Water Quality Data Assessment

The assessment of water quality in North Carolina is required under Sections 303(d) and 305(b) of the Clean Water Act and is to be reported on every two years. This assessment is also known as the Integrated Report. The assessment is conducted in 3 parts:

  • The first part of the assessment is collecting water quality data; DWR and Monitoring Coalitions collect thousands of surface water quality samples throughout NC lakes, rivers, and streams for a variety of parameters.
  • The second part of the assessment is comparing each water quality sample collected to the appropriate North Carolina water quality standard. If enough water quality samples exceed the respective water quality standard for that parameter then the waterbody could be considered impaired depending on the assessment methodology.
  • The third part of the assessment is the assessment methodology. The assessment methodology describes how many exceedances of water quality standards a waterbody can have for a particular pollutant, the data window used for the assessment (usually 5 years), and what integrated reporting category will be assigned to each waterbody-parameter combination.

Each monitored waterbody in North Carolina receives an assessment every two years. The most current assessment is available here. 

What are impaired waters?

Impaired waters are a subset of the assessments made where water quality samples for a particular parameter on a waterbody exceed water quality standards and the assessment methodology has determined that the waterbody is indeed impaired for the particular parameter. Impaired waters are grouped into two categories:

  • Category 4 assessments are those that do not need a TMDL. These are not included in the 303(d) list.
  • Category 5 assessments are those that require a TMDL or TMDL alternative. These Category 5 waters are assembled in a single document (the 303(d) list) and sent to EPA on April 1st of every even-numbered year, per 40 CFR 130.7. EPA must approve, disapprove, or partially approve each 303(d) list. 303(d) files can be found here.

How do I receive important 303(d) or TMDL announcements?

Send a blank email to denr.dwq.TMDL303d-subscribe@lists.ncmail.net then reply to the confirmation email you receive.

How are water quality standards made and do they change? 

To learn about all about water quality standards please visit the water quality standards page.

How is the assessment methodology set and does it change?

The assessment methodology is set to be consistent with North Carolina water quality standards and EPA guidance and generally does not change from year to year unless standards or guidance changes.

Who collects the data?

Data used for water quality assessment is primarily collected by DWR's Ambient Monitoring System, NPDES Discharge Monitoring Coalitions, and Biological Assessment Branch, the NC DHHS Division of Public Health, and the United States Geological Survey. Local governments and environmental groups as well as industry, municipal and university coalitions also provide data. Submitted data sets must include an approved Quality Assurance Project Plan (QAPP) to assure that the data were collected in a manner consistent with agency data. A standing solicitation for data is listed below.

What are the different levels of data?

Data are tiered based on the quality assurance and quality control program and documentation. Each tier has varying applications and levels of regulatory applicability.  Click HERE to learn more about data tiers.

Where to find data?

DWR stores data from the Ambient Monitoring System on EPA's STORET online database.  Guidance on how to search and download data is available on the DWR AMS homepage.

How can you submit data?

DWR invites all interested parties to submit water quality data and information. The quality and reliability of data submitted determines the programs and projects for which the data can be used. DWR uses only the highest quality data for regulatory decision-making and water quality assessment. IF YOU INTEND TO SUBMIT DATA FOR DWR USE, PLEASE CONTACT US BEFORE BEGINNING DATA AND INFORMATION COLLECTION, TO ENSURE THAT WHAT YOU SUBMIT IS USABLE FOR ITS INTENDED PURPOSE. 

The following are required for DWR to accept data for Integrated Report Assessment:

  1. DWR approved Quality Assurance Project Plan
  2. Completed Data Submittal Checklist
  3. All collected data summarized as per the Data Summary Template