Water Well Journal
Issue link: http://read.dmtmag.com/i/668983
M eeting today's food production demand in the 21st century in the United States will depend on ground- water. U.S. agriculture uses 49.5 billion gallons of groundwater per day, on average, for irrigation—65% of the nation's daily total of 76 billion gallons. Sustaining the nation's groundwater resources to meet agricultural needs requires wise use, pump- ing efficiency, locally adapted management, resource monitor- ing, and managed recharge of groundwater storage to assure future supplies. A joint commitment to begin an educational campaign for the agricultural irrigation community was announced on World Water Day, March 22, by the Irrigation Association and the National Ground Water Association at the White House Water Summit. The goal is to help the nation's 121,000 farms enhance water efficiency and reduce energy consumption of their 476,000 irrigation wells. About 170,000 irrigation wells extract groundwater from the Ogallala Aquifer, which extends across eight states from South Dakota to Texas, in one of the most productive agricul- tural regions in the world—serving not only the United States but large parts of the world's food production. In part two of Water Well Journal's three-part series exam- ining major aquifers in the United States, we shift our focus to the Ogallala Aquifer. ● ● ● The Ogallala is the leading geologic formation in the High Plains Aquifer System, which underlies 174,000 square miles. Though there exists several other minor geologic forma- tions in the High Plains Aquifer System, such as the Tertiary Brule and Arikaree and the Dakota formations of the Creta- ceous, these units are often referred to as the Ogallala Aquifer. The Ogallala supplies water for 20% of the corn, wheat, sorghum, and cattle produced in the United States. The Ogallala can hold more than enough water to fill Lake Huron and part of Lake Ontario. Ninety percent of the water pumped out is used to irrigate crops. The Ogallala is a very complex aquifer system composed primarily of unconsolidated clay, silt, sand, and gravel. The Ogallala varies, offering a mix of confined and unconfined aquifers, with virtually all recharge coming from rainwater and snowmelt. The High Plains has a semiarid climate, so recharge is minimal. Generally, the Ogallala is found 50 to 300 feet below the land surface, and the saturated thickness varies greatly as well. The average thickness is about 200 feet, but it exceeds 1000 feet in west-central Nebraska. Both the saturated thick- ness and areal extent of the Ogallala is greater in Nebraska and account for two-thirds of the volume of Ogallala ground- water, followed by Texas and Kansas, each with about 10%. Drilling Challenges Cody Christensen and his staff have a unique viewpoint of drilling in the Ogallala. Located in northeast Nebraska in Hartington, Christensen Well & Irrigation Inc. typically drills on the eastern fringe of the Ogallala. When the company heads west to drill in the heart of the Ogallala, it is usually subcontract work for Cody's childhood friend, Tonny Beck, owner of Beck's Well & Irriga- tion Inc. in Ainsworth, Nebraska. Beck is located in north- central Nebraska. The Ogallala geology typically consists of 1 to 2 feet of topsoil and then sand, Cody says, forcing him to set a surface culvert to keep the hole from caving in underneath the drill rig. Outside of this safety precaution, the Ogallala pales in comparison to drilling in his area of northeast Nebraska which bears glacial till, blue clay, and rock before reaching sand and gravel. "I don't think I've ever hit a rock out in the Ogallala forma- tion," says Cody, who has drilled in the formation since the early 1990s and manages the company with his three younger brothers. "We basically put our drill bit on, drill a hole, and never see it until the hole is done." Christensen Well & Irrigation has one reverse drill rig for irrigation wells and two straight rotary rigs for test holes for irrigation and domestic or stock wells for pastures. The stan- dard depth for an irrigation well in the Ogallala is between 300 and 350 feet. For an average center-pivot 133-acre circle, the average gallons per minute is 800-900 in the Ogallala compared to 600-700 gpm in northeastern Nebraska due to its heavier soils. OGALLALA continues on page 22 (Left) Christensen Well & Irrigation Inc. drills a 380-foot irriga- tion well in May 2014 into the Ogallala Aquifer northwest of Ainsworth, Nebraska. The well was designed to pump 900 gallons per minute for center pivot irrigation. WWJ May 2016 21 Twitter @WaterWellJournl Part two of three: The Ogallala Aquifer By Mike Price Aquifers in the United States