A conceptual model of the hydrogeologic framework, geochemistry, and groundwater-flow system of the Edwards-Trinity and related aquifers in the Pecos County region, Texas

Johnathan R. Bumgarner; Gregory P. Stanton; Andrew Teeple; Jonathan V. Thomas; Natalie A. Houston; Jason Payne; MaryLynn Musgrove

doi:10.3133/sir20125124

USGS · sir20125124

A conceptual model of the hydrogeologic framework, geochemistry, and groundwater-flow system of the Edwards-Trinity and related aquifers in the Pecos County region, Texas

Johnathan R. Bumgarner·Gregory P. Stanton·Andrew Teeple·Jonathan V. Thomas·Natalie A. Houston·Jason Payne·MaryLynn Musgrove

View original source ↗Read source document ↗Export metadata ↓

Abstract

A conceptual model of the hydrogeologic framework, geochemistry, and groundwater-flow system of the Edwards-Trinity and related aquifers, which include the Pecos Valley, Igneous, Dockum, Rustler, and Capitan Reef aquifers, was developed as the second phase of a groundwater availability study in the Pecos County region in west Texas. The first phase of the study was to collect and compile groundwater, surface-water, water-quality, geophysical, and geologic data in the area. The third phase of the study involves a numerical groundwater-flow model of the Edwards-Trinity aquifer in order to simulate groundwater conditions based on various groundwater-withdrawal scenarios. Resource managers plan to use the results of the study to establish management strategies for the groundwater system. The hydrogeologic framework is composed of the hydrostratigraphy, structural features, and hydraulic properties of the groundwater system. Well and geophysical logs were interpreted to define the top and base surfaces of the Edwards-Trinity aquifer units. Elevations of the top and base of the Edwards-Trinity aquifer generally decrease from the southwestern part of the study area to the northeast. The thicknesses of the Edwards-Trinity aquifer units were calculated using the interpolated top and base surfaces of the hydrostratigraphic units. Some of the thinnest sections of the aquifer were in the eastern part of the study area and some of the thickest sections were in the Pecos, Monument Draw, and Belding-Coyanosa trough areas. Normal-fault zones, which formed as growth and collapse features as sediments were deposited along the margins of more resistant rocks and as overlying sediments collapsed into the voids created by the dissolution of Permian-age evaporite deposits, were delineated based on the interpretation of hydrostratigraphic cross sections. The lowest aquifer transmissivity values were measured in the eastern part of the study area; the highest transmissivity values were measured in a faulted area of the Monument Draw trough. Hydraulic conductivity values generally exhibited the same trends as the transmissivity values. Groundwater-quality data and groundwater-level data were used in context with the hydrogeologic framework to assess the chemical characteristics of water from different sources, regional groundwater-flow paths, recharge sources, the mixing of water from different sources, and discharge in the study area. Groundwater-level altitudes generally decrease from southwest to northeast and regional groundwater flow is from areas of recharge south and west to the north and northeast. Four principal sources of recharge to the Edwards-Trinity aquifer were identified: (1) regional flow that originated as recharge northwest of the study area, (2) runoff from the Barilla, Davis, and Glass Mountains, (3) return flow from irrigation, and (4) upwelling from deeper aquifers. Results indicated Edwards-Trinity aquifer water in the study area was dominated by mineralized, regional groundwater flow that most likely recharged during the cooler, wetter climates of the Pleistocene with variable contributions of recent, local recharge. Groundwater generally flows into the down-dip extent of the Edwards-Trinity aquifer where it discharges into overlying or underlying aquifer units, discharges from springs, discharges to the Pecos River, follows a regional flow path east out of the study area, or is withdrawn by groundwater wells. Structural features such as mountains, troughs, and faults play a substantial role in the distribution of recharge, local and regional groundwater flow, spring discharge, and aquifer interaction.

Explore related subjects

Scientific Investigations Report Report

Source-reported bounding extent: 30.25° to 31.5° latitude; -104° to -102° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Johnathan R. Bumgarner, Gregory P. Stanton, Andrew Teeple, Jonathan V. Thomas, Natalie A. Houston, Jason Payne, MaryLynn Musgrove. 2012. A conceptual model of the hydrogeologic framework, geochemistry, and groundwater-flow system of the Edwards-Trinity and related aquifers in the Pecos County region, Texas. https://doi.org/10.3133/sir20125124

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Karst hydrologic processes in carbonate fensters of the western Great Smoky Mountains, Tennessee, 2017–18

The geology of the Great Smoky Mountains in Tennessee and North Carolina is dominated by metamorphic strata. Along the western extent of the range, however, several carbonate fensters expose the Ordovician Jonesboro Limestone along the western edge of the Great Smoky Fault. The fensters (Cades Cove, Tuckaleechee Cove, and Wear Cove) create opportunities for allogenic recharge at the contact between the surrounding, relatively insoluble, strata and the underlying soluble formations, resulting in the development of karst systems. Karst environments have a high degree of connectivity between surface streams and groundwater systems; thus, karst aquifers are inherently vulnerable to contamination from surface activities. Karst environments also provide a specific environment for sensitive biota. Protection of the unique resources of karst environments requires an understanding of the behavior of karst aquifers, knowledge of karst recharge areas, and the mapping of groundwater flow paths. A study began in 2017 to characterize the hydrologic behavior of the karst systems in Great Smoky Mountains National Park through hydrologic monitoring, dye tracing, and seepage investigations. Hydrologic monitoring equipment was installed at several karst hydrogeologic features: two in-cave sites, two major springs, Abrams Creek in Cades Cove, and a karst depression wetland. Dye tracing was conducted to determine resurgences for the cave systems, to delineate spring recharge areas, and to estimate karst groundwater velocities. Seepage investigations along Abrams Creek helped determine if streams were sinking into the Jonesboro Limestone, either at the contact with insoluble strata or as streams flowed across the carbonate fenster. Study results indicate considerable differences in groundwater behavior between the conduit-dominated flow systems in Tuckaleechee Cove compared to the lower-gradient, colluvium-covered karst systems in Cades Cove. Study results also indicate that contaminants in the area of Bull sink and Whiteoak Sink could be rapidly transported through karst groundwater towards springs in Tuckaleechee Cove. Karst resources in Cades Cove are most likely to be affected by local events or activities taking place within the cove itself or in upper Abrams Creek upstream of the Great Smoky Fault. This study provides information on the vulnerability and uniqueness of the karst systems in the western Great Smoky Mountains, which are characterized by complex geology, high-gradient subterranean streams, deep caves, and carbonate fensters.

Tennessee↗

USGS2026

Analysis of groundwater geochemistry in the Lansing, Michigan, area

Groundwater resources in the Lansing, Michigan, area are protected by a wellhead protection plan, but previous studies have indicated that groundwater in this area may be susceptible to surface contamination. The U.S. Geological Survey, in cooperation with the Lansing Board of Water & Light, analyzed geochemical and aquifer characteristics to assess the potential for contamination of groundwater resources. Recharge age categories were determined from tritium concentrations for some wells, and by using ternary diagrams and principal component analysis for other wells. These age classifications, combined with hydrogeologic and geochemical data, were analyzed by using statistical methods to identify trends that may indicate areas of increased groundwater susceptibility. Wells with modern recharge tended to have higher sodium, chloride, and chloride:bromide ratios than did wells with mixed recharge, suggesting greater surface connectivity and potential influence from anthropogenic sources such as road salt. In contrast, wells in the mixed age category exhibited more stable geochemistry and lower constituent concentrations. Classification and regression tree models identified aquifer geometry—particularly the thickness of the uppermost bedrock unit and presence of confining layers—as key predictors of recharge age and geochemical indicators. The trends identified from these analyses could help to reveal locations in the Lansing area that are among the most susceptible to contamination.

Michigan↗

USGS2026

Evaluating the number of realizations (train-test splits) necessary to ensure robust estimates of conventional hydrothermal resource favorability using Monte Carlo cross-validation, the Great Basin, Western USA

Supervised machine learning approaches used to produce favorability maps in resource assessments commonly partition an input dataset into training and testing subsets (that is, through train-test splits). However, if a single split is not representative of underlying resource conditions, the resulting favorability map may be biased, particularly with sparse or heterogeneous datasets. To mitigate the potential for unrepresentative favorability maps, recent works by U.S. Geological Survey researchers have used Monte Carlo cross-validation to implement a large number ( n) of randomized train-test splits to produce n realizations. The realizations are then aggregated using cell-wise median predictions to produce the resulting final favorability map, recognizing that the median will remove extreme values that might have been estimated from a comparatively few unrepresentative realizations. Theoretically, the median prediction at every cell converges to a single estimate as n approaches infinity, and the question addressed herein is: How many realizations are necessary to get a robust estimate (that is, an estimate unaffected by additional realizations)? Therefore, convergence metrics are described to identify the number of train-test splits and realizations needed to make a reliable map using the data and supervised machine learning workflow for conventional hydrothermal resource assessment of the Great Basin of the Western United States. For this study, robust prediction occurs with n approximately equal to 600 realizations, and smaller ensembles (for example, n is approximately equal to 200 or even 100) may be suitable during preliminary or exploratory analyses. Although the resulting threshold numbers will vary depending on the data and modeling approach used, the convergence metrics proposed and applied herein are applicable to other supervised machine learning studies that use Monte Carlo cross-validation.

California, Idaho, Nevada, Oregon, Utah↗