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Logan Wash Mine TR No. 6 <br />The first calculation was conducted to evaluate the flow rate from the mine in the case of head <br />build-up in the mine above the pipe inlet behind the concrete sack and shotcreted dam. The total <br />head loss used was 175 feet from the top of the mine pool to the discharge point in Dry Gulch. <br />The head above the pipe inlet was 4 feet. An iterative technique was used to arrive at the <br />solution. Head losses due to the inlet and any valves were considered minor losses and not <br />incorporated into the calculation. Neglecting the minor losses is reasonable considering the total <br />length of the pipe is 3,000 feet. The calculated flow rate was 0.78 cfs or 350 gpm. This flow <br />rate is approximately 6 times greater than any recorded flow from the mine, and demonstrates <br />that the likelihood of head build-up due to a large influx of water into the mine workings is <br />small. <br />The second calculation is based on the maximum daily discharge of 78,550 gallons per day (gpd) <br />or 54.5 gallons per minute (gpm) [0.122 cubic feet per second (cfs)]. This flow rate is slightly <br />greater than the observed maximum flow rate of 78,545 gpd in the spring of 1998. The pipe <br />sizing calculation was conducted with the assumption that flow will occur under &ee drainage <br />conditions; i.e. no pressure head build-up in the mine. As shown in Attachment C, the pipe size <br />diameter needed for a flow rate of 54.5 gpm is 2 inches. To provide for a suitable safety factor in <br />pipe size, a 4-inch diameter pipe will be installed. A check calculation was conducted to <br />evaluate the pipe size needed under the conditions stated in the first calculation, i.e. a constant <br />head. This calculation is included with the second calculation. The results show that a 4-inch <br />pipe would be sufficient to convey mine water in the constant head condition. <br />3.3 Trench Construction and Pipe Installation <br />The pipeline alignment will be constructed within an excavated trench. Figure 1 shows the <br />proposed pipeline alignment. Trench construction will be conducted with an excavator of <br />appropriate size. The alignment of the trench will be as far on the inside of the Lower Bench <br />road as practicable. Some deviation from this alignment may occur if bedrock prevents suitable <br />burial depths. Due to elevated grade near the intersection of the Upper and Lower Bench access <br />roads, the trench will need to be excavated to a depth of approximately 9 feet. A test excavation <br />conducted in the fall 2004 in this area confirmed that trench construction can be performed <br />without encountering bedrock at this location. <br />Burial depth will be a minimum of 2 feet below existing grade and not to exceed 4 feet except in <br />areas where needed to provide gravity draining conditions. Trench spoil will be placed on the <br />road bed in a location so as to accommodate light truck traffic access and egress to the Lower <br />Bench. Stormwater drainage channels will be maintained as practicable as possible during <br />construction and if damaged, regraded upon completion of trench backfilling. <br />The bottom of the trench will be prepared to receive the pipe. This includes removal of sharp <br />rocks equal to or greater than one-half the pipe diameter. Based on experience in laying pipe for <br />the L-I mine drainage, no pipe bedding will be required. The pipe will be hand assembled in the <br />trench where trench depths are not greater than 4 feet. Deeper trenched sections will require <br />Western Water 8 Land, Ine. 7 <br />