4 Va. Admin. Code § 25-130-816.46

Current through Register Vol. 41, No. 8, December 2, 2024

Section 4VAC25-130-816.46 - Hydrologic balance; siltation structures

(a) For the purposes of this section only, "disturbed area" shall not include those areas-

(1) In which the only surface mining activities include diversion ditches, siltation structures, or roads that are designed, constructed and maintained in accordance with this Part; and

(2) For which the upstream area is not otherwise disturbed by the operator.

(b) General requirements.

(1) Additional contributions of sediment to streamflow or runoff outside the permit area shall be prevented to the extent possible using the best technology currently available.

(2) All surface drainage from the disturbed area shall be passed through a siltation structure before leaving the permit area, except as provided in paragraph (b)(5) or (e) of this section.

(3) Siltation structures for an area shall be constructed before beginning any surface mining activities in that area and, upon construction, shall be certified by a qualified registered professional engineer to be constructed as designed and as approved in the reclamation plan.

(4) Any siltation structure which impounds water shall be designed, constructed and maintained in accordance with 4VAC25-130-816.49.

(5) Siltation structures shall be maintained until removal is authorized by the division and the disturbed area has been stabilized and revegetated. In no case shall the structure be removed sooner than two years after the last augmented seeding.

(6) When a siltation structure is removed, any embankment material and all accumulated sediment shall be placed in designated disposal areas, and the land on which the siltation structure was located shall be regraded and revegetated in accordance with the reclamation plan and 4VAC25-130-816.111 through 4VAC25-130-816.116. Sedimentation ponds approved by the division for retention as permanent impoundments may be exempted from this requirement.

(c) Sedimentation ponds.

(1) When used, sedimentation ponds shall-

(i) Be used individually or in series;

(ii) Be located as near as possible to the disturbed area and out of perennial streams unless such location is approved by the division; and

(iii) Be designed, constructed, and maintained to-

(A) Provide adequate sediment storage volume and provide adequate detention time to allow the effluent from the ponds to meet state and federal effluent limitations;

(B) Have a minimum volume of 0.125 acre-feet per acre of disturbed area draining to it, of which 0.075 acre-feet per acre disturbed shall be sediment storage volume and the remainder shall be detention storage volume;

(C) Treat the 10-year, 24-hour precipitation event ("design event") unless a lesser design event is approved by the division based on terrain, climate, other site-specific conditions and on a demonstration by the permittee that the effluent limitations of 4VAC25-130-816.42 will be met;

(D) Provide a nonclogging dewatering device adequate to maintain the detention time required under paragraphs (c)(1)(iii)(A) and (B) of this section;

(E) Minimize, to the extent possible, short circuiting;

(F) Provide periodic sediment removal sufficient to maintain adequate volume for the design event. The elevation corresponding to the sediment storage volume shall be determined and a bench mark set in the field from which this elevation can readily be established. Sediment shall be removed when its accumulation reaches the cleanout level or more frequently if the operation of the structure is impaired. Sediment removed shall be placed only in disposal areas identified and approved in the reclamation plan;

(G) Ensure against excessive settlement;

(H) Be free of sod, large roots, frozen soil, and acid or toxic-forming coal-processing waste; and

(I) Be compacted properly.

(2) Spillways. A sedimentation pond shall include either a combination of principal and emergency spillways or a single spillway configured as specified in 4VAC25-130-816.49(a)(9).

(d) Other treatment facilities.

(1) Other treatment facilities shall be designed to treat the 10-year, 24-hour precipitation event unless a lesser design event is approved by the division based on terrain, climate, other site-specific conditions and a demonstration by the permittee that the effluent limitations of 4VAC25-130-816.42 will be met.

(2) Other treatment facilities shall be designed in accordance with the applicable requirements of paragraph (c) of this section.

(e) Exemptions. Exemptions to the requirements of this section may be granted if-

(1) The disturbed drainage area within the total disturbed area is small; and

(2) The permittee demonstrates that siltation structures and alternate sediment control measures are not necessary for drainage from the disturbed area to meet the effluent limitations under 4VAC25-130-816.42 and the applicable state and federal water quality standards for the receiving waters.

4 Va. Admin. Code § 25-130-816.46

Derived from VR480-03-19 § 816.46, 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 15, Issue 6, eff. January 6, 1999.

Statutory Authority

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