ASTM D6106-97e1

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e1
Designation: D 6106 – 97
Standard Guide for
Establishing the Nomenclature of Ground-Water Aquifers
This standard is issued under the fixed designation D 6106; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Paragraph 1.9 was added editorially in October 1998.
1. Scope 1.9 This guide offers an organized collection of information
or a series of options and does not recommend a specific
1.1 This guide offers a series of options but does not specify
course of action. This document cannot replace education or
a course of action. It should not be used as the sole criterion or
experience and should be used in conjunction with professional
basis of comparison and does not replace or relieve profes-
judgment. Not all aspects of this guide may be applicable in all
sional judgement.
circumstances. This ASTM standard is not intended to repre-
1.2 This guide contains instructions and suggestions for
sent or replace the standard of care by which the adequacy of
authors of ground-water (hydrogeologic) reports in assigning
a given professional service must be judged, nor should this
appropriately derived and formatted aquifer nomenclature.
document be applied without consideration of a project’s many
Discussed are the water-bearing units that may require name
unique aspects. The word “Standard” in the title of this
identification, which are, ranked from largest to smallest,
document means only that the document has been approved
aquifer system, aquifer, and zone. Guidance is given on
through the ASTM consensus process.
choosing the source of aquifer names, those are from lithologic
terms, rock-stratigraphic units, and geographic names.
2. Referenced Documents
1.3 Included are examples of comparison charts and tables
2.1 ASTM Standards:
that can be used to define the hydrogeologic framework.
D 653 Terminology Relating to Soil, Rock, and Contained
Illustrations of 11 different hypothetical aquifer settings are
Fluids
presented to demonstrate the naming process.
D 1129 Terminology Relating to Water
1.4 Categories of items not suggested as a source of aquifer
D 5409 Guide for the Set of Data Elements to Describe a
names are reviewed because, although they should be avoided,
Ground-Water Site; Part Two—Physical Descriptors
they occur in published documents. These categories are the
D 5434 Guide for Field Logging of Subsurface Explora-
following: time-stratigraphic names, relative position, alpha-
tions of Soil and Rock
numeric designations, depositional environment, depth of oc-
D 5474 Guide for Selection of Data Elements for Ground-
currence, acronyms, and hydrologic conditions.
Water Investigations
1.5 Confining units are discussed with the suggestion that
these units should not be named unless doing so clearly
3. Terminology
promotes an understanding of a particular aquifer system.
3.1 Definitions: Except as discussed as follows, all defini-
Suggested sources of names for confining units correspond to
tions are in accordance with Terminologies D 653 and D 1129.
those for aquifer names, which are lithologic terms, rock-
The following terms are examined in detail in order to clarify
stratigraphic units, and geographic names.
the method of assigning nomenclature to the aquifers and
1.6 It is suggested that in reports that involve hydrogeology,
associated units:
the author should consider first not naming aquifers (see 6.2).
3.2 Introduction—Aquifers do not lend themselves to brief,
1.7 Format and expression styles are assessed along with the
neat, and simple definitions; therefore, a flexible hierarchy of
general cautions related to name selection of aquifers and
terms is used in these guidelines. The terms that are used for
confining units.
water-yielding rocks from largest to smallest are: aquifer
1.8 This guide is a modification of a previously published
2 system (2), aquifer (3), and zone (4). Confining units (3) are
report (1).
discussed because of the stratigraphic relationship with the
water-bearing units.
1 3.2.1 Parallelism between the hierarchy of terms for water-
This guide is under the jurisdiction of ASTM Committee D-18 on Soil and
Rock and is under the direct responsibility of Subcommittee D18.21 on Ground yielding rocks and rock-stratigraphic terms, namely, aquifer
Water and Vadose Zone Investigations.
Current edition approved Aug. 10, 1997. Published October 1997.
2 3
The boldface numbers in parentheses refer to the list of references at the end of Annual Book of ASTM Standards, Vol 04.08.
this standard. Annual Book of ASTM Standards, Vol 11.01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D6106–97
system (group), aquifer (formation), and zone (member), the Glossary of Geology (7) as“ a body of rock that is
should be avoided because water-yielding rocks can cross the sufficiently permeable to conduct ground water and to yield
boundaries of geologic units or constitute only part of a economically significant quantities of water to wells and
geologic unit. The scale of the study also may determine the springs.”
best usage. For example, at the local scale an aquifer system
3.3.1.5 Regardless of the fine points in any definition,
could be defined totally within a single formation and at the
delineating permeable rocks should be the major goal of
regional scale a formation or group could be totally within and
hydrogeologists in mapping and describing an aquifer. By the
only a part of a single aquifer or an aquifer system. Again, the
same token, detailed knowledge of the stratigraphic units and
guidelines for aquifer nomenclature must remain flexible to
post-depositional processes, such as solution, cementation,
meet a variety of hydrogeologic scales and settings.
folding, and faulting, are essential in determining where the
3.2.2 A discussion of the terms aquifer, aquifer system,
boundaries of the aquifer are located and in understanding the
zone, and confining unit is provided here to give authors a
flow system. In addition, hydraulic properties (hydraulic con-
common reference base. Although complete agreement on
ductivity and storage coefficient) throughout the aquifer usu-
these definitions has not been achieved, the terms are adequate
ally are not determined directly but are estimated by indirect
to transfer knowledge from authors to readers of reports. It is
means, such as aquifer tests, analyses of drill cuttings and
not the purpose of these guidelines to formally redefine the
cores, borehole geophysical logging, and surface geophysical
terms or to define new terms to take their place.
surveys.
3.3 Definitions of Terms Specific to This Standard:
3.3.1.6 In many situations, hydrologic estimates and ex-
3.3.1 aquifer, n—This term probably has more shades of
trapolations can be made on the basis of rock type alone
meaning than any other term in hydrology (5), see Terminology
without any determination of hydrologic properties. For ex-
D 653. It can mean different things to different people and
ample, a wide-spread, thick clay separating two sand units
different things to the same person at different times.
tentatively could be designated as a confining unit on the basis
3.3.1.1 Discussion—Meinzer (5) defined an aquifer as “a
of geologists’ logs and borehole geophysical logs alone with-
rock formation or stratum that will yield water in sufficient
out any hydrologic data.
quantity to be of consequence as a source of supply is called an
3.3.2 aquifer system, n—Poland and others (2) define an
aquifer, or simply a water-bearing formation, water-bearing
aquifer system as “a heterogeneous body of intercalated
stratum,or water-bearer. It is water-bearing, not in the sense of
permeable and poorly permeable material that functions re-
holding water, but in the sense of carrying or conveying water.”
gionally as a water-yielding hydraulic unit; it comprises two or
3.3.1.2 Lohman and others (3) refined Meinzer’s definition
more permeable beds (aquifers) separated at least locally by
of an aquifer as “a formation, group of formations, or part of a
aquitards (confining units) that impede ground-water move-
formation that contains sufficient saturated permeable material
ment but do not greatly affect the regional hydraulic continuity
to yield significant quantities of water to wells and springs.”
of the system.”
3.3.1.3 Both of these definitions imply that the aquifer is
3.3.2.1 Discussion—The definition could be more general if
bounded by or is included within the formation(s) (or stratum),
the term aquifers were used in place of permeable beds. Bed
but the concept of the aquifer extending across formational
implies a single stratigraphic unit, whereas, the individual
boundaries is not indicated explicitly. In many local studies
aquifer could include or cross many beds.
covering a few tens to a few hundred square miles, the aquifer
3.3.2.2 Confining unit should be used instead of aquitard
and the formation may be the same. In these studies, few
because the definition of confining unit is broad enough to
problems may exist in defining the aquifer. However, since the
include varying degrees of leakiness.
late 1970s, studies of regional aquifers that may cover hun-
3.3.2.3 The hierarchy of aquifer and aquifer-system names
dreds of thousands of square miles have been made under the
may not always be consistent in practice. Because of differ-
Regional Aquifer-System Analysis (RASA) Program. Results
ences in scales of investigations, individual aquifers may be
from several of the RASA studies have shown that regional
combined into a single aquifer system, which may be only a
aquifers may include numerous formations and rock types and
part of another aquifer system over a larger area. Authors have
that the aquifers cut across formational and lithologic bound-
the responsibility to explain these relationships clearly with
aries so that no one formation is completely representative of
comparison charts and descriptions in the text.
the aquifer.
3.3.3 Confining unit, n—confining bed was defined by
3.3.1.4 In studies of regional scope, the shape and the
Lohman and others (3) as “ . . . a term which will now supplant
boundaries of the permeable rocks that form the aquifer have
the terms aquiclude, aquitard, and aquifuge in reports of the
greater importance to understanding the flow system than do
U.S. Geological Survey and is defined as a body of imperme-
the individual formational boundaries. A definition that places
able material stratigraphically adjacent to one or more aquifers.
less emphasis on the formal term formation (6) and more on
In nature, however, its hydraulic conductivity may range from
permeable rocks has merit. For example, aquifer is defined in
nearly zero to some value distinctly lower than that of the
aquifer. Its conductivity relative to that of the aquifer it
confines should be specified or indicated by a suitable modifier,
RASA, Regional Aquifer-System Analysis Program, a systematic study of a
such as slightly permeable or moderately permeable.”
number of regional ground-water systems that represent a significant part of the
3.3.3.1 Discussion—Although the Lohman and others (3)
water supply of the United States. These studies are managed by the Water
Resources Division of the U.S. Geological Survey. definition of confining bed is descriptive and should be used,
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D6106–97
the term confining unit is more general and appropriate than 3.4.2 Coining new terms for aquifer and aquifer system that
confining bed especially where more than a single bed makes either are synonyms or defined with slightly different meaning
up the confining unit. is not an advancement. It only creates confusion especially
among people that are not hydrogeologists. Use of the term
3.3.3.2 The term bed is not correct usage for a thick
aquiformation also infers an equivalence between aquifer and
sequence of stratigraphic units that could be of member or
formation that is not always correct.
formation rank. Bed is particularly inappropriate when used for
intrusive igneous rocks beneath an aquifer. The term bed has a
4. Significance and Use
formal definition in the 1983 North American Stratigraphic
4.1 An essential requirement of hydrogeologists in evaluat-
Code (6) and should not be used in definitions of aquifer
ing the hydraulic properties of a segment of earth materials is
nomenclature.
to define and map hydrogeologic units, aquifers and confining
3.3.3.3 Many confining units are leaky and in some areas,
units, which are determined on the basis of relative permeabil-
under natural conditions, may contribute significant amounts of
ity. Discussion of the hydrogeologic units is facilitated by
water to the aquifers they confine, and even larger quantities of
individual designations (see Practices D 5409, D 5434, and
water as heads are lowered in the aquifer by pumping. In areas
D 5474).
where withdrawals from aquifers have caused large declines in
4.2 Determinations of hydrogeologic units are based on
head, considerable amounts of water may be derived from
indirect methods, knowledge of the geologic materials (geo-
water stored in the confining unit.
logic mapping, surface geophysical surveys, borehole geo-
3.3.3.4 Poland and others (2) retained the terms aquiclude
physical logs, drill-cuttings and core descriptions, and so
and aquitard in their definitions related to studies of the
forth), and hydraulic testing (aquifer tests, laboratory perme-
mechanics of aquifer systems and land subsidence due to fluid
ability tests on core samples, and so forth).
withdrawal. An aquiclude was defined as a body of saturated
4.3 The physical properties of all rock units will change if
but relatively impermeable material that is characterized by
traced laterally and vertically. The rock units are broken by
very low values of leakance (the ratio of vertical hydraulic
unconformities and faults, which may or may not affect the
conductivity to thickness) and transmits negligible interaquifer
flow of ground-water. The process of designating and naming
flow.
aquifers and confining units, therefore, is a somewhat subjec-
3.3.3.5 An aquitard is a saturated poorly permeable bed that
tive undertaking, and, if not thoroughly documented, can lead
has values of leakance that range from relatively low to
to confusion.
relatively high. Where an aquitard is sufficiently thick, it may
4.4 Guidelines for naming aquifers can help avoid some of
form an important ground-water storage unit.
the confusion and problems associated wi
...