Factors Associated with Sources, Transport, and Fate of Volatile Organic Compounds in Aquifers of the United States and Implications for Ground-Water Management and Assessments

Ground water is used by about one-half of the population
of the United States as a source of potable water, including
nearly all of the 40 million or more people served by domestic
water supplies (Alley and others, 1999). Concern about the
quality of this heavily used resource has led to many small-scale
investigations that define the risk and remediation of concentrated
sources where contaminants are released at one location.
A complementary interest in dispersed sources, those where
contaminants are released over large areas, has led to waterquality
investigations of aquifers. Dispersed sources result from
routine activity prevalent in a given setting. Discharge from
septic systems, runoff from paved surfaces, and volatile organic
compounds (VOCs) in air are examples of dispersed sources.
Large-scale studies can provide an indication of aquifer vulnerability
and the quality of water in the aquifer as a whole, as well
as identify contaminants that present the greatest risk to aquifers.
As part of the National Water-Quality Assessment
(NAWQA) Program of the U.S. Geological Survey (USGS), a
plan was developed to define water-quality conditions of the
most important aquifers in the Nation (Gilliom and others,
1995). The results of these aquifer studies serve as a broad-scale
assessment of water quality and important issues related to
aquifers.