Santee NAWQA

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USGS IN YOUR STATE

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Santee River Basin Study
Significant Findings

Stream and River Highlights

Pesticides (Insecticides, herbicides, and pesticide metabolites, sampled in water)

• The herbicides atrazine, simazine, and tebuthiuron were detected in almost every stream in the Santee Basin, including those in forested areas, at levels below aquatic-life and drinking-water guidelines.
• Four insecticides—malathion, diazinon, chlorpyrifos, and parathion—exceeded aquatic-life guidelines.
• No pesticides exceeded drinking-water standards, though 7 of the 30 compounds detected do not have drinking-water standards and 13 do not have aquatic guidelines.
• Pesticide concentrations had seasonal patterns, with the highest concentrations measured in the spring following application.

Nutrients (Total phosphorus and nitrate [as nitrogen], sampled in water)

• Nitrate concentrations did not exceed drinking-water standards in any streams sampled.
• Average total phosphorus concentrations in four streams were above the U.S. Environmental Protection Agency (USEPA) recommended goal to prevent nuisance aquatic growth.
• The South Fork Catawba River had an average total phosphorus concentration that was four times higher than the USEPA goal and is a significant source of phosphorus to downstream lakes.
• Wastewater discharge and agricultural runoff are major sources of nitrogen and phosphorus.

Trace Elements (Arsenic, mercury, and metals, sampled in sediment)

• Trace metals were detected frequently in bed sediment and tissue, mostly at concentrations within aquatic-life guidelines.
• Arsenic, chromium, and lead exceeded guidelines in a few samples.
• Although concentrations were not high in sediment samples, data suggest that mercury is accumulating in fish and clams in concentrations that are harmful to humans or animals that eat them.
• Sampling by State agencies has resulted in fish-consumption advisories for mercury in 49 rivers and reservoirs in South Carolina.

Organochlorines (Organochorine compounds including DDT and PCB's, sampled in sediment)

• Organochlorine pesticides were detected frequently in bed sediment and tissue.
• Most of these compounds have been discontinued for use for many years but continue to be detected because they are persistent in the environment.
• A derivative of DDT was detected at concentrations exceeding aquatic-life standards in sediment at three agricultural sites.

Volatile Organics (Solvents, refrigerants, fumigants, and gasoline compounds, sampled in water)

• Volatile organic compounds (VOCs) known to occur in the aquifer adjacent to Gills Creek, an urban stream in Columbia, S.C., were frequently detected in the creek as well.
• Although no existing Federal or State drinking-water standards or aquatic guidelines were exceeded, this finding is consistent with the important influence of groundwater quality on stream-water quality.

Bacteria (Fecal coliform bacteria, sampled in water)

• Bacteria levels frequently exceeded South Carolina standards for contact recreation in streams in forested, urban, and agricultural areas.
• Standards were exceeded more frequently in small streams than in large rivers.