IDWR's Director is granted the authority to designate Critical Groundwater Areas (CGWAs) and Groundwater Management Areas (GWMAs) under Idaho Code Title 42, Chapter 233a and
233b, respectively. These sections codify the definitions and bases for designating these special management areas.
A CGWA is all or part of a groundwater basin that does not have sufficient groundwater to provide a reasonably-safe supply for irrigation or other uses at the current or projected rates of withdrawal. IDWR's Director can deny an application for a proposed use if the point of diversion lies within the designated area, and the Directory may require water users to report diversions or other information.
A GWMA is all or part of a groundwater basin that may be approaching the conditions of a CGWA. Applications for new water appropriations may be approved only after it is determined that sufficient supply is available and other prior water rights will not be injured. The Director may require reporting of water use by water users within the area.
The authority for designating areas for regulating groundwater withdrawals from aquifers subject to insufficient supplies was first granted in 1953 through amendments to Idaho's Groundwater Act. However, it was not until 1962 that the first CGWAs were designated in the Oakley Fan area. Amendments to the Act in 1982 granted authority for designating GWMAs. The Grandview-Bruneau area, designated in 1982, was the first GWMA.
The Order designating the Southeast Boise GWMA in 1994 was the first time an advisory committee was required as a part of the initial formation of a GWMA. Since that time, orders requiring the formation of advisory committees have been issued subsequent to the initial formation of the management areas. These committees are to assist in the management of groundwater resources through development of management plans, to establish processes for dispute resolution, and to act as a forum for discussion and communication.