Central Oklahoma’s Bedrock
Groundwater is water located beneath the earths surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water.
In Central Oklahoma, the major bedrock aquifer is the Garber-Wellington aquifer, a subset of the larger Central Oklahoma Aquifer system. The aquifer is named after the two rock formations that the water flows through: the Garber Sandstone and the Wellington Formation.
Introduction to the Aquifer
The world is a watery place. According to estimates from the United States Geological Survey (USGS), over 70 percent of the earth is covered in water, with 96.5 percent of the water in the oceans. But it is the freshwater resources – lakes, rivers, and aquifers –that provide life. It is this water, which is constantly moving from one place to another and from one form to another, which is of the most concern to people (USGS, 2012).
This graphic is an illustration of how water moves through our world. Commonly referred to as the water cycle, water generally starts out as precipitation which has condensed from water vapor in clouds. The water falls as rain, which can become runoff, ground water, or immediately be evaporated again.
Runoff water eventually becomes stream, river, or lake water. It can also infiltrate into the near surface to be transpired by plants, thus becoming water vapor once again. Stream, river, or lake water can also evaporate to become water vapor. It can also move to the ocean, a large reservoir of water which is where much evaporation takes place.
Water that infiltrates down deep into the ground is usually referred to as groundwater. Groundwater generally moves much slower than surface water because rock has pores which the water must now travel through. Water that enters the ground is generally called recharge; the rock that is permanently wet below the ground is called the saturated zone.
Ground water can stay in the ground thousands of years or it can discharge quickly. This depends on the rock type (geology), the rate of movement the water is flowing through the ground, and the distance to the nearest discharge point such as a water well. Ground water can discharge naturally into lakes and oceans, or become surface water in the form of springs.
John Harrington, P.G., CFM
Water Resources Director
Many people refer to “the aquifer” as simply water under the ground and usually conceptualize it as a large underground lake or stream. But this is a very inaccurate picture of what an aquifer is. The water table in an aquifer will almost always be different in different parts of the aquifer. A water well can dry up an area of the aquifer surrounding it; this is impossible to do with a lake without drying up the entire waterbody. Learn more>>
The Garber-Wellington Aquifer is a major bedrock sandstone aquifer in Central Oklahoma. Also referred to as part of the Central Oklahoma Aquifer System, it is comprised primarily of rocks from the Lower Permian-age Garber Sandstone and Wellington Formations (Simpson, 1973). The total thickness of the combined formations is about 1,000 feet. Depth to water varies from less than 100 feet to 350 feet; saturated thickness ranges from 150 to 650 feet. Non-domestic wells completed in the aquifer can yield as much as 600 gallons per minute (gpm) but generally yield from 200 to 400 gpm.