WATERSHED AND WATER QUALITY MODELING TO SUPPORT WATERSHED PROTECTION IN THE PUMPKINVINE CREEK WATERSHED, GEORGIA

This report presents the development and application of a linked watershed and water quality model to the Pumpkinvine Creek watershed, which spans Paulding, Bartow and Cobb Counties, Georgia. This watershed is located west of Atlanta and is beginning to see increased development as urban sprawl marches west from the city. This study was initiated by Paulding County in support of a new NPDES permit request for an expanded wastewater treatment facility that is needed in support of the increasing development in the area. Such studies as the one described in this paper are required by the Georgia Environmental Protection Division (EPD). This paper summarizes the modeling portion of a larger watershed protection and implementation plan conducted by Welker & Associates.The LTI-modified version of the Generalized Watershed Loading Function (GWLF) model was applied to estimate watershed loadings of sediment, nitrogen and phosphorus, while a simple stream transport model based on the Water Quality Analysis Simulation Program (WASP), was used for water quality modeling. These models were successfully calibrated to current conditions and then applied for future (2011) conditions to project loads and concentrations of solids, phosphorus, and nitrogen. The future scenario considers changes in land cover (a 36% increase in the amount of developed land), point source discharges (increased discharges from existing facilities and the construction of the new Pumpkinvine Creek facility) and septic systems (a slight decrease in the number of systems) within the study area. Sediment controls that reduce erosion from all construction sites in the study area by 10% beyond current levels are also simulated in the future scenario.The value of this study is that it not only meets State requirements for a new permit, but also that it helps to characterize current water quality conditions within the study area and identify areas with impacted water quality. This investigation identified three locations in the watershed where the instream water quality is impacted by high fecal coliform and nutrients, indicating a potential raw sewage leak. Furthermore, the requirement of such a study makes the County take a close look at its future land use plan.