ASTM D6025-96(2008)

Groundwater modeling has become an important methodology in support of the planning and decision-making processes involved in groundwater management. Groundwater models provide an analytical framework for obtaining an understanding of the mechanisms and controls of groundwater systems and the processes that influence their quality, especially those caused by human intervention in such systems. Increasingly, models are an integral part of water resources assessment, protection, and restoration studies and provide essential and cost-effective support for planning and screening of alternative policies, regulations, and engineering designs affecting groundwater. It is therefore important that before groundwater modeling codes are used as planning and decision-making tools, their credentials are established and their suitability determined through systematic evaluation of their correctness, performance characteristics, and applicability. This becomes even more important because of the increasing complexity of the hydrologic systems for which new modeling codes are being developed.

Quality assurance in groundwater modeling provides the mechanisms and framework to ensure that the analytic tools used in preparing decisions are based on the best available techniques and methods. A well-executed quality assurance program in groundwater modeling provides the information necessary to evaluate the reliability of the performed analysis and the level to which the resulting advice may be incorporated in decision-making regarding the management of groundwater resources.

This guide is intended to encourage consistency and completeness in the development and evaluation of existing and new groundwater modeling codes by describing appropriate code development and quality assurance procedures and techniques.

In the past, some groundwater modeling codes have been developed that have turned out to be quite useful without having been subject to all of the procedures described in this guide. Nonetheless, the procedures described in this guide will give greater assurances that a code does what its developers intended it to do and that a rational basis is available to judge code adequacy and limitations.

1.1 This guide covers a systematic approach to the development, testing, evaluation, and documentation of groundwater modeling codes. The procedures presented constitute the quality assurance framework for a groundwater modeling code. They include code review, testing, and evaluation using quantitative and qualitative measures. This guide applies to both the initial development and the subsequent maintenance and updating of groundwater modeling codes.

1.2 When the development of a groundwater modeling code is initiated, procedures are formulated to ensure that the final product conforms with the design objectives and specifications and that it correctly performs the incorporated functions. These procedures cover the formulation and evaluation of the code's theoretical foundation and code design criteria, the application of coding standards and practices, and the establishment of the code's credentials through review and systematic testing of its functional design and through evaluation of its performance characteristics.

1.3 The code's functionality needs to be defined in sufficient detail for potential users to assess the code's utility as well as to enable the code developers to design a meaningful code testing strategy. Comprehensive testing of a code's functionality and performance is accomplished through a variety of test methods. Determining the importance of the tested functions and the ratio of tested versus non-tested functions provides an indication of the completeness of the testing.

1.4 Groundwater modeling codes are subject to the software life cycle concept that consists of a design phase, a development phase, and an operational phase. During the operational phase the software is maintained, evaluated regularly, and changed as additional requirements are identified. Therefore, quality assurance procedures should not only be established for software design, programming, testing, and use, but also for code maintenance and updating.

1.5 Quality assurance in the development of groundwater modeling codes cannot guarantee acceptable quality of the code or a groundwater modeling study in which the code has been used. However, adequate quality assurance can provide safeguards against the use in a modeling study of faulty codes or incorrect theoretical considerations and assumptions. Furthermore, there is no way to guarantee that modeling-based advice is entirely correct, nor that the groundwater model used in the preparation of the advice (or any scientific model or theory, for that matter) can ever be proven to be entirely correct. Rather, a model can only be invalidated by disagreement of its predictions with independently derived observations of the studied system because of incorrect application of the selected code, the selection of an inappropriate code, the use of an inadequately tested code, or invalidity of or errors in the underlying theoretical framework.

1.6 This guide is one of a series of guides on groundwater modeling codes and their applications, such as Guides D5447, D5490, D5611, D5609, D5610, and D5718. Other standards have been prepared on environmental modeling, such as Practice E978.

1.7 Complete adherence to this guide may not always be feasible. If this guide is not integrally followed, the elements of noncompliance should be clearly identified and the reasons for the partial compliance should be given. For example, partial compliance might result from inadequacy of existing field techniques for measuring relevant model parameters, specifically in complex systems.

1.8 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.