EPA's National Combined Sewer Overflow Inventory Summary
The Enforcement and Compliance History Online (ECHO) system incorporates combined sewer overflow (CSO) outfall location data from EPA's Integrated Compliance Information System National Pollutant Discharge Elimination System (ICIS - NPDES) as well as information on certain closed CSOs that are not in ICIS - NPDES.
The National Combined Sewer Overflow Inventory was first published to ECHO in May 2023 to reflect the most current inventory of CSOs across the United States. These data are updated weekly, as described on About the Data. Please also see the Known Data Problems page for known data sharing issues that affect data completeness or accuracy for this national inventory. You can also use the National Combined Sewer Overflow Inventory Service to map these outfalls.
On this page:
- Guidance on the National Combined Sewer Overflow Inventory
- Download File Structure
- Data Element Dictionary
ICIS - NPDES is an information management system maintained by the EPA Office of Enforcement and Compliance Assurance to track permit compliance and enforcement status of facilities regulated by the National Pollutant Discharge Elimination System (NPDES) under the Clean Water Act (CWA). ICIS - NPDES is designed to support the NPDES program at the state, regional, and national levels.
Guidance on the National Combined Sewer Overflow Inventory
The National Combined Sewer Overflow Inventory is a comma - separated value (CSV) file labeled as "ALL_CSO_DOWNLOADS.csv". This file is packaged in a ZIP file and available on ECHO Data Downloads.
Please note that state are actively working to update and correct data in ICIS - NPDES. EPA estimates that approximately 90% of CSOs are included in the National Combined Sewer Overflow Inventory (as of September 2023).
Some states have elected to manage closed CSOs outside of ICIS - NPDES. These are marked as such in the National Combined Sewer Overflow Inventory. EPA's Office of Wastewater Management periodically verifies these outfalls with state Water Data Stewards and updates the inventory as appropriate. The last update was September 2023.
Missing attribute data (e.g., CSO latitude and longitude data) means that the authorized state has not yet entered these data into ICIS - NPDES or that the authorized state has elected to manage the closed CSO outside of ICIS - NPDES.
Download File Structure
Data Element Dictionary
The following is a list of the data elements in the National Combined Sewer Overflow Inventory. They are listed in column order (left to right).
This is the concatenation of the NPDES_ID and the PERM_FEATURE_NMBR for the CSO. For CSOs that do not have a PERM_FEATURE_NMBR (i.e., they are managed outside of ICIS - NPDES), this field uses the following convention: [NPDES_ID] - [NO_PFID].
This NPDES number may reflect the permit associated with the CSOs. This element is also identified as EXTERNAL_PERMIT_NMBR in other ECHO download files.
This is the state that issued the NPDES permit associated with the CSOs.
A three - character code indicating the type of organization issuing or granting a permit. All CSOs are permitted by authorized states except for DC, MA, NH, and PR.
- CSO permitted by authorized state: AGENCY_TYPE_CODE = "ST6"
- CSO permitted by U.S. EPA: AGENCY_TYPE_CODE = "EP6"
The number assigned by the Facility Registry Service (FRS) that is used to associate facility records from multiple environmental database systems that are known or believed to represent the same facility.
An 80 - character field that contains the name of the facility.
The street address of the facility.
The name of the supplemental location for the facility.
A 60 - character field that contains the name of the city that is permitted for the CSO.
A five - digit field that contains the FIPS county code in which the permitted facility is located, used in conjunction with the facility state code. A list of codes and descriptions can be found at 2017 FIPS Codes for Counties.
A two - character field that contains the state postal abbreviation for the state in which the permitted facility is located.
A two - character field that contains the EPA Region in which the permitted facility is located.
A 3 - character code indicating ownership type of the facility. The values for permitted facilities with CSOs are:
- CTG - Municipality
- MWD - Municipal or Water District
The horizontal (latitude) of the permitted facility as maintained in ICIS-NPDES.
The vertical (longitude) of the permitted facility as maintained in ICIS-NPDES.
This is the name of the facility having the NPDES permit to discharge pollutants in the water of the United States.
The version of the permit when a modification or reissuance is applied to the permit. A "0" indicates the most recent or current permit version.
Text description for PERMIT_TYPE_CODE. Valid code values and descriptions are below. The values for permitted facilities with CSOs are:
- NPD - NPDES Individual Permit
- UFT - Unpermitted Facility
The date the permit became effective or is scheduled to become effective (MM/DD/YYYY).
The date the permit expired or is scheduled to expire (MM/DD/YYYY).
ICIS - NPDES designates a permit as Effective (EFF), Administratively Continued (ADC), Expired (EXP), Not Needed (NON), Pending (PND), Retired (RET), or Terminated (TRM). Active facilities are those currently in operation (indicated by any status code except NON or TRM).
A 10 - character code indicating if the permitted facility is either a POTW, non-POTW, or federal entity.
A 1 - character code that designates the facility as a major discharger (M), non - major discharger (N), or that no data is available (null values), such as for unpermitted facilities.
Under the Clean Water Act, a major facility is any NPDES facility or actively classified as such by the regional administrator, or in the case of approved state programs, the regional administrator in conjunction with the state director. Major municipal dischargers include all facilities with design flows of greater than one million gallons per day and facilities with EPA/state approved industrial pretreatment programs. Major industrial facilities are determined based on specific ratings criteria developed by EPA/state. Non-major facilities are those not designated as major.
This is a Y/N field that identifies if ICIS - NPDES is configured to track any violations associated with the permitted facility.
This is the latest date when the PERMIT_TRACKING was created or updated by the authorized state.
This is a Y/N field that identifies if ICIS - NPDES is configured to track DMR non-receipt violations associated with the permitted facility.
This is the latest date when the DMR_TRACKING was created or updated by the authorized state.
This is the design flow (in million gallons per day) for the permitted facility associated with CSO.
This is the average flow (in million gallons per day) for the permitted facility associated with CSO.
This is the identifier for the CSO and is unique for a given NPDES_ID.
This is additional text that describes the CSO location or other attributes.
The horizontal (latitude) position coordinate for the CSO in units of decimal degrees.
The vertical (longitude) position coordinate for the CSO in units of decimal degrees.
This is the ICIS - NPDES Characteristic code that the authorized state used to describe the CSO. EPA identifies CSOs for the National Combined Sewer Overflow Inventory when they have one of the following Characteristic codes in ICIS - NPDES:
- CSO - Untreated CSO: A combined sewer overflow is a discharge from a combined sewer system at a point prior to the POTW Treatment Plant. CSOs consist of mixtures of domestic sewage, industrial and commercial wastewaters, and storm water runoff. CSOs are point sources that discharge to waters of the US and need to be tracked in ICIS - NPDES. For data entry purposes, if a CSO does not meet the definition of treated CSO (TCS) or closed CSO (CLS), then it should be classified as a CSO. The majority of CSOs will have the characteristic code CSO.
- TCS - Treated CSO: Treated CSOs are outfalls that receive the minimum CSO treatment described in the CSO Policy, which consists of: primary clarification, solids and floatables disposal, and disinfection, where necessary (see 59 Fed. Reg. 18692-3.II.C.4.a).
- CLS - Closed CSO: Closed CSOs are former outfalls that have since been removed or plugged such that they cannot discharge combined sewage into the environment. Outfalls can be marked with multiple other codes if a closed CSO needs to also be recorded because of other discharges (e.g., SW - MS4 outfall) in addition to the CLS characteristic code.
The full set of ICIS-NPDES Characteristic codes are provided below:
NPDES Characteristic Codes Code Descriptions BIO Sludge/Biosolids CCW Contact Cooling Water CLB Closed Bypass CLS Closed CSO CSO Untreated CSO DEW Dewatering DSW Domestic (Sanitary) Wastewater GRW Groundwater INT Intermittent Flows MNR Manure MOB Mobile NCW Noncontact Cooling Water NDP Non - Domestic Process Water NPD Nonprocess PRC Percolation Pond SW Storm Water TCS Treated CSO TRB Treated Bypass UTB Untreated Bypass WEL Monitoring Well
This is the type for the permitted feature. This value is set to "External Outfall" (EXO) for all CSOs.
The state's name for the water body into which the effluent is discharged for a CSO.
This is the name of the water body as determined by EPA based on the facility or CSO latitude and longitude data and a spatial analysis using the United States Geographical Society's (USGS) National Hydrography Dataset (NHD).
This is the REACH code associated with the CSO. This is the unique 14 - digit code that identifies a continuous piece of surface water with similar hydrologic characteristics. It is assigned to each receiving water body by the United States Geographical Society's (USGS) National Hydrography Dataset (NHD).
This is a Yes/No field that identifies if the CSO is managed in ICIS - NPDES. The CSOs that are marked with "No" (i.e., not managed in ICIS - NPDES) are periodically reviewed by EPA's Office of Wastewater Management.