30 CFR § 817.46 - Hydrologic balance: Siltation structures.
(a) For the purposes of this section only, disturbed areas shall not include those areas -
(2) For which the upstream area is not otherwise distributed by the operator.
(b) General requirements.
(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. The requirements of this paragraph are suspended effective December 22, 1986, per court order.
(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, in any State which authorizes land surveyors to prepare and certify plans in accordance with § 784.16(a) of this chapter, a qualified registered professional land surveyor, to be constructed as designed and as approved in the reclamation plan.
(5) Siltation structures shall be maintained until removal is authorized by the regulatory authority 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 the 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 §§ 817.111 through 817.116 of this chapter. Sedimentation ponds approved by the regulatory authority for retention as permanent impoundments may be exempted from this requirement.
(7) Any point-source discharge of water from underground workings to surface waters which does not meet the effluent limitations of § 817.42 shall be passed through a siltation structure before leaving the permit area.
(c) Sedimentation ponds.
(1) Sedimentation ponds, when used, shall -
(i) Be used individually or in series;
(ii) Be located as near as possible to the distrubed area and out of perennial streams unless approved by the regulatory authority; and
(iii) Be designed, constructed, and maintained to -
(A) Provide adequate sediment storage volume;
(B) Provide adequate detention time to allow the effluent from the ponds to meet State and Federal effluent limitations;
(C) Contain or treat the 10-year, 24-hour precipitation event (“design event”) unless a lesser design event is approved by the regulatory authority based on terrain, climate, other site-specific conditions and on a demonstration by the operator that the effluent limitations of § 817.42 will be met;
(D) Provide a nonclogging dewatering device adequate to maintain the detention time required under paragraph (c)(1)(iii)(B) of this section;
(E) Minimize, to the extent possible, short circuiting;
(F) Provide periodic sediment removal sufficient to maintain adequate volume for the design event;
(G) Ensure against excessive settlement;
(H) Be free of sod, large roots, frozen soil, and acid- or toxic-forming coal-processing waste; and
(I) Be compacted properly.
(d) Other treatment facilities.
(1) Other treatment facilities shall be designed to treat the 10-year, 24-hour precipitation even unless a lesser design event is approved by the regulatory authority based on terrain, climate, other site-specific conditions and a demonstration by the operator that the effluent limitations of § 817.42 will met.
(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 drainage areas to meet the effluent limitations under § 817.42 and the applicable State and Federal water quality standards for the receiving waters.