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9/30/93 <br />Responses to Comments <br />San Luis Reclamation Evaluation Report <br />Page 8 <br />of sulfur such as the ferrous sulfate, sulfuric acid and 502. <br />These constituents have all been used for detoxification at the <br />San Luis facility and hence the total sulfur number includes <br />the nonreactive sulfur forms from the by-products of the <br />detoxification process. This by-product sulfur is not related <br />to acid generation, but will nevertheless appear be included in <br />a total sulfur evaluation and hence will greatly increase the <br />AGP numbers. <br />4.2 Humidity Cell Tests <br />Once the results of the AGP/ANP tests were known, des~pate the <br />fact that the results indicated a lower AGP than the pre- <br />operational test results, BMRI conducted humidity cell test for <br />all samples. As discussed above, the Canadian ggvernment <br />sponsored a study which compared acid generating tests with i ~f ~ti„a,X <br />actual field conditions. This study found that the (humidity ~,,, <br />cell test correctly predicted the acid generation of all of the Leo, <br />tailings sampled. Simulated rainwater is used to predict the <br />effects of the natural precipitation conditions on the tailings ~ <br />material. <br />The massive flush method was utilized in the humidity cell - ,,,,,c <br />tests. This method requires flushing with simulated rainwater n~_ <br />every seventh day. Recycling of the liquid obtained from each <br />~ <br />~ <br />cycle does not occur for two reasons. First, because the test <br />i <br />i ;~. <br />' <br />~ <br />~ <br />s des <br />gned to represent th!• effects of the natural Y <br />~ <br />"~` <br />precipitation cycle on the tailfhgs and the natural cycle does " <br />~ <br />not allow this to happen. Second, the recycling of wader ~u~ •~ ~~''' <br />cause surface coatings to, form on the tailings ®aterial <br />prohibiting reactions which could-~i'gtsduce acid or leach metals, <br />particularly in the case of basic tailings such as the San Luis <br />tailings. When a tailings sample is- leached under natural <br />conditions by rainfall, the soluble salts from the tailings <br />impose a matrix chemistry on the rainwater which subsiequently <br />controls how the rainwater will leach the tailings solids. It <br />is not the rainwater chemistry which buffers the tailings <br />chemistry in respect of the pre fluid pH value, but ralther the <br />opposite. In other words, by using fresh water for every <br />rinse, a worst case for leachabii-icy is presented. <br />4.3 EPA Method 1312 Leachability Telsts <br />A number of questions were raised or~ the EPA 1312 test <br />protocol. The EPA 1312 test method was chosen for several <br />reasons: This test method was developed and is recognized by <br />