Stormwater
Unit :: Phase II Post-Construction
Stormwater Requirements Questions and Answers
Background on Federal Phase II Stormwater Requirements
Since 1990, the Federal Clean Water Act (CWA) and federal regulations require that certain point source discharges of stormwater runoff come under a permit program to assure that their impacts to surface waters are minimized. In North Carolina, the Division of Water Quality implements this federal permit program through the National Pollutant Discharge Elimination System (NPDES). Initially, his program focused on construction and industrial activities in large municipalities (over 100,000 in population). In 1999 (effective early 2000), the federal regulations expanded on the initial Phase I program to require stormwater controls from smaller local government areas (Phase II of the Stormwater Program). These requirements target areas that are experiencing significant growth and construction activities in various forms – residential, commercial, industrial, institutional, transportation, etc. As areas are developed and built-upon area increases, stormwater impacts to surface waters also increase (see Why be Concerned About Stormwater).
The Phase II approach targets areas located within United States Census Designated Urban Areas (UAs). The US Census identifies UAs based on core population and population density (people per square mile). In North Carolina there are seventeen designated UAs affecting more than 160 communities, in whole or in part. Communities that own or operate Municipal Separate Storm Sewer Systems (MS4s) are responsible for NPDES permits for discharges from their MS4.
Unlike most of the states that come under the federal rule, North Carolina counties generally do not own/operate the MS4s in unincorporated areas. As a result, unincorporated county areas where urban development is occurring were not covered by the control measures for stormwater management that the federal regulations intended.
Session Law 2006-246 provides for implementation of Phase II Stormwater Management Requirements. This act established procedures for implementing the NPDES stormwater program for small MS4s. It also established post-construction stormwater management requirements, to be implemented under state permitting authorities, for development activities, outside of the municipal permitted areas, beginning July 1, 2007.
What is this new permitting program?
This new permit program implements the requirements under North Carolina Session Law 2006-246 for certain development activities located within specific unincorporated areas of the State. This Post-Construction Stormwater Permit, which is issued by the Division of Water Quality under state permitting authority, regulates the design, construction, operation, and maintenance of the post-construction stormwater control measures implemented by regulated developments.
Who needs this permit?
As established in Section 4(a) and 4(b) of Session Law 2006-246, the permit covers new development and redevelopment activities that will result in a cumulative disturbance of one acre or more of land and that are located within parts of the unincorporated area established in Section 4(a) and 4(b) of Session Law 2006-246. The coverage area includes the potential extra-territorial jurisdiction (ETJ) of a designated Phase II municipality, the area that is considered an Urbanizing Area (UA) under the federal census designation, and county wide coverage where counties are “tipped in.”
The potential ETJ area of a Phase II municipality is the area extending 1-3 miles beyond its boundaries, depending on the population of the city. This area is referred to as the Municipal Sphere of Influence (MSI). If the municipality is not actually exercising its planning and zoning authority throughout the entire area allowed by statute, then DWQ is to implement the post-construction stormwater management requirements in the area not regulated by the municipality.
Counties are “tipped in” where the county is subject to stormwater management programs administered by the Division equal or exceed seventy-five percent (75%) of the total geographic area of the county.
Counties are also are “tipped in” where the county contains an area that is designated as an urbanized area under the 1990 or 2000 federal decennial census and has an actual population growth rate that exceeded the State population growth rate for the period 1995 through 2004.
Development projects in the tipped in counties must apply for and receive a permit from the DWQ for post-construction stormwater control, if it meets the following provisions:
- Is new development or redevelopment that will cumulatively disturb an acre or more of land,
- Is located in an unincorporated area beyond a Phase II municipality, and
- Is located within an area designated as an MSI, UA, or a County that is “tipped in.”
If your project meets the preceding requirements, use the application forms located at this website to apply for a Phase II Post-Construction Permit from the Division of Water Quality.
As additional cities come into the Phase II program by state designation, the EMC may require stormwater controls in unincorporated areas surrounding those newly designated areas. Session Law 2006-246 directs the EMC (through DWQ) to implement the post-construction stormwater requirements in the delineated unincorporated areas. However, counties may voluntarily accept delegation of the program from the EMC. If a county takes on implementation of the program, the county may choose to apply stormwater standards only in the delineated areas or throughout the county.
How do I know if I am located in a Municipal Sphere of Influence (MSI) or an Urbanizing Area (UA) outside of the ETJ?
Use the map link located on this website to activate an interactive mapping system that was specifically developed for this new permitting program. Enter the project address or the geographic coordinates (latitude and longitude) for the project site. This interactive system will tell you if you are located within an MSI, UA, or a “tipped in” county covered by this state permitting program.
Can any existing stormwater management requirements meet the provisions of this program?
Yes, there are some existing stormwater management programs that can be used to meet the provisions. The following existing stormwater programs are considered to be in compliance.
- Water Supply Watershed Requirements (WS-I, WS-II, WS-III and WS-IV) – 15A NCAC 2B.0212-.0216
- Freshwater High Quality Waters Stormwater Requirements (HQW) – 15A NCAC 2H.1006
- Freshwater Outstanding Resource Waters Stormwater Requirements (ORW) – 15A NCAC 2H.1007
- Neuse River Nutrient Sensitive Waters Stormwater Requirements (NSW) – 15A NCAC 2B.0235
- Tar-Pamlico River Nutrient Sensitive Waters Stormwater Requirements (NSW) – 15A NCAC 2B.0258
- Randleman Lake Water Supply Watershed Nutrient Sensitive Waters Stormwater Requirements – 15A NCAC 2B.0251
In addition, counties may request to be delegated implementation of the program in accordance with Section 10 of Session Law 2006-246.
What if my project is located within the corporate limits or the ETJ of a Phase II municipality?
Within the corporate limits and the planning jurisdiction of a Phase II municipality, the local government will implement the full Phase II permit program including post-construction stormwater control. In these instances, the development is subject to local government approval at the time their permit takes effect rather than permitting under this program. Please contact the local government in whose jurisdiction the project is located for instructions regarding a Phase II Post-Construction Permit from that local government
What does this permit look like?
A stormwater permit shall govern the design, installation, and construction of stormwater management and control practices on the site, including structural Best Management Practices and elements of site design for stormwater management other than structural BMPs.
The permit is intended to provide a mechanism for the review, approval, and inspection of the approach used for the management and control of stormwater for the development or redevelopment site, including structural BMPs or other techniques such as low-impact or low-density design. Also included are requirements for:
- A recorded Operations & Management agreement that is binding on subsequent owners,
- Annual inspections,
- Reporting, and
- Record-keeping.
What are the Stormwater Runoff Requirements Associated with These Permits?
All development and redevelopment to which the permit applies shall comply with the standards of this section.
Low Density Projects
A project that is located within one-half mile of and draining to Shellfish Resource Waters is a low-density project if it contains no more than twelve percent (12%) built-upon area. A project that is not located within one-half mile of Shellfish Resource Waters is a low-density project if it contains no more than twenty-four percent (24%) built-upon area or no more than two dwelling units per acre.
Low-density projects shall comply with each of the following standards:
- Stormwater runoff from the development shall be transported from the development by vegetated conveyances to the maximum extent practicable.
- All built-upon area shall be at a minimum of 30 feet landward of all perennial and intermittent surface waters. A perennial or intermittent surface water shall be present if the feature is approximately shown on either the most recent version of the soil survey map prepared by the Natural Resources Conservation Service of the United States Department of Agriculture or the most recent version of the 1:24,000 scale (7.5 minute) quadrangle topographic maps prepared by the United States Geologic Survey (USGS). An exception to this requirement may be allowed when surface waters are not present in accordance with the provisions of 15A NCAC 2B .0233 (3)(a) or similar site-specific determination made using division-approved methodology.
- Deed restrictions and protective covenants are required by the permittee to ensure that subsequent development activities maintain the development (or redevelopment) consistent with the approved plans. The permittee shall require an enforceable restriction on property usage that runs with the land, such as a recorded deed restriction or protective covenants, to ensure that future development and redevelopment maintains the site consistent with the approved project plans.
High Density Projects
A project that is located within one-half mile of and draining to Shellfish Resource Waters is a high-density project if it contains more than twelve percent (12%) built-upon area. A project that is not located within one-half mile of Shellfish Resource Waters is a high-density project if it contains more than twenty-four percent (24%) built-upon area or more than two dwelling units per acre.
High-density projects shall implement stormwater control measures that comply with each of the following standards:
- High-density projects must use structural stormwater management systems that will control and treat runoff from the first one inch of rain unless the project is in a county that is subject to the Coastal Area Management Act of 1974, in which case the project must use structural stormwater management systems that will control and treat runoff from the first one and one-half inches of rain. In addition, projects that are located within one-half mile and draining to Shellfish Resource Waters must control and treat the difference in the stormwater runoff from the predevelopment and post-development conditions for the one-year, 24-hour storm.
- Draw down the treatment volume no faster than 48 hours, but no slower than 120 hours.
- Discharge the storage volume at a rate equal to or less than the predevelopment discharge rate for the one-year, 24-hour storm.
- All structural stormwater treatment systems used to meet the requirements of the program shall be designed to have a minimum of 85% average annual removal for Total Suspended Solids;
- General engineering design criteria for all projects shall be in accordance with 15A NCAC 2H .1008(c), as explained in the Design Manual;
- All built-upon area shall be at a minimum of 30 feet landward of all perennial and intermittent surface waters. A surface water shall be deemed present if the feature is approximately shown on either the most recent version of the soil survey map prepared by the Natural Resources Conservation Service of the United States Department of Agriculture, or the most recent version of the 1:24,000 scale (7.5 minute) quadrangle topographic maps prepared by the United States Geologic Survey (USGS). An exception to this requirement may be allowed when surface waters are not present in accordance with the provisions of 15A NCAC 2B .0233 (3)(a) or similar site-specific determination made using division-approved methodology.
Deed restrictions and protective covenants are required by the Permittee to ensure that subsequent development activities maintain the development (or redevelopment) consistent with the approved plans. The Permittee shall require an enforceable restriction on property usage that runs with the land, such as recorded deed restrictions or protective covenants, to ensure that future development and redevelopment maintains the site consistent with the approved project plans.
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Areas draining to Class SA waters
For areas draining to Class SA waters, permittees, delegated programs, and regulated entities must:
(1) Use BMPs that result in the highest degree of fecal coliform die-off and control to the maximum extent practicable sources of fecal coliform while still incorporating the stormwater controls required by the project's density level.
(2) Implement a program to control the sources of fecal coliform to the maximum extent practicable, including a pet waste management component, which may be achieved by revising an existing litter ordinance, and an on-site domestic wastewater treatment systems component to ensure proper operation and maintenance of such systems, which may be coordinated with local county health departments.
(3) Prohibit new points of stormwater discharge to Class SA waters and prohibit both increases in the volume of stormwater flow through conveyances and increases in capacity of conveyances in existing stormwater conveyance systems that drain to Class SA waters. Any modification or redesign of a stormwater conveyance system within the contributing drainage basin must not increase the net amount or rate of stormwater discharge through existing outfalls to Class SA waters. Diffuse flow of stormwater at a nonerosive velocity to a vegetated buffer or other natural area capable of providing effective infiltration of the runoff from the one-year, 24-hour storm shall not be considered a direct point of stormwater discharge. Consideration shall be given to soil type, slope, vegetation, and existing hydrology when evaluating infiltration effectiveness.
Trout Waters (TR) waters
In addition to the standards for stormwater handling set out in the design manual, new development and redevelopment that drains in whole or part to class Trout Waters (TR) waters shall design and implement the best stormwater practices that do not result in a sustained increase in the receiving water temperature.
Nutrient Sensitive Waters (NSW)
In addition to the standards for stormwater handling set out in the design manual, new development and redevelopment that drains in whole or part to class NSW waters shall design and implement the best stormwater practices that reduce nutrient loading.
Separation from the seasonal high water table
For BMPs that require a separation from the seasonal high-water table, the separation shall be provided by at least 12 inches of naturally occurring soil above the seasonal high-water table.
How do I Apply For Permit Coverage?
Unless your project area is located within a Phase II MS4 ETJ or a delegated county area, you must apply for permit coverage from the Division of Water Quality. Application Information can be found at this link.
Who Can I Contact With Questions?
A number of general questions can be answered by reviewing the information on the Post-Construction In Unincorporated Areas website. If you have further questions you can contact our division:
By email at: phase2.info@ncmail.net
By mail at: Stormwater Permitting Unit
NC Division of Water Quality
1617 Mail Service Center
Raleigh, NC 27699-1617
By phone at: (919) 733-5083 – ask for staff in the Stormwater Permitting Unit
How does this program relate to the Phase II NPDES Stormwater Program?
The NPDES Phase II Stormwater Permitting Program is targeted toward owners/operators of MS4s as noted in the background area of this Q&A document. Where communities’ own/operate an MS4 (usually municipalities) in designated areas they are responsible for NPDES permits to control the discharge from the MS4s. These permits have a series of control measures including post-construction stormwater control for new development and redevelopment in their jurisdictional area.
The stormwater management requirements outlined here and required in Session Law 2006-246 is related, but not a part of the NPDES program. These requirements recognize that urban development, that can impact surface waters regardless of whether the NPDES requirements apply. To address these concerns, this program requires post-construction stormwater management under state permitting authorities in areas surrounding Phase II municipalities.
Terms and Acronyms Associated with This Program
- Clean Water Act or CWA – the Federal Water Pollution Control Act, also known as the Clean Water Act (CWA), as amended, 33 USC 1251, et. Seq.
- DENR – the North Carolina Department of Environment and Natural Resources
- development – any land disturbing activity which adds to or changes the amount of impervious or partially pervious cover on a land area or which otherwise decreases the infiltration of precipitation into the soil; an exception is rebuilding activity that does not qualify as redevelopment.
- DWQ – the Division of Water Quality, Department of Environment and Natural Resources.
- Municipal Sphere of Influence or MSI - The unincorporated area of a county outside of a municipality designated as an urbanized area under the 1990 or 2000 census by the Bureau of the Census that:
- Extends one mile beyond the corporate limits of a municipality with a population of fewer than 10,000 individuals.
- Extends two miles beyond the corporate limits of a municipality with a population of 10,000 or more individuals but less than 25,000 individuals.
- Extends three miles beyond the corporate limits of a municipality with a population of 25,000 or more individuals.
- Redevelopment - any rebuilding activity unless that rebuilding activity results in no net increase in built-upon area and provides equal or greater stormwater control than the previous development.
- Municipal Separate Storm Sewer System or MS4 - a publicly owned conveyance or system of conveyances (including roads with drainage systems, streets, catch basins, curbs, gutters, ditches, manmade channels, or storm drains):
- That discharges to waters of the United States or waters of the state;
- Designed or used for collecting or conveying stormwater;
- Which is not a combined sewer; and
- Which is not part of a Publicly Owned Treatment Works (POTW) as defined in 40 CFR 122.2
- "Shellfish resource waters" means Class SA waters that contain an average concentration of 500 parts per million of natural chloride ion. Average concentration is determined by averaging the chloride concentrations of five water samples taken one-half mile downstream from the project site that are taken on separate days, within one hour of high tide, and not within 48 hours following a rain event. The chloride ion concentrations are to be determined by a State-certified laboratory.
Can the State designate municipalities?
A public entity that owns or operates a municipal separate storm sewer system (MS4) may be designated as a regulated entity through a State designation process, or under a total maximum daily load (TMDL) implementation plan as provided in Session Law 2006-246 Section 5.
The Commission shall identify a public entity as a candidate for designation as a regulated entity if the municipal separate storm sewer system (MS4) either:
1. Discharges stormwater that has the potential to adversely impact water quality. An adverse impact on water quality includes any activity that causes or contributes to a violation of water quality standards, including, but not limited to, any activity that impairs designated uses or that has a significant biological or habitat impact.
2. Serves a public entity that has not been designated pursuant to subdivision (1) of this section and that has either a population of more than 10,000 or more than 4,000 housing units and either a population density of 1,000 people per square mile or more or more than 400 housing units per square mile.
After review of the public comment, the Commission shall make a determination on designation for each of the candidate public entities. The Commission shall designate a candidate public entity that owns or operates a municipal separate storm sewer system (MS4) as a regulated public entity only if the Commission determines either that:
1. The public entity has an actual population growth rate that exceeds 1.3 times the State population growth rate for the previous 10 years.
2. The public entity has a projected population growth rate that exceeds 1.3 times the projected State population growth rate for the next 10 years.
3. The public entity has an actual population increase that exceeds fifteen percent (15%) of its previous population for the previous two years.
4. The municipal separate storm sewer system (MS4) discharges stormwater that adversely impacts water quality.
5. The municipal separate storm sewer system (MS4) discharges stormwater that results in a significant contribution of pollutants to receiving waters, taking into account the effectiveness of other applicable water quality protection programs.
The Commission shall designate an owner or operator of a small municipal separate storm sewer system (MS4) as a regulated entity if the municipal separate storm sewer system (MS4) is specifically listed by name as a source of pollutants for urban stormwater in a total maximum daily load (TMDL) implementation plan developed in accordance with subsections (d) and (e) of 33 U.S.C. § 1313.
How do these rules affect development in municipalities that were not designated as a “Phase II” regulated entity under the 1990 or 2000 Census?
Development that cumulatively disturbs one acre or more of land located in the incorporated areas of a county, that are not designated as an urbanized area under the most recent federal decennial census, shall comply with the standards set forth in Session Law 2006-246 Section 9 beginning 1 July 2007. The Commission shall administer and enforce the standards for development unless the public entity requests that the Commission delegate administration and enforcement of the stormwater management program to the public entity as provided in Session Law 2006-246 Section 10.
Page last updated: April 18, 2007
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