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. highly degraded residual contaminants Dissolved contaminants are interpreted to degrade <br /> at about the same rate as the groundwater motion where the more aerated edges of the <br /> plume allowed natural in-situ degradation processes to operate upon the plume <br /> Wright had removed about 190 cubic yards of contaminated soil and about 3,225 gallons of <br /> contaminated groundwater with a thin layer of floating product was pumped from the <br /> excavation Since the City needed to have this work performed on a rapid basis, the <br /> cleanup essentially preceded the site assessment The subsurface assessment revealed a <br /> very limited area of contanimants centered on Boring B-3 Monitoring Well MW-1 was <br /> installed at this location for that reason (note the contract sampler inadvertently marked the <br /> sample "MW-3" although the proper well Tracy Auto Stereo monitoring well designation is <br /> MW-1) Contanunants were not observed in any downgradient boring locations On the <br /> basis of the relatively low and declining dissolved concentrations, additional cleanup effort <br /> was not warranted <br /> Estimated Contaminant Mass Balance Removed and Remaining <br /> These contaminant mass calculations are estimates, presented with the following <br /> assumptions The averages from the soil data were used for soil and the tank pit water <br /> sample for groundwater which flooded the excavation The soil contarmnant mass <br /> removed is assumed from the data sets in the attached chemical data tables Calculations <br /> used methods from Lyman, Reidy and Levy (1992) <br /> Soil - Contaminant Mass Estimated Excavated/Removed 1993 <br /> M Assumed residual saturation S (highest), S = 43% <br /> Retention, R = S(porosity n%)(1000 liters/meter) <br /> TPHG Concentrations sum of October, 1993 data <br /> TPHG R = 0 43 x 0 30 x 0 002390 ppm x 0 3 m3/ft3 x 190 ft3 x 7 48 gal/ft = <br /> 0 13 gallons <br /> Benzene was not detected in that data set. <br /> MTBE was not analyzed for that data set. <br /> Soil Mass Estimated Remaining <br /> Assumed using sums of data of March, 2000 <br /> TPHG R = 0 43 x 0 30 x 0 000243 ppm x 0 3 m3/ft3 x 190 ft3 x 7 48 gal/ft = <br /> 0 0 13 2allQns <br /> Benzene R = 0.43 x 0 30 x 0 000003134 ppb x 0 3 m3/ft3 x 4590 ft3 x 7 48 <br /> gal./ft=0 000204 gallons <br /> MTBE was not detected in that data set. <br /> Page 4 <br />