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Although surface water and groundwater are increasingly referred to as one resource, there remain environmental and ecosystem needs to study the 10 m to 1 km reach scale as one hydrologic system. Streams gain and lose water over a range of spatial and temporal scales. Large spatial scales (kilometers) have traditionally been recognized and studied as river-aquifer connections. Over the last 25 years hyporheic exchange flows (1–10 m) have been studied extensively. Often a transient storage model has been used to quantify the physical solute transport setting in which biogeochemical processes occur. At the longer 10 m to 1 km scale of stream reaches it is now clear that streams which gain water overall can coincidentally...
This study proposes the use of several problems of unstable steady state convection with variable fluid density in a porous layer of infinite horizontal extent as two-dimensional (2-D) test cases for density-dependent groundwater flow and solute transport simulators. Unlike existing density-dependent model benchmarks, these problems have well-defined stability criteria that are determined analytically. These analytical stability indicators can be compared with numerical model results to test the ability of a code to accurately simulate buoyancy driven flow and diffusion. The basic analytical solution is for a horizontally infinite fluid-filled porous layer in which fluid density decreases with depth. The proposed...
Toxic contaminants and naturally occurring substances found in the subsurface can exist in multiple phases, and undergo complex reactions including biodegradation. A comprehensive and quantitative understanding of the processes controlling the fate and transport of subsurface contaminants is necessary to develop policies and strategies for managing water-quality conditions in different land use and environmental settings. Numerical models that simulate flow, transport, and reactions are useful tools for understanding the fate of chemicals in the subsurface when used in conjunction with field and laboratory studies. The research efforts of this project consider flow and chemical behavior in the saturated and unsaturated...
A quantitative understanding of the factors controlling the variation of dissolved organic carbon (DOC) in headwater streams is of scientific concern for at least two reasons. First, quantifying the overall carbon budgets of lotic systems is needed for a fundamental understanding of these systems. Second, DOC interacts strongly with other dissolved substances (heavy metals in particular) and plays an important role in the transport of contaminants. In the Snake River near Montezuma, Colorado, measurements of DOC from 1980 to 1986 show rapid decreases in concentration from a peak very early in the snowmelt period. Peak DOC concentrations occur approximately one month prior to peak discharge in the stream. The decline...
Movement of toxic and radioactive substances in aquifer systems occurs in all three phases and is controlled by both hydrologic and chemical forces. Solute movement can be greatly affected not only by physical dispersion, but by other factors such as exchange sorption, chemical kinetics, and ionic distributions. Movement of gases and particulate material in the unsaturated zone are controlled by many additional factors. Knowledge of how these physical and geochemical factors affect prediction of movement of toxic and radioactive wastes is only generally known for ideal systems. This project's objective is to develop field methods and techniques that will yield values for physical and geochemical factors of regional...
a) Developing defensible conceptual models of processes influencing the mass transfer of inorganic contaminants between aqueous and solid phases. b) Translating conceptual models into quantitative models that can be used to predict the influence of mass-transfer processes on contaminant fate and transport in field applications. c) Developing approaches to obtain parameters required to describe contaminant mass transfer in quantitative fate and transport models that are, to the maximum extent possible, independent of field observations. d) Testing these approaches in laboratory experimental studies, field experimental studies, and field-scale plume characterization studies.
The reactive transport of U(VI) in a shallow alluvial aquifer beneath a former U(VI) mill located near Naturita, CO, was simulated using a surface complexation model (SCM) to describe U(VI) adsorption. The groundwater had variable U(VI) concentrations (0.01–20 μM), variable alkalinity (2.5–18 meq/L), and a nearly constant pH equal to 7.1. U(VI) KD values decreased with increasing U(VI) and alkalinity, and these parameters were more important than sediment variability in controlling KD values. Reactive transport simulations were fit to the observed U(VI) and alkalinity by varying the concentration of U(VI) and alkalinity in recharge at the source area. Simulated KD values varied temporally and spatially because of...
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The U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency and the New Hampshire Department of Environmental Services, developed a model for used with MODFLOW-2005 and MODPATH5 to evaluate groundwater flow and advective transport under pre- and post-remediation conditions in the crystalline-rock aquifer in the vicinity of the Savage Municipal Water-Supply Well Superfund site Milford, New Hampshire. In addition, a previously developed model (https://doi.org/10.3133/sir20045176 and https://doi.org/10.3133/ofr20121079) was used with MOC3D to evaluate the solute-transport of tetrachloroethylene (PCE). In 2010 PCE, a chlorinated volatile organic compound, was detected in groundwater from...
Biogeochemical processes associated with the microbial community (algae, bacteria, fungi) constitute the interface between solute transport and biotic production in riverine environments. Identifying and estimating the role of biotic processes such as nitrification and denitrification by bacteria, nutrient uptake and production by epilithic algal films and decomposition of particulate and dissolved organic matter, as well as abiotic processes such as absorption, are important for understanding the linkage between terrestrial, riparian, hyporheic and in-channel contributions to the nutrient chemistry of a drainage network. Relative biotic response to solutes in transport between pristine and anthropogenically modified...
Categories: Project; Tags: Ecology, Solute Transport
The reactive transport of U(VI) in a shallow alluvial aquifer beneath a former U(VI) mill located near Naturita, CO, was simulated using a surface complexation model (SCM) to describe U(VI) adsorption. The groundwater had variable U(VI) concentrations (0.01–20 μM), variable alkalinity (2.5–18 meq/L), and a nearly constant pH equal to 7.1. U(VI) KD values decreased with increasing U(VI) and alkalinity, and these parameters were more important than sediment variability in controlling KD values. Reactive transport simulations were fit to the observed U(VI) and alkalinity by varying the concentration of U(VI) and alkalinity in recharge at the source area. Simulated KD values varied temporally and spatially because of...
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The U.S. Geological Survey, in cooperation with the U.S. Department of the Navy, developed several 3-D groundwater flow models for used with MODFLOW-2005, MODFLOW-NWT, and SEAWAT model codes to evaluate variable-density groundwater flow and contaminant transport in Operable Unit 1 on Naval Base Kitsap in Keyport, Washington. Chlorinated volatile organic compounds (CVOCs) have migrated to groundwater beneath a former 9-acre landfill at Operable Unit 1 (OU-1). The three predominant ground-water contaminants are the chloroethene compounds trichloroethene (TCE), cis-1,2-dichloroethene (cis-DCE), and vinyl chloride (VC). A need for remedial action was identified because some of the contaminants present a potential risk...
The biological and chemical characteristics of aquatic environments depend on a generally complicated balance of physical, chemical, and biological processes. Basic to describing these characteristics is an understanding of transport processes including both advection and mixing. For a given water body, these processes depend heavily on the mass, momentum, and energy transfers at boundaries and the internal response of the system. Many of these transfers and responses are poorly understood. Broad goals of this project are to quantitatively understand the physical processes responsible for the transport of conservative and nonconservative solutes of biological and chemical importance. Through the use of time series...
Categories: Project; Tags: Solute Transport
Saline hydrologic systems provide a wide range of conditions within which to examine hydrochemically important mineral reaction (alteration or genesis) and to better define reactants and products controlling the chemical composition of many natural waters. The effects of complex reactions, in addition to simple solution and hydrolysis, are reflected in relatively gross chemical change and interaction with fine-grained sediment. The objective of this project is to use saline environments to determine mechanisms and relative importance of mineralogic processes which influence the solute composition of natural waters.
Managing water use in riverine and estuarine systems requires an understanding of the governing supply, circulation, mixing, and flushing processes. Qualitative and quantitative evaluation of the hydrodynamic and transport properties of such water bodies can be computed via mathematical/numerical simulation models. To accurately simulate both the temporal and spatial variations of the flow, which significantly define the transport processes, the simulation model must be capable of accounting for hydraulic and tide-induced fluctuations, water withdrawals, discharges, winds, nonuniform geometric configurations, and other manmade or natural factors. Objectives of this project are to investigate and develop various...
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The U. S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, developed a numerical ground-water-flow model, using MODFLOW-2000, to simulate ground-water flow in the Pohatcong Valley including the area within the Pohatcong Valley Ground Water Contamination Site. In 1978, the chlorinated solvents trichloroethene (TCE) and tetrachloroethene (PCE) were detected in thePohatcong Valley in production wells in Washington Borough and Washington Township, Warren County, New Jersey. Subsequent investigation revealed that many domestic wells in Washington and Franklin Townships also were contaminated, and in 1989 the Pohatcong Valley Ground Water Contamination Site was added to the U.S. Environmental...
Streams and their surrounding catchments exchange water and solutes on a range of physical scales. Exchange with the stream may extend into the interstitial areas of the streambed, the hyporheic zone, the riparian area, or the catchment's groundwater flow system. Even at the smaller scales, the exchanges significantly influence solute transport, nutrient cycling, and the aquatic ecosystem. Over the recent decades, considerable attention has been given to the solute transport aspects of stream–groundwater interactions. Stream–groundwater interactions are now being recognized as practical matters to be considered in environmental issues, such as stream restoration and fish habitat. In this chapter, the emphasis is...
    map background search result map search result map MODFLOW-2005, MODPATH, and MOC3D used for groundwater flow simulation, pathlines analysis, and solute transport in the crystalline-rock aquifer in the vicinity of the Savage Municipal Water-Supply Well Superfund Site, Milford, New Hampshire MODFLOW-2000 and MODPATH4 used to simulate groundwater flow and contaminant transport in the Pohatcong Valley, Warren County, New Jersey MODFLOW-2005, MODFLOW-NWT, and SEAWAT models used to simulate variable-density groundwater flow and contaminant transport at Naval Base Kitsap, Keyport, Washington MODFLOW-2005, MODFLOW-NWT, and SEAWAT models used to simulate variable-density groundwater flow and contaminant transport at Naval Base Kitsap, Keyport, Washington MODFLOW-2005, MODPATH, and MOC3D used for groundwater flow simulation, pathlines analysis, and solute transport in the crystalline-rock aquifer in the vicinity of the Savage Municipal Water-Supply Well Superfund Site, Milford, New Hampshire MODFLOW-2000 and MODPATH4 used to simulate groundwater flow and contaminant transport in the Pohatcong Valley, Warren County, New Jersey