Oxygen In Groundwater Research Articles

Pseudofaults resulting from compartmentalized Liesegang bands: update

Abstract Liesegang bands with apparent offset along fractures are common in some calcisiltite beds. Thin sections show, however, that primary laminations are not offset along the fractures. Following the development of fracture sets in the calcisiltite, the fractures were cemented by calcite. This formed polyhedral compartments of low‐permeability calcisiltite bounded by impermeable walls of calcite. Liesegang bands formed when oxygen in ground water diffused into polyhedra containing soluble ferrous iron in pore water. Each joint‐bounded polyhedral compartment behaved as an independent diffusion cell. Liesegang bands with nearly the same pattern and thickness tended to develop in adjacent compartments, but not at the same stratigraphic level; this resulted in the formation of pseudofaults.

Rapid evolution of redox processes in a petroleum hydrocarbon-contaminated aquifer.

Ground water chemistry data collected over a six-year period show that the distribution of contaminants and redox processes in a shallow petroleum hydrocarbon-contaminated aquifer has changed rapidly over time. Shortly after a gasoline release occurred in 1990, high concentrations of benzene were present near the contaminant source area. In this contaminated zone, dissolved oxygen in ground water was depleted, and by 1994 Fe(III) reduction and sulfate reduction were the predominant terminal electron accepting processes. Significantly, dissolved methane was below measurable levels in 1994, indicating the absence of significant methanogenesis. By 1996, however, depletion of solid-phase Fe(III)-oxyhydrox ides in aquifer sediments and depletion of dissolved sulfate in ground water resulted in the onset of methanogenesis. Between 1996 and 2000, water-chemistry data indicated that methanogenic metabolism became increasingly prevalent. Molecular analysis of 16S-rDNA extracted from sediments shows the presence of a more diverse methanogenic community inside as opposed to outside the plume core, and is consistent with water-chemistry data indicating a shift toward methanogenesis over time. This rapid evolution of redox processes reflects several factors including the large amounts of contaminants, relatively rapid ground water flow (approximately 0.3 m/day [approximately foot/day]), and low concentrations of microbially reducible Fe(III) oxyhydroxides ( approximately 1 micromol/g) initially present in aquifer sediments. These results illustrate that, under certain hydrologic conditions, redox conditions in petroleum hydrocarbon-contaminated aquifers can change rapidly in time and space, and that the availability of solid-phase Fe(III)-oxyhydroxides affects this rate of change.

INTERACTIONS BETWEEN GROUND WATER AND SURFACE WATER IN THE SUWANNEE RIVER BASIN, FLORIDA1

ABSTRACT: Ground water and surface water constitute a single dynamic system in most parts of the Suwannee River basin due to the presence of karst features that facilitate the interaction between the surface and subsurface. Low radon‐222 concentrations (below background levels) and enriched amounts of oxygen‐18 and deuterium in ground water indicate mixing with surface water in parts of the basin. Comparison of surface water and regional ground water flow patterns indicate that boundaries for ground water basins typically do not coincide with surface water drainage subbasins. There are several areas in the basin where ground water flow that originates outside of the Suwannee River basin crosses surface water basin boundaries during both low‐flow and high‐flow conditions. In a study area adjacent to the Suwannee River that consists predominantly of agricultural land use, 18 wells tapping the Upper Floridan aquifer and 7 springs were sampled three times during 1990 through 1994 for major dissolved inorganic constituents, trace elements, and nutrients. During a period of above normal rainfall that resulted in high river stage and high ground water levels in 1991, the combination of increased amounts of dissolved organic carbon and decreased levels of dissolved oxygen in ground water created conditions favorable for the natural reduction of nitrate by denitrification reactions in the aquifer. As a result, less nitrate was discharged by ground water to the Suwannee River.

An Assessment of Conventional In Situ Air Sparging Pilot Tests

AbstractShort‐term (< 24 h) pilot tests play a key role in the selection and design of in situ air sparging systems. During air injection, changes in dissolved oxygen in ground water, water levels in wells, soil gas pressures, and soil gas contaminant concentrations are measured. These parameters are assumed to be indicators of air sparging feasibility and performance. In this work we assess the validity of this critical assumption. Data are presented from a study site where a typical short‐term test was conducted for three days, followed by continued operation of a full‐scale system for 110 days. Conventional sampling practices were augmented with more discrete and detailed assessment methods. In addition, a tracer gas was used to better investigate air distributions, vapor flow paths, and vapor recovery efficiency. The data illustrate that conclusions regarding the performance and applicability of air sparging can vary dramatically depending on the monitoring approach used. Samples collected for chemical analyses from conventional monitoring wells were clearly affected by the air sparging during, and for some time after, air injection. Results from this site suggest that typical pilot test measurements might be useful for assessing infeasibility, but do not yield sufficient information to extrapolate to long‐term performance.

GROUND WATER AS A SOURCE OF NUTRIENTS AND ATRAZINE TO STREAMS IN THE SOUTH PLATTE RIVER BASIN1

ABSTRACT: Concentrations of nitrite plus nitrate, ammonia, orthophosphate, and atrazine were measured in streams and ground water beneath the streams at 23 sites in the South Platte River basin of Colorado, Nebraska, and Wyoming to assess: (1) the role of ground water as a source of nutrients and atrazine to streams in the basin, and (2) the effect of land‐use setting on this process. Concentrations of nitrite plus nitrate, ammonia, orthophosphate, and atrazine were higher in ground water than in the overlying streams at 2, 12, 12, and 3 of 19 sites, respectively, where there was not a measurable hydraulic gradient directed from the stream to the ground water. Orthophosphate was the only constituent that had a significantly higher (p ≤ 0.05) concentration in ground water than in surface water for a given land‐use setting (range land). Redox conditions in ground water were more important than land‐use setting in influencing whether ground water was a source of elevated nitrite plus nitrate concentrations to streams in the basin. The ratios of nitrite plus nitrate in ground water/surface were were significantly lower (p ≤ 0.05) at sites having concentrations of dissolved oxygen in ground water ≤ 0.5 mg/L than at sites having dissolved oxygen concentrations ≥ 0.5 mg/L. Elevated concentrations of ammonia or atrazine in ground water occurred at sites in close proximity to likely sources of ammonia or atrazine, regardless of land‐use setting. These results indicate that land‐use setting is not the only factor that influences whether ground water is a source of elevated nutrient and atrazine concentrations to streams in the South Platte River Basin.

Measurement and Interpretation of Low Levels of Dissolved Oxygen in Ground Water

AbstractA Rhodazine‐D colorimetric technique was adapted to measure low‐level dissolved oxygen concentrations in ground water. Prepared samples containing between 0 and 8.0 μmoles · 1‐1 dissolved oxygen in equilibrium with known gas mixtures produced linear spectrophotometric absorbance with a lower detection limit of 0.2 μmoles · 1‐1. Excellent reproducibility was found for solutions ranging in composition from deionized water to sea water with chemical interferences detected only for easily reduced metal species such as ferric ion, cupric ion, and hexavalent chromium. Such effects were correctable based on parallel reaction stoichiometries relative to oxygen. The technique, coupled with a downhole wire line tool, permitted low‐level monitoring of dissolved oxygen in wells at the selenium‐contaminated Kesterson Reservoir in California. Results indicated a close association between low but measurable dissolved oxygen concentrations and mobility of oxidized forms of selenium in the shallow aquifer which were in general electrochemical disequilibrium.

Monitoring Dissolved Oxygen in Ground Water: Some Basic Considerations

AbstractDissolved oxygen (D.O.) concentration has a significant effect upon ground water quality by regulating the valence state of trace metals and by constraining the bacterial metabolism of dissolved organic species. For these reasons, the measurement of dissolved oxygen concentration should be considered essential in most water quality investigations. D.O. measurements have been frequently neglected in ground water monitoring. This is because O2 has often been assumed absent below the water table; measurement of O2, concentrations is not mandated by drinking water standards; and the redox potential has previously been considered an adequate and encompassing electrochemical measurement. Redox potentials, however, cannot adequately predict dissolved oxygen concentrations nor can D.O. concentrations be used to calculate redox potentials.D.O. concentrations can be measured precisely in the field by titration or electrode methods. The best methods of sample recovery are those that use positive pressure displacement devices. A fully adequate sampling procedure will isolate ground water from the atmosphere and will collect samples at restricted depth intervals at ambient temperature and pressure.

Laterite and Bauxite Formation

Simplified model, preferential solubilities of elements over given pH range, availability of oxygen in ground water