USE OF QUANTITATIVE DYE TRACING AND WATER CHEMISTRY TO CHARACTERIZE KARST SPRINGS IN THE HELDERBERG PLATEAU, EAST-CENTRAL NEW YORK

The hydraulic and chemical character of karst groundwater is being interpreted at several karst springs in the Helderberg Plateau of eastern New York. Measurements are made of radionuclides, stable isotopes, and dissolved solids, and the hydraulic geometries of subsurface conduits are interpreted from quantitative dye traces. Radium isotopes are trapped by pumping 200 liters of water through MnO₂-impregnated filters. Dissolved components and other isotopes are analyzed directly from water samples. P_CO2 and saturation indices are calculated with dedicated software. Dye traces are done with either rhodamine-WT or fluorescein, with automatic samplers for recovery. Dye concentrations are measured with a fluorometer. Isotopic analyses are made by the U.S. Geological Survey, Reston, Va. The project is about 80% complete.

Logarithmic plots of dye breakthrough time vs. discharge in water-filled conduits must have slopes of -1 to obey the law of continuity. The plot for a typical open-channel canyon-like cave passage, used as a standard of comparison, has a slope of -0.33. Plots for two inaccessible conduits of unknown geometry have slopes of -0.26 and -0.43, which indicate mainly open-channel vadose caves. Springs fed by diffuse recharge are supersaturated with calcite. Those fed by sinking streams are undersaturated with calcite. All are undersaturated with dolomite. Sulfate is less than 20 mg/L, nitrate <3 mg/L, and chloride <100 mg/L (greatest near roads). Mean P_CO2 for all springs is 0.003 atm, 10 times less than local soil values, which indicates loss of CO₂ from open-channel conduits through openings to the surface. d¹⁸O and dD values in springs fed by sinking streams are similar to those for precipitation during the current season. Those in springs fed by diffuse recharge appear to represent precipitation during the prior season. Mean ²²⁸Ra/²²⁶Ra ratios are 0.81 for springs in the Helderberg Group and 0.50 for springs in the Onondaga Limestone, which show that Helderberg groundwater has greater contact with detrital materials than does the Onondaga groundwater. This contrast may reflect local differences in flow rates and distribution of detrital sediment. The dye-tracing and chemical data show that the sampled springs are fed by karst conduits that are dominantly vadose.