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Mr. Gerald McPhee Northern Coal Company P.O. Box 17583 T.A. Denver, Colorado 80217 Re: Curtis Creek Crossing Our File No. 78-345 Dear Mr. McPhee: D EPARTMENT OF NATURAL RESOURCES D. Monte Pascoe, Executive D~reetor A11NEU Lf1NU RI~,C1,A1~1A'CION 423 Centennial Building, 7373 Sherman Street Denver, Colorado 80203 Tel. (303) 839-3567 ~~I ~I~I~~I~~II~~'~~ 999 David C. Shelton January 27, 1981 Director - With the receipt of your letter of January 6, 1981, in response to the remaining concerns of Jim Pendleton and Roy Cox of our office, the Division finds that the hydrologic and subsidence monitoring system for mining under Curtis Creek is adequate. It is.stipulated that a map locating the additional subsidence monitoring points be forwarded to the Division prior to driving entries under Curtis Creek. As you know, the Division is concerned with Northern's inability to monitor ground water wells due to the surface owner conflict. Northern should continue to pursue a surface owner's agreement to gain access to monitor the wells. The .present monitoring system may not adequately characterize the hydrology of the entire area affected by the Meeker area mines. Monitoring of ground water wells will in all probability be necessary to make a determination of probable hydrologic consequences as required by 4.05.13 of the Colorado Regulations and Section 34-33-110(2)(1) of the Colorado Surface Coal Mining Reclamation Act. Lack of a complete monitoring system including data from ground water wells, may jeopardize the attainment of Permanent Program permit approval for the Meeker area mines.. As previously agreed to in your letter of December 11, 1980, it will be incumbent on Northern to initiate appropriate mitigation measures should monitoring in- dicate that hydrologic problems (e.g. disruption of flows in Curtis Creek and/or depletion of the Curtis Creek alluvial aquifer) are occurring. Northern should be aware .that in the undermining of Curtis Creek, monitoring wells would provide an additional check, along with surface flaw and mine inflow, as to the effect of mining on the alluvial aquifer. Without groundwater monitoring, any significant decreases in surface flow accompanied by increased mine inflows will be attributed to a depletion of the aquifer as a result of mining activity. In the event of interpretive prcblems, worst. case assumptions will rule. S ----'T""C'1. ~ -•~• ""z~L~""""'"'^"'->r. .-. --; .~s:-.iT»--a . _z wa*.^NF+~'--v^-r-s.a~- a.-wrs e--~--+... .. __... .. .. .__ ._ ., .. .. ~ _ ,. .. ~.r-~..-,