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9/30/93 Responses to Comments San Luis Reclamation Evaluation Report Page 9 the EPA as the appropriate test method for determining the leachability of mine waste materials. The second reason that this method was selected to provide data for comparison to the original tailings materials as required by Abatement }`8. EPA 1312 leachability tests were conducted on the original tailings material as discussed in the approved permit and changing analytical methodology at this point would not allow for the required comparison. The U.S. EPA developed the 1312 Method specifically fqr mining type wastes in response to mounting concern by scilentists, industry and regulators alike that other test protocols then currently in use, principally the USEPA 1310 Method EP Toxicity test procedure and the California Assessment Manuhl Waste Extraction Procedure (CAMWET), were unrepresentative of the geochemical conditions in inorganic mining waste systems. Other test protocols, such as the USEPA Method 1310 and 1311 (Toxicity Characteristics Leaching Procedure), use buffered organic leach systems, designed to simulate the type of leaching which might be expected in a sanitary landfill or similar; i.e. an organically controlled chemical envilronment. This is patently not the condition seen in mine waste systems, in general, and is clearly not the case with the San Luis tailings. The EPA 1312 Method requires adjustment of the distilYed water for leaching using a mixture of 60$ laboratory grade sulfuric acid and 40$ laboratory grade nitric acid. These acilds could be present in a tailings system. (Note that BMRI incorrectly identified that a mixture of hydrochloric and nitric acid was used during the September 17th meeting). Accordingly, the choice of EPA Method 1312 is consistent with Federal clnd other states regulatory perception of mine waste leaching and is more realistic and applicable representation of rainwater leaching of tailings than other, organically based leach testing protocols. Leach testing protocols for mining wastes involve agitation of the sample for an 18-24 hour period in a 20 parts licJuid to 1 part solid ratio to attempt to extract as much of the species as possible, irrespective of what might be the field solution kinetics. This type of test is over-robust compared with field conditions in that the tailings will not be shaken for nearly 24 hours in a closed container with a high water to solids ratio as they are being leached naturally. Accordingly, the actual concentrations of species seen in the leachate from such