Best Management Practice Performance and Water Quality Monitoring Before, During and After Road and Tunnel Reconstruction in the Great Smoky Mountains National Park

Hedrick, Kevin

EXECUTIVE SUMMARY: The University of Tennessee (UT) Civil and Environmental Engineering Department monitored the impact of road and tunnel reconstruction on adjacent streams in the Great Smoky Mountains National Park (GSMNP) for the National Park Service and Best Management Practice (BMP) performance. The potential stream impacts of concern were sediment and acid generating geology. Sediment can adversely affect aquatic life and ecosystems by mechanical abrasion, by obstructive silting, by reducing the penetration of light, by providing a surface for the growth of microorganisms, by absorbing or adsorbing chemicals, and by inhibiting normal temperature fluctuations (Swerdon and Kountz, 1973). Anakeesta exposure can upset aquatic life through depression of stream water pH and increased concentrations of toxic mineral elements. BMPs were monitored because little information was available on the performance of these structures and efficiency results help in evaluating each structure's usefulness. Monitoring took place on a reconstruction project 1. 13 km (0.70 mi) in length on US 441 and included two tunnels through Chimney Tops Mountain and Morton Mountain. Reconstruction tasks included repairing the tunneling ( deepening the tunnels, installing rock bolts, placing concrete tunnel sidewalls), roadway excavation, grading, drainage, new road base and paving, constructing guard walls, and other work. This report summarizes the pre-, during and post-construction monitoring from May 2001 through September 2002. During pre- and post-construction periods, grab samples from Walker Camp Prong and the West Prong of the Little Pigeon River (WPLPR) were collected every two weeks at each of four stations: upstream and downstream of the two tunnel reconstruction sites. A passive sampling device was also located at each of the four stations, taking samples at various stage heights during high flows. During construction more frequent sampling occurred at these stations and around BMPs. The BMPs monitored were rock check dams, inlet protection for existing storm drains and disposal areas encapsulating spoil material. The rock check dams and inlet protection were installed to reduce suspended solids totals (by ponding water and allowing heavier particles to settle out). The check dams also reduced erosion by lowering the water's velocity and dissipating energy.