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~ -~ Seneca II-W Prelim. Adequacy - 9 - March 5, 1985 Sediment Control Structure - Ponds, Impoundments, Diversions - Rule 4.05 1. Rule 4.05.9(1)(e) requires that any structure having an embankment in excess of 10 feet in vertical height be designed and constructed in accordance with C.R.S. 37-87-105. These regulations are under the jurisdiction of the State Engineer's Office. In April, 1984, C.R.S. 37-87-114.5 was signed allowing the State Engineer's Office to exempt siltation structures reviewed under C.R.S. 34-33 bylaws. The Division, in consultation with the State Engineer's Office, feels that since Pond 006 is a permanent impoundment designed to function as a siltation structure during mining and reclamation, it qualifies for review under the State Engineer's jurisdiction, and pond designs have been sent to the State Engineer's Office for review. The review will probably take several months, however, as long as the operator commits to complying with the findings of this review, it will not delay the permitting process. 2. Peabody proposes to pump water from the water supply well to Pond 006 for storage and use as dust control. This pond has a gated dewatering device which must be open during mining and reclamation to allow dewatering of the design storm. This may not allow for adequate dead water storage. If Peabody wants dead water storage in this pond, they will need to provide additional pond volume and place the dewatering device to allow dewatering and subsequent adequate storage for the 10-year 24-hour storm. 3. Outflow hydrographs should be presented for the dewatering device to ensure that the pond will be dewatered within 48 hours but no earlier than 24 hours. 4. While velocities in the emergency spillway will not be excessive, the applicant has not mentioned any embankment protection to be utilized. What protection will be utilized in the emergency spillway? 5. No construction details were presented for the sediment pond. These should be included in the permit application. 6. How much material is planned for excavation from the pond and where will this material be disposed of? 7. No plan for pond maintenance, periodic sediment removal, and periodic inspections was presented in the permit application. This should be addressed. 8. No design for the determination of spacing for the anti-seep collars was presented in the permit application. This should be presented. 9. A well permit must be obtained prior to drilling the proposed water supply well.