The development of wastewater treatment facilities to meet effluent standards during peak flow conditions has been neglected in the past. Facilities are frequently designed to accommodate diurnal flow variations on the basis of elimination of significant amounts of infiltration and inflow which would otherwise cause large peak flows. This often proves disappointing when the projected reductions in infiltration and inflow are not realized;Peak flows from sanitary sewer systems are handled traditionally by building flow equalization facilities or by oversizing the conventional treatment facilities. It was felt that a potential alternative to these practices would be the use of split treatment--diverting excess flows to less flow-sensitive treatment processes;This study sought to construct a framework by which split treatment could be considered and evaluated. High rate filtration was judged to be a process with much potential for use in split treatment. Various flow schemes using high rate filtration were examined with regard to both cost and treatment performance. This was done from both a general point of view as well as in a site-specific case study involving Ames, Iowa. Because of the many complex interrelationships involved in treatment performance, a simple computer model was written to aid in the feasibility analysis by simulating the quality of effluent produced by conventional and split treatment systems. Simplified cost formulations were developed using the CAPDET model developed by the Environmental Protection Agency;A conclusion reached in the evaluation was that split treatment using high rate filtration offers a small but significant cost savings over conventional treatment flow schemes and is most feasible when considered in conjunction with plants incorporating primary or secondary effluent filtration in which the filters can be used in a dual function mode. Under proper conditions, split treatment can be accomplished without violating effluent concentration standards for BOD and suspended solids.