IMPACTS TO WATER QUALITY, TENMILE CREEK, WASHINGTON COUNTY, PA

Washington County, located in Southwestern Pennsylvania, is characterized by steep-walled stream valleys and rolling ridgelines. The region has active agriculture and has seen significant development, but is especially known for the recent boom in shale gas extraction as well as legacy coal mining. Beginning in 2011, the Washington County Watershed Alliance, in collaboration with California University of Pennsylvania and other county stakeholders, began monitoring streams in the county to ascertain current water quality and identify emerging and potential threats to water resources. Twenty-two dataloggers were installed throughout the area in streams of varying sizes. Tenmile Creek, which is mostly in the southeastern portion of the county and forms part of the southern county boundary, is host to four of these loggers. Two were placed in the main stem and one each in two separate tributary streams. The dataloggers measure conductivity and water levels in fifteen-minute intervals. Results from continuous readings over the past three years show that stream conductivity data vary predictably in response to precipitation. During the period of observation, conductivity readings decreased immediately following significant rainfall events, but quickly rebounded to levels higher than those before the rainfall. This was followed by a slow decline and then a steady rise until the next precipitation event. Legacy surface and underground mining is likely contributing saline water as these areas are flushed when underground spaces fill. However, evidence suggests that flushing of nearby land surfaces may be the more important contributing factor, as salts are carried by overland flow to the stream. The greatest increases in conductivity are seen at the site with NO mining in the immediate area, but with active farming and shale gas activity, and legacy quarries. This suggests that overland flushing of disturbed lands may play a larger role in water quality. These saline pulses are cause for concern since many of the county’s streams are above suggested values for healthy streams (150-500 μs/cm). These spikes can drive conductivity values as high as 800-900 (µs/cm) for up to a few days at a time.