SECTION 460:20-45-12. Hydrologic balance: siltation structures

(a)   Definitions. For the purposes of this Section only disturbed area shall not include those areas:

(1)   In which the only surface mining activities include diversion ditches, siltation structures, or roads that are designed, constructed and maintained in accordance with this Subchapter; and

(2)   For which the upstream area is not otherwise disturbed by the operator.

(b)   General requirements.

(1)   Additional contributions of suspended solids, sediment to streamflow, or runoff outside the permit area shall be prevented to the extent possible using the best technology currently available.

(2)   All surface drainage from the disturbed area shall be passed through a siltation structure before leaving the permit area, except as provided in Paragraph (b)(5) or (e) of this Section.

(3)   Siltation structures for an area shall be constructed before beginning any underground mining activities in that area, and upon construction shall be certified by a qualified registered professional engineer or registered professional land surveyor to be constructed as designed and as approved in the reclamation plan. The certifying engineer or land surveyor shall have experience in pond construction.

(4)   Any siltation structure which impounds water shall be designed, constructed and maintained in accordance with Section 460:20-43-14 of this Chapter.

(5)   Siltation structures shall be maintained until removal is authorized by the Department and the disturbed area has been stabilized and revegetated. In no case shall the structure be removed sooner than 2 years after the last augmented seeding.

(6)   When siltation structure is removed, the land on which the siltation structure was located shall be regraded and revegetated in accordance with the reclamation

plan and Sections 460:20-45-43 through 460:20-45-46 approved by the Department for retention as permanent impoundments may be exempted from this requirement.

(c)   Sedimentation ponds.

(1)   When used, sedimentation ponds shall:

(A)   Be used individually or in series;

(B)   Be located as near as possible to the disturbed area and out of perennial streams; unless approved by the Department;

(C)   Be designed, constructed, and maintained to:

(i)   Provide adequate sediment storage volume per acre of disturbed area draining into the structure;

(ii)   Provide adequate detention time to allow the effluent from the ponds to meet State and Federal effluent limitations;

(iii)   Contain or treat the 10-year, 24-hour precipitation event ("design event") unless a lesser design event is approved by the Department based on terrain, climate, other site-specific conditions and on a demonstration by the operator that the effluent limitations of Section 460:20-45-9 will be met;

(iv)   Provide a non-clogging dewatering device adequate to maintain the detention time required under Paragraph (c)(1)(C)(ii) of this Section;

(v)   Minimize, to the extent possible, short circuiting;

(vi)   Provide periodic sediment removal sufficient to maintain adequate volume for the design event;

(vii)   Ensure against excessive settlement:

(viii)   Be free of sod, large roots, frozen soil, and acid- or toxic-forming coal processing waste; and

(ix)   Be compacted properly,.

(2)   A sedimentation pond shall include a combination of principal and emergency spillways or a single spillway configured as specified in Paragraph (c)(2)(A) of this Section, designed and constructed to safely pass the applicable design precipitation event specified in Paragraph (c)(2)(B) of this Section, except as set forth in Paragraph (c)(2)(C) of this Section.

(A)   The Department may approve a single open channel spillway that is:

(i)   Of nonerodible construction and designed to carry sustained flows; or

(ii)   Earth- or grass-lined and designed to carry short-term infrequent flows at non-erosive velocities where sustained flows are not expected.

(B)   Except as specified in Paragraph (c)(2)(C) of this Section, the required design precipitation event for a sedimentation pond meeting the spillway requirements of Paragraph (c)(2) of this Section is:

(i)   For a sedimentation pond meeting the size or other criteria of 30 CFR Section 77.216(a), a 25-year 6-hour event, or greater event as specified by the Department.

(ii)   For a sedimentation pond not meeting the size or other criteria of 30 CFR 77.216(a), a 100-year 6-hour event, or greater event as specified by the Department.

(C)   In lieu of meeting the requirements in Subsection (c)(2)(A) of this Section, the Department may approve a sedimentation pond that relies primarily on storage to control the runoff from the designed precipitation event when it is demonstrated by the operator and certified by a qualified registered professional engineer or qualified registered professional land surveyor in accordance with Section 460:20-27-14(a) of this Chapter that the sedimentation pond will safely control the design precipitation event, the water from which shall be safely removed in accordance with current, prudent, engineering practices. Such a sedimentation pond shall be located where failure would not be expected to cause loss of life or serious property damage, except where:

(i)   In the case of a sedimentation pond meeting the size or other criteria of 30 CFR 77.216(a), it is designed to control the precipitation of the probable maximum precipitation of a 6-hour event, or greater event as specified by the Department; or

(ii)   In the case of a sedimentation pond not meeting the size or other criteria of 30 CFR 77.216(a), it is designed to control the precipitation of a 100-year 6-hour event, or greater event as specified by the Department.

(d)   Other treatment facilities.

(1)   Other treatment facilities shall be designed to treat a 10-year, 24-hour precipitation event unless a lesser design event is approved by the Department based on terrain, climate, other site-specific conditions and a demonstration by the operator that the effluent limitations of Section 460:20-45-9 will be met.

(2)   Other treatment facilities shall be designed in accordance with the applicable requirements of Paragraph (c) of this Section.

(e)   Exemptions. Exemptions to the requirements of this Section may be granted if:

(1)   The disturbed drainage area within the total disturbed area is small; and

(2)   The operator demonstrates that siltation structures and alternate sediment control measures are not necessary for drainage from the disturbed area to meet the effluent limitations under Section 460:20-43-9 and the applicable State and Federal water quality standards for the receiving waters.

(f)   Performance standards.

(1)   General requirements. Sedimentation ponds shall be used individually or in series and shall:

(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 Department;

(C)   Meet all the criteria of this Section;

(2)   Sediment ponds shall provide adequate sediment storage per acre of disturbance draining into the structure;

(3)   Detention time. Sedimentation ponds shall provide the required theoretical detention time for the water inflow or runoff entering the pond from a 10-year, 24-hour precipitation event (design event).

(4)   Dewatering. The water storage resulting from inflow shall be removed by a non-clogging dewatering device or conduit spillway approved by the Department.

(5)   Each operator who conducts underground mining activities 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 in accordance with this Section shall not relieve the operator from compliance with applicable effluent limitations as contained in Section 460:20-43-9.

(7)   There shall be no out-flow through the emergency spillway during the passage of the runoff resulting from the 10-year, 24-hour precipitation event or lesser events through the sedimentation pond.

(8)   Sediment shall be removed from the structure when the sediment storage volume is 80% filled;

(9)   An appropriate combination of principal and emergency spillways or a single open channel spillway as specified in 9(c)(2) shall be provided to safely discharge the runoff from a 25-year, 6-hour precipitation event, or larger event specified by the Department. The elevation of the crest of the emergency spillway shall be a minimum of 1.0 foot above the crest of the principal spillway. Emergency spillway grades and allowable velocities shall be approved by the Department.

(10)   The minimum elevation at the top of the settled embankment shall be 1.0 foot above the water surface in the pond with the emergency spillway flowing at design depth. For embankments subject to settlement, this 1.0 foot minimum elevation requirement shall apply at all times including the period after settlement.

(11)   The constructed height of the dam shall be increased a minimum of 5 percent over the design height to allow for settlement unless it has been demonstrated to the Department that the material used and the design will ensure against all settlement.

(12)   The minimum top width of the embankment shall not be less than the quotient of (h+35)/5, where H is the height, in feet, of the embankment as measured from the upstream toe of the embankment.

(13)   The combined upstream and downstream side slopes of the settled embankment shall not be less than lv:5h, with either slope steeper than lv:2h. Slopes shall be designed to be stable in all cases, even if flatter side slopes are required.

(14)   The embankment foundation area shall be cleared of all organic matter, all surface sloped to no steeper than lv:lh, and the entire foundation surface scarified.

(15)   The fill material shall be free of sod, large roots, other large vegetative matter, and frozen soil and in no case shall coal-processing waste be used.

(16)   The placing and spreading of fill material shall be started at the lowest point of the foundation. The fill shall be brought up in horizontal layer of such thickness as is required to facilitate compaction and meet the design requirements of this Section. Compaction shall be conducted as specified in the design approved by the Department.

(17)   If a sedimentation pond has an embankment that is more than 20 feet in height, as measured from the upstream toe of the embankment to the crest of the emergency spillway, or has a storage volume of 20 acre-feet or more, the following additional requirements shall be met:

(A)   An appropriate combination of principal and emergency spillways or a single open channel spillway as specified in 460:20-45-9(c)(2) shall be provided to discharge safely the runoff resulting from a 100-year, 6-hour precipitation event, or a larger event specified by the Department.

(B)   Appropriate barriers shall be provided to control seepage along conduits that extend through the embankment.

(C)   The criteria of the Mine Safety and Health Administration as published in 30 CFR 77.216 shall be met.

(18)   Each pond shall be designed and inspected during construction under the supervision of and certified after construction by a qualified registered professional engineer.

(19)   The entire embankment including the surrounding areas disturbed by construction shall be stabilized with respect to erosion by a vegetative cover or other means immediately after the embankment is completed. The active upstream face of the embankment where water will be impounded may be riprapped or otherwise stabilized. Areas in which the vegetation is not successful or where rills and gullies develop shall be repaired and revegetated in accordance with Section 460:20-45-41.

(20)   All ponds including those not meeting the size or other criteria of 30 CFR 77.216(a) shall be examined for structural weakness, erosion and other hazardous conditions and reports and modifications shall be made to the Department in accordance with 30 CFR 77.216-3. With the approval of the Department, dams not meeting these criteria [77.216(a)] shall be examined four times per year.

(21)   Sedimentation ponds shall not be removed until the disturbed area has been restored, and the revegetation requirements of Section 460:20-45-43 through 460:20-45-46 are met and the drainage entering the pond has met the applicable State and Federal water quality requirements for the receiving stream. When the sedimentation pond is removed, the affected land shall be regraded and revegetated in accordance with Sections 460:20-43-38 through 460:20-45-41, and 460:20-45-43 through 460:20-45-46, unless the pond has been approved by the Department for retention as being compatible with the approved postmining land use under Section 460:20-43-51. If the Department approved retention, the sedimentation pond shall meet all requirements for permanent impoundments of Sections 460:20-45-14 and 460:20-45-15.

[Source: Amended at 12 Ok Reg 117, eff 9-29-94 through 7-14-95 (emergency); Amended at 12 Ok Reg 3592, eff 10-12-95; Amended at 16 Ok Reg 3526, eff 9-13-99]