Monday, February 18, 2008

Coastal Storm Water Rules, Changes, and Amendments

Outline of Coastal Rule Requirements
Affects all land development – residential and non-residential – within 20 coastal counties disturbing 10,000 square feet or more.

If disturbing more than one acre residential or 10,000 sq.ft. non-residential
o Stormwater permit required and
o 50-ft. vegetated buffer for new development; 30 ft. for redevelopment
 Definition of vegetated buffer different in Neuse and Tar-Pam River Basins (can be disturbed; buffer can be a lawn in Dare County) and
o No credit for wetlands in computing built-upon area.

If < ½ mile from and draining to SA waters
o No new points of discharge; no increase in flow to SA waters.
o Level spreaders to diffuse any flow through wetland areas
o 12% or less built-upon area = low density
 No engineered stormwater controls required on site
 Stormwater must be primarily conveyed by vegetated conveyances
o Greater than 12% built-upon area = high density
 Structural stormwater controls required or any BMP
 For structural controls, minimum separation of 12” of natural soil above seasonal high water table
 Need to control and treat the difference in runoff from pre-development/post-development one-year 24-hour storm conditions within property boundary.

If > ½ mile from and draining to SA waters
o 24% or less built-upon area = low density
 Stormwater conveyed primarily by vegetated conveyances
o > 24% built-upon area = high density
 Structural engineered controls required or any BMP
 Will need to store, control and treat runoff from one and one-half inch of rainfall.

If disturbing >10,000 sq. ft. but less than one acre
o No stormwater permit required.
If within ½ mile and draining to SA waters AND built-upon area > 12%
 Collect all rooftop runoff from one-year 24-hour storm in rain barrels or cisterns. All uncovered areas to be paved need to be constructed of permeable pavement or other pervious material OR
 Direct all rooftop runoff from one-year 24-hour storm to a rain garden. All uncovered areas to be paved need to be constructed of permeable pavement or other pervious material OR
 Install any other BMP to control and treat the difference in runoff from pre-development/post development one-year/24-hour storm conditions.
If outside of ½ mile SA waters AND built-upon area > 24%
 Collect all rooftop runoff from the first 1.5 inches of rainfall in rain barrels or cisterns. All uncovered areas to be paved need to be constructed of permeable pavement or other pervious material OR
 Direct all rooftop runoff from the first 1.5 inches of rainfall to a rain garden. All uncovered areas to be paved need to be constructed of permeable pavement or other pervious material OR
 Install any other BMP to control and treat the runoff the first 1.5 inches of rainfall.


15A NCAC 02H .1005 is proposed for amendment with changes as follows:

15A NCAC 02H .1005 STORMWATER REQUIREMENTS: COASTAL COUNTIES
(A) Notwithstanding, the provisions of 15A NCAC 2H .1003(b), all non-residential development activities within the coastal counties that disturb more than 10,000 square feet, including projects that disturb less than 10,000 square feet of land that are part of a larger common plan of development or sale that disturbs more than 10,000 square feet and all residential development activities within the coastal counties which require a stormwater management permit in accordance with Rule .1003 of this Section shall manage stormwater runoff as follows, with exception of NC Department of Transportation activities that shall be regulated in accordance with the provisions of that agency’s existing NPDES Stormwater Permit:
(1) development activities within the coastal counties draining to Outstanding Resource Waters (ORW) shall meet requirements contained in Rule .1007 of this Section and the provisions of Subparagraph (2)(a)(i) below;
(2) development activities within one half mile of and draining to SA waters or within one-half mile of SA waters and draining to unnamed freshwater tributaries to SA waters:
(a) Low Density Option: Development shall be permitted pursuant to Rule .1003(d)(1) of this Section if the development has:
(i) Built upon area of 25 12 percent or less; or proposes development of single family residences on lots with one third of an acre or greater with a built upon area of 25 12 percent or less. Development within 575 feet of the mean high water line of areas designated by the Environmental Management Commission as Outstanding Resource Waters (ORW) shall be limited to a built upon area of 25 percent or less, however, development with a built upon area of greater than 12 percent must comply with the requirements of Sub-Item (b) of this Item.
(ii) Stormwater runoff transported primarily by vegetated conveyances. (Conveyance system shall not include a discrete stormwater collection system as defined in Rule .1002 of this Section.); and
(iii) A 50 foot wide vegetative buffer for new development activities and a 30 foot wide vegetative buffer for redevelopment activities.
(b) High Density Option: Higher density developments shall be permitted pursuant to Rule .1003(d)(2) of this Section if stormwater control systems meet the following criteria:
(i) no direct outlet channels or pipes to SA waters unless permitted in accordance with 15A NCAC 2H .0126;
(ii) control systems must be infiltration systems, wet detention ponds, bioretention systems, constructed stormwater wetlands, sand filters, or alternative stormwater management systems designed in accordance with Rule .1008 of this Section to control and treat the runoff from all surfaces generated by one and one half inches of rainfall or the difference in the stormwater runoff from all surfaces from the predevelopment and post-development conditions for a one-year, 24-hour storm, whichever is greater. Alternatives as described in Rule .1008(h) of this Section may also be approved if they do not discharge to surface waters in response to the design storm;
(iii) runoff in excess of the design volume must flow overland through a vegetative filter designed in accordance with Rule .1008 of this Section with a minimum length of 50 feet measured from mean high water of SA waters; and
(iv) a 50 foot wide vegetative buffer for new development activities and a 30 foot wide vegetative buffer for redevelopment activities.
(c) In addition to the other measures required in this Rule, all development activities, including both low and high density projects, shall prohibit new points of stormwater discharge to SA waters or expansion (increase in the volume of stormwater flow through conveyances or increase in capacity of conveyances) of existing stormwater conveyance systems that drain to SA waters. Any modification or redesign of a stormwater conveyance system within the contributing drainage basin must not increase the net amount or rate of stormwater discharge through existing outfalls to SA waters. Infiltration of stormwater runoff from the 1-year, 24-hour storm or diffuse flow of stormwater at a non-erosive velocity to a vegetated buffer, or other natural area, within the property boundary that is capable of providing effective infiltration of the runoff from the 1-year, 24-hour storm shall not be considered a direct point of stormwater discharge. Permit applicants shall take into consideration soil type, slope, vegetation, and existing hydrology when evaluating infiltration effectiveness.

(3) development activities within the coastal counties except those areas defined in Items (1) and (2) of this Paragraph:
(a) Low Density Option: Development shall be permitted pursuant to Rule .1003(d)(1) of this Section if the development has:
(i) built upon area of 30 24 percent or less; or proposes development of single family residences on lots with one third one-half of an acre or greater with a built upon area of 30 24 percent or less;
(ii) stormwater runoff transported primarily by vegetated conveyances; (Conveyance system shall not include a discrete stormwater collection system as defined in Rule .1002 of this Section.); and
(iii) a 50 foot wide vegetative buffer for new development activities and a 30 foot wide vegetative buffer for redevelopment activities.
(b) High Density Option: Higher density developments shall be permitted pursuant to Rule .1003(d)(2) of this Section if stormwater control systems meet the following criteria:
(i) control systems must be infiltration systems, wet detention ponds, bioretention systems, constructed stormwater wetlands, sand filters, or alternative stormwater management systems designed in accordance with Rule .1008 of this Section;
(ii) control systems must be designed to store, control and treat the stormwater runoff from all surfaces generated by one and one-half inch of rainfall; and
(iii) a 50 foot wide vegetative buffer for new development activities and a 30 foot wide vegetative buffer for redevelopment activities.
(4) Structural stormwater controls required under this Rule shall meet the following criteria:
(a) Remove an 85 percent average annual amount of Total Suspended Solids.
(b) For detention ponds, draw down the treatment volume no faster than 48 hours, but no slower than 120 hours.
(c) Discharge the storage volume at a rate equal or less than the pre-development discharge rate for the 1-year, 24-hour storm. and
(d) Meet the General Engineering Design Criteria set forth in 15A NCAC 02H .1008(c).
(5) For the purposes of this Rule, all areas defined as 404 jurisdictional wetlands or non-404 jurisdictional wetlands shall not be included in the overall project area to calculate impervious surface density. Stormwater runoff from built upon areas that is directed to flow through any wetlands must flow through these wetlands in a diffuse manner with the use of a level spreader.
(6) For structural stormwater controls that are required under this Rule and that require separation from the seasonal high-water table, a minimum separation of two feet is mandated. This separation shall be provided by at least 12 inches of naturally occurring soil above the seasonal high-water table with a minimum soil hydraulic conductivity of 0.52 inches per hour.
(B) Residential development activities within the 20 Coastal Counties that are within one-half mile and draining to SA waters that have a built upon area greater than 12 percent and that do not require a stormwater management permit in accordance with Rule .1003 of this Section but that disturb more than 10,000 square feet of land shall manage stormwater runoff by implementing the following measures specified in Subparagraph (1), (2), or (3) below:
(1) Install rain cisterns or rain barrels designed to collect all rooftop runoff from the one-year, 24-hour storm. Rain barrels and cisterns shall be installed in such a manner as to facilitate the reuse of the collected rain water on site and shall be installed in such a manner that any overflow from these devices is directed to a vegetated area in a diffuse flow. In addition all uncovered driveways, uncovered parking areas, uncovered walkways and uncovered patios shall be constructed out of out of permeable pavement, or other pervious materials. For the purposes of this Rule, permeable pavement is defined as a paving material that allows for the infiltration of stormwater. Permeable pavement materials include, but are not limited to, porous concrete, permeable interlocking concrete pavers, concrete grid pavers, and porous asphalt. Compacted gravel will not be considered as permeable pavement. Other pervious material includes, but is not limited to, wooden slatted decks, or
(2) Direct rooftop runoff from the one-year, 24-hour storm to an appropriately sized and designed rain garden. In addition all uncovered driveways, uncovered parking areas, uncovered walkways and uncovered patios shall be constructed out of out of permeable pavement, or other pervious materials. For the purposes of this Rule, permeable pavement is defined as a paving material that allows for the infiltration of stormwater. Permeable pavement materials include, but are not limited to, porous concrete, permeable interlocking concrete pavers, concrete grid pavers, and porous asphalt. Compacted gravel will not be considered as permeable pavement. Other pervious material includes, but is not limited to, wooden slatted decks, or
(3) Install any other stormwater best management practice that meets the requirements of 15A NCAC 2H .1008 to control and treat the difference in the stormwater runoff from all built upon areas of the site from the predevelopment and post-development conditions for a one-year, 24-hour storm.
(C) Residential development activities within the 20 Coastal Counties that are not within one-half mile and draining to SA waters that have a built upon area greater than 24 percent and that do not require a stormwater management permit in accordance with Rule .1003 of this Section but that disturb more than 10,000 square feet of land shall manage stormwater runoff by implementing the following measures specified in Subparagraph (1), (2), or (3) below:
(1) Install rain cisterns or rain barrels designed to collect all rooftop runoff from the first 1.5 inches of rainfall. Rain barrels and cisterns shall be installed in such a manner as to facilitate the reuse of the collected rain water on site and shall be installed in such a manner that any overflow from these devices is directed to a vegetated area in a diffuse flow. In addition all uncovered driveways, uncovered parking areas, uncovered walkways and uncovered patios shall be constructed out of out of permeable pavement, or other pervious materials. For the purposes of this Rule, permeable pavement is defined as a paving material that allows for the infiltration of stormwater. Permeable pavement materials include, but are not limited to, porous concrete, permeable interlocking concrete pavers, concrete grid pavers, and porous asphalt. Compacted gravel will not be considered as permeable pavement. Other pervious material includes, but is not limited to, wooden slatted decks, or
(2) Direct rooftop runoff from the first 1.5 inches of rain to an appropriately sized and designed rain garden. In addition all uncovered driveways, uncovered parking areas, uncovered walkways and uncovered patios shall be constructed out of out of permeable pavement, or other pervious materials. For the purposes of this Rule, permeable pavement is defined as a paving material that allows for the infiltration of stormwater. Permeable pavement materials include, but are not limited to, porous concrete, permeable interlocking concrete pavers, concrete grid pavers, and porous asphalt. Compacted gravel will not be considered as permeable pavement. Other pervious material includes, but is not limited to, wooden slatted decks, or
(3) Install any other stormwater best management practice that meets the requirements of 15A NCAC 2H .1008 to control and treat the stormwater runoff from the first 1.5 inches of rainfall for all built upon areas of the site.


History Note: Authority G.S. 143 214.1; 143 214.7; 143 215.1; 143 215.3(a);
Eff. September 1, 1995.

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