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-4- <br />Alluvial Valley Floors - 2.06.8 (con't) <br />1. A map showing the extent of unconsolidated streamlaid deposits <br />(greater than 50 ft. in width and greater than 10 acres in size) in or <br />adjacent to the permit area. If such areas are identified, their areal <br />extent should be provided. <br />2. Within the study area (permit area and adjacent areas), identification <br />of all areas of existing or historic flood irrigation. <br />3. Within the areas mapped as unconsolidated streamlaid deposits, <br />identification of those areas where the vegetation suggests subirrigation. <br />4. If areas of unconsolidated streamlaid deposits are identified, a <br />description of the regional flood irrigation practices For similarly <br />sized or smaller watersheds. <br />Portal and Well Sealing: <br />The sealing techniques descriptions and drawings are acceptable, <br />with one deficiency in the company's presentation. The operator fails <br />to discuss whether mine drainage will occur at the location of the portals <br />following reclamation and sealing. The hydrology section should be <br />amended to specifically discuss this topic. <br />Portal Bench and Highwall Stabilit <br />The supplemental materials contain discussions of both operational <br />and backfilled portal bench and highwall slope stability. The applicant <br />and the applicant's consultants both recognize the existence of a slope <br />instability problem on the portal bench facial slope. The applicant <br />has submitted a remedial plan to eliminate this problem in response to <br />an inspection notice of violation (October 22, 1981 letter by Ute <br />Engineering 6 Surveying Company). This design includes installation of <br />a perforated interceptor drain rile and a regrading of the bench surface, <br />both intended to decrease infiltration of moisture into the bench which <br />the applicant believes is the cause of the problem. The applicant <br />further commits, in the amended application, to the completion of <br />appropriate geotechnical and stability analyses and the installation <br />of three standpipe piezometers to monitor the phreatic surface and degree <br />of saturation of the portal bench. This proposal and the applicant's <br />indication of completion of the remedial construction by February of <br />1982 can be approved immediately in order to expedite correction of the <br />problem and completion of the geotechnical analyses. <br />The amended application also commits the applicant to completion of <br />a stability analysis of the proposed final backfilled configuration, <br />including shear strength testing and definition of. the phreatic surface. <br />The application incorporates a regaest for varianco from AOC based upon <br />the existence of steep slope mining conditions within the portal area. <br />This proposal should be approved with the imposition of a completion deadline <br />of six months following approval of the permit. If the applicant is willing <br />to amend the application to include such a deadline commitment it would then <br />be unnecessary to include such a stipulation within the findings document. <br />