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Environmental Institute of Houston > Publications > Annual Reports > 2004 Annual Report > Chicot/Evangeline Aquifer of the Texas Gulf Coast, Groundwater Age and Pathways for Saltwater Contamination

Chicot/Evangeline Aquifer of the Texas Gulf Coast, Groundwater Age and Pathways for Saltwater Contamination

The Chicot/Evangeline aquifer is the primary, and in some cases only, source of fresh water for many of the small towns and rural areas of the Texas Gulf Coast, however, many parts of it are becoming increasingly salty and unusable. Saltwater contamination of this aquifer in neighboring Matagorda County has been attributed to seawater intrusion1 and upwelling of oil-field brines from underlying sedimentary units.2 The purpose of this study are to evaluate if upwelling brine contaminates the aquifer over a broader area than that identified by Bourgeois,2 and if this process is more effective in areas where the Beaumont Formation (which overlies and confines the Chicot aquifer) has been deeply incised and replaced with more permeable fluvial sediments. The study area includes Fort Bend and Brazoria Counties, which lie north and northeast of Matagorda County (Fig. 1) and provide a transect of the aquifer from its proposed recharge area in the northwest to its discharge at the Gulf of Mexico.1 The results of this research can be used in managing groundwater use in this region and can be extended to understanding saltwater contamination of other coastal aquifers in similar geologic settings.

Twenty-nine water samples were collected from the Chicot/Evangeline aquifer for this study (Fig. 1). Chemical (Na, K, Ca, Mg, Sr, Fe, B, Si, Al, P, NO3, pH, Cl, SO4, HCO3, CO3, acetate, I, and Br) and isotope (dD, dO18, dC13, and C14) analyses of the samples are being completed. This study is markedly different from all previous studies of this aquifer (e.g., Dutton and Richter3 and Bourgeois2) in that carbon isotope analyses (dC13) were used to determine the source of carbon, which provided a new perspective on fluid flow in this aquifer. In this region, the Beaumont formation, which is a clay rich layer that overlies the Chicot, is thought to be relatively impermeable preventing recharge or contamination of the aquifer in the study area. In addition, the replacement of the Beaumont in some areas by the more permeable incised valley fill and its effect on recharge has not been considered. The dC13 and C14 analyses completed to date indicate that younger and isotopically lighter carbon with a consistent dC13 value is being added to the aquifer water along its flow path, strongly suggesting there is recharge of younger water through these overlying units to the Chicot aquifer. Initially, a limited number of these carbon analyses were completed to evaluate their usefulness and now based on these results more samples will be analyzed to confirm these findings.

Prior predictions of the source of salt contamination in the Chicot aquifer water based on a hydrologic analysis suggests seawater intrusion,3 where as a later study based on elemental tracers suggests contamination is likely the result of upwelling of oil-field brine from underlying aquifers rather than sea water intrusion.2 Ion analyses indicate that the salt contamination in well 3 (Fig. 1) downstream from the Clemens dome is only from dissolution of halite in the dome. Other wells in the area show a contribution of salt from this same process. The Clemens dome and several others in this area penetrate into the Chicot, but the tops occur 100 m or more below the sampling depths. Ion analyses indicate that other samples from the vicinity of the salt domes and those from the coast are clearly altered by mixing with water from outside of that typically present in the aquifer. dC13 and C14 from a coastal well and a dC13 from near a salt dome support this. We await the additional carbon isotope analyses to determine whether it is seawater or upwelling brine.

References
1A.R. Dutton and B.C. Richter. "Regional Geohydrology of the Gulf Coast Aquifer in Matagorda and Wharton Counties, Texas: Development of a Numerical Model to Estimate the Impact of Water-Management Strategies," report to the Lower Colorado River Authority (IAC (88-89) 0910), Bureau of Economic Geology, University of Texas at Austin, 1990.
2F.M. Bourgeois. "Elemental and Stable Isotope Study to Determine the Source of Salt-Water Contamination in the Chicot Aquifer of the Gulf Coast Aquifer System," Masters Thesis, University of Houston, 1997.
3B.C. Richter and C.W. Kreitler. Geochemical Techniques for Identifying Sources of Ground-Water Salinization. Boca Raton, FL: CRC Press, 1993. 258.
4S. Aronow, W.L. Fisher, J.H. McGowen, and V.E. Barnes. "Geologic Atlas of Texas, Houston Sheet, Scale: 1:250,000," Bureau of Economic Geology, University of Texas at Austin, Austin, TX, 1982.
5T.E. Brown, J.L. Brewton, J.H. McGowen, C.V. Proctor, S. Aronow, and V.E. Barnes. "Geologic Atlas of Texas, Beeville-Bay City Sheet, Scale: 1:250,000," Bureau of Economic Geology, University of Texas at Austin, Austin, TX, 1987.
6Geomap Company. "Northeast Texas Gulf Coast, Executive Reference Map 312," Geomap Company, Plano, Texas, 1992.
7U.S. Geological Survey. "Houston Quadrangle (NH 15-7), 1:250,000 Topographic-Bathymetric Map," U.S. Geological Survey. Reston, VA, 1975.
8C. Gell. "Evaluating Fluid Flow Around the Danbury Salt Dome, Brazoria County, Texas, An Elemental and Stable Isotope Study," Masters Thesis, University of Houston, TX, 1999.

Publications
Banga, T., R.M. Capuano, and D.S. van Nieuwenhuise. "Fluid Flow, Stratigraphy and Structure in the Vicinity of the South Liberty Salt Dome, Texas," Gulf Coast Association of Geological Society Transactions 52 (2002): 25-36.
Banga, T., R.M. Capuano, and A. Bissada. "A Mixing of Meteoric Water and Deep Brine, and Fluid-Isolation Around Salt Domes, SE TexaS, USA," Goldschmidt Geochemistry Conference Proceedings 14 (2004): abstract no 1375.
Banga, T., R.M. Capuano, and D.S. van Nieuwenhuise. "Evidence of Reservoir Compartmentalization from a Coupled Study on Brine Chemistry and Stratigraphy in and Around the South Liberty Salt Dome, Texas," American Association of Petroleum Geologists National Meeting, Technical Program Abstract no 78852. 2003
Hyeong, K. and R.M. Capuano. "Hydrogen Isotope Fractionation Factor for Mixed-Layer Illite/Smectite 60º to 150ºC: New Data from the Northeast Texas Gulf Coast," Geochimica et Cosmochimica Acta 68 (2004): 1529-43.
Hyeong, K. and R.M. Capuano. "Origin of Low-Salinity Pore Water in the Seal Overlying the Geopressured Regime, Northeast Texas Gulf Coast: Implications for Fluid Flow and Sealing," AAPG Annual Convention Abstracts 11 (2002): A83.
Hyeong, K. and R.M. Capuano. "Hydrogen Isotope Fractionation Factor for Mixed Layer Illite/Smectite 0º to 150ºC, New Data from the Northeast Texas Gulf Coast," Geological Society of Korea Annual Meeting 57 (2002): 32.

Presentations
Banga, T., R.M. Capuano, and D.S. van Nieuwenhuise. "Evidence of Reservoir Compartmentalization from a Coupled Study on Brine Chemistry and Stratigraphy in and Around the South Liberty Salt Dome, Texas," American Association of Petroleum Geologists National Meeting, Technical Program Abstract no. 78852, 2003.
Hyeong, K. and R.M. Capuano. "Origin of Low-Salinity Pore Water in the Seal Overlying the Geopressured Regime, Northeast Texas Gulf Coast: Implications for Fluid Flow and Sealing," AAPG Annual Convention Abstracts 11 (2002): A83.
Hyeong, K. and R.M. Capuano. "Hydrogen Isotope Fractionation Factor for Mixed Layer Illite/Smectite 0º to 15ºC, New Data from the Northeast Texas Gulf Coast," Geological Society of Korea Annual Meeting 57 (2002): 32.

Funding and proposals
Chan, C. and R. Capuano. "Establishment of Baseline Measurements and Protocol for Interpreting GPR Monitoring of DNAPL Plumes." Texas Higher Education Coordinating Board, Advanced Technology Program, 2003, $149,500 (not funded).
Vipulanandan, C. and R. Capuano. "Use of Crushed Gravel in Concrete Paving." Texas Department of Transportation, 2003, $170,000 (not funded).

 

Regina M. Capuano, Ph.D., is an associate professor of
geosciences at the University of Houston. She can be reached
at capuano@uh.edu. Steven V. Lindsay is a graduate student
in the Department of Geosciences. He can be
reached at slindsay@uh.edu.

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2004 Annual Report      
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Figure 1. Location of wells sampled in this study. Area of incised valley fill,[4,5] salt dome locations,[6] Bourgeois study area,[2] and Gell study area.[8] Base map from U.S.G.S. Houston Quadrangle, 1975.2.  
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