The Wet Weather Expansion Project (WWEP) is a component of the larger Clean Water Project (CWP) tasked with increasing the wet weather treatment capacity of The Metropolitan District’s (MDC) Hartford Water Pollution Control Facility (HWPCF). At the conclusion of the CWP, which addresses a federal consent decree and a Connecticut DEEP consent order to achieve federal Clean Water Act goals, the HWPCF’s peak wet weather treatment capacity will have increased from 150 to 415 megaliters per day (MLD) (40 to 110 mgd). The WWEP includes construction of innovative dual-use primary clarifiers with the ability to progressively initiate chemically-enhanced primary treatment (CEPT) in conventional primary clarifiers operating in a “dry weather” mode prior to CEPT. The MDC elected to complete a pilot demonstration of CEPT and high-rate disinfection (HRD) to generate and characterize chemical sludge and to provide a continuous source of CEPT effluent for subsequent disinfection testing. Pilot testing was also used to optimize the CEPT design by using wet weather influent to determine performance limits and refine design criteria for the coagulation and flocculation processes as well as demonstrate practical approaches to reduce chemical storage and delivery requirements. Results of special investigations used to identify design criteria for the full-scale CEPT process are presented.