Idaho Administrative Code › Title IDAPA 37 - Water Resources, Department of › Rule 37.03.05 - MINE TAILINGS IMPOUNDMENT STRUCTURES RULES › Section 37.03.05.045 - MINE TAILINGS IMPOUNDMENT STRUCTURES DESIGN CRITERIA

Current through August 31, 2023
The following minimum design criteria shall be used for all
				mine tailings impoundment structures designed for installation in Idaho. These
				limitations are intended to serve as guidelines for a broad range of
				circumstances, and engineers should not consider them as a restriction to the
				use of other sound design criteria. Deviation from this established criteria
				will be considered by the Director in approving plans and specifications.
				(3-30-23)
01.
Embankment
			 Slopes
. (3-30-23)
a. For construction
			 of borrowed fill embankments, in the absence of a stability analysis, the
			 slopes shall be:
Upstream slope
2:1 or flatter
Downstream slope
2:1 or flatter
(3-30-23)
b.
			 Construction by the upstream method shall not be used in the area of the state
			 east of Range 22 E., Boise Meridian, unless the engineer can provide evidence
			 that the construction and operation of the tailings impoundment will achieve a
			 relative density of sixty percent (60%) or greater in the embankment and
			 tailings to prevent liquefaction during earthquake loading. (3-30-23)
c. Safety factors for the embankment shall be
			 at least one and five-tenths (1.5) for static loads and a minimum of one (1)
			 for the static plus the appropriate earthquake load. (3-30-23)
d. To insure sufficient permeability and
			 stability of the embankment, designs will require utilizing materials other
			 than the tailings, when the tailings materials: (3-30-23)
i. Contain greater than seventy-five percent
			 (75%) passing the #200 standard U.S. sieve, or fifty percent (50%) passing the
			 #325 standard U.S. sieve; (3-30-23)
ii. Contain phosphate clays;
			 (3-30-23)
iii. The design calls for
			 the water to be impounded against the embankment; (3-30-23)
iv. Have other properties which makes them
			 unsuitable for use as construction materials. (3-30-23)
e. Embankments designed for the storage of
			 hazardous levels of radioactive materials shall, in addition to any
			 requirements of these regulations, meet the criteria outlined in the Nuclear
			 Regulatory Commission Regulatory Guide 3.11 and the Idaho Radiation Control
			 Regulations administered by the Idaho Department of Environmental Quality.
			 (3-30-23)
f. The design shall
			 consider the need for drains and/or operational procedures to promote
			 consolidation and insure that a low phreatic surface is maintained within the
			 embankment. Drainage pipe shall not be used beneath embankments where excessive
			 or differential settlement may cause failure of the pipes and subsequent piping
			 of the tailings or embankment. When the quality of the mine tailings slurry is
			 such that it will adversely affect the quality of the existing ground water,
			 the design should be coordinated with the Department and the Department of
			 Environmental Quality to insure that all applicable permits are obtained.
			 (3-30-23)
g. Instrumentation of the
			 embankment and/or foundation will be required to insure that the structure is
			 functioning satisfactorily. Standpipe piezometers with an inside diameter
			 greater than one-half (1/2) inch will not be acceptable for use in fine-grained
			 or cohesive soils in order to minimize response time. (3-30-23)
h. Tailings impoundment structures which are
			 constructed using the tailings shall not be constructed or raised during
			 freezing weather to prevent frost lenses in the embankment. Sufficient
			 freeboard must be provided during the summer construction season if the
			 disposal operation is to continue during the winter. (3-30-23)
i. If tailings are to be discharged during
			 times of freezing weather and the embankment is to be constructed using either
			 the upstream or centerline method, the pond shall be of sufficient size to
			 insure that any ice formed in the tailings pond area melts during the next warm
			 season. (3-30-23)