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• • iiiiiiiiiiiniuiii <br /> <br /> STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />DCp•ltlmenl of NaW ml Ke~nur~e5 <br />1{ 1 4 Sherman SL, Koum _' 1 5 <br /> <br />Dcnvt•r, Gilnradn HIL II I II~~~ <br />Phone: 111111 H66- 4567 <br />FA%~ 1]11.{1 H7! HI116 <br /> DEPARTMENT OF <br /> <br />Date: January 29, 1996 ~ ~LJ~ <br />To: Janet Binns K..vKnni"` <br />/ c,n.c~nm <br />/ I~un". S L°chhead <br />From: Kent Gorham ~~ {.e~°~w"•o~«•~~°~ <br />M i<hael tl Long <br />CC: Dan Hernandez D1"iiinDnc"°' <br />RE: Phase I and Phase II Bond Release, La Plata Mine, ,fC-87-082 <br />I have completed review of the 1995 sedimentology Analysis portion <br />of the Phase I and Phase II Bond Release for the La Plata Mine. <br />Review of the methods section indicates that the consultant chose <br />to compare sediment production of an adjacent undisturbed area to <br />the reclaimed area using the Universal Soil Loss Equation. In this <br />case, the two communities being compared are substantially <br />different due to numerous limitations. In this case, it appears <br />that this was un-avoidable. However, normally we would expect to <br />compare the cover and sedimentology characteristics (slopes, soils, <br />etc.) of the reference area to those of the reclaimed area. That <br />way, the model more closely simulates actual conditions. <br />In both areas modeled, slopes are steep. Erodibility values area <br />book values and assume conservative conditions. Cover factors were <br />selected from review of actual data collected and practice was not <br />included in either calculation. <br />Based on the selected input, the calculations indicate the <br />reclaimed area produces less than one-half the sediment of an <br />adjacent area. <br />While modeling is one technique that the Division accepts, there <br />are additional methods to demonstrate that reclaimed areas produce <br />less than, or equal to, sediment loads when compared to the pre- <br />mining condition. Some of these are actual water sampling results, <br />rill and gully reports (demonstrating a lack of same), livestock <br />pond surveys, results of past inspections, and other pertinent <br />qualitative evaluations. As I have not been to the site, I will <br />rely others to conclude that the site is stable and is not <br />presently showing evidence of erosion beyond what is occurring in <br />the native, undisturbed areas. <br />Unless you have concerns of your own, I believe the Division can <br />accept the operators sedimentology model at this site. If you have <br />questions let me know. <br />