Combined Sewer Overflow Program
Combined sewer overflows (CSOs) occur during storm events when a mixture of wastewater and stormwater runoff overflows the combined sewer collection system before receiving treatment at a licensed wastewater treatment facility. These discharges of diluted untreated wastewater violate both State and Federal water pollution laws. Municipalities or Sewer Districts that have CSOs are required to license them with the Maine Department of Environmental Protection. License requirements direct these communities to evaluate their CSO problems and determine cost effective solutions to abate them.
Technical assistance and guidance on CSO abatement are provided to communities from the Bureau of Water Quality, Division of Water Quality Management.
- Michael Riley (207) 287-7766
Division of Water Quality Management
17 State House Station
Augusta, ME 04333-0017
- Annual CSO Progress Report (MS Excel), Instructions (PDF), Procedure to determine “Median Household Income (MHI)” (PDF)
- CSO Activity and Volumes (MS Excel)
- DEP-49-CSO Form for use with Dedicated CSO Primary Clarifiers PDF Version, MS Excel Version
- DEP-49-CSO Form for use with Non-Dedicated CSO Primary Clarifiers, PDF Version, MS Excel Version
CSO communities are required to submit an Annual CSO Progress Report for the previous calendar year to the Department by March 1st. The report also includes a spreadsheet listing of all CSO Activities and Volumes. This information is valuable to the State in determining CSO abatement to date, the extent of the current CSO problem, and the future needs of CSO communities.
Some communities in Maine have constructed primary bypasses of their secondary treatment process to treat all or a portion of their CSO flows. Under wet weather conditions, these facilities are licensed to treat the combined wastewater to primary standards before discharging. Along with the normal monthly license reporting requirements, these facilities must also report bypass flow activity to the Department on either the DEP-49-CSO Form For Use With Dedicated CSO Primary Clarifiers or the DEP-49-CSO Form For Use With Non-Dedicated CSO Primary Clarifiers.
- 38 MRSA §464-2-B (off-site, scan down page to "2-B"). Temporary removal of designated uses; use attainability analysis and creation of subcategory of uses for combined sewer overflows.
- Maine Combined Sewer Overflow 2021 Status Report [PDF]
- Maine Combined Sewer Overflow 2020 Status Report [PDF]
- Maine Combined Sewer Overflow 2019 Status Report [PDF]
- Combined Sewer Overflows in Maine (fact sheet)
- CSO Control Policy (federal)
- Program Guidance on Combined Sewer Overflow Facility Plans (Maine)
- Sewer Separation for Combined Sewer Systems