Section 500. Water impoundments

A. Structures that impound water or sediment to a height of five feet or more above the lowest natural ground area within the impoundment and have a storage volume of 50 acre-feet or more, or impound water or sediment to a height of 20 feet or more regardless of storage volume, shall meet the following criteria (noted in Chapter 18.1 (§ 45.1-225.1 et seq.) of Title 45.1 of the Code of Virginia):

1. Impoundments meeting or exceeding the size criteria set forth in this section shall be designed utilizing a spillway flood and hazard potential classification as specified in the following table:

	Class of Impoundment*	Spillway Design Flood (SDF)**	Minimum Threshold for Incremental Damage Analysis ***
	High Hazard	PMF	0.50 PMF
	Significant Hazard	0.50 PMF	100-year storm
	Low Hazard	100-year storm	50-year storm
	*Size and hazard potential classifications shall be proposed and justified by the operator and shall be subject to approval by the director. Present and projected development in the inundation zone downstream from the structure shall be used in determining the classification. **The complete definitions of hazard potential are those contained in 4VAC50-20-40. ***The establishment of rigid design flood criteria or standards is not intended. Safety must be evaluated in the light of peculiarities and local conditions for each impounding structure and in recognition of the many factors involved, some of which may not be precisely known. Such can only be done by competent, experienced engineering judgment, which the values in the table are intended to add to, not replace.

Reductions in the SDF may be evaluated by use of incremental damage analysis described in 4VAC50-20-52. Note that future development downstream may increase the required SDF.

2. Impounding structures shall be constructed, operated, and maintained such that they perform in accordance with their design and purpose throughout their life.

a. Impoundments shall be designed and constructed by or under the direction of a qualified professional engineer licensed in Virginia and experienced in the design and construction of impoundments.

b. The designs shall meet the requirements of this section and use current prudent engineering practices.

c. The plans and specifications for an impoundment shall consist of a detailed engineering design report that includes engineering drawings and specifications, with the following as a minimum:

(1) The name of the mine; the name of the owner; classification of the impounding structure as set forth in this regulation; designated access to the impoundment and the location with respect to highways, roads, streams and existing impounding structures and impoundments that would affect or be affected by the proposed impounding structure.

(2) Cross sections, profiles, logs of test borings, laboratory and in situ test data, drawings of principal and emergency spillways and other additional drawings in sufficient detail to indicate clearly the extent and complexity of the work to be performed.

(3) The technical provisions as may be required to describe the methods of the construction and construction quality control for the project.

(4) Special provisions as may be required to describe technical provisions needed to ensure that the impounding structure is constructed according to the approved plans and specifications.

d. Components of the impounding structure, the impoundment, the outlet works, drain system and appurtenances shall be durable in keeping with the design and planned life of the impounding structure.

e. All new impounding structures regardless of their hazard potential classification shall include a device to permit draining of the impoundment within a reasonable period of time, and at a minimum shall be able to lower the pool level six vertical inches per day, as determined by the owner's professional engineer, subject to approval by the director.

f. Impoundments meeting the size requirements and hazard potential of high, significant, or low shall have a minimum static safety factor of 1.5 for a normal pool with steady seepage saturation conditions and a seismic safety factor of 1.2.

g. Impoundments shall be inspected and maintained to ensure that all structures function to design specifications.

h. Impoundments shall be constructed, maintained and inspected to ensure protection of adjacent properties and preservation of public safety and shall meet proper design and engineering standards under Chapter 18.1 (§ 45.1-225.1 et seq.) of Title 45.1 of the Code of Virginia. Impoundments shall be inspected at least daily by a qualified person, designated by the licensed operator, who can provide prompt notice of any potentially hazardous or emergency situation as required under § 45.1-225.2 of the Code of Virginia. Records of the inspections shall be kept and certified by the operator or his agent.

i. The operator will prepare an emergency action plan (EAP) that includes the following information:

(1) A notification chart of persons or organizations to be notified, the person or persons responsible for notification, and the priority in which notifications are issued. Notifications shall include at a minimum the division, the local government authority responsible for emergency response, and the Virginia Department of Emergency Management.

(2) A discussion of the procedures used for timely and reliable detection, evacuation, and classification of emergency situations considered to be relevant to the structure and its setting.

(3) Designation of responsibilities for EAP related tasks. Also, the EAP shall designate the responsible party for making a decision that an emergency situation no longer exists at the impounding structure. Finally, the EAP shall include the responsible party and the procedures for notifying to the extent possible any known local occupants, owners, or lessees of downstream properties potentially impacted by a failure of the impounding structure.

(4) A section describing actions to be taken in preparation for impoundment emergencies, both before and during the development of emergency conditions.

(5) Dam break inundation maps. Each sheet of such maps for high and significant potential hazard classification structures shall be prepared and sealed by a professional engineer. Where possible, inundation mapping in the EAP should be provided on sheets no larger than 11 inches by 17 inches to facilitate copying for emergency response.

(6) Appendices containing information that supports and supplements the material used in the development of the EAP, including plans for training, exercising, and updating the EAP.

(7) A section that identifies all parties with assigned responsibilities in the EAP and signed certification by all of those parties that a copy of the EAP has been received.

(8) Times periods for review or revision acceptable to the director.

3. Impoundments shall be closed and abandoned in a manner that ensures continued stability and compatibility with the post-mining land use.

4. The following are acceptable as design procedures and references:

a. The design procedures, manuals and criteria used by the United States Army Corps of Engineers;

b. The design procedures, manuals and criteria used by the United States Department of Agriculture, Natural Resources Conservation Service;

c. The design procedures, manuals and criteria used by the United States Department of Interior, Bureau of Reclamation;

d. The design procedures, manuals and criteria used by the United States Department of Commerce, National Weather Service;

e. The design procedures, manuals and criteria used by the United States Federal Energy Regulatory Commission;

f. Federal Guidelines for Dam Safety: Emergency Action Planning for Dam Owners, United States Department of Homeland Security, Federal Emergency Management Agency, October 1998, Reprinted January 2004; FEMA 64 or as revised;

g. Federal Guidelines for Dam Safety: Selecting and Accommodating Inflow Design Floods for Dams, United States Department of Homeland Security, Federal Emergency Management Agency, October 1998, Reprinted April 2004; FEMA 94 or as revised; or

h. Other design procedures, manuals and criteria that are accepted as current, sound engineering practices, as approved by the director prior to the design of the impounding structure.

B. Impoundments that do not meet or exceed the size criteria of subsection A of this section shall meet the following criteria:

1. Be designed and constructed using current, prudent engineering practice to safely perform the intended function.

2. Be constructed with slopes no steeper than two-horizontal-to-one-vertical in predominantly clay soils or three-horizontal-to-one-vertical in predominantly sandy soils.

3. Safely pass the runoff from a 50-year storm event for temporary (life of mine) structures and a 100-year storm event for permanent (to remain after mining is completed) structures.

4. Be closed and abandoned to ensure continued stability and compatibility with the post-mining use.

5. Be inspected and maintained to ensure proper functioning.

6. Provide adequate protection for adjacent property owners and ensure public safety.

C. Impoundments with impounding capability created solely by excavation shall comply with the following criteria:

1. Be designed and constructed using prudent engineering practice to safely perform the intended function.

2. Be constructed with slopes no steeper than two-horizontal-to-one-vertical in predominantly clay soils or three-horizontal-to-one-vertical in predominantly sandy soils.

3. Be designed and constructed with outlet facilities capable of:

a. Protecting public safety;

b. Maintaining water levels to meet the intended use; and

c. Being compatible with regional hydrologic practices.

4. Be closed and abandoned to ensure continued stability and compatibility with the post-mining use.

5. Be inspected and maintained to ensure proper functioning.

6. Provide adequate protection for adjacent property owners and ensure public safety.

Historical Notes

Derived from Volume 19, Issue 24, eff. September 11, 2003; amended, Virginia Register Volume 30, Issue 06, eff. December 19, 2013.

Statutory Authority

§§ 45.1-161.3 and 45.1-180.3 of the Code of Virginia.