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The main sources of fresh water for all uses in Colorado, Lavaca, and Wharton Counties are the Chicot and Evangeline aquifers. The Jackson Group, Catahoula Sandstone, and Jasper aquifer are minor sources of water and are largely undeveloped in the area. The Chicot aquifer, which consists of discontinuous layers of sand and clay of about equal aggregate thickness, ranges in total thickness from 0 in the outcrop area to about 1,200 feet (366 m) in southern Wharton County. The Evangeline aquifer, which also consists of discontinuous sand and clay layers, ranges in total thickness from 0 at the outcrop to about 1,500 feet (457 m) in Wharton County. The combined thicknesses of the freshwater sands in the Chicot and Evangeline aquifers range from 0 at the outcrop to more than 850 feet (259 m) in Wharton County. Land-surface subsidence as a result of groundwater withdrawal is not a problem at this time. However, more data are needed to determine the extent of subsidence and the relationship between the amount of groundwater withdrawals and the amount of subsidence. The available data indicate that maximum subsidence within the three counties is less than 1 foot (0.3 in), and in most places is less than 0.5 foot (0.15 in).

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Hensell and Hosston Members of the Travis Peak Formation. The total average annual rates of groundwater withdrawals, mostly for public supply, has steadily increased from nearly 0.5 million gallons per day during 1955 to mare than 1.5 million gallons per day during 1980. The principal effect of the long-term development of ground water in the area has been a large decline of water levels in wells. The water level in a well near Narth Fort Hood declined from a depth of 100 feet during 1943 to nearly 480 feet during 1982. The water level in a well at Gatesville was above ground level during 1898. A nearby well had a water level of 476 feet below land surface during 1982. The long-term average of water-level declines for wells in the area ranges from 8 to more than 9 feet per year. The historical confined (artesian) conditions of the principal aquifer have changed to water-table conditions in some areas as the artesian head 9 drops below the base of the confining layer due to pumping. The greater storage property of the unconfined system will decrease the rate of water-level declines. However, well yields will continue to decrease in relation to the general decline of hydraulic head in the aquifer. The ground water in the area is slightly saline and concentrations of some constituents generally exceed chemical-quality limits set by the U.S. Environmental Protection Agency for public water supplies. Hie historical chemical changes in the ground water generally are insignificant and appear unrelated to the large declines of water levels in wells of the area.

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