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1.0 INTRODUCTION In May 2002, Pacific Gas and Electric Company (PG&E) retained Alisto Engineering Group to conduct soil and groundwater sampling to assess the extent of petroleum hydrocarbons detected during construction activities at PG&E's McDonald Island Compressor Station, San Joaquin County, California. A site vicinity map is shown on Figure 1, and a layout of the McDonald Island Compressor Station is shown on Figure 2. 1.1 Purpose and Scope of Work The purpose of the sampling activities was to assess the extent of petroleum hydrocarbons detected in the subsurface in the vicinity of a natural gas condensate valve, as described in the work plan prepared by Alisto dated February 22,2002. As set forth in the work plan, the scope of work for the assessment included the following tasks: • Collection of soil samples from six borings around the excavation and one within the excavation to depths of up to nine feet below grade. • Conversion of each boring into temporary wells to collect grab groundwater samples • Analysis of soil and groundwater samples for specified hydrocarbon ranges and constituents, as well as metals in selected samples. • Evaluation of data and preparation of this report. 1.2 Project Background In the summer of 2001,petroleum hydrocarbon odors were observed during replacement of a natural gas condensate valve at the compressor station of the McDonald Island Gas Storage Facility. Approximately 200 cubic yards of soil was excavated from the area of the valve replacement and was stockpiled onsite. The valve was replaced,but the backfilling of the excavation was postponed pending investigation of the hydrocarbon odors. On August 22,2001, five soil borings, SB-1 through SB-6,were drilled to depths of nine feet for collection of soil samples at 3, 6 and 9 feet below grade. Additionally,eight soil samples,SW-1 to SW-8,were collected at the extent of the excavation and eight soil samples from the stockpiled soil removed from the excavation. Soil samples were analyzed for petroleum hydrocarbons in the gasoline,kerosene, diesel and motor soil ranges, as well as benzene, toluene,ethylbenzene,and total xylenes (BTEX) constituents. Laboratory analysis of the soil samples collected from the borings detected up to 18 milligrams per kilogram (mg/kg) total petroleum hydrocarbons as diesel (TPH-D) and 830 mg/kg total petroleum hydrocarbons as motor oil (TPH-MO). Of the BTEX constituents, only toluene was detected in one sample at concentration of 0.007 mg/kg in reference to a method detection limit of 0.005 mg/kg. Analysis of two soil samples for metals revealed no significant difference between the samples collected from the area impacted by petroleum hydrocarbon and the background sample. f:\02\10-211\211-15\reportdoc 1 .