Eastern Snake Plain Aquifer Overview

The Eastern Snake Plain Aquifer (ESPA) is located in southeastern Idaho. It is Idaho’s largest aquifer system, and one of the largest in the United States. The aquifer is composed primarily of basalts and covers approximately 11,000 square miles. The storage capacity of the upper 500 feet is estimated to be 200-300 million acre feet. Primary discharges are the Thousand Springs area and American Falls/Ft. Hall area. Snow and rainfall from Wyoming, Utah, and Nevada feed into the Snake River and supply the aquifer. The Snake River Plain, which draws from the aquifer, contains 2 million irrigated acres and supports farming operations including potatoes, sugar beets, wheat, barley, beans, peas, alfalfa, dairies, and aquaculture. Output from this region accounts for about 25% of Idaho’s economy. 


Timeline of Developments

2016: The Eastern Snake Plain Aquifer is designated as a Ground Water Managment Area by the Idaho Department of Water Resources.

2016: In 2016, the Legislature approved $28.9 million over three years in recharge funding. The money comes from a mix of general and dedicated funds and federal grants. 

2014: HB 547 allocates $5 million to the Water Resources Board for aquifer recharge with priority given to ESPA. HB 479 grants an additional $4 million one-time allocation to fund recharge infrastructure. Additional one-time funds were allocated in 2015. 

2009: Swan Falls Re-affirmation Agreement between the State of Idaho and the Idaho Power Company. Among a number of stipulations, the agreement requires the state of Idaho to work with Idaho Power in the case of lower hydropower generation with the introduction of diversions.

2009: The Eastern Snake Plain Aquifer Comprehensive Aquifer Recharge Management Plan (CAMP) is signed into law by Governor Butch Otter as part of the State Water Plan. ESPA Comprehensive Aquifer Recharge Management Plan average annual managed recharge targets: Years one through ten: 100,000 acre feet/yr. After ten years, the goal is 250,000 acre feet/yr

2008-2009: IWRB (Idaho Water Resources Board) completes a pilot project to test methods of recharging water into aquifer. The results show that the best case infiltration is about ½ ft/day. Injection wells are a feasible option at most sites, but the cost of permitting and monitoring will increase higher populations, making it less attractive.

2007: Idaho Ground Water Association (IGWA) acquires 29,500 AF of storage water in rental pool for their required mitigation; ran it through canal in fall for seepage.

2006: IWRB recharge rights from the Snake and Wood Rivers come into priority. IRWB requests multiple canals divert their water for aquifer recharge seepage. The result is 60,500 acre feet of total recharge.

2005: The Idaho legislature passes HCR 28, HB 373, and HB 392. This suite of bills provides support to the IWRB to support and fund managed recharge programs.

 1998: IWRB applies for 20 water rights to recharge water from the Snake River, but protests by a number of different groups halt the applications.

 1998: IWRB completes the ESPA Managed Recharge Feasibility Study.

 1995: The Idaho Legislature appropriates $945,000 for recharge efforts to IWRB, and the program administration is then passed along to Water District 1. With this project, natural flow diversion for recharge is made using the irrigation water rights for participating canals.

 1992: South West Irrigation District partners with the federal government to build 13 injection wells in the Eastern Snake Plain.

 1991: The Environmental Protection Agency (EPA) designates ESPA as a sole source aquifer.

 1990’s: Drought leads to an increasing decline in groundwater levels with more pumping and fewer surface water diversions to facilitate recharge.

 1981: The Idaho Water Resources Board (IWRB) issues the Upper Snake Recharge Report recapping the pilot recharge project and analyzing the feasibility of expanding recharges efforts. Legislative action creates the Snake River Aquifer Recharge District, allowing for efforts to continue. About 84,700 acre feet of recharge from 1980-1999 is observed.

 1970: After a 1962 recommendation by the Bureau of Reclamation (BOR) to introduce a recharge project in the Eastern Snake Plain, a pilot recharge project begins in the Egin Lake area.

1960’s: The expansion of irrigation on Eastern Snake Plain leads to an increased reliance on groundwater. Additionally, the growing adoption of more efficient irrigation methods leads to less recharge from irrigation and a decline in groundwater levels.