An aquifer characterization at the Texas A&M University Brazos River Hydrologic Field Site, Burleson Co., Texas

Abstract

The Texas A&M University Brazos River Hydrogeologic Field Site has been established as a test site to conduct research related to non-point source pollution. To better study the transport and fate of agricultural chemicals, the hydrogeological characteristics of the aquifer at this site were studied. The aquifer at the Brazos river site is an alluvial, heterogeneous, unconfined system having a saturated thickness of approximately forty feet. It is comprised of a fluvial deposited fining-upward sequence of gravel, sand, silt and clay. A direct hydrologic interaction between the aquifer at the Brazos river site and the Brazos river has been observed; the higher the river stage, the lower the resultant hydraulic gradient, and the greater the angle at which the flow in the aquifer is directed downstream. The influence of the river on the aquifer level at the site diminishes as distances from the river increase; and is, in fact, slight to none in the far field. The hydraulic conductivity values calculated for the aquifer range from 1.8xl 02 ft/day to 3. 1 xl 02 ft/day. The aquifer at the Brazos river site is unconfined, however it behaves as a semiconfined system because of the contrasting permeability's between the basal gravel zone and the overlying fine sandy unit. This is reflected in both the average storativity values, which range from 5.6xlO-4 to 4.Oxl 0-3 , and the distribution of hydraulic conductivity's in the aquifer. The general nature of the ground water quality in the aquifer is dominantly calcium bicarbonate, being high in concentrations of total dissolved solids, hardness, bicarbonate and alkalinity.