Source and Occurrence of Bromide, Nitrate, and Pesticides in Shallow Ground Water and Surface Water, Montgomery County, New York.
D. W. Hanchar (U.S. Geological Survey, 425 Jordan Road, Troy, New York 12180)
Concentrations of nitrate, selected pesticides, and bromide in water samples collected from tile drains and ditches during April 1994 and July 1995 in an agricultural area of Montgomery County, N.Y., suggest that shallow ground water is an important source of these constituents in surface water. The 0.9-square-kilometer study area, adjacent to Canajoharie Creek, is under cultivation for row crops, primarily corn and soy beans, and is underlain by a surficial aquifer that consists of fluvial sand and gravel overlying lacustrine clay and sand. Overland runoff during storms appears to be minimal because the soil is permeable and flat. Tile drains, used extensively throughout the study area, provide a "short cut" for shallow ground water from the surficial aquifer to the drainage ditches.
Bromide is a natural constituent of ground water in the area and can be used as an indicator of the discharge of ground water to surface water. Bromide concentrations in water from wells completed in the top 3 meters of the surficial aquifer range from 0.02 to 0.2 mg/L (milligrams per liter), and bromide concentrations measured in water from tile drains were within this range, further indicating of a shallow-ground-water source. Water samples collected from one ditch that drains a known area of ground-water discharge consistently contained elevated bromide concentrations (0.07 to 0.14mg/L).
Water sampled from tile drains and ditches had elevated concentrations of nitrate and selected pesticides. Nitrate concentrations in samples from tile drains ranged from 2.7 to 17 mg/L and those in samples from ditches ranged from 2.7 to 10 mg/L. Pesticides detected include atrazine, cyanazine, deethyl atrazine, metolachlor, pendamethalin, and diazinon. The highest concentrations of atrazine and cyanazine in tile drain samples were 1.3 µg/L(micrograms per liter) and 0.15 µg/L, respectively; those in samples from ditches concentrations were 2.1 and 1.1 ug/L, respectively. Elevated concentrations of nitrate and pesticides are associated with elevated bromide concentrations, indicating that shallow ground water is a major source. The highest concentrations of these constituents in samples from tile drains and ditches were measured during and after stormflows, suggesting that the discharge of shallow ground water discharge during storms provides an important source of nutrients and pesticides in surface water in the study area.
Abstact published in American Geophysical Union 1995 Fall Meeting, EOS 76(46). p. F187.
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