Ground‐Water Problems in the Mesozoic Pax Mountain Fault Zone

Abstract

ABSTRACTMore than 100 steeply dipping or vertical Mesozoic fault zones, which cut across Paleozoic igneous and metamorphic rocks, have been reported in the Piedmont and Appalachians of the Carolinas. The present investigation deals with the hydrological problems encountered in exploring for ground water in the Pax Mountain Fault zone. This is the largest known Mesozoic fault in the Carolinas, having a length of more than 75 km and attaining a width of 1 km in places. Subsurface studies of seven wells, which were drilled along the axis of Pax Mountain, South Carolina, show that the composition of the fault rocks is much more complicated than was known heretofore. These rocks consist of angular particles of quartz and feldspar fault breccia enclosed in a kaolinitic clay gouge. They vary greatly in degrees of consolidation and permeability, and these variations were the cause of some serious ground‐water problems. Two wells were dry holes because the intergranular spaces of the breccia were clogged with clay and also because most of the joints were filled with secondary minerals. Three wells, which were drilled in more permeable, but poorly consolidated fault rocks, caved in at a depth of about 80 m just when they had encountered large volumes of water. Two of the seven wells produce potable water, but chemical analyses of the ground water showed that their turbidity values were 6.0 t.u. and 2.0 t.u., which exceed the limit of 1.0 recommended by the South Carolina Department of Health and Environmental Control.