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Water Users and the State of Idaho Are Reviewing Conjunctive Management on the Eastern Snake Plain Aquifer

Water Users and the State of Idaho Are Reviewing Conjunctive Management on the Eastern Snake Plain Aquifer
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By Andrew J. Waldera

After executing a settlement agreement and mitigation plan in 2015, surface water users, groundwater users, and the State of Idaho are again working on solutions to address a declining Eastern Snake Plain Aquifer (ESPA). The aquifer underlies the Snake River plan stretching from roughly King Hill, Idaho in the west to Ashton, Idaho in the east. After some seeming stabilization between 2016 and 2019, aquifer levels resumed declining from 2020 through 2022. Legal conflict between senior surface water users and generally more junior groundwater users has been ongoing since the early 2000s, and while the 2015 agreement between the Surface Water Coalition (SWC) and constituent groundwater districts participating under the larger Idaho Ground Water Appropriators (IGWA) umbrella paused much of the litigation, present day aquifer declines are spurring disputes between the parties once again.

The 2015 Agreement

 In 2015, the SWC and IGWA entered into a settlement agreement and mitigation plan that would allow junior groundwater pumpers to continue pumping out priority under the prior appropriation doctrine provided that IGWA members abided by a mitigation plan designed to stabilize and eventually recover aquifer levels in the ESPA. Senior surface water users on the ESPA are affected by groundwater pumping because the aquifer expresses itself as surface water flows in the Snake River. Of particular interest to the SWC are aquifer-fed baseflows in the river in the Blackfoot to Neely reach immediately upstream of American Falls Reservoir. SWC members rely on reservoir storage water through the irrigation season as natural flows in the river decline as the summer progresses. Because of these hydrologic surface water connections, surface water rights and groundwater are administered in priority together (conjunctively managed) across much of the ESPA.

 The major components of the 2015 Agreement were expected to stabilize at the least, and hopefully recover the aquifer along the way, included IGWA “conservation” commitments of 240 kAF of pumping reductions; state-sponsored aquifer recharge averaging 250 kAF annually; and IGWA provision of 50 kAF of storage water annually procured from others (or the SWC if other willing storage space holders cannot be found). Of the 240 kAF pumping reduction, a portion must be achieved via actual pumping reduction, and a portion can be achieved through additional aquifer recharge above and beyond the state-sponsored component.

 While the state’s recharge “commitment” is in principle only (Idaho is not a party to the 2015 Agreement), the Idaho Water Resource Board funds and implements a large-scale managed aquifer recharge program largely due to the state’s complicity in the over-appropriation of the aquifer historically (particularly in the late 1940s through the 1960s–Idaho and Idaho Power Company promoted and incentivized widespread development of groundwater to support additional agricultural operations across several hundreds of thousands of acres on the Snake River Plain). Today, groundwater pumping from the ESPA totals approximately 1.1 million acre-feet annually, of which 95 percent is for agricultural uses.

2021 Irrigation Season Breach

 After the 2021 irrigation season, the SWC coalition alleged that IGWA breached the 2015 settlement agreement and mitigation plan (Plan) by falling short of the 240,000 AF reduction target. A number of IGWA member districts failed to meet their proportionate share reduction goals by pumping more water than allowed under the Plan. IGWA asserted that the Plan’s 240 kAF conservation requirement applied to others not part of IGWA and, therefore, not part of the Plan. IGWA member pumping reductions hovered closer to 205 kAF annual average based on this assumption of shared conservation credit from others not part of the Plan. IGWA also asserted that the 240 kAF target was not an annual requirement, but one that could be met through multi-year averaging.

 The Director of IDWR disagreed, holding that IGWA breached the Plan during the 2021 irrigation season in the aggregate quantity of 126,620 AF. The Director held that the annual 240 kAF conservation target was IGWA’s alone, and that the target was an annual requirement (i.e., nut subject to multi-year averaging). Ultimately, not all IGWA members breached the Plan—a couple met their targets. Those IGWA member groundwater districts who did breach their proportionate targets (i.e., pumped too much water) were: Aberdeen Falls-Aberdeen (24,826 AF); Bingham (55,951 AF); Bonneville-Jefferson (18,185 AF); Jefferson-Clark (20,796 AF); Magic Valley (2,590 AF); and North Snake (4,272 AF).

 IGWA reached an IDWR-approved settlement with the SWC for the 2021 breach to supply an additional 30,000 AF of storage water to the SWC during the 2023 irrigation season, and an additional 15,000 AF of storage water to the SWC in 2024. These 2023 and 2024 quantities of water are in addition to the baseline annual IGWA requirement to reduce use/provide 240 kAF of water to the SWC under the 2015 settlement agreement and the previously-approved Plan.

The Path Forward 

While IGWA and the SWC reached an interim settlement heading into the 2023 irrigation season concerning the 2021 irrigation season breach, the parties anticipated another breach of the Plan during the 2022 irrigation season (final numbers will not be confirmed until April), and it is becoming clear that current efforts under the 2015 Agreement are not stabilizing the aquifer according to updated IDWR modeling. IGWA, the SWC, and IDWR undertook additional settlement negotiations in February 2023 to address these additional (and larger) issues.

 Currently, the parties are working on an interim agreement for the 2023 irrigation season. Beyond that, they are wrestling with several larger, longer-term questions, including what is the ultimate “recovered” level of/water budget for the aquifer? Over a century of formerly flood irrigation and incidental seepage largely mounded the aquifer to elevations that would not otherwise exist. Once that level is agreed upon, how do the parties get there, and who are the “parties” necessary to achieve the goal? While IGWA members form the majority of groundwater pumpers on the ESPA, there are others, and there are other tributary basins that contribute groundwater flow to the aquifer. On this point, IGWA and the SWC are supporting IDWR efforts to issue a broader groundwater management plan, rather than continuing to stretch the Plan, and those of others involved in the SWC delivery call into what should be a more comprehensive groundwater management plan administering a larger geographic footprint of hydrologically-interconnected use.

Conclusion and Implications

IGWA and the SWC seek to have a larger, more comprehensive groundwater management plan drafted and approved by IDWR by November 1, 2023. This is an ambitious goal, particularly with the introduction of more water users to the negotiation and implementation mix.