Ground-water modeling has become an important methodology in support of the planning and decision-making processes involved in ground-water management. Ground-water models provide an analytical framework for obtaining an understanding of the mechanisms and controls of ground-water 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 ground-water (1).⁴

Successful ground-water management requires that decisions be based on the use of technically and scientifically sound methods for data collection, information processing, and interpretation, and that these methods are properly integrated. As computer codes are essential building blocks of modeling-based management, it is crucial that before such codes are used as planning and decision-making tools, their performance characteristics are established and their theoretical foundation, capabilities, and use documented.

Good code documentation ensures scientific rigor and implementational quality in the development of a code (2). Complete and well-written documentation shortens the learning curve for new users, provides answers to questions from project managers, and supports efficient code selection. Well-structured and indexed documentation provides rapid answers for initiated users. This guide is intended to encourage comprehensive and consistent documentation of a ground-water modeling code.

Earlier surveys of computer models and assessment of specific models indicate that the documents that are supposed to describe and explain these models and their use are lacking in detail, inconsistent in their contents, incomplete with respect to user instructions, inefficient with respect to indexing and structure, and often difficult to obtain (3). This still applies to the documentation of many of the ground-water modeling programs recently released or frequently used (4).

1.1 This guide covers suggested components of the documentation of a ground-water modeling code. Documentation of a ground-water modeling code consists of textual and graphical information recorded during its design, development, and maintenance regarding its capabilities, development history, theoretical foundation, operation, and verification. It is the principal instrument for those involved in its development and use, such as code development and maintenance staff, network managers, code users, and project managers, to communicate regarding all aspects of the software.

1.2 This guide presents the major steps in preparing the documentation of a ground-water modeling code. It discusses the various documentation audiences and addresses the role of printed documentation versus documentation in electronic form.

1.3 This guide is one of a series of guides on ground-water modeling codes and their applications, such as Guides D 5447, D 5490, D 5609, D 5610, D 5611, and D 5718.

1.4 This guide is not intended to be all inclusive. If offers a series of options and considerations, but does not specify a course of action. Documenting certain codes may require supplemental information or replacement of documentation sections by more appropriate elements. This guide should not be used as a sole criterion or basis of comparison, and does not replace or relieve professional judgement in preparing or evaluating documentation of ground-water modeling software.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to its use.

1.6 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This guide 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 guide 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 guide 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.