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How to Do Phase II: Post-Construction Site Runoff Controls. NC STATE UNIVERSITY. Post-Construction Runoff Controls: Agenda for Presentation. 1. What does the permit say you have to do and what kind of help is available? 2. What BMPs can you use? Discussion time

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How to Do Phase II: Post-Construction Site Runoff Controls

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How to Do Phase II:

Post-Construction Site Runoff Controls



Post-Construction Runoff Controls: Agenda for Presentation

  • 1. What does the permit say you have to do and what kind of help is available?
  • 2. What BMPs can you use?
  • Discussion time
  • A new stormwater program on the horizon

What does the permit say you have to do?

  • These BMPs are required:
  • Establish a post-construction stormwater management program.
  • Establish a program that includes BMPs appropriate for the MS4.
  • Establish a program to control sources of fecal coliform to the maximum extent practicable.
  • Establish nutrient sensitive waters (NSW) protection measures (for programs draining to NSW waters).

a) Establish a Post-Construction Stormwater

Management Program

  • Develop, adopt by ordinance, implement, and enforce a stormwater program runoff for new development and redevelopment.
  • The ordinance must be reviewed and approved by DWQ.

Developing a Stormwater Ordinance

The UNC School of Government and the Environmental Finance Center has developed a model stormwater ordinance.

The ordinance includes a section on Illicit Discharges.


(b) Establish strategies which include BMPs

appropriate for the MS4

  • Can combine structural and non-structural BMPs.
  • Adequate long-term operation and maintenance of structural BMPs.
  • Annual inspection reports of permitted structural BMPs performed by a qualified professional.

These areas already comply with Phase II:

  • Water Supply Watershed areas (WS-I - WS-IV)
  • HQW and ORW watersheds
  • Neuse River Basin stormwater program areas
  • Tar-Pamlico River stormwater program areas
  • Randleman Lake Water Supply Watershed

All other areas must meet or exceed this:


(A) No more than two DUs per acre or 24% built-upon area.

(B) Use vegetated conveyances to the maximum extent practicable.


(A) Structural BMPs must control and treat the difference between pre- and post-development conditions for the 1-year 24-hour storm.

(B) Structural BMPs must be designed to achieve 85% average annual removal of total suspended solids.

(C) Stormwater management measures must comply with the requirements listed in 15A NCAC 2H .1008(c).


Establishing BMP Design Standards

DWQ has developed a draft Stormwater BMP Manual.

357 pages!


Stormwater BMP Manual

Stormwater wetlands


Wet detention basin

Dry extended detention basin

Grass swale

Filter strip

Infiltration systems

Manufactured BMPs


Permeable pavement

Rooftop runoff management

Sand filter


Stormwater BMP Manual


Description and purpose



Location/general characteristics



Performance enhancers

Construction guidelines



References and additional resources


Stormwater BMP Manual

  • Comments on the manual are due by September 30th.
  • It will take 3-6 months after September to prepare a final version.

(c) Establish a program to control the sources of fecal coliform to the maximum extent


Control the sources of fecal coliform to the maximum extent practicable. Develop and implement an oversight program to ensure proper operation and maintenance of septic systems. Municipalities must coordinate this program with the county health department.


Septic System Maintenance

This model ordinance provides language that will allow a jurisdiction to enforce maintenance obligations for septic systems.

As a start, the jurisdiction should consider how to

integrate the existing health department permit data for onsite systems into an inventory of onsite systems

in the Phase II jurisdiction.


(d) Establish nutrient sensitive waters (NSW)

protection measures (for programs with

development or redevelopment draining

to NSW waters)

Develop, adopt, and implement an ordinance to ensure that the BMPs for reducing nutrient

loading are selected. In areas where the EMC has approved an NSW Stormwater Management Program, the provisions of that program fulfill the nutrient loading reduction requirement. Develop and include a nutrient application (fertilizer and organic nutrients) management program.


Establishing NSW Protection Measures

Jurisdictions in the Neuse and Tar-Pamlico basins can follow their existing NSW Stormwater programs.

Other Phase II jurisdictions with NSW waters can use the Neuse and Tar-Pamlico programs as examples.


Both low and high density developments must:

Keep all built-upon areas at least 30 feet landward of perennial and intermittent surface waters (USGS and Soil Survey maps).

Have deed restrictions and protective covenants to ensure that future development activities maintain the development (or redevelopment) consistent with the approved plans.


Watershed Protection Plans

Phase II local governments may develop comprehensive watershed protection plans to meet part, or all, of the requirements for post-construction stormwater.


What BMPs can you use?

  • Some examples:
  • Bioretention areas
  • Stormwater wetlands
  • Sand filters
  • Wet ponds
  • Buffers
  • Water reuse
  • Green roofs

Bioretention areas are landscaping features adapted to provide on-site treatment of storm water runoff. Surface runoff is directed into shallow, landscaped depressions.

NCSU campus

Golf course in Kinston


Bioretention areas are usually designed to use many of the pollutant removal mechanisms that operate in forested ecosystems.

Strip mall in Charlotte, NC

NC Aquarium in Dare County


Stormwater wetlands are similar to wet ponds but also incorporate wetland plants into the design. As stormwater runoff flows through the wetland, pollutants are removed through settling and biological uptake.

Constructed wetland in Avery County, NC


Stormwater wetlands are fundamentally different from natural wetland systems. Stormwater wetlands are designed specifically to treat stormwater runoff, and have less biodiversity than natural wetlands.


Sand filters are good options in ultra-urban areas because they consume little space. Underground and perimeter sand filters in particular are well suited to the ultra-urban setting because they consume so surface space.


Sand filters are an excellent option to treat runoff from storm water hot spots because stormwater has no interaction with groundwater.

(Hot spots include areas where vehicles are fueled, serviced, washed or stored and places where hazardous materials are generated or stored.)


Buffers are areas along a shoreline or stream where development is restricted or prohibited. Buffers cleanse stormwater and provide a physical barrier to protect waterways.


Water reuse involves capturing stormwater from a roof before it is discharged into a storm drain. This reduces peak flow and also reduces the need to purchase treated water.


Green roofs are simply a layer of vegetation grown on a layer of soil and drainage material on a rooftop. Rainwater is stored in the layers of drainage material for a short time before it is discharged.


Universal Stormwater Management Program (USMP)

  • DWQ recently initiated the USMP, which would be a voluntary new program.
  • The USMP would allow a local government to implement a single set of post-construction requirements throughout its entire jurisdiction. 
  • The USMP would be more straightforward, easier to implement, and more protective of the natural environment. 

Durham County

Before & After the USMP


Montgomery County

Before & After the USMP