CONDUCTIVITY AND SUSPENDED SEDIMENTS IN KARST AND FRACTURED SPRINGS IN PENNSYLVANIA

The properties of groundwater such as conductivity, discharge, and suspended sediment depend on the geology through which the groundwater travels. Three springs in southeastern Pennsylvania were compared: two karst springs and a spring discharging from sandstone. The sandstone spring has a baseflow discharge around 10 L/s, and flows through fractures in the Stockton formation in Buckingham Township. The Stockton formation is chiefly composed of arkosic sandstone, siltstone, and conglomerates. Both karst springs occur in the Ordovician Epler formation composed of crystalline bluish gray limestone interbedded with dolomite. Bushkill spring in the Lehigh Valley discharges about 3 L/s at baseflow and Nolte spring near Lancaster about 40 L/s.

Storms were monitored using conductivity and water level sensors; the variations in ion and sediment concentrations were analyzed for monthly samples. The conductivity and water levels show distinct storm responses in the karst springs. The Stockton spring shows little response to storms. Ion concentrations remained consistently at low levels (Ca less than 20 mg/L). However, both Nolte and Bushkill springs showed significant variation in sediment and ion concentrations. Ca at Nolte varied between 95 and 115 mg/L and at Bushkill varied between 35 and 65 mg/L. Monthly samples taken from Nolte and Bushkill showed significant amounts of sediment being transported through the karst springs; Nolte spring typically had little sediment in the winter and spring, but 10 to 60 mg/L in the summer and fall. Bushkill spring had several mg/L in the winter and spring, and increased to about 10 mg/L in summer and fall. In contrast, the Stockton spring showed little or no sediment (0 to 5 mg/L). The lack of variation in conductivity, suspended sediment, and ion concentration in the non-karst spring shows how the pathways of groundwater are more complex through karst springs.