Minneapolis, MN: U.S. Department of the Interior, Bureau of Mines, TN 390, 1991 Sep; :1-2
Objective: Analyze variably saturated flow in mining and other environmentally sensitive settings through the use of personal computer (PC) based software. The Problem: There is an increasing need for mining companies to quantify water contaminants and their migration in the unsaturated zone. New and innovative computer models are therefore necessary to more accurately assess the potential impact of mining activities on groundwater resources and the environment Applications for unsaturated flow modeling include (1) assessment of the impact of surface or Underground extraction mining on flow conditions; (2) assessment of various hydrologic designs for resource recovery, such as in heap leaching or in situ leach mining; (3) assessment of the transport of conservative nonreactive constituents in response to migration from spoil piles, or acid mine drainage; and (4) assessment of any combination of the above to facilitate expeditious permitting for mining operations. Since the mid 1970's there has been a proliferation of mathematical models and procedures for solving unsaturated flow problems; however, few of these approaches have been integrated into software for public use. Commercially available unsaturated flow software models typically are limited to a single application and have restricted approaches. For example, computer codes that solve the unsaturated flow problem based on an analytic expression are restricted to a simple geometric shape, homogeneous and isotropic materials, and provide only information regarding pressure and flow conditions in specified wells. The variably saturated computer codes that take advantage of the finite difference or finite element approach are often restricted to either steady state or transient solutions; utilize one specific moisture retention relationship and moisture-dependent permeability function; do not account for hysteresis; and arc used 'With specific hardware such as a mainframe or work station. This restricts their use because the they are hard to interface, and are often poorly documented, support dependent, and expensive. The mining community needs a flexible, more broadly based, variably saturated fluid flow simulator for the PC-platform to more accurately predict fluid movement in the mining environment. Approach: Bureau research developed TWOD, a comprehensive, two-dimensional, finite element, unsaturated fluid flow simulator. TWOD's unique flexibility in spatial and temporal parameters, material properties, and boundary conditions allows users to assess the potential impact of fluid flow in a variably saturated domain. The software code is provided with sample mining problems as an instructional tool for ease of use by technical and nontechnical personnel. This software provides an inexpensive and convenient, yet comprehensive tool for the hydrologist, engineer or researcher performing fluid flow studies in mining and environmental operations. How It Works: TWOD consists of nonproprietary code for analysis of flow under variably saturated conditions. It is written for IBM compatible PC's in FORTRAN 77 language. The program consists of several modules that can be used to solve the transient or steady state variably saturated flow problem in either a vertical or horizontal plane, heterogeneous, and anisotropic porous media using the Galerkin finite element approach. Simplex triangular elements arc used, with moisture retention characteristics described by specifying either the Brooks &. Corey, Brutsaert, or Van Genuchten power functions. Hysteresis is described using the Maulem model. Boundary conditions may include any combination of time varying seepage or pressure along solution domain boundaries and/or at internal node points; unit hydraulic gradient at the lower boundary; and a uniform source and/or sink. The program is documented in detail in the Bureau Information Circular (IC) 9296, entitled, 'TWOD: Two-Dimensional Finite-Element Analysis of Variably Saturated Flow." The IC describes the theory, finite element formulation, and code. User's instructions are provided for the implementation of TWOD in various hydrologic and mining problems. Several example problems are included.
Minneapolis, MN: U.S. Department of the Interior, Bureau of Mines, TN 390