WSSC has over 150 miles of 36-inch and larger Prestressed Concrete Cylinder Pipes (PCCP) water transmission pipelines and is proposing new requirements in its Pipeline Design Manual – originally adopted in 2008 – concerning PCCP and cast iron water pipelines among other matters.
The Washington Suburban Sanitary Commission (WSSC), the eighth largest water and sewer utility in the United States, serves nearly 2 million customers in both Montgomery and Prince George’s Counties. WSSC has over 150 miles of 36-inch and larger Prestressed Concrete Cylinder Pipes (PCCP) water transmission pipelines. PCCP was once the most commonly used material for large diameter water pipelines nationwide. Some of these pipes, however, were produced with brittle reinforcements and explosive eruptions have occurred. Based on results from several studies, WSSC has determined that catastrophic failure of 36-inch and larger PCCP pipelines can extend in excess of 80 feet beyond the pipeline. Therefore, WSSC proposes new requirements in its Pipeline Design Manual – originally adopted in 2008 – concerning PCCP and cast iron water pipelines among other matters.
WSSC’s proposed rule regarding horizontal separation from large diameter (36-inch diameter or larger) water pipelines was previously 25 feet in each direction from the center of the pipe. The proposed rule, which is currently being implemented, states that the minimum setback in each direction from the outer side of the pipe in question is 80 feet from a building or dwelling.
A couple of items to note are:
The 80-foot right of way is a no-building zone, meaning no building or dwelling can be built in the specified area. With regards to WSSC compromising on the 80-foot setbacks, the builder must demonstrate with adequate documentation the ability to mitigate potential damage through use of structural enhancements, building material selections rated to withstand a potential pipeline failure or have their site-specific engineering solutions approved by WSSC. As of yet, they cannot or will not define suitable structural enhancements or what adequate documentation is needed to prove safety and to reduce the horizontal separation.
As a reference, please refer to the modified Common Design Guidelines document that can be found on the WSSC website. The latest pipeline changes, as they relate to the required minimum horizontal separation, or setback, between large diameter water mains and structures, are notated in red in Part Three, Section 3: Pipeline Crossings and Clearances (pages C-3.2 – C-3.3).
Soltesz and other industry representatives continue to communicate with WSSC. For example, Soltesz met with WSSC’s General Counsel’s Office, including the Office of the General Manager, in November of 2011. During that meeting, WSSC shed light on several of their proposed design manual modifications, including the topic of 80-foot setbacks. WSSC also discussed their Bi-County Working Group, who is working to gather input from industry leaders and ensuring their process of rule-making is more transparent.
To date, decisions are still underway for additional revisions to be made to the manual. WSSC has put the finalization of the publication on hold while these updates and other design criteria are still pending. Soltesz continues to monitor the latest status as the manual progresses and more information is made public.