Central Columbia Plateau - Yakima
NAWQA Study - Publications
The Relative Merits of Monitoring and Domestic Wells for Ground-water Quality
Investigations
By Joseph L. Jones and Lonna M. Roberts, U.S. Geological Survey,
Water Resources Division
in Ground Water Monitoring and Remediation,
Vol. 19, No. 3, Summer 1999
Abstract
The results of two studies of the effect of agricultural
land use on shallow ground-water quality indicate that monitoring wells
may be a better choice than domestic wells for studies of pesticide occurrence
or transport or for use as early-warning indicators of potential drinking-water
contamination. Because domestic wells represent the used resource, and
because domestic well water may be affected by historical, rather than
current pesticide and land use practices, domestic wells would be the best
choice for an investigation of drinking water quality. The key difference
between the domestic and monitoring wells appears to be that the monitoring
wells in this study were installed exclusively to sample the shallowest
possible ground water. For these studies, 48 shallow domestic wells
and 41 monitoring wells were randomly located within two land-use settings
(row crops and orchards) in an irrigated agricultural region of eastern
Washington State and sampled for 145 pesticides (including 9 pesticide
degradates) and common water quality indicators. Constructing and sampling
monitoring wells required approximately four times the resources (including
manpower and materials) than to locate and sample domestic wells. Sample
collection and quality assurance procedures and analytical techniques were
identical except that a portable submersible pump was required for monitoring
wells. In both land-use settings, no significant difference in nitrate
concentration was found between well types; however, the average number
of pesticides detected per well was significantly higher (p<0.05) in
the monitoring wells. A greater variety of pesticides was detected in monitoring
wells; many were detected only in monitoring wells. More than 60 percent
of detections of pesticides that were found only in domestic wells were
of compounds that are no longer in use. These differences in ground-water
quality found in this study relate to the depth of the well and are apparently
related to the age of ground water in the two types of wells and the greater
effects of sorption, degradation, dilution, and dispersion that accompany
longer ground-water residence times. The decision to invest resources in
monitoring wells should be made in light of the study objective and should
consider these differences in results from the two types of wells as well
as the relative costs.
Central Columbia Plateau - Yakima
River Basin NAWQA Study
NAWQA Program
Bibliography
Water Resources of Washington
State
U.S. Geological Survey
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wa.water.usgs.gov
/pubs/ja/GWMR_journal_abstract.htm
Last modified: Mon May 11 12:01:57 1998