Pocatello, ID KPVI: What is the Aquifer?

What is the Aquifer?

(Note: This is an excellent article -- well-researched, succinct and well written! Important, water-related definitions below article.)

September 25, 2006

By Doug Andersen, KPVI political specialist dandersen@kpvi.com

KPVI

902 East Sherman

Pocatello, Idaho 83201

800-366-5784 (KPVI) or 208-232-6666

Fax: 208-233-6678

http://www.KPVI.com

To submit comments/news tip: bbaumgartner@kpvi.com

One of the Gem State's most valuable treasures is hidden from view.

Beneath the surface of the ground is a billion acre feet of water; enough water to create a lake 140 feet deep. Political specialist Doug Andersen has more on the state's largest aquifer.

As the State Water Resources Board http://www.idwr.idaho.gov meets to formulate a plan to manage Idaho water, one component is the aquifer. What is it? And what does it do?

Jerry Rigby, chair, Idaho Water Resources Board: "One could say it's like a huge reservoir that, in essence, water goes in and water comes out."

It's 4,000 feet deep in spots, and the Eastern Snake River Plain Aquifer is made mostly of basalt. The combination of rock and sediment yield water. Not like a river, rather a sponge. And it's constantly changing.

Jerry Rigby, chair, Idaho Water Resources Board: "There's basically four different levels in this aquifer."

It spans 11,000 miles from Ashton on the north to King Hill in the west and has 600 times the capacity of the American Falls Reservoir.

Jerry Rigby, chair, Idaho Water Resources Board: "This is an aquifer we are all sitting on and we all need to understand it better."

The aquifer works like this -- water intake, called recharge, comes mostly from irrigation. The other 40% comes from river and aquifer infiltration and precipitation.

Jerry Rigby, chair, Idaho Water Resources Board: "We've gone through a historical drought. Because of that, when we get out of that, assuming we do, optimistic we will, this aquifer, which is a huge aquifer, will replenish itself."

The discharge flows into the Snake River -- 85%. The remaining percentage pumped for other uses.

Jerry Rigby, chair, Idaho Water Resources Board: "It's an accounting system, you only get a reservoir to increase its level when water's being put in."

That accounting is important because of the debate -- legal, political and commercial over water availability.

Jerry Rigby, chair, Idaho Water Resources Board: "It isn't as simple as saying, 'I have a right in this aquifer.'"

Location, priority dates, and more. And then there's the question of damage.

Jerry Rigby, chair, Idaho Water Resources Board: "If we are mining the aquifer, then obviously we need to get on top of it."

That's the charge from the legislature to the Water Resources Board; set a plan to maintain the health of Idaho's largest aquifer.

A new Idaho water management plan is expected to go before the legislature in January.

Related information:

Idaho Department of Water Resources

Jerry Rigby, Chairman jrigby@rigby-thatcher.com, jerry.rigby@idwr.idaho.gov, jrigby@srv.net, jrigby@idwr.state.id.us or idwrinfo@idwr.idaho.gov

P.O. Box 83720

Boise, Idaho 83720-0098

208-287-4800 or 208-356-3633

Fax: 208-287-6700 or 208-356-0768

http://www.idwr.idaho.gov

Important related definitions:

Aquiclude – A geologic formation that is saturated but is incapable of transmitting sufficient quantities of water to a well. Also, this type of formation is not capable of transmitting enough water to be considered as a significant part of the regional ground water system. A layer of clay [that] limits the movement of ground water. – Ground and Surface Water Terminology, Ohio State University http://ohioline.osu.edu/aex-fact/0460.html

Aquifer – A geologic unit (rock or sediment) that can store and transmit water at rates sufficient to supply reasonable amounts of water to wells and springs. – U.S. Department of Energy (DOI) Remediation of the Moab Uranium Mill Tailings, Grand and San Juan Counties, Utah Draft Environmental Impact Statement http://www.eh.doe.gov/nepa/docs/deis/eis0355d/vol_1/chap10.pdf

2. A water-bearing rock unit (unconsolidated or bedrock) that will yield water in a usable quantity to a well or spring. – McGregor Range Draft Resource Management Plan Amendment and Environmental Impact Statement, Prepared for United States Department of the Interior Bureau of Land Management, Las Cruces (New Mexico) Field Office, January 2005. http://www.nm.blm.gov/lcfo/mcgregor/docs/Draft%20RMPA_EIS_01_05_low.pdf (DOI/BLM) Glossary (Pages 259-268 of 282)

3. A water-bearing layer of rock, sand and/or gravel, with sufficient density of pores to allow water to move through the layer. A body of rock that is saturated with water or transmits water. When people drill wells, they tap water contained within an aquifer. A geologic formation, group of formations, or part of a formation capable of storing, receiving and transmitting water. The formation is capable of yielding enough water to support a well or spring. A water-bearing stratum of permeable rock, sand, or gravel. A water-bearing formation that provides a ground water reservoir. Underground water-bearing geologic formation or structure. A geologic formation, group of formations, or part of a formation that stores and transmits water and yields significant quantities of water to wells and springs. A natural underground layer of porous, water-bearing materials (sand, gravel) usually capable of yielding a large amount or supply of water. http://www.epa.gov/ogwdw/pubs/gloss2.html

4. A geologic formation or structure that transmits water in sufficient quantity to supply the needs for a water development; usually saturated sands, gravel, fractures, and cavernous and vesicular rock (Soil Conservation Society of America, 1982). – EPA’s Management Measures for Agricultural Sources Glossary http://www.epa.gov/owow/nps/MMGI/Chapter2/ch2-3.html and National Grassland Plan (USDA Forest Service) http://www.fs.fed.us/ngp/draft/plan/pdf_plan_draft/Dakota_Prairie_Plan/Appendices/appendix_g.pdf

5. A geologic formation that contains sufficient saturated permeable material to yield significant quantities of water to wells and springs. – Yosemite National Park, Merced Wild and Scenic River Revised Comprehensive Management Plan and Supplemental Environmental Impact Statement (SEIS) Chapter VIII: Glossary http://www.nps.gov/yose/planning/mrp/html/14_rmrp_ch8.htm

6. A water-bearing bed or stratum of permeable rock, sand, or gravel capable of fielding considerable quantities of water to wells or springs. – Soil Survey of McDowell County, West Virginia, Issued 2004. http://soildatamart.nrcs.usda.gov/Manuscripts/WV047/1/WVMcDowell9_2005.pdf (page 69 of 115)

7. A geologic formation(s) that is water bearing. A geological formation or structure that stores and/or transmits water, such as to wells and springs. Use of the term is usually restricted to those water-bearing formations capable of yielding water in sufficient quantity to constitute a usable supply for people's uses. – USGS Water Science Glossary of Terms http://ga.water.usgs.gov/edu/dictionary.html

8. An underground geological formation or group of formations, containing usable amounts of groundwater that can supply wells or springs for domestic, industrial, and irrigation uses. Removing more groundwater from an aquifer than is naturally replenished is called overdrafting, and can result in a dropping water table, increased pumping costs, land subsidence (which reduces the future recharge capacity), saltwater intrusion, reduced streamflows in interconnected ground- and surface-water systems, and exhaustion of groundwater reserves. Overdrafting groundwater occurs primarily in the Plains States and the West. (Agriculture, 1997) [Soil or rock below the land surface that is saturated with water. There are layers of impermeable material both above and below it and it is under pressure so that when the aquifer is penetrated by a well, the water will rise above the top of the aquifer.] – Government Affairs: Industry Initiatives – Glossary of Irrigation Terms http://www.irrigation.org/gov/default.aspx?pg=glossary.htm&id=106

[Answering the question: What is the difference between a confined and a water-table (unconfined) aquifer?] A confined aquifer is an aquifer below the land surface that is saturated with water. Layers of impermeable material are both above and below the aquifer, causing it to be under pressure so that when the aquifer is penetrated by a well, the water will rise above the top of the aquifer. A water-table, or unconfined, aquifer is an aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is able to rise and fall. Water-table aquifers are usually closer to the Earth's surface than confined aquifers are, and as such are impacted by drought conditions sooner than confined aquifers. – Frequently Asked Questions [FAQs], USGS [U.S. Geological Survey] Water Resources of Maryland, Delaware and D.C. Area WRD [Water Resources Division] http://md.water.usgs.gov/faq/

Aquifer (confined) – Soil or rock below the land surface that is saturated with water. There are layers of impermeable material both above and below it and it is under pressure so that when the aquifer is penetrated by a well, the water will rise above the top of the aquifer. – USGS Water Science Glossary of Terms http://ga.water.usgs.gov/edu/dictionary.html

Aquifer Recharge Area – The surface area (land or water) through which an aquifer is replenished. – New Jersey Department of Community Affairs: Office of Smart Growth http://www.state.nj.us/dca/osg/plan/stateplan/appendices_glossary.shtml

Aquifer (unconfined) – An aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is able to rise and fall. – USGS Water Science Glossary of Terms http://ga.water.usgs.gov/edu/dictionary.html

Aquifer Storage and Recovery (ASR) – A technology for storage of water in a suitable aquifer via a well during times when excess water is available and recovery from the same aquifer when the water is needed to meet peak emergency or long-term water demands. – Everglades Plan glossary http://www.evergladesplan.org/utilities/glossary.cfm

Aquifuge – A geologic formation that is both impermeable and contains no water. – Ground and Surface Water Terminology, Ohio State University http://ohioline.osu.edu/aex-fact/0460.html

Aquitard – A layer of low-permeability formation immediately above or below an aquifer that retards but does not prevent the flow of ground water to or from the aquifer. It does not readily yield water to wells and springs but may serve as a storage unit for ground water. – U.S. Department of Energy (DOI) Remediation of the Moab Uranium Mill Tailings, Grand and San Juan Counties, Utah Draft Environmental Impact Statement http://www.eh.doe.gov/nepa/docs/deis/eis0355d/vol_1/chap10.pdf

2. A geologic formation that is saturated but is incapable of transmitting sufficient quantities of water to a well. However, this type of formation is capable of transmitting enough water to be considered as a significant part of the regional ground water system. – Ground and Surface Water Terminology, Ohio State University http://ohioline.osu.edu/aex-fact/0460.html

Sole Source Aquifer – An aquifer that supplies 50 percent or more of the drinking water of an area. – EPA Ground Water and Drinking Water Glossary http://www.epa.gov/safewater/glossary.htm and http://www.epa.gov/ogwdw/pubs/gloss2.html