4, Smith Environmental Technology Corporation (Smith) destroyed well MW4 by overdrilling the PVC casing and sandpack in the well boring with 8-inch diameter hollow-stem augers. Smith also wA62514Vepmalwkp.dm 2