A Capital Cost Allocation Model for Multi-Jurisdictional Use Sewers

The District of Columbia Water and Sewer Authority (DC Water) serves the District and a number of suburban jurisdictions. Sewers within the District that serve the suburbs are termed “multi-jurisdictional use” sewers. DC Water recently developed a method to allocate capital costs among jurisdictions for rehabilitating multi-jurisdictional sewers as a consequence of assessing the restoration and renewal needs of its entire sewer system. DC Water's goals for the envisioned cost allocation method were that it be technically sound, equitable, and conform to existing agreements. A working group evaluated both the Manning equation and a field-verified and calibrated computer model of the sewer system as potential tools in devising a cost allocation method that would best achieve these goals. The computer modeling-based method produced more convincing results, most likely due to the authentic pipe and sewershed data built into the model. This method, its application to specific sewers, and relevance to other sewer utilities are reviewed.