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(A) This section is intended to protect water quality for present and future residents of the Town and surrounding regions by limiting the amount of pollutants, including but not limited to nitrogen and phosphorus, in stormwater runoff. Specific objectives include: control of nitrogen and phosphorus export from development, control of peak stormwater runoff, and the use of best management practices.
(B) For the purpose of this section 7.3, the following definitions shall apply:
LARGER COMMON PLAN OF DEVELOPMENT OR SALE
A site where multiple separate and distinct development activities may be taking place at different times on different schedules but governed by a single development plan regardless of ownership of the parcels. Information that may be used to determine a "common plan of development" include plats, blueprints, marketing plans, contracts, building permits, public notices or hearings, zoning requests, and infrastructure development plans. Common Plan of Development is synonymous with “Larger Common Plan of Development”.
REDEVELOPMENT
Any development on previously-developed land.
(A) Nitrogen and Phosphorus Control Plan Required
For purposes of this section, nitrogen and phosphorus control plans shall be required for the following:
(1) Any activity that, alone or as part of a larger common plan of development or sale, disturbs greater than one (1) acre of land in order to establish, expand, or modify a single-unit or duplex residential development or a recreational facility.
(2) Any activity that, alone or as part of a larger common plan of development or sale, disturbs greater than twelve thousand (12,000) square feet of land in order to establish, expand or modify a multifamily residential development or a commercial, industrial or institutional facility.
(3) Any redevelopment alone or as part of a larger common plan of development or sale in order to establish, expand, or modify a multifamily residential development or a commercial, industrial or institutional facility that increases built upon area and has an existing Stormwater Management Plan is subject to this rule regardless of disturbed area.
(4) Any grubbing, stump removal, and/or grading activity that disturbs greater than twelve thousand (12,000) square feet.
(5) Demolition and subsequent construction upon a previously developed site.
(B) Exemptions
(1) For purposes of this section, development or land disturbance shall not include agriculture, mining, or forestry activities.
(2) Existing development as of March 1, 2001 in the Neuse River Basin, is not subject to the requirements of this Section. Expansions to existing development must meet the requirements of this Section. The impervious surface area of the existing development is not required to be included in the nitrogen load attributed to the site expansion. All calculations must use the approved accounting tool.
(3) Redevelopment and/or rebuilding activity which results in no net increase in the built-upon area from that that previously existed and which provides equal or greater stormwater control than that provided by previous development.
(4) In the Cape Fear River Basin any proposed new development that would replace or expand structures or improvements that existed as of December 1, 2001, and that would not result in a net increase in built-upon area shall not be required to meet the nutrient loading targets or high-density requirements, in accordance with Section 4.4.6(D), except to the extent that it shall provide stormwater control at least equal to the previous development.
(C) Nitrogen and Phosphorus Export Standards
(1) Any activity that is required to submit a nitrogen control plan in the Neuse River Basin must achieve a nitrogen export of less than or equal to three and six-tenths (3.6) pounds per acre per year. Any activity that is required to submit a nitrogen and phosphorus control plan in the Cape Fear River Basin must achieve an export rate of less than or equal to two and two-tenths (2.2) pounds per acre per year of nitrogen and eighty-two hundredths (0.82) pounds per acre per year of phosphorus in the Upper New Hope and four and four-tenths (4.4) pounds per acre per year of nitrogen and seventy-eight hundredths (0.78) pounds per acre per year in the Lower New Hope. If the development contributes greater than three and six-tenths (3.6) pounds per acre per year of nitrogen in the Neuse River Basin, greater than two and two-tenths (2.2) pounds per acre per year of nitrogen and/or eighty-two hundredths (0.82) pounds per acre per year of phosphorus in the Upper New Hope, or greater than four and four-tenths (4.4) pounds per acre per year of nitrogen and/or seventy-eight hundredths (0.78) pounds per acre per year of phosphorus in the Lower New Hope, then the table below explains the options available depending whether the development is residential or non-residential.
(2) Notwithstanding the foregoing, in the Cape Fear River Basin, redevelopment that would replace or expand existing structures or improvements and would result in a net increase in built-upon area shall have the option of either meeting the loading standards identified in section 7.3.2 (D)(1) or meeting a loading rate that achieves the following nutrient loads compared to the existing development: in the Upper New Hope Watershed, thirty-five (35) percent reduction in nitrogen and five (5) percent reduction in phosphorus; and in the Lower New Hope Watershed, no increase for nitrogen or phosphorus.
(3) Development subject to this section 7.3 shall attain a maximum nitrogen loading rate on-site of six (6) pounds per acre per year for single-unit, detached and duplex residential development and ten (10) pounds per acre per year for other development, including multi-family residential, commercial and industrial and shall meet any requirements for engineered stormwater controls otherwise imposed by the LDO. An applicant may achieve the additional reductions in nitrogen and phosphorus loading required by this section by making offset payments to the North Carolina Division of Mitigation Services contingent upon the acceptance of payments by that program. An applicant may propose other offset measures, including providing his or her own offsite offset or utilizing a private seller. All offset measures permitted by this ordinance shall meet the requirements of 15A NCAC 02B .0273 (2) through (4) and 15A NCAC 02B .0714.
TABLE 7.3-1: NITROGEN/PHOSPHORUS EXPORT REDUCTION OPTIONS | |
Residential | Commercial/Industrial/Institutional/Local Government/Multifamily Residential |
If the computed export is less than 6.0 lbs/ac/yr, then the owner may either: | If the computed export is less than 10.0 lbs/ac/yr, then the owner may either: |
Install SCMs to remove enough nitrogen to bring the development down to 3.6 lbs/ac/yr in the Neuse River Basin. Install SCMs to bring the nitrogen down to 2.2 lbs/ac/yr and phosphorus to 0.82 lbs/ac/yr in the Upper New Hope and the nitrogen down to 4.4 lbs/ac/yr and the phosphorus to 0.78 lbs/ac/yr Lower New Hope in the Cape Fear River Basin. | Install SCMs to remove enough nitrogen to bring the development down to 3.6 lbs/ac/yr in the Neuse River Basin. Install SCMs to bring the nitrogen down to 2.2 lbs/ac/yr and phosphorus to 0.82 lbs/ac/yr in the Upper New Hope and the nitrogen down to 4.4 lbs/ac/yr and the phosphorus to 0.78 lbs/ac/yr Lower New Hope in the Cape Fear River Basin. |
Pay a one-time offset payment to bring the nitrogen down to the 3.6 lbs/ac/yr in the Neuse River Basin. Pay a one-time offset payment to bring the nitrogen down to 2.2 lbs/ac/yr and phosphorus to 0.82 lbs/ac/yr in the Upper New Hope and the nitrogen down to 4.4 lbs/ac/yr and the phosphorus to 0.78 lbs/ac/yr Lower New Hope in the Cape Fear River Basin. | Pay a one-time offset payment to bring the nitrogen down to the 3.6 lbs/ac/yr in the Neuse River Basin. Pay a one-time offset payment to bring the nitrogen down to 2.2 lbs/ac/yr and phosphorus to 0.82 lbs/ac/yr in the Upper New Hope and the nitrogen down to 4.4 lbs/ac/yr and the phosphorus to 0.78 lbs/ac/yr Lower New Hope in the Cape Fear River Basin. |
Do a combination of SCMs and offset payment to achieve a 3.6 lbs/ac/yr export in the Neuse, 2.2 lbs/ac/yr nitrogen and 0.82 lbs/ac/yr phosphorus in the Upper New Hope and 4.4 lbs/ac/yr nitrogen and 0.78 lbs/ac/yr phosphorus in the Lower New Hope. | Do a combination of SCMs and offset payment to achieve a 3.6 lbs/ac/yr export in the Neuse, 2.2 lbs/ac/yr nitrogen and 0.82 lbs/ac/yr phosphorus in the Upper New Hope and 4.4 lbs/ac/yr nitrogen and 0.78 lbs/ac/yr phosphorus in the Lower New Hope. |
If the computed nitrogen export is greater than 6.0 lbs/ac/yr, the owner must use on-site or regional SCMs to bring the development's export down to 6.0 lbs/ac/yr. Then, the owner may use one of the three options above to achieve the reduction between 6.0 and 3.6 lb/ac/yr in the Neuse River Basin, 2.2 lbs/ac/yr in the Upper New Hope or 4.4 lbs/ac/yr in the Lower New Hope of the Cape Fear River Basin. | If the computed nitrogen export is greater than 10.0 lbs/ac/yr, the owner must use on-site or regional SCMs to bring the development's export down to 10.0 lbs/ac/yr. Then, the owner may use one of the three options above to achieve the reduction between 10.0 and 3.6 lb/ac/yr in the Neuse River Basin, 2.2 lbs/ac/yr in the Upper New Hope or 4.4 lbs/ac/yr in the Lower New Hope of the Cape Fear River Basin. |
Once it has been determined that an offset payment is forthcoming, the owner shall furnish the Town with evidence that the payment for the reductions in nitrogen and/or phosphorus has been made prior to the Town's issuance of a grading permit.
(4) The nitrogen and phosphorus export standards in this ordinance are supplemental to, not replacements for, stormwater standards otherwise required by federal, state or local law, including without limitation any riparian buffer requirements applicable to the location of the development. This includes, without limitation, the riparian buffer protection requirements of 15A NCAC 2B .0267,.0268 and .0714.
(D) Calculation of Nitrogen and Phosphorus Export
(1) The developer shall determine the need for engineered stormwater controls to meet the loading rate targets in the Cape Fear River Basin and Neuse by using the most current approved accounting tool for nutrient loading.
(2) Neuse River buffers and Jordan Lake Buffers required by the Department of Environmental Quality may not be used for compliance with nutrient reduction requirements; however, any portion of Zone 1, Zone 2, or Zone 3 UTB may be claimed as Protected Forest in the approved accounting tool if all the following are met:
(a) No easements, including but not limited to Public or Private Utilities, Retaining Walls, Access, Greenway, Drainage, or Stormwater Control Structure and Access easements, may be located within the area claimed as protected forest.
(b) The area claimed as protected forest must be recorded as Permanently Protected on the plat.
(c) Allowable activities within the Protected Forest are limited to those related to removal of nuisance and invasive and diseased or dying vegetation or in the interest of protecting human safety or property damage.
To meet the requirements of the Town of Cary NPDES Phase II Permit any new development or redevelopment as of July 1, 2005, not exempted pursuant to Section 7.3.2(B) must meet either the low density or high density option requirements described below and in the Neuse Rules. New development or redevelopment in the Swift Creek or Jordan Lake Watersheds must meet the requirements of Section 4.4.6 of the LDO. For purposes of this Section 7.3.3, impervious surface area shall be calculated pursuant to Section 4.4.6(D)(2) of the LDO and the provisions of Section 4.4.6(G) of the LDO shall apply to all engineered stormwater control measures.
(A) Low Density Projects, having no more than two (2) dwelling units per acre or no more than twenty-four (24) percent impervious surface area for all residential and non-residential development, shall transport stormwater runoff by vegetated conveyances to the maximum extent practicable.
(B) High Density Projects, having more than two (2) dwelling units per acre or more than twenty- four (24) percent impervious surface area for all residential and non-residential development, shall implement stormwater control measures that comply with each of the following standards:
(1) The stormwater control measures shall control and treat the difference between the pre-development and post-development conditions for the one (1) year twenty-four (24) hour storm. Runoff volume drawdown shall be a minimum of twenty-four (24) hours, but not more than one hundred twenty (120) hours.
(2) Stormwater control measures shall be designed to achieve a minimum of eighty-five (85) percent average annual removal for Total Suspended Solids (TSS).
There shall be no net increase in peak stormwater run-off flow leaving a development from pre-development conditions for the one (1)-year design storm. New developments are required to minimize damage to subject streams caused by storm flows.
(A) Calculation of Peak Flow
Acceptable methodologies for computing pre- and post-development conditions for the one (1)-year design storm include:
(1) The Rational Method (used when the drainage area is two hundred (200) acres or less)
(2) The Peak Discharge Method as described in USDA Technical Release Number 55 (TR-55) (drainage area is two thousand (2,000) acres or less)
(3) The Putnam Method (drainage area is greater than two thousand (2,000) acres)
(4) USGS Regression Equations, where applicable
The same method must be used for both the pre- and post-development conditions.
(B) Exceptions to Peak Flow Control
Developments with less than ten (10) percent net increase in peak flow of the one (1)-year design storm are not required to control peak flow for the one (1)-year storm from the site. However, if the net increase in peak flow from the new development is greater than ten (10) percent, the entire net increase from pre-development one (1)-year design storm peak flow must be controlled.
All best management practices that are implemented to achieve nitrogen or phosphorus reduction and flow attenuation will require complete legal documentation and a maintenance plan and must comply with all requirements of Section 4.4.6(G), Engineered Stormwater Control Measures.
(Ord. No. 05-001, 1-13-05; Ord. No. 05-015, 9-8-05; Ord. No. 06-009, adopted 4-27-06; eff. 4-27-06; Ord. No. 2007-04, 3-22-07; Ord. No. 2008-LDO-01, 9-25-08; Ord. No. 2010-LDO-01, 1-14-10; Ord. No. 2012-LDO-08, 10-11-12; Ord. No. 2013-LDO-02, 6-13-13; Ord. No. 2014-LDO-03, 8-14-14; Ord. No. 2019-LDO-03, 10-10-19; Ord. No. 2019-LDO-02, 11-21-19; Ord. No. 2022-LDO-02, 4-28-22; Ord. No. 2022-LDO-03, 10-27-22; Ord. No. 2023-LDO-02, 3-23-23)
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