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.~ <br />.~ <br />TO: Dan Mathews <br /> <br />MEMO III IIIIIIIIIIIII III <br />FROM: Jerry Zimpfer <br />RE: Grand Mesa Coal Company Permit Application, Alluvial Valley Floors <br />DATE: December 15, 1981 <br />I have completed reviewing Grand P1esa's Coal Permit Application as <br />revised Flay 8, 1981. This review indicates that there is a strong <br />possibility of mining affecting ward Creek which is a possible Alluvial <br />Valley Floor. The remainder of this memo discusses the Alluvial Valley <br />Floor issue. Another memo will be forthcoming concerning the adequacy <br />of baseline hydrology and protection of the hydrologic balance. <br />The applicant contends that no Alluvial Valley Floors (AVF) exist in <br />or adjacent to the permit area because the alluvial gravels are an upland <br />deposit by mass movement and that irrigation is practiced by the furrow <br />irrigation method. No information was provided concerning~ff'ood irrigation <br />or subirrigation. <br />The information provided is insufficient for the Division to make a <br />proper Alluvial Valley Floor determination. The following additional <br />information should be provided. <br />1. Amore detailed surfical geologic map of all potential alluvial valley <br />floors in or adjacent to the permit area must be provided. These <br />areas designated as Qgy appear to be a combination of alluvium-outwash, <br />debris flows, and pediment gravels. Amore careful mapping would identify <br />those areas which meet the criteria of unconsolidated streamlaid deposits. <br />This map should be verified in the field by the Division prior to making <br />an RVF determination. <br />2. Amore detailed description of the furrow irrigation method practiced <br />in each area in or adjacent to the permit area must be provided. This <br />information is necessary to decide if this furrow irrigation should be <br />considered a type of flood irrigation. <br />3. If it is determined that furrow irrigation is not a type of flood <br />irrigation, the Division must consider the potential for flood irrigation. <br />Therefore, the applicant should submit information concerning the <br />capability of the area to be flood irrigated. (see part II of the OSM <br />June 11, 1980 Technical Guidance Paper for Alluvial Valley Floor <br />Investigations for additional details.) <br />