Water Volume & Use
Municipal wells located along the valley floor ranging from 65 to 450 feet deep extract water from the aquifer. Pumps deliver the water to the ground surface and into the distribution systems for Pocatello and Chubbuck.
Like a bank account balance…..if more water is withdrawn than is deposited or recharged, then the overall volume of water available in the aquifer will decrease. The aquifer is already supplying 80% of its maximum capacity in normal water years, and may be over-pumped during drought periods. If our population grows by an additional 20,000 by the year 2020 (Our Valley, Our Vision build-out analysis), then without significant conservation measures we will be unable to supply the area’s future water needs and other sources of water will be necessary.
In this diagram, the blue arrows indicate the approximate amount of water per year (in million gallons) recharged to the aquifer from the surrounding water shed. The red arrows indicate the approximate amount of water extracted from the aquifer per year from municipal pumping.
Input to the aquifer from recharge:
- 80% of our water (5.4 billion gallons/year) comes from the Scout Mountain/Gibson Jack area.
- 15% (1.1 billion gallons/year) comes through the Portneuf Gap (underground)
- 5% (less than 0.5 billion gallons/year) comes out of Pocatello Creek area (underground)
Extraction from the aquifer through municipal wells:
- We pump 1.1 billions gallons/year out of the southern aquifer (as a result only 5.3 billion gallons/year flow from the southern aquifer into the northern aquifer)
- We pump 6.1 billion gallons/year out of the northern aquifer
- In dry years we may take water in from the Snake River Aquifer. In wet years we discharge a small volume of water into the Snake River Aquifer.
- In general we pump out 7.8 billion gallons/year. Our water recharge (primarily from snowmelt) is a similar amount. However, in some recent years we have taken out more than was put in through recharge.
- Water balance studies by the Idaho Geological Survey and Idaho State University have indicated that future water withdrawals can rise to a total of about 7.5 billion gallons per year without affecting the aquifer’s long-term storage. In 1999, total pumping withdrawals by the cities of Pocatello and Chubbuck exceeded 6.2 billion gallons annually. During the 2000 water year, the combination of additional withdrawal by Pocatello’s newest supply well, #44, and below normal recharge from the Bannock Range, the water table in the southern valley dropped to its lowest level in 30 years. However, most of this decline was attributed to the demand that Well 44 placed on the aquifer.