SITE INFORMATION AND CORRESPONDENCE

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Al Jesena - 4 - 1 March 2000 ' Draft RI for OU#3 NCTS, Stockton When a COPC is found to reach groundwater as leachate, the data is then mixed and diluted in groundwater over a 30-year period. Often COPCs are ruled out as threats to water quality because they have not been found in groundwater monitorin- wells. Sometimes these wells are either crossgradient from the sample location and more than 250 feet away from the sampling location in a hydrogeologically stagnant area(horizontally and vertically), according to the Navy. In order to determine the impacts of contaminated soil on groundwater, the Navy should know the areal extent of the contaminant so volumetric calculations (mass loading) may be calculated. We do not accept Diluting a leachable contaminant in the groundwater using a mixing zone between the point the contaminant reaches groundwater and the nearest well when the associated wells are contaminated. If a contaminant in the soil is found to be leachable based on WET analysis, then discrete groundwater sampling methods should be employed to verify if the groundwater has been impacted by that COPC and to what extent. Furthermore, there may be an accumulative affect on the constituent as it travels vertically through the vadose zone. As.with groundwater sampling, the intent of soil sampling is to characterize and estimate the limits of existing soil contamination. Contaminated soil should be documented in both the horizontal and vertical directions (EPA, 1988). The Policy for Investigation and Cleanup of Contaminated Sites in the Basin Plan, states that the Board's strategy for managing contaminated sites is guided by several important principles, which are based on Water Code Sections 13000 and 13304, the Chapter 15 and Title 27 regulations and State Water Board Resolution Nos. 68-16 and 92-49. An investigation of soil and groundwater to determine full horizontal and vertical extent of pollution is necessary to ensure that cleanup plans are protective of water quality. The goal of the investigation shall be to determine where concentrations of COCs exceed beneficial use protective levels (water quality objectives) and, additionally, where COCs exceed background levels (the zero-impact line). Total Petroleum Hydrocarbons in Soil Appendix K, Table K-1 shows total petroleum hydrocarbons as motor oil, diesel, and gasoline range organics at depths ranging from 0 to 10 feet below ground surface (bgs). Values range from ND to 6900 mg/kg at various depths at all operable units. PCBs and pesticides are also pervasive at all OU #3 IR sites. The Navy states that, "the source of motor oil and diesel in IAS-07 surface soil samples is uncertain, but is probably related to waste disposal activities," yet data sheets and other sections of the report state that these hits are naturally occurring nonpetroleum hydrocarbons. Based on information provided by the Sacramento-Yolo Mosquito Abatement District, DDT was mixed with diesel, as a carrier/solvent, and used for mosquito abatement in the mid 1950s through the mid 1960s, possibly into the early 1970s. Motor oil was used for weed control and not necessarily mosquito abatement because of its high viscosity. Because portions of the island have been used for agricultural purposes, it is suspected that surplus pesticides and used motor oil/diesel/gasoline were spread over the area indiscriminately for disposal, which was acceptable at the time. Used petroleum hydrocarbons drained from Naval or agricultural machinery would account for the detection of PCBs and metals in soil. Kerosene and fuel oil applied at 20 to 40 gallons per acre is a simple and effective [mosquito] larvacide for small bodies of water. Most larvaciding operations are conducted, using emulsions or granular formulations of DDT, dieldrin, chlordane, heptachlor, or lindane at 0.05 to 0.1 pound per acres