Impact of Tunnel Reconstruction on Stream Water Quality in Great Smoky Mountains National Park

Abstract

Few case studies are available on stream water quality monitoring during road construction, especially in highly protected watersheds. Recent reconstruction of two tunnels and approach roads in the Great Smoky Mountains National Park potentially could have impacted the adjacent stream due to sediment and acid-generating geology. To determine whether impact occurred, grab and passive sampling were conducted at stream sites above and below each construction area before, during, and after construction. Performance of individual structural best management practices (BMPs) was also monitored. Due to the small disturbance area, the results showed that tunnel reconstruction had no statistical impact on stream water quality based on comparison of upstream and downstream pH and suspended solids. Surprisingly, median suspended solids concentrations for the stream sampling locations were lowest during construction, ostensibly because construction occurred in winter when the ground was frozen. Differences in stream pH and water quality between construction and pre- and postconstruction phases were attributed to normal seasonal variation. BMP performance was mixed; the efficiency of check dams was dependent upon their ability to pond water.