The first National Water Quality Sampling Station is put into operation on the Potomac at Great Falls. MD and VA sign the Potomac River Compact of 1958, and establish the Potomac River Fisheries Commission. DC and Fairfax County, VA, sign an agreement for Blue Plains to treat a part of the county's wastes. Secondary treatment is added at Blue Plains. The Metropolitan Washington Regional Sanitary Advisory Board is established.
Work begins on a plan to separate DC's combined sanitary and stormwater sewers.
1961 DC installs the first fully automatic stream sampling and recording device on the Potomac. The Potomac River Fisheries Commission begins operations. A comprehensive metro Washington area sewage disposal report is issued. The ACE publishes a comprehensive plan of development for the Potomac, which calls for 16 major dams. The Potomac Interceptor, tying northern Fairfax County and parts of Loudon County, VA, and Montgomery County, MD, to the DC Blue Plains plant, is christened with its first sewage flows.