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CLEA5P_"E�AVER G R O U P I N C En[rran mental Srrt rns TPHd, and BTEX were detected at 5,700 milligrams per kilogram (mg/kg) TPHg, 50 mg/kg TPHd, and 48 mg/kg benzene TPHk, and TPHmo were not detected in any of the four samples On September 25 1997, Clearwater Group (Clearwater) supervised the drilling of sir soil borings to depths from 32 to 38 feet bgs Three of the borings were converted to groundwater monitoring wells (MW-1 through MW-3) Soil samples collected from four of the six borings contained detectable concentrations of petroleum hydrocarbons The highest concentrations of TPHg (570 mg/kg) and benzene (4 0 mg/kg) were detected in the sample from SB-2 at a depth of 25 feet bgs Groundwater samples collected September 29, 1997 from all three monitoring wells contained. detectable concentrations of dissolved petroleum hydrocarbons The highest concentrations of TPHg (32,000 micrograms per liter [gglL]) and benzene (2,200 µg/L) were detected in the sample from monitoring well MW-1 Low concentrations of TPHd were detected in soil samples from SB-5 (11 mg/kg) and SB-6 (2 mg/kg), and in the groundwater sample from MW-1 (300 �Lg/L), however, subsequent groundwater sample results have been non-detect for all three wells, and with approval from the EHD, analysis for TPHd has been discontinued Results of these efforts were presented in Clearwater's Subsurface Investigation Report, dated November 20 1997 Based on these initial investigation results, the EHD requested monitoring wells be installed to better define the aerial extent of soil and groundwater contamination After discussion with Lori Duncan of the EHD, Clearwater subirutted the Workplan for Site Investigation dated November 18, 1998 An addendum to the workplan, dated December 10, 1998 was submitted in response to EHD comments The workplan and addendum were approved by the EHD on December 15, 1998 In January 1999, Clearwater supervised the installation of three additional groundwater monitoring wells (MW-4 through MW-6) to delineate the extent of dissolved-phase contamination The results of the investigation indicated that the extent of sorbed-phase contamination was delineated and existed from approximately 10 to 25 feet bgs near the former USTs Results of the groundwater samples indicated that the extent of dissolved-phase contamination 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 inquines suggested and was latter 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 ZB 178C 2 3131/00