SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

\./ *.WWI 913 Fremont Page 2 had dropped to 1,800 ppb TPH-g, 50 ppb Benzene, 220 ppb Xylenes by September 1994, and 1,420 ppb of TPH-g, 119 ppb of Benzene, 113ppb of Xylenes by December 1994. However, this drop occurred months before the excavation of 125 cubic yards of contaminated soil on December 19, 1994 from the former underground storage tank (UST) area. The excavation was backfilled with clean soil and the contaminated soil was transported to Forward, Inc. for disposal. The soil removal appears to have had little affect on the level of contaminant concentration in MW-2 groundwater. In the four years since the over-excavation, analytical results of MW-2 groundwater ranged from 1183 ppb (7/95) to 4010 ppb (12/97) of TPH-g, 61 ppb (7/98) to 345 ppb (3/95) of Benzene, and 188 ppb (7/95) to 1040 ppb (12/97) of Xylenes. There does not appear to be a reduction trend in any of the contaminants with respect to time. Even with the screen interval below first water, the level of Benzene concentration in MW-2 is above the California Primary Maximum Contaminant Level for public drinking water of 1 ppb Benzene. Analytical results of the soil sample taken from the bottom of the over-excavation at 16 feet 6 inches bsg on December 20, 1994 were 1000 parts per million (ppm) TPH-g, 1.5 ppm Benzene, and 39 ppm Xylenes. However, analytical results of soil samples taken at 20 feet bsg and at 25.5 feet bsg during the construction of MW-2 in April 1994 were non-detect with detection limits of 1 ppm TPH-g, and 0.003 ppm BTEX. 8 soil probe borings were advanced on November 27, 1995 and November 28, 1995, and 3 additional soil probe borings were advanced on January 4, 1996. The deepest of these soil samples was collected at 13 feet bsg. Analytical results of soil samples from 3 soil probe borings designated A-4, B-3, and C-2 toward the direction of MW-4, had contaminant concentrations of 57 ppm TPH-g, 0.116 ppm Benzene, and 3.537 Xylenes in A-4; 2.0 ppm TPH-g, and 0.016 ppm Benzene in B-3; and 2.0 ppm TPH-g in C-2. Analytical results of soil samples collected at 5 feet bsg, 10.5 feet bsg, and 17 feet bsg during the construction of MW-4 were non-detect with detection limits of 0.05 ppm TPH-g, and 0.003 ppm BTEX. The Eighth Quarterly Groundwater Monitoring Reports Details of Placement of Monitoring Well!#4 dated July 30, 1996 prepared by William Hunter concluded: "As indicated on PLATE IV, the limits of soil & water contamination have been fully defined in all directions." According to analytical data and plates contained in reports prepared by William Hunter, the vertical extent of the soil contamination appears to be limited to approximately 17 feet bsg, while the lateral extent of the contamination in the soil is most likely to be limited to approximately 40 feet northeast of MW-2. ORC placement was first suggested as a remediation alternative in Fourth Quarter 1997 Groundwater Monitoring Report dated January 26, 1998 prepared by William Hunter. Mr. Hunter again recommended ORC placement as a relatively inexpensive method of reducing groundwater contamination to acceptable level in Second Quarter 1998 Groundwater Monitoring Report dated August 14, 1998. PHS/EHD agreed that the