Santee River Basin Study
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.