SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Mr. Ken Gillies • • Gillies Trucking 3931 Newton Road, Stockton Page 2 of foot. Utilizing a weight of 125 pounds per cubic foot and the relationship and modifying UEC's equation slightly: W diesel = Vsoil x [(K 35 feet + K 40 feet) - 2] x 1/1,000,000 x 125 Ibs/ft3 Where W = weight, V = volume, and K = contaminant concentration. EHD calculates a mass of 1339.8 pounds of diesel, or, dividing by 7.1 pounds per gallon, 188.7 gallons of diesel for the same example provided by UEC on page 4 of the QR. If one utilizes a soil weight of 100 pounds per cubic foot, the calculated diesel mass would be 1071.9 pounds or 150 gallons of diesel. UEC had calculated an estimate of 80.15 gallons for the example calculation. Therefore, EHD believes the total mass, utilizing the contaminant mass distribution model provided by UEC will be at least twice that calculated by UEC, something on the order of 50,000 pounds or 7,000 gallons (to round off) of diesel. A mass estimate that is as close to the actual mass in place is important for the fate and transport model or leaching model for the sorbed diesel in the event of rising groundwater level or percolating meteoric (rain) waters making contact with the sorbed mass. This is one of the critical issues that must be addressed for closure of your site, as will be discussed further below. Reviewing the soil analytical data from GT-10 (1999) and GT-22 (2005), the concentration trends between the data sets collected 6 years apart are not suggestive of significant TPH-d degradation. Note the following relationships: GT-10 (1999) GT-22 (2005) TPH-d (mg/kg) 45 feet bsg 2090 46 feet bsg 840 50 feet bsg 8830 55.5 feet bsg 9300 55 feet bsg 14,400 57.5 feet bsg 19,000 60 feet bsg 19,000 65 feet bsg 15,500 70 feet bsg 20,200 When groundwater was present in the Modesto Aquifer (approximately 25 to 55 feet bsg — approximate depths cited below may vary if considering average occurrence or specific cross sections), the high concentrations in samples from monitoring well GT-10 showed that significant contaminant transferred from the sorbed state to dissolved state. After the groundwater elevation declined below the Modesto, TPH-d concentrations generally increased in First Riverbank sand (approximately 58 to 70 feet bsg) wells GT- 6 and GT-9, and after declining to non-detectable concentrations in GT-5 returned to fluctuating low concentrations and non-detect concentrations. The remaining three First Riverbank wells (GT-13A, GT-16A and GT-17A) did not exist when groundwater was in the Modesto Aquifer (approx. 25 to 55 feet bsg), but have been periodically (GT-17A) to