WORK PLANS - Laserfiche WebLink

Home Browse Search

Closure Documentation—7500 WEIventh Street, Tracy, CA. Page 17 LNAPL, 2,105,275 grams of contaminants adsorbed onto soil and 525 grams of contaminants dissolved in groundwater. To yield an estimate for the total mass of contaminants in the subsurface at the time the unauthorized release was detected, it is necessary to add the mass of LNAPL in the 2000 gallons of that material extracted from the subsurface at the time the underground tanks were removed and the small amount of LNAPL periodically removed from Monitoring Well MW-7 (see Figure 2 for location) before July 2007. Applying the same methodologies as described in the cited report, the estimated mass of contaminants removed at the time the LNAPL was extracted from the storage tank pits is 6,056,659 grams and the estimated mass removed by intermittent extraction of a total integrated thickness of 3.69 ft. of LNAPL from the 6 in. diameter casing of Monitoring Well MW-7 is 2,194 grams. In addition, an account must be taken for the 521.25 tons (472,870 kilograms) of soil that was removed from the site when affected soil was excavated from beneath the service station pump island. Based on the 1,113 mg/Kg mean concentration of the total petroleum hydrocarbons in that soil, which is based on the concentrations documented in Table 1 in: The San Joaquin Company Inc. (2002), Report on Extended Site Characterization - Former Fueling Station at 7500 West Eleventh Street, Tracy, California. October 2002. the total mass of contaminants shipped off site with that soil is estimated to have been 526,304 grams. Thus, as best can be estimated, the mass of contaminants in the subsurface at the 7500 W. 11th Street site at the time the UAR was detected in 1998 was: Contaminants in LNAPL . 9,239,599 grams Contaminants Adsorbed onto Soil 2,631,579 grams Contaminants Dissolved in Groundwater 525 grams Total Estimated Mass of Contaminants in Subsurface 1.1,871,703 grams At Time of Discovery of UAR(1998) By July 2011, there was no LNAPL present in the subsurface beneath the 7500 W. 11th Street site. Of the total mass of 9,239,599 grams of contaminants originally estimated to be present in the form of LNAPL, an estimated 6,056,659 grams were removed from the tank pits, 2,194 grams were extracted from Monitoring Well MW-7 through July 2007, DEC