Monday, March 31, 2008 : 2:00 p.m.
Yields of Crystalline Rocks in the Piedmont of the Eastern United States
Past hydrogeologic studies of crystalline rock in the Piedmont Physiographic Province of the United States have indicated that fracturing decreases considerably at about 300 feet below land surface and that usable yields of ground water are unlikely from wells deeper than 300 feet. An examination of the extensive data base compiled by the U.S. Geological Survey’s Appalachian Valleys/Piedmont Regional Aquifer-Systems Analysis, however, indicates several areas where yields are substantial from crystalline-rocks deeper that that 300 foot depth. Mean well yield for 4,342 non-domestic wells in crystalline rocks of the Piedmont Physiographic Province is 45 gallons per minute. More that 10 percent of those wells had yields greater than 100 gallons per minute. The maximum reported yield in these crystalline rocks was 1,800 gallons per minute (for a well in marble). Several areas in the southern part of the Piedmont Physiographic Province were identified where well yields increased greatly with depth. Yields as high at 470 gallons per minute were identified in production zones from 400 to 700 feet below land surface. In areas around Atlanta, Georgia, as wells as Statesville and Winston-Salem, North Carolina, significantly productive zones have been found at depths greater than 350 feet. A subregional comparison of yields from wells in crystalline rock north and south of 38 degrees North latitude indicates that the wells to the south have significantly higher yields below 300 feet than those wells north of 38 degrees.
Lindsay A. Swain, URS Corp. From 1969-2002 Mr. Swain was a hydrogeologist with the US Geological Survey. Mr Swain conducted studies on ground water from Hawaii to Maine. During his 33 years with USGS, Mr. Swain published about 2 dozen professional reports. When this paper was originally written but never published, he was Chief of the Piedmont/Appalachian Valleys RASA. After serving as District Chief in the State of Indiana, Mr. Swain retired from the USGS and moved home to California where he is currently employed as a Senior Geologist for URS Corporation in Santa Ana.