Section 69-05.2-16-09 - Performance standards - Hydrologic balance -Sedimentation ponds1. General requirements. Sedimentation ponds must be used individually or in series and: a. Be constructed before any disturbance of the undisturbed area to be drained into the pond. b. Be located as near as possible to the disturbed area and out of perennial streams, unless approved by the commission. c. Meet all the criteria of this section. 2. Sediment storage volume. Sedimentation ponds must provide adequate sediment storage volume. Sediment storage volume must be determined using the universal soil loss equation, gully erosion rates, and the sediment delivery ratio converted to sediment volume, using either the sediment density or other empirical methods derived from regional sediment pond studies if approved by the commission. 3. Detention time. Sedimentation ponds must provide the required theoretical detention time for the water inflow or runoff entering the pond from a ten-year, twenty-four-hour precipitation event (design event). The theoretical detention time must be sufficient to achieve and maintain applicable effluent standards. The calculated theoretical detention time and all supporting materials must be included in the permit application. 4. Dewatering. The stored water must be removed by a nonclogging dewatering device or a conduit spillway approved by the commission, and have a discharge rate to achieve and maintain the required theoretical detention time. The dewatering device may not be lower than the maximum elevation of the sediment storage volume. 5. Each operator shall design, construct, and maintain sedimentation ponds to prevent short circuiting to the extent possible. 6. The design, construction, and maintenance of a sedimentation pond or other sediment control measures do not relieve the operator from compliance with applicable effluent limitations. 7. For sedimentation ponds designed to contain the runoff from a ten-year, twenty-four-hour precipitation event (design event), there must be no spillway outflow as a result of runoff from the design event or lesser runoff events, unless multiple runoff events occur before the pond can be dewatered in accordance with approved plans in the permit. 8. Sediment must be removed from sedimentation ponds on a periodic basis in order to maintain an adequate storage volume for the design event. 9. An appropriate combination of principal and emergency spillways or a single spillway must be provided to safely discharge the runoff from a twenty-five-year, six-hour precipitation event for a temporary impoundment, a fifty-year, six-hour precipitation event for a permanent impoundment, or a larger event specified by the commission. The spillways must be capable of safely discharging the required event when the impoundment is at high water elevation. Commission approval of open channel spillway grades and allowable velocities must be obtained and velocities must be nonerosive. Earth or grass lined spillways may be used only where sustained flows are not expected. 10. The minimum elevation at the top of the settled embankment must be one foot [30.48 centimeters] above the water surface in the pond with the emergency spillway flowing at design depth. For embankments subject to settlement, this minimum elevation requirement applies at all times. 11. The constructed height of the dam must be increased a minimum of five percent over the design height to allow for settlement, unless it has been demonstrated to the commission that the material used and the design will ensure against settlement. 12. The minimum top width of the embankment may not be less than the quotient of (H+35)/5, where H is the height, in feet, or (H+10.7)/5, where H is the height, in meters, of the embankment as measured from the upstream toe of the embankment. 13. The upstream side slope of the settled embankment may not be steeper than a horizontal to vertical ratio of 3:1 and the downstream side slope of the settled embankment may not be steeper than a horizontal to vertical ratio of 2:1. 14. The foundation area must be cleared of all organic matter, all surfaces sloped to no steeper than a horizontal to vertical ratio of 1:1, and the entire foundation surface scarified. Cutoff trenches must be installed if necessary to ensure stability. 15. The fill material must be free of sod, large roots, other large pieces of vegetative matter, and frozen soil, and in no case shall coal processing waste be used. 16. The placing and spreading of fill material must be started at the lowest point of the foundation. The fill must be brought up in horizontal layers in the thicknesses required to facilitate compaction and meet the design requirements of this section. Fill adjacent to structures, pipe conduits, and drainfill or antiseep collars must be compacted to a density equal to that of the surrounding fill by hand tamping or by using manually directed power tampers or plate vibrators. Compaction must be conducted as specified in the approved design. In lieu of the specific design requirements of this subsection and subsections 11 through 14, the operator may demonstrate that the design of the structure has a minimum static safety factor of 1.3 for a normal pool with steady state seepage saturation conditions. 17. If a proposed impoundment can meet the size and other criteria of 30 CFR 77.216, the following additional requirements must be met: a. An appropriate combination of principal and emergency spillways must be provided to safely discharge the runoff from a one-hundred-year, six-hour precipitation event, or a larger event as specified by the commission. b. The embankment must be designed and constructed with a seismic safety factor of 1.2 and a static safety factor of at least 1.5 for a normal pool with steady state seepage saturation conditions, or a higher safety factor as designated by the commission. c. Appropriate barriers must be provided to control seepage along conduits that extend through the embankment. d. The criteria of the mine safety and health administration as published in 30 CFR 77.216 must be met. 18. If an impoundment meets the class B or C criteria for dams (those located where failure would be expected to cause loss of life or serious property damage) in the United States department of agriculture, natural resource conservation service technical release no. 60 (TR-60), Earth Dams and Reservoirs, 1985, the following apply: a. The emergency spillway must comply with freeboard hydrograph criteria found in the minimum emergency spillway hydrologic criteria table in TR-60, or greater event specified by the commission. b. The embankment must be designed and constructed with a seismic safety factor of 1.2 and a static safety factor of at least 1.5 for a normal pool with steady state seepage saturation conditions, or a higher safety factor as designated by the commission. c. Foundation testing, as well as any necessary laboratory testing of foundation material, must be performed to determine design requirements for foundation stability. d. Appropriate barriers must be provided to control seepage along conduits that extend through the embankment. 19. Impoundment inspections. a. A registered professional engineer, or other specialist under the direction of a registered professional engineer, shall inspect each impoundment as required under subdivisions b, c, and d. The registered professional engineer and specialist must be experienced in the construction of impoundments. b. Inspections must be made regularly during construction. Reports for each inspection during construction must be prepared and maintained at or near the minesite. c. After impoundment construction is complete, the registered professional engineer shall promptly provide the commission a certified report that the impoundment has been inspected during construction on a regular basis and it has been constructed as designed and according to the approved plan and this chapter. The report must include a summary of the construction inspections, final storage capacity, and if applicable, a discussion of any deviations from the approved plan. d. After impoundments are operational, they shall be inspected at least yearly until removal of the structure or release of the performance bond. A registered professional engineer shall promptly provide the commission with an annual impoundment inspection report addressing any appearance of instability, structural weakness, or other hazardous conditions, depth and elevation of any impounded water, existing storage capacity, any existing or required monitoring procedures and instrumentation, and any other aspects of the structure affecting stability. A single report can address more than one impoundment; however, the condition of each impoundment must be noted separately. e. A copy of the inspection reports must be maintained at or near the minesite. 20. The embankment, including the surrounding areas and diversion ditches disturbed or created by construction, must be stabilized with respect to erosion and sudden drawdown by a vegetative cover or other means immediately after the embankment is completed. The active upstream face where water will be impounded may be riprapped or otherwise stabilized to protect the embankment from erosion and sudden drawdown. Areas where the reestablishment of vegetation is not successful or where rills and gullies develop must be repaired and revegetated according to section 69-05.2-15-06. 21. In addition to the requirements of subsection 19, all impoundments meeting the criteria of subsections 17 and 18 must be examined according to 30 CFR 77.216-3. Other impoundments must be examined at least quarterly by a qualified person for appearance of erosion, structural weakness, and other hazardous conditions. The annual inspection required by subsection 19 will be considered one of the examinations required by this subsection. 22. Plans for any enlargement, reduction, reconstruction, or other modification of dams or impoundments must be submitted to the commission. Commission approval of these plans is required before modification begins, unless a modification is necessary to eliminate a hazard to public health, safety, or the environment. 23. Sedimentation ponds or other sediment control measures may not be removed until authorized by the commission and the disturbed area has been stabilized and revegetated. The ponds or other measures may not be removed sooner than two years after the last augmented seeding unless the last augmented seeding is a supplemental seeding into an established vegetation stand that is effectively controlling erosion. When the pond is removed, the affected land must be reclaimed, unless the pond has been approved by the commission for retention. If the commission approves retention, the pond must meet all the requirements for permanent impoundments of section 69-05.2-16-12. N.D. Admin Code 69-05.2-16-09
Effective August 1, 1980; amended effective June 1, 1983; June 1, 1986; January 1, 1987; May 1, 1990; May 1, 1992; June 1, 1994; July 1, 1995; May 1, 1999; March 1, 2004; April 1, 2007.General Authority: NDCC 38-14.1-03
Law Implemented: NDCC 38-14.1-24