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26 records · Page 2Linked to original sources
USGS1984

Computer model of one-dimensional equilibrium controlled sorption processes

A numerical solution to the one-dimensional solute-transport equation with equilibrium-controlled sorption and a first-order irreversible-rate reaction is presented. The computer code is written in FORTRAN language, with a variety of options for input and output for user ease. Sorption reactions include Langmuir, Freundlich, and ion-exchange, with or without equal valance. General equations describing transport and reaction processes are solved by finite-difference methods, with nonlinearities accounted for by iteration. Complete documentation of the code, with examples, is included. (USGS)

Water-Resources Investigations Report↗
USGS1988

Nitrogen transport in a shallow outwash aquifer at Olean, Cattaraugus County, New York

Groundwater beneath an industrial park at Olean, New York, contained nitrogen compounds in concentrations that in 1983 ranged from 10 to 1,280 mg/L as nitrogen, mainly in the form of ammonium. Continuous pumping from an industrial well field creates a cone of depression that prevents the nitrogen compounds from migrating to municipal-supply wells, 7,000 ft away. A two-dimensional solute transport model was used to simulate changes in nitrogen concentrations that would result from a permanent shutdown of the well field. The model assumed the nitrogen source decayed at an exponential rate with a decay constant of 0.3/year to account for nitrogen removed from the aquifer by pumping during 1978-84. The source of contamination was found to be sensitive to the volume of pumpage at the industrial well field, which altered the rate of groundwater flow through the contaminated area. Simulations of a permanent shutdown of the well field, assuming nitrogen migrates as a conservative solute, indicated that nitrogen-bearing groundwater would reach the municipal well field within 5 years and the peak concentrations at the municipal well field would range from 2 to 5 mg/L. Simulations of Langmuir adsorption of the dissolved ammonium with a one-dimensional model indicated that the arrival of the solute front at the municipal well field would be retarded by a factor of three.

New York↗
USGS1989

Modification of a method-of-characteristics solute-transport model to incorporate decay and equilibrium-controlled sorption or ion exchange

The U.S. Geological Survey computer model of two-dimensional solute transport and dispersion in ground water (Konikow and Bredehoeft, 1978) has been modified to incorporate the following types of chemical reactions: (1) first-order irreversible rate-reaction, such as radioactive decay; (2) reversible equilibrium-controlled sorption with linear, Freundlich, or Langmuir isotherms; and (3) reversible equilibrium-controlled ion exchange for monovalent or divalent ions. Numerical procedures are developed to incorporate these processes in the general solution scheme that uses method-of- characteristics with particle tracking for advection and finite-difference methods for dispersion. The first type of reaction is accounted for by an exponential decay term applied directly to the particle concentration. The second and third types of reactions are incorporated through a retardation factor, which is a function of concentration for nonlinear cases. The model is evaluated and verified by comparison with analytical solutions for linear sorption and decay, and by comparison with other numerical solutions for nonlinear sorption and ion exchange.

Water-Resources Investigations Report↗
USGS1975

Reactions of aqueous aluminum species at mineral surfaces

Aqueous aluminum solutions containing 4.5 ? 10 4 molar aluminum in 0.01 molar NaC104 were partly neutralized with NaOH to give OH:A1 mole ratios from 1.40 to 2.76. Measured amounts of montmorillonite, kaolinite, volcanic ash, or feldspathic sand were added to provide an area of inert surface. Reactions that occurred during 100 days of aging were compared with those in similar solutions without added surfaces, studied in earlier work. Adsorption of monomeric species Al(H20)6+3, AlOH(H2O)5+2, and Al(OH)2(H2O 4? on the added surfaces follows a cation exchange mass law equilibrium model, and adsorption is essentially complete in 1 hour. Only minor changes in monomeric aluminum species occurred after that. Rapid adsorption of polynuclear aluminum hydroxide species also occurs and follows the pattern of the Langmuir adsorption isotherm. In the absence of surfaces, the polynuclear ions slowly increase in size and become microcrystalline gibbsite during aging. Electron micrographs showed microcrystalline gibbsite was present or surfaces after aging only 2 days. However, the analytical data suggest this material must have been adsorbed after it had already attained a near-crystalline state. Adsorbed polynuclear aluminum hydroxide species were not extensively converted to microcrystalline gibbsite during 100 days of aging.

Water Supply Paper↗
USGS2002

The role of water in the formation of reversed micelles: An antimicellization agent

Micellization of sodium bis(2-ethylhexyl) phosphate in n-heptane has been studied under controlled environmental conditions by dynamic and static light scattering. The results clearly show that a trace amount of water has a very dramatic effect on reversed micellization. In contrast with results in the literature, water can function as an antimicellization agent. The generality of and the evidence for supporting the current view that water is a prerequisite for the formation of reversed micelles are discussed and criticized.

Langmuir↗
USGS1987

The solubilities of some major and minor element minerals in ground waters associated with a sandstone-hosted uranium deposit

Ground-water samples from 41 wells penetrating basal Oakville sandstone (Miocene) in S Texas were chemically analysed to identify chemical changes related to nearby U orebodies. The coverage included a 240 km 2 area which contains several fault-related U deposits. Factors affecting the hydrochemistry include: 1) relatively high permeabilities of buried fluvial-channel sediments; 2) upwards leakage of brines along growth faults into the aquifer; 3) development of a redox interface (Eh = 0 volts) within the aquifer; and 4) the semi-arid climate. Variations in the saturation index (SI) for chemically reduced minerals of U, As, Mo, Se and for associated minerals such as pyrite outlined the position of known deposits. The SI increases towards zero as the deposits are approached from updip distances of 3-4.5 km, then decreases again downdip. The radiogenic pathfinders Ra and Rn showed very strong anomalies with ore, but diminished to background levels at short distances from ore. A strong He anomaly is deflected in the direction of ground-water flow away from the ore.-R.A.H.

Bulletin de Mineralogie↗