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~_ Y ~~ ~~ w r~ w ~-~ ~=- TUTTLE APPLEGATE RINDAHL, INC. Consultanu for Land and Resource Development Mr^. Aick. Ever•ist, Jr. L. G. Ever ist, Inc. S+aly 19, 1968 Page 4 The f~~ur•th and final itern addressed in c~ur• invest igat i•~n nas t•~ d•~ witn cr•eat ino a wet nti ne and ai 1•~wing fi•~ws to ent er• the pit'. area from Lone Tree Crew.. The crass sections that were oL~t ted give a definitive answer-. As shown, the mining oper•at ion ice, ~~. minimum of 'c"c' feet ab•~ve the stream channel invert ~~f L•~ne Tree Creek.. Tn er•efor•e, it is phys icai ly intp•~ssible P•~r fI•~ws fr•otti this Creek. t•~ enter- the mining area unless the stream is Y"I•~w1nc_ 2c feet deep thr•~~uph this area. The U. S. G. S. has calculated the mean ann+_~aI discharge of the Lane Tree Creek. basin <23 square miles) to be i, 463 acre-feet. TAH calculated a 54+0 year- storm for- th15 basin using the C•~lor•ad~~ Water- Conservation Ooar•d Technical Manual No. 1. This ntan+aal ie: very rough end should ~~nly be used far est intat ing purposes. The results of this calculation show a peak. discharge f~~r L•~ne TreE:e Creek of 2?, 000 cfs. The channel capacity •~f Lone Tree Ct^eek. was calculated using mannings formula for- open channel fl•~w. Th E~ results of this calc+_~lat i~'+ri are n~~t exact but glues a r•eas~~nab le estimate ~~f depth of flow. The depth +~f flow in Lone Tree Cr•eef~. during a 500 year st•~r•nt would range from 10 t~~ 15 feet. Ther•efor•e, based on this data, it does n•~t appear- possible for• stream ch anr~el flt~ws t•~ enter- the mining site, ever+ d+_~ring a 500 year- storm. The proposed mining ~~perat ic+n is not designed to create a wet mining pit as is commonly seen along nta~or r•iver•s such as thc~ 5~~+ath Platte. The cress secti~~ns and the r•eclantati~~n plan sh~~w that p~~sit ive dr•ainaae will be maintained throughout the pit. In addit i•~n, the mining wi 11 be dune an average 'c'c feet ab•~ve the Lone Tree Creek. channel, thus prevent ino nrior•at YOn of surface flews thr~~ugh the al luviunt 1nt•~ the pit. Based .ten this data, if the mining and reciantation plan arse followed as designed, it i~:~ physically intp~~ssible f~•r this ~~perat ion t~~ impound either surface or groundwater flows in the area. A summary of o+_~r investigation and this letter is es foll~~ws: 1. Dased on borehole Oata and infortirat ion found from the U. S. Geological Survey, the proposed mining plan will not exp~~se gr•oundwater• either during the oper•at ion or• after mining Yip: completed.