168 research outputs found
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Sources and Ages of Ground Water in Unconfined and Confined Aquifers Beneath the U.S. High Plains
Groundwater is a valuable resource in unconfined and confined aquifers beneath the U.S. High Plains, but little is known about its age or hydrologic history. Thirty-two samples of groundwater were collected for measurement of δD, δ18O, δ13C, 14C, 3H, and 36Cl/Cl and ionic constituents from the unconfined High Plains aquifer in the Ogallala Formation and from confined aquifers in various hydrostratigraphic units beneath the southern, central, and northern High Plains. All samples of unconfined and confined groundwaters plot along the meteoric water line. δD and δ18O from the unconfined aquifer are consistent with the Modern distribution of meteoric water across North America. δD and δ18O from the confined aquifer likewise vary from south to north across the High Plains, but beneath the southern and central High Plains mean compositions are lighter in the confined aquifer than in the unconfined aquifer. Beneath the northern High Plains, δD and δ18O are the same or heavier in the confined aquifer than in the overlying unconfined aquifer. In combination, these trends show that the north-to-south range in stable isotopic compositions within the various confined aquifers is smaller than observed in the unconfined aquifer. Although age dates are uncertain, preliminary calculations suggest that unconfined groundwaters are probably less than 1,000 years old and locally as young as 25 years. Ages of groundwaters in the confined aquifers are between 20 and 32 thousand years and similar in the different study areas. Age of groundwater appears to increase along the inferred intrastratal flow path in the confined aquifers but is determined by leakage rate as well as lateral velocity. The range in isotopic composition in confined aquifers supports earlier findings that seawater temperature and patterns of atmospheric circulation during the Late Pleistocene were different from conditions affecting Modern recharge across the High Plains.Bureau of Economic Geolog
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Review of Data on Hydrogeology and Related Issues in Andrews County, Texas
Technical issues for siting a low-level radioactive waste repository in Andrews County, Texas, include ensuring that a considered site satisfies the licensing requirements spelled out in state regulations (TRCR Part 45). Most of Andrews County is underlain by the High Plains aquifer, which includes the Ogallala Formation as well as older Cretaceous formations. The presence of this aquifer should be expected to pose a great deal of questions from regulators and the public for licensing a low-level radioactive waste repository. Available maps do not unambiguously identify any area of Andrews County where the High Plains aquifer is absent. Possible areas that merit further evaluation include the WCS Site near the state line with New Mexico and the south-central part of the county near the border with Ector and Winkler Counties.Bureau of Economic Geolog
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Sources and Ages of Ground Water in Unconfined and Confined Aquifers Beneath the U.S. High Plains
Groundwater is a valuable resource in unconfined and confined aquifers beneath the U.S. High Plains, but little is known about its age or hydraulic history. Thirty-two samples of groundwater were collected for measurement of δ^18O, δD, Δ^14C, tritium, and ^36Cl/^Cl, as well as ionic constituents from the unconfined High Plains aquifer in the Ogallala Formation and from confined aquifers in various hydrostratigraphic units beneath the southern, central, and northern High Plains. All samples of unconfined and confined groundwaters plot along the meteoric water line. δ^18O and δD from the unconfined aquifer are consistent with the modern distribution of meteoric water across North America. δD and δ^18O from the confined aquifer likewise vary from south to north across the High Plains, but beneath the southern and central High Plains, mean compositions are lighter in the confined aquifer than in the unconfined aquifer. Beneath the northern High Plains, δD and δ^18O are the same or heavier in the confined aquifer than in the overlying unconfined aquifer. In combination, these trends show that the north-to-south range in stable isotopic compositions within the various confined aquifers is smaller than observed in the unconfined aquifer. Although age dates are uncertain, preliminary calculations suggest that unconfined groundwaters are probably less than 1,000 years old and locally as young as 25 years. Ages of groundwaters in the confined aquifers are between 20 and 32 ka and similar in the different study areas. Age of groundwater appears to increase along the inferred intrastratal flow path in the confined aquifers but is determined by leakage rate as well as lateral velocity. The range in isotopic composition in confined aquifers supports earlier findings that seawater temperature and patterns of atmospheric circulation during the Late Pleistocene were different from conditions affecting modern recharge across the High Plains.Bureau of Economic Geolog
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Adjustment of Parameters to Improve the Calibration of the Og-n Model of the Ogallala Aquifer, Panhandle Water Planning Area
Data for this report is available at the Texas Data Repository: https://doi.org/10.18738/T8/KCMM0AThis study involved adjusting parameters within a model of the Ogallala aquifer in the northern part of the Texas Panhandle and adjacent parts of New Mexico, Oklahoma, and Kansas. The model, known as the "Ogll-n" GAM (Groundwater Availability Model) or Panhandle Water Planning Area (PWPA) model, was developed in 2000, updated in 2001 for the Panhandle Water Planning Group, and is one of the GAM models adopted by the Texas Water Development Board (TWDB). Major adjustments included:
- Assigning elevation of the base of the Ogallala aquifer to selected model cells,
- Applying recharge rates to parts of the aquifer in the model based on soil properties, and
- Modifying parameters of the MODFLOW Drain and GHB (general head boundary) packages used to simulate the flow of groundwater at the edge of the aquifer.
The steady-state (predevelopment) model error (RMSE or root mean square error) was reduced by more than 3 feet to 32 feet, which is less than 2 percent of the change in hydraulic head in monitoring wells across the model area. The RMSE error in all counties was lowered to less than 10 percent. For example, the RMSE error for Roberts County was reduced from about 26 to 22 feet, which is less than 5 percent of the hydraulic-head change across the county. The transient model RMSE error was reduced by about 6 feet to 53 feet, which is about 2 percent of the hydraulic-head change across the model area. For instance, the transient-model RMSE for Roberts County was reduced from 51 to 45 feet, which is about 6 percent of hydraulic-head change across the county. The transient-model RMSE for 10 of the 17 counties with monitoring well data is less than 10 percent. The largest RMSE (17 percent) was for Randall County where model-edge boundary conditions highly impact simulation results.Bureau of Economic Geolog
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Analysis of Drawdown for Three Ground Water Projects in Roberts County, Texas and Comparison to the 50-Percent Goal
Three water production projects have been proposed in and adjacent to Roberts County, Texas, and are in various stages of planning, permitting, construction, and implementation. The projects are referred to as the Amarillo, Mesa, and Canadian River Municipal Water Authority (CRMWA) projects. The total pumping from the Ogallala aquifer in these projects is anticipated to be more than 280,000 acre-feet/year. Additional permit applications for groundwater development in the Roberts County area are expected.
This study was performed at the request of the Panhandle Groundwater Conservation District to evaluate whether these projects, at an average pumping rate of 1 acre-foot/acre per year or at some lower average pumping rate, might meet District aquifer management goals. These projects were evaluated in various combinations. Three scenarios treated each project by itself. Three more scenarios combined the three projects in pairs. A seventh scenario analyzed all three as simultaneous projects. An eighth scenario evaluated hypothetical production from the entire Roberts County area. The scenarios were evaluated using a groundwater flow model of the Ogallala aquifer developed for the Panhandle Regional Water Planning Group.Bureau of Economic Geolog
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Groundwater Recharge in Texas
Groundwater recharge is critical in evaluating water resources. Recharge estimates are required for groundwater models being developed as part of the Groundwater Availability Modeling program at the Texas Water Development Board. The purpose of this study was to assess the status of data on recharge for the major aquifers in Texas, evaluate the reliability of the recharge estimates, develop conceptual models for recharge for each of the aquifers, review techniques for quantifying recharge, and recommend appropriate techniques for quantifying the recharge of each of the major aquifers.
Recharge rates for all major aquifers were compiled from published reports. The Edwards aquifer is the most dynamic, and recharge rates are highly variable spatially and temporally. Recharge is fairly accurately quantified using stream-gauge data. Estimates of recharge rates in the Carrizo-Wilcox aquifer range from 0.1 to 5.8 in/yr. The higher recharge rates occur in the sandy portions of the aquifer (i.e., the Carrizo and Simsboro Formations). Reported recharge rates for the Gulf Coast aquifer (0.0004 to 2 in/yr) are generally lower than those for the Carrizo-Wilcox aquifer. In both the Carrizo-Wilcox and Gulf Coast aquifers, higher recharge rates are estimated in upland areas containing sandy soils. Regional recharge rates in the High Plains aquifer, outside irrigated areas, are generally low (0.004 to 1.7 in/yr), whereas playa-focused recharge rates are much higher (0.5 to 8.6 in/yr). Irrigated areas also have fairly high recharge rates (0.6 to 11 in/yr). Recharge rates in the Trinity and Edwards-Trinity Plateau aquifers generally range from 0.1 to 2 in/yr. The Seymour aquifer has recharge rates that range from 1 to 2.5 in/yr. Recharge rates for the Hueco-Mesilla Bolson and the Cenozoic Pecos Alluvium are represented as total recharge along mountain fronts and valley floors.Bureau of Economic Geolog
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Appraisal of groundwater in storage in the Ogallala aquifer beneath the Duncan Ranch, Hutchinson and Roberts Counties, Texas
This study assesses and evaluates groundwater storage in the Ogallala aquifer beneath Duncan Ranch in Hutchinson and Roberts Counties, Texas. Data used for mapping the base and water table of the Ogallala aquifer included results from 10 boreholes drilled on Duncan Ranch, water-level readings at nearby wells, data on the elevation of the top of red beds in the vicinity of Duncan Ranch, and parameters mapped in the regional computer model of the Ogallala aquifer. Gamma and resistivity logs from the 10 Duncan Ranch boreholes were used as a basis for estimating water quality.
A best estimate of the volume of water in place in sands and gravels of the Ogallala aquifer beneath Duncan Ranch is 380,000 acre-feet. Different estimates of porosity give a range in water volume from approximately 320,000 to 440,000 acre-feet. The best estimate is the midpoint of this range, calculated within each section on Duncan Ranch. Chloride (Cl) concentration estimated for a subset of this volume averages 85 mg/L. Because the resistivity method overestimates Cl concentration of less than 15 mg/L, the true average is probably less than 85 mg/L. All of this water volume might not be recoverable. Hydrogeologic modeling would provide a technical basis for evaluating the performance of various well-field scenarios but was beyond the scope of this study.Bureau of Economic Geolog
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Surface Water Hydrology of the Proposed Low-Level Radioactive Waste Isolation Site, Hudspeth County, Texas
This report describes the surface-water hydrology at the proposed low-level radioactive waste isolation site in Hudspeth County, Texas. The objective of these investigations was to evaluate the flooding potential at the site based on computer simulation of runoff from observed and hypothetical rain events. Analytic techniques and assumptions used in this study are based on recommendations of federal and state regulatory agencies regarding flood insurance and dam safety criteria. Published topographic maps, aerial photographs, and site surveys were used for delineating drainage basins and surface-water pathways on the study area. Surface-water runoff volumes were calculated for rain events monitored at the site during the study period. Hydrologic computer models were employed to determine correlation of rainfall to surface-water runoff. These computer models were calibrated using rainfall and stream-flow data measured at the site. Flood profiles were calculated for 100-yr and probable maximum rain events, which were estimated from historical data. The following conclusions regarding the flooding potential at the study area were drawn on the basis of these studies:
(1) Computer simulation indicates that floods resulting from hypothetical 100-yr and probable maximum precipitation events are contained within existing channels in the study area, leaving large interchannel areas unflooded. Some overland sheet flow is encountered over the flat area, but the velocities of flow are very small.
(2) Rainfall events recorded during the 1988-1989 period were short and localized. The response of runoff to rainfall is rapid and the duration of the peak water flow after rainfall is relatively short.
(3) Flow velocities range from 3 to 13 ft/sec (0.9 to 4 m/sec) in channels and are lower over flat areas. Maximum depth of flow due to a 100-yr flood in the better-defined channel on the central part of the study area is about 5 ft (1.5 m).Bureau of Economic Geolog
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Geologic and Hydrologic Controls on Reservoir-Scale Variability in Formation-Water Compositions
Subsurface formation waters exhibit regional trends in measured chemistries, but the data also exhibit marked local variance that has not been adequately described or explained. An integrated study of chemical, petrologic, and fluid-pressure data from a well-characterized natural gas field in the Gulf Coast basin will allow us to determine reservoir-scale controls on chemical and diagenetic variability. Understanding the controls on chemistry can provide insight into fluid flow and rock-water interactions in similar geologic settings. Knowledge of solute distributions will aid in the assessment of compartmentalization within reservoirs and fluid communication between reservoirs. Such assessment is relevant not only to improved hydrocarbon exploitation but also to the safe injection of chemical wastes. Finally, understanding small-scale chemical changes would further the interpretation of regional variations in water chemistry, diagenetic facies, and fluid flow within the Cenozoic section of the Gulf Coast basin. This interpretation is potentially important in the study of hydrocarbon migration and entrapment.
We propose to sample in detail formation waters from Stratton Field in Nueces and Kleberg Counties, Texas, in order to map and interpret chemical variations within and between individual reservoirs. The results of water analyses will be mapped with respect to facies and reservoir geometries and features such as faults in order to determine stratigraphic, structural, and hydraulic controls on chemical variability. Hydrochemical data will be compared with mineralogic analyses of core, and geochemical modeling will be conducted. Results will be assessed in terms of the extent of rock-water equilibration to determine plausible reaction and mixing sequences along flow paths.Bureau of Economic Geolog
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Sources of Salt-Water Pollution in Western Tom Green County
Tom Green County is situated within the discharge zone of the Permian Basin regional flow system in West Texas. Analysis of hydrochemical facies and ionic ratios of major chemical constituents suggests that a significant portion of the saline groundwater in the area is a combination of subsurface brine flowing eastward from the Permian Basin and locally recharged, shallowly circulating meteoric water. Aquifers that typically contain relatively fresh water in outcropping Paleozoic rocks exhibit the presence of brine and hydrocarbons at shallow depths ranging from 200 to 900 feet (60 to 270 meters) just a few tens of miles to the west. The chemical composition of groundwater is closely linked to the outcrop of Paleozoic formations from which brine is discharged.Bureau of Economic Geolog
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