An investigation of low flow and stormwater runoff bacteria content from rural and urban areas was conducted over a two and a half year period. Data were obtained from total coliform, fecal coliform, fecal streptococci, Salmonella sp., Pseudomonas sp., and Staphylococcus sp. for comparison to densities in known polluted sources such as secondary treated chlorinated municipal wastewater. The usefulness of the currently employed indicator groups of bacteria was evaluated with respect to the accompanying densities of pathogens. The hygienic quality of water when compared to new bacteriological water quality standards for contact and noncontact recreation was considered. Settling of stormwater suspended solids was closely associated with bacterial reductions in the water column. The most useful indicators of pathogen content in stormwater runoff were fecal coliforms. Total coliforms and fecal streptococci were poor indicators of pathogenic bacteria densities. Chlorine and ozone doses for disinfection of stormwater containing high (approximately 200 mg/l) suspended solids may exceed 8 mg/l and 32 mg/l, respectively. Regrowth of total coliforms occurs following disinfection. Indicator group densities in urban stormwater runoff can easily exceed rural runoff densities with continual increases occurring throughout a storm event. Fecal coliform densities exceeded 2,000/100ml in 13 to 24 monitored hydrographs and exceeded 200/100ml in 22 of those hydrographs. Fecal coliforms and fecal streptococci yielded the highest correlations with the physical factors, flow, suspended solids, and turbidity.

Grant no. R802433. Includes bibliographical references (pages 79-82).