SITE INFORMATION AND CORRESPONDENCE

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• / 1 Mr. Andrew A. Woods - 2 - 16 December 1998 Sodium is more complex. Sodium can be adsorbed to soils that have a high cation exchange capacity, such as clays. However, past discharges may have saturated the soil beneath Ponds 1 and 2 such that sodium can be leached. Data are needed on the leachability of sodium from the soils beneath Ponds 1 and 2. The proposed total and soluble sodium analyses can provide an indication of the sodium leachability factor. An adsorption factor of one should be assumed given that the past level of discharge has likely saturated the sodium adsorption sites. A water quality goal for chloride in soil can be established using the waste limit for Class III landfills which recommends a soluble concentration limit of 106 mg/1 for low attenuation soils. There is no recommendation for a Class III landfill waste limit for sodium, but a sodium taste threshold of 135 mg/1 for sodium chloride has been reported (Water Quality Criteria, 1963). This document also reports that a sodium concentration of 200 mg/1 may be injurious to persons with cardiac or circulatory diseases. Therefore, a water quality goal of 135 mg/l for sodium based on the taste threshold shall be used in establishing the soil cleanup goal. 3. In addition to the need to close Ponds 1 and 2, there is a need to make progress in the off-site groundwater investigation. This investigation has been delayed for over a year and a half for various reasons including denials of property access. I have discussed the access problems with Mr. David Weisenberger, General Manager of the Banta Carbona Irrigation District and wrote a letter dated 10 December 1998 urging him to continue negotiating with APC for a property access agreement. I am hopeful that in the near future, this property access issue will be resolved. Another off-site issue is the groundwater plume north of APC's Tracy facility. Groundwater monitoring data collected for the Defense Distribution Depot San Joaquin, Tracy Facility (DDJC-Tracy) groundwater investigation identified carbon tetrachloride and chloroform groundwater plumes north of APC's Tracy facility. The recently completed Record of Decision for the DDJC-Tracy determined that DDJC-Tracy is not responsible for this plume. Past sampling by Board staff which we reported to APC in a 26 November 1997 letter found carbon tetrachloride and chloroform at concentrations of 2,100 µg/1 and 29,000 µg/1, respectively, in APC's process wastewater. These chemicals are also found in the groundwater beneath the site at concentrations as high as 310 µg/l of carbon tetrachloride and 4,000 µg/1 of chloroform as stated in the Second Quarter 1998 Monitoring and Sampling Report, dated 5 August 1998. These data show that APC is a probable source for the carbon tetrachloride and chloroform plumes north of the APC facility. Therefore, the off- site investigation of groundwater contamination from the APC facility must be expanded to determine the relationship between the APC site and the carbon tetrachloride/chloroform plume and to define the extent of the plume. This expanded off-site investigation should build on the existing data obtained for the DDJC-Tracy investigation. APC should contact Mr. Marshall Cloud (209-982-2086) to obtain information and access to the DDJC-Tracy groundwater data.