4501_HendersonCounty_MSWLF_RevisedLandfillGasRemediationPlan_DIN26731_20160915

Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation

REVISED LANDFILL GAS
REMEDIATION PLAN –
METHANE EXCEEDANCES AT
METHANE MONITORING WELL
MP-4
Closed Henderson County Municipal Solid Waste
Landfill, Permit No. 45-01
Henderson County, North Carolina

Submitted To:
Henderson County Solid Waste Division
191 Transfer Station Drive Hendersonville, NC 28791

Submitted By: Golder Associates NC, Inc. 5B Oak Branch Drive
Greensboro, NC 27407

September 2016 0839-650616.600
PL
A
N

September 2016 i 0839-650616.600

final henderson co msw lf lfg remediation plan.docx
Table of Contents
COVER LETTER
1.0 INTRODUCTION ............................................................................................................................... 1
2.0 BACKGROUND................................................................................................................................. 1
3.0 METHANE MONITORING WELL MP-4 EVALUATION .................................................................... 2
4.0 PROPOSED REMEDIATION ............................................................................................................ 2
4.1 Best Management Practices ......................................................................................................... 3
4.2 Installation of Cut-Off Trench ........................................................................................................ 3
5.0 CONCLUSIONS ................................................................................................................................ 3
6.0 REFERENCES .................................................................................................................................. 4
List of Figures
Figure 1 Methane Concentration Trend Graph for Methane Monitoring Well MP-4
List of Drawings
Drawing 1 Groundwater Surface Contour Map – March 15, 2016 Drawing 2 Landfill Gas Remediation Plan
Drawing 3 Landfill Gas Remediation Plan Details

September 2016 1 0839-650616.600

final henderson co msw lf lfg remediation plan.docx
1.0 INTRODUCTION
This Landfill Gas (LFG) Remediation Plan has been prepared by Golder Associates NC, Inc. (Golder) for
the closed Henderson County Municipal Solid Waste (MSW) Landfill in Henderson County, North Carolina
(NC), due to sporadic LFG exceedences in methane monitoring well MP-4. The Plan has been prepared
in accordance with Title 15A of the North Carolina Administrative Code (NCAC) Subchapter
13B.1626 (4)(c). The Henderson County Landfill, which consists of a closed municipal solid waste (MSW)
and a closed construction and demolition (C&D) landfill, is maintained by the County under Permit No.
45-01 issued by the NC Department of Environmental Quality (NC DEQ).
2.0 BACKGROUND
The location of the facility is shown on the inlay on Drawing 1. As presented, the closed Henderson
County Landfill is located approximately 3 miles northwest of the city of Hendersonville, off Stoney
Mountain Road. The County maintains an approximately 120-acre landfill facility that consists of a
closed, unlined C&D over MSW facility; a closed, unlined C&D facility; a closed, unlined facility formerly
operated by the Tennessee Valley Authority (TVA); and an active transfer station. A white goods area, a
yard waste disposal area, and a beneficial reuse area are also present on the property.
The facility has been in operation since the 1940s, beginning with the TVA landfill. The MSW landfill
opened in 1960. In January 1998, the MSW facility ceased accepting MSW waste and began placing
C&D waste over the MSW waste. After closure of the C&D-over-MSW area in 2001, a new C&D landfill
began operation on the southeastern portion of the facility property. The C&D-over-MSW area was
capped with a modified clay cap. The County ceased accepting waste at the stand-alone C&D landfill on
June 30, 2008, and completed closure activities on June 30, 2009.
The landfill is bounded to the north and east by residential and undeveloped wooded properties, to the
south by Stoney Mountain Road and residential and wooded properties, and to the west by a tributary of
Mill Pond Creek, a NC Department of Transportation maintenance yard, and a Henderson County School
bus maintenance facility. Topographic relief at the landfill ranges from approximately 2170 to 2590 feet
above mean sea level. Surface drainage from the facility is predominantly to the southwest toward
several streams along the western and southern portions of the property. These features drain into Mill
Pond Creek located southwest of the landfill.
The County monitors methane at six compliance methane monitoring wells (MP-1, MP-3, MP-4, MP-7,
MP-8, and MP-9) and three assessment methane monitoring wells (MP-6, TR-2, and TR-3) located
around the MSW landfill on a quarterly schedule. Additionally, the County monitors three compliance
methane monitoring wells (LFG-1, LFG-2, and LFG-3) around the closed C&D landfill. The County
currently monitors eight structures (activity building, animal shelter, break house, bus garage,
convenience center building, maintenance shop, scalehouse, and the Trace barn) on County property in
close proximity to the MSW or C&D landfill.
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final henderson co msw lf lfg remediation plan.docx
Methane monitoring well MP-2 was removed from the compliance network and abandoned during the
construction of the new landfill entrance and scalehouse. Well MP-5 was removed from the compliance
network and fitted with a turbine vent and TR-1 abandoned as specified in the LFG Remediation Plan –
Phase 2, which was approved by the NC DEQ on January 21, 2015.
An active LFG extraction system was operated by a third party (NC Municipal Gas Partners, LP/Enerdyne
Power Systems) from 1998 to April 2013. NC Municipal Gas Partners, LP terminated their contract with
the County on April 1, 2013, and shut down and removed components of the system.
Methane concentrations from well MP-4 exceeded the lower explosive limit (LEL) during the June and
September 2015 quarterly monitoring event. As documented in the Third Quarterly Methane Monitoring
Report of 2015, a turbine vent was installed onto landfill gas vent EW-4, which is located in close
proximity to MP-4, due to these exceedances. Methane concentrations from MP-4 once again exceeded
the LEL during the June 2016 event, but were below the LEL during the September 2016 event.
Due to sporadic detections of methane above the LEL in MP-4 during quarterly methane monitoring
events, the County is proceeding with producing this revised LFG Remediation Plan, which describes the
steps to reduce LFG migration and to protect human health and the environment if methane
concentrations exceed the LEL in MP-4 during future quarterly events.
3.0 METHANE MONITORING WELL MP-4 EVALUATION
Methane concentrations from well MW-4 have fluctuated since its initial LEL exceedance in July 2012, but
did not exceed the LEL again until the June 2015 quarterly monitoring event. After a second exceedance
from MP-4 during the September 2015 quarterly event, a turbine vent was installed onto landfill gas vent
EW-4, which is located in close proximity to MP-4. Methane concentrations subsequently decreased
below the LEL for the next two quarterly events, but the concentration exceeded the LEL once again
during the June 2016 event. The concentration of methane from MP-4 was below the LEL during the
September 2016 event. A graph showing the historical methane readings for available data from MP-4 is
included as Figure 1.
Methane monitoring well MP-4 has a total depth of approximately 19.5 feet below ground surface. An
installation record for this well cannot be located; therefore, the screened interval is unknown. The well is
located approximately 37 feet from the edge of waste. During a field investigation of MP-4 and the
surrounding area in August 2016 by Golder staff, liquid was measured in MP-4 at approximately 8 feet
below ground surface. The groundwater surface contour map from the March 2016 water quality
monitoring event is included as Drawing 1 for reference.
4.0 PROPOSED REMEDIATION
Proposed remediation activities for addressing the elevated methane concentrations observed in the
methane monitoring well MP-4 are discussed in the following sections. They include best management
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final henderson co msw lf lfg remediation plan.docx
practices that include repairs to the landfill cap and the installation of a cut-off trench between the MSW
waste unit and methane monitoring well MP-4.
4.1 Best Management Practices
The County has begun improvements to the landfill cap on the northwest slope of the MSW waste unit.
These improvements include grading to divert runoff from the landfill cap to decrease the amount of
infiltration of precipitation into the waste unit. The County has also reseeded sections of the cap to
stabilize the slope. The County will continue to monitor the improvements and other sections of the cap
for additional repairs.
4.2 Installation of Cut-Off Trench
Contingent upon future exceedance of the LEL from MP-4, the County proposes to install a cut-off trench
between the waste unit and methane monitoring well MP-4 in order to vent LFG that may be migrating
from the landfill toward MP-4. The proposed trench is to be approximately 250 feet long and 2 to 4 feet
wide and will be located as shown on Drawing 2. The trench will be dug to an average depth of 20 feet
below ground surface. Well MP-4 has total depth of approximately 19.5 feet below ground surface. The
depth of waste in the northwest corner of the waste unit is not expected to exceed the depth of the trench,
based on available information.
The back wall of the trench will be lined with an impermeable barrier and backfilled with stone. Perforated
6-inch schedule 80 polyvinyl chloride (PVC) pipe will be installed approximately 4 feet below ground
surface along the length of the excavation. Non-perforated 6-inch schedule 80 PVC pipe will be attached
to the perforated pipe and extend above ground to vent accumulated landfill gas. A vent located 50 feet
from each end of the trench will be installed. The vents will be topped by passive wind-driven turbine
vents. The upper 2 feet of the excavation will be backfilled with a relatively impermeable soil. A detail of
the construction of the cut-off trench is shown on Drawing 3.
The installation of the proposed cut-off trench will be initiated within 90 days of any future LEL
exceedances from methane monitoring well MP-4. Routine quarterly methane monitoring will continue on
a quarterly basis. If there is no indication of a declining trend in methane concentrations at the end of one
year after installation, additional remediation will be recommended.
5.0 CONCLUSIONS
This LFG Remediation Plan has been prepared in response to sporadic detections of methane above the
LEL in compliance methane monitoring well MP-4 at the facility. The remedial activities consist of
installing a cut-off trench between the waste unit and MP-4, contingent upon any future LEL exceedances
from MP-4.
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final henderson co msw lf lfg remediation plan.docx
6.0 REFERENCES
Golder Associates NC, Inc., September 26, 2013. Landfill Gas Remediation Plan – Phase 1; Closed
Henderson County Landfill, Permit No. 45-01; Henderson County, North Carolina.
Golder Associates NC, Inc., January 6, 2015. Landfill Gas Remediation Plan – Phase 2; Closed
Henderson County Landfill, Permit No. 45-01; Henderson County, North Carolina.
Golder Associates NC, Inc., September 30, 2015. Methane Monitoring Results – Third Quarterly Event of
2015; Closed Henderson County Landfill, Permit No. 45-01; Henderson County, North Carolina.
Golder Associates NC, Inc., June 20, 2016. Methane Monitoring Results – Second Quarterly Event of
2016; Closed Henderson County Landfill, Permit No. 45-01; Henderson County, North Carolina.
Golder Associates NC, Inc., September 13, 2016. Methane Monitoring Results – Third Quarterly Event of
2016; Closed Henderson County Landfill, Permit No. 45-01; Henderson County, North Carolina.
Golder Associates NC, Inc., July 25, 2016. Water Quality Monitoring Report, First Semi-Annual 2016
Sampling Event and Corrective Action Monitoring; Closed Henderson County Landfill, Permit No. 45-01;
Henderson County, North Carolina.

FIGURE

METHANE CONCENTRATION TREND GRAPH FOR METHANE
MONITORING WELL MP-4

PROJECT No. PHASE Rev FIGURE
0839650616 600 0 FIGURE 1
HENDERSON COUNTY

HENDERSON COUNTY CLOSED MSW LANDFILL
PERMIT NO. 45-01

CLIENT
CONSULTANT
PROJECT
TITLE YYYY-MM-DD
PREPARED
DESIGN
REVIEW
APPROVED
DYR
DYR
RPK
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2016-08-25

Path: document1 | FileName: DOCUMENT1

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HENDERSON COUNTY CLOSED MSW AND C&D LANDFILL
PERMIT # 45-01
HENDERSON COUNTY
GROUNDWATER SURFACE CONTOUR MAP
MARCH 15, 2016
EXISTING 10 FT. CONTOUR
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LIMITS OF WASTE
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INJECTION WELL
NOT MEASURED
LEGEND
NOTES
REFERENCES
SITE LOCATION MAP
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1. NON-PERFORATED 6" PIPE INSTALLED ON BOTH ENDS OF PASSIVE VENT
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PROPOSED LANDFILL GAS
REMEDIATION TRENCH DETAIL
NOT TO SCALE
NOTES:
1. NEAR-SURFACE HORIZONTAL EXTENSION OF PLASTIC BARRIER AND
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HENDERSON COUNTY CLOSED MSW AND C&D LANDFILL
PERMIT # 45-01
HENDERSON COUNTY
LANDFILL GAS REMEDIATION PLAN DETAILS
TITLE
PROJECT NO.REV.
PROJECTCLIENT
CONSULTANT
PREPARED
DESIGNED
REVIEWED
APPROVED
YYYY-MM-DD
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Golder Associates NC, Inc.
5B Oak Branch Drive
Greensboro, NC 27407 USA
[phone] - Phone
[phone] - Fax