Bi-County Water Supply Main Alignment Study

Fact Sheet


  • In September 2004, WSSC Commissioners approved a $9.9 million contract to Black and Veatch of Gaithersburg, Maryland to begin planning and design work on a Bi-County water supply main project.
  • The contract includes 30 percent minority business participation from the following firms: Peer Consultants, P.C.; McKissack & McKissack, Inc.; A. Morton Thomas & Associates, Inc.; T.L. Brown Associates, Inc.; and Dacco Sci, Inc.
  • The Bi-County water supply main is approximately 5.5 miles of 84-inch diameter water supply main connecting an existing 96-inch diameter main at the intersection of I-270 and Tuckerman Lane to another existing 96-inch diameter main in the area where Rock Creek crosses I-495 in Montgomery County.
  • The new supply main will help transport clean drinking water from WSSC's Potomac Water Filtration Plant (WFP) to eastern Montgomery County and most of Prince George's County. The Potomac plant produces approximately three-quarters of the water used by WSSC's 1.6 million customers.
  • The new supply main will alleviate capacity limitations from an existing 54-inch diameter main that delivers water from the Potomac WFP to the existing 96-inch diameter main at Rock Creek and I-495.
  • The Bi-County water supply main project was first identified in the late 1960's. Since that time, WSSC and Montgomery and Prince George's County planning agencies have been monitoring water system performance, water pressure, demand and growth patterns to determine an appropriate project implementation.
  • With this project, WSSC is not seeking additional water withdrawals from the Potomac river.
  • The planning phase, which should start in Fall 2004 and be complete in late 2005 / early 2006, will address possible alignments, construction methods, costs, community/historical/environmental impacts and extensive community outreach.


  • Providing a constant, reliable supply of safe, clean water to our customers is our number one priority.
  • Based on current demands and projections, the need for the Bi-County water supply main becomes evident by the end of this decade.
  • The Bi-County water supply main will allow WSSC to continue to meet future water supply needs and expectations of our customers, and provide constant, reliable water for daily use and fire protection during peak use periods, droughts and emergencies such as Hurricane Isabel. Additionally, the supply main will provide water system redundancy in the event of an emergency or maintenance-related problem (water main break).
  • While a valuable long-term initiative, water conservation practices are not expected to reduce the need for this project. Additionally, planned upgrades to WSSC's Potomac and Patuxent WFPs will not reduce the need for the Bi-County water supply main project.
  • Short-term impacts of not having this project include low water pressure -- below 30 pounds per square inch (psi) -- and loss of water storage for fire fighting and emergency supply in the Silver Spring area. This will have an impact on WSSC's ability to provide water at sufficient pressure for fire protection.
  • Below 30 psi, customers may notice a decrease in water system performance when using multiple plumbing fixtures simultaneously. Low pressure also presents the possibility that unexpectedly high flows (such as flow from an open hydrant) will result in complete loss of water.
  • Longer-term impacts may include system-wide mandatory water restrictions during high demand and drought conditions, reduced ability to supply water to Prince George's County during emergencies and development restrictions throughout much of Montgomery and Prince George's Counties.


  • WSSC plans to use public meetings, briefings, its website, quarterly customer bill inserts, fact sheets and media communications to inform and update officials, customers and other stakeholders about the project.
  • The preferred Bi-County water supply main alignment and construction method will be selected with input from community, environmental and county officials. Input will be solicited from all interested parties on an ongoing basis.
  • Following planning phase completion in late 2005 / early 2006, WSSC will seek concurrence of Montgomery and Prince George's County Councils on the preferred alignment and construction methods (i.e. tunneling and/or open cut). Upon approval from both Councils, WSSC will begin design work on the selected alternative.
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