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<br />The costs to install slurry walls at waste containment sites are higher than the costs to line clean <br />water reservoirs using a slum wall. This is partially due to the need to conduct chemical <br />compatibility testing and [he higher degree of quality control used at waste containment sites. <br />The applicant proposes a $3.00 per sq. ft. unit cost for slurry wall installation, and based on <br />review of recent bids for slum walls around gravel pits on [he Front Ranee, this is believed to be <br />appropriate. The slum wall bond, whether it is for installation around the entire reservoir <br />perimeter or is a 20 percent contingency bond as discussed above, should not be released until the <br />Division of Minerals and Geology and [he Oftce of the Stale Engineer are satisfied that [he <br />specified leakage criteria has been met. <br />As stated above, it is pertinent [o [he bond amount that the depth to bedrock used in estimating <br />the extent of the slurry wa{I required is accurately determined and [hat nature of the bedrock is <br />investigated. The applicant should provide information from boreholes at the site showing the <br />depth to gravel and the type of bedrock present. any variability in the bedrock encountered, and <br />the depth of weathering in the bedrock. It is implicit to the proposed slurry wall plan that the <br />bedrock is a competent seepage barrier, and this is most likely to be the case. However, if <br />fractured zones, sandy lenses or layers, or deeply weathered bedrock are present, pit floor lining <br />or a deeper bedrock keyway for the slurry wall may be required. Either solution would increase <br />the reclamation costs that may be imposed upon the State in a bond forfeiture and must be <br />covered by the bond. Assuming that the borehole information demonstrates that the bedrock is <br />no more than 36 feet below the surface and is an adequate seepage barrier, the following estimate <br />is provided for the Ft. Lupton Sand and Gravel Mine Slurry Wall. <br />36'depth x 8222' length x $3.00/sq.ft. _ $887,976.00 direct costs <br />If the 20% regulated construction bond is selected the required bond for slum wall installation <br />would be $177,595.00. <br />These estimates are substantially more than the $96,664.00 estimated by the applicant in Exhibit <br />L. It appears that in the applicant's estimate inadvertently applies a unit cost per sq. ft. to a <br />volume in cubic yards. <br />Reeulatorv Responsibilities <br />The appl icant states that the final approval and success criteria for the performance of the slurry <br />wall to seal and isolate the reservoir-storage from the surrounding alluvial aquifer lies with the <br />State Engineer, which is of course true. In fact, the most straightforward mechanism for release <br />of a slurry wall bond is for an Operator to demonstrate and document compliance with the State <br />Engineer's lined reservoir performance standards. However, the Division of Minerals and <br />Geology is required to hold financial warranties sufficient to assure that the State Engineer's <br />standards will be me[. A copy of [he Memorandum of Understanding between the Division of <br />Minerals and Geology and the Office of the State Engineer is attached and describes the division <br />of responsibilities between the two agencies. <br />3. The Division estimated the cost to reclaim the site based on the information in the mining and <br />reclamation plan. As noted above, the cost for installation of the slurry wall are substantially <br />more than the $96,664.00 estimated by the applicant in Exhibit L. It appears that in the <br />applicant's estimate inadvertently applies a unit cost per sq. ft. to a volume in cubic yards. <br />