Laserfiche WebLink
v` s)r: ~k,b~~Vol~~me 1r <br /> <br />EXNIl~I-T Z-Z <br />r K-66 APIkouEp 9~a4~96 <br />TECHNICAL REVISION <br />HAYDEN GULCH MINE <br />-D«-n1a,>1 e <br />~I ~ I I~ ~ I~ ~ ~~ ~~~~ ~I~ <br />999 <br />Doc Date:12/11I2001 <br />POND HGS PRINCIPAL SPILLWAY STRUCTURE MODIFICATION <br />1.0 INTRODUCTION <br />H-G Coal Company (HGCC) is submitting herewith an application for a Technical Revision (TR) to <br />Permit No. C-80-003. The purpose of this submittal is to describe a design change to the principal <br />spillway structure for pond HG-8. The location of pond HG-8 is shown on Figure 1, Pond HG-8 <br />Watershed, <br />2.0 DISCHARGE STRUCTURE DESIGN MODIFICATION <br />As shown on Figure 2, HG-8 Discharge Structure Modification, the current principal spillway <br />structure at Pond HG-8 consists of a reinforced concrete structure backfilled with f 4 inch cobble. <br />The discharge system utilizes a 18 inch gated CMP outlet barrel pipe with a 12 inch CMP riser. The <br />invert elevation of the 18 inch gate is approximately 7,381.5 feet above mean sea level (MSL). The <br />barrel pipe slopes at approximately 0.0264 ft/ft. The top of the 12 inch riser is set at 7,387.9 feet <br />above MSL. <br />During the spring of 1996, HGCC implemented a shrub enhancement program. Pond HG-8 was <br />identified by HGCC, the Colorado Division of Minerals and Geology (Division), and the Colorado <br />Division of Wildlife (CDOW) as a desirable location for the shrub augmentation planting due to the <br />constant water source. To provide a permanent, stable, water impoundment and enhance soil <br />moisture conditions surrounding the pond, HGCC determined that an optimal water level for the pond <br />was 7,384.8 feet above MSL. <br />Monitoring by HGCC personnel indicates that spring RSP-2 and/or other pond inflows total <br />approximately 50 gallons per minute into the pond. To maintain the water level at the proposed <br />permanent elevation, HGCC proposes to install a 4 inch diameter HPDE decant pipe with an invert <br />elevation of 7,384.8 feet above MSL. Design details for the proposed 4 inch decant pipe are shown <br />on Figure 1. In conjunction with the installation of the 4 inch decant pipe, HGCC will replace the <br />existing 18 inch gated value with awater-tight cap or plug. <br />A sediment survey performed by HGCC in October 1995 and recent SEDCAD modeling indicate that <br />presently, pond HG-8's available storage capacity is approximately 11.89 acre-feet, assuming three <br />yeazs of sediment accumulation and that the pond is empty. SEDCAD modeling performed in <br />support of the principal spillway design change indicate, that with a permanent pool elevation of <br />7,384.8 feet above MSL, 6.30 acre-feet of the available storage would be filled with water. This <br />indicates that with a permanent water level at 7,384.8 feet above MSL, HG-8 would have 5.59 acre- <br />c:\87'MgB~primaryWiul~erg.Va 7/16/96 <br />