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WELLS FARGO BANK PROPERTY REVISED 49 SOUT14 WILSON WAY PRIVILEGED&CONFIDENTIAL J+. STOCKTON, CALIFORNIA MAY 3, 1999 Page 7 'i Based on'Ithe above calculations there is approximately 560.2 pounds or 86.4 gallons of TPH-g remaining in the soil beneath the subject site. TPH-g Concentrations in Groundwater Groundwater samples collected from Wells MW-2 and iVIW-4 and Boring g B-5 during the last quarterly groundwater monitoring event were reported to contain TPH-g in concentrations ranging from.3.8 to 13 ppm. Benzene was detected in Well MW-2 and Boring B-5 in concentrations of 8 and 2 ppb. Wells MVV-1 and MW-3 were reported to not contain detectable concentrations of TPH-g or BTEX. No fuel oxygenates were detected in any of the groundwater samples collected during the last quarterly sampling event. A summary of the results of groundwater sampling at the subject site is provided in Table L. Mass Balance Analysis for TPH-g in Groundwater A Mass Balance Analysis was conducted to determine they approximate amount of TPH-g dissolved 'within the groundwater beneath the subject site. In order to calculate the approximate amount of TPH-g, the thickness of the impacted aquifer was estimated to be approximately 30 feet thick. This thickness was based'upon concentrations of TPH-g detected within soil samples collected in this area. Additionally, the total porosity was assumed to be equal to the effective porosity. TPI -g concentrations within the groundwater were based upon the average of TPH-g concentrations reported in Wells 3 MW-2 and MW-4, and Boring B-5. The estimated total -amount of TPH-g dissolved in the groundwater beneath the site is as follows: Porosity =38.67% Estimated area and thickness of impacted aquifer= 1,052 square feet, 30 feet thick Estimated volume of the impacted aquifer= 31,560 cubic feet Average TPH-g concentration in groundwater= 8.4 ppm 31,560 cubic feet x 38.67% = 12,204 cubic feet of pore space 12,204 cu. ft. x 7.48 gallons/cu. ft x 8.4 = 0.76 gallo s of TPH-g 1,000,000 or 0.76 gallons x 6.48 lbs./gallon = 4.9 lbs. of TPH-g li Based on the above calculations, there is approximately 14.9 pounds or 0.76 gallons of TPH-g dissolved in the groundwater beneath the subject site. It is Building Analytics' opinion that, based on the relatively small area affected, the low concentrations of BTEX in the soil and groundwater, and the relatively small volumes of i