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<br />Memo to Tom Schreiner 2 May 15, 1999 <br />Reeulated Construction Option <br />The applicant may provide design drawings and specifications for the installation of the slurry wall along <br />with a quality assurance/quality control plan. These documents would be binding under the terms of the <br />permit, and the Division would require a statement [ha[ these plans and drawings, once approved. could no[ <br />be altered without consent by the Division. The operator would be required [o advise the Division of the <br />schedule for construction of the slurry wall so that inspections could be scheduled at appropriate times <br />during installation. The operation would be further required to provide a construction report detailing [he <br />installation of the slurry wall, describing any problems that occurred, and listing the results of testing that <br />was conducted under the approved quality assurance/quality control plan. A certification would be required <br />to accompany the construction report with a statement from the quality assurance engineer that the slurry <br />wall was constructed in accordance with the approved plans and specifications. <br />With the level of regulatory control over the installation of [he slurry wall described above, the Division <br />would gain a high degree of assurance that ground water will not leak into the pit a[ a rate in excess of 0.03 <br />ft'/day/ft2. With this level of assurance, the contingency bonding for repair or replacement of 20 percent of <br />the total linear feet of slurry wall would be acceptable. The number of linear fee[ a slurry wall and the <br />slurry wall installation costs for the Cooley Reservoir site are discussed below. <br />Performance Bondine Option <br />In [his option, the operators would be left [o their own devises in the design, installation, and testing of [he <br />slurry wall, but would be required to demonstrate that the slurry wall limits leakage into the pit in <br />accordance with the State Engineer's criteria. In this case, the Division would no[ have regulatory control <br />over construction of the slurry wall, and should bond for the cost to install a complete replacement slurry <br />wall. The performance bonding option considers the worst case scenario where the slurry wall has been <br />installed and the pit has been mined out, but it is determined [ha[ the slurry wall leaks in excess of 0.03 <br />ft'/day/ft'. Another consideration that enters into bonding for [his worst case scenario is the potential for <br />leakage into the pi[ through the bedrock pi[ floor. Unless the applicant can provide a geological evaluation <br />of the Cooley Reservoir pi[ floor bedrock that demonstrates that leakage will no[ occur, the Division should <br />bond for sealing fractured or sandy bedrock that may be uncovered during mining and that may leak in <br />excess of established criteria. <br />Reservoir Filline <br />Past practices by [he Division in permitting lined reservoirs included a requirement to provide bond <br />sufficient to purchase enough water from a reliable source to fill [he reservoir one time. Numerous gravel <br />pits have been reclaimed or are proposed to be reclaimed as lined storage reservoirs since the passage of <br />Senate Bill 120 in 1989. It has become clear that there is a great demand for lined storage in over <br />appropriated basins and in particular the South Platte basin, so it is no longer a substantial concern [o the <br />Division that lined reservoirs will not be filled and put to their intended beneficial use. In the worst case. <br />virtually any reservoir could be filled eventually by using junior water rights in priority. For these reasons, <br />