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• <br /> <br />waste dump is 50%. In the past, this ratio has been closer to 25% sorter <br />reject due to installation, maintenance, and general downtime of the ore <br />sorter. A review of the mine production records in terms of truck loads of <br />sorter reject and mine development rock shows this 50% ratio to be correct. <br />It should be noted that based upon a literature review and telephone <br />communications with primary researchers, Cotter has concluded that it is <br />virtually impossible to address the problem of the effects of acid i°ain on <br />the waste rock at this time. <br />1. Studies conducted by Lewis and Grant in the Ralston Cree4: area <br />show only that the pH of precipitation has changed over the past thT•ee years. <br />This situation does not follow any pattern and is, therefore, unpredictable. <br />Their conclusion is that the change in pH is not caused by the Denver urban <br />• plume or "brown cloud," and that more research is necessary. <br /> 2. Climatologists at NOAA have a 5 year data base of rain along the <br />Front Range, showing the average pH to be 6.3. .This is higher than rain in a <br />standard atmosphere, 5.7, and can be attributed to the alkaline soils in the <br />region, which are entrained into the atmosphere and act as condensation nuclei <br />for precipitation. <br />3. Cotter, on the weekend prior to the study described in Section 2.2, <br />checked the pH of a three-inch snowfall and found it to be 7.2. This would <br />indicate the data from NOAA is more accurate with respect to pH along the <br />Front Range. <br />4. Cotter has conducted one experiment which simulated the rainfall <br />conditions associated with a 100 year, 6 hour flood on the reclaimed waste dump, <br />assuming, for the purposes of conservatism, that the waste dump is comprised <br />• of sorter reject only. These data are included in Section 2.2 At ttie request <br />of the Colorado Department of Health, Cotter will conduct an additional study <br />(See Section 5.2) when conditions are appropriate. <br />o ,~ <br />