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SHLPHE~ L<~~ <br />Scptetnber 27, 1999 SMI #]00267 <br />Mr. James Dillie <br />Colorado Division of Minerals &Geology <br />1313 Sherman, Room 215 <br />Denver, Colorado 80203 <br />Subject: Changes to the Draft Diversion Channel Desie,3t in the East Pit Area, San Luis <br />Project, Costilla County, Colorado for Battle Mountain Resources, Inc. <br />Deaz Mr. Dillie: <br />Per your telephone request, this letter discusses mutually agreed upon changas to the "Draft <br />Diversion Channel Design in the East Pit Area, San Luis Project; Costilla County, Colorado" <br />report prepazed for Battle Mountain Resources, Inc (BMRI). <br />1) On page 2, Section 12.2, the next to last sentence refers to a curve number of 89 for the <br />reclaimed waste rock azea -This should be a curve number of 87 to be co~tsistent with the <br />HEC-1 run and Table 1. <br />2) Discharge into the backfilled West Pit and the Stormwater Management Plan. (SWMP) -The <br />BMP (standpipe) located in the middle of the West Pit will remain open. "The outfall will not <br />be removed following construction of the slurry wall. The BMP will Yemain open to <br />continue diverting stormwater runoff and trapping sediment in the West Pit area. <br />3) Gabions instead of grouted riprap -Due to the late season start of construction of the <br />diversion channels, gabion baskets will be used on the steep slope areas instead of grouted <br />riprap. A revised Table 3 showing the channel segments where gabions will be used is <br />attached. <br />4) Technical Specifications - A revised copy of Appendix E, Technical Specifications; is <br />attached that includes installation of gabion baskets. Channel Segments 5, 12; 16, and 18 <br />will be lined with gabion baskets. A three-inch layer of grout (gunite) will Used to cover the <br />top of the baskets to reduce the interface velocities with the waste rock aAd to protect the <br />wire. <br />5) Energy Dissipaters -Energy dissipaters will be constructed of gabion baskets covered with <br />grout (gunite) to divert the flow from steeply-sloped channels into tha shallow-sloped <br />channels. Gabion baskets aze frequently used at the outlet of culverts for energy dissipation <br />as standazd engineering practice as shown on the attached figures from the Maccaferri <br />Gabions, Inc. brochure. <br />L'noi>ovunral G~ Endinrc>ing Contvltann <br />3801 Auromauon V(>ay. Suite 100 <br />Fors Collins. cr) 80525 <br />Phone: (970) 223-9600 <br />k`az: (970) 22;i-7171 <br />vrnw._hepmill.com <br />d0 'd 595 'ON Hd.~ ~ 8Z-9I 1dOW 66-1Z-d3S <br />