Multi-Sector General Permit Additional Implementation Measures (AIM) Data Download Summary

ECHO incorporates EPA's Multi-Sector General Permit (MSGP) Additional Implementation Measures (AIM) data in the Industrial Stormwater Facility Search. This dataset is updated quarterly. The data refresh date is indicated in the file name on the data download page.

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MSGP AIM Description 

The MSGP covers stormwater discharges associated with industrial activities where EPA is the permitting authority. This dataset provides data related to facilities that have triggered Additional Implementation Measures (AIM) as described in Part 5.2 of the 2021 MSGP. AIM is triggered by an exceedance of a benchmark monitoring parameter, which can occur from two "triggering events", either 1) an exceedance of the four-quarterly annual average for a parameter or 2) fewer than four quarterly samples if a single sample of the sum of any sample results within the sample year exceeds the benchmark threshold by more than four times the parameter (indicating that an exceedance of the annual average is certain).

There are three AIM levels: Level 1, Level 2, Level 3. All operators subject to benchmark monitoring requirements begin in baseline status at the start of their permit coverage. A triggering event occurring bumps the status of the facility up to the next AIM Level, unless an exception is claimed and/or approved. After a triggering event occurs, an operator must continue quarterly monitoring for the parameter(s) that caused the AIM triggering event at all affected discharge points, until four additional quarters of monitoring do not result in an exceedance triggering event. The MSGP AIM requirements create a sequential advancement through the AIM levels with clear "resetting" to baseline status if benchmark threshold responses are met within the required deadlines.

Guidance on the MSGP AIM Dataset 

The Multi-Sector General Permit Additional Implementation Measures is a comma - separated value (CSV) file labeled as "aim_triggering_events.csv". This file is packaged in a ZIP file and available on ECHO Data Downloads

General information including the NPDES ID, facility address, and EPA region are included in this dataset, as well as more granular data such as the monitoring period triggered start and end date, AIM level, discharge point, parameter, and threshold. 

Data is only available in areas where EPA is the permitting authority where the MSPG applies. 

Download File Structure 

ElementData TypeLength

Data Element Dictionary 

The following is a list of the data elements in this dataset. They are listed in column order (left to right).


The unique identifier for the Master General Permit for a General Permit Covered Facility.


The unique identifier for a permit.

Facility Name

The name of the supplemental location for the facility.

Facility Address 1

The street address of the facility.

Facility Address 2

The street address of the facility.

Facility City

A 60-character field that contains the name of the city in which the facility is located. 

Facility State

A two-character field that contains the state postal abbreviation for the state in which the facility is located.

Facility Zip Code

A 9-character field that contains the U.S. Postal Zone Improvement Plan (ZIP) code for the area in which the operator is located.


The EPA Region in which the facility is located.

Monitoring Period Triggered Start

The start date of the monitoring period during which the facility triggered the AIM Level indicated.

Monitoring Period Triggered End

The end date of the monitoring period during which the facility triggered the AIM Level indicated.

AIM Level

The current Level of Additional Implementation Measures (AIM) that the facility has triggered based on benchmark exceedances for a given discharge point and parameter. If the facility has an active exception, the AIM Level is set to Baseline.  

Discharge Point

The location where collected and concentrated stormwater flows are discharged from the facility such that the first receiving waterbody in which the discharge flows, either directly or through a separate storm sewer system, is a water of the U.S.


The parameter for which the facility must monitor to determine overall effectiveness of stormwater control measures in controlling pollutants in stormwater discharge.


The threshold is the numeric value above which represent a level of concern for a specific parameter.


Effluent limits based on Effluent Guidelines.

Annual Average

Calculated by adding all reported monitoring results collected in the sampling year and dividing by four. For more information, refer to Part 5.2.2 of the 2021 MSGP.

Active Exception

Lists whether the facility has claimed an exception as listed in Part 5.2.6 of the 2021 MSGP, and is not subject to AIM corrective actions. If the facility has an active exception, the AIM Level is set to Baseline for the discharge point and parameter.