REV105268 - Laserfiche WebLink

Home Browse Search

iii iiiiiiiiiiiiiiii • STATE OF COLORADO DIVISION OF lv11NERALS AND GEOLOGY Department of Nmural Re<ources I i I ;Sherman SL. Room _15 Dam eq Colorado 80203 Phone 1303)8h6-3567 FAS. ISU31 N32-8106 June 20, 2000 1~ D I V 15 1 0 V O F MINERALS Sc GEOLOGY 0.ECLA MATIpN MINING•SAFETY Mr Bill Lyle 6111 o..rns Gnvrrnor Battle Mountain Resources Inc Gri; E. lValdrer PO Box 1627 E.z<„r„e D„e<+„r Battle Mountain N V 89820 ~+~<n,el e. wrtti Dw~sion Dueclor Re: Revised Stormwater Management System, San Luis Project, M-88-112 Dear Mr. Lyle: The Division received and reviewed BMRI's Technical Revision 29 (T.R.-29) submittal regarding a request to construct (or revise) new detention and retention ponds and a stonrtwater conveyance channel to route stormwater runoff from the upgradient watershed areas (from the West Pit) through the West Pit to two retention ponds and through the existing BMP (drop structure and culvert) to the Rito Seco. The revised stormwater management system was necessary due to the recent construction of a diversion system across waste dump "C" and the construction of the ponds and R!O facilities within the West Pit. Stormwater runoff into the West Pit would have exceeded the outlet capacity of the existing stotmwater management system as a result of the recent construction activities. There are a couple of items that need to be addressed: 1) The text of T.R.-29 contains references to various drawings that are confusing. For instance, on page 4 (second to the last paragraph) it is stated that "drawings 6 and 8 provide additional information on the channel design:' There is no drawing 8 and drawing 6 contains cross section information of the retention ponds, no[ the channel design (that is contained on drawing 5). You refer to drawing 8 on pages 4 and 5. Please address. 2) It is stated in T.R.-29 on page 2 that previous documents "provide the watershed peak flow and cortesponding runoff hydrograph into the West Pit area." However, according to the submittal, it is stated that "the resulting peak runoff from the upgradient watershed is approximately 152 cfs" which does not appear to represent the projected peak flow from the referenced documents. The watershed upgradient of the Pink Gneiss area is projected to contribute 172 cfs (from [he Interim Evaporation Pond System Design submittal) and the watershed above waste dump "C" is projected to contribute 72 cfs. This amounts to 244 cfs, not 152 cfs. The difference may be because the diversion ditch in the West Pit was designed for the 100 year, 24 hour event not the 10 year, 24 hour event (a 2.4 inch precipitation event versus a 1.9 inch event). Please address.