SITE INFORMATION AND CORRESPONDENCE

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Mr. Eric Jenks 0 - 2 - 0 7 September 2000 The report states that five monitoring wells encircle the JTF Stockton facility, and each well is between 100 and 300 feet from suspected source areas. Although MW -2 and MW -3 are upgradient and side gradient of the facility based on the first monitoring event, they contain nitrate concentrations ranging from 79 to 102 mg/l. An additional well should be installed upgradient of facility operational influences in order to determine background groundwater quality. I concur with the report's recommendation that an upgradient well should be considered after several quarters of monitoring are completed in order to verify the groundwater flow direction. Results of the Phase lI investigation of January 1999 (reported in the 1 July 1999 Site Investigation Work Plan) show ammonium at 2,370 mg/kg in soil at 10 feet bgs at the old tank farm, and an underlying grab groundwater sample showed ammonium at 1,120 mg/l (STO1). At the applicator wash area, soil contains ammonium concentrations of approximately 1,000 mg/kg from 0 to 10 feet bgs, but a grab groundwater sample only contained 1.5 mg/1 ammonium (STO3). The subsequent grab groundwater investigation of November 1999 (reported in the 30 January 2000 Site Investigation Work Report) found ammonium concentrations ranging from 95 to 400 mg/l in the groundwater between STO1 and STO3. Even though the monitoring well samples showed no detection of ammonium, it appears as though a significant source area for ammonium may be present. Any remediation proposal for the site will need to address this source area. The November 1999 grab groundwater investigation found MTBE near the fuel island ranging from 40 to 1,000 ug/1, and petroleum hydrocarbons as diesel ranging from not detected to 1,700 ug/1. The monitoring well samples did not contain MTBE or petroleum hydrocarbons. Future monitoring events will determine if these compounds are confined to the site. Nitrate concentrations ranged from 69 mg/1 to 160 mg/1, significantly greater than the water quality goal of 10 mg/l, and MW -5 contained 1,2,3-trichloropropane at 1.5 ug/1, higher than the water quality goal of 0.005 ug/l. Additional monitoring wells and/or investigation may be needed to identify the extent of constituent migration. Nitrate concentrations notwithstanding, I concur with the report's conclusion that compounds detected in the grab groundwater investigations are not laterally extensive. The report proposes to obtain additional groundwater samples from the monitoring wells to confirm the lateral extent of previously identified groundwater contaminants, and to determine whether aquifer conditions are suitable for in-situ anaerobic biodegradation of volatile organic compounds and nitrate. GeoSyntec proposes to analyze grab groundwater samples for oxidizable nitrogen, ammonium, volatile organic compounds, and fumigants, in addition to general chemistry parameters evaluating redox conditions. The parameters listed include a range of water quality indicators that will present a view of the oxidation state of groundwater. I approve the proposed work. Draft MRP A regular groundwater monitoring program is required for the monitoring wells to formally track groundwater elevations, groundwater gradient, and constituent movements. A draft MRP is