the report presents evidence that natural geologic sources of phosphorus increase the problem in these two basins. Based on analysis of ground-water and stream samples from areas throughout the Coastal Plain, ground water that empties into streams in some parts of the basins contains high concentrations of phosphorus. Phosphorus in ground water discharging to streams of the Neuse and Tar River Basins is often 0.2 part per million (ppm) or more. Based on published guidelines, streams draining directly into ponds, lakes, or estuaries should have phosphorus concentrations less than 0.05 ppm to prevent nuisance algal growths.

Relative to 19 other basins studied as part of the USGS NAWQA Program across the United States, the Tar and Neuse River Basins have some of the highest (upper 25 percent) nutrient concentrations observed. In general, highest concentrations of nutrients occurred in agricultural and urban streams.

Other findings from the report include:

• Of shallow ground-water samples collected from 49 wells throughout the Coastal Plain of Virginia and North Carolina, 4 percent exceeded the 10-ppm drinking-water standard for public water supplies. Although shallow ground water is not commonly used for public water supplies, it is used for water supply by rural residents in many counties. The highest nitrate concentrations in ground water occurred in sandy, well-drained soils. High nitrate concentrations in water can cause "blue baby syndrome" and is the primary reason why the drinking-water standard was established.

• Of the 47 pesticides tested in stream samples, 45 were detected. The most commonly detected pesticides were atrazine, alachlor, metolachlor, and prometon. Generally, concentrations did not exceed drinking-water standards, although drinking-water standards have not been established for all compounds.

• Of the 47 pesticides tested in ground-water samples from 49 monitoring wells, 14 compounds were d
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Contact: Gerald L. Ryan
glryan@usgs.gov
(919) 571-4000
United States Geological Survey
16-Apr-1998


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