20110514 Ver 1_WRC Comments_20110701

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To: Ian McMillan
From: Tom Covington
CC:
Date: 1 July
Re: DWQ RFI
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Please find enclosed a cc of a response to an RFI from Joanne Steenuis, DWQ.
Thank you,
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Tom Covington
Facilities Construction and Capital Projects Engineer
919-707-0154 (o)
919-218-2064 (m)
1
K"?A' North Carolina Wildlife Resources Commission 9
30 June 2011
NCDENR - DWQ
Attn: Joanne Steenhuis
127 Cardinal Drive Extension
Wilmington, NC 28405
RE: Lewis Road Boating Access Area, Hamsptead
Project 20110514
Pender County
Dear Ms. Steenhuis:
[JUL o r eon
I received a letter dated 24 June, requiring additional information based on the excerpt below:
1) After your e-mail response dated June 20, 2011, the DWQ still has concerns about
the stability of the fill proposed for the boat ramp. Whether the fill is soil or rip rap,
the DWQ has concerns that the fill will not remain in the footprint of the boat ramp
and the potential of the fill to cause a water quality violation. Please explain why a
cofferdam or similar structure will not be feasible for this project and provide a
detailed construction sequence that will show the DWQ that the fill will not migrate
outside the proposed footprint for the boat ramp and cause a water quality violation.
The standard method of construction for WRC boat ramps is to pour the ramp on high ground,
prepare the subgrade of the ramp with F of class B riprap covered by 6" of 57 stone, and then
push the ramp down the prepared slope to its final resting place. The ramp rides up over the top
of the stone, displacing very little and disturbing almost nothing outside the prepared footprint.
The WRC has been building boat ramps in the manner discussed for the last 15 years, and has
never been cited for a water quality violation due to this operation, as the riprap and 57 stone
have prevented any soil, soil fill or rock subgrade from washing.
We prefer this method over a cofferdam for several reasons, which include a much lower overall
cost, quicker construction time, less in-water work, and fewer environmental impacts. The
placement and maintenance of a cofferdam involve the purchase and setting of sheet piling by
driving, vibrating, or washing in, excavation of a sump hole or low point in which a pump is
DIVISION OF ENGINEERING SERVICES
Mailing Address: 1720 Mail Service Center • Raleigh, NC 27699-1720
Office Location: 1751 Varsity Dr. • Raleigh, NC 27606 -Telephone: [phone] • Fax: [phone]
PAGE 2 6/30/2011
placed, either a constant running of the pump or pumping down the water intrusion every day,
performing the work in muddy conditions, and then the removal and hopeful reuse of the sheet
piling. The contractor disturbs the existing ground in a footprint larger than the ramp itself when
placing in order to have room to work, has to pump muddy water to the high ground and let it be
treated by a sedimentation control device before being released back into the waterbody, and
then further disturbs the ground when removing the sheet piles. In addition, cofferdams
normally extend the project schedule, costs, and manpower significantly. There is additional
time and equipment required to drive the sheeting, dewater, and then remove the sheeting, which
increases the amount of in-water work and disturbance to the existing ground and local flora and
fauna. Also, with the slab poured in place, there has to be allocated set-up time before the
sheeting can be removed, during which time dewatering must continue to take place, especially if
the ramp is poured in sections. This additional time results in direct costs for equipment rental
and repair, crew hours, and project overhead such as per-diems, project management, and other
administrative costs.
WRC has agreed to use Class B riprap in place of soil fill, which is noted and explained below in
the construction sequence, but feel that the use of a cofferdam has a much larger potential for in-
water impacts and potential water quality issues, so we request to continue our current
construction methods, details of which follow.
Construction sequencing for placement of breakwater and ramp at Lewis Road
1. Survey in locations of all corners of wall, and build batterboards in the water to attach
stringline for proper pile placement.
2. Place turbidity barrier to enclose entire area of pile work.
3. Only remove existing bulkhead in the areas where the wall and docks go, leave the rest of
the existing bulkhead in place until ramp grading is ready to take place.
This will keep the existing soil from washing.
4. Starting from the land, drive wood piles on both sides of both walls for the vinyl
sheeting and dock construction.
Place 4x6's on piles to act as sheeting guides.
6. Drive vinyl sheet piles for both sides of the project.
7. Finish installing 4x6s and cap boards.
Site now has all vinyl sheeting and wood piles installed, creating a containment area on both
sides, which will not allow any material to escape from the sides.
DIVISION OF ENGINEERING SERVICES
Mailing Address: 1720 Mail Service Center - Raleigh, NC 27699-1720
Office Location: 1751 Varsity Dr. - Raleigh, NC 27606 -Telephone: [phone] - Fax: [phone]
PAGE 3
6/30/2011
While the wall work is going on, stockpile Class B riprap on site, and pour ramps in an upland
location.
Remove the rest of the existing bulkhead inside the new vinyl retaining wallibreakwater.
9. Instead of using earth fill, Place Class B riprap in fill areas.
Riprap has been stored on site so can be placed much quicker than if allowed to be placed as it
arrives via truck from the quarry. This results in higher costs due to double handling of the
material, but allows for a minimum amount of time spent on in-water work, decreasing any
chance of impacts.
10. 57 Stone will be placed in a 6" lift after the placement of the riprap.
Based on examination of the cross sections and proposed contours, there will be no disturbance
of any existing ground with the exception of a very small amount of cut at the very base of the .
ramp. This will allow the soil to remain in its in-situ compacted state, lessening the chance of
any erosion due to soil swell after disturbance. There will be absolutely no chance of any soil
washing out at the toe of the ramp, as no soil will have been placed. Class B riprap is 5" to 12"
size stone, and will not be washed away by tidal surges or boat wake. The class B will be used
up to 6" below the proposed concrete ramp, which will then be choked with 57 Stone. Riprap
will be placed by track hoe, and graded to ramp subgrade specifications with a dozer and track
hoe. The equipment weight and tracking while placing will further lock in the stone, preventing
movement.
11. The concrete ramps, which will have previously been poured and allowed to sit at least a
minimum of 7 days to reach a partial design strength, will then be pushed in from high
ground.
The ramps are poured with a beveled edge in the front, which allows them to ride up over the 57
stone, and not dig in and push stone out and away as they moves down the slope.
12. Once the ramps are placed, the crew will then check the toe of the ramps to ensure that no
riprap has in fact migrated. If they do find any, it is removed at that time, due to the
potential to cause damage to boats and props during the loading and unloading process
once the site is open to the public.
The grading and fill operation at Lewis Road would probably take about a day, and the ramp
push ought to take about a half a day. Pour length has not been determined yet, but worst case
the ramp would be pushed to above the high water mark, another section would be poured on
high ground, and then the ramp would be pushed the rest of the way, another operation that
would result in additional in water work of a few hours.
DIVISION OF ENGINEERING SERVICES
Mailing Address: 1720 Mail Service Center • Raleigh, NC 27699-1720
Office Location: 1751 Varsity Dr. • Raleigh, NC 27606 -Telephone: [phone] • Fax: [phone]
PAGE 4
6/30/2011
The "push slab" method is endorsed by several states, include the South Carolina Dept of Natural
Resources, and SOBA, the States Organization for Boating Access. New York State DOT
requires that the push slab method be used when constructing boating launch ramps. In the
interest of the boaters, the environment, and based on the current economic climate and increased
scrutiny of the proper use of public funds, we request that we be allowed to fill using Class B,
and continue our tried and true method of pushing the slab in. If you have any more questions or
need any more information, please don't hesitate to contact me at 919-707-0154 or
[e-mail]
Sincerely,
0 V-k CovltiCI'M J
Tom Covington, PE
North Carolina Wildlife Resources Commission
Facilities Construction and Capital Projects Engineer
Cc: Ian McMillan, DWQ
Holley Snider, DCM
Dave Timpy, COE
Doug Huggett, DCM
DIVISION OF ENGINEERING SERVICES
Mailing Address: 1720 Mail Service Center • Raleigh, NC 27699-1720
Office Location: 1751 Varsity Dr. • Raleigh, NC 27606 -Telephone: [phone] • Fax: [phone]