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Modeling of Contaminant Movement Near Pumping Wells: Saturated‐Unsaturated Flow with Particle Tracking
Author(s) -
Akindunni Festus F.,
Gillham Robert W.,
Conant Brewster,
Franz Thomas
Publication year - 1995
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/j.1745-6584.1995.tb00281.x
Subject(s) - aquifer , plume , hydraulics , flow (mathematics) , hydraulic head , particle (ecology) , mechanics , soil science , groundwater , geology , effluent , environmental science , geotechnical engineering , environmental engineering , engineering , thermodynamics , aerospace engineering , oceanography , physics
A transient axisymmetric saturated‐unsaturated numerical flow model was coupled with a particle tracking model to investigate the movement of contaminants when a shallow unconfined aquifer is pumped at a constant rate. The particle tracking model keeps track of locations and masses of solutes in the aquifer, and the time of capture by the well. At the end of each time‐step the flow model solves the Richard's equation for the hydraulic head distribution from which elemental velocities are calculated. Solutes are then displaced for a period equivalent to the time‐step using both the magnitude and direction of the elemental velocities. Numerical experiments were performed to investigate effluent concentrations in wells with screens of different length and in different positions relative to zones of stratified contamination. At early times of pumping the effluent concentrations were similar to the concentrations adjacent to the well screen, but at late times, the concentrations approached the vertically averaged concentration in the aquifer. Time to attain the vertically averaged concentration was determined by the well geometry, initial location of the contaminant plume in relation to the well screen, and hydraulic properties of the aquifer. The results are consistent with the hydraulics of flow to a pumping well and of particular importance, they demonstrate that short‐term pump tests could give erroneous design concentrations for pump‐and‐treat systems. The model provides a means of quantifying arrival times and mixing ratios. It could therefore provide a useful means of designing production wells in aquifers with stratified contamination and more efficient recovery systems for aquifer remediation.