Charles W. Kreitler

Nitrogen-isotope ratio studies of soils and groundwater nitrate from alluvial fan aquifers in Texas☆

Average nitrate concentrations of 54 water samples from the Lockhart and Taylor alluvial carbonate gravel aquifers (central Texas) and of 37 groundwater samples from Seymour alluvial siliceous gravel aquifer are 75 and 138 mg/l, respectively. The dominant nitrate sources over the aquifers are cultivated land with ammonium-type fertilizer and animal wastes from livestock and domestic waste. Kreitler has previously identified two ranges of nitrogen-isotope values (δ 15N) for soil nitrate under different land uses in west Texas: nitrate originating from nonfertilized, cultivated fields (δ 15N range, +2 to +8‰ with an average of +4.9‰), and nitrate from animal wastes (δ 15N range, +10 to +22‰ with an average of +14.4‰). The δ 15N of fertilizer nitrogen used on the Lockhart and Taylor fans ranges from −7.4 to +1.9‰. The δ 15N range of 20 soil nitrate samples from 15 cultivated fields on the two alluvial fans is +2 to +14‰ with an average of +8.8‰. This δ 15N range for ammonium-fertilized, cultivated fields is more positive than the δ 15N range of nonfertilized fields because of volatilization of ammonia depleted in 15N during and after fertilizer application, which leaves nitrate enriched in 15N. The δ 15N of groundwater nitrate from irrigation wells on the two fans range from +3.3 to +10.8‰ with an average of +7.3‰. Groundwater from domestic wells on the two fans has higher nitrate concentrations and a more positive δ 15N range (+6.7 to +18.2‰ with an average of +11.1‰) than wells located in the cultivated fields. Nitrate contamination of wells located in cultivated fields results primarily from cultivation with ammonium-type fertilizers, whereas animal wastes are contaminating domestic well waters.

Nitrogen-isotope analysis of groundwater nitrate in carbonate aquifers: Natural sources versus human pollution

Results of nitrogen-isotope analyses of nitrate in the waters of the Cretaceous Edwards aquifer in Texas, U.S.A., indicate that the source of the nitrate is naturally-occurring nitrogen compounds in the recharge streams. In contrast, nitrogen isotopes of nitrate in the fresh waters of the Pleistocene Ironshore Formation on Grand Cayman Island, West Indies, indicate that human wastes are the source of the nitrate. The Cretaceous Edwards Limestone is a prolific aquifer that produces principally from fracture porosity along the Balcones Fault Zone. Recharge is primarily by streams crossing the fault zone. Rainfall is ∼ 70 cm yr.−1, and the water table is generally deeper than 30 m below land surface. The δ15 N of 73 samples of nitrate from Edwards waters ranged from + 1.9 to + 10‰ with an average of + 6.2‰. This δ15 N range is within the range of nitrate in surface water in the recharge streams (δ15N range = + 1 to + 8.3‰) and within the range of nitrate in surface water from the Colorado River, Texas, (δ15N range = + 1 to + 11‰). No sample was found to be enriched in 15N, which would suggest the presence of nitrate from animal waste (δ15N range = + 10 to + 22‰). The Ironshore Formation contains a small freshwater lens that is recharged entirely by percolation through the soil. Average rainfall is 165 cm yr.−1, and the water table is within 3 m of land surface. The δ15 N of four nitrate samples from water samples of the Ironshore Formation ranged from + 18 to + 23.9‰, which indicates a cesspool/septictank source of the nitrate. Limestone aquifers in humid environments that are recharged by percolation through the soil appear to be more susceptible to contamination by septic tanks than are aquifers in subhumid environments that feature thick unsaturated sections and are recharged by streams.

Hydrogeology of sedimentary basins

Abstract Hydrogeologic environments in sedimentary basins are as variable as are the different types of basins. Important hydrologic characteristics can be used to distinguish the different types of basin: (1) the topographic setting as determined by the geologic and structural history of the basin; (2) permeability distribution within the basin; and (3) potential energy distributions and flow mechanisms. These parameters control residence times of waters, rates and directions of saline groundwater flow and the origin and chemical composition of the saline waters. The Gulf Coast and Palo Duro Basins, Texas, exemplify two end member types of sedimentary basins. The Gulf Coast Basin is a relatively young, Tertiary-age basin which is presently compacting; fluid movement is from the overpressured, undercompacted sediments up the structural dip or up fault zones into the hydrostatic section, natural fluid pressures are either hydrostatic or overpressured. The Palo Duro is an older, Paleozoic-age basin that has been tectonically uplifted. Fluid flow is gravity driven from topographically high recharge areas to discharge in topographically low areas. Fluid pressures are subhydrostatic. Fluids discharge more easily than they are recharged. Not all flow is derived by a simple recharge discharge model. Brines may flow from other basins into the Palo Duro Basin and waters may discharge from the Palo Duro Basin into other basins. Areal differences in the chemical composition of the basin brines may be the result of different origins.

Geochemistry and hydrodynamics of deep-basin brines, Palo Duro Basin, Texas, U.S.A.

Abstract Permeable strata of the Deep-Basin Brine aquifer system underlie bedded Permian evaporites in the Palo Duro Basin, Texas Panhandle. Formation water samples collected from four U.S. Department f of Energy test wells and two independent oil and gas company wells in the basin were analyzed for chemical and isotopic compositions to characterize the geochemical environment and to determine the origin and compositional evolution of the water. Formation waters are Na Cl brines that contain 140 to 290 g/l total dissolved solids (TDS). Chemical and isotopic compositions suggest grouping the brine samples into one of two types. Samples from western Palo Duro Basin have high Cl:Br ratios, Sr isotopic ratios that are significantly more radiogenic than Permian seawater or precipitates from Permian seawater, and oxygen isotopic compositions that are depleted with respect to values predicted for equilibrium with calcite under in situ conditions. Samples from central and eastern Palo Duro Basin have low Cl:Br ratios, Sr isotopic ratios only slightly radiogenic relative to Permian marine Sr, and oxygen isotopic compositions that suggest equilibration with calcite. The concentrations of major and minor ions appear to be controlled by equilibrium with calcite, dolomite, anhydrite, celestite, low albite, microcline, and Na-smectite. High Na activities drive ion exchange reactions, which, coupled with maintenance of chemical equilibrium, elevate the concentrations of divalent cations and lower the concentrations of dissolved SO 4 and carbonate. The origin and evolution of deep-basin brines are interpreted from chemical and isotopic compositions integrated with results of previous geological and hydrogeological investigations. Brines from western Palo Duro Basin acquired salinity by dissolving halite along a lateral flow path from the recharge zone; radiogenic Sr was derived from detrital silicate minerals and oxygen isotopic equilibrium with aquifer minerals has not been attained. Brines from central and eastern Palo Duro Basin originated as either recharge that achieved chemical and isotopic equilibrium with the host rock during long residence times or as Permian seawater concentrated by evaporation. Regional chemical and isotopic variations augment the results of hydrogeological modeling: brines in the western part of the basin flow from the west and southwest where siliciclastic sedimentary rocks predominate; brines in the central and eastern parts of the basin flow from the south and southwest where carbonate strata predominate.

Hydrologic hydrochemical characterization of texas frio formation used for deep-well injection of chemical wastes

Hydrologic hydrochemical investigations were conducted to determine the long-term fate of hazardous chemical waste disposed in the Texas Gulf Coast Tertiary formations by deep-well injection. The study focused on the hydrostatic section of the Frio Formation because it is the host of a very large volume of injected waste and because large data bases of formation pressures and water chemistry are available.Three hydrologic regimes exist within the Frio Formation: a shallow fresh to moderately saline water section in the upper 3,000–4,000 ft (914–1,219 m); an underlying 4,000- to 5,000-ft-thick (1,219- to 1,524-m) section with moderate to high salinities: and a deeper overpressured section with moderate to high salinities. The upper two sections are normally pressured and reflect either freshwater or brine hydrostatic pressure gradients. Geopressured conditions are encountered as shallow as 6,000 ft (1,829 m). The complexity of the hydrologic environment is enhanced due to extensive depressurization in the 4,000- to 8,000-ft-depth (1,219- to 2,438-m) interval, which presumably results from the estimated production of over 10 billion barrels (208 × 106 m3) of oil equivalent and associated brines from the Frio in the past 50 yr. Because of the higher fluid density and general depressurization in the brine hydrostatic section, upward migration of these brines to shallow fresh groundwaters should not occur. Depressured oil and gas fields, however, may become sinks for the injected chemical wastes.Water samples appear to be in approximate oxygen isotopic equilibrium with the rock matrix, suggesting that active recharge of the Frio by continental waters is not occurring. In the northern Texas Gulf Coast region salt dome dissolution is a prime process controlling water chemistry. In the central and southern Frio Formation, brines from the deeper geopressured section may be leaking into the hydrostatic section. The lack of organic acids and the alteration of Frio oils from samples collected from depths shallower than approximately 7,000 ft (2,133 m) suggest microbial degradation of organic material. This has useful implications for degradation of injected chemical wastes and needs to be investigated further.

Hydrochemistry of the Falls City Uranium Mine Tailings Remedial Action Project, Karnes County, Texas

ABSTRACT Acidic tailings and tailings solutions, created by sulfuric acid processing of uranium ores, were disposed of on the outcrop of the Whitsett Formation (Eocene). These solutions have recharged the sandstones of the Whitsett since the 1960s. Previous workers found a large, complex, and unexplained pattern of contamination. Our study determined the extent and nature of contamination by (1) characterizing the geology and hydrology of the two shallow aquifers at the site, (2) determining the chemistry of the contaminant source (tailings solutions), and (3) identifying geochemical reactions that have altered the composition of contaminant plumes within each aquifer. The tailings solutions are composed of sodium chloride and neutral sulfate salts of aluminum and ammonium, with lesser amounts of iron, calcium, magnesium, potassium, and sodium sulfate. Hydrolysis of aluminum sulfate produces an acid pH (3 to 4). Also, aluminum sulfate is a pH buffer, and it controls acidity of the tailings solutions. Cation exchange and neutralization by calcite modify the tailings solutions as they migrate through the aquifers. These reactions explain chemical patterns, which delineate five separate contaminant plumes in the aquifers. In the Deweesville sandstone, cation exchange has removed ammonium from acidic contaminant plumes. However, neutralization is incomplete because of the paucity of calcite in the Deweesville. In contrast, in the calcite-rich Conquista fossiliferous sandstone, cation exchange and complete neutralization by calcite have removed most contaminant ions. Those contaminant plumes are delineated by elevated concentrations of calcium and carbon dioxide. The amount of contamination in both aquifers is much smaller than that estimated previously. End_of_Record - Last_Page 762-------

Deep well injection of liquid wastes in saline formations

The AGU Hydrology Section and the International Association of Hydrologists sponsored a symposium on Deep Well Injection of Liquid Wastes in Saline Formations at the AGU Spring Meeting in Baltimore, Md., on May 17, 1988. The symposium was convened by Charles Kreitler (University of Texas, Austin), Chet Miller (Du Pont, Wilmington, Del.), and John Vecchioli (U.S. Geological Survey, Tallahassee, Fla.). John Atcheson, the director of the U.S. Environmental Protection Agencys (EPA) task force on Hazardous Waste Restriction, opened the session with remarks on EPAs concerns over the practice of deep well injection of liquid wastes. These concerns have resulted in several programs nationwide that have been researching the interaction of the injected wastes with host saline formations. The papers at the symposium summarized many of these studies. Papers covered hydrogeologic characterization of the host formations, monitoring strategies, mathematical solutions and their benefits, potential for earthquakes and hydrofracturing, and geochemical reactions of the injected waste. The papers elicited numerous questions and comments on the pros and cons of the injection process. It was clear that there was no consensus to the acceptability of the injection process, and that additional research is needed to learn more about how wastes interact with geologic media.

Cap-Rock Formation and Diagenesis, Gyp Hill Salt Dome, South Texas: ABSTRACT

Cap rock from Gyp Hill salt dome, Brooks County, south Texas, was formed by salt dome dissolution that left a residuum of anhydrite sand, which was subsequently cemented by gypsum and at a later time altered to gypsum by fresh meteoric groundwater. The cap rock consists of gypsum at the surface (0 to 90 m) and gypsum-cemented anhydrite above the salt (90 to 273 m). Samples from the salt contain 13 to 42% disseminated anhydrite crystals and < 1.0% dolomite rhombs in halite. The cap-rock-salt boundary is marked by a cavity several meters high. Salt dissolution has concentrated the insoluble material into an anhydrite sandstone with 20% porosity at the base of the cap rock. Cap rock porosity is largely occluded within 6 m above salt by poikilotopic gypsum cement and crush d anhydrite laths (presumably from the overburden pressure of the cap rock). A transition zone occurs between 90 and 120 m below the surface where anhydrite is being completely hydrated to gypsum. Above this zone, the cap rock is entirely gypsum and indicates flushing by fresh meteoric groundwater. Through the total thickness, anhydrite is in disequilibrium, as evidenced by the gypsum cement and embayed anhydrite laths. End_of_Article - Last_Page 1556------------

Suitability Studies of Salt Domes in East Texas Basin for Geologic Isolation of Nuclear Wastes: ABSTRACT

The suitability of salt domes in the East Texas basin (Tyler basin), Texas, for long-term isolation of nuclear wastes is being evaluated. The major problems concern hydrologic and tectonic stability of the domes and potential natural resources in the basin. These problems are being approached by integration of dome-specific and regional hydrologic, geologic, geomorphic, and remote-sensing investigations. Hydrologic studies are evaluating basinal hydrology and groundwater flow around the domes to determine the degree to which salt domes are dissolving, their rates of solution, and the orientation of saline plumes in the freshwater aquifers. Subsurface geologic studies are being conducted: (1) to determine the size and shape of specific salt domes, the geology of the strata immediately surrounding the domes, and the regional geology of the East Texas basin; (2) to understand the geologic history of the dome growth and basin infilling; and (3) to evaluate potential natural resources. Geomorphic and surficial geology studies are determining whether there have been dome growth and tectonic movement in the basin during the Quaternary. Remote-sensing studies are being conducted to determine (1) whether dome uplift has altered regional lineation patterns in Quaternary sediments and (2) whether drainage density and ruggedness ratios indicate Quaternary structural movement. By means of the screening criteria of McClain and others, Oakwood and Keechi domes were chosen as possible candidate domes. Twenty-three domes were eliminated because of insufficient size, too great a depth to salt, major hydrocarbon production, or previous use (e.g., liquid propane storage or salt mining or brining). Detailed geologic, hydrologic, and geomorphic investigations are being conducted around Oakwood and Keechi salt domes. End_of_Article - Last_Page 1605------------