The chromograph, a new analytical tool for laboratory and field use

Abstract

Water supplies in the Greater Atlanta Region, Georgia, are obtained mainly from surface-water sources, but there is concern that these sources may be unable to meet rising demands. This study indicates that large quantities of good-quality ground water are obtainable from selected sites in the crystalline rocks of the area. Hydrogeologic investigations of 1,051 wells that produce 20 to nearly 500 gallons per minute revealed that large supplies can be developed where favorable structural, stratigraphic, and topographic features result in localized increases in bedrock permeability. These features are described in detail and methods are presented for using them in selecting sites for locating high-producing wells. Most of the site-selection methods are applicable to the north half of the report area, which has rectangular and trellis drainage systems, but their use is restricted in the south half where a dendritic drainage system predominates. Borehole geophysical logs and core drilling revealed that some of the highest production wells derive water from 1- to 8-inch wide horizontal fractures. These fractures occur in a variety of topographic settings and are believed to be stress-relief fractures. (USGS)