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. A S S O C I A T E S I N C <br /> Monitoring data collected from the site indicate groundwater is present at approximately 25 feet <br /> below ground surface (bgs) with an east-northeasterly gradient. <br /> 3.0 BACKGROUND <br /> ' 3.1 UST Removal <br /> In March 1990, one 1,000-gallon underground storage tank (UST) and all associated piping and <br /> ' dispensing equipment were removed and transported off-site. Laboratory analysis of soil <br /> samples collected from beneath the former 1,000-gallon UST location indicated the presence of <br /> detectable concentrations of ethylbenzene and xylenes. After the tank was removed, the area of <br /> excavation of the former tank was backfilled with backfill material provided by Stockton Service <br /> Station Equipment. <br /> 3.2 Initial Subsurface Investigation <br /> On January 8, 1998, an ATC geologist supervised the advancement of one soil boring to 41.5 <br /> feet below ground surface (bgs). Soil samples were collected and submitted for analysis of total <br /> petroleum hydrocarbons as gasoline and diesel (TPHg and TPHd) by EPA Method 8015; and <br /> volatile organic compounds (VOCs) by EPA Method 8260. A Hydropunch groundwater sample <br /> was collected and analyzed for TPHg, TPHd, VOCs, and halogenated volatile organic <br /> compounds (HVOCs) by EPA Method 801018020. <br /> ' Petroleum hydrocarbon constituents were detected in soil samples collected from boring SB I. <br /> The highest reported constituent concentrations were observed at 5.5 feet bgs and appeared to <br /> attenuate rapidly with depth. Trace amounts of petroleum hydrocarbon constituents were also <br /> detected in the groundwater sample collected from soil boring SB 1. The January 1998 <br /> subsurface investigation results are detailed in ATC's Summary Report for Subsurface <br /> Investigation, dated February 4, 1998. <br /> ' 3.3 Remediation Activities <br /> In September 1998, ATC supervised the excavation of approximately 70 tons of impacted soil. <br /> The soil was transported and disposed of at an appropriate landfill on the same day it was <br /> excavated. The excavation was limited on two sides by buildings and overhead lines. <br /> Confirmation samples collected from the excavation indicated there was residual contamination <br /> remaining. <br /> 3.4 Additional Subsurface Investigation <br /> ' Also in September 1998, ATC supervised the advancement of four soil borings around the <br /> former excavation area. Three of the borings were completed as groundwater monitoring wells. <br /> Analytical data indicated the soil and groundwater at the site is impacted with total petroleum <br /> w.�172951reportsklos Lire.doe 2 <br />