20080787 Ver 1_401 Application_20080508

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Robert J. Goldstein & Associates, Inc.
ENVIRONMENTAL CONSULTANTS
1221 Corporation Parkway, Raleigh, NC 27610
Tel: [phone] Fax: [phone]
email: [e-mail]
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WE ARE SENDING YOU Attached ? Under separate cover via
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? Copy of letter ? Change order ?
RE:
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WETLANDS AND STORMWATER BRAN
following items:
? Samples ? Specifications
COPIES DATE NO. DESCRIPTION

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THESE ARE TRANSMITTED as checked below:
x For approval ? Approved as submitted ? Resubmit copies for approval
? For your use ? Approved as noted ? Submit copies for distribution
>. ? As requested ? Returned for corrections ? Return corrected prints
? For review and comment ?
? FOR BIDS DUE 19 ? PRINTS RETURNED AFTER LOAN TO US
REMARKS
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SIGNED:
PROOUOIIa: mess I- Ww. r,n 01471 If enclosures are not as noted, kindly notify us at once.
Office Use Only: Form Version March 05
0
USACE Action ID No. DWQ No. 8 0 7 8 7
(If any particular item is not applicable to this project, please enter "Not Applicable" or "N/A".)
1. Processing
1. Check all of the approval(s) requested for this project:
? Section 404 Permit ® Riparian or Watershed Buffer Rules
? Section 10 Permit ? Isolated Wetland Permit from DWQ
? 401 Water Quality Certification ? Express 401 Water Quality Certification
2. Nationwide, Regional or General Permit Number(s) Requested: Neuse Buffer Authorization
3. If this notification is solely a courtesy copy because written approval for the 401 Certification
is not required, check here: ?
4. If payment into the North Carolina Ecosystem Enhancement Program (NCEEP) is proposed
for mitigation of impacts, attach the acceptance letter from NCEEP, complete section VIII,
and check here: ?
5. If your project is located in any of North Carolina's twenty coastal counties (listed on page
4), and the project is within a North Carolina Division of Coastal Management Area of
Environmental Concern (see the top of page 2 for further details), check here: ?
II. Applicant Information p ? ?
1. Owner/Applicant Information MAY 7 2008
Name: City of Raleigh Parks and Recreation Department
Mailing Address: Attn: Mr. Victor Lebsock oEr4R • WATER cwt 0
Raleigh, North Carolina 27602
Telephone Number: 919-890-3285 Fax Number: Not Available
E-mail Address: [e-mail]
2. Agent/Consultant Information (A signed and dated copy of the Agent Authorization letter
must be attached if the Agent has signatory authority for the owner/applicant.)
Name: Christopher Hopper
Company Affiliation:Robert J. Goldstein and Associates, Inc.
Mailing Address: 1221 Corporation Parkway, Ste. 100
Raleigh, North Carolina 27610
Telephone Number: 919-872-1174 Fax Number: 919-872-9214
E-mail Address: chopper& j aaCarolina.com
Page 5 of 13
III. Project Information
Attach a vicinity map clearly showing the location of the property with respect to local
landmarks such as towns, rivers, and roads. Also provide a detailed site plan showing property
boundaries and development plans in relation to surrounding properties. Both the vicinity map
and site plan must include a scale and north arrow. The specific footprints of all buildings,
impervious surfaces, or other facilities must be included. If possible, the maps and plans should
include the appropriate USGS Topographic Quad Map and NRCS Soil Survey with the property
boundaries outlined. Plan drawings, or other maps may be included at the applicant's discretion,
so long as the property is clearly defined. For administrative and distribution purposes, the
USACE requires information to be submitted on sheets no larger than 11 by 17-inch format;
however, DWQ may accept paperwork of any size. DWQ prefers full-size construction
drawings rather than a sequential sheet version of the full-size plans. If full-size plans are
reduced to a small scale such that the final version is illegible, the applicant will be informed that
the project has been placed on hold until decipherable maps are provided.
1. Name of project: 2008 - Hammond Road Culvert Maintenance
2. T.I.P. Project Number or State Project Number (NCDOT Only): NA
3. Property Identification Number (Tax PIN): 1703809413 (east of Hammond Road) and
1703708635 (west of Hammond Road)
4. Location
County: Wake Nearest Town: City of Raleigh
Subdivision name (include phase/lot number): none
Directions to site (include road numbers/names, landmarks, etc.): From Raleigh, take
Wilmington Street south. Park at intersection of Fayetteville Street and follow Greenwav_
east to pedestrian tunnel under Hammond Road (Figure 1)
Site coordinates (For linear projects, such as a road or utility line, attach a sheet that
separately lists the coordinates for each crossing of a distinct waterbody.)
Decimal Degrees (6 digits minimum): 35.7567 ON -78.6349 °W
6. Property size (acres): Parcel sizes are 1.99 ac (west side) and 20.98 (east side)
7. Name of nearest receiving body of water: Walnut Creek
8. River Basin: Neuse River
(Note - this must be one of North Carolina's seventeen designated major river basins. The
River Basin map is available at http://h2o.enr.state.nc.us/admin/mgps/.)
9. Describe the existing conditions on the site and general land use in the vicinity of the project
at the time of this application: The project site is along a City of Raleigh recreational
greenway trail. The trail is paved, and adjacent to Hammond Road and commercial uses on
the north and Walnut Creek on the south (Figure 2). The streamside area adjacent to the
Page 6 of 13
proposed activities is vegetated with grass and herbs. Upslope of the proposed activities is a
stormwater ditch parallel to the I-440 on-ramp off of Hammond Road south. This ditch is
shown on the Wake Co" Soil Survey as a stream feature, but was determined to be
ephemeral. This was verified in the field by Mr. Steve Mitchell (NCDWQ on 06 May 2004.
The ditch is forested with bottomland hardwood species. Immediately west of the drainage
ditch is an automotive repair facility and salvage yard.
10. Describe the overall project in detail, including the type of equipment to be used:
See attached.
11. Explain the purpose of the proposed work: The purpose of the proposed work is to clean
out deposited sediment from within the pedestrian tunnel, and to discourage regular high-
flows from entering the tunnel.
IV. Prior Project History
If jurisdictional determinations and/or permits have been requested and/or obtained for this
project (including all prior phases of the same subdivision) in the past, please explain. Include
the USACE Action ID Number, DWQ Project Number, application date, and date permits and
certifications were issued or withdrawn. Provide photocopies of previously issued permits,
certifications or other useful information. Describe previously approved wetland, stream and
buffer impacts, along with associated mitigation (where applicable). If this is a NCDOT project,
list and describe permits issued for prior segments of the same T.I.P. project, along with
construction schedules. The trail was constructed under 2004 permits USACE Action ID
200421186) and NC DWO 04-0838). No prior authorizations are known to the project owners.
The proposed activities are not connected to those secured for construction, but rather are needed
for maintenance and abatement of excessive future maintenance.
V. Future Project Plans
Are any future permit requests anticipated for this project? If so, describe the anticipated work,
and provide justification for the exclusion of this work from the current application.
The intent of this work is to minimize the recurrence interval of required maintenance. The
tunnel will continue to accommodate seasonal high flows and the passage of flood waters.
VI. Proposed Impacts to Waters of the United States/Waters of the State
It is the applicant's (or agent's) responsibility to determine, delineate and map all impacts to
wetlands, open water, and stream channels associated with the project. Each impact must be
listed separately in the tables below (e.g., culvert installation should be listed separately from
riprap dissipater pads). Be sure to indicate if an impact is temporary. All proposed impacts,
permanent and temporary, must be listed, and must be labeled and clearly identifiable on an
accompanying site plan. All wetlands and waters, and all streams (intermittent and perennial)
should be shown on a delineation map, whether or not impacts are proposed to these systems.
Wetland and stream evaluation and delineation forms should be included as appropriate.
Page 7 of 13
Photographs may be included at the applicant's discretion. If this proposed impact is strictly for
wetland or stream mitigation, list and describe the impact in Section VIII below. If additional
space is needed for listing or description, please attach a separate sheet.
1. Provide a written description of the proposed impacts: See attached.
2. Individually list wetland impacts. Types of impacts include, but are not limited to
mechanized clearing, grading, fill, excavation, flooding, ditching/drainage, etc. For dams,
separately list impacts due to both structure and flooding.
Wetland Impact
Site Number
(indicate on map) Type of Impact Type of Wetland
(e.g., forested, marsh,
herbaceous, bog, etc.) Located within
100-year
Flood lain
es la Distance to
Nearest
Stream
(linear feet) Area of
Impact
(acres)
None

Total Wetland Impact (acres) 0
3. List the total acreage (estimated) of all existing wetlands on the property: NA
4. Individually list all intermittent and perennial stream impacts. Be sure to identify temporary
impacts. Stream impacts include, but are not limited to placement of fill or culverts, dam
construction, flooding, relocation, stabilization activities (e.g., cement walls, rip-rap, crib
walls, gabions, etc.), excavation, ditching/straightening, etc. If stream relocation is proposed,
plans and profiles showing the linear footprint for both the original and relocated streams
must be included. To calculate acreage, multi ly length X width then divide by 43 560
Stream Impact
Number
(indicate on ma)
Stream Name
Type of Impact
Perennial or Intermittent? Average
Stream Width
Before Impact Impact
Length
(linear feet) Area of
Impact
(acres)
None

Total Stream Impact (by length and acreage) 0
5. Individually list all open water impacts (including lakes, ponds, estuaries, sounds, Atlantic
Ocean and any other water of the U.S.). Open water impacts include, but are not limited to
fill, excavation, dredging, flooding, drainage, bulkheads, etc.
Page 8 of 13
Open Water Impact
Site Number
(indicate on ma) Name of Waterbody
(if applicable)
Type of Impact Type of Waterbody
(lake, pond, estuary, sound, bay,
ocean, etc.) Area of
Impact
(acres)
None

Total Open Water Impact (acres) 0
6. List the cumulative impact to all Waters of the U.S. resulting from the project:
Stream Impact (acres): 0
Wetland Impact (acres): 0
Open Water Impact (acres): 0
Total Impact to Waters of the U.S. (acres) 0
Total Stream Impact (linear feet): 0
7. Isolated Waters
Do any isolated waters exist on the property? ? Yes ® No
Describe all impacts to isolated waters, and include the type of water (wetland or stream) and
the size of the proposed impact (acres or linear feet). Please note that this section only
applies to waters that have specifically been determined to be isolated by the USACE.
NA
8. Pond Creation
If construction of a pond is proposed, associated wetland and stream impacts should be
included above in the wetland and stream impact sections. Also, the proposed pond should
be described here and illustrated on any maps included with this application.
Pond to be created in (check all that apply): ? uplands ? stream ? wetlands
Describe the method of construction (e.g., dam/embankment, excavation, installation of
draw-down valve or spillway, etc.): NA
Proposed use or purpose of pond (e.g., livestock watering, irrigation, aesthetic, trout pond,
local stormwater requirement, etc.): NA
Current land use in the vicinity of the pond: NA
Size of watershed draining to pond: NA Expected pond surface area: NA
VII. Impact Justification (Avoidance and Minimization)
Specifically describe measures taken to avoid the proposed impacts. It may be useful to provide
information related to site constraints such as topography, building ordinances, accessibility, and
financial viability of the project. The applicant may attach drawings of alternative, lower-impact
site layouts, and explain why these design options were not feasible. Also discuss how impacts
were minimized once the desired site plan was developed. If applicable, discuss construction
techniques to be followed during construction to reduce impacts.
See attached.
Page 9 of 13
VIII. Mitigation
DWQ - In accordance with 15A NCAC 2H .0500, mitigation may be required by the NC
Division of Water Quality for projects involving greater than or equal to one acre of impacts to
freshwater wetlands or greater than or equal to 150 linear feet of total impacts to perennial
streams.
USACE - In accordance with the Final Notice of Issuance and Modification of Nationwide
Permits, published in the Federal Register on January 15, 2002, mitigation will be required when
necessary to ensure that adverse effects to the aquatic environment are minimal. Factors
including size and type of proposed impact and function and relative value of the impacted
aquatic resource will be considered in determining acceptability of appropriate and practicable
mitigation as proposed. Examples of mitigation that may be appropriate and practicable include,
but are not limited to: reducing the size of the project; establishing and maintaining wetland
and/or upland vegetated buffers to protect open waters such as streams; and replacing losses of
aquatic resource functions and values by creating, restoring, enhancing, or preserving similar
functions and values, preferable in the same watershed.
If mitigation is required for this project, a copy of the mitigation plan must be attached in order
for USACE or DWQ to consider the application complete for processing. Any application
lacking a required mitigation plan or NCEEP concurrence shall be placed on hold as incomplete.
An applicant may also choose to review the current guidelines for stream restoration in DWQ's
Draft Technical Guide for Stream Work in North Carolina, available at
http://h2o.enr.state.nc.us/ncwetlands/stringide.html.
1. Provide a brief description of the proposed mitigation plan. The description should provide
as much information as possible, including, but not limited to: site location (attach directions
and/or map, if offsite), affected stream and river basin, type and amount (acreage/linear feet)
of mitigation proposed (restoration, enhancement, creation, or preservation), a plan view,
preservation mechanism (e.g., deed restrictions, conservation easement, etc.), and a
description of the current site conditions and proposed method of construction. Please attach
a separate sheet if more space is needed.
See attached.
2. Mitigation may also be made by payment into the North Carolina Ecosystem Enhancement
Program (NCEEP). Please note it is the applicant's responsibility to contact the NCEEP at
[phone] to determine availability, and written approval from the NCEEP indicating
that they are will to accept payment for the mitigation must be attached to this form. For
additional information regarding the application process for the NCEEP, check the NCEEP
website at http://h2o.enr.state.nc.us/wro/index.htm. If use of the NCEEP is proposed, please
check the appropriate box on page five and provide the following information:
Page 10 of 13
Amount of stream mitigation requested (linear feet): None
Amount of buffer mitigation requested (square feet): None
Amount of Riparian wetland mitigation requested (acres): None
Amount of Non-riparian wetland mitigation requested (acres): None
Amount of Coastal wetland mitigation requested (acres): None
IX. Environmental Documentation (required by DWQ)
1. Does the project involve an expenditure of public (federal/state/local) funds or the use of
public (federal/state) land? Yes ® No ?
2. If yes, does the project require preparation of an environmental document pursuant to the
requirements of the National or North Carolina Environmental Policy Act (NEPA/SEPA)?
Note: If you are not sure whether a NEPA/SEPA document is required, call the SEPA
coordinator at [phone] to review current thresholds for environmental documentation.
Yes ? No
3. If yes, has the document review been finalized by the State Clearinghouse? If so, please
attach a copy of the NEPA or SEPA final approval letter. Yes ? No ?
X. Proposed Impacts on Riparian and Watershed Buffers (required by DWQ)
It is the applicant's (or agent's) responsibility to determine, delineate and map all impacts to
required state and local buffers associated with the project. The applicant must also provide
justification for these impacts in Section VII above. All proposed impacts must be listed herein,
and must be clearly identifiable on the accompanying site plan. All buffers must be shown on a
map, whether or not impacts are proposed to the buffers. Correspondence from the DWQ
Regional Office may be included as appropriate. Photographs may also be included at the
applicant's discretion.
1. Will the project impact protected riparian buffers identified within 15A NCAC 2B .0233
(Meuse), 15A NCAC 2B .0259 (Tar-Pamlico), 15A NCAC 02B .0243 (Catawba) 15A NCAC
2B .0250 (Randleman Rules and Water Supply Buffer Requirements), or other (please
identify)? Yes ® No ? Neuse: (211.0233)
2. If "yes", identify the square feet and acreage of impact to each zone of the riparian buffers.
If buffer mitigation is required calculate the required amount of mitigation by applying the
buffer multipliers.
Zone* Impact Multiplier Required
(square feet) Mitigation
1 80ft2 3 (2 for Catawba) 0
2 1.5
Total 80ft p
* Zone I extends out 30 feet perpendicular from the top of the near bank of channel; Zone 2 extends an
additional 20 feet from the edge of Zone 1.
Page 11 of 13
3. If buffer mitigation is required, please
Donation of Property, Riparian Buffer
Riparian Buffer Restoration Fund). Ple
within 15A NCAC 2B .0242 or .0244, or
discuss what type of mitigation is proposed (i.e.,
Restoration / Enhancement, or Payment into the
ase attach all appropriate information as identified
.0260.
XI. Stormwater (required by DWQ)
Describe impervious acreage (existing and proposed) versus total acreage on the site. Discuss
stormwater controls proposed in order to protect surface waters and wetlands downstream from
the property. If percent impervious surface exceeds 20%, please provide calculations
demonstrating total proposed impervious level.
See attached.
XII. Sewage Disposal (required by DWQ)
Clearly detail the ultimate treatment methods and disposition (non-discharge or discharge) of
wastewater generated from the proposed project, or available capacity of the subject facility.
A
XIII. Violations (required by DWQ)
Is this site in violation of DWQ Wetland Rules (15A NCAC 2H.0500) or any Buffer Rules?
Yes ? No 2
Is this an after-the-fact permit application? Yes ? No
XIV. Cumulative Impacts (required by DWQ)
Will this project (based on past and reasonably anticipated future impacts) result in additional
development, which could impact nearby downstream water quality? Yes ? No
If yes, please submit a qualitative or quantitative cumulative impact analysis in accordance with
the most recent North Carolina Division of Water Quality policy posted on our website at
httn://h2o.enr.state.nc.us/ncwetlands. If no, please provide a short narrative description:
NA
XV. Other Circumstances (Optional):
It is the applicant's responsibility to submit the application sufficiently in advance of desired
construction dates to allow processing time for these permits. However, an applicant may
choose to list constraints associated with construction or sequencing that may impose limits on
work schedules (e.g., draw-down schedules for lakes, dates associated with Endangered and
Threatened Species, accessibility problems, or other issues outside of the applicant's control).
Page 12 of 13

Ma
Applicant/Agent's Signature I Date
(Agent's signature is valid only if an authorization letter from the applicant is provided.)
Page 13 of 13
May US 2000 6:2JPM HP LHSEHJL1 FHX P.2
To Whom It May Concern:
This letter authorizes Robert J. Goldstein & Associates (consultant) to act as
authorized agents of The City of Raleigh Parks and Recreation Department, in submitting
a Neuse River Riparian Area Buffer Rule Authorization PCN Application for
maintenance activities associated with the Walnut Creek Greenway pedestrian culvert
under Hammond Road in the City of Raleigh, Wake County, NC. The proposed
maintenance activity is located at the intersection of the Walnut Creek Greenway and
Hammond Road, immediately adjacent to Walnut Creek. This letter authorizes the
Consultant to sign and submit a courtesy PCN for the proposed project, with the intent of
obtaining authorization in writing that the City is authorized to conduct the required
maintenance activities, as required by NCDWQ.
Sincerely,
Printed Name, Address, Contact Information:
_Mr. Victor Lebsock
-City of Raleigh Parks and Recreation Department
_222 West Hargett Street, Ste. 608
-Raleigh, NC 27602
I
March 2008 City of Raleigh Neuse River Riparian Buffer Authorization Request,
City of Raleigh Parks and Recreation Department Walnut Creek Greenway Trail,
Hammond Road Pedestrian Tunnel.
Attachments to Pre-Construction Notification Application
Project Background and Need
The proposed project is located along the City of Raleigh Walnut Creek Greenway Trail
(Figure 1). The functionality of the existing pedestrian tunnel under Hammond Road
(S.R. 2026) has been compromised several times during the past year because of flooding
and sediment deposition. The flooding enters the tunnel on the upstream side via a dip
(low spot) between the northern bank of Walnut Creek, and the concrete barrier on
stream side of the pedestrian tunnel at about the same elevation as the floor of the tunnel.
A stormwater ditch parallels Hammond Road (Figure 2), and drains through a culvert
under the greenway trail at the problem area. Contributions from both the stormwater
ditch and Walnut Creek were investigated to determine the source of the sedimentation
inside the pedestrian tunnel. Lack of volume and available sediment from the ditch, and
wrack lines formed by flows from Walnut Creek have led to the determination that high
flows within Walnut Creek are the source of excessive sediment accumulation.
The culvert comprises five boxes, the northern of which is the pedestrian tunnel. Under
current normal flow conditions, the stream favors the southern two boxes. Slightly
higher flows utilize the southern four boxes. The floor of the pedestrian tunnel is elevated
24 inches above the bed of its adjacent stream box.
Several photos are included below to illustrate the problem this project aims to remedy.
The photo on the left was taken west of Hammond
Road, looking downstream. The pedestrian tunnel is
on the left, behind the half-wall. The wash line
visible on the left (north) bank was created following
high precipitation events on March 5t' and 7a'. Three
quarter inch of rain fell on the 5t', and one and a
quarter inches fell on the 7a'. These measurements
are based on ?-
I USGS
Stream Gage
# 0208735012, 14,500 valley-feet upstream on
Rocky Branch.
To better illustrate the location of the problem,
the photo on the right shows the transition from
the half-wall to stream bank. The base of the
stake visible in this photo is roughly at the wash

line mentioned above. Based on NC Climate Retrieval and Observations Network Of the
Southeast (CRONOS) data from Lake Wheeler, precipitation was recorded in 27 of the
past 180 days. Five of these events were greater than one inch, and the March 7 event
was the smallest of the five recorded.

i
These frequent events have
caused a regular maintenance
problem for the City of Raleigh
when overflows deposit
sediment in the pedestrian
tunnel (left), and adversely
impact Raleigh residents
utilizing the City's Greenway
system (right).
Data Sources:
1- USGS Real-Time Water Data for USGS 0208735012, Rocky Branch Below Pullen
Drive at Raleigh, NC. Available: http://waterdata.usgs.Pov/nc/nwis/uv
2 - NC CRONOS Lake Wheeler Field Lab (LAKE) Data, Data Retrieved From 27 Sept
2007 through 24 March 2008. Available: http://www.nc-
climate. edu/dynamic scripts/cronos/
Although not available to import to GIS mapping, the trail is visible on Google Maps
(www. google. com/mans).
PCN & III (10) Description of Project, In Detail
The below photograph conceptually illustrates the proposed activity. The photo was
taken from a mid-channel bar in Walnut Creek, looking north at the project location. The
wall on the stream side of the pedestrian
tunnel entrance will be extended out along the
geenway streamside shoulder to deflect
regular high-flows back into the channel. The
dashed i ed I I iie indicates Ordinary High Water
(OHW), above which the USACE does not
laim jurisdiction. This was identified in the
field by RJG&A biologist Chris Hopper, and
verified by US Army Corps of Engineers
Wake County Agent, Mr. Jamie Shern. The
greenway shoulder will be excavated roughly
along the black line to accommodate flow
deflection materials (large rip-rap or pre-cured concrete slabs). The glue polygon
illustrates the approximate extent of these materials after completion.
No concrete will be used to secure the structure. The completed structure will not be
completely impervious to water, but rather deter excessive amounts of water from
entering the pedestrian tunnel. The pedestrian tunnel will continue to pass flood waters
with negligible impact on capacity. The structure will be comprised of large rock or
concrete materials.
Silt fencing will be placed on the down slope side of the project area and staked in above
OHW. The entire project area comprises approximately 80 ft2 of grassed riparian buffer.
The disturbance area will be about 20 feet long and four feet wide. The existing concrete
wall is 9.5 inches wide, and the completed structure will be comparable in width (finished
footprint about 20 ft). Initial excavation (roughly along black line on above photo) will
be conducted with either a Bobcat or rubber-tired backhoe. Final excavation will be
conducted manually to accommodate seating the deflecting materials. To the extent
practicable, existing grass will be removed intact and replaced upon completion.
Deflecting materials will be either large rip-rap or pre-cured concrete slabs. The slabs
would be cut from the concrete wall on
the downstream side of this culvert
(right). If acceptable to NC DOT, the
downstream concrete wall will be cut
into long strips and placed on the
upstream end to deflect high flows back
into Walnut Creek. The downstream
wall is well above OHW, and no stream
or buffer impacts will result from its
deconstruction.
No concrete, rebar, or other anchoring

devices or adhesives will be used to
secure the deflecting structure. Therefore the materials will need
substantially resistant to hydrostatic forces expected during flood events.

w
to be large and
The sediment existing in the pedestrian tunnel will be removed prior to construction of
the deflecting wall, or deconstruction of the source wall. The greenway contractor will
dispose of the accumulated sediment at an off-site, upland location.
PCN & VI (1) Description of Proposed Impacts
The below description assumes that NC DOT will approve removal of the downstream
wall (photo above) and use its concrete to create the deflecting wall upstream. In the
event that this is not approved, large rip-rap materials will be used instead. The entire
project is expected to require two to three days to complete.
Prior to any activities, the contractor will place sediment fencing on the downstream side
of both upstream and downstream walls. All construction will be during dry weather and
normal flows in Walnut Creek. After removal of accumulated sediment in the pedestrian
tunnel, the contractor will deconstruct the downstream pedestrian tunnel wall by cutting it
into long slabs. These slabs will be moved to the upstream wall construction site.
Outward and upstream from the existing upstream pedestrian wall, an area about 80 ft2
(20 x 4) will be excavated to a depth of two feet or less to accommodate placement of the
concrete slabs. To the extent practicable, existing grass will be removed intact to be
replaced after completion. The excavation will occur no closer to the stream than the
deflecting wall will be placed. Manual excavation of the footprint area will eliminate
mechanical errors. After placement of the slabs, the displaced soil will be replaced
around the deflecting structure and the original grass placed over the area as sod. The
remaining area will be seeded grass to stabilize the soil.
PCN & VII Impact Justification (Avoidance and Minimization)
The current problem was anticipated during construction, and project engineers provided
3-inch PVC drainage holes through the pedestrian tunnel wall every 10 feet to drain flood
waters back into the box culvert containing the creek. However, once inside the tunnel
the stream velocity (scour potential) effectively goes to zero. As the level of Walnut
Creek subsides, water drains from the pedestrian tunnel through the drain holes. Because
of the slow rate of discharge (limited by the gradual reduction of creek flows), sediment
settles out and clogs the tunnel. The contractor has removed sediment twice since
construction, and a third effort is necessary.
A second proposal has been presented that would create an off-line impoundment of
stormwater along the drainage feature west of and parallel to the Hammond Road on-
ramp to I-440. The water would be stored in an offline pond, and used by City staff to
periodically `flush' the tunnel. This proposal would be more costly to build, destructive
to existing vegetation in the swale, add to facilities maintenance concerns, and pose a
threat to the trail in the event of a breach.
Adjusting the slope of the tunnel floor to facilitate drainage is prohibited by NC DOT.
The City has no misconceptions about the maintenance inherent with this structure, but
wishes to minimize the interval between needed maintenance activities to the extent
practicable.
Construction activities will be conducted to minimize potential impacts to Walnut Creek
through the use sediment fencing, short duration of construction activities, and timing
construction to occur during dry weather and low-flow conditions. Pre-cured concrete
obtained from the existing downstream wall will minimize potential impacts to aquatic
life.
PCN & VIII (1) Description of Mitigation Plan
The purpose of the proposed project is to protect the City of Raleigh's greenway
facilities. Pursuant to 15A NCAC 2B .0233 (6), this activity is allowable without
mitigation, and none is proposed.
No impacts to stream or wetland resources are proposed, and the finished project will
result in 20 ftz of impacts to streamside riparian grasses. The reduction in needed
maintenance activities, typically conducted with a bobcat bucket, will reduce the
potential for stream impacts.
Secondary and cumulative impacts are not expected, and no mitigation is proposed.
Direct impacts will be mitigated onsite by protecting the stream with sediment fencing
and manual excavation to seat the deflection materials. Mechanical excavation will be
used to remove the bulk of topsoil, but manual removal of soil is necessary to securely fit
the materials and minimize the risk of temporarily sidecast soil from reaching the stream.
PCN 4 XI Discuss Stormwater Controls
As discussed in previous responses, stormwater controls will be comprised of
construction timing, methods, and physical barriers. Construction will be conducted
during dry periods and low-normal stream flows. The required excavation will be
finished manually, and all materials temporarily sidecast on the paved trail or its
landward shoulder. After the structure is complete, soil will be replaced on the landward
side of the wall, and intact sod replaced. The remaining disturbed area reseeded with
grass to stabilize the soil. Excess material will be removed by the greenway contractor,
along with accumulated sediment inside the pedestrian tunnel, and properly disposed of
off-site.
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s f' ` ?? Figure ?. Project Area Aerial Photograph with T+?pographs'
City of Raleigh Walnut Creek Greenway Trail Hammond
Road Pedestrian Culvert. Flooding and Sediment Abateme t
o Project. City of Raleigh. Wake County, North Carolina.
70 0 70 140 Feet
Wake County GIS: 2-foot contours; 2005 b&w photo