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IlI Exhibit "E" Reclamation Plan 6.4.5 <br />A) "In order for the Division to calculate the required warranty, a detailed design, <br />construction and QA/QC for the proposed method is required....the slurry wall design, <br />construction and QA/QC has to be approved by the State Engineer's Office." <br />Response: <br />Please see the INFORMATION BELOW PROVIDED BY RJH CONSULTANTS, INC. THE <br />ENGINEERING COMPANY DOING THE PROJECT ENGINEERING. <br />Soil Bentonite Items <br />"A soil-bentonite cutoff trench (liner] will be constructed around the perimeter of the area to mined prior <br />to mining. The primary purposes of this soil-bentonite trench will be to isolate the water within the <br />mining area from the groundwater regime to reduce pumping costs during mining and impacts to the <br />groundwater regime that could occur from sustained pumping. This trench will also become a critical <br />element of the final reclamation plan that includes below ground raw water storage. <br />Based on data from limited preliminary geotechnical borings, the subsurface profile generally consists of <br />about 4 to 15 feet of clayey low plastic overburden soils above about 20 to 33 feet of sand and gravel <br />alluvial soils above bedrock consisting of claystone of the Pierre Shale Formation. The depth to <br />groundwater varies from about 6 to 15 feet. <br />The soil-bentonite cutoff trench will be designed to meet the "Design Standard" as described in the State <br />Engineer Guidelines far Lining Criteria for Gravel Pits (August 1999}, as amended. The liner design will <br />be designed by a Colorado registered engineer who is experienced in the design and construction of soil- <br />bentonite cutofftrenches. <br />Based on the current available subsurface information and the experience of the design engineer on other <br />similar projects, the trench is expected to be 2.5 feet wide and would extend between 3 and 10 feet into <br />the bedrock. The actual depth of penetration will depend on the properries of the bedrock and results of <br />seepage modeling performed during design and after more subsurface data is collected. The soil- <br />bentonite backfill will be designed to have a hydraulic conductivity of no more than 1x10"' cmisec. The <br />mixture of the overburden clayey soils with the sand and gravel and bedrock will create awell-graded <br />backfill with adequate fines to easily achieve the required hydraulic conductivity. The quantity of <br />bentonite required to achieve the target hydraulic conductivity will be based on mix designs that are <br />performed during final design. <br />Leakage testing of the liner will be completed at the completion of mining according to the criteria <br />described in the State Engineer Guidelines for Lining~Criteria for Gravel Pits (August 1999), as <br />amended.,' <br />