Alabama Administrative Code › Title 880 - ALABAMA SURFACE MINING COMMISSION › Chapter 880-X-10C - PERFORMANCE STANDARDS SURFACE MINING ACTIVITIES › Section 880-X-10C-.20 - Impoundments

Current through Register Vol. 42, No. 9, June 28, 2024
(1) General requirements. The requirements of this Paragraph apply to both temporary and permanent impoundments.
(a) 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 section.
(b) Design certification. The design of impoundments shall be certified in accordance with 880-X-8F-.11(1) as designed to meet the requirement of this part using current, prudent, engineering practices and any design criteria established by the Regulatory Authority. The qualified, registered, professional engineer shall be experienced in the design and construction of impoundments.
(c) Stability.
1. An impoundment meeting the size or other criteria of  30 CFR 77.216(a)  or located where failure would be expected to cause loss of life or serious property damage 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.
2. Impoundments not meeting the size or other criteria of  30 CFR 77.216(a), except for a coal mine waste impounding structure, and located where failure would not be expected to cause loss of life or serious property damage shall have a minimum static safety factor of 1.3 for a normal pool with steady state seepage saturation conditions or meet the requirements of 880-X-8F-.11(3)(c).
(d) Freeboard. Impoundments shall have adequate freeboard to resist overtopping by waves and by sudden increases in storage volume.
(e) Foundation.
1. 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), foundation investigation, as well as any necessary laboratory testing of foundation material, shall be performed to determine the design requirements for foundation stability.
2. 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.
(f) Slope protection shall be provided to protect against surface erosion at the site and protect against sudden draw down.
(g) 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.
(h) Spillways. An Impoundment shall include either a combination of principal and emergency spillways or a single spillway configured as specified in Paragraph (1)(h)1. of this section, designed and constructed to safely pass the applicable design precipitation event specified in paragraph (1)(h)2. of this section, except as set forth in paragraph (3)(b) of this section.
(1) The Regulatory Authority 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.
2. Except as specified in paragraph (3)(b) of this section, the required design precipitation event for an impoundment meeting the spillway requirements of paragraph (1)(h) of this section is:
(i) For an impoundment 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 Regulatory Authority.
(ii) For an impoundment not meeting the size or other criteria of  30 CFR 77.216(a), a 25-year 6-hour event, or greater event as specified by the Regulatory Authority.
(i) The vertical portion of any remaining highwall shall be located far enough below the low-water line along the full extent of highwall to provide adequate safety and access for the proposed water users.
(j) Inspections. A qualified registered professional engineer or other qualified professional specialist under the direction of a professional engineer, shall inspect each impoundment as provided in paragraph (1)(j)1. of this section. The professional engineer or specialist shall be experienced in the construction of impoundments.
1. 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.
2. The qualified registered professional engineer shall promptly after each inspection required in paragraph (j)(1) of this section provide to the Regulatory Authority a certified report that the impoundment has been constructed and/or maintained as designed and in accordance with the approved plan and this chapter. The report shall include discussion of any appearance of instability, structural weakness or other hazardous condition, 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.
3. A copy of the report shall be retained at or near the minesite.
(k) Impoundments subject to  30 CFR 77.216  must be examined in accordance with  30 CFR 77.216-3. Other impoundments shall be examined at least quarterly by a qualified person designated by the operator for appearance of structural weakness and other hazardous conditions.
(l) Emergency procedures. If any examination or inspection discloses that a potential hazard exists, the person who examined the impoundment shall promptly inform the Regulatory Authority of the finding and of the emergency procedures formulated for public protection and remedial action. If adequate procedures cannot be formulated or implemented, the Regulatory Authority shall be notified immediately. The Regulatory Authority shall then notify the appropriate agencies that other emergency procedures are required to protect the public.