The Impact of Rainfall on Flows and Loadings at Georgia’s Wastewater Treatment Plants

Inflow and Infiltration (I/I) is extraneous water that enters a sewage treatment plant via groundwater infiltration or direct stormwater entry into sewers. This study is an attempt to quantify I/I impacts based on an assessment of influent and effluent data from twenty-four wastewater treatment plants (WWTPs) in Georgia with design capacities of 37,850 m/d (10-mgd) or greater. Twelve-months of operating data from the 2003 calendar year were evaluated. The objectives of the study were to determine the effect of rainfall intensity on the volumetric flow rate to each WWTP; and the relationship between flow rate and the influent biochemical oxygen demand (BOD) and influent Total Suspended Solids (TSS) concentrations. Moderate to strong correlations were observed between rainfall intensity and volumetric flow rate; and volumetric flow rate and influent BOD and TSS concentrations. Weak correlations were observed for some of the relationships when applied to the complete data set; however, stronger correlations were achieved by performing statistical analyses of variance and pooling subsets of the data. Peaking factors were similar to those reported in the literature.