Santee River Basin Study
Significant Findings

THIS PROJECT HAS BEEN COMPLETED AND IS BEING ARCHIVED IN ITS FINAL CONFIGURATION

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.