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MEMORANDUM TO t Barbara Coler, Chief a , Ca /EPA Statewide Cleanup Operations Division Fetewdtoo DISC, Region 2 GovC1Oor Central Valley 700 Heinz Avenue, Suite 200 Regional water Berkeley, CA 94710-2737 Quality Control Board 3443 Routier Road FROM: Thommasas R. Pinkos Suite Sacramento,CA Assistant Executive Officer 95827.3098 (916) 255-3000 DATA t 23 January 1997 FAX (916) 255-3015 BIIBJYCT: 1, 4-DIOXANE Based on the discussion at our meeting on Monday, 6 January 1997, I will revise my memorandum dated 20 December 1996 as follows: Staff of the Central Valley Regional Board will regulate dioxane in generally the same manner as any other constituent that may affect water quality or beneficial uses. Therefore staff will proceed in accordance with the following guidance: 1. 1, 4-Dioxane should be analyzed and reported at sites where there is a reasonable expectation that it may be present (e.g. , at locations with high chlorinated solvent concentrations in groundwater, since 1, 4-dioxane is added to chlorinated solvent as a stabilizer; 1, 4-dioxane has been detected in groundwater at Aerojet, Southern Pacific's Sacramento Rail Yard and other sites in Region 5 where solvents were extensively used and spilled) . Such analysis and reporting should generally result in no added cost since it will usually accompany the analysis and reporting of a target solvent, if the appropriate method is chosen (see below) . If the analysis and reporting of dioxane will result in a significant additional cost to the responsible party, then staff should evaluate such cost against the benefit and value of the added analysis. The current Proposition 65 regulatory level for 1, 4-dioxane of 15 gg/l in water and the Cal/EPA cancer potency factor, which is equivalent to 1.3 µg/l at the 1-in-a-million risk level, are based on standard toxicologic scaling from laboratory animals to humans . Recent information on differences in the metabolism of 1, 4-dioxane by laboratory animals and humans indicates that the above numerical criteria may be overly conservative. Cal/EPA's Office of Environmental Health Hazard Assessment has been requested to review Recycled Paper Our ini cion is to preserve and enhance the quality of California's water resources for the benefit of present and fume generations.