Water Quality in the Connecticut, Housatonic, and Thames ... - USGS

WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT
Comparison of Ground-Water Quality in the Connecticut, Housatonic, and Thames River Basins with
Nationwide NAWQA Findings
Water-quality characteristics were evaluated for ground-water studies in each NAWQA
Study Unit. Ground-water resources were divided into two categories:
(1) drinking-water aquifers, and (2) shallow ground water underlying agricultural or
urban areas. Summary scores were computed for each characteristic for all aquifers and
shallow ground-water areas that had adequate data. Scores for each aquifer and shallow
ground-water area in the Connecticut, Housatonic, and Thames River Basins were
compared with scores for all aquifers and shallow ground-water areas sampled in the 20
NAWQA Study Units during 1992–95. Results are summarized by percentiles; higher
percentile values generally indicate poorer quality compared with other NAWQA
ground-water studies. Water-quality conditions for each drinking-water aquifer also are
compared to established drinking-water standards and criteria for protection of human
health. (Methods used to compute rankings and evaluate standards and criteria are
described by Gilliom and others, in press.)
(FC)
(FO)
(UR)
PESTICIDES
(AG)
Pesticide detection was common from
wells in agricultural areas, with detection
in more than 80 percent of wells
sampled. Concentrations were generally
low, with only two samples exceeding the
drinking water standards. Pesticides were
also commonly detected in urban wells,
but were detected much less frequently in
forested areas and drinking-water
(bedrock) wells.
EXPLANATION
Fractured crystalline–bedrock aquifer (FC)
Agriculture (AG)
Urban (UR)
Forest (FO)
Ranking of ground-water quality relative
to all NAWQA ground-water studies —
Darker colored circles generally indicate
poorer quality. Bold outline of circle
indicates one or more standards or criteria
were exceeded.
Greater than the 75th percentile
(among the highest 25 percent
of NAWQA ground-water studies)
Between the median and the 75th percentile
Between the 25th percentile and the median
(FC)
(FO)
(UR)
(AG)
NITRATE
Nitrate concentrations in shallow ground
water under agricultural areas generally
were greater than the national median
concentration, and 15 percent of these
wells exceeded the drinking-water
standard for nitrate. In contrast, nitrate
concentrations in other shallow ground
water and bedrock wells generally were
less than the national median for
NAWQA sites.
Less than the 25th percentile
(among the lowest 25 percent
of NAWQA ground-water studies)
20 Water Quality in the Connecticut, Housatonic, and Thames River Basins, 1992-95