GEOCHEMISTRY AND SEDIMENT COMPARISONS BETWEEN A KARST SPRING AND WELL

Water can travel from recharge to discharge areas through different combinations of matrix, conduit, and fracture pathways in karst aquifer systems. To better understand the pathways, we collected samples from two locations in a karst aquifer in northeastern PA. The first location was a spring discharging to the Bushkill Creek, and the second location was a well drilled into a conduit about 300 m west of the spring. The samples were collected bi-weekly and analyzed for ion and sediment content. In-situ temperature, pH, and conductivity data were also collected at both sites bi-monthly.

The bicarbonate values at the spring were consistently lower than that of the well samples taken at the same time. The differences were as high as 300 mg/L and as low as 50 mg/L. Conductivity measurements in the spring were also consistently 100 to 250 uS/cm lower than the well. Suspended sediment concentrations were higher in the well (typically 100’s mg/L and reaching several g/L). The spring typically had less than 10 mg/L, but values up to 100 mg/L were observed in storm sampling.

Although the well is drilled into a cavity (at a depth of 18 m, 1 m in height) and has notable sediment, it seems to yield water that has chemical characteristics of matrix flow (high TDS). The spring, on the other hand, is more dilute, suggesting shorter recharge pathways.