Abstract |
Section 303(d) of the Federal Clean Water Act requires states to identify waterbodies that are not meeting water quality standards and to develop total maximum daily pollutant loads for those waterbodies. A total maximum daily load (TMDL) is the amount of a pollutant that a waterbody can assimilate without exceeding the established water quality standards for that pollutant. Through a TMDL, pollutant loads can be allocated to point sources and nonpoint sources discharging to the waterbody. The study area for this project is the Ten Mile Creek watershed in central Arkansas. The study area is part of the Arkansas Department of Environmental Quality (ADEQ) Planning Segment 4E and is located within the Arkansas River Valley ecoregion. Land use in the study area is about 55% pasture and 44% forest. Ten Mile Creek is included on the draft 2004 Arkansas 303(d) list as not supporting the aquatic life use due to exceedances of numeric criteria for turbidity. The applicable numeric criteria for turbidity for this reach are 21 NTU (primary value) and 40 NTU (storm-flow value). ADEQ historical water quality data were available for one location on Ten Mile Creek. These data were analyzed for long term trends, seasonal patterns, relationships between concentration and stream flow, and relationships between turbidity and total suspended solids (TSS). These analyses showed no significant seasonal pattern or relationship between concentration and stream flow, but higher turbidity levels tended to correspond with higher TSS values. This TMDL was expressed using TSS as a surrogate for turbidity because turbidity cannot be expressed as a mass load. Regressions between TSS and turbidity were developed for both base flow and storm-flow, but the base flow regression was not used to set a target TSS concentration because the correlation was too low. The storm-flow regression equation was used with the numeric turbidity criteria to develop target TSS concentrations of 10 mg/L (corresponding to the primary turbidity criterion of 21 NTU) and 19 mg/L (corresponding to the storm-flow turbidity criterion of 40 NTU). |