La. Admin. Code tit. 43 § XV-5333

Current through Register Vol. 50, No. 11, November 20, 2024

Section XV-5333 - Hydrologic Balance: Impoundments

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 Number 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. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR Part 51. Copies may be obtained from the National Technical Information Service (NTIS), 5285 Port Royal Road, Springfield, Virginia 22161, order Number PB 87-157509/AS. Copies can be inspected at the OSM Headquarters Office, Office of Surface Mining Reclamation and Enforcement, Administrative Record, Room 660, 800 North Capitol Street, Washington, D.C., or at the Office of the Federal Register, 800 North Capitol Street, NW., Suite 700, Washington, D.C.

2. Impoundments meeting the criteria of 30 CFR 77.216(a) shall comply with the requirements of 30 CFR 77.216 and § 5333.

3. Design Certification. The design of impoundments shall be certified in accordance with §2725. A as designed to meet the requirements of Chapter 53 using current prudent engineering practices and any design criteria established by the office. The qualified registered professional engineer shall be experienced in the design and construction of impoundments.

4. Stability

a. 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) 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 §5333. 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 or meet the requirements of §2725. C 1

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. Sufficient foundation investigations and laboratory testing shall be performed in order to determine the design requirements for foundation stability. 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), foundation investigation, as well as any necessary laboratory testing of foundation material, shall be performed 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 §5333. A.9 a, designed and constructed to safely pass the applicable design precipitation event specified in §5333. A.9 b, except as set forth in §5333. C 2

a. The office 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 §5333. C 2, the required design precipitation event for an impoundment meeting the spillway requirements of §5333. 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 office;

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 office;

iii. for an impoundment not included in §5333. A.9.b.i and ii, a 25-year 6-hour or greater event as specified by the office.

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 or other qualified professional specialist, under the direction of the professional engineer, shall inspect the impoundment. The professional engineer or specialist 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 office 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 office 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 SCS 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 SCS 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 office of the finding and of the emergency procedures formulated for public protection and remedial action. If adequate procedures cannot be formulated or implemented, the office shall be notified immediately. The office shall then notify the appropriate agencies that other emergency procedures are required to protect the public.

B. Permanent Impoundments. A permanent impoundment of water may be created, if authorized by the office in the approved permit, based upon the following demonstration:

1. the size and configuration of such impoundment will be adequate for its intended purposes;

2. the quality of impounded water will be suitable on a permanent basis for its intended use and, after reclamation, will meet applicable state and federal water quality standards, and discharges from the impoundment will meet applicable effluent limitations and will not degrade the quality of receiving water below applicable state and federal water quality standards;

3. the water level will be sufficiently stable and be capable of supporting the intended use;

4. final grading will provide for adequate safety and access for proposed water users;

5. the impoundment will not result in the diminution of the quality and quantity of water utilized by adjacent or surrounding landowners for agricultural, industrial, recreational or domestic uses;

6. the impoundment will be suitable for the approved post-mining land use;

7. the design precipitation event for the spillways for a permanent impoundment meeting the size or other criteria of 30 CFR 77.216(a) is a 100-year, 6-hour event, or greater event as specified by the office;

8. the design precipitation event for the spillways for a permanent impoundment not meeting the size or other criteria of 30 CFR 77.216(a) is a 25-year, 6-hour event, or greater event as specified by the office.

C. Temporary Impoundments

1. The office may authorize the construction of temporary impoundments as part of a surface coal mining operation.

2. In lieu of meeting the requirements in §5333. A.9 a, the office may approve an impoundment that relies primarily on storage to control the runoff 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:

a. impoundments meeting the SCS Class B or C criteria for dams in TR-60, or the size or other criteria of 30 CFR 77.216(a) shall be designed to control the precipitation of the probable maximum precipitation of a 6-hour event, or greater event specified by the office;

b. impoundments not included in §5333. C.2.a shall be designed to control the precipitation of the 100-year 6-hour event, or greater event specified by the office.

La. Admin. Code tit. 43, § XV-5333

Promulgated by the Department of Natural Resources, Office of Conservation, LR 5:395 (December 1979), amended LR 14:441 (July 1988), LR 20:447 (April 1994), LR 24:2285 (December 1998).

AUTHORITY NOTE: Promulgated in accordance with R.S. 30:901-932.