Trinity Aquifer Research Articles

Rule of Capture and Urban Sprawl: A Potential Federal Financial Risk in Groundwater-Dependent Areas

This paper illustrates the potential federal financial risk created by groundwater overabstraction, rapid urbanization, competing economic interests, and institutional arrangements in groundwater-dependent areas of Texas. In the Upper Trinity Groundwater Conservation District, located in the Dallas–Fort Worth metropolitan area, urban sprawl creates suburbanized rural areas reliant upon the Upper Trinity Aquifer. In the past 10 years, competition of economic interests for groundwater has intensified, as the area has experienced rapid urban sprawl combined with escalating Barnett Shale hydraulic fracturing activity, which coincided with two extreme droughts in 2006 and 2011. Urban sprawl generates business opportunities and tax revenues for state and local governments in the short term, but if groundwater overabstraction leads to land subsidence, financial risk is transferred to the federal government through increased risk exposure from federal housing loans and government-backed residential lending.

Solutes and potential sources in a portion of the Trinity aquifer, Texas, USA

Concentrations of several solutes––arsenic, nitrate, chloride, and bromide––along with total dissolved solids (TDS) in a portion of the Trinity aquifer were compiled, mapped, and evaluated relative to regional land use and geology. Agriculture and oil/gas production are significant land uses and potential sources of groundwater contamination in the study area. Data were compiled from 60 wells with a median depth of 245 ft (75 m). Only two observations surpassed the 44.3 mg/L drinking water standard for nitrate, and no observations exceeded the 10 µg/L standard for arsenic. A statistically significant, negative correlation was apparent between nitrate and well depth. The median chloride concentration was 28.7 mg/L; however, the maximum level was more than double the secondary drinking water standard of 250 mg/L. Nearly half of the TDS observations exceeded the secondary drinking water standard of 500 mg/L. Most chloride/bromide ratios were between 100 and 300; the median value was 184. Two mapped chloride/bromide ratios above 1,000 were consistent with evaporite dissolution. Results suggest modest impacts to groundwater quality from a combination of natural and human sources, the latter potentially including agriculture and oil/gas production.

Court Upholds USEPA Emergency Order

Trinity American Corporation owns and operates a polyurethane foam plant in North Carolina. The top layer of Trinity's land contains an aquifer allowing groundwater to flow downstream. Thus, any contaminants dumped on Trinity's property that migrate to this aquifer would ultimately travel west‐ southwest away from the property. A second lower aquifer carried water in a less certain way, although the two were interconnected. Prior owners of Trinity's property had regularly emptied vats of solvent wastes on the ground. Trinity also engaged in extensive dumping and waste mismanagement. About 100 homes in the area drew their well water from water migrating from the Trinity aquifers. USEPA issued an emergency order under the Safe Drinking Water Act (SDWA) requiring Trinity to test all water supply wells in that area every 90 days until the contaminant levels were under permitted federal regulations. When the wells exceeded maximum safe levels, Trinity was required to provide safe drinking water until USEPA determined that the contaminant levels were safe. Trinity sought review of the order. The appellate court rejected Trinity's contention that USEPA cannot rationally find imminent and substantial endangerment requiring prompt emergency action because no evidence existed that anyone was actually drinking contaminated water. The court said the SDWA does not require such evidence, and all that USEPA needs to issue an emergency order is information that a contaminant, which is likely to enter an underground source of drinking water, may imminently and substantially endanger the health of people who may use the water system. The court dismissed the petition for review of the order.

Abstract: Petrophysical Characterization of the Trinity Aquifer in North Texas 

Abstract: Petrophysical Characterization of the Trinity Aquifer in North Texas 

Water-Level Declines in the Woodbine, Paluxy, and Trinity Aquifers of North-Central Texas: ABSTRACT

ABSTRACT Ground-water mining of the Woodbine, Paluxy, and Trinity aquifers has led to substantial water-level declines in North-Central Texas since the turn of the century. Water-level maps constructed from R. T. Hill's 1901 well survey data show that water levels were initially above land surface before development. Numerous wells were drilled for water supply because the wells flowed at land surface. Water levels declined rapidly, and many of the wells around Fort Worth stopped flowing by 1914. Many of these wells were then abandoned, which slowed the rate of water-level decline. Since the turn of the century, water levels have declined nearly 850 ft in the Trinity aquifer in the Fort Worth area. As of 1990, water levels had declined about 400 ft in the Woodbine aquifer near Dallas and 450 ft in the Paluxy aquifer near Fort Worth. Maps drawn on the basis of water-level measurements in 1935, 1955, 1960, 1970, 1980, and 1990 show how the shape of potentiometric surfaces has evolved during the century. This great drawdown in water levels has increased pumping costs, reversed ground-water flow directions in the Dallas-Fort Worth and Sherman areas, and may have affected water quality. Land subsidence from water-level decline has not been observed in North-Central Texas, perhaps because of the structural stability of the geologic units or a consolidation time lag. Pumping costs and water-quality problems have caused many ground-water users to switch to surface sources of water. Consequently, the rate of water-level decline has decreased in some parts of the aquifers, and in the case of the Paluxy aquifer, this may have caused recent water-level recovery.

Identifying Flow Intervals by Pore Geometry and Petrophysics: Middle Trinity Aquifer (Lower Cretaceous Limestone)

A core from the Lower Cretaceous middle Trinity aquifer of southern Kendall County, Texas, was analyzed to compare its petrographic and petrophysical properties to its hydraulic flow characteristics. The analyses helped determine flow intervals in the core. Flow intervals are defined as vertical zones having similar geologic (depositional and diagenetic) history, petrophysical properties, and hydraulic conductivity characteristics. The information gathered from the study of a single core may be integrated with similar data from other cores or well logs to define 'flow units.' Methodology involved visual and image analysis examination of thin sections and epoxy pore casts of samples to evaluate pore geometry (pore size, pore throat size, pore interconnectivity, and pore throat size heterogeneity). Samples were thus grouped into pore-type families. Representative samples from each pore-type family were tested for air and brine permeability, porosity, and mercury injection capillary pressure. Pore throat size distributions obtained from the capillary pressure analyses were compared to the data derived from the pore casts and thin sections. Pore geometry evaluated correlated well with mercury capillary pressure data for the most permeable zone of the core. Geologically, this flow interval consists of a porous, medium-grained peloid grainstone that is characterized by large pores connectedmore » by large pore throats. Wherever present, such pore throat to pore body size ratios enhance flow through the rock. Correlation between pore geometry and capillary pressure data deteriorate in packstones with increasing micrite mud content and wackestones with increasing dolomitization. These lower correlations are due to decreasing pore throat size and increasing pore throat size heterogeneity in these rocks.« less

Hydrologic investigations of the groundwaters of central Texas using [formula omitted] disequilibrium

U-234 U-238 disequilibrium can be used as a natural tracer in the groundwaters of central Texas. Utilizing the analytical methods of isotope dilution and alpha-particle spectrometry in monitoring variations in the uranium isotopic activity ratios and concentrations of natural waters, it is possible to evaluate the hydrogeology of the Trinity aquifer in terms of (a) the general groundwater circulation pattern, (b) the differentiation of water bodies upon the basis of their uranium signatures, and (c) the determination of absolute flow rates beyond the age limits of other techniques.

Uranium deposition and Th-234 alpha-recoil: An explanation for extreme U-234/U-238 fractionation within the trinity aquifer

234Th alpha-recoil appears to be a valid mechanism for explaining the generation of extreme 234U/ 238U disequilibria found in the waters of the Trinity aquifer.