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�I 19 October 2012 AGE-NC Project No. 97-0312 Page 13 of 22 concentrations as high as 520 mg/kg and 32,000 mg/kg, respectively, in a sample collected approximately 2 feet below the east end of UST No.3 and at concentrations of 1,000 mg/kg and 11,000 mg/kg, respectively, in a sample collected at approximately 17 feet bsg below the UST No. 6 excavation. TPH-g and TPH-d were detected in piping/dispenser samples 6-0 at concentrations as high as 1,200 mg/kg and 16,000 mg/kg, respectively; BTEX constituents were detected at concentrations as high as 60 mg/kg (xylenes). h Once released to the subsurface, the contaminants migrated through the fine-grained silty material below the UST areas, to a vertical depth of approximately 20 to 30 feet bsg at the �`� northeastern UST location (UST Nos. 1 through 5), and to depths of 70 to 75 feet bsg west of the former UST No. 6 location. Contamination in the area of former UST Nos. 1 through 5 does not appear to extend below 40 feet bsg; petroleum hydrocarbons were not detected in soil samples collected below 30 feet bsg from soil boring B14. West of the former UST No. 6 area, vertical migration of TPH-g and BTEX contaminants appears to extend to depths as great as approximately 70 feet to 75 feet bsg. In a soil sample collected from boring MW-1 at 70 feet bsg, TPH-g and TPH-d were detected at concentrations of 5.3 mg/kg and 80 mg/kg, respectively; however, no petroleum hydrocarbon constituents were detected in a sample collected at 85 feet bsg from the same boring. Low detections r of TPH-g and BTEX were reported in soil samples collected from boring MW-9 at depths of 90 feet and 100 feet bsg; however, no petroleum hydrocarbon contamination has been reported in groundwater samples collected from the well to date. Currently, the Alaral extent of ads rbed petroleum hydrocarbon contamination is defined to the northeay boring MW-3, to the northwest by borings B4 and B25, to the west by boring MW-2, d to the south by borings B29, B22, and MW-4. The soil data lacks significant detections of 1,2-DCA in the most recent data, possibly demonstrating the vertical migration of this contaminant through soil without substantial attenuation or k41t adsorption to soil. The adsorbed petroleum hydrocarbon contamination appears to be C'° its adhered to fine-grained soil, based on the reduction of dissolved hydrocarbon �a " contamination with upward fluctuations of the groundwater table. �' 1-0 5.2. IMPACT TO GROUNDWATER Significant concentrations of TPH-g, TPH-d, BTEX, and MTBE were detected in grab groundwater samples collected at 65 feet bsg in soil borings B14, B15, and B17. Historically, TPH-g has been detected in the on-site groundwater monitoring wells at a maximum concentration of 3,400 pg/I (MW-1, December 1992); TPH-g has been detected consistently only in well MW-5, with sporadic detections in wells MW-2 through MW-4; TPH-g was only detected in well MW-6 during its initial groundwater monitoring event in June 1999. TPH-d was detected at a maximum concentration of 350,000 pg/I in MW-1 in September 1992; TPH-d was detected consistently in MW-1 until the well was destroyed V Advanced GeoEnvironmental,Inc. v