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Preliminary Results from Ground-water Studies in an Agricultural Watershed of the Coastal Plain of North Carolina

National Symposium on Water Quality, Gary Pederson ed., American Water Resource Association Technical Publications Series 94-4, p. 201.
By Timothy B. Spruill

Abstract

Thirteen shallow wells, 2 deep wells, and a surface-water site in the Pete Mitchell Swamp basin located in the North Carolina Coastal Plain were sampled to describe ground-water quality along a ground-water flow system, determine principal causal factors of concentrations of selected chemical constituents in ground water and surface water, and to relate findings to managing potential water-quality problems.

Major ionic composition of ground water and surface water was elevated due to sulfate and calcium leaching from applied agricultural chemicals. Specific conductance of surface' water was elevated at least 4 times the expected value for unimpacted or forested streams (200 microsiemens per centimeter (us/cm) versus 50 us/cm. Nitrate-nitrogen concentrations of the surface water, although elevated above expected values of less than 0.01 mg/L for unpolluted streams, was below 3 mg/I. This was much less than the maximum of 15 mg/L observed in ground water beneath irrigated and fertilized fields indicating denitrification, plant uptake or dilution of ground water. Median concentration from all 13 shallow wells was 5 milligrams per liter. The pesticides alachlor and atrazine, as well as more than 100 others, were not detected in any of the ground-water samples, but were almost always detected in surface-water samples. These results suggest that concentrations of pesticides in the stream are largely due to deposition of pesticides on the bed which desorb into the water column, and not from contaminated ground-water discharge.

Spruill, T.B., 1994, Preliminary results from ground-water studies in an agricultural watershed of the Coastal Plain of North Carolina: National Symposium on Water Quality, Gary Pederson ed., American Water Resource Association Technical Publications Series 94-4, p. 201.