Groundwater Modeling and Aquifer Analysis
Groundwater Flow Modeling
Groundwater flow modeling is generally used to determine the quantity of groundwater available for use or direction and distance of dissolved contaminant migration. It is also used to define the limits of a capture zone for a recovery well (or well field), or for delineating a wellhead protection area (or recharge area) for a water supply well. We have usually used analytical means to model these situations using the Theim (1906) equilibrium constant discharge formula to estimate distance-drawdown relationships. In order to estimate the long-term yield and drawdown of a recovery or water supply well (or well field) we usually use the Cooper-Jacob (1946) modified non-equilibrium constant discharge method for making projections. Because many of the situations encountered in New England involve unconfined (water-table) aquifers, we have used Prickett's type curve solution (1965) for making allowances for unconfined conditions and delayed aquifer drainage.
Analytical modeling can be very time-intensive and, therefore expensive. We have used the U.S. Geological Survey Two-Dimensional Solute Transport (MOC), Version 3.0 (Konikow and Bredehoeft, 1989) to evaluate the transport of certain volatile organic compounds on a number of sites. It can be obtained from the International Ground Water Modeling Center (IGWMC). This model has been used to assess the distribution of hydrocarbon concentrations around a active contaminant source to evaluate various remedial scenarios including source control, attenuation resulting from microbial decay, effect of groundwater recovery wells, and recharge sources. The illustration above shows a simple grid layout for solute transport modeling. Such models can be used to predict the time required for remediation or for natural attenuation by existing or enhanced processes in the subsurface. A number of more recently developed models are available.
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