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non - structural barriers constructed underground to stop the flow of groundwater. Soil - bentonite <br />slurry walls are the most common type of slurry wall used in Colorado and the United States. <br />For the Treiber Lakes slurry wall, cement may be added to the slurry and backfill for added <br />stability and strength. <br />The Treiber Lakes slurry wall will be constructed with a long reach excavator, clamshell, or <br />other suitable trenching equipment. A trench approximately 3 to 5 feet wide and 100 to 150 feet <br />in length is established by excavating through the entire length of the alluvium and several feet <br />into the shale bedrock below. The total slurry wall depth from top to bottom will be <br />approximately 20 feet. The trench is filled with slurry that stabilizes the excavation and begins <br />to seal the sides of the trench. A blend of soil excavated from the trench, dry bentonite, and <br />borrow soils are mixed at the surface and placed into the trench in a semi -fluid state by a <br />bulldozer or second excavator, displacing the bentonite slurry in the trench. As backfill is added, <br />additional trench is excavated and the displaced bentonite slurry fills the new length of trench. <br />Once the backfill operation is complete, the soil - bentonite backfill sets up slightly and acts like a <br />soft clayey soil. The upper few feet of the trench is backfilled with clean soils to stabilize and <br />protect the top of the slurry wall. <br />Other considerations for slurry wall construction include a stable and sizable working area along <br />the trench alignment. The slurry wall alignment on the outside of the existing lakes is primarily <br />on stable, native soils and should not present a challenge for construction equipment. The <br />working area becomes relatively narrow in some areas, but construction activities should not be <br />hampered even in these sections. Along portions of the slurry wall alignment, the working area <br />will need to be located on previously reclaimed 3H:1 V slopes above the existing lake water <br />surface. Preparation of the slurry wall alignment in these locations will include grading a 50 -foot <br />wide, relatively flat working space into the slope. <br />Since the lake and future reservoir cavities are already excavated, the slurry wall will be <br />constructed around the two lakes. In addition to the slurry wall surrounding the two lakes, a <br />slurry wall may be constructed between the two lakes in order to increase storage capacity and <br />future operational efficiency. Although the slurry wall between the two lakes may be <br />constructed, it is not necessary to separate the lakes from the surrounding alluvial aquifer and is <br />not necessary to complete the reclamation plan. <br />Reclamation Measures/Materials Handling <br />Backfilling and grading will primarily be associated with construction of the slurry wall. In <br />preparation for slurry wall construction, a combination road and working pad will be graded <br />along the slurry wall alignment. The grading will produce a relatively flat, stable surface <br />approximately 50 to 100 feet in width. During grading of the road/working pad, fill, overburden, <br />and topsoil materials will be separated into stockpiles for use in slurry wall construction or <br />reclamation. When slurry wall construction is complete, the road/working pad will be final <br />graded for stability and an operations and maintenance access route will be left in place. The <br />route will be reclaimed with topsoil and grass seeding as a low traffic dirt road. <br />Once the slurry wall is constructed, additional grading of the reservoir slopes and bottom may be <br />performed. Prior to slope grading, topsoil shall be removed and stockpiled for later use. During <br />Treiber Lakes <br />DRMS 112 Permit Application <br />Page 9 <br />