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Post-Construction Stormwater Management Permitting

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1. What ordinance regulates Post Construction Stormwater Management in the City of Winston-Salem?

Chapter 75 Article IV of the City of Winston-Salem’s Code of Ordinances is the regulatory document for this activity.

2. Are all developments subject to requiring a permit or providing post construction Stormwater management controls?

No. Not all developments are subject to a permit or required to provide post construction Stormwater management controls. Permitting and controls depend on the size of the development and if certain thresholds are exceeded then a permit will be required. If certain thresholds are not exceeded then a development may be exempt from some, or all, of the provisions of the Post Construction Stormwater Management ordinance. If they are exempted from all of the provisions then a permit and hence management would not be required. Some developments may also be excluded from the provisions of the ordinance based on grandfathering etc.

3. Does the City of Winston-Salem review plans for Post Construction Stormwater permitting in the County and in other municipal areas such as Clemmons, Kernersville etc.?

No. The City of Winston-Salem post construction Stormwater management reviews and hence permitting is only applicable to the city limits of Winston-Salem. Developers should contact other municipal or State authorities for areas outside of the City limits for permitting reviews and questions. 

NOTE: The City of Winston-Salem DOES review plans within areas of the Salem Lake Watershed located in the County area for compliance with the Chapter C of the UDO Environmental ordinance and developers should submit appropriate Stormwater management plans to the City for review in those cases.

4. What developments or redevelopments are excluded from the City of Winston-Salem’s Post Construction Stormwater Management ordinance provisions and therefore would not be required to apply for a permit

Developments which are excluded from the City of Winston-Salem’s Post Construction Stormwater management ordinance provisions would include: 

1.  A development or redevelopment that received a grading permit or building permit prior to the effective date of the ordinance (September 2008)
2.  A site specific development or redevelopment plan or site specific phases development or redevelopment plan that was submitted prior to the effective date of the ordinance, approved within 6 months of the effective date of the ordinance and which has made substantial progress within two years of the site plan approval (Note: These plans are typically plans that received a Planning Board approval for example prior to the effective date of the ordinance)
3.  Any development or redevelopment activity which has received a Stormwater management plan approval prior to the effective date of the ordinance and substantial progress is made within 2 years of the effective date of the ordinance
4. A right that has vested statutory or local law prior to the effective date of the ordinance.

5. What constitutes “substantial progress”?

If grading activities had occurred on the site and the developer is able to document or prove such activities, then this would constitute substantial progress. Also, construction of infrastructure such as streets, drainage systems, utilities etc. would also constitute substantial progress.

6. What developments or redevelopments may be exempt from some, or all, of the provisions of the City of Winston-Salem’s Post Construction Stormwater Management ordinance?

There are a number of exemptions which may be applicable to site developments or redevelopments. They are as follows: 

1. Developments that cumulatively disturb less than one acre during construction and are not part of a large common plan or phased development are exempt from the water quality provisions of the ordinance
2.  A development that creates less than 20,000 sq.ft. of a net increase in impervious area above and beyond what already existed on the site before the development or redevelopment took place is exempt from the water quantity provisions of the ordinance
3.  Any redevelopment activity for which the proposed impervious area is equal to or less than the preexisting impervious area shall be exempt from all the provisions (quality and quantity) of the ordinance
4.  Activities exempt from permit requirements of Section 404 of the federal Clean Water Act as specified in 40 CFR 232 (primarily, ongoing farming and forestry activities)
5.  For any development or redevelopment that cumulatively disturbs less than 3 acres, is not part of a large common plan of development, redevelopment or sale and is less than 24% impervious, then the standards for Stormwater quantity management shall be limited to controlling only the peak rates for the two and ten year design storms.

7. Are there any development projects or activities that are not subject to this ordinance?

Yes. Public works projects such as road projects and greenways (typically referred to as linear projects) shall follow the NC Department of Transportation BMP’s outlined in NCDOT’s “Stormwater Best Management Practices Toolbox” to the extent practicable and shall be permitted accordingly.

8. What developments or redevelopments are subject to adhering to some or all of the provisions of the post construction Stormwater management ordinance provisions?

Those developments or redevelopments that are not excluded or exempt (as addressed in prior FAQ’s). An engineer must determine what provisions, quality, quantity, or both, apply should no exclusions or exemptions be met.

9. When are the quality provisions of the ordinance applicable to developments that are not exempt or excluded?

When a development or redevelopment disturbs greater than 1 acre during construction, or disturbs less but is part of a larger common plan or phased development where all phases combined are expected to disturb more than 1 acre and there is an increase in impervious area. If this is the case a development must apply for a post construction Stormwater management permit that addresses the applicable low density or high density quality provisions of the ordinance.

10. When is a development considered low density and thus must only comply with the ordinance low density water quality provisions?

When a development is less than 24% impervious (built upon) area or less than 2 units/acre.

11. When is a development considered high density and thus must comply with the ordinance high density water quality provisions?

When a development exceeds 24% impervious area and is greater than 2 units/acre.

12. How is project density percentage determined?

There are two methods a designer can choose in the calculation of project density: 

1. Project density can be calculated as the total built upon area divided by the total project area; 
2. A project with existing development may use the calculation above as described or shall have the option of calculating the project density as the difference of total built upon area minus the existing built upon area divided by the difference of total project area minus the existing built upon area.

13. When is a development subject to the water quantity provisions of the ordinance?

When it proposes to create more than 20,000 sq.ft. of net new impervious area.

14. What constitutes impervious area or built upon area?

That portion of a development or redevelopment that is covered by impervious of partially pervious surface including, but not limited to, buildings, pavement and gravel areas such as roads, parking lots, paths and recreation facilities such as tennis courts which does not allow water to infiltrate through the surface into the subsoil.

15. What are examples of surfaces that would not be considered impervious or built upon area?

Surfaces such as a slatted deck, the water area of a swimming pool and pervious paving material that absorbs water and allows it to infiltrate through the material such as pervious asphalt or pervious concrete would not be considered impervious or built upon. Also, a surface of number 57 stone as designated by the American Society for Testing and Materials, laid at least four inches thick over a geotextile fabric, a trail that is either unpaved or paved as long as the pavement is porous with a hydraulic conductivity greater than 0.001 centimeters per second (1.41 inches per hour), landscaping material including but not limited to gravel, mulch, sand and vegetation placed on areas that receive pedestrian or bicycle traffic or on portions of driveways and parking areas that will not be compacted by the weight of a vehicle such as the areas between sections of pavement that support the weight of a vehicle shall not be considered as impervious area.

16. Is existing impervious area required to be managed or treated?

No. Existing impervious area is not required to be managed or treated unless it cannot be bypassed around the Stormwater management system which in that case it must be accounted for in the design calculations. Similarly, off site areas are not required to be managed or treated unless they cannot be bypassed around the system.

17. What is the design manual that the City of Winston-Salem references and adheres to for Stormwater Management Plan designs?

NCDEQ’s Stormwater Design Manual and its constituent chapters and sections.

18. What does SCM or BMP mean?

SCM is an acronym for “Stormwater Control Measure”. BMP is an acronym for “Best Management Practice”. They are the same thing, just a different way of referring to them.

19. If a development is considered low density in regards to water quality is management required?

No. Low density developments do not have to manage for water quality. However, they must meet all applicable low density provisions of the ordinance and design manual such as use of vegetative conveyances to the maximum extent practicable, provision of stream buffers off of all perennial and intermittent streams/conveyances and adherence to the Minimum Design Criteria of the Low Density chapter of the NCDEQ Stormwater Design Manual.

20. When and where do stream buffers apply and what are the requirements for such buffers?

Stream buffers apply to all developments that contain a perennial or intermittent stream or conveyance that is located on the property proposed to be developed and that falls under either the low or high density water quality provisions. The buffer width is based on the amount of proposed disturbance during construction. If there is 1 to 10 acres of disturbance the buffer width is 30 feet as measured from the top of bank on both sides of the conveyance. If there is 10 to 50 acres disturbance the buffer width is 50 feet and finally greater than 50 acres of disturbance requires a 100 foot buffer. No matter the width of the buffer, in all cases where they apply no built upon area shall be permitted within any of the full width of the buffer zone. The inner half of the buffer closest to the stream bank shall not be disturbed during construction while the outer half of the buffer may be disturbed and graded but no built upon area is allowed within it.

21. What is considered a perennial or intermittent stream or conveyance?

Anything that is marked as a stream on either the USGS maps or the soil survey maps for the site is considered a perennial or intermittent stream or conveyance. If an engineer wished to dispute this then they must have a NCDEQ certified individual provide documentation indicating that it is not such a conveyance.

22. If a development is considered high density in regards to water quality is management required?

Yes. In addition to meeting all applicable low density requirements, high density developments must capture and treat the first inch of runoff (the water quality design storm) in an approved SCM (or multiple SCM’s should the designer choose to use multiple SCM’s) that is listed as a primary SCM in the design manual and ensure all MDC’s (Minimum Design Criteria) listed in the design manual for that particular device are met.

23. What are some examples of primary SCM’s?

Wet detention ponds, constructed wetlands, sand filters, bio-retention cells, permeable pavement, stormfilters and bayfilters are some examples of primary SCM’s.

24. If a development exceeds 20,000 sq.ft. in net new impervious area and the water quantity provisions apply, is management required?

This is up the designer and City Stormwater staff. Management is usually the chosen option but the designer also has the option of providing a “no adverse impact downstream study” in lieu of management if indeed a no adverse impact situation can be proven and with the permission of Stormwater staff.

25. What constitutes a no adverse impact study?

The designer must assess and satisfy all of the applicable Stormwater quantity management requirements as specified in section 75-303 of the ordinance at a minimum ensuring that the study addresses those items and hence shows there are no impacts such as flooding, erosion of land and waterways and other such impacts to downstream properties and also properties located immediately upstream.

26. The no adverse impact study must assess impacts to a suitable point downstream. Where or how far downstream is this point located?

The point downstream is chosen based on agreement or gaining the concurrence of City Stormwater staff and is either: 

1. a point downstream where drainage from the proposed site development or redevelopment represents less than ten percent of the total watershed area draining to that point (typically referred to as the 10% guideline). This is the most common study point analyzed; 
2. a point downstream where drainage from the development or redevelopment site enters a FEMA established floodway; 
3. a point where the Stormwater Director knows of no existing Stormwater problems that the proposed development or redevelopment is likely to exacerbate or 
4. a point where there are no public road crossings or other public infrastructure that may be adversely impacted by an increase in runoff from the proposed development or redevelopment. 

Note: This determination/study shall not alter any requirements related to the Stormwater quality provisions of the ordinance

27. If management is to be provided for quantity what are the design storm events that must be managed or attenuated?

For the proposed development or redevelopment the peak runoff rates for the post developed site must be managed to be at or below the pre development peak runoff rates for the 2, 10 and 25 year storm events of minimum 6 hour duration. In addition the increase in the 25 year volume must be shown to be stored in the device and this volume released or drawn down over a 2 to 5 day period.

28. What type of SCM’s can be used to attenuate for these quantity requirements?

The designer has more options available to them for quantity management as compared to the water quality management. Usually most of the quality SCM’s will also be able to attenuate the quantity requirements. However, in some cases a designer may not be able to design a quality SCM adequately to also attenuate for quality and will “daisy chain” SCM’s together so that one achieves the quality control and the other the quantity control. Examples of SCM’s used to achieve quantity attenuation include, but are not limited to, wet detention ponds, wetlands, sand filters, dry detention basins, underground cisterns or oversized piping, underground infiltration systems etc.

29. Is there a variance procedure allowed for in cases where it’s impossible to treat or capture all proposed impervious area or in cases where for example its impossible not to avoid an impact to a buffe

Yes. In such cases the applicant must complete a variance application form stating the case for requesting and been granted a variance and submit it to the Stormwater Director for his review. It is at the discretion and judgement of the Stormwater Director whether to approve the variance or not.

30. Is there a financial surety required for permitted Stormwater management systems?

Yes. The amount of surety depends on how the developer intends the system to be owned and operated in the future. For one owner type developments (usually commercial) the developer is typically the entity that will be the party who will own, operate and maintain the system. In that case the developer must provide the City of Winston-Salem with a non-refundable cash surety equal to 4% of the construction cost of the Stormwater management system. This surety is then deposited into a City maintained “catastrophic failure account”. For developments where the system will be owned, operated and maintained by a HOA (Home Owners Association) or a POA (Property Owners Association), the surety required from the developer is 15% of the construction cost of the Stormwater management system. The developer in this case must establish an escrow account and have an escrow agreement in place with the approval of the City and fund that escrow account with the 15% cost at the time of permitting. The HOA or POA, whichever is the case, is then required to deposit funds, based on an operation and maintenance expense estimate that will need approval at the time of permitting, into that established escrow account in the next 10 years after as-built certification.

31. When and how is the developer’s surety amount determined?

The surety amount is determined at the time of permitting. The design engineer for the proposed development must submit a sealed engineer’s cost estimate of the cost of constructing the Stormwater management system for approval to the Stormwater Division. Once approved by Stormwater staff the surety will be the required percentage amount (4% of 15% depending on the type of future owner – see last question) of this overall approved estimate. Submittal of the certified contractors bid tab of the construction cost of the system will also be an acceptable means of determining the surety.

32. When and how is the HOA or POA’s, whichever is applicable, cost for their future surety funds determined?

The amount of funds that are required to be deposited by a HOA or POA into the escrow account in future years after certification and approval of as-builts is determined at the time of permitting by the engineer submitting a sealed engineer’s estimate of the cost of the annualized operation and maintenance. The HOA or POA will be required to deposit two-thirds of this amount into the escrow account within 5 years of the as-built approval date and deposit the remainder of the funds into the account within 10 years of the as-built approval date.

33. Is there an Operation and Maintenance Agreement required as part of permitting?

Yes. One of two City standard Operation and Maintenance Agreement templates, whichever is applicable, must be used in the permitting process. One such agreement is for “one owner” type of developments and is a two party agreement between the City and the developer. The other agreement used in HOA or POA type developments is a three party agreement between the City, the developer and the HOA or POA.

34. What constitutes an Operation and Maintenance (O&M) Agreement?

The Operation and Maintenance (O&M) Agreement contains the main body of the agreement (the template described in the last question) and also 3 exhibits that must be attached to the back of the agreement. These exhibits are: Exhibit A – A legal description of the property on which the development is taking place; Exhibit B – A copy of the recorded plat of the required private drainage and access easements for the Stormwater management system, or, a legal description of the blanket easement that covers the entire property and Exhibit C – The O&M Manual(s) for the specific type of Stormwater management system used. The agreement including all exhibits must be prepared and signed by the owner and notarized and submitted to the City Stormwater Division for review and signature. Upon approval and signature by City officials the owner must then record this agreement at the Forsyth County Register of Deeds office and provide a copy of the recorded agreement back to the City for their files.

35. When is a Post Construction Stormwater Management permit issued?

A Post Construction Stormwater Management permit is issued once the Stormwater Management plan and its supporting design documentation has been reviewed and approved, the financial surety has been provided and the Operation and Maintenance Agreement has been recorded.

36. Once a development that has a Stormwater management system construction is complete what does the owner/engineer have to do to continue to satisfy their permit?

Once construction of the system is complete and it is functioning as designed the engineer of record must submit to the Stormwater Division a set of sealed as-built plans and records that certify that the system is complete and functioning as designed/permitted. Once received the Stormwater engineer will conduct an inspection of the system and assuming there are no issues with the system will then notify the owner (the entity who signed the recorded O&M Agreement) of the need to now start inspecting and maintaining the system per the recorded agreement and operation manual. Records of all inspections and if applicable maintenance must be submitted annually to the Stormwater Division on the date of the certification of the system (anniversary of notification sent to owner by the Stormwater Engineer).

37. How often must an owner inspect the system?

This depends on the type of SCM(s). The owner should refer to the recorded O&M Agreement and specifically Exhibit C which contains the frequency of inspections. A wet detention basin should for example be inspected monthly and within 24 hours of any rain event greater than 1 inch, a sand filter should be inspected quarterly and within 24 hours of any rain event greater than 1 inch etc.

38. Who should carry out the inspections?

A North Carolina Registered Professional Engineer or Landscape Architect or an individual who has attained a BMP inspector certification through NC State. The inspector should include his/her credentials in the submittal of inspection reports.

39. Are there any other Agreements other than an Operation and Maintenance Agreement required as part of permitting?

It depends. If a Home Owners Association or Property Owners Association (HOA/POA) is intended to be the entity responsible for the long term Operation and Maintenance of the system then in addition to the Operation and Maintenance Agreement approved and recorded an Escrow Agreement also needs to be approved and recorded as part of the permitting process. If the developer is to be the long term Operation and Maintenance entity then this escrow agreement is not required.