A variety of practices to reduce nutrient loading to surface waters are approved by the Division of Water Resources (DWR). These nutrient reduction practices, which include design criteria and credit calculation methods, are available for use toward compliance with requirements of new or existing development stormwater rules, as well as for generating nutrient reduction credits for trading or offset. They supplement the growing set of stormwater control measures (SCMs) approved by the Division of Energy, Mineral and Land Resources (DEMLR) for new development post-construction runoff treatment. Developers can also buy nutrient offset credits from the Division of Mitigation Services (DMS) or from private providers approved by DWR to meet some of their nutrient reduction requirements.
For new development, the Stormwater Unit of the Division of Energy, Mineral and Land Resources (DEMLR) has authority for establishing and revising the set of acceptable SCMs for post-construction stormwater control. The Stormwater Unit partners with the NPS Planning Branch of DWR and stormwater researchers to set and revise nutrient credit assignments for these practices. The set of new development SCMs and their nutrient crediting specifications has been revised and is presented in the “2023 NC Stormwater Control Measure Credit Document”. Design guidance and Minimum Design Criteria for these SCMs can be found at DEMLR’s Stormwater Design Manual page.For development occurring under older Neuse and Tar-Pamlico stormwater rules, in January 2019 DWR authorized the use of an expanded set of SCMs described in Table A-3 of the Document for rule compliance. The Division’s March 2023 approval memorandum (located at the end of the document) explains that this interim expansion will be replaced by the set of practices available in the SNAP tool v4.2.0 (below) once readopted Neuse and Tar-Pamlico stormwater rules go into effect in each local jurisdiction.
SNAP (Stormwater Nitrogen and Phosphorus) v4.2.0 is DWR’s updated spreadsheet tool used to estimate nitrogen and phosphorus in stormwater runoff from development sites and nutrient reductions provided by stormwater treatment. As of March 2023, it is the approved tool for regulatory compliance with stormwater requirements in all Nutrient Management Strategy watersheds (Falls, Jordan, Neuse, and Tar-Pamlico), and for alternative riparian buffer mitigation compliance in all watersheds with buffer regulations. Local jurisdictions implementing these rules will be adopting use of SNAP v4.2.0 in staggered groups over the course of 2023 and early 2024. Developers should contact their local jurisdiction to determine when to start using SNAP v4.2.0. It may also be used across the state for non-regulatory-compliance purposes such as planning, modeling, grant applications, etc. All of the Stormwater Control Measures that follow DEMLR’s Minimum Design Criteria, as well as custom SCMs, can be modeled with this tool.
•Compressed SNAP v.4.2.0
•SNAP v4.2.0 Users Manual
•Webapp: Average Annual Precipitation and Nutrient Management Strategy Watersheds
•SNAP v4.2.0 Approval Memo (appended to end of Users Manual)
If you have questions about using SNAP you can post them to the SNAP Users Listserv, or send your questions directly to Trish D’Arconte (firstname.lastname@example.org ). To subscribe to the listserv, send an email to SNAPToolemail@example.com with only the word “subscribe” in the subject or body of the email. Make sure to check your Junk Mailbox for the subscription confirmation email.
In local jurisdictions where older Neuse or Tar-Pamlico Stormwater Rules are still in effect, developers should continue to use the calculation method laid out in the Neuse Model Program or the Tar-Pamlico Model Program. Where the previous version of SNAP (version 4.1) is in effect in local jurisdictions while they update their ordinances, you can still download the compressed SNAP version 4.1 and the Version 4.1 Users’ Manual.
DMS and other providers have received approval from DWR to use SNAP version 4.2. 0for generating buffer mitigation credits in accordance with 15A NCAC 02B .0295(o)(9), as noted in the above approval memo.
Two SNAP training classes were held in March 2023. Videos and materials can be found here:
Nutrient reductions may be generated to meet Existing Development Stormwater rule requirements through either retrofitting of existing developed lands using the SCMs and accounting described above or implementation of other nutrient reduction practices as described in the Nutrient Catalog.
Nutrient offset is a form of trading allowed by the Division of Water Resources under each set of rules governing the four Nutrient Management Strategy watersheds in NC. Other forms of trading are also allowed as provided for within the different strategies’ rules. Effective September 2020, 15A NCAC 02B .0703 addresses procedural requirements for nutrient offsets, including geographic scope, project standards, payment conditions, and other issues.
Developers, wastewater treatment facilities, and others can often meet a portion of their nutrient reduction requirements by purchasing nutrient offset credits. These credits are generated by riparian restoration/enhancement projects constructed elsewhere within the watershed, either by private mitigation providers or the NC Division of Mitigation Services (DMS).
The predominant nutrient reduction practice used by those seeking to generate nutrient reduction credits for sale is the restoration and enhancement of riparian forested buffers on agricultural lands. The Division allows the use of forested buffer restoration and enhancement as described in 15A NCAC 02B .0295(n)(2-4) to award a nutrient reduction benefit of 75.7 lbs/yr nitrogen and 4.88 lbs/yr phosphorus. Such projects must meet design criteria.
Other practices are also eligible to generate nutrient reduction credit for sale (e.g., stormwater control measures), but to date, these have not been as cost-effective as buffer restoration.
Developers seeking nutrient offset credits should first consult with their local government permitting authority for routine inquiries. Requests for nutrient offset credits require the submission of a form approved by the local government. Users of the SNAP Tool can generate a generic nutrient offset request form within SNAP. Developers in the Neuse (outside Falls) and Tar-Pamlico watersheds have a different form to use.
For additional questions regarding this topic, please contact DEQ representatives as directed below.
For questions regarding nutrient offset credit purchases, please contact your local government permitting representative. Additional inquiries regarding nutrient offset or trading may be directed to: Joey Hester firstname.lastname@example.org or Rich Gannon email@example.com
For questions regarding nutrient accounting tools and reduction practices, please contact: Trish D’Arconte firstname.lastname@example.org
For questions about nutrient credit purchases from the NC Division of Mitigation Service's In-lieu Fee Program, please contact: Kelly Williams, NCDMS In-Lieu Fee Program Coordinator, 919-707-8915 or Kelly.Williams@ncdenr.gov.