Future groundwater availability, quality dependent on conservation efforts

By: Kay Ledbetter

VERNON – Two Texas A&M AgriLife Research scientists recently completed an evaluation of groundwater resources in the Trinity and Woodbine aquifers under the Dallas-Fort Worth metroplex and published their findings in an international journal, Science of the Total Environment.

The map depicts the Trinity and Woodbine aquifers, which were primarily studied under the Dallas-Fort Worth metroplex. (Texas A&M AgriLife Research)

“Characterization of Groundwater Resources in the Trinity and Woodbine Aquifers in Texas” was completed by Dr. Srinivasulu Ale, AgriLife Research geospatial hydrology assistant professor, and Dr. Sriroop Chaudhuri, his post-doctoral research associate, both in Vernon.

The primary goal of this research was to map and analyze the changes in water levels and quality between 1960 and 2010 in these two aquifers, Chaudhuri said. The data used for the analysis was provided by the Texas Water Development Board.

Statistics show groundwater accounts for about 59 percent of the total state water supply and 36 percent of municipal water supplies of the state. Prolonged over-drafting in different parts of the state, coupled with adverse climatic conditions have raised serious concerns over future groundwater availability and quality, the scientists said.

The Trinity Aquifer is a major aquifer extending across much of the central and northeastern part of the state. The Woodbine Aquifer is a minor aquifer located in northeast Texas and overlies the Trinity Aquifer. Both aquifers provide water for municipal, industrial, domestic, livestock and small irrigation supplies, Ale said.

The region in north central Texas centering on the Dallas–Fort Worth metroplex is served by these two aquifers. Dallas, Denton, Tarrant, Collin and Ellis counties support a huge urban population, making the Trinity aquifer among the most extensively used aquifers in the state.

As a result of intense groundwater extraction and depletion over time, 18 counties in this region have been included in the list of Priority Groundwater Management Areas of the state by the Texas Commission on Environmental Quality. The management areas are designated as currently experiencing or expected to experience critical water issues within the next 25 years.

“We combined aquifer-based and county-based hydrologic analyses to assess spatio-temporal changes in groundwater levels and quality between 1960 and 2010 in the Trinity and Woodbine aquifers underlying the study region,” Ale said.

Overall, he said, county-based assessment of groundwater resources revealed a distinct spatial zonation pattern across the study area. Counties having shallower groundwater levels, least water-level decline, and low salinity occur on the western flanks and counties with deeper groundwater levels and higher salinization are on the eastern flank.

“Identification of such hydrologic zones within an established framework of groundwater management, such as the Priority Groundwater Management Areas, underscores the necessity for further subdivision of management areas and implementation of zone-specific groundwater protection and/or restoration strategies,” Ale said.

Chaudhuri said characterization of groundwater resources in the Trinity and Woodbine aquifers revealed contrasting problems in these aquifers. In the Trinity, progressive groundwater level decline and its impact on groundwater quality degradation are the major concerns to sustainable development. In the Woodbine, groundwater resources are at risk more from higher salinity and chemical contamination that exceed safe drinking water quality standards.

Ale said recommendations to improve water availability in the region include: purchase of water from other entities, water conservation, voluntary redistribution of water resources, performing residential water audits, brush control, landscape irrigation restriction, water reuse, conjunctive use of surface and groundwater, and enhancing public awareness against water waste.

Chaudhuri said some of the hydrochemical studies performed or currently under way in this area, however, indicate potential concerns over surface water use. The concern is due to water quality issues, such as reduction of dissolved oxygen levels resulting from stormwater runoff and waste disposal activities, rising E. coli and perchlorate concentrations.

Already the U.S. Environmental Protection Agency has outlined implementation of different green infrastructure/low impact development measures such as vegetative roofs, bioswales and porous paving to “harvest” rainwater and allow it to soak into the ground. These practices aid natural replenishment of the aquifers by reducing urban stormwater runoff, soil erosion and nonpoint source pollution, all of which lead to surface water degradation and natural habitat loss, he said.

Natural filtration is also expected to wash the salts away from the plant root zone. This allows better root network development, reduces water hardness, lowers concentrations of harmful chemicals and helps maintain near-neutral groundwater pH, thus improving overall potable water quality, according to a Texas Water Development Board study.

Increasing groundwater monitoring activities in this region is highly desirable, the two scientists said. A major hindrance to assessing existing groundwater conditions in this region is the consistent drop in available groundwater level and quality observations in both aquifers.

For a better appraisal of the existing water level and quality conditions, Ale said they recommend the establishment of a more spatially-intensive and frequent monitoring scheme and use of a prior knowledge of existing water levels and quality conditions to locate future monitoring wells.

“Assessment of the regional water budget in response to various stressors such as drought and groundwater pumpage, taking into account the regional geology, aquifer hydrostratigraphic interactions and aquifer properties, soil and land use, will also be useful to provide recommendations for meeting the growing water needs in this region,” Ale said.