The City of Collinsville operates a wastewater treatment plant at 300 Simpson Street that is staffed 24 hours per day by Illinois State Licensed Wastewater Treatment Plant Operators. The plant's design capacity is rated at 5.85 million gallons per day. The average daily flow in 2013 was approximately 3.93 million gallons per day (MGD) with a total treatment of 1.44 billion gallons of wastewater. Originally constructed in 1972, the plant has gone through many extensive upgrades and improvements. The most recent improvement, completed in 2012, was an upgrade to increase the plant's capacity to the current rating of 5.85 MGD from 3.5 MGD. It remains a state-of-the-art facility, ensuring full compliance with the Environmental Protection Agency (EPA) regulations and protecting the public's health and environment. The Collinsville Wastewater Treatment Plant was the recipient of the “Illinois Wastewater Treatment Plant of The Year” in 1997. In addition to the processing and treatment of Collinsville's wastewater, the wastewater plant also treats the wastewater from the Village of Maryville and Mounds Public Water District.
A staff of seven full time employees are responsible for maintaining the City's Wastewater Collections System. Duties include cleaning and inspection of sewer mains, repairs to the system, tapping new services into existing sewer mains and support of the wastewater plant operations. The sewer collection system is comprised of 110 miles of sewer mains, approximately 1,200 man holes and 13 lift stations. City residence are responsible for the service lines from the building to the main. In the event of a sewer backup, residents are encouraged to immediately contact the Wastewater Department at the emergency contact number below.