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Logan Wash Mine TR No. 8 <br />trench extending from the existing trench that currently holds the 001 mine water discharge pipe. <br />The Outfall 001 infiltration trench will diverge from the existing pipeline trench alignment in the <br />northern area of the bench and will extend approximately 50 feet in a westerly direction towards <br />the west - central portion of the Lower Bench (Figure 1). <br />The 002 pipeline extends from the Lower Bench Vault to a stormwater channel drain, located on <br />the northwestern part of the Lower Bench. The 002 pipeline infiltration trench will be excavated <br />within the existing pipeline alignment. <br />Conventional excavation equipment (backhoe and excavator) will be used to carefully expose the <br />existing pipelines during infiltration trench construction. The land surface will be excavated to <br />form a small, relatively shallow elongated depression or swale for each trench. Dimensions of <br />the trenches will be approximately 50 feet long by 5 feet deep by 4 feet wide (bottom width) and <br />24 feet wide (top width). Side slopes will be approximately 2:1 (2 feet horizontal to 1 foot <br />vertical). Excavated material will be used to form a shallow broad berm around the perimeter of <br />the trench. The berm height is not expected to exceed 3 feet above the surrounding grade and <br />will serve to deflect stormwater run -on from entering the trench. A conceptual drawing of the <br />trench is shown in Figure 2. <br />The materials that comprise the Lower Bench are unconsolidated broken oil shale and marlstone <br />of the Parachute Creek Member of the Green River Formation, the same formation that <br />encompasses the underground mine workings. Percolation tests were conducted on the ground <br />surface in the area of the proposed trench. Infiltration rates ranged from 2.6 to 59 inches /hour. <br />For a 3 gallon per minute mine water discharge, the area needed to infiltrate this discharge at the <br />observed rates ranges from 4.9 ft2 to 111 ft2, respectively. To provide for a margin of safety, the <br />trench will be sized to accommodate an infiltration flux area of approximately 200 ftZ. The 200 <br />ft` basal infiltration area would accommodate a mine discharge of approximately 5.5 gpm or 1.8 <br />times the average discharge rate (since August 2011) at the lowest observed infiltration rate of <br />2.6 inches /hour. <br />An estimated 30 cubic yards of waste rock will be excavated to construct the trench. Final grade <br />preparation will include compaction of the trench slopes and berms with excavation equipment. <br />No top soil amendments or seeding will be conducted at this time. <br />Surface preparation will include grubbing of the ground surface to remove all vegetation and <br />loose surface rock. This work will be conducted with a small bulldozer. All grubbed materials <br />will be pushed stockpiled on the perimeter of the planned excavation area. If developed topsoil <br />or other tine materials are present in the near surface waste rock, the materials will be isolated as <br />berm material for the trench. <br />7.0 Erosion Control <br />During excavation of the infiltration trenches, erosion control structures will be installed and <br />maintained to mitigate the potential of excessive erosion due to storm run -on and runoff events. <br />Western Water & Land, Inc. 6 <br />