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ri r1 pp pp 0 4D�Q� • CLEARWATER G R O U P Environmental Services remained undelineated downgradient from the former UST system However, high contaminant concentrations in cross-gradient position of wells suggested that off-site sources may be contributing to contamination detected beneath the site Initial inquiries suggested and was later confirmed that there is existing fuel transport line in the area if the site, and that it is currently filled with nitrogen gas Based on this information, Clearwater recommended additional investigation along South Fresno Avenue to better understand the distribution of contamination and possible contribution from potential off-site sources The results of this phase of investigation were presented in Clearwater's Well Installation and Groundwater Monitoring Report - First Quarter 1999 In March 2000, Clearwater supervised the completion of one hydropunch, six soil borings, and the destruction of MW-5 Three of the borings were converted into monitoring wells (MW-5B, MW-7, and MW-8) All three wells were placed can the downgradient portion of the plume to help determine the downgradient extent of contaminants The hydropunch was performed in the former UST location to assess the vertical extent of groundwater contamination at 36 feet bgs Three soil borings were performed to define the lateral extent of soil and groundwater contamination an the northeastern portion of the site and assess possible off-site sources A total of three soil samples and one groundwater sample were analyzed from each boring Soil concentrations of TPHg and BTEX were only detected in boring MW-5B The highest soil concentration of TPHg (1,000 mg/kg) was detected at 25 feet bgs in MW-5B This sample was also analyzed for TPH as let fuel and contained 55 mg/kg Detectable concentrations of BTEX were present in soil samples collected from boring MW-5B at 25 feet and 35 feet bgs MTBE was not detected by EPA method 8260 in any of the soil samples analyzed Groundwater concentrations of TPHg and BTEX were detected in borings SB-9, MW-5B, MW-7 and MW-8 The highest groundwater concentration of TPHg (9,700 gg/L) was detected in MW-5B MTBE was not detected by EPA method 8260 in any of the groundwater samples analyzed Geologyand hvdrogeology Subsurface lithologies encountered during drilling consisted predominantly of silty clay, with subsidiary clayey sand with occasional sandy lenses Groundwater has been observed beneath the site from 4 71 feet bgs(MW-2 on March 9,2000)to 1196 feet bgs(MW-3 on September 29 1996) Groundwater elevation measurements within the last 12 months have indicated groundwater to flow generally to the south-east at a gradient ranging from 0 0005 ft/ft on May 30,2001 and 0 018 ft/ft on February 13, 2001 7B178C Workplan for remedial feasibility testing 3 August 2001