EVIDENCE FOR CONDUIT FLOW IN THE SHARON SANDSTONE/CONGLOMERATE, NORTHEAST OHIO

The Lower Pennsylvanian Sharon Sandstone/Conglomerate is the most important bedrock aquifer in Northeast Ohio. It consist of quartz-rich well rounded, well sorted coarse-grained sandstones and conglomerates with a porosity ranging from 6 to 34%. Outcrops of the Sharon contain channelized springs, abandoned spring channels, and continuous vugs that are about 5 cm in diameter and over one meter long. A high spatial variability in the chemical composition of spring waters was observed, with closely spaced springs having widely different chemistries. As an example the TDS of two springs separated by less than 100 meters differed by 1200 mg/L. The high spatial variability in chemical composition indicates that the springs are hydrologically isolated from each other and flow is occurring through well-defined channels or conduits. A database was compiled of 671 sets of hydraulic properties estimated from specific capacity analysis. The average hydraulic conductivity is 179 gpd/ft² (8.45 X 10^-5 m/s), however it ranged over 4 orders of magnitude from 1.4 gpd/ft² (6.61 X 10^-7 m/s), to 15,937 gpd/ft² (7.52 X 10^-3 m/s). The measured permeability of samples of Sharon is 1.5 X 10^-3 cm/sec (32 gpd/ft²) Jost (1994). However, 59% of the Sharon wells have a hydraulic conductivity greater than 32 gpd/ft². The expected range of hydraulic conductivity of sandstones is from 10^-3 to 10 gpd/ft² and for karst limestones is between 10 and 10⁵ gpd/ft² (Freeze and Cherry, 1979). The range observed for the Sharon aquifer is more similar to karst limestones than sandstones suggesting that flow through the Sharon aquifer is characterized by conduit flow. A combination of the outcrop and subsurface data indicates that flow within the Sharon Sandstone/Conglomerate is channelized, and characterized by a network of channels with multiple high permeability pathways along bedding planes, fractures and joint networks.