REXBURG, Idaho (AP) — Beneath the soil of eastern Idaho is one of its greatest assets: The Eastern Snake River Plain Aquifer.

    One of the largest in the Northwest, the aquifer curves south from Ashton to Twin Falls, then west to Hagerman. The water flow is the size of Lake Erie, with an estimated volume of 200 billion cubic feet, according to the Idaho Water Resource Board.

    The resource was a major catalyst in turning the region from a high-tundra desert to acres of farmland. For more than a century, it has provided water to growers, fish farms and eastern and southern Idaho communities.

    But it’s shrinking at a steadily increasing pace, according to a study by the U.S. Geological Survey released in May.

    While there remains more than enough water in the short-term, state and national water experts estimate that unless action is taken, the aquifer could reach dangerous lows within several decades, threatening agriculture and Idaho communities.

    “One of the biggest problems we have — that most people don’t realize — is that municipal wells are not going to be able to handle increased population growth,” said state Rep. Dell Raybould, R-Rexburg. “We have to have more surface storage to recharge the aquifer and cover that increased need (from) municipalities.”

    Raybould, a longtime water advocate, sits on the House Resource and Conservation Committee.

    The aquifer’s continued decline has come into sharper focus this year because of an extended drought.

    This spring, the Idaho Water Resource Board and local canal companies could only spare some 3,600 acre-feet of excess water to recharge the aquifer, said Brian Patton, state bureau chief of the board.

    One acre-foot of water is enough to fill half of an Olympic-sized swimming pool.

    That’s a far cry from the average 100,000 acre-feet of water the partnership has poured into the aquifer annually since 2009.

    But even during good recharge years, the amount of water returning to the aquifer is less than half of the average 214,000 acre-feet that has been lost from storage annually since 1952, Patton said.

    Aquifer recharge and the effects of groundwater depletion is a frequent discussion in the Legislature. But what is less talked about is how aquifer depletion will affect rapidly growing cities.

    One of the fastest growing communities in eastern Idaho is Rexburg, where city officials already are experiencing an overused aquifer.

    The last time Rexburg expanded its groundwater usage was in 1991, when the city had a population of about 12,000. Today, with a population exceeding 30,000, Rexburg, on hot July days, expends all of its allocated pumped water and 3 million gallons of its 4.25 million gallon surface storage in a single day. Within 18 months, city officials expect growth of about 5,000 people.

    “The volume we can maintain on a peak day is less and less each year, and when our tanks go down, we are immediately out of water,” Public Works Director John Millar said.

    The answer is to pump more water, but that requires obtaining a new water right from the Idaho Water Resource Board, something that since the early 1990s has been difficult. Rexburg applied three years ago and is still waiting.

    “Currently, it is nearly impossible to get a well water permit from the state,” Mayor Richard Woodland said. “But unless they give us more water permits, we’ll run out of water.”

    The problem is twofold. First, the board has upheld a moratorium on issuing new water rights in the Snake River Basin since 1992 in an effort to limit the depletion of the aquifer, as well as protect the rights of senior water users, according to board records.

    The other issue is downstream, where growers and irrigators are concerned issuing additional groundwater rights will limit their ground and surface water. A group of Twin Falls canal companies, called the Surface Water Coalition, protested Rexburg’s request, resulting in several years of negotiation.

    The issue was resolved after Rexburg developed a mitigation plan, which was met with the coalition’s approval.

    By law, Rexburg would be required to mitigate any new water taken from the aquifer, either through diverting its surface water rights downstream or participating in managed aquifer recharge and returning the water underground.

    Despite the resolution, Rexburg is still not approved.

    The issue, according to Lynn Tominaga, executive director of Idaho Ground Water Appropriators, is that both Rexburg and southern cities such as Twin Falls have senior water rights. Between the two cities, however, are many users with junior water rights, who may use the water before it gets to Twin Falls, despite its senior water right.

    Tominaga suggested Rexburg purchase an established water right from an Upper Valley farmer, to avoid infringing on the water rights of downstream users. But that process is far more expensive because the city would have to purchase the land attached to the water right.

    Board officials declined to discuss Rexburg’s specific case. But Patton said obtaining new water rights will remain a very difficult prospect until the aquifer is stabilized.

    And more problems likely will arise in the future as more growing communities demand new groundwater rights from the ever depleting aquifer.

    “We have to figure out some way to store this excess water that goes to the ocean and store it in the aquifer,” Raybould said. “Within a few years, if we don’t do something and the aquifer keeps going down, (our municipal populations) are going to be in serious trouble.