Mississippi Administrative Code › Title 11 - Mississippi Department of Environmental Quality › Part 8 - Geology Regulations › Chapter 2 - Mississippi Commission on Environmental Quality Regulations Governing Surface Coal Mining › Subchapter 2.5 - Permanent Program Performance Standards › Rule 11-8-2.5-53 - Permanent Program Performance Standards Surface Mining Activities › Section 11-8-2.5-53-5327 - Hydrologic Balance: Impoundments

Current through June 25, 2024
(a) General
					 Requirements. The requirements of this Subsection apply to both temporary and
					 permanent impoundments.
(1) Impoundments
					 meeting the Class B or C criteria for dams in the U.S. Department of
					 Agriculture, Soil Conservation Service Technical Release No. 60 (210-VI-TR60,
					 Oct. 1985), "Earth Dams and Reservoirs," 1985 shall comply with "Minimum
					 Emergency Spillway Hydrologic Criteria" table in TR-60 and the requirements of
					 this section. The technical release is hereby incorporated by reference. Copies
					 may be obtained from the National Technical Information Service (NTIS), 5285
					 Port Royal Road, Springfield, Virginia 22161, order No. PB 87-157509/AS. Copies
					 can be inspected at the Office of Surface Mining Reclamation and Enforcement,
					 1951 Constitution Avenue, N.W., Washington, DC, or at the Office of the Federal
					 Register, 800 North Capitol Street, NW., suite 700, Washington, DC.
(2) Impoundments meeting the criteria of
					 30
					 CFR 77.216(a) shall comply
					 with the requirements of
					 30
					 CFR 77.216, §
												53-9-45,
					 and this Section.
(3) Design
					 Certification. The design of impoundments shall be certified in accordance with
					 § 2725(a) as designed to meet the requirements of this Rule using current
					 prudent engineering practices and any design criteria established by the
					 Department. The qualified registered professional engineer shall be experienced
					 in the design and construction of impoundments.
(4) Stability.
(A) Impoundments meeting the Class B or C
					 criteria for dams in TR-60, or the size or other criteria of
					 30
					 CFR 77.216(a) shall have a
					 minimum static safety factor of 1.5 for a normal pool with steady state seepage
					 saturation conditions, and a seismic safety factor of at least 1.2.
(B) Impoundments not included in §
					 5327(a)(4)(A), except for a coal mine waste impounding structure, shall have a
					 minimum static safety factor of 1.3 for a normal pool with steady state seepage
					 saturation conditions.
(5) Freeboard. 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.
(6) Foundation
(A) Foundation and abutments for the
					 impounding structure shall be designed to be stable under all phases of
					 construction and operation of the impoundment. For an impoundment meeting the
					 Class B or C criteria for dams in TR-60, or the size or other criteria of
					 30
					 CFR 77.216(a), sufficient
					 foundation investigations and laboratory testing shall be performed in order to
					 determine the design requirements for foundation stability.
(B) 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.
(7) Slope protection shall be
					 provided to protect against surface erosion at the site and to protect against
					 sudden drawdown.
(8) Faces of
					 embankments and surrounding areas shall be vegetated, except that faces where
					 water is impounded may be riprapped or otherwise stabilized in accordance with
					 accepted design practices.
(9)
					 Spillways. An impoundment shall include either a combination of principal and
					 emergency spillways or a single spillway configured as specified in §
					 5327(a)(9)(A), designed and constructed to safely pass the applicable design
					 precipitation event specified in § 5327(a)(9)(B), except as set forth in
					 § 5327(c)(2).
(A) The Permit Board 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 §
					 5327(c)(2), the required design precipitation event for an impoundment meeting
					 the spillway requirements of § 5327(a)(9) is:
(i) 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 Permit Board.
(ii) For an impoundment meeting or exceeding
					 the size or other criteria of
					 30
					 CFR 77.216(a), a 100-year
					 6-hour event, or greater event as specified by the Permit Board.
(iii) For an impoundment not included in
					 § 5327(a)(9)(B)(i) and (ii), a 25-year 6-hour or greater event as
					 specified by the Permit Board.
(10) The vertical portion of any remaining
					 highwall shall be located far enough below the low-water line along the full
					 extent of the highwall to provide adequate safety and access for the proposed
					 water users.
(11) Inspections. A
					 qualified registered professional engineer, shall inspect the impoundment. The
					 registered professional engineer shall be experienced in the construction of
					 impoundments.
(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, upon completion of construction, shall promptly provide
					 to the Department a certified report that the impoundment has been constructed
					 as designed and in accordance with the approved plan and these regulations. In
					 addition, the qualified registered professional engineer shall, after each
					 annual inspection, promptly provide to the Department a certified report that
					 the impoundment has been maintained in accordance with the approved plan and
					 these regulations. Each such report shall include discussion of any appearances
					 of instability, structural weakness or other hazardous conditions, depth and
					 elevation of any impounded waters, existing storage capacity, any existing or
					 required monitoring procedures and instrumentation, and any other aspects of
					 the structure affecting stability.
(C) A copy of the report shall be retained at
					 or near the minesite.
(12) Impoundments meeting the Class B or C
					 criteria for dams in TR-60, or the size or other criteria of
					 30
					 CFR 77.216 must be examined in accordance
					 with
					 30
					 CFR 77.216-3. Impoundments not meeting the
					 Class B or C criteria for dams in TR-60, or subject to
					 30
					 CFR 77.216, shall be examined at least
					 quarterly. A qualified person designated by the operator shall examine
					 impoundments for the appearance of structural weakness and other hazardous
					 conditions.
(13) Emergency
					 Procedures. If any examination or inspection discloses that a potential hazard
					 exists, the person who examined the impoundment shall promptly inform the
					 Department of the finding and of the emergency procedures formulated for public
					 protection and remedial action. If adequate procedures cannot be formulated or
					 implemented, the Department shall be notified immediately. The Department shall
					 then notify the appropriate agencies that other emergency procedures are
					 required to protect the public.