Potential Sources of Recharge to the Carrizo-Wilcox Aquifer in the Wintergarden Area of Southwest Texas
Presented on Tuesday, March 17, 2015
F. Paul Bertetti, P.G.1 and Ronald Green, Ph.D., P.G.2, (1)Geosciences and Engineering Division, Southwest Research Institute, San Antonio, TX, (2)Geosciences and Engineering Division, Southwest Research Institute
The Carrizo-Wilcox Aquifer is the principal source of fresh water in the Wintergarden region of Southwest Texas. Over the past century, groundwater levels have dropped continuously, even in the early Twentieth Century (ca. 1930) when pumping is estimated to be less than half of current usage. Although pumping has generally declined over the past 20 years, primarily due to reductions in irrigated acreage, pumping demands have increased recently due to hydraulic fracturing associated with the production of oil and gas from the Eagle Ford Shale. In some areas, groundwater levels are now more than 400 feet below their pre-development estimates.
Evaluation of the sustainability of the southern Carrizo-Wilcox Aquifer requires an understanding of the sources and magnitude of recharge. Current groundwater availability models for the Southern Carrizo-Wilcox estimate recharge using precipitation and the extent of the Carrizo‑Wilcox outcrop. However, studies by the authors and others of the southern Carrizo‑Wilcox Aquifer suggest distributed recharge is extremely limited. Rather, studies by the authors indicate that subflow from the Edwards Aquifer and secondary aquifers in Uvalde County is a major source of water to the Carrizo-Wilcox Aquifer in the Wintergarden area.
Hydrochemical evidence from recent analyses indicates of the nature of recharge to the southern Carrizo-Wilcox Aquifer is distinctly different for specific zones of the aquifer in the Wintergarden region. Based on information derived from this work, several hypotheses can be developed to address the nature of recharge in the Wintergarden region: (1) the Carrizo-Wilcox Aquifer in northern Zavala and Frio Counties receives or has received in the past substantial recharge from an Edwards Aquifer-like source(s), (2) the recharge source changes eastward toward Atascosa County, and (3) the recharge source for the Crystal City-Carrizo Springs area of western Zavala and Dimmit counties is different from that of northern Zavala County.
F. Paul Bertetti, P.G.
Geosciences and Engineering Division, Southwest Research Institute, San Antonio, TX
F. Paul Bertetti is a principal scientist in geochemistry at the Geosciences and Engineering Division, Southwest Research Institute® in San Antonio, Texas. Mr. Bertetti conducts field and experimental investigations to evaluate and understand the relationships between the aqueous geochemistry and hydrology of the subsurface. He has used hydrochemical data and modeling in numerous studies to characterize flow, recharge, and interconnectivity of several major aquifers, including the Edwards, Edwards-Trinity, and Carrizo-Wilcox aquifers in south Texas. Mr. Bertetti also conducts field, laboratory, and modeling studies to examine the sorption and ion-exchange behavior of dissolved radionuclides and other inorganic constituents.
Ronald Green, Ph.D., P.G.
Geosciences and Engineering Division, Southwest Research Institute
Ronald T. Green is an Institute Scientist in hydrology at Southwest Research Institute® in San Antonio, Texas.
