16 Tex. Admin. Code § 12.347 - Hydrologic Balance: Permanent and Temporary Impoundments
(a) General Requirements. The requirements of
this subsection apply to both temporary and permanent impoundments.
(1) Impoundments meeting the significant or
high hazard class criteria of dams in the U.S. Department of Agriculture
(USDA), Natural Resources Conservation Service Technical Release No. 60
(210-VI-TR60, July 2005), Earth Dams and Reservoirs, shall comply with the
table of Minimum Auxiliary Spillway Hydrologic Criteria in Technical Release
No. 60 (TR-60), which is incorporated by reference, and the requirements of
this section. Copies may be obtained on the USDA website.
(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 of this section.
(3) The design of impoundments shall be
certified in accordance with §
12.148(a) of
this title (relating to Reclamation Plan: Ponds, Impoundments, Banks, Dams, and
Embankments) as designed to meet the requirements of this part using current,
prudent, engineering practices and any design criteria established by the
Commission. The qualified professional engineer shall be experienced in the
design and construction of impoundments.
(4) Stability.
(A) An impoundment meeting the significant or
high hazard class criteria for dams in TR-60, or the size or other criteria of
30 CFR
77.216(a), shall have a
minimum static 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) An impoundment not included in
subparagraph (A) of this paragraph, 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
§
12.148(c) of
this title (relating to Reclamation Plan: Ponds, Impoundments, Banks, Dams, and
Embankments).
(5)
Impoundments shall have adequate freeboard to resist overtopping by waves and
by sudden increases in storage volume. Impoundments meeting the significant or
high hazard class criteria for dams in TR-60 shall comply with the freeboard
hydrograph criteria in the Minimum Auxiliary Spillway Hydrologic Criteria table
in TR-60.
(6) Foundations.
(A) 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 significant or high
hazard class 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 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) An impoundment shall
include either a combination of principal and auxiliary spillways or a single
spillway configured as specified in subparagraph (A) of this paragraph,
designed and constructed to safely pass the applicable design precipitation
event specified in subparagraph (B) of this paragraph.
(A) The Commission may approve a single
open-channel spillway that is of nonerodible construction and designed to carry
sustained flows or 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 subsection (c)(2) of this section, the required design precipitation event
for an impoundment meeting the spillway requirements of this paragraph is:
(i) for an impoundment meeting the
significant or high hazard class criteria for dams in TR-60, the auxiliary
spillway hydrograph criteria in the Minimum Emergency Spillway Hydrologic
Criteria table in TR-60, or greater event as specified by the
Commission;
(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 Commission; and
(iii) for an impoundment not included in
clauses (i) and (ii) of this subparagraph, a 25-year, 6-hour event, or greater
event as specified by the Commission.
(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) A qualified
professional engineer or other qualified professional specialist under the
direction of a professional engineer, shall inspect each impoundment as
provided in subparagraph (A) of this paragraph. The professional engineer or
specialist shall be experienced in the construction of impoundments.
(A) Inspections shall be made regularly
during construction, upon completion of the construction, and at least yearly
until removal of the structure or release of the performance bond.
(B) The qualified professional engineer shall
promptly after each inspection required in subparagraph (A) of this paragraph,
provide the Commission 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 hazard 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.
(C)
A copy of the report shall be retained at or near the
minesite.
(12)
Impoundments meeting the NRCS significant or high hazard class 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 NRCS
significant or high hazard class 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) If any examination or inspection
discloses that a potential hazard exists, the person who examined the
impoundment shall promptly inform the Commission of the finding and of the
emergency procedures formulated for public protection and remedial action. If
adequate procedures cannot be formulated or implemented, the Commission shall
be notified immediately. The Commission 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 Commission 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 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; and
(6) the impoundment will
be suitable for the approved postmining land use.
(c) Temporary Impoundments.
(1) The Commission may authorize the
construction of temporary impoundments as part of a surface coal mining
operation.
(2) In lieu of meeting
the requirements of subsection (a)(9)(A) of this section, the Commission 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 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 NRCS significant
or high hazard class 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 as specified by the Commission; and
(B) impoundments not included in subparagraph
(A) of this paragraph shall be designed to control the precipitation of the
100-year, 6-hour event, or greater event as specified by the
Commission.
Notes
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