4 Va. Admin. Code § 25-130-816.49

Current through Register Vol. 41, No. 6, November 4, 2024

Section 4VAC25-130-816.49 - 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 No. 60 (210-VI-TR60, Oct. 1985), "Earth Dams and Reservoirs," shall comply with the "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. PB87-157509/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) 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.

(3) Design certification. The design of impoundments shall be certified by a qualified registered professional engineer as designed to meet the requirements of this Part using current, prudent engineering practices, and any other criteria established by the division. The qualified registered professional engineer shall be experienced in the design and construction of impoundments.

(4) Stability.

(i) 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.

(ii) Impoundments not included in paragraph (a)(4)(i) of this section, 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. In lieu of engineering tests to establish compliance with the minimum static safety factor of 1.3, earth embankments whose top widths are no less than 10 feet and whose embankment slopes are 2h:1v or flatter may be used provided that the permittee documents that a minimum static safety factor of 1.3 can be met using the graphical solution methods outlined in the "Bureau of Mines Report of Investigations/1981, RI 8564, Factor of Safety Charts for Estimating the Stability of Saturated and Unsaturated Tailings Pond Embankments, United States Department of Interior."

(5) Freeboard. Impoundments shall have adequate freeboard to resist overtopping by waves and by sudden increases in storage volume. The minimum freeboard shall be one foot. 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.

(i) 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 Class B or C criteria for dams in TR-60, or the size or other criteria of 30 CFR 77.216(a), foundation investigations, as well as any necessary laboratory testing of foundation material shall be performed to determine the design requirements for foundation stability.

(ii) 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 and minimize seepage. The pool area shall be cleared of all brush and trees unless the requirement is waived by the division.

(iii) The most impervious material available shall be used in the cutoff trench and center portion of the dam. If sandy or gravelly material is encountered, it shall be placed in the outer shell, preferably in the downstream portion of the dam.

(7) Slope protection. Slope protection shall be provided to protect against surface erosion at the site and protect against sudden drawdown.

(8) Vegetation. 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 paragraph (a)(9)(i) of this section, designed and constructed to safely pass the applicable design precipitation event specified in paragraph (a)(9)(ii) of this section, except as set forth in paragraph (c)(2) of this section.

(i)

(A) The division may approve a single open-channel spillway that is:

(1) Of nonerodible construction and designed to carry sustained flows; or

(2) Earth- or grass-lined and designed to carry short-term, infrequent flows at non-erosive velocities where sustained flows are not expected.

(B) Temporary ponds that do not meet the size or other criteria of 30 CFR 77.216(a) and located where failure would not be expected to cause loss of life or serious property damage, may use a single spillway of the pipe and riser design if the riser is no less than 15 inches in diameter, the barrel is no less than 12 inches in diameter, and a properly designed anti-vortex device and trash rack are securely installed on top of the riser.

(ii) Except as specified in paragraph (c)(2) of this section, the required design precipitation event for an impoundment meeting the spillway requirements of paragraph (a)(9) of this section is:

(A) For an impoundment meeting the SCS 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 division.

(B) For an impoundment meeting or exceeding the size or other criteria of 30 CFR 77.216(a), a 100-year six-hour event, or greater event as specified by the division.

(C) For an impoundment included in paragraphs (a)(9(ii)(A) and (B) of this section, a 25-year six-hour event, or greater event as specified by the division.

(10) 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 (a)(10)(i) of this section. The professional engineer or specialist shall be experienced in the construction of impoundments.

(i) 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.

(ii) The qualified registered professional engineer shall, within two weeks after each inspection required in paragraph (a)(10)(i) of this section, provide to the division a certified report that the impoundment has been constructed and/or maintained as designed and in accordance with the approved plan and this chapter. Construction certified in previous reports need not be recertified after each annual inspection. 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.

(iii) A copy of the report shall be retained at or near the minesite.

(11) Examinations. 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 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 appearance of structural weakness and other hazardous conditions.

(12) Emergency procedures. If any examination or inspection discloses that a potential hazard exists, the permittee shall promptly inform the division of the finding and of the emergency procedures formulated for public protection and remedial action. If adequate procedures cannot be formulated or implemented, the division shall be notified immediately. Notification shall be by the fastest available means and followed in writing. The division 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 division 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 postmining land use.

(c) Temporary impoundments.

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

(2) In lieu of meeting the requirements in paragraph (a)(9)(i) of this section, the division 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 or qualified registered professional land surveyor in accordance with 4VAC25-130-780.25(a) 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:

(i) 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 six-hour event, or greater event as specified by the division; or

(ii) Impoundments not included in paragraph (c)(2)(i) of this section shall be designed to control the precipitation of a 100-year six-hour event, or greater event as specified by the division.

4 Va. Admin. Code § 25-130-816.49

Derived from VR480-03-19 § 816.49, eff. December 15, 1981; amended, eff. June 28, 1982; October 28, 1982; December 14, 1982; October 11, 1983; December 27, 1983; May 8, 1984; June 22, 1984; August 2, 1984; October 16, 1985; January 7, 1987; July 22, 1987; November 25, 1987; October 12, 1988; December 26, 1990; July 1, 1991; July 17, 1991; November 20, 1991; July 7, 1992; May 5, 1993; October 19, 1994; Virginia Register Volume 12, Issue 2, eff. November 15, 1995; Volume 15, Issue 6, eff. January 6, 1999.

Statutory Authority

§§ 45.1-161.3 and 45.1-230 of the Code of Virginia.