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Closure Documentation—7500NPKt Eleventh Street, Tracy, CA, %.N?l Page 18 and an additional total integrated thickness of 0.8 ft., amounting to an estimated mass of 48 grams following that date through the time no more LNAPL was detected in the well. Thus the total mass of contaminants extracted in the form of LNAPL is estimated to have been 6,058,910 grams, which leaves an estimated 3,180,698 grams unaccounted for, but which loss can be attributed to natural bioremediation of LNAPL. The mass of contaminants adsorbed to soil in July 2011 cannot be estimated reliably because new borings were not drilled at that time to provide for new analyses of soil samples and the expenditure of public money for such activities by the California Underground Storage Tank Cleanup Fund for the academic exercise of making a close estimate for a mass balance calculation is clearly not justifiable. It is clear that the natural attenuation and bioremediation observed to be reducing the concentrations of contaminants in groundwater will also have, to some degree, remediated the soil. An important part of this process is desorption of contaminant from soil.particles and their dissolution in groundwater, which tends to cause the concentration of contaminants in groundwater to temporarily increase until they are again reduced by the processes of natural attenuation. Under these circumstances, for the present purposes we will assume that the mass of contaminants adsorbed onto soil remains the same as it was estimated to be for July 2007 except for the contaminant mass shipped off site when the soil beneath the service station pump island was remediated. That amounts to an estimated 2,631,579 grams - 526,304 grams which equals 2,105,275 grams remaining adsorbed onto soil in the subsurface as of July 2011. With respect to the mass of contaminants dissolved in groundwater in July 2011, the same procedure used in the cited report can be used by applying the results of groundwater analyses in Table 2 and the plume geometry shown in Figure 3 in: Dietz Engineering and Construction, Inc. (2011), Groundwater-quality Monitoring Report July 2011, Former Fueling Station, 7500 West Eleventh Street, Tracy, California. October 2011. The mean concentration of all fuel hydrocarbons in groundwater at the 7500 W. 1 ith Street site in July 2011 was 490 µg L and the area of the plume was approximately 270,091 square meters. With the zone of affected groundwater having a thickness of approximately 3.5 meters, the total volume of soil containing affected groundwater is estimated to be 945,319 cubic meters, i.e., 94,519,000 liters. Taking the porosity of the soil to be 0.3 and the mean concentration of the contaminants to be 490 µg/L, then the estimated mass of contaminants dissolved in groundwater as of July 2011 is approximately 139 grams, which is 326 grams less than the mass of 525 grams estimated to have been dissolved in groundwater at the time the UAR was discovered in 1998. The reduction can be attributed to natural bioremediation. Thus, the total estimated mass of contaminants in the subsurface at the 7500 W. 11 th Street site in July 2011 is as follows: DEC