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<br /> <br />may flow during the thunderstorms but the infiltration rate will be very <br />low during the short period of thunderstorm activity and exposure of the <br />rainwater to rock surfaces within the pile will also be of short duration. <br />The small amount of salts that may be leached from the pile will not in- <br />filtrate the local aquifers but will flow down Logan Wash to Roan Creek. <br />In summary, Dry Gulch will flow only when other nearby gulches will flow. <br />Only small amounts of material will be leached. These will not infiltrate <br />into the groundwater system but will flow, greatly diluted, into Roan Creek <br />and the Colorado River. <br />The drainage area above and near the waste pile was divided into tlir°e2 <br />sub-areas as shown in Figure 1, and the rational formula Q = CiA used <br />to estimate runoff where Q is peak discharge in cfs, C is a dimensionless <br />runoff coefficient, i is rainfall intensity in inches per hour, and A is <br />the drainage area in acres, (Todd, 1970). See Table 1. The rainfall <br />intensity in inches per hour, i, was selected as 1. Miller, Frederick, <br />and Tracey (1970) list the 100 year - 6 hour precipitation as 2 inches <br />for the upper Logan Wash area. A 1-inch-per-hour estimate, then, is <br />conservative. Total discharge at the toe of the dump rack disposal pile <br />is the sum of the 3 Q's shown on Table 1, or 349 cfs. <br />As discussed in the section on stability in this paper, pore pressure will <br />not build up in the dump because of the generally coarse size of the broken <br />material. The small amount of the fine material will be insufficient to <br />plug the dump and diminish porosity. <br /> <br />It is desirable to have permeability of the pile as low as possible so that <br />