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COMMENTS RY COLORADO NINEO LAND RECLAMATION DIVISION' COMMENT 2. The design of the recently constructed pond at Pit 4 has not yet been approved under the permanent program by the Division. Water would be discharged from a 30" diameter culvert primary spillway onto a 600-foot slope mapped as a landslide deposit with slope gradients approaching 50%. Figure 9 indicates riprap placement for a short distance below both the emergency and primary spillways, but no further detail is provided. As required by Rule 4.05.7, a plan for a discharge structure designed according to standard engineering design procedures should be submitted to the Division. Energy dissipation should be provided wherever design flow velocities would result in erosion. Diversion of discharge flows along the contour to the adjacent stream channel may be an acceptable approach. RESPONSE A 6-inch diameter plastic pipe will be attached to the end of the 30" diameter primary spillway discharge pipe, The plastic pipe will be attached in a manner that diverts all low flows while not diminishing the ultimate capacity of the pipe, as shown on the attached sketch. The 6" diameter plastic pipe will extend directly down the natural slope, discharging into Grassy Creek. Intermittent anchors will be provided to structurally secure the pipe. This will eliminate the erosion potential under all conditions less severe than the 10 year-24 hour precipitation event. COMMENT 3. Statements in the text and Table 4 seem to indicate that the pond at Pit 4 has been sized to store the volume of a 10 year-24 hour precipi- tation event together with a one year accumulation of sediment without discharging. However, Figure 9, the Detail Drawing, indicates the water level in the pond resulting from a 10 year-24 hour storm would be two feet above the level of the primary spillway riser. The applicant should clarify whether any water would be discharged from the primary spillway as a result of a 10 year-24 hour or smaller runoff event. RESPONSE The existing riser pipe (principal spillway) crest elevation is 7522.50. The emergency spillway crest is 7524.50. The riser pipe crest will be extended 1 foot to elevation 7523.5. An area/capacity curve for the existing sediment pond was developed based on actual field measurements. This area/ capacity curve is attached. The curve shows that with the . extended riser the entire volume of the 10 year-24 hour event can be stored. A small amount of water would be discharged through a 5-inch diameter hole in the riser which is discussed in response to the next comment. 2-ss zzz-32