Linking DMR and TRI Data in the Water Pollutant Loading Tool

The Water Pollutant Loading Tool presents and compares wastewater discharge data from ICIS-NPDES and TRI. For ICIS-NPDES data, the Loading Tool calculates pollutant loadings using permit and DMR data. For TRI, the tool uses facility-reported annual masses of chemical discharges to surfaces waters and transfers to POTWs. The tool presents loads from both systems as pounds per year and as toxic-weighted pounds per year to account for variations in toxicity among pollutants.

The DMR/TRI comparison features throughout the Loading Tool allow users to compare discharges across these two programs at the industry, chemical, and facility level for each available year of data. However, it is important to understand differences between the DMR and TRI data, as well as the programs that drive the collection of these data, when analyzing results.

This page provides an overview of how DMR and TRI data are linked and considerations for comparing these datasets. For more information about DMR and TRI data in the Loading Tool, see About the LT Data. For advanced users, Comparing CWA, NPDES, DMR Data and TRI Data (PDF) (20 pp, 735 K) provides an in depth discussion of considerations in comparing the two datasets.

  • DMR data: The Clean Water Act requires all point source dischargers to obtain a NPDES permit, and report compliance with NPDES permit limits via monthly DMRs submitted to the permitting authority. The permitting authority then enters the reported DMR data into ICIS-NPDES, including pollutant concentration and quantity values and identification of any types of permit violations.
  • TRI data: TRI is the common name for Section 313 of the Emergency Planning and Community Right-to-Know Act (EPCRA). Each year, facilities that meet certain thresholds must report their estimated releases and other waste management activities for listed toxic chemicals. Facilities must report the quantities of toxic chemicals recycled, collected, and combusted for energy recovery, treated for destruction, or disposed.

Data Considerations

Data considerations when comparing DMR and TRI data are presented in Table 1 below.

Table 1. DMR and TRI Data Considerations for the Comparative Analysis
Data Scope/LimitationsDMR ConsiderationsTRI Considerations
Facility universeAlthough the Clean Water Act requires all dischargers to submit DMRs to their permitting authority, not all facility, permit, or discharge monitoring data are uploaded into ICIS-NPDES. EPA places greater priority on major dischargers, and requires authorized states to enter facility, permit, and DMR information for these dischargers. Before the NPDES eReporting Rule became effective, EPA required a more limited set of data for non-major dischargers.Facilities may be exempt from reporting due to industry classification or number of employees.
Discharge universeDMR data capture surface water discharges from industrial facilities and POTWs. The data do not capture wastewater transfers to POTWs from industrial or domestic sources.TRI data capture discharges from industrial facilities to receiving streams and industrial transfers to POTWs. The data do not capture POTW discharges to surface waters or domestic wastewater transfers to POTWs.
Chemical universeFacilities only report discharges of pollutants for which their NPDES permit requires them to monitor. Other pollutants may be discharged but are not reported on DMRs.Facilities only report chemicals on the TRI list and may be exempt from reporting discharges of certain chemicals due to activity thresholds.
Industry classificationICIS-NPDES does not require SIC code information. As a result, some NPDES permits do not have any information to determine industrial classification.

The primary industrial activity reported in DMR data may differ from the primary industrial activity reported in TRI.
The primary NAICS code in TRI is associated with the facility's revenues, and may not relate to its pollutant discharges.
Data qualityData entry errors and incorrectly identified units of measure can significantly impact loading calculations.Facilities can use engineering estimates to report pollutant releases. Not all releases are based on measurements.

Data Linkages

To facilitate comparisons between the two datasets, the Loading Tool uses several crosswalks to link the data by facility, pollutant, and industry sector, as described below.

Facility Crosswalk

The Loading Tool uses EPA Facility Registry Service (FRS) identification numbers to link NPDES permit numbers to TRI facility IDs (TRIFIDs). FRS uniquely identifies a facility by assigning an identification number (FRS ID), and uses this FRS ID to link together all regulatory program database records (such as permit IDs and facility IDs that facilities use in reporting to EPA). ICIS-NPDES identifies facilities using NPDES permit numbers, while TRI identifies facilities using a unique TRIFID. Both data systems provide the corresponding FRS ID for each NPDES permit and TRIFID.

However, the relationship between NPDES permits and TRIFIDs is not always a one to one match. Matches may be one to one, many to one, one to many, or many to many. To account for the complex facility relationships, the Loading Tool presents all facility counts and discharge information at the FRS ID level, which may include several NPDES permits and TRIFIDs. Please refer to the DMR/TRI Facility Crosswalk (CSV) (37 MB) for current facility linkages.

Pollutant Crosswalk

DMRs use parameter codes to identify pollutants. These parameter codes are specific to the chemical identity (chemical abstract service (CAS) number) and analysis type. As a result, multiple parameter codes may exist for a single CAS number (e.g., total residual chlorine, free available chlorine).

In TRI, chemicals are identified, for the most part, using chemical abstract service (CAS) numbers. TRI also includes chemical categories, such as glycol ethers and chlorophenols, which comprise multiple CAS numbers. In some cases, TRI chemicals can be double-counted with TRI chemical categories. For example, 2,4,5-Trichlorophenol is a TRI chemical but also falls under the chlorophenols chemical category.

To avoid double counting, EPA grouped TRI chemicals within their broader chemical categories, and produced a list of unique chemical groups that link to multiple CAS numbers. EPA used the CAS numbers to identify the DMR parameters and TRI chemicals that should be included in each chemical group. To match DMR data to TRI-reported discharges, and to avoid double-counting within DMR and TRI, EPA groups and sums the pollutant discharges in DMR and TRI data to the chemical group level and matches on a unique chemical group ID. Please refer to the DMR/TRI Pollutant Group Crosswalk (XLSX) (134 K) for specific groupings.

Industry Crosswalk

DMR data classify industrial activity primarily using 4-digit Standard Industrial Classification (SIC) codes while TRI classifies industrial activity using 6-digit NAICS codes. The relationship between 4-digit SIC codes and 6-digit NAICS codes is complex and can be a many-to-many match for certain industrial categories. To simplify the industry comparisons for this analysis, EPA grouped SIC codes and NAICS codes into 27 industry sectors:

  • Apparel
  • Beverage and Tobacco Products
  • Chemicals
  • Computer and Electronic Products
  • Electrical Equipment
  • Fabricated Metal Products
  • Food
  • Furniture
  • Hazardous Waste
  • Leather and Allied Products
  • Machinery
  • Merchant Wholesalers, Non-durable Goods
  • Mining
  • Miscellaneous Manufacturing
  • Nonmetallic Mineral Products
  • Paper
  • Petroleum and Coal Products
  • Plastics and Rubber Products
  • Primary Metals
  • Printing and Publishing
  • Publishing
  • Textile Mills
  • Textile Products
  • Transportation Equipment and Allied Services
  • Utilities
  • Wood Products
  • All Other Miscellaneous Manufacturing

These sectors are consistent with the TRI Covered Industries described in EPA's TRI reporting guidelines. Please refer to the DMR/TRI Industry Crosswalk (XLSX) (56 K) for the specific industry sector linkages.