GROUND WATER IN ORANGE COUNTY, NORTH CAROLINA

With reference to conditions in the Piedmont and Blue Ridge Provinces

Charles C. Daniel, March 2008

SUMMARY

1. Ground water is the most abundant available fresh water resource.

2. Ground-water systems store water and transmit water. Thus, a ground¬water system serves both as reservoir and conduit.

3. The aquifer system in Orange County is a two-part system composed of fractured bedrock overlain nearly everywhere by regolith.

4. Most ground water in the County is stored in the regolith. The average
saturated thickness of regolith is about 27 ft. On average, available water in
storage in the regolith is slightly less than 1 million gal/acre.

5. The saturated thickness of regolith varies with topographic setting and hydrogeologic unit.

6. Ground water in storage is less affected by drought than surface water.

7. Ground water is recharged by the infiltration of precipitation in upland areas.
Mean ground-water recharge in Orange County, based on data from 12 rainage basins, is 365 (gal/day)/acre.

8. Recharge varies seasonally with precipitation and evapotranspiration.

9. Ground water in Orange County is obtained primarily from wells.

10. The average well yield in Orange County is 17.6 gal/min. 90 percent of all
wells yield more than 2 gal/min, and half of all wells yield more than 10 gal/min.

11. Two areas in the county contain wells with maximum yields ranging from
25 gal/min to more than 100 gal/min. There areas are in the northwestern and
southwestern parts of the County.