FIELD DOCUMENTS AND WORK PLANS 2000-2003

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WASTE DISCHARGE REQUOMENTS • 4 MARLEY COOLING TOWER COMPANY SAN JOAQUIN COUNTY TENTATIVE chromium in the aquifer and vadose zone to precipitate it out of solution. Sodium dithionite is proposed as research indicates it has the ability to alter the oxidation/reduction state of the groundwater,thereby immobilizing chromium. Ethanol is proposed as an organic carbon source to stimulate microbial growth and produce reducing conditions to precipitate chromium out of solution. Ethanol is highly soluble in water, and is easily obtained. Phase 1 is proposed to address the high concentrations of hexavalent chromium in the shallow groundwater adjacent to and downgradient of the former retort pit(range of 5,000 to 200,000 micrograms/liter(parts per billion)). Once these concentrations have been reduced,the residual chromium in the vadose zone is proposed to be addressed in Phase 2. The Discharger has provided information to indicate that in situ remediation research has shown that introduction of an organic carbon source into groundwater stimulated microbial activity that in tum used up dissolved oxygen and created strongly reducing conditions. Under these strongly reducing conditions hexavalent chromium was reduced to trivalent chromium and precipitated on the soil matrix. Furthermore,research also indicates that this reaction was not reversible under natural conditions(i.e. the absence of a strong oxidant)in groundwater. In effect,the precipitated trivalent chromium would not be re-oxidized to hexavalent chromium and re-mobilized under naturally occurring conditions. 15. During Phase 1,the Discharger proposes to inject up to 9 pounds of reagent grade sodium dithionite or 400 litres(about 105 gallons)of food grade ethanol in monitoring well MW-206 over a maximum of 40 days or until oxidation reduction potential(ORP)readings of-50 mV or less have been achieved for 30 days and chromium concentrations have declined. Field monitoring and groundwater sampling will be conducted to evaluate effectiveness of meeting the desired ORP. After results have been evaluated and it has been determined that chromium concentrations have declined and are relatively stable, slow release oxygen compounds(ORC)manufactured by Regenesis Bioremediation Products, San Clemente, California will be introduced into well MW- 206 to verify that trivalent chromium is not oxidized to hexavalent chromium and thereby increase chromium concentrations in groundwater. If the results indicate that the reducing conditions cannot be created in the shallow groundwater and the chromium concentrations are not declining, then this pilot test will be terminated. If the results indicate that chromium concentrations decline in response to the sodium dithionite or ethanol dosing,a larger scale pilot study in the shallow groundwater will be implemented. The lager study will include the introduction of ethanol into wells MW-6,MW-101,MW-105,MW-106,MW-206,MT-1,MT-2,MT-4,MT-8,P-228,P-229, and P-231. The amount and frequency of dosing will be based on the results of the initial phase of the pilot test using well MW-206. Sodium dithionite proposed for this pilot test is a powder 89 to 91 percent sodium dithionite(sodium hydrosulfite). The remainder is an alkali stabilizer. The product is essentially free of heavy metals. Ethanol is a liquid,highly soluble in water,and is easily obtained. 16. During Phase 2, the Discharger proposes to inject up to 31 pounds of reagent grade sodium dithionite or 43 litres (about 12 gallons) of food grade ethanol will be introduced into the flushing system injection wells (IW-1, IW-2, IW-3, IW-4, and IW-5)using a metering pump. If sodium dithionite is used, it will be injected at a rate to produce a concentration of approximately 50 mg/1 to achieve the desired ORP of-50 mV or less. If ethanol is used, it will be injected for 15 minutes every hour at a rate to produce a concentration ranging from 100 to 1000 mg/1 in the injected flow to achieve the desired ORP of-50 mV or less. If the evaluation of the results indicates that chromium concentrations have decreased but still 08/22/02 2:02 PM Marley Cooling