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Harold S. Peters; PE, CSP, REA 2048 Hickok Road EI Dorado Hills, CA 95630 p stignq(916) 933-3804 July 3, 1992 JUN 15 1993 Robert Huntley ENVIRONMENTAL HEALTH Stockton Plating PERMIT/SERVICES 632 South El Dorado treet Stockton, CA 95206 Dear Mr. Huntley: This will confirm wha I have previously discussed with you relative to the treatment of concentrations of cya 'de less than 100 mg/kg in your industrial wastewater stream. The treatment of cyanide pe ormed at Stockton Plating is not treatment of hazardous waste because the concentration of cy nide is less than the threshold regulated under the criteria in Title 22. There are two criteria t at relate to cyanide being a hazardous waste. The first is reactivity and the second is toxicity. oth criteria have been evaluated by the Waste Evaluation Unit of the Department of Toxic ubstances Control. Copies of the documents that were considered definitive by the Waste Evaluation Unit are attached. The most sensitive of the two criteria is 250 mg HCN/Kg. Tre tment of less than 100 mg/kg of free cyanide is sufficiently below this regulatory guidelines t at confirmation testing is not required. The first and most sensi ive criteria for cyanide is reactivity. The US EPA criteria for reactivity is based on testing the olution to determine the generation of HCN gas. Based upon many requests for a numerica guideline instead of a test procedure,the US EPA determined that 250 mg HCN/Kg should b used in the absence conducting the test. This is undoubtedly a conservative number so that no testing should be required for any concentration less than this valve. The second criteria is b sed on toxicity. The evaluation dated June 22, 1990 that is attached is an evaluation based o "extremely hazardous" criteria. The applicable extremely hazardous criteria is an LD50 of 50 mg/kg. The "hazardous" criteria is 5000 mg/kg. This is a ratio of 100 to 1. Therefore, dividin the result of 67,840 ppm by 100 will give 678 ppm of free HCN as the threshold for being haz rdous. In summary, treatment f cyanide of less than 100 ppm of free HCN is obviously not treatment of hazardous waste bas d on cyanide being the dominant characteristic. There is one other situation that is slightly more complex to evaluate, however that situation does not appear applicable to the situati n at Stockton Plating. If any of the regulatory a envy staff have any questions about this topic, please feel free to have them contact me. Sincerely, Harold S. Peters; PE, C I P, REA