In certain areas of the state, water management practices and land uses, in combination with hydrogeologic conditions, have increased the potential for ground water quality degradation. Idaho's ground water quality monitoring program results confirm that levels of ground water degradation deemed significant have occurred in specific areas across the state. This negatively impacts water quality and potentially threatens domestic water supplies, aquaculture, agriculture, mining, industrial, and other ground water beneficial uses.

The Division of Environmental Quality (DEQ) is designated as the primary agency to coordinate and administer ground water quality protection programs for the state. [Ground Water Quality Protection Act of 1989, Idaho Code §39-120] Various state and local agencies have responsibilities for and are involved in implementing the Ground Water Quality Plan (adopted in 1992 and amended in 1996).

The Ground Water Quality Rule IDAPA 16.01.11.400.02 and IDAPA 16.01.11.400.03 sets forth a number of alternative actions the DEQ may follow when a numerical ground water quality standard has been exceeded, as well as when one has not been exceeded but significant degradation of the ground water has been detected. IDAPA 16.01.11.400.02 also sets forth the general criteria to be used in determining the significance of degradation. The policy provides further guidance to the DEQ in determining significant degradation in areas with multiple potential sources of contamination and developing responses to that degradation.

DEQ may initiate an evaluation at any time to determine whether ground water quality trends identify an area as being significantly degraded or having impaired beneficial uses. Areas will be screened for selection if they are deemed to have significant degradation as set forth in the Ground Water Quality Rule, IDAPA 16.01.11.400.02.b. Water quality data used to identify degraded areas should involve samples that are representative of the aquifer in question and/or representative of the impacted beneficial use.

Designation of significantly degraded ground water quality areas may be based on: (1) ground water monitoring data that indicate the ground water quality has already become degraded to the extent that it does not meet established water quality standards or data that indicate a statistically significant trend such that it is likely that the ground water quality may become contaminated at an unacceptable level, considering the criteria set forth in IDAPA 400.02b, in the foreseeable future; or (2) ground water data or other information that indicate that a group of facilities, operations or activities have injured an established beneficial use(s) or may injure an established beneficial use(s) in the foreseeable future.

Area designation or boundary modification shall be presented in a concise, factual report form and shall contain: (1) supporting ground water quality data; (2) maps or geographic information system coverages showing sample sites with corresponding data references; (3) information on how the sample locations were selected and analytical methods used; and (4) a general description of and rationale for the proposed or modified ground water quality management area boundary.

In addition to the above items, a designation may include recommendations from agencies, organizations and groups having jurisdiction over ground water or surface water programs, information on potential contaminant sources, and suggestions on voluntary or regulatory mechanisms that can be used to help manage the proposed area.

Delineation of significantly degraded ground water quality areas requires a determination of the potential area of impact or the known location and aerial extent of the contaminant of interest. Criteria to guide delineation of significantly degraded areas shall include, but not be limited to, the following: (1) areas which generally contain a specific type or class of contaminant; and (2) areas that are generally greater than 10 square miles and generally represent multiple sources of contamination. Smaller areas may be considered where multiple sources of contamination are impacting beneficial uses.

Each area will be defined by the boundaries of aquifers or portions of aquifers which contain the contaminant of interest, land use information, and/or other considerations deemed appropriate by the DEQ. Boundaries may be revised as additional data or information are made available to better define the degraded area.

The DEQ, with input from other agencies and the public, will establish a state-wide priority list for managing significantly degraded ground water quality areas. This list will be used to prioritize the implementation of protective management strategies or corrective action measures throughout the state.

The list will distinguish the relative priority of the degraded areas based upon: (1) the severity or urgency of the problems or potential problems; (2) the relative potential of the contamination to impact drinking water sources as defined by delineated source water protection areas; (3) the relative potential of the contamination to exceed state water quality standards or impair designated beneficial uses; and (4) the ground water quality trends within the degraded area.

A public comment period will be provided after development of the initial priority list and biennially after that. The DEQ will revise the list as needed to address appropriate public comments or to incorporate updated information on ground water quality data. After each revision, the DEQ will provide public notice of the availability of the list.

DEQ shall ensure the participation of and coordination with the public and relevant agencies and entities during the development of management strategies. Once an affected portion of an aquifer has been designated as a significantly degraded area, the DEQ will work with local groups, other agencies, and the public to develop ground water quality management strategies for that area. The first step prior to the development of any strategy will be determining if there are current or planned water quality management activities in the area; reviewing these activities with the implementing authority; and incorporating, where appropriate, the activities into the final strategy. DEQ may, when appropriate, request the formation of an advisory committee, or may use other existing advisory groups such as the agricultural ground water quality coordination committee or watershed advisory groups, to provide recommendation regarding the development of management strategies.

The strategies will focus on prevention, protection, and remediation measures to maintain or improve water quality or prevent impairment of a beneficial use. Strategies may include a number of activities such as: collecting additional data and conducting studies related to hydrogeology, water quality, water use, land use, and population projections; executing local agreements or other contracts; applying voluntary and/or regulatory control measures designed to protect the area; determining if the contamination is the result of historical practices or natural causes; applying remediation techniques, and other duties as appropriate.

The DEQ, in coordination with other agencies and stakeholders, will be responsible for reviewing and ensuring that the activities are consistent with the overall goals of the Ground Water Quality Plan, Ground Water Quality Rule, Agricultural Coordination Committee, and IDWR/ISDA/DEQ Memorandum of Understanding. Special emphasis will be placed on public education, implementation of effective best management practices and best practical methods, technical assistance, and other forms of mitigation.

Upon completion of the local ground water management strategy implementation, DEQ and other appropriate agencies, will assess the data for the purpose of evaluating the effectiveness of the strategy. The high priority designation will be removed from areas when management strategies have proven to be protective of aquifer water quality and beneficial uses.