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<br />DATE: Thursday, November 16, 2000 <br />TO: Gregg Squire <br />FROM: Allen Sorenson <br />RE: Mamm Creek Gravel Pit, Roaring Fork Resources, File No. M-2000-113 <br />In order to evaluate geomorphic stability issues related [o the Mamm Creek Pit application, the <br />following documents have been reviewed: <br />• the original application package submitted by Roazing Fork Resources; <br />• the Mamm Creek Pit 100 yeaz flood plain maps prepared by Balaz and Associates; <br />• the letter from Grant Brothers dated October 5, 2000 discussing the application; <br />• the adequacy review memo from Tom Schreiner dated November 1, 2000; <br />• the letter describing the city of Rifle's concerns with the application and dated November 1, 2000. <br />Based on this review, it has been determined that the following issues must be addressed before the <br />Division can make a recommendation to approve the Mamm Creek Pit application. <br />1. The application states [hat the estirnnred depth of mining in the renewable resource area will be 5 <br />feet. The shallow depth of excavation combined with the proposed 150 foot unmined barriers at <br />either end of the renewable resource area make it unlikely that this excavation would have <br />significant adverse impact on the Colorado River geomorphology. However, the language required <br />to make the reclamation permit enforceable must be an unequivocal commitment from the <br />Applicant that mining in the renewable resource area will not exceed 5 feet. Limitation on the depth <br />of excavation is one of the mitigating factors for in-stream gravel harvesting discussed in the <br />Division of Minerals and Geology "In-Stream Aggregate Extraction and Reclamation Guidance <br />Document," dated August 1998. As discussed in Tom Schreiner's memo, the Operator must <br />establish baseline cross sections in the renewable resource area with permanent survey monuments <br />located outside the area to be disturbed. The depth of mining can then be periodically evaluated and <br />documented. <br />2. The application states that [he 150 foot unmined barrier at the upstream end of the renewable <br />resource azea will include large boulders placed along the toe of the slope for stabilization of the <br />bank in high flow events. The Division envisions this installation as being a headcutting prevention <br />measure, but the configuration of the installation is not clear in the text of the application. The <br />Division will require that the Applicant provide sketches and/or cross-sections to illustrate the <br />