Section 312 IAC 25-6-81 - Underground mining; hydrologic balance; siltation structuresAuthority: IC 14-34-2-1
Affected: IC 14-34
Sec. 81.
(a) Siltation structures shall be constructed according to the following: (1) Additional contributions of suspended solids sediment to stream flow or run-off 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 subdivision (5) or section 77 of this rule.(3) Siltation structures for an area shall be constructed before beginning any surface mining activities in that area and, upon construction, shall be certified by a qualified registered professional engineer to be constructed as designed and as approved in the reclamation plan.(4) Any siltation structure that impounds water shall be designed, constructed, and maintained in accordance with section 84 of this rule.(5) Siltation structures shall be maintained until removal is authorized by the director and the disturbed area has been stabilized and revegetated in accordance with the reclamation plan and sections 111 through 122 of this rule so that the following requirements are met: (A) Removal of the structure will not result in violations of applicable water quality standards in the receiving stream.(B) Postmining drainage is shown to be of the approximate quality of the drainage from the area prior to mining.(C) If baseline data is unavailable concerning the quality of drainage before mining, it is shown to be of the approximate quality of drainage from similar areas of unmined land. In no case shall the structure be removed sooner than two (2) years after the last augmented seeding.
(6) When the siltation structure is removed, the land on which it was located shall be regraded and revegetated in accordance with the reclamation plan and sections 115 through 122 of this rule. Siltation structures approved by the director for retention as permanent impoundments shall meet all the requirements for permanent impoundments of sections 84 and 90 of this rule.(7) Any point source discharge of water from underground workings to surface waters that does not meet the effluent limitations of section 77 of this rule shall be passed through a siltation structure before leaving the permit area.(b) Siltation structures, where utilized individually or in series, shall be as follows: (1) Located as near as possible to the disturbed area and out of perennial streams unless approved by the director.(2) Designed, constructed, and maintained to achieve each of the following: (A) Provide adequate sediment storage volume.(B) Provide adequate detention time to allow the effluent from the ponds to meet Indiana and federal effluent limitations.(C) Contain or treat the ten (10) year, twenty-four (24) hour precipitation event (design event) unless a lesser design event is approved by the director based on terrain, climate, other site-specific conditions, and on a demonstration by the operator that the effluent limitations of section 77 of this rule will be met.(D) Provide a nonclogging dewatering device adequate to maintain the detention time required under clause (B).(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-forming or toxic-forming coal processing waste.(I) Be compacted properly.(J) For siltation structures with embankments, achieve a minimum of two (2) feet of freeboard above pool stage and one (1) foot of freeboard above the design peak discharge elevation which is in response to the design storm specified in subsection (d)(2), or greater amount of freeboard as specified by the director.(c) The design, construction, and maintenance of a siltation structure or other sediment control measures under this section do not relieve the permittee from compliance with applicable effluent limitations as contained in section 77 of this rule.(d) A siltation structure shall include either a combination of principal and emergency spillways or a single spillway configured as specified in subdivision (1), designed and constructed to safely pass the applicable design precipitation event specified in subdivision (2), except as set forth in subdivision (3). Spillway construction shall be as follows: (1) The director may approve a single open channel spillway that is: (A) of nonerodible construction and designed to carry sustained flows; or(B) earth-lined or grass-lined and designed to carry short term infrequent flows at nonerosive velocities where sustained flows are not expected.(2) Except as specified in subdivision (3), the required design precipitation event for a siltation structure meeting the spillway requirements of this section is as follows: (A) For a siltation structure meeting the size or other criteria of 30 CFR 77.216(a), a one hundred (100) year, six (6) hour event, or greater event as specified by the director.(B) For a siltation structure meeting the Class B or C criteria for dams in TR-60, the emergency spillway hydrograph criteria in the "Minimum Emergency Spillway Hydrologic Criteria" table in TR-60, or greater event as specified by the director.(C) For a siltation structure not meeting the size or other criteria of 30 CFR 77.216(a) or not meeting the Class B or C criteria for dams in the NRCS publication Technical Release No. 60 (TR-60), a twenty-five (25) year, six (6) hour event, or greater event as specified by the director.(3) In lieu of meeting the requirements in subdivision (1), the director may approve a siltation structure that relies primarily on storage to control the run-off from the design precipitation event when it is demonstrated by the operator and certified by a qualified registered professional engineer that the siltation structure will safely control the design precipitation event, the water from which shall be safely removed in accordance with current, prudent engineering practices. Such a siltation structure shall be located where failure would not be expected to cause loss of life or serious property damage, except where: (A) in the case of a siltation structure meeting the Class B or C criteria for dams in the NRCS publication Technical Release No. 60 (TR-60) or 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 six (6) hour event, or greater event as specified by the director; or(B) in the case of a siltation structure not meeting the size or other criteria of 30 CFR 77.216(a) or not meeting the Class B or C criteria for dams in the NRCS publication Technical Release No. 60 (TR-60), it is designed to control the precipitation of a one hundred (100) year, six (6) hour event, or greater event as specified by the director.(e) Other treatment facilities shall be designed as follows: (1) To treat the ten (10) year, twenty-four (24) hour precipitation event unless a lesser design event is approved by the director based on terrain, climate, other site-specific conditions, and a demonstration by the operator that the effluent limitations of section 77 of this rule will be met.(2) Designed in accordance with the applicable requirements of subsection (b).Natural Resources Commission; 312 IAC 25-6-81; filed Jun 21, 2001, 2:53 p.m.: 24 IR 3551, eff Dec 1, 2001; filed Apr 1, 2004, 3:00 p.m.: 27 IR 2463, eff Jan 1, 2005; readopted filed May 29, 2007, 9:51 a.m.: 20070613-IR-312070146RFA; readopted filed Sep 19, 2013, 10:12 a.m.: 20131016-IR-312130125RFAReadopted filed 3/26/2019, 3:40 p.m.: 20190424-IR-312190011RFA