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Mr. Kyle Christie ` February 27, 1995 Page 2 investigation was required by the County. Hydrocarbons were identified in the soil samples collected from approximately 10 feet below the ground surface (bgs). At the time of drilling, the depth-to-groundwater was approximately 12 feet bgs. In March 1989, groundwater monitoring wells ATR-5, ATR-6, and ATR-7 were installed, at the direction of the County, to further define the extent of hydrocarbons in the groundwater. The results of this investigation indicated that hydrocarbons were not present in the groundwater in the locations of ATR-6, but were identified in ATR-5 and ATR-7. In October 1990, off-site groundwater monitoring wells ATR-9, ATR-10, ATR-11, and ATR-12, on-site soil boreholes BH-1, and BH-2, and groundwater extraction well TEX-I were drilled. The purpose of this phase of investigation was to define the extent of hydrocarbons in the groundwater off site and in the soil near the underground storage tank (UST) complex. In addition, a step drawdown pumping test was performed on groundwater extraction well TEX-1. The results of this phase of the investigation indicated that hydrocarbons were not present in the groundwater off site in the east, south, or west directions. Minor hydrocarbon concentrations were identified in the soil samples collected from boreholes BH-1 and BH-2. The results of this investigation, including the pump test, are included in BC's March 5, 1991, Supplemental Site Investigation Report. .J Off-site groundwater monitoring wells ATR-8 and ATR-11 were scheduled to be installed in October 1990 but because of delays in obtaining off-site access permission wells ATR-8 and ATR-1 I were installed in August 1991. Soil samples collected from monitoring well ATR-I 1 and soil samples collected from ATR-8 did not contain significant hydrocarbon concentrations. Free phase hydrocarbons have been identified on the groundwater in well ATR-8. ARCO is in the process of analyzing free phase product from well ATR-8, ATR-3 and well SMW-1 (installation discussed below). The purpose of the analysis is to determine if the source of the free phase product in well ATR-8 could be from the same source as dissolved phase hydrocarbons that have been identified in on-site wells (ATR-3 and SMW-1). The results of this analysis will be presented in a separate letter report at a later date. In May 1993, five soil boreholes (B I through 135) were drilled and sampled on the north end of the pump islands. Roux and Associates of Concord, California, (Roux) oversaw the drilling of these soil boreholes. The purpose of the soil boreholes was to determine if new USTs could be placed in this area based on the presence of hydrocarbons in the soil. The analytical results of the soil samples from these boreholes indicated that hydrocarbons were present in the soil to the north of the pump islands with the highest concentrations near the western (closest to building) pump island. Because of the presence of hydrocarbons in this area, ARCO decided not to relocate the USTs and replaced them in the existing UST location on the south side of the ARCO building. 0272Q95SEN7524,REP0RT5\7524-03,L-i QMS-PS2200