Town of Apex

6.1.12 Structural SCMs

A)  Professional Design

B)  Design, Location, and Landscaping of Structural SCMs

1. Specific requirements for structural SCMs shall be in accordance with the NC DWQ Stormwater SCM Manual and the Town of Apex Standard Specifications and Standard Details;

2. Structural SCMs shall be designed to remove 85% of total suspended solids in the permanent pool and store runoff from a one-inch rainfall from the site above the permanent pool;

3. The designed runoff storage volume shall be above the permanent pool;

4. The discharge rate from these systems following the one-inch rainfall design storm shall be such that the runoff does not draw down to the permanent pool level in less than two days and that the pond is drawn down to the permanent pool level within at least five days;

5. The mean permanent pool depth shall be a minimum of three feet;

6. The inlet structures shall be designed to minimize turbulence using baffles or other appropriate design features;

7. Retention basins, detention basins, headwalls, outlet structures, concrete flow channels, rip rap channels, and other drainage improvements shall be screened with plant material and/or berms and situated in the least visible location or, if visible, incorporated into the natural curves of the land;

8. Detention and retention basin embankments and the detention or retention basin itself shall be extensively landscaped with wet tolerant plant materials with the intention of re-creating a seasonal high water wet eco-structure; a list of guidelines for preferred plant materials can be found in the NC DEQ Stormwater Design Manual;

9. Detention or retention facilities shall be sized to accommodate the future growth of vegetation planted in the basin; and

10. In lieu of peripheral fencing, detention and retention basin edges shall be contoured and shaped to form low angles at primary water line thereby ensuring greater pedestrian safety.

11. All supporting calculation submittals for each proposed structural SCM shall include and comply with the latest version of the NC DWQ SCM supplement.

C) Identification on Site Plan/Subdivision Plan/Final Plat of SCM 

E)  Changes or Amendments to Plans and Specifications and/or Operation and Maintenance Agreement

F)  Compliance Prior to Receiving Plat Approval or Certificate of Occupancy

Subject to Subsection (G) below, prior to approval of a final plat (with respect to a subdivision), issuance of a certificate of occupancy (with respect to a site plan),  or commencement of a use for any development upon which a structural SCM is required, the owner shall have installed the improvements required by this Article and shall have received the approval of the Environmental Programs Manager with respect to the improvements. Upon installation of the required improvements, the Environmental Programs Manager or his designee shall inspect the structural SCM and the owner shall demonstrate that the required structure is in place, that it is operational, that it complies with all relevant portions of Sec. 6.1.12 Structural SCMs, and shall submit to the Environmental    Programs Manager actual “as built” plans for the structure, which shall include the information listed in Article 6 Overlay Districts, and Section 1.06(c) Stormwater Drainage System of the Town of Apex Standard Specifications and Standard Details, certifying completion of the same.

G)  Performance Guarantees

1. 1. As provided in a, b, and c below, in lieu of prior performance otherwise required by this Article, the Town may accept a performance guarantee that the improvements required by this Article will be constructed according to the Town’s specifications at the owner’s expense. Guarantees shall comply with the requirements of this Subsection G.

1. 1. 1. Site plan: In lieu of performance prior to the issuance of a temporary certificate of occupancy related to a site plan, a performance guarantee may be provided by the owner guaranteeing the installation of the improvements required by this Article. Improvements guaranteed under this Subsection a. shall be constructed by the owner within one (1) year after issuance of the temporary certificate of occupancy. All improvements required by this Article related to a site plan, shall be constructed prior to the issuance of a permanent certificate of occupancy. 

1. 1. 2. Phased site plan: In lieu of performance prior to the issuance of a temporary or permanent certificate of occupancy related to a phased site plan, a performance guarantee may be provided by the owner guaranteeing the installation of the improvements required by this Article for each phase. All improvements guaranteed under this Subsection b. shall be completed prior to the issuance of certificates of occupancy for 90% of the buildings within that phase, or within 60 days after receipt of written notice that the Stormwater and Utility Engineering Manager has determined that the contributing drainage area to the SCM is sufficiently stabilized to install the SCM, whichever occurs first. 

1. 3. Subdivisions: In lieu of performance prior to approval of a Final Plat for subdivisions, a performance guarantee may be provided by the owner guaranteeing the installation of the improvements required by this Article. All improvements guaranteed under this Subsection c. shall be completed prior to the issuance of certificates of occupancy for 90% of the lots within the subdivision. If the subdivision is to be phased, all improvements within or required for each phase shall be completed prior to issuance of certificate of occupancy for 90% of the lots within that phase.
2. Performance guarantee. Performance guarantees shall be provided by the owner in the amount equal to 125% of the total construction cost of the required SCM. The total cost of the structural SCM(s) shall include all construction costs, including but not limited to, the cost of materials, landscaping, seeding and soil stabilization, grading, excavation and fill. The owner shall submit his estimate of this amount subject to review, modification, and approval by the Stormwater and Utility Engineering Manager. Such estimate shall be signed and sealed by a licensed North Carolina professional engineer, landscape architect, or land surveyor. Guarantees required by this Section may be in the form of a surety bond enforceable at the sole discretion of the Town and in the form prescribed by the Town, a letter of credit that meets the specifications of Sec. 7.5.17 Irrevocable Letter of Credit in Lieu of Surety Bond or Other Guarantee of Performance, certified check drawn in favor of the Town, or cash deposited with the Town. 
3. Duration of performance guarantee. Performance guarantees shall run until the requirements of Sec. 6.1.12 have been satisfied and the Stormwater and Utility Engineering Manager has given final approval of the required SCM(s). 
4. Default. Failure of the owner to construct, repair, and if necessary, reconstruct the SCM(s) as required by Sec. 6.1.12 is a default. Upon such default, the Town may obtain and use all or any portion of the performance guarantee necessary to complete the improvements.
5. Costs in excess of performance guarantee. In the event the Town calls the performance guarantee required by this Section and the reasonable cost of performance exceeds the amount of the performance guarantee the Town may collect the difference from the owner. 

H)  Maintenance and Maintenance Guarantees

1.  Duty to maintain and maintenance and defects guarantee. The owner is responsible for all maintenance and repair of improvements required by this Article. In addition to the Operation and Maintenance Agreement required by Sec. 6.1.12.D, with respect to a subdivision, a maintenance and defects guarantee shall be provided by the owner in the amount equal to 25% of the total construction cost of the SCM to ensure proper maintenance and repair prior to conveyance of the improvements to a property owners association. The maintenance and defects guarantee shall be submitted to the Town of Apex prior to SCM final approval. The owner shall submit his estimate of this amount subject to review, modification, and approval by the Stormwater and Utility Engineering Manager. Such estimate shall be signed and sealed by a licensed North Carolina professional engineer, landscape architect, or land surveyor. Guarantees required by this Section may be in the form of a surety bond enforceable at the sole discretion of the Town and in the form prescribed by the Town, a letter of credit that meets the specifications of Sec. 7.5.17 Irrevocable Letter of Credit in Lieu of Surety Bond or Other Guarantee of Performance, certified check drawn in favor of the Town, or cash deposited with the Town. 

1. 2. Duration of maintenance and defects guarantee for subdivision. The maintenance and defects guarantee shall be in effect for one (1) year after the SCM final approval date issued by the Town’s Stormwater and Utility Engineering Manager or designee. 

1. 3. Default. Upon failure of the owner to maintain the SCM as required, the Town may obtain and use all or any portion of the maintenance and defects guarantee necessary to continue maintenance of the structure. 

I)  Inspection

1. Inspect once a year. On an annual basis after completion of construction of a SCM, the owner shall submit to the Stormwater and Utility Engineering Manager an inspection report for that structure from a qualified registered North Carolina professional engineer, surveyor, or landscape architect performing services only in their area of competence. The inspection report shall be on a form provided by the Stormwater and Utility Engineering Manager. An initial inspection report shall be provided to the Stormwater and Utility Engineering Manager beginning one (1) year from the date of submittal of the certified as-built plans to the Town and each year thereafter on or before the date of the as-built certification. 

2. Inspection by Town of Apex. All property within the Primary Watershed Protection District and/or the Secondary Watershed Protection District shall also be subject to inspection by the Stormwater and Utility Engineering Manager or his designee. Such inspections may include, but are not limited to, reviewing maintenance and repair records, sampling discharges, surface water, groundwater, and material or water in SCMs, and evaluating the condition of SCMs.

3. Corrective action. If at any time the Town of Apex determines that corrective actions or improvements to a SCM are required, the Town of Apex shall notify the owner of the needed corrections and of the date by which the work is to be completed. All corrective work shall be consistent with the approved operation and maintenance agreement.