Land areas characterized by a unique, homogeneous combination of
natural and human-related factors, such as row-crop cultivation on glacial-till soils.
Land-Use Studies (LUS)
Investigations of the concentrations and distribution of water-quality constituents
in recently recharged groundwater (generally less than 10 years old) associated with
the most important regionally significant Environmental Settings of land use and
hydrogeologic conditions in each Study Unit. For each study, usually a combination of
20 to 30 shallow existing and observation wells are sampled. Two to four studies
typically are completed in each Study Unit during the first cycle of NAWQA.
A reconnaissance sampling effort to determine if recently
recharged water containing agricultural chemicals was present at the water
table under irrigated fields in the central High Plains study area.
The study of vertical gradients in ground-water chemistry and age of water
in the aquifer to develop an understanding of ground-water
residence times and recharge rates and to provide a
better understanding of contaminant sources/sinks in the aquifer.
The review and analysis of existing water-quality data to provide
a historical perspective on the water quality in the Study Unit, to assess strengths
and weaknesses of available information, and to evaluate initial implications for
water-quality management and study design.
Major Aquifer Study (MAS)
Broad assessment of the water-quality conditions of the major aquifer
of each Study Unit. The Sub-Unit Survey relies primarily on sampling existing wells
and, wherever possible, on existing data collected by other agencies and programs.
* Modified from Gilliom and others (1995).