312 IAC 25-6-84 Underground mining; hydrologic balance; permanent and temporary impoundments

Sec. 84. (a) This section applies to both temporary and permanent impoundments and must satisfy the following conditions: (1) An impoundment meeting the Class B or C criteria for dams in the NRCS publication Technical Release No. 60 (TR-60) or an impoundment meeting the size or other criteria of 30 CFR 77.216(a) shall comply with the requirements of 30 CFR 77.216 and this rule. (2) The design of impoundments shall be certified in accordance with 312 IAC 25-4-87 as designed to meet the requirement of this rule using current, prudent engineering practices and any design criteria established by the director. The qualified registered professional engineer shall be experienced in the design and construction of impoundments. (3) Impoundments must meet the following criteria for stability: (A) An impoundment meeting the Class B or C criteria for dams in the NRCS publication Technical Release No. 60 (TR-60) or an impoundment meeting the size or other criteria of 30 CFR 77.216(a) shall have a minimum static safety factor of one and five-tenths (1.5) for a normal pool with steady state seepage saturation conditions and a seismic safety factor of at least one and two-tenths (1.2). (B) Impoundments not meeting the Class B or C criteria for dams in the NRCS publication Technical Release No. 60 (TR-60) or not meeting the size or other criteria of 30 CFR 77.216(a), except for a coal mine waste impounding structure, shall have a minimum static safety factor of one and three-tenths (1.3) for a normal pool with steady state seepage saturation conditions. (C) In lieu of meeting the static safety factor requirements of clause (B), the applicant may elect, in order to ensure stability for temporary impoundments not meeting the Class B or C criteria for dams in the NRCS publication Technical Release No. 60 (TR-60) or not meeting the size or other criteria of 30 CFR 77.216(a) to grade as follows: (i) The side slopes of the settled embankments shall not be steeper than two (2) horizontal to one (1) vertical on the upstream slopes. (ii) The downstream slopes shall not be steeper than three (3) horizontal to one (1) vertical. An impoundment constructed within these guidelines shall not be approved for permanent postmining land use until the criteria for permanent impoundments of this section have been satisfied. (4) The size and configuration of the impoundment shall be adequate for its intended purposes. Impoundments shall have adequate freeboard to resist overtopping by waves and by sudden increases in storage volume. Impoundments meeting the Class B or C criteria for dams in TR-60 shall comply with the freeboard hydrograph criteria in the "Minimum Emergency Spillway Hydrologic Criteria" table in TR-60. (5) Foundations and abutments for an impounding structure shall be stable during all phases of construction and operation and shall be designed based on adequate and accurate information on the foundation conditions. For an impoundment meeting the size or other criteria of 30 CFR 77.216(a) or the Class B or C criteria for dams in the NRCS publication Technical Release No. 60 (TR-60), foundation investigation, as well as any necessary laboratory testing of foundation material, shall be performed to determine the design requirements for foundation stability. All vegetative and organic materials shall be removed and foundations excavated and prepared to resist failure. Cutoff trenches shall be installed, if necessary, to ensure stability. (6) Slope protection shall be provided to protect against surface erosion at the site and protect against sudden drawdown. (7) An impoundment shall include either a combination of principal and emergency spillways or a single spillway configured as specified in clause (A), designed and constructed to safely pass the applicable design precipitation event specified in clause (B), except as set forth in subsection (c)(1). (A) The director may approve a single open channel spillway that is: (i) of nonerodible construction and designed to carry sustained flows; or (ii) earth-lined or grass-lined and designed to carry short term, infrequent flows at nonerosive velocities where sustained flows are not expected. (B) Except as specified in subsection (c)(1), the required design precipitation event for an impoundment meeting the spillway requirements of this section is as follows: (i) For an impoundment 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. (ii) For an impoundment 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. (iii) For an impoundment 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. (8) The vertical portion of any remaining highwall must be located far enough below the low water line, along the extent of the highwall, to provide adequate safety and access for proposed water users. If surface run-off enters the impoundment, the side slope must be protected to prevent erosion. (9) A qualified registered professional engineer or other qualified professional specialist under the direction of a professional engineer, either of whom shall be experienced in the construction of impoundments, shall inspect each impoundment according to the following provisions: (A) Inspections shall be made regularly during construction, upon completion of construction, and at least yearly until removal of the structure or release of the performance bond. (B) The qualified registered professional engineer shall, within thirty (30) days after each inspection required in clause (A), provide to the director a certified report that the impoundment has been constructed or maintained, or both, as designed and in accordance with the approved plan and this article. The report shall include discussion of the following: (i) Any appearance of instability, structural weakness, or other hazardous condition. (ii) Depth and elevation of any impounded waters. (iii) Existing storage capacity. (iv) Any existing or required monitoring procedures and instrumentation. (v) Any other aspects of the structure affecting stability. (C) A copy of the report shall be retained at or near the mine site. (D) Impoundments subject to 30 CFR 77.216 or meeting the Class B or C criteria for dams in the NRCS publication Technical Release No. 60 (TR-60) must be examined in accordance with 30 CFR 77.216-3. (E) Impoundments that do not meet the size or other criteria of 30 CFR 77.216(a) or do not meet the Class B or C criteria for dams in the NRCS publication Technical Release No. 60 (TR-60) shall be examined at least quarterly by a qualified person designated by the permittee for appearances of instability, structural weakness, or other hazardous conditions. At least one (1) of the quarterly examinations conducted during the calendar year shall be certified by a qualified registered professional engineer and shall include a discussion of any appearances of instability, structural weakness, or other hazardous conditions, any other aspects of the structure affecting stability, and a statement indicating the pond has been maintained in accordance with the approved plan and this section. This examination shall be conducted during the period of October 1 through December 31 of each calendar year. The certified examination report shall be submitted to the director within thirty (30) days of the examination. Impoundment examinations shall be conducted until the impoundment has been removed or until final bond release in accordance with 312 IAC 25-5-16. If the operator can demonstrate that failure of the structure would not create a potential threat to public health and safety or threaten significant environmental harm, the following impoundments shall be exempt from the examination requirements of this clause, following approval by the director: (i) Impoundments that are completely incised. (ii) Water impounding structures that impound water to a design elevation no more than five (5) feet above the upstream toe of the structure and that can have a storage volume of not more than twenty (20) acre-feet; provided the exemption request is accompanied by a report sealed by a qualified registered professional engineer licensed in the state of Indiana, accurately describing the hazard potential of the structure. Hazard potential must be such that failure of the structure would not create a potential threat to public health and safety or threaten significant environmental harm. The report shall be field verified by the director prior to approval and periodically thereafter. The director may terminate the exemption if so warranted by changes in the area downstream of the structure or in the structure itself. (iii) Impoundments that do not facilitate mining or reclamation, including, but not limited to, the following: (AA) Sewage lagoons. (BB) Landscaping ponds. (CC) Pools or wetlands in replaced stream channels. (DD) Existing impoundments not yet used to facilitate mining. (EE) Ephemeral waterbodies. (FF) Active mining pits. (GG) Differential settlement pools. (10) If any examination or inspection discloses that a potential hazard exists, the person who examined the impoundment shall promptly inform the director of the finding and of the emergency procedures formulated for public protection and remedial action. If adequate procedures cannot be formulated or implemented, the director shall be notified immediately. The director shall then notify the appropriate agencies that other emergency procedures are required to protect the public. (b) Permanent impoundments of water may be authorized by the director upon the basis of the following demonstration: (1) The quality of the impounded water shall be suitable, on a permanent basis, for its intended use and, after reclamation, will meet applicable Indiana and federal water quality standards, and discharge of water from the impoundment will meet applicable effluent limitations and shall not degrade the quality of receiving waters to less than the water quality standards established under applicable Indiana and federal laws. (2) The level of water shall be sufficiently stable to support the intended use. (3) Water impoundments shall not result in the diminution of the quality or quantity of water used by adjacent or surrounding landowners for agricultural, industrial, recreational, or domestic uses. (4) The size and configuration of the impoundment are adequate for the intended purposes. The impoundment has an adequate freeboard to resist overtopping by waves and by sudden increases in storage volume. (5) The impoundment will be suitable for the approved postmining land use. (6) The design, construction, and maintenance of structures shall achieve the minimum design requirements applicable to structures constructed and maintained under the Watershed Protection and Flood Prevention Act, P.L.83-566 (16 U.S.C. 1006). (7) Final grading will provide for adequate safety and access for proposed water users. (8) For final cut and permanent incised impoundments, final graded slopes down to the water level shall not exceed in grade thirty-three and one-third percent (33 %) or the lesser slope needed to do the following: (A) Protect the public health and safety. (B) Enable the permittee to place topsoil on the slope under section 75 of this rule and to revegetate the slope under sections 115 through 122 of this rule. (c) The director may authorize the construction of temporary impoundments as part of an underground coal mining operation. In lieu of meeting the requirements in subsection (a)(7)(A), the director may approve an impoundment 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 impoundment will safely control the design precipitation event, the water from which shall be safely removed in accordance with current, prudent engineering practices. Such an impoundment shall be located where failure would not be expected to cause loss of life or serious property damage, except where in the case of an impoundment: (1) 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 (2) 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. (d) All embankments of temporary and permanent impoundments, and surrounding areas and diversion ditches disturbed or created by construction, shall be graded, fertilized, seeded, and mulched to comply with the requirements of sections 115 through 122 of this rule after the embankment is completed. The active, upstream face of the embankment where water is 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 to comply with the requirements of sections 115 through 122 of this rule. (e) Plans for any enlargement, reduction in size, reconstruction, or other modification of dams or impoundments shall be submitted to the director and shall comply with the requirements of this section. Except where a modification is required to eliminate an emergency condition constituting a hazard to public health, safety, or the environment, the director shall approve the plans before modification begins.