The Metropolitan St. Louis Sewer District (MSD) was formed on February 9, 1954, when voters approved the Plan of the District. MSD started operation and maintenance activities in January 1956 in an area roughly composed of the City of St. Louis and the portion of St. Louis County east of Interstate 270. Most of the remainder of St. Louis County was annexed by MSD in 1977. MSD is a public agency and is the only special district in Missouri created under a provision of the State Constitution. MSD's responsibilities include the interception, collection and treatment of wastewater, as well as stormwater management. MSD's current boundaries cover 525 square miles and encompass all of St. Louis City and approximately 90 percent of St. Louis County. MSD serves a population of approximately 1.3 million and has over 425,000 single-family residential, multi-family residential and commercial/industrial accounts. MSD currently operates seven wastewater treatment facilities, treating a combined average of 370 million gallons of sewage per day. MSD operates and maintains 9,790 miles of sewers. The age of sewers maintained by MSD ranges in age from less than a year old to 150 years old.