SITE INFORMATION AND CORRESPONDENCE

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Tom Pinkos -2- 28 August 1996 applying it to a release from a waste tank of waste oil, samples would not need to be collected and analyzed for heavy metals if it was not known that the metals existed in the tank at the time of the release. However, in reality, spills from waste oil tanks are routinely analyzed for metals due to the potential presence of heavy metals in waste oil. This is analogous to 1,4-dioxane and the release of TCE or 1,1,1-TCA. Not all of those solvents contain 1,4-dioxane, but there is also a potential for its presence. Remediation of a solvent containing 1,4-dioxane having been released to ground water causes problems with treatment if the 1,4-dioxane must be removed prior to discharge of the treated ground water. As stated above, 1,4-dioxane is not removed from water by either air stripping or carbon adsorption, the two primary methods used to treat water contaminated with volatile organics such as TCE. A destruction technology such as ultraviolet enhanced with peroxide is necessary. Thus, the concentration of 1,4-dioxane that will be in the extracted ground water needs to be known so that treatment can be developed to meet any discharge limitations. Ultraviolet/oxidation treatment is not inherently an additional cost burden over the traditional VOC treatment methods of air stripping and carbon adsorption. For example, the ultraviolet treatment method is being used at the Davis Transmitter Site, McClellan Air Force Base, Aerojet, and the Sacramento Army Depot as part of their groundwater cleanup systems. At McClellan, it was determined that it was more cost-effective to switch from an air-stripper with incineration of the off- gas to the ultraviolet technology. The estimated cost savings from the switch is $300,000 per year. At the Davis Transmitter Site, ultraviolet treatment was more cost-effective than carbon alone due to the presence of vinyl chloride which will use a considerable amount of carbon to achieve discharge limitations. Aerojet uses ultraviolet treatment due to the presence of other contaminants that are similar to dioxane in that they are not readily treatable using air-stripping or carbon adsorption. Thus, depending upon the influent contaminants, enhanced ultraviolet treatment can be the treatment method of choice even without dioxane. The presence of dioxane may necessitate switching from a treatment system such as air-stripping to ultraviolet treatment. If the cost is more, it would only be an incremental cost increase. Establishing Effluent Limitations and Cleanup Standards All contaminants/pollutants are potential contaminants of concern when establishing effluent limitations for the discharge of the treated water and aquifer/vadose zone cleanup standards, regardless of the risk values. The risk values are considered when developing the effluent limitations and cleanup values when deviations from background concentrations in the receiving water and/or ground water are to be allowed. Currently, the Proposition 65 limitation of 15 gg/I is the highest value that would be allowed to be discharged to a surface water or to ground water from a ground water treatment system. Prop 65 states that it is illegal to discharge a significant amount of a carcinogen or reproductive toxin to a source of drinking water with the value of 15 µg/I based on a cancer potency factor developed by OEHHA and the 1 x 10"s cancer risk level. In addition, treatment to lower concentrations might be necessary as dictated by the policies contained in the Basin Plan (ie., non-degradation and remo,.al to the extent technically and economically feasible). The Prop 65 value is established in law and must