The Eagle Foothills could welcome 20,000 homes by 2040. Where will they get water?

This story was originally published on August 9, 2007.

Although most Eagle residents haven’t heard of the Pierce Gulch Sand Aquifer, it is likely to become the center of public and scientific debate in the coming months.

The issue: whether there’s enough water in the Foothills north of Eagle to serve the up to 20,000 new homes are expected to be built there in the next 35 years without negatively impacting existing water users.

Developer M3 Eagle Companies is proposing to build 8,160 houses on 6,000 acres north of Eagle. The area is outside Eagle’s city limits and growth boundary, but M3 is seeking a path toward annexation. To provide water for those homes, M3 has filed a water rights application for 42.5 cubic feet per second, or about 27 million gallons per day. That’s a maximum diversion rate.

M3’s hydrology consultant, Ed Squires of Boise-based Hydro Logic Inc., said this week that the company plans to file another application reducing that to about 27.3 cfs , or about 17.6 million gallons a day.

Squires said the number the public should focus on is the average daily usage, not the maximum diversion rates listed in the water rights application.

“The maximum diversion rate would probably never occur,” Squires said. “That would be every well (pumping) at its maximum rate of diversion all at once, all at the same time and every use taking water.”

He estimates M3’s average daily water usage would be about 16 cfs, or 10 million gallons per day. Comparatively, the city of Meridian has an average daily water usage in the summer of about 15 million gallons.

Idaho Department of Water Resources can’t issue new water rights if they will disrupt existing water users. So M3 hired Hydro Logic to do a $1 million study.

The report, released in May, says that most existing wells in the area are up-gradient in the flow system from the M3 site. It describes a newly identified regional aquifer — the Pierce Gulch Sand Aquifer — that flows westward under Boise, Eagle and Star to the Payette River Basin. The report characterizes the aquifer as “moderately to highly productive.”

“The groundwater proposed to be withdrawn by M3 for its development will be from subsurface flow that already has departed the Boise Basin, so that impacts to existing area water users in the lowlands near Eagle are predicted to be small,” according to Hydro Logic’s report.

Concerned North Ada residents want an independent study.

David Head, a member of the citizen-activist North Ada County Foothills Association who is following water issues for the group, said Hydro Logic’s report is just a theory until it gets a peer review and is supported by an independent study.

“They did a nice job on it,” Head said. “Somebody needed to get this started, but it’s just the scratch on the surface if you really want to understand what (development is) going to do to the Foothills.”

Head said it’s important for the state to get a good handle on water resources in the Foothills, not just to protect existing water users, but also to be sure that water rights can be allocated fairly to all of the Eagle Foothills property owners, not just M3.

The state water chief agrees.

“It’s the role of IDWR to provide an overview of studies and to make its own determination on water availability,” Director David Tuthill said.

North Ada residents petitioned the Water Resources Department last year to do an independent study of the area, but no money was budgeted for fiscal 2008.

Since then, officials have moved a proposed study higher on their list of priorities.

“We recognize that this is an area where growth is imminent,” Tuthill said. “That is what brought this area to second priority, above a dozen other basins.”

The Treasure Valley Hydrologic Project, a multiyear study by IDWR that began in 1996, studied water sources in the Treasure Valley. But that expansive water study didn’t extend into the Foothills.