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Logan Wash Mine TR No. 8 <br />The composition of the waste rock is primarily coarse angular marlstone rock fragments that <br />vary from less than a centimeter to tens of centimeters in size. Near the surface, some soil -like <br />fine material may occupy pore spaces between rock fragments. The LW -001 mine water is <br />expected to infiltrate quickly into the waste -rock, and pore pressures are not expected to reach <br />levels that would be of concern for slope stability. <br />The Lower Dump has been in existence since approximately 1980. There is no available <br />information describing construction of the dump. There are no documented or observed physical <br />indications that the dump has subsided or shown instability problems. The fact that there are no <br />signs or indications of slope failures given the age of the dump, past irrigation of seedlings on the <br />face of the dump, and the dump's exposure to rapid snowmelt and intense precipitation events <br />provide evidence that the waste dump is expected to remain stable over time. <br />Monitoring of the Lower Dump will be conducted during normal mine site inspections. DRMS <br />will be notified if inspections indicate a potential slope stability problem. <br />Surface percolation tests were conducted in the area for the proposed infiltration trench. The <br />results are shown in Table 5. These data indicate that infiltration rates are sufficiently high to <br />accommodate the LW -001 mine water discharge. No ponding of water is expected and <br />infiltration will be relatively rapid. <br />6.0 Infiltration Trench Construction <br />Construction of the infiltration trench on the Lower Bench will involve disturbance within a <br />bonded previously disturbed area that has not been released by DRMS; therefore there will be no <br />new disturbed acreage. As shown in Figure 1, two separate trenches are proposed. One trench <br />will be constructed adjacent to the existing Outfall 001 pipeline alignment, and the other trench <br />will be constructed within the existing Outfall 002 pipeline alignment. <br />Consistent with the Articles of Designation between the Colorado Department of Natural <br />Resources and OOSI (September 2013), a plant survey will be conducted prior to ground staking <br />the trench site and particular attention will focus on any occurrence of the threatened species <br />Penstemon dibilis (Parachute penstemon or Parachute beardtongue). If the Penstemon dibilis is <br />discovered in the construction area, the selected construction area will be modified so as not to <br />disturb this species of plant. If the construction area cannot be modified, the state (Colorado <br />Natural Areas Program) will be consulted, and if necessary, an alternate construction plan will be <br />prepared. The surface of the Lower Bench consists of unconsolidated waste rock; no naturally <br />developed topsoil exists. Some natural vegetation exists on the bench and the location of the <br />trench will be selected so as to reduce disturbance of this naturally- established vegetation. <br />The Lower Bench currently contains buried mine drainage pipelines for both Outfalls 001 and <br />002. From the Lower Bench Vault, the 001 mine water pipe is buried in the same trench as the <br />retort water drainage pipe; the trench is located near the interface of the Lower Bench and the toe <br />of the Upper Dump. Construction of the 001 infiltration trench will involve excavation of a spur <br />Western Water & Land, Inc. 5 <br />