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way associated with County Road 361. Therefore, a discharge pipeline was located in an area of the tailing impoundment feature such that pipeline length as well as internal basin cut-and-fill requirements were optimized (Figure 7-A) to establish the post-reclamation drainage pathway. A further consideration was minimization of excavation requirements as associated with pipeline construction. A major design consideration was the incorporation of a minimum 100-foot setback from the impoundment crest to mitigate impoundment stability and erosion concerns. This setback provision was made in conjunction with post- excavation backfill compaction requirements to fully restore the existing impoundment crest integrity. The longitudinal cross-section along the proposed culvert alignment indicates a controlling slope gradient of 4% along the initial 100 feet of pipeline. Evaluation of culvert sizing indicates that an 18-inch diameter pipe with smooth interior (Manning's value of "n" = 0.010) will satisfactorily convey the required 13.0 cfs under half-full flow conditions. Full-flow conditions indicate a maximum flow capacity of approximately 27 cfis. Both flow velocities exceed recommended minimum (per ASCE guidelines for gravity flow) "self-cleaning" velocities. General design specifications include a flared inlet (with a field constructed security/trash grate installed), followed by an approximate 100-foot @ 4% slope run. A 22-1 /2 degree elbow will direct the line downward at a point underlying the existing tailing impoundment crest. The continuation of an approximate 60-foot @ 43% slope run will result in a nominal 3 to 4-foot trench depth (and an approximate 2-foot resultant cover) along the face of the tailing impoundment down to the vicinity of the impoundment toe. At that location, a 22-1/2 degree elbow will redirect flow outward along an approximate 10-foot @ 20°~ slope run equipped with a flared outlet (optional -dependent on field conditions) discharging to a coarse rock apron immediately above and extending to the high-flow bank level of Sneffels Creek. 3.0 SUMMARY Based on the indicated data and criteria, the drainage system defined within this report will satisfactorily convey the 100-year/24-hour precipitation event. Construction of the proposed drainage culvert will avoid encroachments upon County rights-of-way while protecting the structural integrity of the existing tailing feature. Design drawings, associated run-off calculations and culvert design data are provided in the accompanying appendices. 3