INVESTIGATION OF THE LEONA AQUIFER: IS IT AN UNDERUTILIZED SUSTAINABLE RESOURCE?

The Quaternary Leona Formation consists of deposits of sediment eroded from the Edwards Plateau and is a minor aquifer. The Leona Formation near Lockhart, TX, was deposited by the ancient Blanco River before stream piracy caused the river to switch to its current course. The aquifer has historically been a municipal water source in Lockhart and was used for irrigation in the 1950’s drought. It is still the water source for many households and is also used for livestock and lawn/garden irrigation. The Leona is primarily cross-bedded or massive gravel with sand and clay lenses adding heterogeneity. Hydraulic conductivity from grain size analyses and lab experiments range from 10⁰ to 10^-7cm/sec. Non-uniform soil horizons cap the aquifer, with soil thicknesses varying from over two meters to a few centimeters. Recharge to the aquifer is from infiltration of precipitation. Deep desiccation cracks speed up infiltration after dry periods. Numerous springs and seeps discharge water around the perimeter of the aquifer and springflows range from 19 lps to slow seeps. Water table maps show that groundwater generally flows to the southeast to where the water table drops below the base of the Leona Formation into the permeable Wilcox Group. The elevation of the water table rises only during large rainfall events or prolonged wet periods. Extensive agricultural land use and a shallow water table makes water quality a major concern in the Leona aquifer. Nitrate levels range from 3.5 ppm as nitrate to over 70 ppm; fertilizers are the primary source of nitrate. The Leona aquifer can be a supplemental resource in Central Texas as the population grows. Water quality of the Leona aquifer makes it undesirable as a source of drinking water (in some areas), but suitable for other uses with lower water quality requirements.