Laserfiche WebLink
RULE 4 PERFORMANCE STANDARDS <br />.+C'�.,:54!!H�'..- 'ss'tr WPYIT.�' *.'"FWi"':Mte�''. r ^#�N.f..�i. rA ^. '..+M« '.'N t^^^a J:... ,. :,v, a.a'^.5,9 •,c.A^r,�m.�,' yat *.:i ^PVgA(5v.4s!,.� >" i5'^Y&�f ,84e.� ro$i- �i:',"° *i}' <br />The ongoing mining activities within each watershed of the permit area will create constantly changing <br />hydrologic conditions. The design models are generally based on a static, theoretical scenario, utilizing <br />SEDCAD 4, which considers the worst -case scenario wherein mine phasing has caused impacts to the entire <br />disturbance area and reclamation has not yet been attained for any areas. Refer to Map 41 A for a delineation <br />of the areas used for these modeling purposes as well as the individual maps associated with each SEDCAD <br />run. The dates indicated on Map 41 A are for development of the worst -case scenario for hydrologic modeling <br />and are not a definitive schedule for mining and reclamation activities. <br />It is Colowyo's contention that the proposed models represent nothing more than our best hydrologic <br />estimates for a described worst -case condition. The intent of the modeling is to aid in the design of <br />sedimentation ponds to predict compliance with applicable effluent standards. A primary limitation of the <br />modeling and subsequent designs is the available existing topography, which is very coarse at a 25 -ft interval. <br />Colowyo believes it would be an inappropriate use of the SEDCAD models to use them as an enforcement <br />tool for such operations as topsoil stripping; backfilling, grading, reclamation, etc. Furthermore, more <br />detailed topography must be obtained to verify results prior to implementation. <br />The scenario used for the sedimentation ponds corresponds to an active, disturbed operation. In terms of <br />groundwater, Colowyo's pits have remained essentially dry. Pumping of pit water (precipitation induced <br />surface runoff) into sedimentation ponds is not anticipated. Discharges from the ponds will remain in <br />compliance with Colowyo's CDPS Discharge Permit. The use of flocculants in sedimentation ponds may <br />also be used in accordance with the provisions of the CDPS Permit. <br />Sediment will be removed from all sedimentation ponds on an as needed basis or when the sediment level will <br />not allow effective treatment of the runoff resulting from the 10 -year, 24 -hour precipitation event in <br />accordance with Rule 4.05.2. Quarterly inspections will note the level of sediment in each pond. Ponds will <br />typically be cleaned of sediment when water levels are lowest, and the least amount of precipitation is <br />expected. The removed sediment will be used as topsoil or subsoil if it meets the suitability criteria discussed <br />under Section 2.04.9. The Division will be notified of this determination if the material is selected as <br />overburden material that can be substituted for or as a supplement to topsoil. <br />All sedimentation ponds will be designed so that the minimum elevation at the top of the settled embankment <br />is at least one foot above the elevation of the water surface in the pond with the emergency spillway flowing <br />at design depth. <br />Colowyo will design, construct, and maintain the sedimentation ponds to prevent short- circuiting to the extent <br />possible. As a general rule, the inflow to the ponds will be at the opposite end from the outflow area. The <br />constructed height of the sedimentation pond embankment will be designed to allow for settling. During <br />construction, a registered professional engineer will ensure that the appropriate embankment height is <br />accomplished. For all sedimentation ponds, the entire embankment, including the surrounding areas disturbed <br />by construction, will be seeded after the embankment is completed, using the Topsoil Stockpile /Pond <br />Embankment seed mix described below. The active upstream side of the embankment where water will be <br />impounded will be riprapped or otherwise stabilized, where necessary. Areas in which revegetation is not <br />successful or, where rills and gullies develop, will be repaired and revegetated. <br />Colowyo will inspect the condition of each sediment pond, sediment trap, orfuture postmining stock reservoir <br />on a quarterly basis. All of these types of structures meet the requirements of an impoundment, and the <br />inspection procedures will meet the requirements under Rule 4.05.9 (17). Previously, Colowyo has received a <br />waiver from quarterly inspections for several existing stock reservoirs within the current permit area as <br />described under Section 4.05.9. This waiver changed the inspection frequency to annual. Following <br />construction of any future postmining stock reservoir proposed in the South Taylor area, Colowyo may <br />request a similar waiver but until that is approved, the quarterly frequency would apply. Results of all <br />impoundment inspections will be submitted annually. <br />South Taylor /Lower Wilson — Rule 4, Page 7 Revision Date: 7/21/14 <br />Revision No.: MR -135 <br />