Monitoring the Effects of Highway Construction in the Sedgefield Lakes Watershed, September 4, 2007

摘要

This report summarizes the results of a water quality monitoring project to document the effects of the construction of the I40 bypass around Greensboro on the water quality of residential lakes in the Sedgefield and Kings Mill communities. This project was a continuation of the monitoring at 6 locations begun during HWY 2004- 26. At each monitoring site, discharge was monitored continuously and samples of stream discharge collected on a flow-proportional basis throughout the project. All samples were analyzed for total suspended solids (TSS), total solids, and turbidity. A recording raingage was also maintained for all of the monitoring period in the Sedgefield lakes watershed and in-situ measurements of temperature, dissolved oxygen, conductivity, and pH were made periodically at each site. Monitoring data at all sites documented continued elevated sediment export and turbidity during the construction period as compared to the pre-construction period. The greatest increase in sediment export and turbidity occurred at the upstream site on the Tilly tributary. For this site, which was located just downstream of the highway corridor, a large percentage of the sediment load during the entire construction period was associated with two tropical storm systems that occurred in September 2004. At this time the highway was particularly susceptible to erosion because more than 20 ft of fill had recently been added to bring the road surface to near grade and the sideslopes were not vegetated yet. Increases in sediment loading and turbidity at the other sites during highway construction were less severe and more like what would be expected. Mean turbidity levels during construction at all sites downstream of highway construction were greater than 50 NTU. Limited monitoring of temperature, specific conductance, DO, and pH for all six sites showed that highway construction had little, if any, effect on these parameters, except possibly temperature, which appeared to increase at Tilly-up and Kings Mill-down, but this was not confirmed at the other sites. There were not enough samples analyzed to determine if the highway construction had any effect on nitrogen and phosphorus concentrations in discharge.