PSCU 2018: Hydrogeology Watered Down
Water covers over 70 percent of the planet, but that doesn’t mean it’s all drinkable. You would never want to take a sip from the ocean because the salt would dehydrate you, and just like you, plants and animals need fresh water to survive. That’s what makes groundwater such a huge deal to the agriculture industry, especially in the High Plains. Clay Kilmer, PG, explained some techniques for extracting groundwater and how we can protect groundwater resources in his presentation for PSC University 2018, Hydrogeological & Environmental Geoscience Support for Engineering Projects.
What is Groundwater?
Clay began his presentation by teaching the class about what happens after it rains. Once precipitation hits the ground, he described some runs along the surface into lakes and rivers. Some are absorbed into the ground and collects beneath the surface in underground spaces called aquifers. Groundwater accounts for around 30 percent of the planet’s freshwater while only about one percent comes from lakes and rivers, according to the International Groundwater Resources Assessment Centre. Not all earth, however, can absorb enough groundwater to create an aquifer. Unconsolidated sand and gravel have more interstitial spaces, making them great environments for groundwater to collect. “Other materials like clays or bedrock,” Clay explained, “allow very little groundwater to pass through them, so they do not typically hold enough water to make an aquifer.”
How is Groundwater Extracted?
Depending on the geology of the site, different drilling techniques are used to safely extract groundwater. One method is direct circulation drilling, which circulates drilling mud through the drill stem and pushes it to surface with the drill cuttings up the annulus, the space between the drill stem and the surrounding formation. This method is usually the less expensive of the two, less effective at removing the drill cuttings, and less able to accommodate larger diameter holes that are required for large irrigation, municipal, or industrial projects. Reverse circulation drilling, on the other hand, flows in the opposite direction, from the annulus to the drill stem. It’s usually more expensive but can accommodate larger diameter holes.
The Ogallala Aquifer
Clay contextualized this information by discussing the vital role the Ogallala Aquifer plays in West Texas and Eastern New Mexico communities. The Ogallala underpins eight states from South Dakota to Texas and provides the region with groundwater for agricultural, residential, and industrial use. The High Plains is an agricultural giant and contributes millions of dollars’ worth of cattle and crops to the economy. It is also dependent on groundwater from the Ogallala.
The Ogallala is an unconsolidated aquifer, meaning it’s made of loose sediment instead of solid rock. This type of formation “is more unstable and likely to slough or cave in,” said Clay, making it more challenging to drill a hole and keep it open long enough to install well casing for support. To protect the formation, Clay explained that “drilling mud is used to circulate through the hole during the drilling process to remove the drill cuttings and stabilize the hole.”
Clay also described how the Ogallala Aquifer, as well as other groundwater resources in the region, are protected by state and local government agencies. These agencies use a regional groundwater flow model called the High Plains Groundwater Availability Model (HPGAM), a program that simulates water flow, recharge, and loss for the Ogallala, to determine the best preservation methods.
“The HPGAM,” Clay said, “is used by the Texas Water Development Board and local Groundwater Conservation Districts to identify areas where groundwater resources may be short and control permitting, installing and groundwater pumping.” These regulations further groundwater conservation and affect where and when groundwater can be extracted.
What’s the Big Deal?
According to the United States Department of Agriculture, the Ogallala Aquifer provides water to nearly one-fifth of the wheat, corn, cotton, and cattle produced nationally. A strong understanding of drilling methods and hydrogeology helps our engineers deliver the best results to our clients and provide sustainable solutions to preserve aquifers like the Ogallala for future generations.