THE EFFECTS OF EXTREMELY HIGH DENSITY SEPTIC SYSTEMS ON SURFACE WATER QUALITY IN GWINNETT COUNTY, GEORGIA

Gwinnett County, Georgia, a suburb of the Metro-Atlanta area, experienced rapid residential growth in the 1970’s & 80’s, but was not matched by growth in infrastructure for residential waste treatment. The number of septic systems within the county grew to over 85,000 with a density of 487 septic systems per square mile. The EPA defines high density as 40 septic systems per square mile, thus the density of Gwinnett County is extremely high density. This extreme density has reduced the surface water quality for streams in the Yellow and Alcovy River basins within the county. It was found that with an average rainfall between 5 to 15 mm, flushing of the soil occurs and an increase in fecal coliform is recorded within surface waters in the septic dense areas. It was also observed that with an increase in rainfall there was an increase in biochemical oxygen demand, Nitrate, Cu, Mg, Mn, Cr, Ca, P, and Zn, also from this flushing effect. Surface water temperature increased when there was higher fecal coliform within the surface water. There was good correlation between mean annual rainfall and the mean annual fecal coliform for the Yellow and Alcovy river basins since 1970. Water quality data shows that areas of high density septic systems have affected the surface water quality in the streams of Gwinnett County, GA.