BOISE — The Idaho Senate Resources and Environment Committee endorsed a proposal to expand the area over which Eastern Snake Plain Aquifer water is managed.

Snake River tributaries eventually would be included in ESPA water-rights administration if Senate Bill 1341 passes.

The Lake Erie-sized aquifer underneath much of the state’s southeast and south-central regions has been in decline for decades. Business and residential growth, and irrigation systems are among the factors.

The legislation “provides clarification and expansion of common groundwater supply” in the eastern Snake River plain, according to its purpose statement.

It aims in part to involve more users in potential solutions, according to supporters. The 1992 common-groundwater supply map should be updated to reflect current science, and tributary impacts should be considered in future management decisions, they said.

“What we are trying to discover with conjunctive management is the impact that irrigation and other businesses and municipalities have on that aquifer,” Sen. Van Burtenshaw, R-Terreton, one of the bill’s sponsors, said during a Feb. 14 hearing.

Idaho manages groundwater and surface water together.

“Our desire is to make sure that this aquifer can produce into perpetuity,” Burtenshaw said. “In order to do that, we need to understand all the water coming in and all the water coming out.”

“If folks are contributing to the challenges and the difficulties, they should also be part of the solution,” said Paul Arrington of the Idaho Water Users Association.

Arguments against SB 1341 included that more time is needed for planning before the law is changed, and that some tributary basins that would be brought into ESPA administration are already subject to recently increased groundwater monitoring and management.

Farmers and canal companies in the Teton River Basin, near the Wyoming border, recently said they had not heard of the idea to include Snake tributaries, and “I have not been part of these conversations to possibly tap Teton Basin’s surface and groundwater rights,” said Driggs Mayor August Christensen.

“Our farmers have not, our counties have not,” she said. “If all of our water rights could possibly be taken from us because all of them are junior, we need to be part of this conversation.”

The proposed expansion of the common groundwater supply area is tied to recent scientific modeling of the ESPA and does not simply add every Snake tributary into aquifer-management decisions, Arrington said. Decisions would follow extensive study and a hearing process.

In tributary basins where state-designated critical groundwater areas and approved groundwater management plans exist, the Department of Water Resources director could not expand the common-supply area unless the plan is deemed insufficient to manage the impacts of withdrawals on tributary aquifers or the ESPA, according to the bill text.

While everyone who impacts the aquifer should participate in helping to preserve it, “we need to make it clear that this change will include an expanded area of those who are in the line of fire, with everything up to and including curtailment,” said Sen. Jim Guthrie, R-McCammon.