SUMMARY OF MAJOR FINDINGS
Stream and River Highlights
Surface water sampled in the Santee River Basin and
coastal drainages generally meets existing Federal and State guidelines
for drinking-water quality and protection of aquatic life. However, urban
and agricultural land uses have affected water quality, as indicated by
elevated concentrations of bacteria, pesticides, and nutrients in basins
dominated by these land uses.
|The Santee River Basin and coastal drainages (the
"Santee Basin") is an approximately 24,000-square-mile area
in North and South Carolina that encompasses the Blue Ridge Mountains,
the Piedmont, and the Coastal Plain (Fenneman, 1946). Most of the
3.5 million people in the Santee Basin live in urban areas. Eighty-six
percent of the water used in homes and for industry is treated surface
water withdrawn from rivers of reservoirs. Ground water is the main
water source for rural households.
- 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.
- 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 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.
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 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
ground-water quality on stream-water quality.
- 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.
- Biological communities in urban and agricultural
streams had fewer species of fish and invertebrates that can tolerate
contamination than forested and mixed land-use streams. This suggests
that contaminants resulting from these land uses affect the natural
communities that live in these areas, although factors such as habitat
alteration can cause similar changes in biological communities.
Ground water in the Santee Basin generally meets existing
Federal and State standards for drinking water except with respect to
nitrate, which failed to meet the drinking-water standard in almost one-half
of the shallow monitoring wells sampled in agricultural areas, and radon,
which did not meet proposed standards in about one-half the drinking-water
wells sampled basinwide. Pesticides were detected frequently in urban,
agricultural, and drinking-water supply wells, but only two samples exceeded
drinking-water standards. Many wells contained low concentrations of numerous
synthetic chemicals related to industry, household use, and motor vehicles,
and a few of these chemicals were at levels above drinking-water standards.
- Pesticides were detected in 17 of 90 wells sampled
in drinking-water supply aquifers. Of the 34 detected, only 2 pesticides
exceeded drinking-water standards, but 11 of the detected pesticides
do not have standards. Most wells in agricultural and urban areas contained
at least one pesticide, but only two wells in urban areas had concentrations
that exceeded drinking-water standards.
- Nitrate is the only nutrient that was detected in
significant concentrations in ground water, and it exceeded drinking-water
standards in almost one-half of the shallow monitoring wells in agricultural
areas. Although this finding indicates significant contamination of
shallow ground water, most drinking-water wells are located in deeper
aquifers. Nitrate in the Piedmont and Sandhills aquifers was elevated
above natural concentrations but exceeded standards in only two wells.
The Floridan aquifer, which is protected for the most part by confining
units in the study area, had relatively low concentrations of nitrate.
Radon, a naturally occurring radioactive gas, was detected in almost
all wells sampled in drinking-water aquifers. Over one-half of the wells
had concentrations that exceeded proposed Federal drinking-water standards.
Most of the wells with radon concentrations that exceeded the proposed
standard are located in the Piedmont aquifer.
- VOCs were detected in 27 of 30 monitoring wells
in an urban setting. Most compounds were detected at extremely low levels;
however, the concentrations of trichloroethylene, a solvent, and methyl
tert-butyl ether, a gasoline additive, were above a drinking-water
standard and an advisory level, respectively, in one well each. Thirteen
of the 35 compounds detected do not have drinking-water standards. VOCs
in drinking-water supply aquifers were detected throughout the Santee
Basin, but no concentrations exceeded drinking-water standards.
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U.S. Geological Survey Circular
Hughes, W.B., Abrahamsen, T.A., Maluk, T.L., Reuber, E.J., and Wilhelm, L.J., 2000, Water Quality in the Santee River Basin and Coastal Drainages, North and South Carolina, 199598: U.S. Geological Survey Circular 1206, 32 p., on-line at https://pubs.water.usgs.gov/circ1206/