HomeMy WebLinkAbout5802_Madison_MSWLF_LFGRequest_FID1776827_20230314Anchor QEA of North Carolina, PLLC ANCHOR
231 Haywood Street 0EA
Asheville, North Carolina 28801
828.281.3350
March 1, 2023
Jaclynne Drummond
Division of Waste Management/Solid Waste Section
1646 Mail Service Center
Raleigh, North Carolina 27699-164
Re: Madison County Closed Landfill
Permit No. 58-02
Summary of Landfill Gas Investigation
Dear Ms. Drummond,
Anchor QEA of North Carolina, PLLC, is pleased to submit this report of landfill gas mitigation
services associated with the Closed Madison County Municipal Solid Waste (MSW) Landfill (Permit
No. 58-02) located near the intersection of U.S. Highway 25/70 Bypass and Long Branch Road (State
Route 1582) in Marshall, North Carolina.
Background
Madison County monitors landfill gas in accordance with the April 23, 2010, Landfill Gas Monitoring
Plan. This plan was developed to meet the monitoring criteria outlined in the December 21, 1995,
Closure Letter for the Madison County Landfill, which operated under Permit 58-02. The following is
a chronology of events related to the landfill gas issues at the closed landfill as described in the
Facility Inspection Reports121:
• December of 2010 to 2011—Landfill gas probes were installed around the perimeter of the
facility boundary. Following installation of the gas probes, quarterly monitoring commenced
and has been ongoing since that time.
• March 24, 2011—Methane concentrations exceeded the threshold values, and the County
notified the North Carolina Department of Environmental Quality (DEQ).
• July 21, 2011—The landfill gas (LFG) interceptor trench between GP-5 and GP-6 along the
facility boundary was completed.
• December 5, 2011—The Facility Inspection Report identified violations of
15A NCAC 13B .0503(2)(a) for exceeding the lower explosive limit for gases at the property
boundary.
December 5, 2011, Facility Inspection Report, Madison County Permit No. 58-02, North Carolina Division of Waste Management,
Solid Waste Section.
z January 16, 2018, Facility Inspection Report, Madison County Permit No. 58-02, North Carolina Division of Waste Management,
Solid Waste Section.
s March 15, 2022, Facility Inspection Report, Madison County Permit No. 58-02, North Carolina Division of Waste Management, Solid
Waste Section.
\\Wcl-fs1\asheville\Projects\Madison County\2022-0620 LFG Mitigation\Drafts\2023-0301-Madison County LFG Mitigation Trench Rpt.docx
March 1, 2023
Page 2
• 2012—A second LFG interceptor trench was installed near GP-6.
• May 12, 2017—GP-6 exceeded threshold values.
• November 17, 2017—GP-5 and GP-6 exceeded threshold values.
• January 16, 2018—Facility Inspection Report identified violations of
15A NCAC 13B .0503(2)(a) for exceeding the lower explosive limit for gases at the
property boundary.
• August 27, 2018—Response to Landfill Gas Exceedances (Anchor QEA 2018) was submitted.
Letter documents that GP-6 was abandoned and replaced with GP-6R and that GP-5 would
be monitored for seasonal changes in methane.
• August 22, 2018—Landfill Gas Monitoring Plan (Anchor QEA 2018) was completed.
• March 2022—A Request for Extension of Time (Anchor QEA 2022) was submitted. The
request noted setbacks as a result of the COVID 19 Pandemic.
• March 24, 2022—DEQ granted extension until September 30, 2022.
In May and June of 2022, Anchor QEA reviewed the existing historical data and performed a
geophysical evaluation of the landfill cap in the areas of GP-5 and GP-6R to verify the location of the
landfill gas trench, the edge of waste, and if possible, determine the depth to bedrock. The results of
this investigation are described below along with recommendations for next steps.
Review of Historical Data
Anchor QEA reviewed the following historical site data and documents to gain an understanding of
the subsurface conditions to the best extent possible.
• Boring logs for monitoring wells and landfill gas monitoring points
• Design drawing of the landfill gas trench and passive vent system
• Current and historical topography to understand the aspect of the original landform slope
compared to the landfill cap
• Landfill Gas Monitoring Plan, McGill Associates (April 20, 2010)
• Apparent Landfill Gas Compliance Limit Exceedance & Remediation Plan (Madison County or
McGill Associates) (May 2011)
• Facility Compliance Inspection Report (DEQ Division of Waste Management Solid Waste
Section) (January 16, 2018)
• Phased Assessment Plan and Upgrade of Monitoring Network (Altamont Environmental, Inc.)
(March 2, 2011)
Geophysical Evaluation
On June 23 and July 27, 2022, Anchor QEA oversaw Seramur & Associates, PC (S&A) perform a
ground -penetrating radar (GPR) survey of the area between GP-5 and GP-6R. GPR was chosen for its
ability to pick up anomalous signatures between material types in the subsurface at depths of up to
March 1, 2023
Page 3
12 feet below ground surface. Two field visits were performed to run a total of 44 transects that
evaluated the area between GP-5 and GP-6R. The flatter areas of the landfill cap were also evaluated
using a grid array to produce a three-dimensional understanding of the subsurface anomalies.
Anchor QEA provided S&A with an aerial image of the proposed landfill gas interception trench
location, for reference in the field. S&A performed two field evaluations and provided reports
following each site visit. The reports described field observations, the anomalies identified in transect
and grid arrays. The anomaly locations and depths were compared to the approximate trench
location outlined in the 2011, McGill Associates, Apparent Landfill Gas Compliance Limit Exceedance
& Remediation Plan (2011 Plan). Based on S&A's findings, anomalies indicative of buried gravel were
observed in areas near the approximate location of the landfill gas interception trench depicted in
the 2011 Plan. Additional anomalies were identified as possible edge of waste (EOW), unknown
features, and some were indicative of possible buried gravels.
Extremely dry ground conditions created a challenge during data collection and interpretation for
the first field visit. The challenges caused decreased contrast between the dielectric properties of the
landfill cap and landfill gas interception trench. Another challenge identified by S&A includes
possible interference in the radar reflections due to landfill gas, venting from the PVC trench pipes,
and potentially impacting the dielectric properties of the matrix material. A final challenge identified
by S&A on the second field visit, is an increased collection depth while collecting transect data,
which may have reduced reflection definition in some of the deeper profiles.
Attachment 1 provides the geophysical reports by S&A, and Figure 1 provides a summary of their
investigation findings.
Comprehensive Site Model
Based on historical data and the results of the Geophysical Evaluation, Anchor QEA has compiled a
working comprehensive site model (CSM). The CSM consists of schematic cross sections that show
the relationships (as best as can be determined) between the landfill cap, EOW, landfill boundary and
the position of the landfill gas trench, monitoring probes and passive vents (Figures 2 to 3).
The landfill gas trench and passive vents were installed by Madison County personnel. Anchor QEA
has asked the county for information regarding the construction of the trench and vents; however,
per the county official, documentation is not available.
The landfill gas monitoring probes GP-1 to GP-11 were installed in December 2010 (Altamont
Environmental 2011). In 2011, the landfill gas trench was installed, based on the design drawings
from McGill Associates (2011). The trench was installed with approximately 3 feet of compacted soil
backfill over the top of approximately 5 feet of gravel backfill, a minimum of 2 feet wide, and to be
March 1, 2023
Page 4
installed between the approximate waste limit and facility boundary (McGill Associates 2011). These
design elements are incorporated into the cross sections shown in Figures 2 to 3.
Landfill gas has historically been an issue at landfill gas probes GP-6 and GP-5. These locations are
near the highest points of elevation prior to landfill construction. GP-6 was decommissioned and
replaced with GP-06R located approximately 130 feet to the southeast in July 2018. GP-6R has not
had landfill gas exceedances since its installation.
The landfill fills in a north -to -south trending valley, which coincides with the strike of the local
geologic structures in the area. Anchor QEA compared pre -landfill topography to the current
topography of the landfill to get a sense of the orientation of the original slopes of the valley. Based
on the collected topographic data, the occurrence of landfill gas at the GP-5 and the former GP-6
locations would be expected. The side slopes of the former valley rise toward these two points;
therefore, it makes sense that the landfill gas would rise through the deposited waste and seek the
areas of highest elevation.
The cross sections provided as Figures 2 to 3, show the presently understood relationship between
the property boundary, EOW, the landfill gas mitigation trench, and the pre -landfill and post -landfill
topography. Migration pathways leading to GP-5 exist, based on its elevated landfill gas detections.
The current trench may be too shallow and too far away from GP-5 to fully capture landfill gas
migrating beneath the subsurface. While there is an existing line of passive vents immediately east of
GP-5, their construction details are unknown and should be evaluated to determine their depths and
if they were constructed as part of a landfill gas trench system. In the vicinity of GP-5, there is room
for an additional trench to be installed between the EOW and GP-5 (Figures 3 and 4).
Recommendations
Based on review of the CSM, Anchor QEA, is recommending that a vacuum test be performed on the
existing passive vents to determine if the vents are installed in the trench and whether or not air can
travel through the trench. The test can be performed by selecting a passive vent and attaching a
vacuum pump to it. The other vents in the immediate area would be sealed with a cap that has a
manometer installed. When the vacuum pump is operated, passive vents that are interconnected by
the landfill gas trench should respond to the pressure drop caused by the vacuum. Vents that
respond will be identified and their locations considered with regards to the existing landfill gas
trench. Total depths of the existing passive vents in the vicinity of GP-5 should be measured and
their construction should be evaluated with an intrinsically safe downhole camera to determine their
integrity. Excavation between responsive vents should be performed to determine construction
details of the landfill gas trench.
March 1, 2023
Page 5
Options for Mitigation
Based on the results of this investigation and the recommendations above, the option being
considered for mitigating the landfill gas detections in GP-5 is the installation of a new landfill gas
trench located between GP-5 and PV5. The results of the vacuum test and evaluation of the depth
and integrity of the existing vents will help determine the design approach for a new landfill gas
trench.
Sincerely,
Chuck Pippin, PG
Senior Managing Geologist
cc: Rob Howell, Principal, Anchor QEA
Attachments
Figure 1
Summary of Ground -Penetrating Radar Survey
Figure 2
Schematic Cross -Section A to A' Showing Interpreted Landfill Gas Trench
Figure 3
Schematic Cross -Section B to B' Showing Interpreted Landfill Gas Trench
and GP-5 Location
Figure 4
Summary of Recommendations and Options
Attachment 1
Seramur and Associates Geophysical Reports
Figures
LEGEND:
O Passive Vent
® Gas Probe Location
■ Cross -Section Line
Anomalies Related to Trench
O Anomalies Related to Potential Edge
of Waste
August GPR Transect with Transect No.
June GPR Transect with Transect No.
Location of Landfill Gas Trench Based
on Geophysical Anomalies
Interpreted Change in Material Type
(Potential Edge of Waste)
® GPR Grid Area
Approximate Edge of Waste
0 Landfill Parcel Boundary
4-Foot Topographic Contours
NOTES:
1. Aerial imagery from Esri Online Services,
2020.
2. Topographic Contours from NCDOT, 2007.
3. Approximate Edge of Waste Based on McGill
Associates May 2011, Apparent Landfill Gas
Compliance Limit Exceedance & Remediation.
4. GPR - Ground Penetrating Radar
0
0 70
Feet
Publish Date: 2023/01/04, 9:22 AM I User: cpippin
Filepath: Q:\lobs\MadisonCounty_NC_1500\Maps\LandfillGas_TrenchLocation\PostAugustSurvey\AQ_Fig1_Summary_of_Geophysics.mxd
kZANCHOR Figure 1
QEA `'`'`: Summary of Ground Penetrating Radar Survey
Madison County Closed Solid Waste Management Facility, Permit No. 58-02
A
2140 ;
2135
2130
2125
7120
2115
w 7110
7105
2100
2095
2090
2085
LEGEND
Section
B to B'
el
Q4,-IS V-yt�l gV6ykl
4 Q`,1 h�Q J 1�
0 100 200 300 400 500 600 700 804
Distance Along Section (feet)
R Representation of vapor path
_1
Passive vent
(red color indicate
LFG detected at vent)
Anomaly interpreted to
correspond with trench
Pre -landfill topography
Current topography
Assumed 4-foot cap
Filepath: [file address information]
ANCHOR
Notes:
Schematic cross section constructed parallel to assumed location of the landfill gas trench.
1 GRP Transect The red dots represent observed anomalies in the ground -penetrating radar geophysical survey. The anomalies are interpreted to represent the
1 top -of -gravel bedding of the landfill gas trench.
1
1 Shown is the current topography, the re -landfill topography, and an interpreted 4-foot cap layer. Areas where current topographyand the pre -
landfill pP P Y P
landfill topography do not match are assumed to be filled with native soils, fill, or bedrock or they are assumed to have been altered overtime.
The edge of waste is out of the plain of this cross section.
Figure 2
Schematic Cross Section A to A' Showing Interpreted Landfill Gas Trench
Madison County Closed Solid Waste Management Facility, Permit No. 58-02
6
2150
2145
2140
2135
2130
2125
a)
2120
0
nz
2115
w
2110
2105
2100
2095
2090
2085
2080
2075
Filepath: [file address information]
kZANCHOR
QEA
Approximate
Edge of Waste
Section
I
Cap —
0 50 100 150 200 250 300 350
Distance Along Section (feet)
LEGEND
R Representation of vapor path
Passive vent r Anomaly interpreted to
(red color indicate correspond with trench
LFG detected at vent)
Pre -landfill topography
Current topography
Assumed 4-foot cap
Interpreted Landfill Gas
Trench Location Based on
historical data and GPR
anomalies.
Landfill gas probe
Potential Location of New
Landfill Gas Trench
1 GRP Transect
i
1
Notes:
Schematic cross section constructed perpendicular to the assumed location of the
landfill gas trench and through GP-05.
Shown is the current topography, the pre -landfill topography, and an interpreted
4-foot cap layer. White areas where current topography and the pre -landfill
topography do not match are assumed to be filled with native soils, fill, or bedrock
The approximate edge of waste based on McGill Associates May 2011, Apparent
Landfill Gas Compliance Limit Exceedance & Remediation.
The interpreted Edge of Waste is based on anomalies observed in the
ground -penetrating radar survey that appear to be material type transitions
interpreted to be possible edge of waste.
Figure 3
Schematic Cross Section B to B' Showing Interpreted Landfill Gas Trench and GP-05 Location
Madison County Closed Solid Waste Management Facility, Permit No.
Publish Date: 2023/03/13, 5:00 PM I User: cpippin
Filepath: Q:Vobs\MadisonCounty_NC_1500\Maps\LandfillGas_TrenchLocation\PostAugustSurvey\AQ_Fig4_MadisonClosed_LFG_Recommendations.mxd
ANCHOR
QEA
LEGEND:
Passive Vents to be Vacuum Tested to
Determine Interconnectivity via
Landfill Gas Trench'
® Gas Probe Location
Assumed Landfill Gas Trench Installed
00 Between 2013 and 2015
■ Proposed Landfill Gas Trench
Location of Landfill Gas Trench Based
0 on Geophysical Anomalies
1j1 Approximate Edge -of -Waste
0 Landfill Parcel Boundary
— 4-Foot Topographic Contours
NOTES:
1. Aerial imagery from Esri Online Services,
2020.
2. Topographic Contours from NCDOT, 2007.
3. Approximate Edge of Waste Based on McGill
Associates May 2011, Apparent Landfill Gas
Compliance Limit Exceedance & Remediation.
4. Date shown with passive vent location ID
indicates approximate installation date.
0
0 35
Feet
Figure 4
Summary of Recommendations and Options
Madison County Closed Solid Waste Management Facility, Permit No. 58-02
Attachment 1
Seramur and Associates Geophysical
Reports
Seramur & Associates, PC
165 Knoll Drive
Boone, NC 28607
July 5, 2022
Mr. Chuck Pippin, PG, RSM
Senior Managing Geologist
Anchor QEA
231 Haywood Street
Asheville, NC 28801
Re: Geophysical survey to locate a gravel trench at the closed Madison County landfill, Long Branch Road,
Marshall, NC
Dear Mr. Pippin:
Seramur and Associates, PC has completed a geophysical survey to locate a gravel trench at the closed Madison
County landfill on Long Branch Road, Marshall, NC (Figure 1). It is our understanding that a trench extends along
the perimeter of the closed landfill. This trench is about 3 feet deep, and the base of the trench is reportedly filled
with gravel. A map was provided showing the approximate trench location or "hypothetical trench location" as it
will be referred to in this report.
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Anchor QEA
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Site Location Map
Madison County Landfill
Seramur & Associates, PCo
N
Source: u.S.G.S.
Marshall, NC
Boone, NC
Feet
The National Map
Figure 1. Topographic map of the study area.
Phone: 828.264.0289 seramur(cr�,icloud.com Cell: 828-773-0499
Geophysical Surveys
Seramur & Associates collected Ground Penetrating Radar (GPR) in two grids and along twenty-six transects.
These were located along an approximately 650 foot section of the hypothetical trench location (Figure 2).
Figure 2. Site map showing hypothetical trench location, GPR transect and grids.
A GPR survey was completed using a Geophysical Survey Systems, Inc. UtilityScan GPR System with a 350 MHz
hyperstacking antenna. This GPR system is equipped with a calibrated survey wheel. The GPR grid data has been
processed and modeled using GPR Slice® software. The GPR data processing included adjusting time zero,
completing a background removal, and adjusting the time variable gain to enhance deep reflections. Three-
dimensional models of the GPR grid data were produced with GPR Slice® software. Each depth slice is a
horizontal slice or plan view of the reflections across a 0.3-foot thickness of the subsurface. The GPR profiles show
a cross-section of the subsurface directly under the path of the antenna down to a depth of 9.0 feet.
The Pythagorean Theorem was used to establish two rectangular grids. The plan was to lay out the grids where the
hypothetical trench location map showed a turn or change in direction of the trench. Once in the field it was
determined that it was too steep to place a grid along the southeastern section where the trench changed direction.
This Grid was offset to the southwestern end of the hypothetical trench location. Grid 2 was place where the trench
reportedly changed direction in the northeastern portion of the study area (Figure 2). Geophysical grid data was
collected along transects at a four -foot spacing.
Twenty-six additional transects of GPR data were collected in the areas where it was not possible to collect grid
data because of the steep slope (Figure 2). Eight of the transects covered the slope on the western edge of the
landfill and the remaining eighteen covered the slope located along the northern edge of the landfill. These transects
were spaced at approximate 20-foot intervals across the hypothetical trench location.
Seramur & Associates, PC 2
Q PVC pipe
■ Edge of waste marker
• Field -selected anomal
— Field -selected trench I
+ Transect
"_; Grid
■
I Figure 3 I Madison County Landfill, I I 0 25 50 75 100 Feet N
Seramur &Associates, PC A
Anomalles Identified in the Field Long Branch Road, Boone, NC
Source: Esri, Buncombe County, & NC DOT Marshall, NC 28753 0 7.5 15 22.5 30 Meters
Figure 3. Site map with field selected trench location.
A Juniper Systems, Inc. Geode GNSS Receiver was used to survey the location of the transects, GPR grid corners,
field observed anomalies, and other landfill features. The GPR data was observed in the field as each transect was
collected. Reflections or hyperbolas observed on the tablet screen and possibly associated with a gravel trench
were flagged in the field and mapped with the GPS (Figure 3).
These anomalies were marked with white flags and orange flagging tape and were used to map out the "field
selected trench location" (Figure 3). The processed GPR profiles were review back in the office and additional
anomalies were identified. These additional anomalies were overlaid on our site plan and an "interpreted trench
location" was established (Figure 4).
Findings
The GPR survey identified seven sets of "anomalies of interest" (Table 1).
Anomaly
Figure(s)
Field Selected Anomalies
Red Circles and Red Line on Figures 3 and 5
Interpreted Trench Location Anomalies
Purple Circles and Purple Line on Figures 4 and 5
Additional Anomalies on Transects 6-9
Green Circles on Figure 4
Additional Anomalies on Transects 15-20
Green Circles and Line on Figure 5
Edge of Waste in Grid 1
Orange Line on Figure 6
Edge of Waste in Grid 2
Orange Line on Figure 6
Deep Anomaly in Grid 2
Green Line on Figure 4
Table 1. Anomalies identified in the GPR data and figure(s) showing anomaly locations.
Seramur & Associates, PC 3
0 PVC pipe
■ Edge of waste marker
O Additional anomaly
• Interpreted trench anomaly
Interpreted trench locat
Transect
Grid
■
0 O
1
NX
Grid 2 J
Figure 4 I Madison County Landfill, I Seramur Associates, PC I 025 50 75 100 Feet IN
Interpreted Trench Location Long Branch Road, o
Boone, NC
Source: NC CGIA, Maxar, and Esd Marshall, NC 28753 0 7.5 15 22.5 30 Meters
Figure 4. Site map with interpreted trench location and additional anomalies.
Anomalies possibly associated with a gravel trench were mapped along twenty of the twenty-six transects. A set of
linear anomalies was identified between Grids 1 and 2 and interpreted as the most likely alignment of the gravel
trench (purple circles and line on Figure 4). This set of anomalies aligns well with the field selected trench location
for much of the distance between the two grids (purple line and red circles on Figure 5). The potential gravel
trench appears as medium amplitude reflections on these GPR profiles (Figure 7). These two interpretations
diverge to the south as they approach Grid 1. This alignment between the two grids also appears to align with a
linear feature on a 2010 aerial photograph (Figure 8). Our field personnel also noted a slight color change in the
vegetation along this alignment.
Additional anomalies (hyperbolas) were observed on Transects 6 through 9 (green circles on Figure 4). These
anomalies were also recognized in the field as they align with the field selected trench alignment (Figure 5). A
second linear set of anomalies were observed on Transects 15, 18, 19, and 20 (green circles and line on Figure 4).
This set of anomalies is southeast of the interpreted trench alignment. These anomalies could be related to objects
in the buried waste. They appear along a buried surface, but their linear arrangement could indicate a trench
(Figure 9).
Seramur & Associates, PC 4
0 PVC pipe
■ Edge of waste marker
• Field -selected trench location
Hypothetical trench location
— Interpreted trench locat
+ Transact
C _; Grid
■
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Figure 5 S
I Madison County Landfill, I 0 25 50 75 100 Feet A I
eramur &Associates, PC
IN
Potential Trench Locations Long Branch Road, Boone, NC
Source: NC CC IA, Maxar, and Fsri Marshall, NC 28753 0 7.5 15 22.5 30 Meters
Figure 5. Site map showing the trench location selected in the field and the interpreted trench location.
A linear set of low to medium amplitude reflections extends north to south across Grid 1 (red dashed line on depth
slice, Figure 10). Initially, this set of reflections was thought to be the alignment of the gravel trench. After further
review of the data, it was determined that this linear reflection follows the edge of the landfill cell (edge of waste).
High amplitude reflections are present at depth on many of the GPR profiles in Grid 1 (red ovals on GPR profiles,
Figure 10). These appear to be the clearest images of reflections that could represent the gravel trench. There is
more than one anomaly on some of the transects and these are marked in green.
A linear, arcuate set of medium to high amplitude reflections extends across Grid 2 on the 1.6 to 1.9 foot depth slice
(Figure 11). This linear set of reflections align with the edge of waste observed on the GPR profiles. This shallow
set of reflections is interpreted as the edge of waste. A deeper set of medium to high amplitude reflections align
with the shallow reflections in the southern portion of the grid, but then turns to the southwest about halfway across
the grid (Figure 12). This is the type of reflection that a gravel -lined trench would produce, but the source of this
anomaly is not known. The profiles for Grid 2 were thoroughly reviewed and it was not possible to trace the deep
anomaly across the grid.
Seramur & Associates, PC 5
0 PVC pipe 0 T �
■ Edge of waste marker �
Edge of waste r. ' IJ'
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ood GridGrid 2 Oak
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Figure 6 Madison County Landfill, 0 25 50 75 100 Feet N
Edge of Waste Long Branch Road, Seramur o Associates, PC � n
Boone, NC /V
Source: NC CGIA, Maxar, and Esn Marshall, NC 28753 0 7.5 15 22.5 30 Meters
Figure 6. Site map showing the edge of waste.
Seramur & Associates, PC 6
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Figure 7. GPR profiles for transects between Grids 1 and 2 showing the interpreted trench location (red circles)
additional anomalies (green circle) and edge of waste (black arrow and red dashed line).
Seramur & Associates, PC 7
Figure 8.2010 aerial photograph showing linear feature that aligns with the field selected and interpreted trench
locations.
Seramur & Associates, PC
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is used to mark an anomaly that is located on a buried surface. Red circles/ovals denote interpreted trench location.
Red dashed line and black arrows indicate the edge of waste.
Seramur & Associates, PC 9
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Figure 10. Broad, high amplitude reflections in Grid 1 interpreted to be produced by the gravel trench (red ovals on
profiles and purple circles on GPR slice). More than one reflection is present on some of the profiles (green ovals on
profiles and circles on depth slice). Red dashed line and black arrows denote edge of waste.
Seramur & Associates, PC 10
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x (ft)
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Figure 12. A linear, high amplitude reflection in Grid 2 is observed on three GPR depth slices imaging reflections about
2 feet deep.
Seramur & Associates, PC 12
0 PVC pipe
■ Edge of waste marker
C0120 CC740
,u'
`
Five-foot buffer
CC16
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0
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Figure 13 Madison County Landfill,
Seramur & Associates, PC
0
25 50 75 100 Feet
N
Potential trench location buffer
Long Branch Road,
Boone, NC
�
A
Source: NC CGIA, Maxar, and Esri
Marshall, NC 28753
0
7.5 15 22.5 30 Meters
Figure 13. Site map showing a five-foot buffer around all potential trench locations.
A gravel lined trench in a homogeneous matrix of a silt loam soil should produce a clear, high amplitude reflection
on the GPR profiles. This was observed in Grid 1. Soil conditions were very dry and county employees stated that
they had not had any rain for an extended period of time. The transect data was collected on a steep slope. Soils on
this slope would be well drained, this in combination with the dry weather resulted in very subtle reflections along
the interpreted trench location.
The location of the trench in Grid 2 is uncertain. The field work identified a few anomalies in Grid 2 that could be
associated with a gravel trench, but a linear set of anomalies was not observed on the GPR profiles in the processed
data. The gravel trench may follow the field selected location; however, it could not be confirmed with the
processed data.
The edge of waste locations were identified, compiled, and mapped on Figure 6. A 5-foot buffer was established
around the field selected trench location and the interpreted trench location (Figure 13). Five-foot buffers were also
established around the additional anomalies on the transects (15, 18, 19, and 20) and the deep linear anomaly in
Grid 2. Seramur & Associates recommends that the 5-foot buffers around the field -selected and interpreted trench
locations be avoided without further investigation. It is also recommended that the additional transect anomalies
and the deep Grid 2 anomaly be investigated further if these areas are to be disturbed.
Seramur & Associates, PC 13
Thank you for the opportunity to assist in completing a Geophysical survey to investigate the location of the gravel
trench at the closed Madison County landfill, Long Branch Road, Marshall, NC.
Sincerely,
16 '-': --- -- ' a, � �
Keith C. Seramur, P.G.
Consulting Geologist
Appendix A
GPR Grid and Transect Data
Seramur & Associates, PC 14
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