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. Rationale-Recommendation for Approval • July 26, 2000 Page 8 WAD CN of 0.2 mg/L. Since CRMW-3, located downgradient of [he above well is a compliance point set by DMG under Amendment No. 7, any adverse impact to ground water for the additional compliance parameters will be identified in that well. SGMW wells have been located in Squaw Gulch since 1994, and the Mined Land Reclamation Board allowed CC&V to place overburden upgradient of these wells. The groundwater monitoring wells located in the area were not considered vital (little or only intermittent groundwater flow was detected) so no compliance point was set under Amendment No. 7. The Division felt and still feels that since most of the surface water that expresses itself as groundwater will end up in the Moffat Tunnel, and that given the intermittent production of these early monitoring wells, and the fact that the Colorado Department of Public Health and Environment did not consider this drainage to be impacted by the operation, that no permit conditions or parameters needed to be set for the discharge. DMG believes that the new wells, which appear to be producing wells, could be used to gather baseline data to set compliance parameters. The approved numeric permit conditions for the existing compliance wells under Amendment No. 7 are as follows. A. Well CRMW-3B-63 (Arequa gulch): (a) pH range from 6 to 9, (b) Sulfate @ 1070 mgJL, (c) WAD CN @ 0.2 mg/L, (d) ZINC @ 2.0 mg/I., and (e) Manganese @ 8.1 mg/L. B. Well GVMW-8-A (Grassy Valley): (a) pH range from 6.5 to 8.5, (b) Sulfate @ 250 mg/L, (c) WAD CN @ 0.2 mg/L, (d) ZINC @ 2.0 mg/L, and (e) Manganese @ 1.0 mg/L. C. Well WCMW-6-234 (Bateman Creek): (a) pH range from 6.5 to 8.5, (b) Sulfate @ 250 mg/L, (c) WAD CN @ 0.2 mg/L, (d) ZINC @ 2.0 mg/L, and (e) Manganese @ 0.2 mg/L. 24. The 100-year, 24-hour design is not adequate, the design should be for much larger events. (R. Fay) DMG Response: For surface water diversion design, the Division utilized the design criteria for surface water diversion structures set by the Office of Surface Mining (OSM) Diversion Design Manual and the SED-CAD program, which accounts for peak flows and sedimentation. Based on the above criteria, any structure designed for [he 100-year, 24-hour event is considered a permanent structure. The 3.5 inches of rainfall for the 100-year, 24-hour event was selected for the region from [he U.S. National Oceanic and Atmospheric Administration's Isopluvial map. The peak runoff for the selected areas was calculated based on Soil Conservation Technical Release No. 55, "Procedures for Determining Peak Flows in Colorado". The procedure utilized the following parameters to determine peak flows or surface runoff from different watersheds: (1) precipitation, whether it occurs in the form of rain or snow; (2) soil and vegetative cover; and (3) mechanical treatment on a watershed, along with its topography and shape. All surface water designs for Amendment No. 8 are based on [he above criteria and meet the Division's requirements. In addition, all diversion channels that are designed to carry greater than 5 fps (five feet per second) will be appropriately rip-rapped to minimize erosion. The area did receive more than the usual amount of rainfall during the past few years. However, all surface water diversion structures are inspected during the spring and summer and have always been found to handle the flow adequately with minimum maintenance.