About Loading Tool Data

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 Data Sources for the Water Pollutant Loading Tool

The Loading Tool uses discharge monitoring and permit data from Integrated Compliance Information System - National Pollutant Discharge Elimination System (ICIS-NPDES). ICIS-NPDES is a database that automates entering, updating, and retrieving discharge monitoring and permit data.

Dischargers submit discharge monitoring data to their permitting authority using discharge monitoring report (DMR) forms. The permitting authority then enters these data into ICIS-NPDES and checks whether the discharger is in compliance with the NPDES permit requirements. Facilities report pollutant discharge monitoring data in their DMR as mass-based quantities (e.g., pounds per day) and/or concentrations (e.g., mg/L); however, discharges are reported using a wide variety of units.

Permit data include NPDES permit limits for water quality parameters (e.g., dissolved oxygen and temperature), specific chemicals (e.g., phenol), bulk parameters (e.g., biochemical oxygen demand), and flow. The permitting authority enters these data into ICIS-NPDES. ICIS-NPDES also include information on the facility’s permit requirements, such as monitoring frequency. The ICIS-NPDES database:

  • Is national in scope, including data from all 50 states and 21 U.S. territories and tribes;
  • Contains discharge data that facilities determine through effluent chemical analyses and metered flow; and
  • Include information for facilities in all point source categories that discharge directly to receiving streams.

The tool also includes wastewater pollutant discharge data from EPA's Toxics Release Inventory (TRI). Data are available for the years since 2007. Users can search TRI data to find the facilities with the largest pollutant discharges to surface waters or sewage treatment plants (a.k.a. Publicly-Owned Treatment Works or POTWs). Users can also compare the DMR data search results against TRI data search. The tool clearly labels the source of data when displaying search results but does not mix TRI or DMR data when calculating pollutant discharges. See the Basics of TRI Reporting and Factors to Consider When Using TRI Data for more information.

Other data sources used by the Loading Tool include:


Water Pollutant Loading Tool Database Sources and Updates
Data SourceContactProcessUpdate ScheduleLast Update
Integrated Compliance Information System - National Pollutant Discharge Elimination System (ICIS-NPDES)EPA/Office of Enforcement and Compliance Assurance (OECA)Prior to 2014, EPA manually pulled data from ICIS-NPDES on an annual basis and made monthly error correction updates. In August 2014, EPA began using a continuous process to capture changes in ICIS-NPDES (inserts, updates, deletes). EPA also automatically calculates pollutant discharge estimates on a weekly schedule.WeeklyChanges in ICIS-NPDES data are captured continuously and compiled. The Loading Tool processes the data weekly and makes these data and the related pollutant loading estimates available.
Substance Registry Service (SRS)EPA/OEIThese data are automatically retrieved.Weekly 
Impaired Water BodiesEPA/OECAEPA imports data from ATTAINS from the ECHO Data Mart.Weekly 
HUC-12sEPA/OWEPA imports the HUC-12 information from the ECHO Data Mart, which uses the Office of Water's WATERS database.Weekly 
Toxics Release Inventory (TRI)EPA/Office of Environmental Information (OEI)EPA downloads data from the EPA TRI website (i.e., U.S. 1 and 3b tables).AnnualDecember 2018
TRI Pollution Wastewater Treatment InformationEPA/OEIEPA downloads data from a TRI web service.AnnualAugust 2014
Clean Watersheds Needs Survey (CWNS)EPA/OWMThese data are manually provided by EPA's Office of Wastewater Management (OWM) when the CWNS data are available.Approximately every four years (2008, 2012, etc.)2008
Crosswalk linking pollutants contributing to a water body impairmentEPA/OECAEPA updates its ICIS-NPDES parameter to water body impairment data crosswalk manually on an annual basis.AnnualJune 2014
Counties with ESA-listed aquatic speciesU. S. Fish and Wildlife Service, ECOS PMEPA requests the U.S. Fish and Wildlife Service manually extract data from the Environmental Conservation Online System (ECOS). These data are then updated in the database supporting the Loading Tool.As provided by the program office2013
NAICS CodesU.S. Census BureauEPA manually downloads data from the U.S. Census Bureau website.After each future NAICS update2012 (Tool is using the most currently available data)
Steam Electric Industry - EIA/NPDES ID Match-UpEPA/OW

EPA's Office of Water provided these data to OECA for inclusion in the Loading Tool.


 (95 K)

Update via error correction2012
Facility Program Flags
CWA Pretreatment Program Flag (PRET)EPA/OWM

EPA's Office of Water provided these data to OECA for inclusion in the Loading Tool.

(182 K)

Update via error correctionMay 2011
POTWs with Combines Sewer Overflows (CSOs)EPA/OWM

EPA's Office of Water provided these data to OECA for inclusion in the Loading Tool.


(102 K)

Update via error correctionFebruary 2009
Pesticide-Producing EstablishmentsEnvirofacts

EPA's Section Seven Tracking System (SSTS) tracks pesticide producing establishments. The Loading Tool's Custom Search allows you to identify facilities that are in the SSTS. EPA manually downloads data from the FRS EZ Query using 'SSTS' in the 'PGM_SYS_ACRNM' filter.

(102 K)

As provided by the program office2013
Abandoned Hazardous Waste SitesEnvirofacts

EPA's Comprehensive Environmental Response, Compensation, and Liability Information System (CERCLIS) database supports the cleanup of abandoned hazardous waste sites (a.k.a. 'Superfund' sites). The Loading Tool's Custom Search allows you to identify facilities that are in CERCLIS. EPA manually downloads data from the FRS EZ Query using 'CERCLIS' in the 'PGM_SYS_ACRNM' filter.

(159 K)

As provided by the program office2013
Oil Spill Prevention ProgramEnvirofacts

EPA's OIL database contains information on Spill Prevention, Control and Countermeasure (SPCC) and Facility Response Plan (FRP) subject facilities to prevent and respond to oil spills. The Loading Tool's Custom Search allows you to identify facilities that are in OIL. EPA manually downloads data from the FRS EZ Query using 'OIL' in the 'PGM_SYS_ACRNM' filter.


 (316 K)

As provided by the program office2013
Facilities in Chesapeake Bay TMDLChesapeake Bay TMDL, Appendix Q

EPA's Total Maximum Daily Load (TMDL) for the Chesapeake Bay lists facilities in the Chesapeake Bay that contribute to the water quality impairment. These facilities are listed in Appendix Q-1 of the TMDL.


 (390 K)

Update via error correctionAugust 2014

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 Data Scope and Limitations

Before you begin your searches, there are some things you should know about the scope and limitations of the pollutant loadings calculated by the Loading Tool:


 DMR Data

Facility Universe

The Loading Tool contains information for industrial and municipal point source dischargers. While the Loading Tool includes discharges for more than 60,000 facilities, it is not a complete inventory of all discharges permitted under the Clean Water Act.

Although the Clean Water Act requires all point source dischargers to obtain a NPDES permit and monitor their wastewater, not all facility, permit, or discharge monitoring data are uploaded into ICIS-NPDES. For example, non-major facilities were not required to submit permit or DMR data to EPA prior to December 21, 2016 (phase 1 implementation of the NPDES eReporting Rule).

There are also differences between the states on sharing facility level data with EPA’s ICIS-NPDES database for general permit covered facilities (e.g., oil and gas extraction facilities, construction stormwater sites). EPA and states issue general permits to increase the efficiency of the permit program as multiple similar facilities can be regulated under one permit.

Use the State Statistics and Loadings Search to download state statistics and loadings for each year for individual permits.

The Loading Tool only calculates loads for permit types that correspond to NPDES permit coverage: NPDES Individual Permit (NPD) and General Permit Covered Facility (GPC). All other permit types are excluded.

Other types of Clean Water Act releases that are not available in the Loading Tool include:

  • Wastewater releases from industrial facilities that are connected to a publicly-owned treatment works (POTW) sewerage system (e.g., indirect discharges), regulated through the CWA Pretreatment Program;
  • Biosolids monitoring data, regulated through the CWA Biosolids Program;
  • Discharges related to wet-weather events, such as stormwater from municipal separate storm sewer systems (MS4s), stormwater from industrial facilities, discharges from construction activities, combined sewer overflows, sanitary sewer overflows, and concentrated animal feeding operations (CAFOs).

Pollutant Universe

The Loading Tool includes thousands of pollutant parameters, including specific chemicals (e.g., phenol), bulk parameters (e.g., biochemical oxygen demand), temperature, and wastewater flow. However, these pollutants do not account for all pollutants discharged to U.S. waters.

  • ICIS-NPDES only includes information about discharges of pollutants that a facility is required by permit to monitor; facilities are not required to monitor or report all pollutants they actually discharge.
  • Discharge data are entered into ICIS-NPDES using a variety of measurement units. The Loading Tool can only calculate mass discharges for pollutants that are measured either as mass quantities or concentrations. Therefore, some pollutants, such as toxicity parameters measured as percent, are excluded from loading calculations. Further, the Loading Tool cannot calculate a load for concentration measurements if a corresponding wastewater flow measurement is not provided.
  • DMR data are recorded in ICIS-NPDES in a variety of measurement units. EPA uses conversion factors to calculate loads (e.g., 2.205 pounds/kilogram). These pollutant loads are not rounded to avoid reporting insignificant figures. This allows users to replicate the calculated pollutant loads from the reported DMR data. 

Matching Facilities to Watersheds

The Loading Tool matches facilities to receiving watersheds based on a facility's latitude and longitude coordinates and watershed spatial data in the Natural Resources Conservation Service's Watershed Boundary Dataset. The Loading Tool cannot establish a match between a facility and a watershed if either:

  • The facility does not have latitude or longitude coordinates; or
  • There are no spatial data for the receiving watershed.

The Loading Tool uses names from the USGS Geographic Names Information System (GNIS). The GNIS is closely integrated with the Watershed Boundary Dataset (WBD), which makes these data more useful for plotting on maps and for watershed modeling and other research. Not all water bodies receiving wastewater discharges have names in the GNIS and the not all names in the GNIS match the names that facilities provide in their NPDES permit application.

See Watershed Data for further information about how the Loading Tool matches DMR facilities to receiving watersheds.

Data Quality

DMR data may be entered into the ICIS-NPDES database manually, which can lead to data-entry errors. The database supporting this online tool uses data extracts from ICIS-NPDES with regular error correction updates from EPA's Integrated Error Correction Process. The Integrated Error Correction Process allows EPA to track and incorporate into the Loading Tool database error corrections submitted by the public. EPA also works with states to identify any error corrections that they make to their data outside of the Integrated Error Correction Process.

Intermittent Dischargers

Some facilities have intermittent discharges and may have one or more outfalls that don't discharge for one or more months. ICIS-NPDES has ways of identifying when there is no discharge at a particular outfall for an entire monitoring period. In such cases, the Loading Tool does not calculate pollutant loads for these outfalls during these monitoring periods.

EPA also developed a methodology with the states to estimate intermittent discharges that occurring within a monitoring period (e.g., there is a discharge from the outfall but it only occurs two days out of the monthly monitoring period). Specifically, the Loading Tool uses three ICIS-NPDES "Duration of Discharge" codes for identifying these intermittent dischargers: 50037, 82517, and 81381. The Loading Tool will automatically adjust the pollutant loading calculation such that the calculation only estimates pollutant discharges for the time when the outfall is discharging (e.g., two days in the month instead of the entire month).

However, there is a limitation with ICIS-NPDES data in that not all NPDES permits require permittees to submit Duration of Discharge codes when there are intermittent discharges that occur within a monitoring period. Consequently, the tool may overestimate pollutant discharges for these intermittent dischargers that do not report the Duration of Discharge codes. NPDES permittees with intermittent discharges are encouraged to engage with their permit writers to add one of the Duration of Discharge codes to their DMR. NPDES permittees may also contact EPA if the Duration of Discharge codes are not yet in their DMR.

 TRI Data


Facility Universe

TRI reporting is limited to industrial facilities (i.e., POTWs do not report to TRI) and not all industry sectors report to TRI. Additionally, small establishments (less than 10 employees) are not required to report, nor are facilities that don't meet the reporting thresholds. Thus, facilities reporting to TRI may be a subset of an industry. See the Basics of TRI Reporting and Factors to Consider When Using TRI Data for more information.

Pollutant Universe

TRI reporting focuses on toxic pollutant discharges and does not include common wastewater pollutants like Total Suspended Solids and Biochemical Oxygen Demand, which can be important factors when assessing the potential impact to surface waters. Additionally, the TRI Program does not require additional monitoring, so reported releases are often, in part, based on estimates instead of measurements, and due to TRI guidance, may differ greatly from DMR data, especially at facilities with large wastewater flows. Finally, certain chemicals (e.g., polycyclic aromatic compounds (PACs), dioxin and dioxin-like compounds, metal compounds) are reported as a class, not as individual compounds. Because the individual compounds in most classes have widely varying toxic effects, the potential toxicity of chemical releases may be inaccurately estimated.

Matching Facilities to Watersheds or to POTWs

TRI reporting does require facilities to report the names of the surface water bodies and POTWs that receive their wastewater discharges. See Sections 5.3 and 6.1 in TRI Form R. However, these reported names are not standardized or indexed to USGS's NHD or EPA's Federal Registry Service (FRS).

See Watershed Data for further information about how the Loading Tool matches TRI facilities to receiving watersheds.

Data Quality

The TRI Program conducts a number of activities every year to ensure the quality of TRI data reported to EPA. These activities range from providing extensive reporting guidance, intelligent reporting software, and training to facilities prior to the reporting deadline as well as data validation and analysis after the data are received. See TRI Data Quality Program Information for more information on these activities.

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Watershed Data and Maps

In addition to calculating pollutant loads, the Loading Tool matches pollutant discharges to receiving watersheds and retrieves the name of the receiving water body and available information about its impairment status.

The U.S. Geologic Service (USGS) defines watersheds in the U.S. and Caribbean using unique Hydrologic Unit Codes (HUC). These codes consist of two to twelve digits based on six levels of classification:

  • Region (first-level, 2-digit HUC);
  • Subregion (second-level, 4-digit HUC);
  • Accounting unit (third-level, 6-digit HUC);
  • Cataloguing unit (fourth-level, 8-digit HUC);
  • Watershed (fifth-level, 10-digit HUC); and
  • Subwatershed (sixth-level, 12-digit HUC).

The Loading Tool uses the 12-digit HUC (HUC-12) to identify watersheds in its searches. The Loading Tool uses HUC-12s to define major U.S. watersheds to provide geographic search criteria for the Water Pollution Search, Custom Search, and several Everyday Searches. Please review HUC Maps and Codes for Major U.S. Watersheds for more details.

The Loading Tool relates facility discharges to HUC-12s and uses the HUC-12s to retrieve other watershed information, including the Water Body Name, REACH Code, and an indicator for whether the stream is listed on EPA's 303d list of impaired waters. The Loading Tool uses the ECHO Data Mart to obtain this information.

The Loading Tool uses several web services to provide additional watershed information.

  • UPSTREAM/DOWNSTREAM:The Loading Tool uses this service to obtain the locations and unique identifiers of the nearest upstream and downstream watershed monitoring stations from the facility. The map on the Facility Results page displays the station locations and provides a link to additional station information from EPA’s STOrage and RETrieval Data Warehouse (STORET).
    • Area of Loading Tool: Pollutant Loading Reports
    • Description: Plot on Google map markers showing the nearest upstream and downstream STORET watershed monitoring stations with links in the pop-up bubbles to their station information page.
    • Values Passed: REACH code
    • Values Received: Latitude, Longitude, org_id, station_id (used to hyperlink to station page) for each monitoring station
    • Source: WATERS Upstream/Downstream JavaScript Library Service: https://ofmpub.epa.gov/waters10/UpstreamDownStream.Service?pNavigationType=[upstream = UT or UM; downstream = DD or DM] &pStartReachcode= [REACH code]&pTraversalSummary=TRUE&pFlowlinelist=FALSE&pEventList=STORET&pStopDistancekm=50

      For more information, see the Office of Water API Documentation.

 HUC Maps and Codes for Major U.S. Watersheds

The Water Pollution Search provides a drop down menu of major US Watersheds that users can select for their query. Many of these watersheds comprise several HUC-12s.

(2.1 MB)

The maps below show the boundaries of each Major U.S. Watershed as defined by the Loading Tool. EPA’s menu of major U.S. watersheds includes the following:

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Chesapeake Bay.pdf (775.09 KB)
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Delaware Bay.pdf (177.25 KB)
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  • Mississippi-Atchafalaya River Basin
Mobile Bay.pdf (222.56 KB)
  • (1 pg, 223 K)
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Tampa Bay.pdf (240.96 KB)
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