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Development of principal aquifer frameworks
NAWQA study units in the principal aquifers selected for primary focus of
Cycle II ground-water quality studies are working together to develop
principal-aquifer frameworks that can be used to assess similarities and
differences in water quality within and among the principal aquifers.
Development of the framework for each principal aquifer includes consideration
of 3 primary characteristics that, based on current knowledge, might help account
for differences or similarities in water quality at a regional scale within and among
principal aquifers. The 3 primary characteristics are:
- The physical framework of the principal aquifer;
- Measures of the relative susceptibility of each stratum of the principal aquifer to contamination; and
- Measures of the potential vulnerability of each stratum of the principal aquifer to contamination.
Each aquifer framework is developed by considering a combination of factors related to
the stratum's physical framework, relative susceptibility, and potential vulnerability
that are deemed most relevant to that principal aquifer. The physical framework could
include measures such as physiography, lithology, stratigraphy and geology. Measures
of the relative susceptibility are those that consider the ease with which water enters
and moves through aquifer material, possibly including hydraulic conductivity and
transmissivity, recharge rate, the presence or absence of an overlying confining unit,
the confined/unconfined nature of the aquifer, ground-water travel time (age of the
ground water in the stratum), thickness and characteristics of the unsaturated zone,
and pumping. Measures of potential vulnerability are those that consider both aquifer
susceptibility and the proximity and characteristics of contaminant sources, possibly
including features related to anthropogenic sources of contaminants, such as up-gradient
land use (i.e. urban, agricultural, undeveloped, etc), factors related to natural
sources of contaminants, such as the mineralogy of the aquifer material, and the
geochemical composition of each stratum.
For additional information on the framework for each principal
aquifer, see the web page for that principal aquifer.
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