(a) Scope. For the purposes of this section only, disturbed areas 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 §§12.330-12.343, this section, and §§12.345-12.403 of this title (relating to Permanent Program Performance Standards--Surface Mining Activities); and
  (2) for which the upstream area is not otherwise disturbed by the operator.
(b) General requirements.
  (1) Additional contributions of suspended solids 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 (5) of this subsection or subsection (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 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 §12.347 of this title (relating to Hydrologic Balance: Permanent and Temporary Impoundments).
  (5) Siltation structures shall be maintained until the disturbed area has been stabilized and revegetated and removal is authorized by the Commission. In no case shall the structure be removed sooner than two years after the last augmented seeding.
  (6) When a siltation structure is removed, the land on which the siltation structure was located shall be regraded and revegetated in accordance with the reclamation plan and §§12.390-12.395 of this title (relating to Revegetation: General Requirements, to Revegetation: Use of Introduced Species, to Revegetation: Timing, to Revegetation: Mulching and Other Soil Stabilizing Practices, and to Revegetation: Standards for Success). Sedimentation ponds approved by the Commission for retention as permanent impoundments may be exempted from this requirement.
(c) Sedimentation ponds.
  (1) When used, sedimentation ponds shall:
    (A) be used individually or in series;
    (B) be located as near as possible to the disturbed area and out of perennial streams unless approved by the Commission; and
    (C) be designed, constructed, and maintained to:
      (i) provide adequate sediment storage volume. The minimum sediment storage volume shall be equal to the three year accumulated sediment volume from the drainage area to the pond. The sediment volume shall be determined using the Universal Soil Loss Equation, gully erosion rates, and the sediment delivery ratio converted to sediment volume, using either the sediment density or other empirical methods approved by the Commission;
      (ii) provide adequate detention time to allow the effluent from the ponds to meet state and federal effluent limitations. The minimum detention time without a chemical treatment process shall be 10 hours;
      (iii) contain or treat the 10-year, 24-hour precipitation event ("design event") unless a lesser design event is approved by the Commission based on terrain, climate, other site-specific conditions and on a demonstration by the operator that the effluent limitations of §12.340 of this title (relating to Hydrologic Balance: Water-Quality Standards and Effluent Limitations) will be met;
      (iv) provide a nonclogging dewatering device adequate to maintain the detention time required under clause (ii) of this subparagraph;
      (v) minimize, to the extent possible, short circuiting;
      (vi) provide periodic sediment removal sufficient to maintain adequate volume for the design event;
      (vii) ensure against excessive settlement;
      (viii) be free of sod, large roots, frozen soil, and acid- or toxic-forming coal-processing waste; and
      (ix) be compacted properly.
  (2) A sedimentation pond shall include either a combination of principal and auxiliary spillways or single spillway configured as specified in §12.347(a)(9) of this title (relating to Hydrologic Balance: Permanent and Temporary Impoundments).
(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 Commission based on terrain, climate, other site-specific conditions and a demonstration by the operator that the effluent limitations of §12.340 of this title (relating to Hydrologic Balance: Water-Quality Standards and Effluent Limitations) will be met.
  (2) Other treatment facilities shall be designed in accordance with the applicable requirements of subsection (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 operator demonstrates that siltation structures and alternate sediment control measures are not necessary for drainage from the disturbed area to meet the effluent limitations under §12.340 of this title (relating to Hydrologic Balance: Water-Quality Standards and Effluent Limitations) and the applicable state and federal water-quality standards for the receiving waters.

Source Note: The provisions of this §12.344 adopted to be effective November 4, 1997, 22 TexReg 10640; amended to be effective December 28, 2020, 45 TexReg 9503