ARCHIVED REPORTS XR0000194 - Laserfiche WebLink

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R10/71-51-iC Review of the zero concentration maps (for benzene, toluene, and xylenes taken together) suggest that the contaminated area, centered near the former fuel underground tank location, increase from an area of approximately 17,700 square feet from 5-foot below grade, increasing to approximately 24,000 square feet at 25-foot depth, maximizing to approximately 49,000 square feet at 45-foot depth, and then gradually decreasing to approximately 20,000 square feet at the groundwater interface The impacted soil, contaminated with gasoline-derived coin�ou_nds which include berizene,�oluene and xy enema s—tea vo uma pro mxi ately 65,200 cubic yards Figures 26, 27, and 28 {See Appendix J} present zero concentration maps of benzene, toluene and xylenes, respectively, in the groundwater The maps indicate that the contamination generally moves in the northeasterly and southeasterly directions This distribution appears to be supported by the groundwater flow direction illustrated in Figure �f 29 (Appendix K) Based on the water level data collected on October 22, 1993, the �I�o groundwater elevation contour map is presented in Figure 29 (see Appendix K) The groundwater flow direction in the vicinity of monitoring well MW8 is to the west, in the , vicinity of MW9 is to the east, and in the vicinity of MW1, MW2, MW3, MW4, MW10, MW14, and MW24 is to the north The area of the groundwater impacted by gasoline- derived contaminants which include benzene, toluene, and xylenes has an approximate length of 350 feet (from the north boundary to the south boundary) and a width of approximately 300 feet (from the east boundary to the west boundary) It occupies an area of approximately 60,000 square feet, or roughly one-third of the Shop 10 facility area Because the porosity of the soil is unknown and the depth of the contaminated groundwater area is not also known, an estimate of the volume of contaminated groundwater cannot be made Groundwater contamination was found to be highest in MW10 which is located within the former underground tank area Gasoline-derived contaminants were also found in lower levels in wells MW11, MW12, MW13 and MW14 Contaminant levels in MW10 and MW11 exceeded State action levels for drinking water and EPA maximum contaminant levels (MCLs) for Public Water Supplies (see Table 9, Appendix C) Detailed evaluation of Remedial Action Options Identified the following alternatives that are recommended to be implemented in combinations o In Situ Containment by effectively capping the area to address privately the soil contamination issue and reduce contaminant infiltration into the groundwater The present worth cost estimate of this option is $103, during a five-year period operation 4