Significance and Use
An essential requirement of hydrogeologists in evaluating the hydraulic properties of a segment of earth materials is to define and map hydrogeologic units, aquifers, and confining units, which are determined on the basis of relative permeability. Discussion of the hydrogeologic units is facilitated by individual designations (see Practices D5409, D5434, and D5474).
Determinations of hydrogeologic units are based on indirect methods, knowledge of the geologic materials (geologic mapping, surface geophysical surveys, borehole geophysical logs, drill-cuttings and core descriptions, and so forth), and hydraulic testing (aquifer tests, laboratory permeability tests on core samples, and so forth).
The physical properties of all rock units will change if traced laterally and vertically. The rock units are broken by unconformities and faults, which may or may not affect the flow of groundwater. The process of designating and naming aquifers and confining units, therefore, is a somewhat subjective undertaking, and, if not thoroughly documented, can lead to confusion.
Guidelines for naming aquifers can help avoid some of the confusion and problems associated with hydrogeologic studies if the guidelines are straight forward to apply, flexible, and applicable to studies of a variety of scales from site-specific to regional.
The guidelines that follow include discussions of the terminology of aquifer nomenclature, the definition of the hydrogeologic framework, the suggested procedures for naming aquifers, and examples of naming aquifers.
These guidelines have resulted from numerous discussions on the subject of aquifer nomenclature among hydrogeologists. Although unanimous agreement on these proposals has not been achieved, the exercises provided an extremely useful purpose in creating additional thought and discussion.
Scope
1.1 This guide covers a series of options but does not specify a course of action. It should not be used as the sole criterion or basis of comparison and does not replace or relieve professional judgement.
1.2 This guide contains instructions and suggestions for authors of groundwater (hydrogeologic) reports in assigning appropriately derived and formatted aquifer nomenclature. Discussed are the water-bearing units that may require name identification, which are, ranked from largest to smallest, aquifer system, aquifer, and zone. Guidance is given on choosing the source of aquifer names, those are from lithologic terms, rock-stratigraphic units, and geographic names.
1.3 Included are examples of comparison charts and tables that can be used to define the hydrogeologic framework. Illustrations of eleven different hypothetical aquifer settings are presented to demonstrate the naming process.
1.4 Categories of items not suggested as a source of aquifer names are reviewed because, although they should be avoided, they occur in published documents. These categories are the following: time-stratigraphic names, relative position, alphanumeric designations, depositional environment, depth of occurrence, acronyms, and hydrologic conditions.
1.5 Confining units are discussed with the suggestion that these units should not be named unless doing so clearly promotes an understanding of a particular aquifer system. Suggested sources of names for confining units correspond to those for aquifer names, which are lithologic terms, rock-stratigraphic units, and geographic names.
1.6 It is suggested that in reports that involve hydrogeology, the author should consider first not naming aquifers (see 6.2).
1.7 Format and expression styles are assessed along with the general cautions related to name selection of aquifers and confining units.
1.8 This guide is a modification of a previously published report (1).
1.9 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.