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S 1 • Sail - Contaminant Mass Estimated Removed Assumed residual saturation S (highest), S = 43% Retention, R = S(porosity n%)(1000 hterstmeter) TPHG R= 0 43 x0 30 x 0 000997 ppm x 0 3 m3/ft3 x 4390 ft3 x 7 48 gal/ft= 1 32 gallons Benzene R = 0 43 x0 30 x 0 000001541 ppb x 0 3 m3/ft3 x 4590 ft3 x 7 48 gallft = 0 000204 atlolons Soil Mass Estimated Remainina TPHG R = 0 43 x0 30 x 0 001328 ppm x 0 3 m3/ft3 x 2700 ft3 x 7 48 gal/ft= 1 03 gallons. -- Benzene R =-9 43 x0 30 x 0 000003134 ppb x 0 3 m3/ft3 x 4590 ft3 x 7 48 gal/ft== 0 000204 gallons Water(capillary)-Estimated Mass Remaining Water (capillary, tank pit dates estimated aquifer vicinity of tank pit area C = V(n) C observed C = 2700 ft3 x 0 3 x 7 48 gal/ft x 0 000042 ppm = 0 25 gal TPHG. C = 2700 ft3 x 0 3 x 7 48 gal/ft x 0 000003600 ppb = 0 021 gal Benzene Discussion - Excavated and Residual Contaminant Mass The calculated estimates indicate that a very low quantity of residual contaminants are present bath in the capillary fringe and area of farmer tank pittwell MW-1 The range of concentrations suggests that these residuals, as well as those in excavated soil, were "tightly" absorbed onto the soil The lack of hydrocarbons at well MW-4 supports this assumption since at the concentrations observed, some models of contaminants movement would predict movement Column experiments have demonstrated that soil absorption may hold from about 9% to 25% of the total spill mass (Wilson and other, 1988) Working models of MTBE suggest more rapid solubility and movement than STEX fuel components, however, the observed data above show that these contaminants are effectively Immobile Well MW-4, located on the most conservative flowline (and historically most consistent flow trend) has not displayed contaminant amval In our opinion, this further substantiates this conclusion of absorbed and immobile contaminants The residual calculated quantities are minimal Conclusions and Recommendations Wright has completed the excavation of contaminated soil in the vicinity of the former underground tank pit source and well MW-1 It is assumed that the removal of this contaminated soil will remove the low concentration contaminants observed at MW-1 •