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Uranium exceeds standards due to supply well operation ...
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Water-quality affected by short-circuit pathways ...
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Simulations show young water beneath confining unit ...
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Local conditions affect contaminant movement ...
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The study of public-supply well vulnerability to contamination
from compounds commonly found in the environment is one of five
national priority topics being addressed by the National
Water-Quality Assessment (NAWQA) Program. The Transport of
Anthropogenic and Natural Contaminants to Supply Wells (TANC)
study began in 2001 with the following general objectives...
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Identify the dominant contaminants and sources of those contaminants in public-supply wells in representative water-supply aquifers across the Nation
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Assess the effects of natural processes (such as degradation) and human activities (such as irrigation) on the occurrence of contaminants in public-supply wells in representative aquifers
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Identify the factors that are most important to incorporate into public-supply well vulnerability assessments in different settings and at different spatial scales
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Develop simple methods and models for screening public-supply wells for vulnerability to contamination in unstudied areas and from newly emerging contaminants
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Increase understanding of the potential effects of water-resource development and management decisions on the quality of water from public-supply wells
Unique Characteristics of the TANC Study
Sampling at different depths -- The
screened or open intervals of public-supply wells are
commonly from tens to hundreds of feet in length; therefore,
water from these wells is generally a mixture of waters of
different ages that enter the well at different depths and
are associated with different potential sources of
contamination. Using a USGS-developed sampler (Izbicki
and others, 1999 and
Izbicki,
2004), the TANC study is collecting samples at multiple
depths in pumping public-supply wells to ascertain where and
how contaminants from different sources enter the wells.
Evaluating multiple settings and
scales -- Consistent methods
are being used to collect and analyze data, and
investigations are being conducted at both regional (tens to
thousands of square miles) and local scales (less than 10
square miles). Regional-scale investigations are allowing
for comparison of important contaminant-transport mechanisms
in water-supply aquifers across the Nation. Local-scale
investigations build upon the regional-scale efforts and are
focusing on understanding common transport and
transformation processes within the contributing areas of
public-supply wells.
Exploring the consequences of
uncertainty -- To make
informed decisions about activities at a particular
location, decision-makers need to know whether the location
is contributing recharge to public-supply wells. They also
need information about traveltimes between potential
contaminant sources and public-supply wells. Because this
information cannot be measured directly, decision-makers
must rely on estimates that are inherently uncertain (due to
limitations in the methods). The TANC study is exploring the
consequences of this uncertainty, and helping
decision-makers understand these consequences, by comparing
estimates from traditional and probabilistic modeling
approaches with actual water-quality data from public-supply
wells.
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U.S. Department of the Interior | U.S. Geological Survey
