3402_HanesMillMSWLF_PilotStudyProposal_AlterFinalCover_DIN26788_20160909

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[phone]

September 19, 2016
Mr. Ming Chao
North Carolina Department of Environmental Quality
450 Hanes Mill Road, Suite 300
Winston-Salem, NC 27105

Re: Draft Modification of Permit No. 34-02
Hanes Mill Road Landfill

Dear Ming Chao,
On behalf of the City of Winston-Salem, we are transmitting herewith the enclosed Permit Modification for
the completion of a pilot project to demonstrate the effectiveness of alternative final cover systems at the
Hanes Mill Road Landfill. Two hard copies are enclosed for your reference and an electronic copy is being
transmitted under separate cover.
The proposed pilot project pilot project would include installation of both an exposed geomembrane and an
artificial turf final cover system over an approximate 9-acre area of the landfill. The City of Winston-Salem is
proposing to evaluate the performance and costs to install and maintain the alternative final cover system in
order to determine whether it would be suitable for consideration as a proposed replacement for the
currently permitted final cover system of the landfill.
The City proposes to NCDEQ that the pilot project be a stand-alone project and requests approval of the
conceptual plans and details. Final engineering plans and specifications for the alternative closure system
would be submitted for information prior to construction.
Should you have any questions, or wish to meet to discuss this application further, please do not hesitate to
contact me at [phone].
Sincerely,
HDR Engineering, Inc. of the Carolinas

Jeffrey S. Murray, P.E, BCEE
Senior Project Manager
Enclosure
Cc: Ed Gibson, City of Winston-Salem
1
Chao, Ming-tai
From:Murray, Jeffrey <[e-mail]>
Sent:Monday, September 19, 2016 10:18 AM
To:Chao, Ming-tai
Cc:[e-mail]; Mussler, Ed; Plummer, Michael
Subject:Hanes Mill Road Landfill - Permit Modification for Pilot Study of Alternative Final Cover
Attachments:Permit Mod Transmittal 091916.pdf; !PermitMod_AltFinalCvrPilotProject_HanesLF.pdf
Follow Up Flag:Flag for follow up
Flag Status:Flagged
Mr. Chao,

Please find enclosed a transmittal letter and permit modification application document for a proposed pilot study of
alternative final cover systems at the Hanes Mill Road Landfill in Winston-Salem.

Two hard copies of the application are being forwarded to your attention.

Please do not hesitate to contact me should you have any questions or would like to coordinate a meeting with DEQ staff,
HDR and the City to discuss this further.

Thank you,

Jeffrey S. Murray, P.E., BCEE
Senior Project Manager
HDR
555 Fayetteville Street, Suite 900
Raleigh, NC 27601
D 919.232.6682 M 919.302.6814
[e-mail]
hdrinc.com/follow-us

Permit Modification
Application
Alternative Final Cover System Pilot Project
Hanes Mill Road Landfill
Winston-Salem, North Carolina
September 19, 2016

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City of Winston-Salem | Permit Modification Application – Alternate Final Cover System Pilot Project
Contents
i
Contents
I. Purpose .............................................................................................................................. 1
II. Background ........................................................................................................................ 1
III. Proposed Closure Area ....................................................................................................... 1
IV. Alternative Final Cover System ........................................................................................... 2
V. Stormwater Management .................................................................................................... 2
VI. Permit Application ............................................................................................................... 3
VII. Calculations ........................................................................................................................ 4
A. Wind ................................................................................................................................ 4
B. Gas Pressure .................................................................................................................. 4
C. Ballast/Anchor System .................................................................................................... 4
D. Drainage .......................................................................................................................... 4
E. Infiltration ......................................................................................................................... 5
F. Additional Calculations .................................................................................................... 5
VIII. Performance Metrics ........................................................................................................... 5
A. Visual Inspections ........................................................................................................... 5
B. Material Sampling ............................................................................................................ 5
C. Reporting ......................................................................................................................... 6
IX. Conclusions ........................................................................................................................ 6
Appendices
Appendix A - Drawings
Appendix B - Initial Stormwater Calculations
City of Winston-Salem | Permit Modification Application – Alternate Final Cover System Pilot Project
Contents
ii
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City of Winston-Salem | Permit Modification Application – Alternate Final Cover System Pilot Project
Purpose

1

I. Purpose
The purpose of this application is to obtain approval from the North Carolina Department of
Environmental Quality (NCDEQ) to perform a pilot project for an alternative final cover system at
the Hanes Mill Road Landfill Expansion. The pilot project would include installation of both an
exposed geomembrane and an artificial turf final cover system over an approximate 9-acre area
of the landfill. The City of Winston-Salem (the City) is proposing to evaluate the performance
and costs to install and maintain the alternative final cover system in order to determine whether
it would be suitable for consideration as a proposed replacement for the currently permitted final
cover system of the landfill. The City understands that approval of an alternative final cover
system would require a subsequent permit modification and coordination with NCDEQ.
II. Background
The Hanes Mill Road Landfill is owned by the City of Winston-Salem and operated by the
Winston-Salem/Forsyth County City/County Utilities Commission. The facility is located west of
U.S. Highway 52, between Hanes Mill Road and Ziglar Road and consists of two major areas:
the original landfill area, which is now closed, and a lined expansion area which is active.
Currently, approximately 51 acres of the 90 acres of the expansion area have been constructed
with construction of the 14 acre Cell 5, commencing in March 2016. A portion of the sideslopes
of Cells 1 and 2 of the expansion area have intermediate cover in place and are suitable for
construction of a final cover system.
The landfill received the most recent permit to construct on October 8, 2010. As-built
certification documentation for Cells 3 & 4 was submitted in August of 2011 and the permit to
operate was provided by NCDEQ dated October 18, 2011.
The September 2010 construction permit application describes the currently permitted final
cover for the landfill which consists of four layers from bottom up: an 18-inch compacted soil
liner; a geomembrane; a drainage layer; and a 18-inch erosion layer (consisting of 12 inches of
suitable on-site borrow material and 6 inches of topsoil).
III. Proposed Closure Area
The active landfill was assessed for areas that are at or near final elevations and are suitable for
the pilot project. Approximately 9 acres on the southern slope of Phase 1 were identified for
consideration (see Drawing 00C-01). The proposed pilot project area is below the existing active
landfill access road, is constructed at 3:1 final slopes, and is southward facing. This area was
chosen because it avoids design and construction complications associated with incorporating
the existing access roadway, drains to a single stormwater sediment basin, and provides a good
test of exposure for assessing impacts of ultraviolet (UV) radiation and oxidation on the
alternative final cover system.
City of Winston-Salem | Permit Modification Application – Alternate Final Cover System Pilot Project
Alternative Final Cover System

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IV. Alternative Final Cover System
The purpose of the pilot project is to evaluate the performance of an alternative final cover
system over time in order to determine if it is a suitable alternative to the traditional, currently
permitted final closure system for the remainder of the landfill. The alternative final cover system
will include two components, an exposed geomembrane and an artificial turf final cover system.
The exposed geomembrane final cover system would consist of a geomembrane placed directly
on top of the prepared intermediate cover and up to 6 inches of bedding soil. The artificial turf
final cover system would also consist of a geomembrane placed directly on top of the prepared
intermediate cover and up to 6 inches of bedding soil but would add an artificial turf on top of the
bedding soil. The artificial turf final cover system would also include an integral drainage
system. See Drawing 00C-01 for cross sections of the two alternative final cover systems.
Prior to the installation of the alternative final cover systems, the depth of the intermediate cover
will be confirmed to be at least 12 inches and the intermediate cover will be prepared by
removing any vegetation and large or protruding stones and placing up to an additional 6 inches
of bedding soil to fill in any low spots and provide a smooth subgrade.
The alternative final cover system will be ballasted with anchor trenches, percussive driven
earth anchors, sand infill (for an artificial turf final cover system), geotextile windscreen or a
combination of ballast systems. The pilot project drawings show examples of the typical anchor
trenches located at the toes of slopes and vertically spaced over the project areas to secure the
system and restrict wind uplift impacts. The vertical interior anchor trenches would only be
required for the exposed geomembrane alternative, as the artificial turf system resists wind uplift
with the sand infill and wind turbulence generated by the grass blades. Final configuration and
size and spacing of the anchor trenches or anchoring system will be based on engineering
calculations for wind uplift and gas pressure, and would be defined in the construction permit
application.
Emergency gas vents may be necessary to relieve pressure on the geomembrane of the
alternative final cover system and prevent stress and strain within the geomembrane. Drawing
00C-03 contains details showing an example emergency gas vent. An emergency gas vent
would be located within each panel area created by the perimeter anchor trenches, or at least
one every acre. Should adjustments to the active gas collection system not be effective in
increasing the capture of landfill gas in certain areas to reduce the build-up of pressure beneath
the geomembrane, then the active gas collection system could be connected to the emergency
gas vent port. The Forsyth County Title V permit will be amended in order to accommodate
emergency relief and/or system connections.
Approval from NCDEQ for completing the pilot project with both alternative cover systems is
being sought in this permit application.
V. Stormwater Management
The proposed pilot project area is within the drainage area of the existing Sediment Basin #1.
The basin was evaluated to see how the pilot project would affect the flow into and out of the
City of Winston-Salem | Permit Modification Application – Alternate Final Cover System Pilot Project
Permit Application

3

basin. The total drainage area to Sediment Basin #1 is 35 acres. For conservativeness, we
modeled the exposed geomembrane final cover system, and its smooth surface, for
development of time of concentration and peak flow rates for the pilot project area.
Sediment Basin #1 currently provides temporary storage and treatment of run-off from a 35 acre
area of the Cells 1 and 2, consisting of stabilized intermediate cover soils. During a 25-year 24-
hour storm the basin would reduce a peak run-off of 93.6 cubic feet per second (cfs) to 38.6 cfs.
Based on initial calculations, the pilot project of 9 acres and remaining 26 acres of intermediate
cover would generate a total peak flow of 134.9 cfs which the existing basin and outlet control
could reduce to approximately 41.9 cfs. In order to reduce the peak discharge rate to the
existing peak 38.6 cfs, the basin size (bottom area) would need to be expanded by
approximately 12,000 square feet to provide additional peak flow storage. The calculations
provided in Appendix B include sediment basin analyses for the as-constructed basin and
treatment and management of flow from the 35-acre drainage area under three scenarios:
intermediate cover, permitted final cover system and nine-acre pilot project with 26 acres of
intermediate cover.
The sediment basin analysis for the pilot project assumes that the basin does not have any
significant accumulation of sediment that would affect the available storage. Prior to installation
of the pilot project, any sediment accumulated in the basin would be dredged to the designed
conditions and any re-work necessary to increase the size of the basin would be completed.
The drawings depict the conceptual stormwater management system details including cover
terraces, downdrains, downdrain and terrace connections, and the toe drain connection to the
existing drainage ditches. During final design of the pilot project, the size and configuration of
the stormwater conveyance features will be assessed for management of the estimated 25-
year, 24-hour storm flow rates. In addition, the retention and treatment requirements for
stormwater run-off from the pilot project will be confirmed with the City of Winston Salem during
design.
Expansion of the pilot project area would likely require evaluation and modification of Sediment
Basin #1 and other affected sediment basins and related conveyances in order to accommodate
the increase in peak flow rates and to address stormwater treatment requirements required by
the City of Winston Salem ordinances.
VI. Permit Application
The City proposes to NCDEQ that the pilot project be a stand alone project and requests
approval of the conceptual plans and details. Final engineering plans and specifications for the
alternative closure system would be submitted for information prior to construction. If at the end
of the pilot project, the City decides to continue with one of the alternative final cover system for
the remaining areas to be closed, then a permit modification application with the revised plans
would be submitted for the additional landfill areas. The following table summarizes the plans
that may need revision based on an initial review of closure related content in the current permit.

City of Winston-Salem | Permit Modification Application – Alternate Final Cover System Pilot Project
Calculations

4

Plan Section in Plan Topic
Facility Report Sections 2.3.3 (Final Cap System) & 2.3.4
(Drainage, Erosion and Sediment Control)
Final cover system design &
vegetation, etc.
Engineering Plan Section 3.1.6 (Cap System Design) Final cover system design
Closure Plan Most of the plan Final cover system design, etc.
Post-Closure Plan Most of the plan Maintenance of the final cover
system, etc.
Closure & Post-Closure
Cost Analysis
Most of the analysis Cost of Closure & Post-
Closure

VII. Calculations
The following calculations will be required in order to determine the appropriate design for the
alternative final cover system pilot project.
A. Wind
The stresses caused by wind uplift must be understood in order to determine the appropriate
anchoring and ballast system requirements for the alternative final cover system materials.
Calculations for wind uplift will be performed prior to construction.
B. Gas Pressure
Calculations will be completed to estimate the potential for gas pressure buildup beneath the
geomembrane, based on experience and field data with respect to surface emission monitoring.
Gas pressure can induce similar stresses on the exposed geomembrane as wind and any uplift
and strain can induce stronger interaction with wind. Final design will assess whether the
emergency vents are sufficient or if a surface collection systems should be employed beneath
the alternative final cover system to reduce gas uplift pressure.
C. Ballast/Anchor System
The ballast system may consist of anchor trenches, percussive driven earth anchors, sand (for
an artificial turf), geotextile wind screen, or a combination of ballast systems. The appropriate
calculations will be performed in order to determine the appropriate design of the ballast
system(s) for the alternative final cover system.
D. Drainage
The alternative final cover system will require a modification to the drainage design of the final
cover as the proposed alternative final cover systems will not provide the initial infiltration,
storage, and evapotranspiration that the traditional, currently permitted system would provide.
Higher stormwater run-off curve numbers must be applied to the alternative final cover system.
The design of the sediment basins, perimeter berm drainage ditches, downdrains, drainage
terraces, and culverts etc. must be evaluated for the increased peak flow rate and additional
volume associated with the pilot project. Conversely, the anticipated sediment load is greatly
reduced with the alternative cover system.
City of Winston-Salem | Permit Modification Application – Alternate Final Cover System Pilot Project
Performance Metrics

5

E. Infiltration
15A NCAC 13B .1627 Closure and Post-Closure Requirements for MSWLF Facilities requires
the final cover system to have a permeability less than or equal to the permeability of the base
liner system, or in-situ soils underlying the landfill, or the permeability specified for the final
cover in the effective permit, or a permeability no greater than 1 x 10-5 cm/sec, whichever is
less. The least permeable layer in the base liner system is the geomembrane and the final cover
system includes a geomembrane. Therefore the cover system is deemed to be functionally
equivalent to the base liner system with regard to infiltration without the need for further
modeling. This is consistent with NCDEQ’s position related to Subtitle D final cover systems.
F. Additional Calculations
Additional calculations that will be performed include evaluation of a material’s resistance to hail
damage and extreme temperature conditions.
VIII. Performance Metrics
The performance of the alternative final cover system will be evaluated on a regular basis and
will include visual inspections and material sample testing.
A. Visual Inspections
Visual inspections will be performed quarterly with the goal of identifying any degradation in the
system. The visual inspections will include review of the anchor system, geomembrane surface
and seams, penetration boots, and stormwater management system, including the drainage
terraces, downdrains, perimeter channels and Sediment Basin #1. Visual inspections will also
be conducted after major storm events.
Any defects observed would be repaired by a qualified individual and a repair log maintained
indicating repair number, physical location and type of repair completed.
B. Material Sampling
Testing of the geomembrane materials will be performed on an annual basis to track the affects
of UV and oxidation. Test panels will be provided on the alternative final cover system that will
be used for sample testing (shown on Drawings 00C-01 and Drawing 00C-03). These test
panels will provide samples of both exposed and parent materials without damaging the
alternative final cover system due to cutting out samples. Testing on the samples will include
material tensile strength and elongation (ASTM D6693) puncture resistance (ASTM D4833),
and HPOIT for UV degradation (ASTM D5885). Tests will be completed on an exposed sample
and parent material from the south facing slope each year in order to track effects of
degradation.
All exposed polyethylene geomembrane materials are susceptible to degradation from exposure
to solar UV rays, photo oxidation and temperature effects. The manufacturer includes stabilizers
and antioxidants, including carbon black, to delay the degradation and retain the desired
materials properties for as long as practical and economical for the material’s service life.
City of Winston-Salem | Permit Modification Application – Alternate Final Cover System Pilot Project
Conclusions

6

Over time, the stabilizers and anti-oxidants become depleted and the polymers can begin to
break down, altering the physical and mechanical properties of the geomembrane. The duration
of time before oxidation begins impact material strength is based on the particular stabilizer
package utilized and true exposure to the harmful UV rays. Alternative final cover systems that
utilize an artificial turf and sand ballast or windscreen ballast provide a sacrificial layer above the
geomembrane that would prolong the service life of the geomembrane better than a completely
exposed system of that same material.
Laboratory testing and field demonstrations of exposed geomembrane systems are
demonstrating that a service life of well over 30 years can be achieved. However, within that
service life, one should expect to observe some changes to the material properties, in particular
the elongation properties over time as some oxidation occurs. The design of the anchoring
system will need to consider the installed material’s properties as well as the estimated
condition of the geomembrane toward the end of its service life.
By tracking the UV resistance and material properties annually, the City can track the rate of
depletion of the stabilizers and the effects of any oxidation of the material compared to the
designed conditions for the alternative final cover system.
C. Reporting
Annual reports will be prepared for NCDEQ documenting the visual inspections and the material
sample testing. Any deficiencies in the alternative final cover system will be noted in the annual
report.
IX. Conclusions
This permit application proposes a pilot project where, for a portion of the landfill, the currently
permitted final cover system is modified from a traditional final cover system to an exposed
geomembrane cover system and an artificial turf cover system. The purpose of the pilot project
is to determine, with time, if either the exposed geomembrane and or the artificial turf cover
systems are a suitable alternative to the traditional final cover system and can be applied to the
rest of the landfill. A proposed pilot area has been selected and the design of the alternative
final cover system has been discussed. Sediment Basin #1 will be revised in order to
accommodate the runoff characteristics of the alternative final cover system. Calculations will be
conducted to confirm suitable performance of the alternative final cover system relative to
anchoring, wind uplift, and other material-specific design standards.

City of Winston-Salem | Permit Modification Application – Alternate Final Cover System Pilot Project
Appendices

A
Appendix A - Drawings

Pilot Project Site Plan
Cap Details 1
Cap Details 2
Cap Details 3

City of Winston-Salem | Permit Modification Application – Alternate Final Cover System Pilot Project
Appendices

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City of Winston-Salem | Permit Modification Application – Alternate Final Cover System Pilot Project
Appendices

B
Appendix B - Initial
Stormwater Calculations

City of Winston-Salem | Permit Modification Application – Alternate Final Cover System Pilot Project Appendices

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HDR Computation
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- - - - -PER�ANErH R.O.W
100 YEAR FLOOD PLAlfJ
840--PROPOSEDTOP OFOPERATIOt<ALCOVER cm<TOURS
EXISTlfJG COrHOURS
SILT FENCE
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8
Table 8.03b
Value of Runoff Coefficient
(C) for Rational Formula
Land Use C Land Use C
Business:
Downtown areas
Neighborhood areas
Residential:
Single-family areas
Multi units, detached
Multi units, Attached
Suburban
Industrial:
Light areas
Heavy areas
Parks, cemeteries
Playgrounds
Railroad yard areas
Unimproved areas
Streets:
Asphalt
Concrete
Brick
Drives and walks
Roofs
0.70-0.95
0.50-0.70
0.30-0.50
0.40-0.60
0.60-0.75
0.25-0.40
0.50-0.80
0.60-0.90
0.10-0.25
0.20-0.35
0.20-0.40
0.10-0.30
0.70-0.95
0.80-0.95
0.70-0.85
0.75-0.85
0.75-0.85
Lawns:
Sandy soil, flat, 2%
Sandy soil, ave.,
2-7%
Sandy soil, steep,
7%
Heavy soil, flat, 2%
Heavy soil, ave.,
2-7%
Heavy soil, steep,
7%
Agricultural land:
Bare packed soil
Smooth
Rough
Cultivated rows
Heavy soil no crop
Heavy soil with
crop
Sandy soil no crop
Sandy soil with
crop
Pasture
Heavy soil
Sandy soil
Woodlands
0.05-0.10
0.10-0.15
0.15-0.20
0.13-0.17
0.18-0.22
0.25-0.35
0.30-0.60
0.20-0.50
0.30-0.60
0.20-0.50
0.20-0.40
0.10-0.25
0.15-0.45
0.05-0.25
0.05-0.25
0.10-0.25
0.15-0.45
0.05-0.25
0.05-0.25
NOTE: The designer must use judgement to select the appropriate C
value within the range for the appropriate land use. Generally, larger
areas with permeable soils, flat slopes, and dense vegetation should
have lowest C values. Smaller areas with slowly permeable soils, steep
slopes, and sparse vegetation should be assigned highest C values.
Source: American Society of Civil Engineers
8.03.6 Rev. 6/06

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