 WSSC connected its trunk sewers near Washington, DC into the Blue Plains system beginning in the 1930s, as the treatment plant began operation.The commission built its first sewage treatment plant in Bladensburg in the 1940s; in the 1950s this plant was closed as additional connections were made to the Blue Plains system.Most of the WSSC sewers in Montgomery County are now served by the Blue Plains plant, except for the northern portion of the county, which is served by the Seneca plant (opened in the 1970s).