Triple Bottom-Line Assessment of Alternatives for a Large-Diameter Transmission Main from a Congested 280-MGD Water Treatment Plant Site

摘要

Due to a series of high impact failures of prestressed concrete cylinder pipe (PCCP) in its water distribution system, the Washington Suburban Sanitary Commission (WSSC) has developed an aggressive program of field condition assessment to identify pipes in danger of failure. However, it found that it was not able to apply these techniques to the two parallel PCCP pipes located within its primary water treatment facility, the Potomac Water Filtration Plant, because the flow demands would not permit the existing 78-inch line to be removed from service for condition assessment. A Business Case evaluation was convened to develop and compare alternatives for installing a full capacity redundant transmission line to carry finished water from the plant, which was complicated by the severely congested nature of the facility, which had grown and been added to multiple times in its history. The alternatives were evaluated using Triple Bottom Line techniques for cost, societal and environmental impacts. Alternatives considered included a tunnel, multiple near surface alignments, and pump station reconfigurations, plus the "No Action" and "Status Quo" options.