National Water-Quality Assessment (NAWQA) Program
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 about NAWQA's Regional Assessments of Aquifers, refer to USGS Fact Sheet 2005-3013.