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~; TUTTLE APPLEGATE RINDAHL, INC. Consultants for Land and Resource Development Mr•. Sohn Doerfer Mi reed Land Reclamation Divisi~~n July 2c, I966 Page 6 Channel velocities ar•e also a ct~ncern thr•o+agh the mining area. Your- observation oP it Fps velocit les in channelizeci areas is correct. These conditions cur•r-ent ly exist in +anmined portions of the basin. Protection +~f the entr•ancc~:~ t~~ the channel can be done by dumped slope protection such as buried concrete r•ubb le, r•ipr•ap, revegetat ion, artificial. meanders t~~ slow Y"lows d~~wn. Reasonable measures will be taken to reduce velocities as nr+_~cfi as is pr•act ical, however, there ar•e areas in existence rn~w where fiigher velocities occur during ma,7or storms. Water quality degr•adat ion is always a concern. We ar•e in the process of working with the State Department of flea ltFr ft-+r certificat i~~n under^ the 401 r•egulat ions that apply to a Corps of Engineers 404 permit. Our conversations with Mr. John Farrow of this Department indicate that we will have some minimum design st andar•ds to prevent discfi ar•ge .]r"" material fr+anr active mining areas <10 year event). Tfie erosion contr•o! meas+ar•e pr••~posed for both +aplands and lowlands mining areas are reasonable to minimize the addition of sediment to the stream. As pr•evio+asiy poinL-eci out, this stream is ephemeral and nra,7or i~~adings to the stream w+~uld only occ+.ar during storm events. Low fr•eq+aency st+~rms such as the I00 year event are going to have a large anro+ant of sediment car•r led regardless of wfietfier• mining i=:: g~~ing ~~n ~~r not. The concern about impacting the cottonw+~ods along the stream channel are valid. We have proposed a monitoring pr•+~oram ti:] determine what tfie lowering of the gro+andwater table will d+~ to the health of tfie trees. This iower•ing will not occur at: an instant one+~+~s point in time. Material r•emovai is expected to progress down the valley at approximately 1l9~ mile of stream channel per year. The average slope ~~f Coal Creek. is approximately 25 feet per mile. This wo+_tld mr~an that the drop in gr•+~undwater w~~uld ~~ccur over- a three year period. This Dives the trees an oppor•t +anity to p+1t down new r~~•~ts as the water level drops. Our inq+airies and st+_~d ies have shown that no one r•eai ly has a definite answer- on thc± impacts. That is why we have a s~~lid nr~-~nitor•ing program in place. If it becomes apparent that the cottonwoods arc st r•essed due t~~ mining, there the mitigation meas+ares will be instituted.