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Jrstultattd Niass of Petroleum H3 drocarbons Constituents Remaining m Groundn►ater Colber goat Works,401 North Stockton Street,Stockton,California Page 3 • calculation (i e for the contour interval between 0 pg/L and 100 pg/L, a concentration of 100 U94, was used for the calculation) Typically, it is assumed that the average between the higher and lower contour concentration for a particular interval would be a good approximation of the representative concentration for a particular contour interval volume In order to calculate the mass of TPHg, benzene, and MTBE in each contour interval, it is necessary to multiply the volume of water in each iso-contour by the highest concentration within each iso-contour The volume of water needs to be converted from cubic feet into liters to ensure consistency with units The conversion for water is one cubic foot is equal to 28 3 liters Sample calculations for the mass of TPHg contained outside the 100 pg/L contour for groundwater is as follows Mass.,,,, =100 pg/L*28 3 Ul ft' k 5,394 ft' = 15,265,020 pg Converting these numbers into pounds is a simple mathematical conversion of dividing by one billion (1 x 109) and then multiplying by 2 20462 pounds/kilogram for the groundwater This gives a mass of 0 034 pounds of TPHg between the 0 pg/L iso-contour and the 100 pg/L iso- contour for groundwater In order to calculate the total mass of TPHg, benzene, and MTBE in groundwater, it is necessary to follow the same equations above for each of the contour areas The total estimated mass for TPHg, benzene, and MTBE are summarized in Tables 4, 5, and 6, respectively CONCLUSIONS AND RECOMMENDATIONS Based on the minor detections of petroleum hydrocarbon constituents in the 20-foot samples collected from hydropunch borings SB-20 and SB-21 and that these samples were collected from soil beneath the static water level, the estimated mass of TPHg, benzene, and MTBE remaining in soil was not re-calculated based on the most recent laboratory analytical data According to groundwater elevation data from the October 1999 sampling event, groundwater flow beneath the subject site is to the northeast at an approximate hydraulic gradient of 0 018 ft/ft This flow direction proves to be away from the Stockton Deep Water Channel located directly south of the site The mass of TPHg, benzene, and MTBE remaining in groundwater beneath the subject is approximately less than t/z pound for each constituent REPORT DISTRIBUTION Ms Lynn Swanson Colberg Boat Works, LLC . P O Box 1288 Stockton, CA 95201