TEMPERATURE, CONDUCTIVITY, TURBIDITY AND LEVEL RESPONSES TO PRECIPITATION OF PHREATIC WATERS EXPOSED IN CAVE FISSURES: IMPLICATIONS FOR DEEP GROUNDWATER FLOW IN THE SHENANDOAH VALLEY KARST

Analysis of time series data for water quality parameters in phreatic cave fissures suggests complex circulation patterns within karst aquifers in Cambro-ordovician aged carbonate rocks of the Shenandoah Valley. Since late summer, 2011, automatic loggers in three phreatic fissure in caves in the South Fork Shenandoah River basin, Virginia have measured water level, electrical conductivity, and temperature hourly, with turbidity added in 2012. Madison Saltpetre cave (MSC, Grottoes, VA) is developed in the Cambrian Conococheague Formation, while 100km to the north Brother Dave’s Cave (BDC) and Power Plant Pit (PPP) are developed in the lower Ordovician aged Rockdale Run Formation. MSC levels rise slowly following precipitation events, ranging approximately one meter, while conductivity, temperature, and turbidity remain constant. Unlike MSC, BDC and PPP respond strongly to precipitation, though in very different ways despite their ~100m proximity. PPP shows large increases in level (R=6m) and turbidity with sharp decreases in conductivity; BDC shows short-lived, moderate increases in level (R=1m), turbidity, and conductivity. Water levels at PPP and BDC do not track consistently, suggesting these water bodies are hydrologically isolated under at least some conditions. In response to precipitation, PPP temperatures increase in summer and decrease in winter, while those in BDC increase following winter events. Base flow conductivity and temperature are higher at PPP than MSC or BDC. These data suggest that MSC exposes phreatic water with little surface connection, PPP upwelling water with surface stormwater inputs, and BDC shallow phreatic water mixing with upwelling waters displaced by remote infiltration of surface waters.