Geologic, hydrologic, and geochemical interpretations of mineral deposits as analogs for understanding transport of environmental contaminants     

Richard B. Wanty  Byron R. Berger 《Journal of Geochemical Exploration》2006,88(1-3):162

Base- and precious-metal mineral deposits comprise anomalous concentrations of metals and associated elements, which may be useful subjects for study as analogs for migration of environmental contaminants. In the geologic past, hydrothermal mineral deposits formed at the intersection of favorable geologic, hydrologic and geochemical gradients. In the present, weathering of these sulfide-rich deposits occurs as a result of the interplay between rates of oxygen supply versus rates of ground or surface-water flow. Transport and spatial dispersion of elements from a mineral deposit occurs as a function of competing rates of water flow versus rates of attenuation mechanisms such as adsorption, dilution, or (co)precipitation. In this paper we present several case studies from mineralized and altered sedimentary and crystalline aquifers in the western United States to illustrate the geologic control of ground-water flow and solute transport, and to demonstrate how this combined approach leads to a more complete understanding of the systems under study as well as facilitating some capability to predict major flow directions in aquifers.  相似文献   

Magnetic survey of topsoils in Windsor–Essex County, Canada     

Ruiping Shi  Maria T. Cioppa   《Journal of Applied Geophysics》2006,60(3-4):201-212

Windsor–Essex County is a major cross-border truck and transportation route, with significant localized industrialization as well as rural and farming areas. Magnetic property measurements (in-field and laboratory susceptibility, frequency-dependent susceptibility, hysteresis properties, thermomagnetic and thermosusceptibility curves, anhysteretic and isothermal magnetizations) were made in order to determine the potential for using such variables to distinguish between natural and anthropogenic pollutants. In-field magnetic susceptibility measured on 324 soil sampling sites on a 0.5–2 km grid spacing through Windsor–Essex County ranged from 3.7 × 10^− 6 to 305.2 × 10^− 6 SI (average 36.2 ± 35.8 × 10^− 6 SI), and showed that high magnetic susceptibility values were obtained on soil sampling sites in and around the cities/towns of Windsor, Harrow, Olinda and Oakland and near the beaches of Point Pelee National Park (PPNP) and Deerbrook, whereas lower susceptibility values were observed in near the towns of Lakeshore and Essex. On this grid spacing, Highway 401 (the major truck route) did not show anomalous susceptibility values; however, closer (1–3 m) sampling on other roads did show anomalously high values, suggesting that the coarser grid spacing may have missed anomalies. Laboratory measurements indicated that the dominant magnetic mineral in the Windsor–Essex County soils is magnetite; however, the grain size is variable. Pseudo-single domain (PSD)–multidomain (MD) magnetite is generally found on beaches and in PPNP, whereas single domain (SD)–PSD magnetite has been found near the City of Windsor and other towns. While certain correlations exist between some anthropogenic activities and the measured magnetic susceptibility and magnetic property values, no overall correlation can be made. A variety of geologic and anthropogenic factors must be considered when interpreting the origin of the magnetic signal in a particular area.  相似文献   

Scaling Laws and Experimental Modelling of Contaminant Transport Mechanism through Soils in a Geotechnical Centrifuge     

P. R. Kumar 《Geotechnical and Geological Engineering》2007,25(5):581-590

This paper presents the results of a research program conducted on the geotechnical centrifuge to investigate contaminant transport mechanism through the soil mass. The mechanism that governs contaminant transport through soil mass is discussed, the principles of geotechnical centrifuge modelling are outlined, and relevant scaling laws that govern the relationship between a centrifuge model and the prototype, with respect to the problem of contaminant transport, are presented. Modelling of models has been established to validate the experimental results. It has been concluded that the geotechnical centrifuge can be used as an experimental tool to simulate field scale problems.  相似文献   

Contaminant transport modeling in marine clays   总被引：1，自引：0，他引：1  

G. Rajasekaran  K. Murali  S. Nagan  V. Amoudhavally  V. Santhaswaruban   《Ocean Engineering》2005,32(2):117-194

The need to develop various offshore containment systems encourages the contaminant transport study in marine clays. In the present investigation, an attempt has been made to examine six cases of contaminant transport in marine clays. Adequate literature background on the chemical diffusion of soils, and the earlier reported modeling techniques relevant to the present work have been highlighted. These methods enable a rapid examination of the impact of contaminant physical properties on the environment over a period of time. The numerical results of this study help to understand the chemicals transport phenomena in the marine environment especially at sea bed.  相似文献   

Numerical modeling of three-dimensional contaminant migration from dissolution of multicomponent NAPL pools in saturated porous media     

K. Y. Lee  C. V. Chrysikopoulos 《Environmental Geology》1995,26(3):157-165

A three-dimensional model for contaminant transport resulting from the dissolution of multicomponent nonaqueous phase liquid (NAPL) pools in three-dimensional saturated subsurface formations is developed. The solution is obtained numerically by a finite-difference scheme, and it is suitable for homogeneous porous media with unidirectional interstitial velocity. Each dissolved component may undergo first-order decay and may sorb under local equilibrium conditions. It is also assumed that the dissolution process is mass transfer limited. The nonaqueous phase activity coefficients of the NAPL pool components are evaluated at each time step. The model behavior is illustrated through a synthetic example with a NAPL pool consisting of a mixture of TCA (1,1,2-trichloroethane) and TCE (trichloroethylene). The numerical solution presented in this work is in good agreement with a recently developed analytical solution for the special case of a single component NAPL pool. The results indicate the importance of accounting for the necessary changes in the organic phase activity which significantly affects the equilibrium aqueous solubility.Notation C liquid phase solute concentration (solute mass/liquid volume) (M L^–3) - C _s single component aqueous saturation concentration (solubility) (M L^–3) - C ^w equilibrium aqueous solubility (M L^–3) - D molecular diffusion coefficient (L² t ^–1) - D _e effective molecular diffusion coefficient (L² t ^–1) - D _x longitudinal hydrodynamic dispersion coefficient (L² t ^–1) - D _y lateral hydrodynamic dispersion coefficient (L² t ^–1) - D _z hydrodynamic dispersion coefficient in the vertical direction (L² t ^–1) - I() integer mode arithmetic operator - k local mass transfer coefficient (Lt ^–1) - k ^* average mass transfer coefficient (Lt ^–1) - L length - l _x ,l _y pool dimensions inx andy directions (L) - ll _x ,l _y x andy Cartesian coordinates of the pool origin (L) - M number of moles remaining in a pool (moles) - M initial number of moles (moles) - n finite-difference scheme time level - R retardation factor (dimensionless) - t time (t) - U _x average interstitial velocity (Lt ^–1) - x, y, z spatial Cartesian coordinates (L) - X dimensionless mole fraction - dimensionless activity coefficient - _w viscosity of water (=0.8904 cp at 25°C) - decay coefficient (t ^–1) - ^* tortuosity ( 1) - i,j, k finite-difference scheme grid indicators - p component number indicator - P total number of components - s pure single component - o nonaqueous phase - w aqueous phase  相似文献   

Fate of persistent organic pollutants in the water column: does turbulent mixing matter?     

Jurado E  Zaldívar JM  Marinov D  Dachs J 《Marine pollution bulletin》2007,54(4):441-451

The effect of vertical turbulent mixing on the dynamics of persistent organic pollutants has long been overlooked and its role is still hardly understood. Here we present the first comprehensive analysis of the role of turbulent diffusion on the distribution of those contaminants and its interplay with sinking fluxes. To this end, a 1D dynamic coupled hydrodynamic-contaminant model has been developed and applied to a Mediterranean continental shelf environment. The hydrodynamic sub-model is adapted from COHERENS, the contaminant sub-model is an improvement from the BIODEP model and considers the contaminant in 3 phases: dissolved-colloidal-particulate. The simulation highlights the role of turbulence in determining the POP distribution and variability in the water column. In short, turbulent flux of contaminants strengthens the upward diffusion of sediment entrained contaminants and determines the extent to which inputs from the atmosphere mix into the water column. It acts in parallel with degradation and sinking fluxes, the combined effect yielding a surface enriched - depth depleted - benthic layer enriched region distribution, which presents similarities to reported experimental measures.  相似文献   

A possible approach for Tier 2 risk assessments of polluted sites: Framework,computer spreadsheet and application     

《Computers and Geotechnics》2014

Owing to the increasing attention placed on problems concerning site pollution that environmental geotechnics deals with, an implementation of Tier2 risk assessment (forward and backward mode) is proposed and developed in a computer spreadsheet. Consistently with a Tier 2 approach, contaminant migration is described by analytical solutions of transport models using site-specific parameters. The calculations are implemented with Microsoft Excel® while the user interfaces, which manage the various worksheets, were built with Visual Basic®. The spreadsheet was validated by comparing it with other available software that implement the same model for a given migration pathway. In the present version, the computer tool is consistent with Italian guidelines for Tiers 2 risk assessment. However, the tool can be easily adapted to comply with different regulations and recommendations. Some illustrative examples of applications are given in the paper: a case study of risk assessment for contaminated site is illustrated and a sensitivity analyses of transport factors to site-specific parameters is presented.  相似文献   

The origin of fluoride in groundwater supply to Hermosillo City, Sonora, México   总被引：1，自引：0，他引：1  

L. Valenzuela-Vásquez  J. Ramírez-Hernández  J. Reyes-López  A. Sol-Uribe  O. Lázaro-Mancilla 《Environmental Geology》2006,51(1):17-27

Anomalous high fluoride concentration up to 7.59 mg/dm³ is found in groundwater from “La Victoria” area. This water is used to supply drinking water to Hermosillo City, Sonora. Geochemistry of groundwater, relationship between physicochemical parameters, hydrogeology and geologic setting were correlated to define the origin and the geochemical mechanisms of groundwater fluorine enrichment. High fluoride concentration is associated with high bicarbonates, pH and temperature, and it decreases toward the west and south of the area. Fluoride is in negative correlation to calcium concentration. Sodium sulphate facies of regional deep water flow are related to high fluoride concentration. High electric resistivity rocks associated with granites from the Sierra Bachoco basement might be the deep source of fluoride. Outcropping of Sierra Bachoco in the west causes upward regional flow. Groundwater of longer residence time can be pumped there. The anomalous area is restricted to “La Victoria” because calcareous paleozoic rocks outcrop to the south.  相似文献   

Field scale impacts of spatially correlated relative permeability in heterogeneous multiphase systems     

G.P. Grant  J.I. Gerhard  B.H. Kueper 《Advances in water resources》2007

Two-dimensional numerical simulations of two-phase (DNAPL-water) flow in spatially correlated random fields demonstrate the influence of nonwetting phase (NWP) relative permeability–saturation (k_r,N–S_W) relationships correlated to porous media intrinsic permeability (k). Both the volume of porous media invaded by the NWP and the length of time during which the NWP is migrating are under predicted if k_r,N–k correlation is not accounted for in the model formulation. Not accounting for the k_r,N–k correlation resulted in under predicting the volume of porous media invaded by up to approximately 10%, which is likely not significant for many practical applications. However, not accounting for the k_r,N–k correlation resulted in under predicting field scale migration times by up to a factor of 4, which is likely significant in that the migration times are on the order of years to several decades for the DNAPL (1,2-DCE) considered in this study. The under prediction of migration times was greater for lower permeability aquifers.  相似文献   

Groundwater contaminant transport including adsorption and first order decay     

Jaco J. A. van Kooten 《Stochastic Environmental Research and Risk Assessment (SERRA)》1994,8(3):185-205

This study deals with the transport of a contaminant in groundwater. The contaminant is subject to first order decay or linear adsorption. Its displacement can be modeled by a random walk process in which particles are killed at exponentially distributed times. Dirichlet problems are derived for the rate and mean time at which contaminated particles reach a particular part of the boundary of a certain domain. These Dirichlet problems are solved asymptotically for two types of 2D-flow patterns: flow parallel to the boundary of a domain and arbitrary flow towards a well in an aquifer.  相似文献