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WZ1 INC <br /> The horizontal extent of contamination is defined by a series of laboratory analytical results <br /> from soil samples collected from soil borings and monitoring well borings around the former <br /> tank location These soil borings and monitoring wells are reported to contain TPH-G and <br /> associated VOCs A stapled pattern is depicted on Exhibit 7 which represents the estimated <br /> extent of soil hydrocarbon contamination <br /> Exhibits 8 and 9 depict the estimated vertical extent of petroleum hydrocarbon soil <br /> contamination in the subsurface of the site along cross-sections A-A' and B-B' A map and <br /> cross sections A-A' and B-B', which depict the iso-concentrations of hydrocarbon <br /> constituents remaining in the soil, are included in Appendix IV McLaren (1989a) depicted <br /> the estimated vertical extent of soil petroleum hydrocarbon contamination to extend from <br /> immediately beneath the former underground storage tank at a depth of seven to 12 feet <br /> bgs vertically downward to approximately 40 feet bgs <br /> Using the dimensions of the estimated areal extent of 1,750 square feet for the petroleum <br /> hydrocarbon soil plume and a thickness of approximately 32 feet, an approximate total <br /> volume of 1,620 cubic yards of contaminated soil is estimated to be present <br /> Evidence to suggest that no additional downward migration of petroleum hydrocarbon <br /> compounds has occurred in the soil column include 1) the presence of a silty clay found <br /> throughout the site at approximately 40 feet below ground surface that is inferred by <br /> McLaren (1989a) to have provided a physical barrier to downward migrating hydrocarbon <br /> compounds, and 2) a series of deep soil samples collected from monitoring wells MW-1, <br /> MW-2, MW-3 and MW-6 that are all reported to contain petroleum hydrocarbon <br /> constituents below analytical method detection limits or trace concentrations <br /> Groundwater Hydrocarbon Contamination <br /> Concentrations of benzene in groundwater that were above California State Department <br /> of Health Services Maximum Contaminant Levels (MCLS) for drinking water were detected <br /> in monitoring wells MW-1, MW-3 and MW-6 All other VOCs which were detected in <br /> 19150011 005 24 <br />