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STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Department of Natural Resources <br />7313 Sherman St., Room 215 <br />Denver, Colorado 80203 <br />Phone: (303) 8663567 <br />FAX: (303) 832-8106 <br />C7 EaV <br />Date: / March 6, 2006 <br />To: ~ Russ Means, Grand Junction Field Office <br />From: ~ Harry Posey ~Z~~`G~~ <br />Kate Pickford <br />I~ocS <br />COLORADO <br />DIVISION O F <br />MIN SRALS <br />GEOLOGY <br />RECLA NATION•NINING <br />SA FETY•SCIENCE <br />Bill Owens <br />Governor <br />Russell George <br />Executive Director <br />Ronald W. Canany <br />Division Director <br />Natural Resource Tmstee <br />RE: / Third Review: DMO status Cotter Corporation Uranium Mines, Montrose County: <br />JD-6 Mine, M-1977-310 <br />'~ C-JD-8 Mine, M-1984-014 <br />~ JD-9 Mine, M-1977-306 <br />'GSM-18 Mine, M-1987-116 <br />This review responds to the February 7, 2006 (reed Feb 8) letter in "RE: Response to the January 17, <br />20061etter from the Colorado Department of Mining and Geology (DMG)." In that letter, the Operator's <br />consultant, GeoScience Services, further explained and interpreted results of hydrologic modeling and <br />modeling assumptions pertinent to potential Designated Mining Operation (DMO) status for the above- <br />captioned mines. This review covers all previous submittals regarding DMO status by reference. <br />The applicant explained, and the Division accepts, that the model simulations evaluate dispersion and <br />diffusion, rather than dilution of potential contaminants in the unsaturated zone, and not necessarily the <br />saturated zone, beneath waste rock that has the potential to release acid and/or toxic substances to <br />groundwater, according to SPLP test results. <br />The Division considers the following features or assumptions as either acceptable or "conservative." <br />1. A "realistic" modeling approach would include the effects of sorption. By ignoring the potential <br />effects of sorption in the model, the model is "conservative." <br />2. The model assumes that waste rock piles would contribute a constant discharge under a constant <br />head. This is an acceptable means of handling the calculation for dispersion the unsaturated zone, <br />and simplifies the modeling without compromising its accuracy or utility. <br />3. The model assumes that waste rock piles will release contaminants to the unsaturated zone or <br />elsewhere in concentrations indicated by the SPLP results. This assumption is very conservative. <br />SPLP test results tend to overestimate contaminant concentrations for several reasons, namely: <br />a. the surface area of the test samples far exceeds that actually available in the field; <br />b. tumbling the samples for the SPLP test maximizes exposure between fluid and rock; and <br />c. tumbling produces some degree of autogenous grinding, which further increase surface and <br />exaggerates the contact between fluid and rock. <br />4. The model assumes that surface water inflow, into bedrock, which is comprised of mudstone, <br />siltstone and sandstone, equals 1/10 of the average annual rainfall. This is very conservative. <br />Office of Office of Colorado <br />Mined Land Reclamation Active and Inactive Mines Geological Survey <br />