David L. Parkhurst

• MS
• Research Hydrologist at United States Geological Survey

In the U.S., about 44 million people rely on self-supplied groundwater for drinking water. Because most self-supplied homeowners do not treat their water to control corrosion, drinking water can be susceptible to lead (Pb) contamination from metal plumbing. To assess the types and locations of susceptible groundwater, a geochemical reaction model t...

Variably saturated groundwater flow, heat transport, and solute transport are important processes in environmental phenomena such as the natural evolution of water chemistry of aquifers and streams, the storage of radioactive waste in a geologic repository, the contamination of water resources from acid-rock drainage, and the geologic sequestration...

The Water, Energy, and Biogeochemical Model (WEBMOD) was used to simulate daily variations of chemical weathering, isotopic fractionation, and hydrology for two research watersheds in the U.S. Geological Survey’s Water, Energy, and Biogeochemical Budget (WEBB) program. Andrews Creek drains 1.74-km² of granite at the continental divide in Rocky Moun...

Brackish groundwater (BGW) is increasingly used for water supplies where fresh water is scarce, but the distribution and availability of such resources have not been characterized at the national scale in the United States since the 1960s. Apart from its distribution and accessibility, BGW usability is a function of the chemical requirements of the...

Calculating the solubility of gases and minerals at the high pressures of carbon capture and storage in geological reservoirs requires an accurate description of the molar volumes of aqueous species and the fugacity coefficients of gases. Existing methods for calculating the molar volumes of aqueous species are limited to a specific concentration m...

Alkaline chemicals are commonly added to discharges from coal mines to increase pH and decrease concentrations of acidity and dissolved aluminum, iron, manganese, and associated metals. The annual cost of chemical treatment depends on the type and quantities of chemicals added and sludge produced. The AMDTreat computer program, initially developed...

Phast4Windows is a Windows® program for developing and running groundwater-flow and reactive-transport models with the PHAST simulator. This graphical user interface allows definition of grid-independent spatial distributions of model properties—the porous media properties, the initial head and chemistry conditions, boundary conditions, and locatio...

PHREEQC version 3 is a computer program written in the C and C++ programming languages that is designed to perform a wide variety of aqueous geochemical calculations. PHREEQC implements several types of aqueous models: two ion-association aqueous models (the Lawrence Livermore National Laboratory model and WATEQ4F), a Pitzer specific-ion-interactio...

The geochemical model PHREEQC is capable of simulating a wide range of equilibrium reactions between water and minerals, ion exchangers, surface complexes, solid solutions, and gases. It also has a general kinetic formulation that allows modeling of nonequilibrium mineral dissolution and precipitation, microbial reactions, decomposition of organic...

The new IPhreeqc module provides an application programming interface (API) to facilitate coupling of other codes with the U.S. Geological Survey geochemical model PHREEQC. Traditionally, loose coupling of PHREEQC with other applications required methods to create PHREEQC input files, start external PHREEQC processes, and process PHREEQC output fil...

The AMDTreat computer program (. Treatment with caustic chemicals typically is used to increase pH and decrease concentrations of dissolved aluminum, iron, and/or manganese in large-volume, metal-laden discharges from active coal mines. Generally, aluminum and iron can be removed effectively at near-neutral pH (6 to 8), whereas active manganese rem...

Results of reactive-transport modeling are useful in understanding many subsurface hydro-geochemical problems, including the movement of natural and anthropogenic contamination. However, development of a site-specific reactive-transport model is a difficult process involving translation of geographic, hydrologic, and chemical information into the f...

The Retsof salt mine in upstate New York was flooded from 1994 to 1996 after two roof collapses created rubble chimneys in overlying bedrock that intersected a confined aquifer in glacial sediments. The mine now contains about 60 billion liters of saturated halite brine that is slowly being displaced as the weight of overlying sediments causes the...

Theory is derived from the work of Urey (Urey H. C. [1947] The thermodynamic properties of isotopic substances. J. Chem. Soc. 562–581) to calculate equilibrium constants commonly used in geochemical equilibrium and reaction-transport models for reactions of individual isotopic species. Urey showed that equilibrium constants of isotope exchange reac...

Natural unsaturated-zone gas profiles at the Amargosa Desert Research Site near Beatty, Nevada show an increase in the partial pressure of CO2 (PCO2) from ˜36 Pa at the land surface to ˜900 Pa at the 110-m deep water table. The CO2 profiles show generally increasing delta 13C values with depth, from a time-weighted-average -180/00 in the root zone...

A parallel algorithm for the reactive-transport simulator PHAST was developed for a Beowulf cluster of Linux PCs. The Local Area Multicomputer implementation of the Message Passing Interface standard was used for communication among processors. PHAST simulates reactive transport by operator splitting the calculation into a flow and transport step a...

PHREEQC version 2 is a computer program written in the C programming language that is designed to perform a wide variety of low-temperature aqueous geochemical calculations.

Geochemical mole-balance models are sets of chemical reactions that quantitatively account for changes in the chemical and isotopic composition of water along a flow path. A revised mole-balance formulation that includes an uncertainty term for each chemical and isotopic datum is derived. The revised formulation is comprised of mole-balance equatio...

The National Water-Quality Assessment pilot project for the Central Oklahoma aquifer examined the chemical and isotopic composition of ground water, the abundances and textures of minerals in core samples, and water levels and hydraulic properties in the flow system to identify geochemical reactions that occur in the aquifer and rates and direction...

Gross-beta activity has been used as an indicator of beta-emitting isotopes in water since at least the early 1950s. Originally designed for detection of radioactive releases from nuclear facilities and weapons tests, analysis of gross-beta activity is widely used in studies of naturally occurring radioactivity in ground water. Analyses of about 80...

NETPATH is an interactive Fortran 77 computer program used to interpret net geochemical mass-balance reactions between an initial and final water along a hydrologic flow path. Alternatively, NETPATH computes the mixing proportions of two to five initial waters and net geochemical reactions that can account for the observed composition of a final wa...

A revised, updated summary of equilibrium constants and reaction enthalpies for aqueous ion association reactions and mineral solubilities has been compiled from the literature for common equilibria occurring in natural waters at 0-100°C and 1 bar pressure. The species have been limited to those containing the elements Na, K, Li, Ca, Mg, Ba, Sr, Ra...

A computer program is presented that simulates geochemical reactions in brines and other concentrated electrolyte solutions using the ioninteraction virial-coefficient approach for activity-coefficient corrections developed by Pitzer. Reaction-modeling capabilities include calculation of (1) aqueous speciation and mineral saturation indices, (2) mi...

Calculations using the aqueous model from WATEQ and an aqueous model modified from WATEQ were compared to experimental mean activity coefficients for various salts to determine the range of applicability and the sources of errors in the models. An ion-association aqueous model was derived by least-squares fitting of ion-association stability consta...

The water quality of the Central Oklahoma aquifer was assessed using the information available through 1987. The following conclusions were drawn from the available data and the contingency-table statistics. The word common is used to describe situations where approximately 10% or more of the data exceeded a water quality standard: (1) groundwater...

A U.S. Geological Survey report is presented on a computer program incorporating Pitzer's equations for the calculation of geochemical reactions in brines.

Methods are described for developing geochemical reaction models from the observed chemical compositions of ground water along a hydrologic flow path. The roles of thermodynamic speciation programs, mass balance calculations, and reaction-path simulations in developing and testing reaction models are contrasted. Electron transfer is included in the...

Sand-size aggregates of vivianite crystals occur in the uppermost sediments of the Potomac River estuary immediately downstream from the outfall of a sewage treatment plant at the southernmost boundary of the District of Columbia, USA. They are most abundant in a small area of coarse sand (dredge spoil) which contrasts with the adjacent, much finer...

Abstract Kinetic results of published laboratory studies of calcite dissolution and precipitation in the system CaO-MgO-Na2O-K2O-CO2-H2SO4- HCl-H2O are used to test the surface mechanism model of Plummer, Wigley, and Parkhurst (1978; Amer. Jour. Sci. 278, 179-216). This mechanism model includes: 1) three simultaneous reactions at the mineral-aqueou...

Kinetic results of published laboratory studies of calcite dissolution and precipitation in the system CaO-MgO-Na//2O-K//2O-CO//2-H//2SO//4-HCl-H//2O are used to test the surface mechanism model of L. N. Plummer, T. M. L. Wigley, and D. L. Parkhurst. This mechanism model includes: 1) three simultaneous reactions at the mineral-aqueous solution inte...

This paper reports the results of experimental studies on the dissolution of cleavage rhombs of Iceland spar in the pure calcite-water system, using both the ″pH-stat″ and ″free drift″ methods. The data were obtained over a wide range of fluid composition varying bulk fluid pH from 2. 0 to 7. 0 and bulk fluid P//c//o//(//2//) from near 0. 0 to 1. 0...

Chemical analyses are presented for 47 sediment samples from the Tar Creek drainage in the Picher mining area of northeast Oklahoma. The samples were taken in December 1983, June 1984, and June 1985. All of the samples were taken downstream from mine-water discharge points of abandoned lead and zinc mines. the 34 samples taken in December 1983 and...

PHAST is a computer program for simulation of reactive-transport in three dimensions, which has been developed by the U.S. Geological Survey. The simulator is used to model constant-density ground-water flow, in confined or unconfined conditions, coupled with multi-component solute transport and a wide range of chemical reactions, including mineral...

Thesis (M.S.)--Stanford University, 1985.