A minimum of eighty-five percent (85) average annual removal for Total Suspended Solids (TSS) through the use of any combination of structural or non-structural BMPs.

Nutrient reduction requirements.

4. Nitrogen and Phosphorus export standards: All development that meets the requirements of this division must limit nitrogen export to 4.0 pounds per acre per year (lbs/ac/yr) and phosphorus export to 0.4 pounds per acre per year (lbs/ac/yr) through some combination of the following:

   1. Construction of allowable onsite or offsite stormwater management facilities.

   2. Participation in an approved "regional" or "jurisdictional-wide" facility or strategy.

   3. Dedication of "open space" and/or "conservation" easements. Easements may be onsite or offsite subject to the sections16-37.4(c), (d) and (e) of this division. Offsite land conservation offsets that drain to the same classified water as the development and meet the criteria specified in 16-37.4(d) may be approved by the stormwater administrator.

   4. Pay a one-time offset payment using the latest nitrogen and phosphorus offset payment calculations and fee as specified in the Nutrient Offset Payments Rule (15A NCAC 02B.0240, latest revisions). Use of offset payment option is subject to the following and provisions in

Allowable BMP practices.

4. All stormwater management facilities must be designed in accordance with this division and the Stormwater BMP Manual.

5. Allowable BMPs for nutrient reduction for use within the city are listed in the Stormwater BMP Manual.

6. Specific use of any particular device or strategy is subject to the approval by the stormwater administrator.

Peak runoff control.

1. No net increase in peak stormwater runoff.

2. Development shall not result in an increase in peak stormwater runoff leaving the site from the pre-development conditions for the one-year-24-hour storm event.

3. Runoff volume drawdown time shall be a minimum of twenty-four (24) hours, but no more than one hundred twenty (120) hours depending on the type of BMP used.

4. Calculation methods shall be in accordance with the standards specified in the Stormwater BMP Manual.

5. Exceptions to the peak flow requirements.Peak flow control is not required for developments that met items a and b or item c of the following:

   1. The overall impervious surface area is less than fifteen (15) percent of the total site and the remaining pervious portions of the site are utilized to the maximum extent practical to convey and control the stormwater runoff; and

   2. The increase in peak flow between the pre-development and post-development conditions does not exceed ten (10) percent; or

   3. The director of engineering makes a determination that stormwater detention at this particular location will increase flooding, accelerate erosion or negatively impact existing drainage problems in the area. In such cases, an alternate method of peak attenuation management may be required.