Ground-water levels in the Floridan-Midville aquifer in the Breezy Hill area, Aiken and Edgefield Counties, South Carolina, April 1999-November 2000

The Breezy Hill area in Aiken and Edgefield Counties of west-central South Carolina is a rapidly growing region in need of increasing amounts of ground water. From 1995 to 1998, the local water utility increased ground-water withdrawals in the Breezy Hill area from 1.4 to 2.1 million gallons per day to meet water-supply demands. As development continues, future demands for ground water will likely put stress on the surfaceand ground-water resources of the area. To address this issue, the U.S. Geological Survey, in cooperation with Aiken County, compiled and interpreted geologic and hydrologic data needed to map the ground-water system in the Breezy Hill study area.

The Breezy Hill study area consists of four interfluvial areas comprising the regions between Horse and Little Horse Creeks, Little Horse and Hightower Creeks, Hightower Creek and Franklin Branch, and Franklin Branch and Mims Branch. Across the interfluvial areas, the average elevation of the water-level surface ranged from 200 to 480 feet above sea level, and the average saturated thickness of the Floridan-Midville aquifer ranged from less than 20 to 70 feet thick. A water-level contour map of the surface of the Floridan-Midville aquifer indicates that recharge to the aquifer occurs mainly within the interfluves. Recharge is derived principally from precipitation, although there is some potential for ground-water recharge from underlying crystalline rocks. Ground water discharges along the flanks of the interfluves into the bounding streams where the elevations of the ground water and streams coincide.

From April 1999 to November 2000, calculated long-term normal precipitation totaled about 84.0 inches; however, actual recorded precipitation totaled 69.2 inches, representing about a 17.6 percent decrease in precipitation during this period. Published estimates of annual evapotranspiration range from 30 to 35 inches.

A U.S. Geological Survey surface-water gaging station located near the center of the study area on Little Horse Creek monitors runoff from a drainage area of 26.6 square miles. Average annual flow for the station for water years 1990-2000 was 33.8 cubic feet per second. From April 1999 to November 2000, the monthly average flow was less than the average monthly flow for the longterm record, excluding December 1999 to March 2000 when no data were collected. Monthly average flow for Little Horse Creek exceeded the normal monthly flow during June and July 1999.

Ground water in the Breezy Hill area is principally withdrawn from the unconfined Floridan- Midville aquifer. Ground-water withdrawals by the local water utility increased 37 percent from 1989 to 2000 (315.2 to 500 million gallons, respectively). From January 1999 to December 2000, the utility exceeded the long-term monthly average groundwater withdrawals for every month except September and December 2000. Calculated long-term monthly ground-water withdrawals by the utility for a 20-month period from April 1999 to November 2000 totaled 674 million gallons; however, actual ground-water withdrawals totaled 883 million gallons, which is 31 percent more than the long-term average ground-water withdrawals for the production wells.

Published estimates of average annual ground-water recharge rates for the study area range from 13 to 15 inches per year. A base-flow recession analysis of streamflow data for Little Horse Creek provided an estimated recharge rate of 14.9 inches per year for the drainage area. Using an estimated average porosity ranging from 30 to 35 percent observed in sand-aquifer cores, the average annual recharge of 13 to 15 inches would cause a 3.6- to 4.1-foot water-level change to the saturated thickness of the aquifer, if applied instantaneously. The water-level declines observed in wells from April 1999 to November 2000 approximated an average decline of 4 feet.

From November 1999 to November 2000, ground-water levels in six wells near utility pumping centers declined 2 to 5 feet. Long-term waterlevel declines of 10.27 and 11.50 feet were measured in two wells between May 1992 and April 2000, respectively.