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1',igc 2 <br />Turn Gillis <br />!larch Z2, 1g87 <br />T will dwe(1 hcceafter upon thu question of demonstrating the required <br />s t.rbili ty u: the rcc•laimed confi guraf:ien of the permit area, whatever it <br />may bc. <br />As referred to i.n my memo of August 12, 1980, which was forwarded to the <br />applicant, the Otchacd Valley mine site is located w.iChia an area of potential <br />slope instability. The Colorado Geological Survey (Rahc Junye, et, al.), in <br />accordance with house Dill 1091 (C. R.S. 1973, 29-65.1.-101, et. se .), has <br />rrmpped the Dowie quadrangle and five adjoining quadrangles to delineate areas <br />of geologic ha::ards that could cause an economic loss or affect the safety <br />of citizens of Colorado. Copies of the segment of that rmzp which pertains <br />to the Orchard NaZley sucface facilities and the corresponding explanations <br />arc attached to this memorandum for the applicant's information. The maps <br />divide the area of the mine's surface improvements into areas designated <br />as "potentially unstable slope", "potentially unstable slope and expansive <br />soil or roc}:", "rock, fall", "rock. fall and expansive soil or rock.", and <br />"sheet flow flooding and erosion". 1'he entire Orchard Valley mine surface <br />facility area is designated as one or another potential geologic hazard. <br />I have er.aminerl low altitude (1:G000 scale) stercographic aerial photography <br />of the Ot'chard Valley permit area, firnrn under contract for the Colorado AfLRD <br />on September .20, 2980. As is characteristic in the area of the north fork <br />of the Gunniswr River, the mine site's geomorphic surface features suggest <br />numerous past episodes of mass movertiont phenomena (landsliding, rack fall, <br />etc.). Discrete slope failures arc evident on the photography in the uphill <br />slope of the permanent diversion ditch located at the upslopc boundary of the <br />surface facility area. 71n additional slope failure is evident to the immediate <br />west of sediment pond N9, below the mine site. The areas of instability above <br />the diversion ditch appear to b~, located astride the lateral shear zones of a <br />large pre-e>:isting landslide mass. These observations, corroborated by <br />inspections performed by G14LRD perso+vrel, accentuate the importance of considering <br />potential rrvrs; movenknt hazard: in evaluating the stability of any proposed <br />reclaimed configuration for the Orch~rrrl Valley Mine. <br />In summary, the Orchard Valley mine site has been designated as a potential <br />geologic ha::.~rd, and the designation has been substantiated by both aerial <br />and field examinations. In li~lliC ul the existence of /rutential geologic <br />h: r,:n r~]s, it is dpprol~rin(c Ihnt nrul l~r r+posnd zc•c l,~imr:d ccn(i<luration for the <br />Orchard l',r11cq !line incnrponrt~~ ,r thorough gcotuclui.ic•a1 invcsCigation. Tho <br />regulatory agencies involved in approving the plan for such facilities would <br />be seriously remiss in t:hcir ohligat.i.on to protect the health and safety of <br />the citizens if they fail to require a thorough enyincering design in keeping <br />with the rurrc~nt state-of-the-art, as would the applicant. <br />(cont'd) <br />lid i w , <br />