Mont. Admin. r. 17.24.642 - PERMANENT IMPOUNDMENTS AND FLOOD CONTROL IMPOUNDMENTS
(1) Permanent impoundments are prohibited unless
constructed in accordance with ARM
17.24.504 and
17.24.639 and have open-channel
spillways that will safely discharge runoff resulting from a 100-year, six-hour
precipitation event, assuming the impoundment is at full pool for spillway design or
larger event specified by the department. The department may approve a permanent
impoundment upon the basis of a demonstration that:
(a) the quality of the 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;
(b) discharge of water from the impoundment will
not degrade the quality of receiving waters to less than the water quality standards
established pursuant to applicable state and federal laws;
(c) the level of water will be sufficiently stable
to support the intended use;
(d)
adequate safety and access to the impounded water will be provided for proposed
water users;
(e) water impoundments will
not result in the diminution of the quality or quantity of water used by adjacent or
surrounding landowners for agricultural, industrial, recreational, or domestic
uses;
(f) the design, construction, and
maintenance of structures will achieve the minimum design requirements applicable to
structures constructed and maintained under the Watershed Protection and Flood
Prevention Act. PL
83-566(16 USC 1006). Requirements for
impoundments that meet the size or other criteria of the mine safety and health
administration, 30 CFR
77.216 (a) are contained in U.S. soil conservation
service's Technical Release No. 60 (210-VI-TR60, October 1985, as revised through
January 1991), "Earth Dams and Reservoirs," (TR-60). Requirements for impoundments
that do not meet the size or other criteria contained in
30 CFR
77.216 (a) are contained in U.S. soil conservation
service's Practice Standard 378, "Ponds," October 1978. The technical release and
practice standard are hereby incorporated by reference. Technical Release No. 60 and
Practice Standard 378 are on file and available for inspection at the Helena office
of the Department of Environmental Quality, 1520 E. 6th Ave., Helena, MT 59601;
and
(g) the impoundment will be suitable
for the approved postmining land use.
(2) All permanent impoundments must meet the
design and performance requirements of ARM 17.24.639.
(3) All permanent impoundments must be routinely
maintained during the mining operations. Ditches and spillways must be
cleaned.
(4) All permanent impoundments
must be inspected and certified to the department by a qualified licensed
professional engineer, immediately after construction and annually thereafter, as
having been constructed and maintained to comply with the requirements of this
section. Inspection reports must be submitted until phase IV bond release.
Certification reports must be submitted to the department annually, either
concurrently with the annual report (ARM
17.24.1129) or with the second
semi-annual hydrology report (ARM
17.24.645(8) and
17.24.646(2)). The
operator shall retain a copy of each report at or near the minesite. Certification
reports must include statements on:
(a) existing
and required monitoring procedures and instrumentation;
(b) the design depth and elevation of any
impoundment waters at the time of the initial certification report or the average
and maximum depths and elevations of any impounded waters over the past year for the
annual certification reports;
(c)
existing storage capacity of the impoundment; and
(d) any other aspects of the impoundment affecting
stability.
(5)
(a) Flood control impoundments are located
upstream of disturbance areas for the purpose of preventing or controlling flooding
or discharge and are not designed for sediment control or to be permanent.
(b) Flood control impoundments with embankments
must be constructed in accordance with (1)(f) and ARM
17.24.639(7) through
(21), and be inspected, maintained and certified
according to (3), (4)(a), (4)(d), and (6) and ARM
17.24.639(22) and
(23).
(c) Excavated flood control impoundments:
(i) must be in compliance with ARM
17.24.639(18);
(ii) must have perimeter slopes that are stable;
and
(iii) must be protected against
erosion where surface runoff enters the impoundment area.
(d) An initial pond certification report and
inspections must be made for excavated flood control impoundments in accordance with
ARM 17.24.639(28)(b). If
the volume of the flood control impoundment is used in determination of required
volume for a downstream pond, annual certification reports are required in
accordance with (4)(a), (4)(c), and (4)(d).
(e) Prior to construction, flood control
impoundments must be approved by the department.
(6) Permanent impoundments and flood control
impoundments with embankments meeting the size or other criteria of
30 CFR
77.216 (a) or the Class B or C criteria for dams
in TR-60 must be routinely inspected by a qualified licensed professional engineer
or by someone under the supervision of a qualified licensed professional engineer,
in accordance with 30 CFR
77.216-3.
(7) Plans for any enlargement, reduction in size,
reconstruction, or other modifications of permanent impoundments and flood control
impoundments must be submitted to the department and must comply with the
requirements of this subchapter. Except where a modification is required to
eliminate an emergency condition constituting a hazard to public health, safety, or
the environment, the modification must not be initiated until the department
approves the plans.
Notes
AUTH: 82-4-205, MCA; IMP: 82-4-231, MCA
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