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HYDRO30237
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HYDRO30237
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Last modified
8/24/2016 8:49:00 PM
Creation date
11/21/2007 12:08:15 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1981015
IBM Index Class Name
Hydrology
Doc Date
11/9/2005
Doc Name
Findings Document on Discontinuing Sediment Pond Maintenance
Permit Index Doc Type
Correspondence
Media Type
D
Archive
No
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Site Stability Assessment <br />Backfill slopes appear stable, with no evidence of slumping, caving, or excessive erosion <br />There is gully erosion present within the disturbed area, but such erosion is limited to areas <br />impacted by concentrated flow from offsite areas; for the most part within planned, permanent <br />drainage channels. The extent of gully development is not out <br />of character with the surrounding environment. <br />There was a significant storm event in early September 2005, that would appear to have been the <br />most intense runoff event that has occurred at the site since the 2000 reclamation project was <br />completed, but there were no apparent problems due to the event. The steep riprapped channel <br />segment held up well, despite evidence of significant flow. Segments of the non-riprapped <br />segment of the primary channel above and below the riprapped segment experienced additional <br />downcutting in some locations. A short tributary gully on the lower segment of the #1 bench <br />outslope did not appear to have enlarged appreciably due to the September 2005 runoff event. <br />There was limited, minor rill erosion on portions of the steep #1 bench outslope and the backfilled <br />#2 mine portal location. There was no evidence of erosion on the well vegetated lower facility <br />reclaimed areas, and only minor rill erosion in isolated locations along the reclaimed road. The <br />only significant erosion that occurred due to the recent storm event was within drainages that <br />convey concentrated flow from offsite locations up-slope of the reclaimed area. The drainages on <br />the reclaimed area have eroded in some locations, but the extent of erosion and nature of the <br />drainages is not out of character with the high gradient erosional channels and arroyos that are <br />typical of undisturbed watersheds along the base of the Bookcliffs. <br />Since 2000, when the most recent reclamation and drainage improvements were undertaken, a <br />mix of annual and perennial vegetation has become established on the bottom of the sediment <br />pond. It is apparent that there has been very minimal additional deposition of sediment in the <br />pond in the past five years. Height of the primary spillway riser above the sediment at the base of <br />the riser has remained approximately 4.5 feet during that time. October 2003 and September <br />2005 photographs of the sediment pond are included in Enclosure 3. <br />Vegetation cover along the reclaimed road, the relatively flat upper bench area, and the lower <br />facility reclamation areas is quite good, with a combination of four-wing saltbush (Atriplex <br />canescens), shadscale (A. confertifolia), rabbitbrush (Chrysothamnus nauseosus), western <br />wheatgrass (Agropyron smithir), and Indian ricegrass (Oryzopsis hymenoides), present at varying <br />densities in these areas. Seeded perennials have also become established on the steep, south <br />facing slopes of the #1 Bench outslope, and the smaller, #2 Mine backfill slope, however cover <br />and density of perennials is significantly lower in these areas. The perennial species appear to <br />be well established and robust. Seedlings of several species were noted on the site in 2005, and <br />the perennial shrubs and grasses appear to have produced a good seed crop this year. Total <br />ground cover (litter, rock, and live vegetation) exceeds 75%, and appears to be adequate to <br />control erosion, as evidenced by the minimal erosion observed on the steep reclaimed slopes five <br />years after seeding, despite evidence of a high intensity runoff event that occurred earlier in the <br />month. <br />4 <br />
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