Ariz. Admin. Code § R18-13-1004 - Operating Criteria

A. 40 CFR 257.80 through 40 CFR 257.84, revised as of December 14, 2020 (and no future editions) are incorporated by reference, modified by the following subsections, and on file with ADEQ:

B. 40 CFR 257.82(a)(3) is amended as follows: "(3) The inflow design flood is:

(i) For a high hazard potential CCR surface impoundment, as determined under § 257.73(a)(2) or § 257.74(a)(2), the probable maximum flood;

(ii) For a significant hazard potential CCR surface impoundment, as determined under § 257.73(a)(2) or § 257.74(a)(2), the 1,000-year flood or, for new impoundments and lateral expansions, 0.5 PMF, whichever is greater;

(iii) For a low hazard potential CCR surface impoundment, as determined under § 257.73(a)(2) or § 257.74(a)(2), the 100-year flood or, for new impoundments and lateral expansions, 0.25 PMF, whichever is greater; or

(iv) For an incised CCR surface impoundment, the 25-year flood."

C. In addition to the requirements in 40 CFR 257.82(a), the following requirements are added:

1. Inflow Design Flood Requirements. For new impoundments and lateral expansions, an owner or operator shall ensure that the total freeboard is the largest of the following:

a. The sum of the inflow design flood maximum water depth above the spillway crest plus wave run up.

b. The sum of the inflow design flood maximum water depth above the spillway crest plus 3 feet.

c. A minimum of 5 feet.

2. Surface Impoundment Site and Reservoir Area Requirements

a. An owner or operator shall demonstrate that reservoir storage during the inflow design flood will not result in incremental adverse consequences during the inflow design flood. In determining whether a discharge will result in incremental adverse consequences, the Director shall evaluate whether the owner or operator has taken any or all of the following actions: issuing public notice to upstream affected property owners, complying with flood insurance requirements, adopting emergency action plans, conducting mock flood drills, acquiring flood easements or other acquisitions of real property, or other actions appropriate to safeguard the CCR surface impoundment site and reservoir.

b. The owner or operator shall clear the reservoir storage area of debris.

c. The owner or operator shall place borrow areas a safe distance from the upstream toe and the downstream toe of the CCR surface impoundment to prevent a piping failure of the CCR surface impoundment.

d. The owner or operator shall keep the top of the CCR surface impoundment and appurtenant structures accessible by equipment and vehicles for emergency operations and maintenance.

D. In addition to the requirements in 40 CFR 257.82(b), the following requirement are added:

1. Emergency Spillway Requirements. An owner or operator of a new CCR surface impoundment with emergency spillways or a lateral expansion of a CCR surface impoundment with emergency spillways shall:

a. Construct each spillway in a manner that avoids flooding in excess of the flooding that would have occurred in the same location under the same conditions before construction. The owner or operator of a CCR surface impoundment shall demonstrate that a spillway discharge would not result in incremental adverse consequences. In determining whether a spillway discharge of a CCR surface impoundment would result in incremental adverse consequences, the Director shall evaluate whether the owner or operator has taken any or all of the following actions: issuing public notice to downstream property owners, complying with flood insurance requirements, adopting emergency action plans, conducting mock flood drills, acquiring flow easements or other acquisitions of real property, or other actions appropriate to safeguard the CCR surface impoundment site and flood channel.

b. Include a control structure to avoid head cutting and lowering of the spillway crest for spillways excavated in soils or soft rock. In the alternative, the design may provide evidence acceptable to the Director that erosion during the inflow design flood will not result in a sudden release of the reservoir.

c. Provide each spillway and channel with a minimum width of 10 feet and suitable armor to prevent erosion during the discharge resulting from the inflow design flood.

d. Ensure that downstream spillway channel flows do not encroach on the CCR surface impoundment unless suitable erosion protection is constructed.

e. Not construct bridges or fences across a spillway unless the construction is approved as part of the CCR facility permit. The CCR facility permit may include conditions regarding the design and operation of the spillway and fencing, based on safety concerns.

f. Not use a pipe or culvert as an emergency spillway unless specifically approved in the CCR facility permit following review of the CCR surface impoundment design and site characteristics.

2. Outlet Works Requirements. An owner or operator shall ensure that a CCR surface impoundment that has outlet works has a low-level outlet works that:

a. Is capable of draining the reservoir to the sediment pool level or CCR surface. A low-level outlet works for a high or significant hazard potential CCR surface impoundment shall be a minimum of 36 inches in diameter. A low-level outlet works for a low hazard potential CCR surface impoundment shall be a minimum of 18 inches in diameter.

b. Has a filter diaphragm or other current practice measures to reduce the potential for piping along the conduit.

c. Has accessible outlet controls when the spillway is in use.

d. Has an emergency manual override system or can be operated manually.

e. Is constructed of materials appropriate for loading condition, seismic forces, thermal expansion, cavitation, corrosion, and potential abrasion. The owner or operator shall not use corrugated metal pipes or other thin-walled pipes except as a form for a cast-in-place concrete conduit. The owner or operator shall construct outlet conduits of cast-in-place reinforced concrete. The owner or operator shall design each outlet to maintain water tightness. The owner or operator shall construct each outlet to prevent the occurrence of piping adjacent to the outlet.

f. Has an operating or guard gate on the upstream end of any gated outlet.

g. Has an outlet conduit near the base of one of the abutments on native bedrock or other competent material. The entire length of the conduit shall be supported on foundation materials of uniform density and consistency to prevent adverse differential settlement.

h. Has an upstream valve or gate capable of controlling the discharge through all ranges of flow on any gated outlet conduit.

i. Has a trashrack designed for a minimum of 25% of the reservoir head to which it would be subjected if completely clogged at the upstream end of the outlet.

j. Has an outlet conduit designed for internal pressure equal to the full reservoir head and for superimposed embankment loads, acting separately.

E. 40 CFR 257.83(a)(1)(i) is amended to read: "At intervals not exceeding seven days, inspect for any appearances of actual or potential structural weakness and other conditions which are disrupting or have the potential to disrupt the operation or safety of the CCR unit. The owner or operator shall increase the frequency of observation when the reservoir is full, during heavy rains or flooding, and following an earthquake."

F. 40 CFR 257.83, titled "Inspection requirements for CCR surface impoundments", subsection (b)(1) is amended to read: "If the existing or new CCR surface impoundment or any lateral expansion of the CCR surface impoundment is subject to the periodic structural stability assessment requirements under § 257.73(d) or § 257.74(d), the CCR unit must additionally be inspected on a periodic basis by a qualified professional engineer to ensure that the design, construction, operation, and maintenance of the CCR unit is consistent with recognized and generally accepted good engineering standards. The owner or operator shall notify the Director and submit a written summary of the engineer's qualifications at least 14 days before the scheduled inspection. The inspection must, at a minimum, include:"

G. In addition to the inspection requirements for CCR surface impoundments in 40 CFR 257.83(b)(1), the following requirements are added:

1. Inspection of any permanent monument or monitoring installations;

2. Assessment of all parts of the CCR surface impoundment that are related to the CCR surface impoundment's safety; and

3. A recommendation regarding the safe storage level of the impoundment.

H. In addition to the inspection requirements for CCR surface impoundments in 40 CFR 257.83(b)(5), the owner or operator shall notify the Department within 24 hours and in writing within five days if a deficiency or release could result in harm to human health or the environment or has resulted in a release. The owner or operator shall notify the Department in writing within 14 days of all other deficiencies under 40 CFR 257.83(b)(5).

I. In addition to the inspection requirements for CCR surface impoundments in 40 CFR 257.83, the following requirements are added:

1. Notwithstanding 40 CFR 257.73(a)(2)(i) and (ii) and 40 CFR 257.74(a)(2)(i) and (ii), a qualified professional engineer shall review the hazard potential classification of each CCR surface impoundment during each subsequent inspection under § 257.83(b)(4)(i) and revise the classification in accordance with current conditions.

2. Maintenance and Repair

a. An owner shall perform general maintenance and ordinary repairs that do not impair the safety of the CCR surface impoundment. General maintenance and ordinary repair activities listed under this subsection do not require prior approval of the Director. These repair activities include:

i. Removing brush or tall weeds.

ii. Cutting trees and removing slash from the embankment or spillway. Small stumps may be removed provided no excavation into the embankment occurs.

iii. Exterminating rodents by trapping or other methods. Rodent damage may be repaired provided it does not involve excavation that extends more than 2 feet into the embankment and replacement materials are compacted as they are placed.

iv. Repairing erosion gullies less than 2 feet deep on the embankment or in the spillway.

v. Grading the surface on the top of the CCR surface impoundment embankment or spillway to eliminate potholes and provide proper drainage, provided the freeboard is not reduced.

vi. Placing additional riprap and bedding on the upstream slope, or in the spillway in areas that have sustained minor damage and restoring the original riprap protection where the damage has not yet resulted in erosion and weakening of the CCR surface impoundment.

vii. Painting, caulking, or lubricating metal structures.

viii. Patching or caulking spalled or cracked concrete to prevent deterioration.

ix. Removing debris, rock, or earth from outlet conduits or spillway channels and basins.

x. Patching to prevent deterioration within outlet works.

xi. Replacing worn or damaged parts on outlet valves or controls to restore them to original condition or its equivalent.

xii. Repairing or replacing fences intended to keep traffic or livestock off the CCR surface impoundment or spillway.

b. General maintenance and ordinary repair that may impair or adversely affect safety, such as excavation into or near the toe of the CCR surface impoundment, construction of new appurtenant structures for the CCR surface impoundment, and repair of damage that has already significantly weakened the CCR surface impoundment shall be performed in accordance with this Article. The Director shall determine pursuant to R18-13-1017 whether general maintenance and ordinary repair activities not listed in paragraph (a) will impair safety.

J. Subsections (B) through (I) of this Section are based on Arizona dam safety standards additional to those in 40 CFR 257, subpart D, as incorporated in this Article, and do not apply to:

1. CCR surface impoundments with a maximum height of less than 6 feet, regardless of storage capacity;

2. CCR surface impoundments with a maximum height of between 6 and 25 feet and a storage capacity of less than 50 acre-feet; or

3. CCR surface impoundments with a maximum height greater than 25 feet and a storage capacity of 15 acre-feet or less.

Notes

Ariz. Admin. Code § R18-13-1004

New section made by final rulemaking at 31 A.A.R. 1363, effective 6/1/2025.