20110260 Ver 1_More Info Received_20110921

The University of North Carolina at Chapel Hill
- Department of Environment, Health & Safety
1120 Estes Drive Ext., CB# 1650
Chapel Hill, North Carolina 27599-1650
September 20, 2011
Karen Higgins
North Carolina Department of Environment and Natural Resources
Division of Water Quality
Wetlands, Buffers, Stormwater, Compliance and Permitting
1650 Mail Service Center
Raleigh, North Carolina 27699-1650
Reference: Response to June 3, 2011 Request for More Information with 90-Day Extension
The
DWQ Project # 11-0260 ? t,
The University of North Carolina at Chapel Hill D D
Orange County
North Carolina S E P 2 1 2011
Dear Ms. Higgins: DENR•WATER QUALITY
WETLANDS AND sTmoTER BRANCH
The following responses are provided to address the remaining comments contained in
your June 3, 2011 Request for More Information pertaining to the Individual Permit (IP)
Application for the Carolina North Project. The Department of Environment and Natural
Resources, Division of Water Quality (DWQ) previously granted The University of
North Carolina at Chapel Hill (UNC-CH or University) a 90-day extension in order to
respond to comments 1 and 2. Each DWQ comment is provided in italics and the
University's response follows:
This project is subject to Stormwater Management Plan (SMP Requirements for
Applicants Other Than the North Carolina Department of Transportation (see
http://portal.ncdeni-.org/iveb/wq/swp/ws/401/certsandpernzits/.5wmanagement). For each
proposed BMP, please provide a completed BMP Supplement Form with all required
items (see hyp:Aportal.nedenr.or??/ti>>eb/wq/ws/su/binp-manual).
The 50-year Carolina North development shown in the IP Application for Carolina North
will occur in phases that correspond to projects funded for design and construction. For
each project, SMP approval will be sought from DWQ or the Town of Chapel Hill, which
is a certified local government. The Carolina North Phase 1 SMP is provided with this
submittal and includes a completed BMP Supplemental Form.
2. Is this project being reviewed by the North Carolina State Clearinghouse under SEPA?
If so, has a FONSI or FOSI been generated? Please provide this documentation or a
timeline as to when it may be submitted if applicable.
The project is being reviewed by the North Carolina State Environmental Review
Clearinghouse (Clearinghouse) under the State Environmental Policy Act (SEPA). A
FONSI was prepared for the project and was submitted to the Clearinghouse. The review
close date for the FONSI is September 26, 2011.
{000493 50.DOC }

UNC-CH understands that no impacts to wetlands, waters or protected buffers are
authorized at this time. If you have any questions regarding this submittal or need
additional information, please contact me at [phone] or Jill Coleman at (919) 843-
3246.
Sincerely,
r?Xl Y ` ?
Sharon A. Myers, L.G.
Environmental Compliance Officer
Cc: Ms. Jill Coleman
Dr. Daniel Elliott
Ms. Mary Beth Koza
Mr. Kevin Nunnery
Mr. Bruce Runberg
Mr. Andy Williams
Ms. Anna Wu
{00049350.DOC}Page 2 of 2
ul
THE UNIVERSITY
of NORTH CAROLINA
at CHAPEL HILL
Basis of Stormwater
Design for Carolina
North Parking Lot -
Initial Phase /( 0?
s -
? P 2 ?011
W Df M""TER
"""?NDSgiypSTAl1Ty
?ENBRgNCN
September 2011
Prepared by: Biohabitats, Inc.
9/16/2011
Contents
1 Introduction .............................................................................................................................1
2 Site Description ........................................................................................................................ 1
3 BMP Description and Satisfaction of Regulatory Requirements .............................................1
APPENDIX A - Design Plans: DWQ 401 Stormwater Submittal - September 2011
APPENDIX B - Design Calculations
APPENDIX C - Supplemental Form
APPENDIX D - Soils Investigation Report
APPENDIX E - Maintenance Plan
1 Introduction
As part of the requirements for the North Carolina Division of Water Quality's (DWQ) 401/404
certification, this stormwater plan was developed for the parking lot which is the first
infrastructure at Carolina North to be designed.. The stormwater plan complies with the 401
water quality certification requirements. Specifically, a bioretention area was designed in
accordance with the NCDENR Stormwater BMP Manual to treat runoff from the parking lot. The
bioretention meets the 401 water quality requirements of 85% total suspended solids and 30%
nutrient reduction.
2 Site Description
The portion of the Carolina North site that will be redeveloped into a parking lot is currently
part of the Horace Williams Airport. The area consists of an existing hanger, paved airplane taxi
ways and tie-down areas, and associated managed turf grass.
Under existing conditions, drainage from this area flows east and southeast via overland flow,
drainage swales, and culverts to an intermittent stream. This stream enters an extensive storm
drain system downstream of Estes Drive Extension then discharges into Cole Springs Branch, a
tributary of Bolin Creek.
The proposed parking lot will consist of parking lot islands, landscaped areas, and a stormwater
treatment practice. Grading of the site is such that there is limited additional area that flows to
the parking lot. All non-parking lot surfaces in the drainage area are either landscaped or part of
the stormwater Best Management Practice (BMP). The proposed parking lot is graded to
provide sheet flow of stormwater toward the northeast where treatment can be provided (See
attached plans - Appendix A: DWQ Stormwater Submittal - September 2011). Discharge from
the bioretention will exit the site using an existing conveyance.
Under existing and proposed conditions, this site discharges to design point CS3 as shown in
Maps 3 and 4 of the Stormwater Concept Plan for Carolina North, which is Appendix F of the
Individual Permit Application for Carolina North.
3 BMP Description and Satisfaction of Regulatory Requirements
The entire watershed area associated with the parking lot is 3.4 acres in size and 72.6%
impervious. A bioretention area will be installed along the northern edge of the parking lot to
receive sheet flow. A gravel verge / grassed filter strip on a 3:1 slope is utilized as pretreatment
to allow sediment deposition, even spreading of influent runoff, and to slow down the runoff.
One foot of ponding depth is provided in the system to store the water quality event. Due to the
presence of poorly infiltrating clay soils, appropriately sized underdrains (with clean-outs) are
1
utilized to draw down the ponded water within 12 hours, and drain the bioretention media to
two feet below the surface within 24 hours.
In this region of North Carolina, the water quality design storm is one inch. The simple method
was used to calculate the water quality volume. Given the desired ponding depth within the
bioretention area, the BMP surface area was determined. Runoff in excess of this volume enters
and bypasses the bioretention treatment via an overflow structure located on the eastern end
of the facility. The underdrains are also tied into this structure with watertight connections.
All drainage from the underdrains and overflow structure are conveyed via reinforced concrete
pipe to an existing conveyance.
The bioretention fill media utilized for this BMP meets all criteria from the NCDENR Stormwater
BMP Manual. This includes an appropriate sand/clay/organic breakdown and an acceptable p-
index value. As the system will be planted with trees and shrubs, 3 feet of bioretention media is
utilized.
The bioretention is overlain with a 4-inch layer of double shredded mulch. An array of trees,
shrubs, and herbaceous species are utilized in the design. The bioretention area is broken into
two planting zones to account for varied soil moisture and standing water conditions. Such
divisions are necessary to ensure that plants are installed in conditions that will ensure
maximum survival according to their environmental needs.
Per the NCDENR Stormwater BMP Manual, this properly designed bioretention area is given
credit for 85% total suspended solids, 35% total nitrogen, and 45% total phosphorus removal.
As such, this design meets the 401 water quality criteria. Further, the 401 diffuse flow
requirement is waived with the use of an appropriate water quality BMP, which is also satisfied
by this design.
All calculations for the bioretention area are presented in Appendix B.
2
APPENDIX A - Design Plans:
DWQ 401 Stormwater Submittal - September 2011
Permit Number:
(to be provided by DWQ)
OF'N AT §
_y [
HCDENR
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION APPLICATION FORM
BIORETENTION CELL SUPPLEMENT
This form must be filled out, printed and submitted.
The Required Items Checklist (Part 111) must be printed, filled out and submitted along with all of the required information.
I. PROJECT INFORMATION
Project name Carolina North
Contact name Jon Hathaway, PE, PhD - Water Resources Engineer, Biohabitats, Inc.
Phone number 919-518-0311
Date September 16, 2011
Drainage area number n/a
II. DESIGN INFORMATION
Site Characteristics
Drainage area 148,397 ftz
Impervious area 107,801 ftZ
Percent impervious 72.6% %
Design rainfall depth 1.0 inch
Peak Flow Calculations
Is pre/post control of the 1-yr, 24-hr peak flow required? N (Y or N)
1-yr, 24-hr runoff depth n/a in
1-yr, 24-hr intensity n/a in/hr
Pre-development 1-yr, 24-hr peak flow n/a ft3/sec
Post-development 1-yr, 24-hr peak flow n/a ft3lsec
Pre/Post 1-yr, 24-hr peak control #VALUE! ft3lsec
Storage Volume: Non-SA Waters
Minimum volume required 8,703.0 ft3
Volume provided 8,850.0 ft3 OK
Storage Volume: SA Waters
1.5 runoff volume N/A ft3
Pre-development 1-yr, 24-hr runoff N/A ft3
Post-development 1-yr, 24-hr runoff N/A ft3
Minimum volume required #VALUE! ft3
Volume provided N/A ft3 #VALUE!
Cell Dimensions
Ponding depth of water 12 inches OK
Ponding depth of water 1.00 ft
Surface area of the top of the bioretention cell 8,850.0 ft2 OK
Length: 426 ft OK
Width: 21 ft OK
-or- Radius n/a ft OK
Media and Soils Summary
Drawdown time, ponded volume 8 hr OK
Drawdown time, to 24 inches below surface 16 hr OK
Drawdown time, total: 24 hr
In-situ soil:
Soil permeability nla in/hr OK
Planting media soil:
Soil permeability 1.50 in/hr OK
Soil composition
% Sand (by volume) 86% OK
% Fines (by volume) 10% OK
Form SW401-Bioretention-Rev.8
June 25, 2010 Parts I and 11. Design Summary, Page 1 of 3
Permit Number:
(to be provided by DWQ)
% Organic (by volume) 4% OK
Total; 100%
Phosphorus Index (P-Index) of media 20 (unitless) OK
Form SW401-Bioretention-Rev.8
June 25, 2010 Parts I and II. Design Summary, Page 2 of 3
Permit Number:
(to be provided by DWQ)
Basin Elevations
Temporary pool elevation
Type of bioretention cell (answer "Y" to only one of the two following
questions):
Is this a grassed cell?
Is this a cell with trees/shrubs?
Planting elevation (top of the mulch or grass sod layer)
Depth of mulch
Bottom of the planting media soil
Planting media depth
Depth of washed sand below planting media soil
490.70 fmsl
N (Y or N)
Y (Y or N) OK media depth
489.7 fmsl
4 inches OK
486.3 fmsl
3.4 ft
0.3 ft
Are underdrains being installed?
How many clean out pipes are being installed?
What factor of safety is used for sizing the underdrains? (See
BMP Manual Section 12.3.6)
Additional distance between the bottom of the planting media and
the bottom of the cell to account for underdrains
Bottom of the cell required
SHWT elevation
Distance from bottom to SHWT
Internal Water Storage Zone (IWS)
Does the design include IWS
Elevation of the top of the upturned elbow
Separation of IWS and Surface
Planting Plan
Number of tree species
Number of shrub species
Number of herbaceous groundcover species
Additional Information
Does volume in excess of the design volume bypass the
bioretention cell?
Does volume in excess of the design volume flow evenly distributed
through a vegetated filter?
What is the length of the vegetated filter?
Does the design use a level spreader to evenly distribute flow?
Is the BMP located at least 30 feet from surface waters (50 feet if
SA waters)?
Is the BMP localed at least 100 feet from water supply wells?
Are the vegetated side slopes equal to or less than 3:1?
Is the BMP located in a proposed drainage easement with access
to a public Right of Way (ROW)?
Inlet velocity (from treatment system)
Is the area surrounding the cell likely to undergo development in the
future?
Are the slopes draining to the bioretention cell greater than 20%?
Is the drainage area permanently stabilized?
Pretreatment Used
(Indicate Type Used with an "X" in the shaded cell)
Gravel and grass
(8'inches gravel followed by 3-5 ft of grass)
Grassed swale
Forebay
Other
Form SW401-Bioretention-Rev.8
June 25, 2010
Y (Y or N)
9 OK
10 OK
1ft
485 fmsl
483 fmsl
2ft OK
N (Y or N)
nla fmsl
#VALUE! ft
#VALUE!
3
3
9 OK
Y (Y or N) OK
NIA (Y or N) Enter Data
NIA ft
N/A (Y or N) Enter Data
Y (Y or N) OK
Y (Y or N) OK
Y (Y or N) OK
NIA (Y or N) Insufficient ROW location.
0.98 ft/sec OK
N (Y or N) OK
N (Y or N) OK
Y (Y or N) OK
X
OK
Parts I and 11. Design Summary, Page 3 of 3
Permit Na.
(b be -ig- d by DWI)
Ill. REQUIRED ITERIS CHECKLIST 7-71
Please indicate the page or plan sheet numbers where the supporting documentation can be found An incomplete submittal package will
result In a request for addfllonal IMormadon. This will delay final review and approval of the preject. Initial in the space provided to
indicate the following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a
requirement has not been mat, attach ]uslificatlon.
Pagel Plan
Intuals Sheet No.
JPA_ SMd I
1. Plans (1' - 5U or larger) of the entire site showing:
Ap `k? Design st ultimate Kama-oul,
Off-site drainage (if applicable),
Delineated drainage basins (include Rational C ooeffiaerit per basin),
Cell dimensions,
Pretrcehnent system,
High flaw bypass system,
Maintenance access,
- Recorded drainage easement and public right of way (ROW).
Clean out pipe locations,
- Overflow device, and
Boundaries of drainage easement.
OW aJ ? 2. Plan details (1' = 30' or larger) for the bioretention cell showing
h Cell dimensions
Pretreatment system,
High flow bypass system,
Maintenance access,
Recorded drainage easement and public right of way (ROW),
Design at ultimate build•oul,
- Oft-site drainage (d applicable),
Clean out pipe locations,
Overflow device, and
Boundaries of drainage easement.
Indicate the P-Index between 10 and 30
3. Section view of the bioretention cell (1' = 2(7 or larger) showing:
?x A Side slopes, 3:1 or lower
Underdrain system (if applicable), and
Biorelerdion cell layers (ground level and slope, pre-treatment. Portding depth, mulch depth, 611 media
depth, washed sand filter fabric (or choking stone if applicable), #57 stone, underdrams (d applicable),
SHWT level(s), and overflow structure]
41 4. A soils report that is based upon an actual field investggelim soil borings, and infiltration tests. The
results of the soils report must be verified in the field by DWO, by completing & submitting the soils
investigation request form. County soil maps are rat an acceptable source of soils information. All
elevations shall be in feet mean sea level (fmsq. Results of soils tests of both the planting soil and the in
situ soil must include:
Sal permeability,
Sal composition (% sand, %lines, %organic), and

_ \
1 p1Y P-index
5. A detailed plaiting plan (1' = 2(Y or larger) prepared by a qualified individual showing:

k A variety of suitable species,
Sizes, spacing and locations of plantings,
Total quantity of each type of plant spea6ed,
- A planting detail,
The source nursery for the plants, and
Fertilizer and watering requirements to establish vegetation.
L I? 6. A construction sequence that shows how the bioretention cell will be protected from sediment until the
entire drainage area is stabilized
??1k} AW&LILR 7. The supporting calculations (including underdra in calculations, if applicable).
A 8. A copy of the signed and notarized inspection and maintenance (18M) agreement. SPA e k?A rlGl1 tW1 IV) At;iG1G tX C
-NA 9. A copy of the deed restriction.
Form S1nM M4NWeWn9W-Rev.7 Pert tn, Page 1 or 1
Bioretention Cell Supplement Form - Explanation of Selected Items
Section II Design Information
Per the 401water quality requirements, no peak flow mitigation is required for this stormwater
design. Thus, for questions on the supplemental form regarding peak flow reduction (lines 30-35
of the Design Summary), the designer input "n/a."
No infiltration into in situ soils is assumed for this design. Underdrains are installed to properly
drain the bioretention cell. Thus, no in situ soils information is provided in line 67 of the Design
Summary section of the supplemental form (the designer replied "n/a").
The designers understand that no diffuse flow requirement is present for this stormwater plan
given the use of a BMP that provides adequate nutrient removal. Thus, on lines 116-118 of the
Design Summary section of the supplemental form, the designers have responded "n/a."
Section III Required Items Checklist
Item 1: Plans of the site are included in Appendix A, Sheet 2.
• The plans show the Phase 1 build-out. For ultimate build-out conditions, refer to the maps in
Appendix A of the Individual Permit Application for Carolina North.
No easements are recorded on University land as it is a State property. As State property, those
seeking entry for inspection and maintenance purposes have right-of-entry. In lieu of drainage
easements, the University's stormwater engineers require designers to show the maintenance
corridors in stormwater submittals. The University stormwater engineers review all projects on
campus and ensure that maintenance access to existing stormwater infrastructure is
maintained.
Item 2: Plan details for the bioretention cell are included in Appendix A, Sheet 3. Details for the
overflow structure are shown on Sheets 5 and 6.
• See explanations for Item 1.
Item 3: Section view of the bioretention cell is shown in Appendix A, Sheet 4
Item 4: The soils report is included as Appendix D.
• No infiltration into in situ soils is assumed for this design. Underdrains are installed to properly
drain the bioretention cell. Therefore, no on-site infiltration tests were performed as part of the
soil site investigation report.
For the on-site soil investigation, only the seasonal high water table was determined by a
Licensed Soil Scientist.
Item 5: Detailed planting plans are included in Appendix A, Sheets 7 and 8.
Item 6: A construction sequence is included in Appendix A, Sheet 9.
Item 7: The supporting calculations are included as Appendix B.
Item 8: The I&M plan is included as Appendix E.
• The I&M plan is not signed and notarized. DWQ holds the University responsible for
inspecting and maintaining all BMPs on campus through the University's NPDES Phase II
permit. The University's stormwater engineers require each designer to submit a site-specific
I&M plan. After construction, a University stormwater engineer meets the University's
Grounds stormwater crew on site to review the BMP features and maintenance requirements.
The University stormwater engineers enter the BMP into the GIS inventory and the preventive
maintenance software. The site specific I&M plans are incorporated with a BMP information
binder given to the Grounds stormwater crew who perform BMP maintenance. Preventive
maintenance work orders are automatically generated for the Grounds stormwater crew. The
University stormwater engineer performs a formal inspection once per year. Additionally,
Grounds crews and stormwater engineers conduct frequent, informal, visual inspections.
Item 9: No deed restriction is included.
0 As discussed, no deed restriction has been included because this is State property.
APPENDIX D - Soils Investigation Report
Biohabitats
SM'TIIEAST BIMUGIOX
8218 Creedmoor Road, Suite 201
Raleigh, NC 27613
tel [phone]
far 919-518-0313
www.biohabitats.com
MEMORANDUM
Date: August 26, 2011
To: NCDENR Stormwater Permitting Group
From: Kevin Nunnery, Ph.D., LSS
RE: Soils Report for Phase 1, Carolina North Stormwater BMP, UNC-
Chapel Hill
On July 21, 2011 the soil was sampled on the Carolina North property at the location of the
proposed stormwater bioretention BMP for Phase 1 of the project. The soil core location
coordinates are: 35° 56' 05.89"N, 79° 03' 37.75"W. This location is adjacent to a taxi lane for
the Horace Williams Airport, in a grassy area. The airport runway was constructed on rolling
topography during World War II, and fill is present across the entire site. The evidence of fill is
noted in the soil characteristics listed below.
Depth inches Soil Color Soil Texture
0-6 7.5YR 6/6 sand clay loam
6-38 fill material, mixed 50%-50% 10YR 8/6 and 5YR 4/6 clay loam
38-46 5YR 6/8 silty clay loam
46-56 fill material, mixed 50%-50% 10YR 8/6 and 5YR 4/6 ..
cla loam
56-76 5YR 6/6 silty clay loam
76-84 5YR 6/8 silty cla loam
84-102 fill material, mixed 60%40% 5YR 6/8 and 10YR 7/6 cla loam
The elevation at the soil boring location is 491.5 feet above mean sea level (MSL). The invert of
the proposed BMP is 485 feet above MSL. The depth of the soil core was 102 inches (8.5 ft) or
an elevation of 483 feet above MSL.
Soils Report
Page 2
Based on the high chroma of the soils and lack of redoximorphic features, there were no
indications of the seasonal high water table encountered to a depth of 102 inches (8.5 ft.) or an
elevation of 483 feet above MSL. No indications of a seasonal high water table were encountered
from the elevation of the invert of the proposed BMP (485 feet MSL) to a depth of 483 feet
MSL, or two feet below the proposed invert.
Kevin Nunnery, Ph.D., NC icensed Soil Scientist #1235
Biohabitats, Inc.
APPENDIX E - Maintenance Plan
Permit Number:
Bioretention Operation and Maintenance Plan
The bioretention area will be inspected and maintained according to the University of
North Carolina at Chapel Hill's Stormwater Infrastructure Inspection and Maintenance
Manual and the information below.
Important operation and maintenance procedures:
- Immediately after the bioretention cell is established, the plants will be watered
twice weekly if needed until the plants become established (commonly six
weeks).
- Snow, mulch or any other material will NEVER be piled on the surface of the
bioretention cell.
- Heavy equipment will NEVER be driven over the bioretention cell.
- Special care will be taken to prevent sediment from entering the bioretention cell.
Inspection activities shall be performed as follows. Any problems that are found shall
be repaired immediately.
BMP element: Potential problems: How I will remediate the roblem:
The entire BMP Trash/debris is resent. Remove the trash/ debris.
The perimeter of the Areas of bare soil and/or Regrade the soil if necessary to
bioretention cell erosive gullies have formed. remove the gully, and then plant a
ground cover and water until it is
established. Provide lime and a
one-time fertilizer application.
The inlet device: stone Stone verge is clogged or Remove sediment and clogged
verge covered in sediment. stone and replace with clean stone.
The pretreatment area Flow is bypassing Regrade if necessary to route all
pretreatment area and/or flow to the pretreatment area.
gullies have formed. Restabilize the area after grading.
Sediment has accumulated to Search for the source of the
a depth greater than three sediment and remedy the problem if
inches. possible. Remove the sediment and
restabilize the pretreatment area.
Erosion has occurred. Provide additional erosion
protection such as reinforced turf
matting or riprap if needed to
prevent future erosion problems.
Weeds are present. Remove the weeds, preferably by
hand.
Page 1 of 2
Permit Number:
BMP element: Potential problems: How I will remediate the problem:
The bioretention cell: Best professional practices Prune according to best professional
vegetation show that pruning is needed practices.
to maintain optimal plant
health.
Plants are dead, diseased or Determine the source of the
dying. problem: soils, hydrology, disease,
etc. Remedy the problem and
replace plants. Provide a one-time
fertilizer application to establish the
ground cover if a soil test indicates
it is necessary.
Tree stakes/wires are present Remove tree stake/wires (which
six months after planting. can kill the tree if not removed).
The bioretention cell: Mulch is breaking down or Spot mulch if there are only random
soils and mulch has floated away. void areas. Replace whole mulch
layer if necessary. Remove the
remaining much and replace with
triple shredded hard wood mulch at
a maximum depth of three inches.
Soils and/or mulch are Determine the extent of the clogging
clogged with sediment. - remove and replace either just the
top layers or the entire media as
needed. Dispose of the spoil in an
appropriate off-site location. Use
triple shredded hard wood mulch at
a maximum depth of four inches.
Search for the source of the
sediment and remedy the problem if
possible.
A soil test shows that pH has Dolomitic lime shall be applied as
dropped or heavy metals recommended per the soil test and
have accumulated in the soil toxic soils shall be removed,
media. disposed of properly and replaced
with new planting media.
The underdrain system Clogging has occurred. Wash out the underdrain system.
if applicable)
The drop inlet Clogging has occurred. Clean out the drop inlet. Dispose of
the sediment off-site.
The drop inlet is damaged Repair or replace the drop inlet.
The receiving water Erosion or other signs of Contact the permitting authority.
damage have occurred at the
outlet.
Page 2 of 2