Hydrogeology and Water Quality of the Pepacton Reservoir Watershed in
Southeastern New York. Part 1. Concentrations of pesticides and their
degradates in stream baseflow, 2000-2001
by Patrick J. Phillips and Paul M. Heisig
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 03-4137
ABSTRACT
Baseflow samples were collected from 20 small streams
in the Pepacton Reservoir watershed in Delaware County,
N.Y., from December 2000 through November 2001 as part
of an investigation to define the occurrence of pesticides in
shallow ground water in watersheds containing either a recent
(2001) corn crop, a previous (1993-94) corn crop, or no
history of row-crop cultivation. Baseflow water quality was
assumed to represent the chemical quality of shallow ground
water within the drainage area above each sampling site.
Baseflow samples were analyzed for 57 pesticides and
pesticide degradates. Three herbicides (atrazine, metolachlor
and simazine) and three herbicide degradates (alachlor ESA
[ethanesulfonic acid], deethylatrazine, and metolachlor
ESA) were detected, but no concentrations exceeded any
Federal or State water-quality criteria, and the maximum
concentrations of all compounds except metolachlor ESA
were less than 0.10 microgram per liter. The most frequently
detected compounds (atrazine, metolachlor, deethylatrazine
and metolachlor ESA) are either those typically used on corn
crops, or those whose parent compounds are commonly used
on corn crops and have been detected in streams that drain
row-crop settings elsewhere in New York State. The pesticide
and pesticide-degradate concentrations in baseflow samples
collected in December 2000 and July 2001 samples generally
corresponded to the amount of cornfield acreage in each
watershed in 2001.
The types of pesticides detected, and their median
concentrations, were similar to those noted in two previous
ground-water studies in row-crop areas elsewhere in upstate
New York. Also the SAM ratios (ratio of metolachlor ESA
concentration to metolachlor concentration) for the Pepacton
samples were similar to those for ground-water samples from
other agricultural settings in upstate New York, but were
significantly higher than that for stormflow and baseflow
samples collected in 1997-98 from Canajoharie Creek,
an upstate stream that drains row-crop farmland. These
comparisons confirm that the baseflow samples were derived
from, and were representative of, ground water in their
respective watersheds. Late-summer decreases in atrazine and
deethylatrazine concentrations at a site where corn was grown
in 2001 may have resulted from the seasonally dry conditions
and the accompanying decrease in ground-water discharge
from the upper-most part of the surficial aquifer system to
streams. The lack of a similar decrease in metolachlor ESA
concentrations during this period may reflect the transport of
metolachlor ESA to deeper parts of the surficial aquifer that
continued to discharge to streams during the dry period.
Citation: Phillips, P.J. and Heisig, P.M., 2004,
Hydrogeology and Water Quality of the Pepacton Reservoir Watershed in
Southeastern New York. Part 1. Concentrations of pesticides and their
degradates in stream baseflow, 2000-2001:
U.S. Geological Survey Water-Resources Investigations Report 03-4137, 13 p.
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