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TOTAL PETROLEUM HYDROCARBONS (gasoline mage) MASS M SOIL AND GROUNDWATER Appendix B contains the table and figures used to calculate the mass of gasoline range hydrocarbons, in the soil and groundwater associated with this site Based on water sample concentrations obtained from the August 12, 2002 sampling of the wells, Isoconcentration figures were developed for the A water zone and B the water zone A 5 foot by 5 foot square grid was used (25 square foot area per square) to determine the lateral extent of each concentration isoconcentration contour Contour intervals are > 50 ug/L, > 1,000 ug/L, > 10,000 ug/L, > 20,000 ug/L, > 30,000 ug/L, > 40,000 ug/L and > 50,000 ug/L 6 feet was used as the thickness of the A zone and 7 feet was used as the thickness of the B zone The lateral extent of each isoconcentration was determined by counting the number of squares (25 square foot areas) that were contained between each contour interval, and multiplying the number of squares by 25 and then by 6 for the A zone thickness or 7 for the B zone thickness The resulting figure represents the cubic feet for each isoconcentration area for the A and B zones An assumption of 30% porosity was used to represent the cubic area occupied by the groundwater This 30% area was then converted into liters and then multiplied by the average concentration of the individual isoconcentrations in mg/L The concentration used for each isoconcentration is the average between the high and the low concentration within the isoconcentration area in mg/L This gives a value of mg TPHg for each isoconcentration area The mg are converted to pounds and the pounds to gallons, see Table 3 - Pounds TPH(gasoline range) in soil in Appendix B TPH(gasoline range) for soil mass was calculated in a similar fashion, using the 25 square foot areas and multiplying by the thickness in feet, averaging the individual isoconcentrations and converting the resulting mg TPHg to pounds and then to gallons The following mass for TPHg were determined Soil interval 6 - 12 foot depth = 3,115 pounds, soil interval 12 - 16 foot depth = 2,520 pounds, soil interval 16 - 22 foot depth = 1,742 pounds, soil interval 22 - 26 foot depth = 99 pounds, groundwater A zone = 117 pounds and groundwater B zone = 4 pounds for an estimated total of 7,492 pounds (1,189 gallons) of TPHgasoline To determine the mass of TPHgasoline that would remain after the proposed excavation, figures were developed to show the contaminates removed at various depths, see Appendix B -Figures 8A, 813, 8C and Table 3 Excavating to the 12 foot depth will remove and estimated 3,059 pounds of TPHg Excavating to the 16 foot depth, base of the A Zone sand, would remove an additional 2,412 pounds of TPHg for an accumulative removal of 5,471 pounds, or 73% of the TPHg mass associated with the soils ILEMTATIONS The services performed by Western Geo-Engineers, a corporation under California Registered Geologist #3037 and/or Contractors License 4513857, will be conducted in a manner consistent with the level of care and skill ordinarily exercised by members of our profession currently 5 Sanchez ADD PT I0-2002