Comparison of nitrate, pesticides, and volatile organic compounds in samples from monitoring and public-supply wells, Kirkwood-Cohansey aquifer system, southern New Jersey

The number and total concentration of
volatile organic compounds (VOCs) per
sample were significantly greater in water from
public-supply wells than in water from shallow
and moderate-depth monitoring wells in the
surficial Kirkwood-Cohansey aquifer system in
the Glassboro area of southern New Jersey. In
contrast, concentrations of nitrate (as nitrogen)
and the number and total concentration of
pesticides per sample were statistically similar
in samples from shallow and moderate-depth
monitoring wells and those from public-supply
wells.
VOCs in ground water typically are
derived from point sources, which commonly
exist in urban areas and which result in
spatially variable contaminant concentrations
near the water table. Because larger volumes of
water are withdrawn from public-supply wells
than from monitoring wells, their contributing
areas are larger and, therefore, they are more
likely to intercept water flowing from VOC
point sources. Additionally, public-supply
wells intercept flow paths that span a large
temporal interval. Public-supply wells in the
Glassboro study area withdraw water flowing
along short paths, which contains VOCs that
recently entered the aquifer system, and water
flowing along relatively long paths, which
contains VOCs that originated from the
degradation of parent compounds or that are
associated with past land uses. Because the
volume of water withdrawn from monitoring
wells is small and because shallow monitoring
wells are screened near the water table, they
generally intercept only relatively short flow
paths. Therefore, samples from these wells
represent relatively recent, discrete time
intervals and contain both fewer VOCs and a
lower total VOC concentration than samples
from public-supply wells.
Nitrate and pesticides in ground water
typically are derived from nonpoint sources,
which commonly are found in both agricultural
and urban areas and typically result in lowlevel,
relatively uniform concentrations near
the water table. Because nonpoint sources are
diffuse and because processes such as
degradation or sorption/dispersion do not occur
at rates sufficient to prevent detection of these
constituents in parts of the aquifer used for
domestic and public supply in the study area,
concentrations of nitrate and pesticides and
numbers of pesticide compounds are likely to
be similar in samples from shallow monitoring
wells and samples from public-supply wells.
Results of a comparison of (1) the general
characteristics of, and water-quality data from,
public-supply wells in the Glassboro study area
to available data from public-supply wells
screened in the Kirkwood-Cohansey aquifer
system outside the study area, and (2) land-use
settings, soil characteristics, and aquifer
properties in and outside the study area indicate
that the findings of this study likely are
applicable to the entire extent of the Kirkwood-
Cohansey aquifer system in southern New
Jersey.