Impact of land use on fecal coliform levels in surface waters of Fairfax County, Virginia

Elevated levels of fecal coliforms in the surface waters for Fairfax County have been of concern because of the inherent public health issues. This dissertation analyzed the Fairfax County Health Department monitoring data from 1986 through 1999 and developed statistical models to explore the impact of land use on fecal coliform levels. The explanatory variables included the water chemistry data, impervious surface, the NRCS curve number, drainage area, precipitation, stream flow and land use. Individual regression models for each watershed were developed to investigate the geographic variability in the models. A regional model was developed using the land use data from the Northern Virginia Regional Commission for 1997, and spanned a five year period (1995 through 1999). The results of this regional model indicate that impervious surface is the major explanatory variable, contributing 40% of the variability in fecal coliform levels in the model (R2 = 0.6585). Impervious surface is highly correlated with land use, and is positively correlated with High Density Residential (R2 = 0.6108) and negatively correlated with Open Spaces (R2 = -0.3538) and Low Density Residential (R2 = -0.2851). Impervious surface is an indicator of conditions that result in higher levels of fecal coliform levels. With increased urban land use, areas of land that can filter runoff from precipitation events are severely reduced.