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~4 <br />4 <br />III'll'll!II"I'AI <br />.t~,~w <br />'~ <br />awREncE c. w~+irE ~.E. <br />1650 M. STREET PENROSE. COLORADO 81240 719-372-6461 <br />~C~C~~C~ <br />July 17, 1991 <br />Cathy Begej, Lead Specialist <br />Mined Land Reclamation Division <br />1313 Sherman Street, Suite 215 <br />Denver, Colorado 80203 <br />.lUL 2 t 199i <br />,~linsa L3tlL <br />Rzfi~n'~tirn viviS~ar: <br />Subject: Mined Land Reclamation Division letter dated <br />1991 concerning Rule 4.05.6, Combination Spillways <br />Dear Mrs. Begej: <br />May 15, <br />In accordance with the Divisions letter of May 15, 1992 and the <br />modifications to Rule no. 4.05.6 the Sedimentation Ponds at Twin <br />Pines No. 2 Mine have been reanalyzed to attempt t o comply with <br />the requirements for a separate emergency spillway. Review of the <br />Sedimentation Ponds at the Mine is as follows: <br />trTWIN PINES COAL SALES PONO <br />The Sedimentation Pond at Twin Pines Coal Sales was designed by <br />the Sail Conservation Service prior to 1983. An emergency <br />spillway was included in the design and construction of the pond. <br />To the best of my knowledge and belief the pond has not spilled <br />during storm events which have in all probability exceeded the 10 <br />year, 24 hour event. The pond does collect all of the run off <br />from the disturbed area of the Coal Sales facility. <br />BENCH POND AT THE MINE SITE <br />The "Bench Pond" at the mine site was originally constructed in <br />1985 under the contract for the Mine Site Preparation. The pond <br />was excavated to a depth of about 15 feet in the original <br />interbedded sandstone and shale formation. There is a minimum <br />distance of 30 feet from the tap of the excavation to the edge of <br />the slope descending to the access road. The pond has about a 3 <br />foot berm around the top of the two unexcavted sides. There is <br />approximately 6 feet of free board from the top of the 24 inch <br />spillway to the top of the berm. Run-off from the northerly mine <br />areas enters the pond through an 18 inch diameter CMP. Run off <br />from the southerly areas enters through a 24 inch CMP. <br />Approximately 40 gpm of mine water flaws into the 24 inch CMP. <br />The drainage into the ponds is separated by a raise in grade in <br />the roadway on the west side of the pond. The down slope side of <br />the Mine Site and road to the North Spoil Area is protected by a <br />3 foot berm. During major storm events ponding will occur behind <br />the inlet culverts, thus providing additional detention for run <br />