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. • • iii iuiiiiiniiiiii <br />999 <br />~~ Cripple Creek & Victor Gold Mining Company <br />A Joint Ventura -Pikes Peak Mining Company, Manager <br />(~ R 7 Operations Office Englewood Office <br />!~~?~L~1V'/ P.O. Boz 191, 2755 State Highway 67 5251 DTC Parkway. Suite 700, Englewood <br />Victor, Colorado 80860 Colorado 80111 <br />(719) 689-2977 • FAX (719) 689-3254 (303) 889-0700 • FAX (303) 889-0707 <br />July 20, 1994 <br />SENT BY FACSIMILE -COPY FOLLOWS BY MAIL <br />Mr. Berhan Keffelew <br />Environmental Protection Specialist _ <br />Colorado Department of Natural Resources ~F : ~., l i~; r, <br />Division of Mines and Geology <br />Office of Mined Land Reclamation /U( ,22 1984 <br />1313 Sherman Street, Room 215 ~;,,,~, <br />Denver, Colorado 80203 y °'~ °'rur;~r~, <br />J 6 t'Nv. <br />Opy <br />Reference: Cresson Project: Permit Number M-80-244: Ironclad T,iilin~ Material - <br />Completion of Assessment of Water Quality -Addendum. <br />Dear Mr. Keffelew: <br />In response to the inquiry regarding our letter to you of July 8, 1994, we of'er the following. <br />The seepage and mixing model was re-computed for the underdrain area of Alaqua Gulch based <br />on more realistic assumptions than were employed in the Application; that is, they were <br />performed recognizing that the Ironclad material was to be separated from :he overlying and <br />underlying underdrain materials, and separated from water in the underdrain, by synthetic liner <br />material. We re-modeled the system based on the revised assumption that tl~n (10) percent of <br />the surface area of the soil liner material (Ironclad) allowed seepage. Tht: ten percent was <br />discussed as a reasonably protective assumption given that the seepage was Highly unlikely to <br />occur. It is discussed some more below. <br />This seepage water was then assumed to mix with 7343 gpm in the underdrain. The gpm rate <br />was predicated on the drain flowing full at the narrow portion of the underdrai ~. The prediction <br />was also developed for only 14 gpm which is a little higher than the average and which would <br />actually flow in the pipes well beneath the soil liner. The 14 gallon per mir ute is believed to <br />be an unrealistic underdrain flow for modeling because at that rate the flow ~+ill be completely <br />consumed in the pipe in the underdrain. It is highly unlikely, and probably impossible, that at <br />14 gpm, any parts of the Ironclad material would be in contact with that water because it would <br />flow at the base of the underdrain if, for some reason, it were not in the four-inch solid HDPE <br />pipe. <br />Justifying the selection of the ten percent is the fact that synthetic geomelnbrane liners are <br />carefully, and properly, installed, and then such installations are assumed by the EPA to contain <br />one hole, ten square millimeters in area, per acre of liner. Extending this frequency to the area <br />of synthetic liner that is located on top of the underdrain (4.6 acres), there n fight be 46 square <br />