SEDIMENT TRANSPORT THROUGH THE KNOX AQUIFER AT BOOTLEGGER SPRING, OAK RIDGE, TENNESSEE

Practices to mitigate the impacts of construction sites on water quality are focused on measures to control sediment in stormwater runoff. If no sinkholes are evident on the site, the controls are usually established downslope of the disturbed area and losses of sediment through the subsurface are not considered in erosion control plans. Sediment transport through swallets that form during or after construction activities is often not noticed unless sediment discharges through a spring that is used for water supply or is designated as habitat for sensitive species. Bootlegger Spring in the University of Tennessee Forest Resources AgResearch and Education Center in Oak Ridge has been impacted by siltation due to swallet formation in borrow pits on Chestnut Ridge on at least two occasions. Both in 1995, and again in 2014, tracing with fluorescent dye was used to confirm the source of sediment in the spring. The most recent tracing investigation was conducted from November 16, 2014 through November 19, 2014 during and immediately following a rain event. In addition to dye concentrations, spring stage, temperature, specific conductance, and turbidity were monitored. Turbidity was correlated with suspended solids analyses and used to estimate the total suspended load discharged through the spring. During this moderate rainfall event of about 3 centimeters in approximately 24 hours, some 200 kilograms of sediment passed through the spring. For larger rainfall events such as the two during October 6 through October, 15, 2014, the sediment load through the spring likely exceeds a ton of sediment per acre disturbed.