GROUND WATER EXPLORATION AND DEVELOPMENT IN IGNEOUS AND METAMORPHIC ROCKS: PART I-INFLUENCING FACTORS AND CONSIDERATIONS

Exploration for, and development of, ground water in deformed igneous and metamorphic rocks in regions with a sub-tropical weathering environment have been little studied, and are poorly understood. Much of the funded research and many of the recent and current studies in this regard have focused on the physics of ground water movement in fractured rock. During the last several decades these studies have been driven by environmental contaminant delineation and remediation problems and concerns. For this, the objectives are quite different from that required for exploration and development of water as a resource, where the quantity, quality, and sustainability of the resource are of utmost importance.

Thirty years of exploration and development of ground water resources in igneous and metamorphic rocks of the southeastern United States has convinced us that, among the many factors that influence ground water in these rocks, the single most important factor is rock type. Rock type directly influences all other parameters, i.e., reaction to stress, weathering, and topography. Without knowing the detailed geology of an area, all other factors influencing ground water lack a full and meaningful context.

For success in ground water exploration and development in igneous and metamorphic rocks, more than an understanding of the physical parameters controlling ground water movement is necessary. The interrelationships, both physical and spatial, of rock type, structure, type and depth of weathering, and topography must be known and understood. Each of these variables has numerous significant variations. Combine this with observations that the influence of each of these variables on ground water is relative rather than absolute, and it becomes obvious that ground water exploration and development data in metamorphic and igneous rocks must be site specific.

Many Hydrologists/Geologists/Hydrogeologists making decisions on ground water exploration and development -and writing laws/rules/guidelines regulating such- lack either the ability or the time, or both, to geologically map the areas of concern. 1:24,000-scale geologic maps serve as an excellent beginning for more detailed study and analysis.