SEWER DESIGN PRACTICES – ARE WE USING THE RIGHT CRITERIA OR CREATING MORE SSOS?

Many sewer agencies and consulting engineers are using older “tried and true” formulas, graphs, and guidelines for sewer hydraulic design. With increasing attention to reduction and elimination of sanitary sewer overflows (SSOs), many of which are attributable to inadequate sewer system capacity, it is time to re-examine our basis of sewer hydraulic design. Are references like the 10 States Standards, individual state sewer design criteria, and sewer agency in-house design criteria still relevant?The wastewater industry has been performing detailed infiltration/inflow studies for over 25 years. What has been learned can be applied for creating better sanitary sewer design criteria to reduce the future occurrence of SSOs. In this paper, actual data from I/I studies for 20 wastewater agencies in six states (Kansas, Kentucky, Minnesota, Missouri, Ohio, and Texas) are presented and compared, and guidelines for appropriate sewer design criteria are developed.