SITE INFORMATION AND CORRESPONDENCE

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Ms. Mary Serra August 19,2002 Page 2 and 13 feet below ground surface(bgs). Based on the historic groundwater elevations, the hydraulic gradient is essentially flat(estimated at 0.002 feet per foot(ft/ft)). The following investigations have been conducted to assess petroleum hydrocarbons in the subsurface soil and groundwater at the Site: • An investigation by Technical and Ecological Services (1993), • A site survey and regional well search by Smith Environmental Technologies, (1996), • A Preliminary Environmental Assessment performed by Harding Lawson Associates (1997), and • A Site Characterization Study performed by CH2M HILL (1998). In addition,groundwater monitoring for constituents of concern has been conducted quarterly, by TES in November 1999,and by CH2M HILL from August 2001 through the present. In, 1999 the McMullin Dehydrator Station was chosen for a PG&E demonstration study to develop a cost-effective solution to site remediation. The results showed that the concentration of petroleum hydrocarbons in soil varied considerably both before and after the injection of ORC. The conclusion of this study was that is difficult to determine whether the ORC increased biodegradation rates. The April 2002 groundwater monitoring sampling results show non-detect levels of petroleum hydrocarbons in all of the offsite wells except MW-1 where TPH-d was the only analyte detected (at a low concentration of 1.4 mg/L). Groundwater data obtained during quarterly monitoring events indicate that TPH compounds in groundwater,appear to be contained within the site boundaries. Distribution of Petroleum Hydrocarbons in Soil and Groundwater Results from previous investigations indicate elevated TPH-d and TPH-k concentrations in soil at depths between 2.5 to 13.5 feet bgs (maximum TPH-d concentration detected at 7,000 mg/kg). BTEX compounds were detected near the former reboiler and former sump location (northeast portion of the Station). The highest concentrations of BTEX in soil samples are as follows:benzene (8.3 mg/kg) at 12 ft bgs;ethylbenzene(89 mg/kg) at 12 ft bgs;toluene (25 mg/kg) at 12 ft bgs and xylenes (170 mg/kg) at 12 ft bgs. The highest BTEX concentrations were collected from samples from boring ORC-3B located south of the former sump. Figure 2 provides a summary of the results with the corresponding depths of detection. Soil sample results are summarized in the Supplemental Site Assessment and Interim Remedial Action PIan, McMullin Dehydrator Station,March 2002. The goal of the project is to decrease the quantity,extent and/or volume of the contaminants of concern(COC's) in soil and groundwater at the site. Interim Remedial Strategy and Rationale The proposed interim remedial strategy is to excavate soil in the source area along the northeastern perimeter of the site and to monitor petroleum hydrocarbons in the groundwater. Source excavation has been selected because the Site is inactive and accessible and the extent of