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VVL1 INC groundwater were reported in concentrations well below established drinking water standards The horizontal extent of groundwater contamination at the site, as shown in Exhibit 7, is estimated to extend a maximum distance of 80 feet down-gradient of the former tank site The maximum areal extent of hydrocarbon-contaminated groundwater is estimated to be approximately 18,000 square feet based on the pattern shown in Exhibit 7 The vertical extent of hydrocarbon-contaminated groundwater is estimated to extend from the groundwater surface elevation to approximately 20 to 35 feet below ground surface or the interpreted base of the hydrocarbon-contaminated soil as depicted on Exhibits 8 and 9 An estimated maximum volume of hydrocarbon-contaminated groundwater can be inferred using the areal extent of groundwater contamination depicted on Exhibit 7, an estimated plume thickness of approximately 12 feet as averaged from Exhibits 8 and 9 and an average porosity value of 20 percent for the sediments These parameters yield an estimated initial volume of approximately 1,223,424 liters of hydrocarbon-contaminated groundwater beneath or down-gradient from the former underground storage tank site Assuming an average total petroleum hydrocarbon as gasoline fuel concentration in the groundwater of 1 0 mg/l, the 1,223,424 liters of hydrocarbon-contaminated groundwater would have contained approximately 1 22 liters of gasoline fuel in the subsurface during the 1989 time period 19150011005 25