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Significance and Use
Subsurface fluid flow modeling is a well established tool that can aid in studying and solving soil and groundwater problems.
Evaluation of more complex problems has been allowed as a result of advances in computing power and numerical analysis, yet confusion and misunderstanding over application of models still exists. As a result, some inappropriate use occurs and some problems which could be readily addressed are not.
The purposes of this guide are to introduce the basic concepts of subsurface fluids modeling and to show how models are described and categorized.
This guide should be used by practicing groundwater modelers, purchasers of modeling services, and by those wishing to understand modeling.
1.1 This guide covers an overview of subsurface fluid-flow (groundwater) modeling. The term subsurface fluid flow is used to reduce misunderstanding regarding groundwater, soil water, vapors including air in subsurface pores, and non-aqueous phase liquids. Increased understanding of fluid-flow phenomena is the combined result of field investigations and theoretical development of mathematical methods to describe the observations. The results are methods for modeling viscous fluids and air flow, in addition to water, that are practical and appropriate.
1.2 This guide includes many terms to assist the user in understanding the information presented here. A groundwater system (soils and water) may be represented by a physical, electrical, or mathematical model, as described in 6.4.3. This guide focuses on mathematical models. The term mathematical model is defined in 3.1.11; however, it will be most often used to refer to the subset of models requiring a computer.
1.3 This guide introduces topics for which other standards have been developed. The process of applying a groundwater flow model is described in Guide D5447. The process includes defining boundary conditions (Guide D5609), initial conditions (Guide D5610), performing a sensitivity analysis (Guide D5611), and documenting a flow model application (Guide D5718). Other steps include developing a conceptual model and calibrating the model. As part of calibration, simulations are compared to site-specific information (Guide D5490), such as water levels.
1.4 Model use and misuse, limitations, and sources of error in modeling are discussed in this standard. This guide does not endorse particular computer software or algorithms used in the modeling investigation. However, this guide does provide references to some particular codes that are representative of different types of models.
1.5 Typically, a computer model consists of two parts; computer code that is sometimes called the computer program or software, and a data set that constitutes the input parameters that make up the boundary and initial conditions, and medium and fluid properties. A standard has been developed to address evaluation of model codes (see Practice E978).
1.6 Standards have been prepared to describe specific aspects of modeling, such as simulating subsurface air flow using groundwater flow modeling codes (see Guide D5719) and modeling as part of the risk-based corrective action process applied at petroleum release sites (see Practice E1739).
1.7 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this guide may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project's many unique aspects. The word “Standard” in the title of this document means only that the document has been approved through the ASTM consensus process.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D4105 Test Method for (Analytical Procedure) for Determining Transmissivity and Storage Coefficient of Nonleaky Confined Aquifers by the Modified Theis Nonequilibrium Method
D5447 Guide for Application of a Ground-Water Flow Model to a Site-Specific Problem
D5490 Guide for Comparing Ground-Water Flow Model Simulations to Site-Specific Information
D5609 Guide for Defining Boundary Conditions in Ground-Water Flow Modeling
D5610 Guide for Defining Initial Conditions in Ground-Water Flow Modeling
D5611 Guide for Conducting a Sensitivity Analysis for a Ground-Water Flow Model Application
D5718 Guide for Documenting a Ground-Water Flow Model Application
D5719 Guide for Simulation of Subsurface Airflow Using Ground-Water Flow Modeling Codes
E943 Terminology Relating to Biological Effects and Environmental Fate
E978 Practice for Evaluating Mathematical Models for the Environmental Fate of Chemicals
E1739 Guide for Risk-Based Corrective Action Applied at Petroleum Release Sites
ICS Number Code 13.060.10 (Water of natural resources)