§ 26-129. Standards for stormwater control measures.

(a)

Evaluation according to contents of design manual. All stormwater control measures and stormwater treatment practices (also referred to as best management practices, or BMPs) required under this article shall be evaluated by the stormwater administrator according to the policies, criteria, information, technical specifications, standards, and the specific design criteria for each stormwater practice in the design manual. The stormwater administrator shall determine whether BMPs in the plan will be adequate to meet the requirements of this article.

(b)

Determination of adequacy; presumptions and alternatives. Stormwater treatment practices that are designed, constructed, and maintained in accordance with the criteria and specifications in the design manual shall be presumed to meet the water quality and quantity performance standards of this article. Whenever a plan proposes to utilize a practice or practices not designed and constructed in accordance with the criteria and specifications in the design manual, the applicant shall have the burden of demonstrating that the practice shall satisfy the water quality and quantity performance standards of this article. The stormwater administrator may require the applicant to provide the documentation, calculations, and examples necessary for the stormwater administrator to determine whether such an affirmative showing is made.

(c)

Separation from seasonal high water table. For structural stormwater controls that are required under this section and that require separation from the seasonal high water table, a minimum separation of two feet is required. Where a separation of two feet from the seasonal high water table is not practicable, the division of water quality may grant relief from the separation requirement pursuant to the alternative design criteria set out in 15A NCAC 02H .1008(h). No separation from the seasonal high water table is required for a secondary stormwater best management practice that is used in a series with another stormwater best management practice.

(d)

Additional standards. The following additional standards shall apply:

(1)

Remove an 85 percent average annual amount of total suspended solids;

(2)

For detention ponds, draw down the treatment volume no faster than 48 hours, but no slower than 120 hours;

(3)

Discharge the storage volume at a rate equal to or less than the predevelopment discharge rate for the one-year, 24-hour storm; and

(4)

Meet the general engineering design criteria set forth in 15A NCAC 02H .1008(c).

(Code 2003, § 32-40; Ord. No. 09-05, 3-19-2009)