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APPENDIX E DISSOLVED MASS/VOLUME ASSUMPTIONS AND CALCULATIONS ARROYO'S SMOG SHOP 3012 East Waterloo Road, Stockton, California Assumptions: • The distribution of maximum dissolved hydrocarbon concentrations at the site can be approximated utilizing the formula for an elliptical cylinder.The distribution of the plume can be separated into two contoured areas (i.e. 1,000 pg/I and 100.pg/I; Figure 6). • The effective porosity of soil at the site is estimated to be 35% (i.e. silt). • The thickness of dissolved plumes were derived using the screened depth of wells at the site (20 feet). • Figure 6 was generated utilizing a computer assisted drafting program. The program has a specific function to calculate the area of a selected object-, such as each area between the above referenced TPH-g isoconcentration intervals. For the dissolved TPH-g plume (Figure 6), the program determined the area of the 1,000 pg/I contour interval to be 448 ft2 and the 100 pg/I contour interval to be 1,198 ft2. • The area and volume of each contoured zone within the plume can be estimated utilizing the computer assisted drafting program to determine the area between the above referenced 1,000 and 100 contour intervals, and then multiplying the area by the height of wells screens installed at the site (20 feet). The area of a cylinder can be used to illustrate the shape of the dissolved TPH-g plume, and calculated by the following formula: I i V = AREA-h, where "area" is determined through the drafting program (Figure 6) and "h" is the height of wells screens installed at the sit. 1) For the estimated 1,000 pg/I inner contour interval; A1,000 = 448 ft2 and h = 20 ft (height estimated and averaged from cross sections) Utilizing TPH-g data from well MW-1 (1,100 pg/I) and the 1,000 tag/I contour line, the average dissolved TPH-g concentration is estimated to be 1,050 ug/I (equivalent to 0.00000105 grams per milliliter). A ml is very nearly equivalent to a cubic centimeter of water, which by definition equals one gram, this concentration is nearly a unitless number. The volume is given by: ft2 3 V1,000=A,, x h =448 x 20 ft = 8,960A1,000 I