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s • Memo to Erica Crosbv 2 March 22, 2000 The Division proposes that two permitting options are suitable for assuring that the post mining land use of developed water resources will be established at the Ft. Lupton Sand and Gravel Mine site through the installation of slurry walls. These options are described below. Regulated Construction Oration The applicant may provide design drawings (current submittal is adequate) and specifications for [he installation of the slurry wall along with a quality assurance/quality control plan. These documents would be binding under the terms of the permit, and the Division would require a statement that the plans and specifications, once approved, could not be altered without consent by the Division. The operator would be required to advise the Division of the schedule for construction of [he slurry wall so that inspections could be scheduled at appropriate times during installation. The operator would be further required to provide a construction report detailing the installation of the slurry wall, describing any problems that occurred, and listing the results of testing that was conducted under the approved quality assurance/quality control plan. A certification would be required [o accompany the construction report with a statement from the quality assurance engineer that the slurry wall was constructed in accordance with the approved plans and specifications. With the level of regulatory control over the installation of the slurry wall described above, the Division would gain a high degree of assurance that the design standard leakage criterion of 0.03 ft;/day/fr' would be met. With this level of assurance, contingency bonding for repair or replacement of 20 percent of the total linear feet of slurry wall would be acceptable. The number of linear feet of slurry wall and the slurry wall installation costs for the site are discussed below. A table summarizing a typical specification and quality control plan is attached. Performance Bonding Oation In this option, the operators would be left to their own devises in the design, installation, and testing of the slurry wall, but would be required to demonstrate that the slurry wall limits leakage into the pit in accordance with the State Engineer's criteria. In [his case, the Division would not have regulatory control over construction of the slurry wall, and should bond for the cost to install a complete replacement slurry wall. The performance bonding option considers the worst case scenario where the slurry wall has been installed and the pit has been mined out, but it is determined that the slurry wall leaks in excess of 3x0.03 f[3/day/ft''. Another consideration that enters into bonding for this worst case scenario is the potential for leakage into the pit through the bedrock pi[ floor. Unless the applicant can provide a geological evaluation of the proposed pit floor bedrock that demonstrates that leakage will not occur, the Division should bond for sealing fractured or sandy bedrock that may be uncovered during mining and that may leak in excess of established criteria (3x0.0015 ft'/day/ft').