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� 1 <br /> Mr. Michael C. Refer <br /> CAMAS America, Inc. �S <br /> 12 September 1994 <br /> Page 4 <br /> of the rock mass surrounding the will <br /> It is important to note that during mining dewaterin g <br /> temporarily occur. Upon subsequent filling of the reservoir, some storage losses will occur refill <br /> the void space in the rock mass that was drained by mining. Reestablishing this "passive" storage <br /> surrounding the reservoir will result in some loss of diverted water during the initial filling of the <br /> reservoir. This loss is anticipated to be a temporary condition associated with reestablishing a higher <br /> ground water table controlled by the reservoir pool elevation and it is distinct from steady state <br /> seepage losses that might occur after the reservoir has been established. <br /> DATED LINING COST EVALUATION <br /> In arch 1994 letter report, Haley & Aldrich provided cost estimates for alternative schemes <br /> seal posed reservoir. The alternatives consisted of placing low permeability soil on the <br /> horizon nches and either grouting behind or applying shotcrete to vertical highwall fac ese <br /> cost es ' umed a worse case scenario of sealing the entire reservoir area. We h pon t <br /> ed <br /> our cost evalu to include 1) new cost estimates for sealing the entire reservoir ar ed on the <br /> new reservoir co on filled to hold 500 ac-ft; 2) our best engineering judge about the <br /> percentage of the r it that will actually need treatment and the associated s g costs; and 3) a <br /> proposed methodology plementing reservoir sealing using a phased ob onal approach that <br /> will allow for targeted s of areas observed to be leaking while avoi ' eedless treatment of <br /> areas where the natural rock ides an acceptable reservoir. <br /> Cost Estimate-Sealine Entire R <br /> The reservoir horizontal surface area was ated a plan of the current configuration and <br /> vertical face area was calculated based on the igh walls for that configuration. The <br /> horizontal surface area of such a reservoir is app ely 8.4 acres and the wetted vertical face area <br /> is approximately 6.8 acres. Cost estimates w e ed for placing low permeability soil material <br /> on all horizontal surfaces within the resery ' ea, an er neat cement grouting along a single <br /> row grout curtain behind, or shotcretin vertical faces. <br /> Development of soil lining costs ed 12 inches of soil plac the horizontal reservoir surfaces. <br /> It was assumed that on-site so" mprised of waste materials fro crushing operation amended <br /> with between 2 to 5 percent rite by weight could be placed on rizontal surfaces. The total <br /> required quantity of included approximately 13,500 cubic yards it amended with <br /> between 460 and 115 of bentonite. The total estimated cost for soil 1 the benches ranged <br /> from$168,000 to ,000, depending on the percentage bentonite required. suggest a line item <br /> cost estimate fo item of$200,000. <br /> Neat cem uting was evaluated as a means to reduce the permeability of exposed -wall faces. <br /> A s' w of grout holes located approximately eight feet from the exposed face was ed. <br /> G oles would be drilled from each bench at six foot spacings to depths approximately to <br /> all heights resulting in approximately 63,000 linear feet of grout holes. Estimated grout <br /> Xirllk <br />