HomeMy WebLinkAbout20030065 Ver 1_Riparian Buffer Authorization_20030122.~ ,
~ Soil & Environmental Consultants, PA
11010 Raven Ridge Road Raleigh, North Cazolina 27614 Phone: (919) 846-5900 Fax: (919) 846-9467
www.SandEC.com
January 21, 2003 ~~'°~-
DENR-DWQ ~ "~ 2 ~ ~
Wetland Group ~~ '
Q WI•~i i:i ~ ~ ~ ~ ~kl~tlP
Attn: Mr. Bob Zarzecki ,~ ~ ~ WRTEF, i,AaiY `>E.CI'!ON
2321 Crabtree Blvd. Suite 205 ~D `~"~ °
~~
Raleigh, NC 27604 <~~
Dear Mr. Zarzecki: tf
The purpose of this correspondence is to request a major variance from the Neuse
River Basin Maintenance of Riparian Areas rules on behalf of HWB Inc., Mr. David
Weil, president.
In August of 2002 we met on-site to evaluate the area and have met and/or
discussed the project a number of times since then. Our client has agreed to implement all
the suggestions we mutually developed regarding redevelopment of part of the site.
The project is located due south of the intersection of Hwy 70 and Hwy 581 in
Wayne County, just east of Goldsboro, NC (see Figure 1). The site is currently developed
and contains numerous metal buildings and impervious parking areas. Figure 2 is an
aerial photo of the entire property owned by HWB Inc. and specifies the area where the
proposed buffer impact would occur and the proposed on-site buffer mitigation areas.
Also enclosed are photos of the "ditch" and adjacent buffer area that is proposed to be
impacted. The photos show views from Hwy 70 (Photo 1) and Hwy 581 (Photo 2). As
you can see there is very little forest vegetation adjacent fo the feature. Figure 3 indicates
the existing woody vegetation, grass, and existing impervious area adjacent to the ditch
and also has a breakdown of buffer impacts. Even though the vast majority of buffer
impacts (0.76 acres out of 0.96 acres) are to grass areas the client proposes to mitigate on-
site at the required 3:1 ratio for Zone 1 impacts and 1:5 for Zone 2 impacts by restoring
forest vegetation to areas currently occupied by either grass or gravel parking areas (see
Figure 4).
While we concur that the proposed feature to be impacted "scores" high enough
to be classified as a stream by current DWQ criteria, we would like to point out the soils
present on-site adjacent to the ditch according to the soils survey are the Craven soils
series. Such soils are described by MRCS as moderately well drained upland soils on
rounded sides of divides. Therefore, it is unlikely that a natural stream existed in the area.
Rather the channel was probably dug historically to drain the poorly drained Rains soils
that are present west of Hwy 581.
Charlotte Office: Greensboro Office: Hicko Office:
236 LePhillip Court, Suite C 3817-E Lawndale Drive 710 Boston Road
Concord, NC 28025 Greensboro, NC 27455 Taylorsville, N 28681
Phone: (704)720-9405 Phone: (336)540-8234 Phone (828) 35-5820
Fax: (704)720-9406 Fax: (336)540-8235 Fax: (828) 35-5820
Figure 5 shows the proposed redevelopment plan for the site, which indicates an
approximate location of a Stormwater wetland for treatment of Stormwater generated at
the proposed redeveloped area. Currently there are no redevelopment plans for the
remainder of the site. However, since the site lies within Wayne County's jurisdiction, if
the balance of the area were redeveloped, compliance with the Neuse River Nutrient
Removal Standards will be required. A preliminary Stormwater management plan for the
site by S&EC dated 12/20/2002 and the required Extended Wetland Worksheet are also
enclosed.
The following list demonstrates the need for a variance:
Practical difficulties, hardships and uniqueness-
Much of the site contains existing impervious surface (1.84 acres out of 2.99
acres) that currently requires no treatment of its Stormwater.
2. Even the grassed area adjacent to the ditch is compacted and allows very little
infiltration (behaves like impervious).
3. The ditch bisects the property making major highway road frontage required for
such a redevelopment as proposed impossible.
4. The area of the site is zoned "HI" Heavy Industry by Wayne County, the
proposed redevelopment is allowed by this zoning.
5. The site was originally developed in the very early 1970's.
Why the general purpose of the intent of the rule is preserved and water quality will be
better protected if the variance is granted. None of the following will occur if the variance
is not issued.
DWQ typically requires treatment of Stormwater only for new impervious surface
on a site. The proposed plan will treat the entire 2.99 acres on-site and .41 acres of
offsite impervious surface. Currently 1.84 acres on-site and .41 acres offsite is
untreated.
2. The existing ditches on-site have very little to no woody buffer adjacent to them.
If approved 2.45 acres of woody buffer will be restored along the ditches as
shown in Figure 2 and Figure 4. These buffers will treat run off from existing
impervious surface as well as preserve them into the future. Since there is
existing impervious surface adjacent to these ditches the owner is not only
restoring a buffer but also giving up the right to continue to use the areas for
parking, storage, and driveways.
Even after doing all of the above the client will still have to pay into the WRP to
meet the nitrogen load removal standards required under the Neuse River Basin-
Nutrient Sensitive Waters Management Strategy: Basinwide Stormwater
Requirements. Based on preliminary evaluation this could be up to a $9200.00
offset payment.
Please call if you have questions or need further information in order to support
this request before the EMC.
Sincerely,
C ~- ,~ C
~~
Kevin Martin
President
OFFICE USE ONLY: Date Received Request #
State of North Carolina
Department of Environment and Natural Resources
Division of Water Quality
Variance Request Form
Neuse River Basin: Nutrient Sensitive Waters Management Strategy
Protection and Maintenance of Riparian Areas Rule (15A NCAC .0233)
" ~_
NOTE: This form maybe photocopied for use as an original.
Part 1: General Information
1. Applicant's name (the corporation, individual, etc. who owns the project):
HWB. Inc.
2. Print Owner/Signing Official (person legally responsible for the facility and its compliance)
Name: David Weil
Title: Vice President
Street address: 106 E. Walnut Street
City, State, Zip: Goldsboro. NC 27533
Telephone: (919734-1111
Fax: (919) 734-0877
3. Project Name (Subdivision, facility, or establishment name -consistent with project name on
plans, specifications, letters, operation and maintenance agreements, etc.):
Rosewood Industrial Park
4. Location of Facility
Street address: Intersection of Highway 70W and 581
City, State, Zip: Goldsboro. NC 27530
County: Wayne
Latitude/longitude: Lat: 35° 25' 30"/Long: 78° 03' 55"
5. Directions to facility from nearest major intersection (Also attach a map):
Site is adjacent to and due south of the intersection of Hwy 70 and 581. West side of
Goldsboro. NC. see Figure 1)
6. Contact person who can answer questions about the facility:
Name: David Weil
Telephone: (919 734-1111
Fax: (919) 734-0877
Email: dweil(a~weilent.com
7. Requested Environmental Management Commission Hearing Date: 2/12/03
Version 1: September 1998
Part 2: Demonstration of Need for a Variance
__ __ _.
NOTE: The variance provision of the Neuse Riparian Area Rule allows the Environmental Management
Commission to grant a variance to an affected party when the following conditions apply on a given project:
(a) practical difficulties or hardships would result from strict application of the rule:
(b) such difficulties or hardships result from conditios which are peculiar to the property involved; and
(c) the general purpose and intent of the Rule would be preserved, water quality would be protected and
substantial justice would be done if the variance were granted.
This part of the application is to explain how the project meets criteria (a) and (b).
Attach a detailed description (2-3 pages) explaining the following:
• The practical difficulties or hardships that would result from strict application of the Rule.
• How these difficulties or hardships result from conditions that are unique to the property
involved.
• Why reconfiguring and/or reducing the built-upon area to preserve a greater portion of the
riparian area is not feasible on this project. If economic hardship is the major
consideration, then include a specific explanation of the economic hardship and the
proportion of the hardship to the entire value of the project.
Part 3: Water Quality Protection
'! NOTE: This part of the application is to explain how the project meets criterion (c): the general purpose and
intent of the Rule would be preserved, water quality would be protected and substantial justice would be done if
'the variance were granted.
1. Briefly summarize how water quality will be protected on this project. Also attach a detailed
narrative (1-2 pages) describing the nonstructural and structural measures that will be used
for protecting water quality and reducing nitrogen inputs to surface water.
Please see attached 12/20/02 S&EC. PA Conceptual Stormwater Study for the project.
2. What is the total project area in acres? 3.4 acres
3. Which of the following permits/approvals will be required for this project?
CAMA Major
X Sediment/Erosion Control
X 401 Certification/404 Permit
Variance Request Form, page 2
Version 1: September 1998
Part 3: Water Quality Protection, continued
4. Complete the following information for each drainage basin. If there are more than two
drainage basins in the project, attach an additional sheet with the information for each basin
provided in the same format as below.
Project Information Drainage Basin 1 Drainage Basin 2
Receiving stream name unnamed tributary of Little
River
Receiving stream class' WS IV
Drainage basin area (total2) 4.5 acres
Existing impervious area3 (total2) 1.84 acres
Proposed impervious area3 (total2) 3.4 acres
Impervious area3 (on-site) 73.1%
Impervious area3 (total2) 75.6%
Impervious area3 Drainage basin 1 Drainage basin 2
On-site buildings 0.43 acres
On-site streets --
On-site parking 2.20 acres
On-site sidewalks 0.36 acres
Other on-site ---
Total on-site 2.99 acres
Off-site 0.41 acres
Total 3,40 acres
' The intemet site for this information is http://h2o.enr.stafe.nc.us/strmclass/alpha/neu.html
2 Total means on-site plus off-site area that drains through the project.
3 Impervious area is defined as the built-upon area including, but not limited to, buildings, parking areas,
sidewalks, gravel areas, etc.
5. How was the off-site impervious area listed above derived?
Street surface areas from Highways 70 and 581
6. What will be the annual nitrogen load contributed by this site after development in pounds per
acre per year without structural BMPs ( Stormwater pond, wetland, infiltration basin, etc)?
Attach a detailed plan for all proposed structural Stormwater BMPs.
Drainage
basin Size of
drainage
basin
ac Post-development
nitrogen loading rate
without BMPs°
Ibs/ac/ r BMP nitrogen
removal
effciency'r
% Final nitrogen
loading rate
(Ibs/ac/yr) Final nitrogen
loading from
drainage basin
Ibs
1 4.5 acres 16.31 Ibs/aclyr 40% 9.7916s/ac/yr 9.791bs/ac/ r
2
3
4
5
Totals ~.____ ------ --~._
a Attach calculations and references.
s Attach calculations and references.
Variance Request Form, page 3
Version 1: September 1998
Part 3: Water Quality Protection, continued
7. The applicable supplemental form(s) listed below must be attached for each BMP specified:
Form SWU-102 Wet Detention Basin Supplement
Form SWU-103 Infiltration Basin Supplement
Form SWU-105 Curb Outlet System Supplement
Form SWU-106 Off-Site System Supplement
Form SWU-107 Underground Infiltration Trench Supplement
Form SWU-109 Innovative BMPs Supplement
Part 4: Submittal Checklist
A complete appplication submittal consists of the following components. Incomplete submittals
will be returned to the applicant. The complete variance request submittal must be received 90
days prior to the EMC meeting at which you wish the request to be heard. Initial below to
indicate that the necessary information has been provided.
Applicant's Item
Initials
_.._....,,,~..,/~,._, Original and two copies of the Variance Request Form and the attachments
listed below.
_~ • A vicinity map of the project (see Part 1, Item 5)
_. _...~ ............._. Narrative demonstration of the need for a variance (see Part 2)
_ .................................. • A detailed narrative description of stormwater treatment/management (see Part
3, Item 1)
- --- Calculations supporting nitrogen loading estimates (see Part 3, Item 6)
• Calculations and references supporting nitrogen removal from proposed BMPs
(see Part 3, Item 6)
---- -- - Location and details for all proposed structural stormwater BMPs (see Part 3,
Item 6)
------------ -------- . Three copies of the applicable Supplement Form(s) for each BMP and/or
narrative for each innovative BMP (see Part 3, Item 7)
• Three copies of plans and specifications, including:
0 Development/Project name
_........._._._ .._........._ .................. 0 Engineer and firm
0 Legend and Wort arrow
0 Scale (1" = 100' or 1" = 50' is preferred)
0 Revision number & date
0 Mean high water line (if applicable)
0 Dimensioned property/project boundary
0 Location map with named streets or NC State Road numbers
_............_....~ .............................__ 0 Original contours, proposed contours, spot elevations, finished floor
._........_..._...._..._......._....._._. elevations
0 Details of roads, parking, cul-de-sacs, sidewalks, and curb and gutter
0 Footprint of any proposed buildings or other structures
------------ -------------- 0 Wetlands delineated, or a note on plans that none exist
0 Existing drainage (including off-site), drainage easements, pipe sizes, runoff
-- calculations
-- - 0 Drainage basins delineated
--------------- ----------- 0 Perennial and intermittent streams, ponds, lakes, rivers and estuaries
0 Location of forest vegetation along the streams, ponds, lakes, rivers and
estuaries
Variance Request Form, page 4
Version 1: September 1998
Jan 16 03 04:02p David Weil 919 734-0877 p.2
Part S: Det!d Restrictions
By your signature in Part 7 of this application, you certify that all structural stormwaler best
management practices required by this variance shall be located in reeorcted atormwater
easements, that the easements will run with the land, that the easements cannot be changed or
deleted without concurrence from the state, and That the easements will be recorded prior to the
sale of any lot.
Part 6: Agent Authorization
1f you wish to desl9nale submittal authority to another individual or firm so that they may provide
information on your behaN, please complete this sscNon:
Designated agent (individual orflrm): ~,~yin_,~art_i~. S&~ P~, „r.
Meiling address: l l o i o B~xeu..~..8a~_ ._ ~"
City, Stale, ZP~ __~.~,~c.._~~.?~~ 4 ".. ...-.." ~.-._...._._._........_.___..._
Telephone: X19 ~4~~~,Q,.,,_,_,,.~_~~,,,. ~._.
Fax: 919-8~}6-94b7 _ ,,,._,,,,,,,__.~._....._~...._,.._.,.....__........
Small: ksa~lr~.n~sandec,com __ ~..
Part 7: Applicant's Certification
I, ~~tg. _,,,_pby~ d h-.eil,-,,,~,,~_pr..e~idanx_„~ (print or type name of person listed
In Part I, Item 2), certify that the information inGuded on this permit application form is CorreG,
ihat the project will be constructed in conformance with the approved plans and that the deed
restrictions in accordance with Part 5 of this form wiH be recorded with all roquired permit
conditions.
Signature:
Date:
Title:
Vice Presid®nt . ___~~_ "" ~-__._ ~. ..._...__...._
Varlence Request Fo-m, pope 5
Version 1: 6eDtemt~er 1988
DWQ Project No.
DIVISION OF WATER QUALITY - 401 EXTENDED DETENTION WETLAND WORKSHEET
I. PROJECT INFQRMATIO (plgase complete~he following information):
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Project Name: YIN ~
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Contact rerson: A r i clt. ~ ~ Sr-- ~ ~'1~ a ~ rhone Numbcr: (~11 ~1) b - 5yI • . ~x ~f-. /
For projects with multiple basins, specify which basin this worksheet applies to: nl/a
~Pr~Y ~'S
Permanent Pool Elevation - ft. (elevation of the orifice invert out) ~1%n~l L7av'hn)
Temporary Pool Elevation - ft. (elevation of the outlet structure invert in)(GM~1 DaSrtih~
Permanent Pool Surface Area ~~ `~ ~7 _ sq. ft. (water surface area at permanent pool elevation) t'D,/S ur~~
Drainage Area ~ ac. (on-site and off-site drainage to the basin)
-
Impervious Area
b
S
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A
F ~`~ ac. (on-site and off-site drainage to the basin)
n2 aui5~
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Micro Pool Surface Area 9 ~ sq. ft. (at permanent pool elevation approximately 15%)
D,D2 QwlS1
Temporary Pool Volume /2~ 57$ cu. ft. (volume detained on top of the permanent pool) ~p,2~1 ~-G-~~.~
SA/DA used 3.3 Li (surface area to drainage area r tio)
Diameter ofOrifice - in. (draw down orifice diameter) ~5~'9a ~ i n ~~~~ I ~ Si hr,
II. REQUIRED ITEMS CHECKLIST
Initial in the space provided to indicate the following design requirements have been met and supporting
documentation is attached. If a requirement has not been met, attach an explanation of why.
Applicants Initials
n/~ The temporary pool controls runoff from the 1 inch rain.
The basin side slopes are no steeper than 3:1.
A planting plan for the marsh areas with plant species and densities is provided.
Vegetation above the permanent pool elevation is specified.
An emergency drain is provided to drain the basin.
The temporary pool draws down in 2 to 5 days.
~~ F a Sediment storage is provided in the permanent pool.
`~~ ,~ A sediment disposal area is provided.
l ~ v ~" Access is provided for maintenance.
\~ ~ ~ s ~ A site specific, signed and notarized operation and maintenance agreement is provided.
The drainage area (including any offsite area) is delineated on a site plan.
Plan details for the wetland are provided.
Plan details for the inlet and outlet are provided.
IVD7e 4 //-- )) // ~~l I/ //__
St~Pcih-t s; k N,c..7''7~;~5. Q',lM~[~95~b,n t ~ ~~LvF *1b~n S ~ll.vt -9cf
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n na -~NV~I Acc..~,/~~n S ~/J , o~~i ~~,~-a / c% 5! 7n P 1'/0. ~ v,~/~
h~ r~ quir,~~ ~'r/~ ~,//. ~~ rb-~, ~/~ ~,~ 7 ~-s w.,,~S /~r,r ~. GJ~r,rt
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December 20, 2002
S&EC Project No. 7325
Mr. David Weil
Weil Enterprises
P.O. Box 2063
Goldsboro, NC 27533
Environmental Consultants, PA
Road Raleigh, North Cazolina 27614 Phone: (919) 846-5900 Fax: (919) 846-9467
Re: Highway 581 and Highway 70 Property
Preliminary Stormwater Study
Wayne County, North Carolina
Dear Mr. Weil:
As requested, Soil & Environmental Consultants, PA, (S&EC) has completed a preliminary
stormwater study for part of the referenced property in Wayne County, NC. As part of the
permitting process you will be required to treat stormwater runoff associated with this
development in addition to treating or bypassing existing Stormwater runoff which currently
drains to the site.
We discussed the project site with Mr. Bob Zarzecki of the North Carolina Department of
Environment and Natural Resources (NCDENR), Division of Water Quality (DWQ), on
August 20, 2002. Based on this discussion it is our understanding that the design and
construction of an extended detention wetland (or Stormwater wetland) will be required for
treatment of stormwater on the property as part of the variance process and to comply with the
Neuse Basin Nutrient Removal Strategy.
The purpose of this study was to determine the approximate size (or footprint) of an extended
detention wetland required to treat stormwater from the site. This wetland would serve to treat
site stormwater through the removal of Total Suspended Solids (TSS) in accordance with the
North Carolina Best Management Practices (BMP) Manual. The wetland would also serve to
treat Stormwater for Total Nitrogen (TN) reduction in accordance with the Neuse River Basin:
Model Stormwater Program for Nitrogen Control.
This letter report presents our assumptions on future site conditions, preliminary feature sizing
rationale, and briefly describes potential stormwater features. Permitting issues associated with
Chazlotte Office: Greensboro Office: Hicko Office:
236 LePhillip Court, Suite C 3817-E Lawndale Drive 710 Boston Road
Concord, NC 28025 Greensboro, NC 27455 Taylorsville, NC 28681
Phone: (704)720-9405 Phone: (336)540-8234 Phone (828)635-5820
Fax: (704)720-9406 Fax: (336)540-R235 Fax: (828)635-5820
Mr. David Weil Page 2 December 20, 2002
any jurisdictional stream and/or wetland impacts have been addressed under a separate
correspondence. The permit from the U.S. Army Corps of Engineers (USAGE) will be requested
in January 2003. However, the required 401 Water Quality Certification from DWQ cannot be
requested until after a variance from the Neuse River Buffer rules is granted by the
Environmental Management Commission (EMC). We anticipate being heard in the February
2003 EMC meeting and will submit the 401 application as soon as a variance is approved.
For the purpose of this letter the terms "extended detention stonmwater wetland," "stormwater
wetland," and "constructed wetland," are to be used interchangeably and all refer to an extended
detention Stormwater wetland as described in the Stormwater BMP manual.
Authorization
Engineering services for a Preliminary Stormwater Study for the referenced parcel were
authorized by acceptance of Soil & Environmental Consultants, PA, Project Request Form,
Project No. 7325, on November 21, 2002, by Mr. David Weil of Weil Enterprises.
Project Description and Location
The proposed development site is located northwest of the City of Goldsboro, immediately
southeast of the Highway 581 /Highway 70 interchange in Wayne County, NC. See Figure 1.
According to Preliminary Plans prepared by Alvolis Engineering, PA, of New Bern, NC, the
subject tract consists of approximately 3.4 acres of primarily developed property.
We understand from you (the client) that a combined Bojangles Restaurant & Fuel Warehouse is
proposed for construction on the site. The proposed development is projected to impact
approximately 3701inear feet of existing channelized stream which generally flows west to east
across the site. In order to meet the requirements of the North Carolina Division of Water
Quality 401 Permit certification (associated with the proposed stream impacts), you are required
to complete a Stormwater Plan to treat stormwater discharge from the site.
Whenever possible it is your intention to intercept and divert off-site Stormwater prior to arrival
on site. However, undiverted off-site drainage from the adjoining property as well as on-site
drainage will require treatment or diversion in accordance with the requirements of the North
Carolina Department of Environment and Natural Resources, Division of Water Quality.
Extended Detention Wetland Performance and Regulatory Stormwater Treatment
Standards
Treatment of Stormwater runoff is required in accordance with the North Carolina Stormwater
Management rules. The North Carolina Department of Environment and Natural Resources
11010 Raven Ridge Road (919) 846-5900
Raleigh, North Carolina 27614 Fax (919) 846-9467
Mr. David Weil Page 3 December 20, 2002
(NCDENR), Division of Water Quality (DWQ), Best Management Practices (BMP) manual
outlines design requirements necessary to meet the pollutant removal design standard of 85
percent removal of Total Suspended Solids (TSS). Based on the BMP manual, an extended
detention wetland is assumed to have a TSS removal efficiency of 85 percent. A detention time
of two to five days is required to meet this level of efficiency. Typically, a small embankment
(or dam) and outlet device are used to detain stormwater runoff for sedimentation of suspended
particles and biological treatment of pollutants.
Based on the project location within the Neuse River Basin, the parcel must also be evaluated for
its contribution of Total Nitrogen (TN) being delivered to the receiving watercourse (an unnamed
tributary of the Little River). Constructed properly, extended detention wetlands also contribute
significantly to the removal of TN. According to the Neuse River Basin: Model Stormwater
Program for Nitrogen Control, dated August 30, 1999, extended detention wetlands are currently
considered to remove 40 percent of the TN from stormwater inflow. Stormwater wetlands,
incidentally, are cited as having the highest TN removal rates of any of the commonly accepted
stormwater BMP's currently in use.
As described in the cited program literature, for commercial and residential development, the
rules require that nitrogen export of 3.6 pounds per acre per year (lbs/ac/yr) or less be achieved.
In the case where proposed commercial development results in TN export rates less than 10.0
lbs/ac/yr, then the owner may either;
1) Install BMPs to remove enough nitrogen to bring the development down to 3.6
lbs/ac/yr, or
2) Pay aone-time offset payment (to the NC Wetlands Restoration Program, WRP) of
$330/lb to bring the nitrogen down to 3.61bs/ac/yr, or
3) Do a combination of BMPs and offset payment to achieve the 3.6 lbs/ac/yr export.
If a particular development has a computed export rate greater than 10.0 lbs/ac/yr, then the owner
must use on-site BMPs to bring the development's export down to 10.0 lbs/ac/yr. Then, the
owner may use one of the three options described above to achieve the nitrogen reduction
between 10.0 lbs/ac/yr and 3.6 lbs/ac/yr.
Based on our discussion with the Division of Water Quality, we understand that once treated for
TSS and TN removal, stormwater from an extended detention wetland can be discharged directly
into the receiving watercourse. It is our understanding that based on the project location, all
proposed stormwater treatment devices must be reviewed and approved by the engineering staff
at DWQ.
11010 Raven Ridge Road (919) 846-5900
Raleigh, North Carolina 27614 Fax (919) 846-9467
Mr. David Weil Page 4 December 20, 2002
Proposed Site Development and Drainage Systems
For the purpose of stormwater feature sizing we assumed that limited off-site stormwater (that
from the highways to the north) would require treatment, and thus approximately 4.5 acres of
drainage area would require treatment in the extended detention wetland. Drainage currently
entering the site from the west and south will be passed through the site by piping and/or
relocating the existing channelized stream that bisects the front (northern) part of the tract.
Since we are unaware of the grading details of the proposed development we have only evaluated
site stormwater for the conditions depicted on the plan provided. We have assumed that future
grading would direct stormwater in a generally southward direction away from the
aforementioned highway intersection. In order to meet the regulatory treatment requirements, all
on-site storm drainage must be designed to drain to a sediment forebay of the extended detention
wetland.
Site Constraints on Stormwater Treatment
Site constraints included the proposed development, property lines, the highways and associated
right-of--ways, existing buildings on adjoining properties, and any surface or subsurface conduits
used to transport discharges from the existing (to be impacted) intermittent stream. In large part,
these site constraints limit the areas available for stormwater treatment.
Future Stormwater planning to included grading, pipe network layout, and outfall locations
should all be carefully considered for compatibility with potential locations selected for the
construction of an extended detention wetland. Construction access to the site, as well as
permanent maintenance access to the required sediment forebay (for sediment removal and
disposal) should also be considered during site planning and layout.
Additionally, erosion and sediment control plans, including both temporary and permanent
structures should be planned accordingly so as not to interfere with wetland construction. It may
be possible to use some part of the area slated for the Stormwater wetland as part of the sediment
treatment system during site construction, thus potentially reducing overall construction costs.
The engineering firm responsible for this aspect of the project will need to be instructed to
closely coordinate their work with S&EC to ensure compliance with the requirements of the
variance and wetland permits.
Wetland Surface Area and Footprint
The Stormwater wetland footprint was estimated based on the required surface area (forebay,
planted wetland, and outlet micropool) as well as a temporary storage volume sufficient to handle
11010 Raven Ridge Road (919) 846-5900
Raleigh, North Carolina 27614 Fax (919) 846-9467
Mr. David Weil Pale 5 December 20, 2002
the runoff from the first one inch of rainfall from the contributing drainage area. The shape of
the wetland footprint maybe adjusted to work within the property boundary limitation provided
by the property boundaries and other site constraints.
Based on a review of the proposed site plan, drainage area delineation estimate approximately 4.5
acres will contribute runoff requiring treatment. Of this area, 3.4 acres (building and parking
footprints only) was considered to be 100 percent impervious resulting in an impervious
percentage of approximately 76 percent (rounded to 80 percent for design purposes).
A permanent pool depth of three feet was selected for these analyses as prescribed in the design
guidance. This resulted in a design Surface Area to Drainage Area (SA/DA) ratio of 3.36. Using
methods described in the BMP manual, the constructed wetland was sized with a minimum
wetland surface area of 6,587 square feet (ft.2) or approximately 0.15 acres.
A temporary water quality pool is also required to provide storage volume sufficient to handle
the runoff associated with the first one inch of rainfall which falls on the contributing drainage
area. Using the "Simple Method" described in the BMP manual we estimated a required volume
of approximately 0.29 acre-feet (12,578 ft.3). Considering a wetland surface area of 0.15 acres,
we find a resultant temporary pool depth of approximately 2 feet is needed.
According to the BMP manual, a forebay established by a weir must be included to encourage
early settling of larger particles before they enter the wetland area. The forebay surface area is
typically required to be approximately 15 percent of the overall wetland surface area footprint.
The sediment forebay should be constructed to accept discharge from the proposed piped (or
otherwise conveyed) stormwater from the site. The number and location of the concentrated
stormwater inlets from the site will depend on the proposed development grading and storm drain
design. Typically approximately 70 percent of the footprint is finely graded to an elevation of
zero to six inches above Normal Pool elevation. The remaining 15 percent of the footprint is
maintained as open water in the form of micropools and open channels including a small pool at
the wetland outlet.
Without refined site topographic data it is unclear if an earthen fill embankment maybe required
to form the perimeter (or a portion of the perimeter) of the constructed stormwater wetland.
Whether the wetland is formed by excavation, embankment construction, or a combination of the
two specific grading is necessary. It is typically desired to grade the slopes of the temporary
water quality pool not steeper than 6H:1 V for safety purposes and to provide additional area for
plant material. Typically slopes not steeper than 3H:1 V should be used on both the inside
(upstream) and outside (downstream) slopes of the wetland and its embankment, starting at top
of the temporary water quality pool. The crest with for the embankment should be at least 10 feet
to allow for ease of construction and future maintenance. Based on available topographic
11010 Raven Ridge Road (919) 846-5900
Raleigh, North Carolina 27614 Fax (919) 846-9467
Mr. David Weil Page 6 December 20, 2002
mapping, elevation change are slight, accordingly the volume of fill material necessary for
construction of an embankment is not expected to be significant.
Nitrogen Export Rate Calculations
We estimated Nitrogen Export rates associated with the proposed development using methods
outlined in the Neuse River Basin: Model Stormwater Program for Nitrogen Control guidelines.
For the purposes of our initial estimates we assumed that 3.4 acres would be developed as
described above. We also assumed that the remaining 1.1 acres would be Permanently Protected
Managed Open Space (grass, landscaping, etc.). This category, along with Impervious Surface
(roads, parking lots, roofs, etc.) are defined in the literature for use in calculations of TN. The
resulting TN export from development was calculated at approximately 73.41bs/yr, with a
nitrogen export coefficient of 16.31 lbs/ac/yr.
Since the export coefficient is greater than l O lbs/ac/yr a BMP must be used to reduce the
coefficient below the l O lbs/ac/yr threshold. The proposed BMP (extended detention wetland)
can be assumed to reduce TN by 40 percent to 9.791bs/ac/yr. At this point additional BMPs, an
offset payment, or a combination of the two would be required to meet the 3.61bs/ac/yr standard.
If the offset payment is proposed as the only option, then we estimate the offset payment at
6.19 lbs/ac/yr (9.79 -3.60) times 4.5 acres times $330/lbs or approximately $9,200.
Conclusions and Recommendations
For planning purposes we are providing the following conclusions and recommendations:
The overall basin size at the toe of the perimeter slope can be estimated at approximately
2 to 3 times the surface area of the permanent stonnwater wetland pool depending on site
conditions. Accordingly, we recommend that a useable area of 0.3 to 0.45 acres be
reserved for construction of the extended detention wetland. The attached site plan shows
possible locations of the stormwater wetland. Please advise us of your preferred location.
2. It should be remembered that the stormwater wetland footprint may vary significantly
depending on local topography, and as such, close consideration should be given to the
selection of wetland location and orientation. Property boundary stand-offrequirements
should be confirmed.
We understand that no site soils evaluation has been performed to date. The design and
construction of select stonmwater treatment devices (to include stormwater wetlands) can
be complicated or unsuitable depending on the results of such an evaluation. We
recommend that we be allowed to review the selected stormwater wetland location for
11010 Raven Ridge Road (919) 846-5900
Raleigh, North Carolina 27614 Fax (919) 846-9467
Mr. David Weil Page 7 December 20, 2002
suitability and to ascertain that the reserved area is adequate for the stormwater wetland
and its appurtenances are compatible with the results of our site soils evaluation.
4. As described in our project scope, Soil & Environmental Consultants, PA, will design the
components of the stormwater wetland, to include the primary spillway structure and its
components, the emergency spillway, inlet and outlet protection, and wetland plantings.
However, we recommend that such design services be delay until such time that a
variance is granted by the EMC.
5. All on-site storm drainage from areas to be treated should be designed to drain through
gravity means to the sediment forebay of this constructed wetland. All other drainage
from off-site areas, should be diverted around the site and away from the wetland forebay
if possible.
6. All of the site constraints previously listed should be confirmed prior to final design of a
stormwater wetland (or other stormwater or development features) to ensure no conflicts
exist. This will require that the engineer responsible for the site planning and local
permitting coordinate with S&EC.
Other Considerations
Coordination of other design professionals' work is required to make this or any stormwater
system function as intended. Design and construction of other site features (ie. facilities
expansion, road network, etc.) should consider the possibility that changes to Construction Plans
and Technical Specifications may become necessary after regulatory review comments are
received on any stormwater plan.
Because we are unaware of the exact details of proposed development depicted on the current
development plans we have only performed a limited site stormwater evaluation. This evaluation
only considered the site conditions depicted on the drawings provided. Accordingly any changes
to this depiction are likely to impact our evaluation and recommendations of potential site
stormwater features.
Consideration should also be given to the use of other stormwater features such as bioretention
areas and infiltration devices. While these alternative treatment devices may not be suitable for
treatment of all site stormwater requirements, they are effective in TSS and TN removal (and
potential offset payment reductions). Additionally, these alternatives can potentially reduce the
space required, construction effort, and associated costs required for more conventional treatment
devices. These devices also provide improvements to the proposed development site in the form
of vegetated parking lot islands and other landscaped buffers which are not only functional for
stormwater treatment but aesthetically appealing as well.
11010 Raven Ridge Road (919) 846-5900
Raleigh, North Carolina 27614 Fax (919) 846-9467
Mr. David Weil Page 8 December 20, 2002
Limitations
It should be remembered that this report is preliminary and that our evaluations, conclusions, and
recommendations are based on project and site information available to us at the time of this
letter report. Recommendations presented in this letter may require modification if there are any
changes in the project or site conditions, or if additional data about the project or site becomes
available in the future. Additionally, decisions regarding any outstanding permit issues or
policies issued by governing regulatory agencies are beyond our control, and as such
modifications to our evaluation, conclusions, and/or recommendations maybe necessary.
If you have any questions concerning this submittal, or if we may be of further service, please do
not hesitate to call us. We appreciate the opportunity to work with you.
Sincerely,
SOIL & ENVIROr(~~~~t
~~~0
`~ ~FF,SS/~
4
SEAL
Patnck K. Smit~ P. 0296
N.C. License No'.2 .___.~~
Attachments: Fi
~NSULTANTS,PA
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Figure 2, Proposed Site Plan
Appendix A -Preliminary Stormwater Calculations
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Nitrogen Export Rate Calculations: ~a~ Iti~ I$ ~ OZ
Method 2
Quantifying TN Export from Residential /Industrial /Commercial Developments
when Footprint of all Impervious Surtaces are Shown
Calculation Steps:
Step 1 Determine area for each type of land use and enter in in Column (2).
Step 2 Total the areas for each type of land use and enter at the bottom of Column (2).
Step 3 Multiply the areas in Column (2) by the TN export coefficients in Column (3) and enter in Column (4).
Step 4 Total the TN exports for each type of land use and enter at the bottom of Column (4).
Step 5 Determine the export coefficient by dividing the total TN export from uses at the
bottom of Column (4) by the total area at the bottom of Column (2).
Column #
(1) (2) (3) (4)
Type of Area TN Export TN Export
Land Cover (acres) Cceff. from Use
Ibs./ac./ r. IbsJ r.
Peranently Protected Undisturbed 0.00 0.60 0.00
Open Space (forest, unmown meadow)
Permanently Protected Managed 1.10 1.20 1.32
Open Space (grass, landscaping, etc.)
Impervious Surfaces (roads, parking, 3.40 21.20 72.08
lots, driveways, roofs, paved storage
areas, etc.)
TOTAL 4.50 73.40
Total Nitrogen Export Coefficient = ~l;ti:31
NOTE: If TN export rate is greater than 10.0 IbsJac./yr. then a BMP must be installed
to remove enough Nitrogen to bring the TN export rate below 3.6 IbsJacJyr.
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BUFFER MITIGATION
STACKHOUSE INC
WEIL ENT.
HWY 70 & HWY 581
WAYNE COUNTY, NORTH CAROLINA
NOVEMBER 2002
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BUFFER MITIGATION
RESTORA TION AREA UP TO 50-100'
106,804 SO. FT. (2.45 AC.)
/ TOP OF BANK
/ EXISTING FOREST VEGETATION
SOIL & ENVIRONMENTAL CONSULTANTS, PA
11010 Raven Ridge Rd., Raleigh North Carolina 27614 (919)846-5900 (919)846-9467 Fx
FIGURE 4
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PROPOSED SITE PLAN
STACKHOUSE INC ~ SOIL & ENVIRONMENTAL CONSULTANTS, PA
WEIL ENT.
H WY 70 & H WY 581 11010 Raven Ridge Rd., Raleigh North Carolina 27614 (919) 846-5900 (919) 846-9467 Fx
WAYNE COUNTY, NORTH CAROLINA
NOVEMBER 2002 FIGURE 5
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