Impact of Groundwater Seepage Flow on DO TMDL Development

It is evident that numerous surface water bodies directly intersect with the groundwater table in Central and South Florida. Therefore, strong interaction of surface water and groundwater occurs and groundwater seepage can become an important component in terms of flow budget and water quality.To quantify the impact of groundwater seepage flow on Dissolved Oxygen (DO) TMDL development, a recently calibrated and validated HSPF (Hydrological Simulation Program in FORTRAN, Bicknell et al, 2005) water quality model and a newly developed EFDC (Environmental Fluid Dynamics Code, Hamrick, 1992) water quality model were used for further analyses. A series of ensitivity analyses were conducted to evaluate how typical variations of groundwater seepage flow, DO concentration, and temperature affect the DO concentration of a surface water body.Model simulations show that contrary to one's intuition, low DO concentrations associated with groundwater seepage flow do not always reduce, but may actually increase, the DO oncentration of a surface water body with increase of groundwater seepage volume.