WQ0013419_Sludge Landill Investigation_20220804

4 Blanchard Road, P.O. Box 85A Cumberland, ME 04021
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220568.00 20220804NCDEQ.docx
ENVIRONMENTAL  CIVIL  GEOTECHNICAL  WATER  COMPLIANCE
August 4, 2022

Landon Davidson
Regional Supervisor - Water Resources
Water Quality Regional Operations
2090 U.S. 70 Highway
Swannanoa, NC 28778-8211

Subject: Sinkhole Investigation
Davidson River Village Closed Sludge Landfill

Dear Mr. Davidson:

INTRODUCTION

On Friday, July 8, 2022 during a routine inspection, a sinkhole was discovered at the Davidson River
Village closed Sludge Landfill Site in Pisgah Forest, North Carolina. The site retains wastewater treatment
sludge from the former Ecusta Paper Mill. Figures 1 and 2 (attached) show views of the sinkhole. The
sinkhole occurred sometime between July 5, 2022 and July 8, 2022. On discovery, the sinkhole was
estimated to have a diameter of approximately 25 feet and a depth of approximately 15 feet.

On Monday, July 11, 2022, Jill Urey authorized formation of a team of Glatfelter consultants and
engineers to investigate the sinkhole’s effects on the Sludge Landfill Site.

BACKGROUND

The dam was constructed in 1976. Soil materials used to construct the dam were excavated from a ravine
area (to the north) that now forms the landfill. A report by Law Engineering Testing Company (LETCo.)
dated November 23, 1976, documents the dam’s construction, and includes the following information:

Dam Maximum Height (Main Dam) Approx. 75 ft
Dam Crest Length Approx. 425 ft
Dam Crest Elevation1 2,186 ft
Dam Crest Width 15 ft
Dam Outboard Slope Angle 3 Horizontal: 1 Vertical
Dam Inboard Slope Angle (i.e., landfill
side)
2 Horizontal: 1 Vertical

Notes:
1. 2005 survey of the dam by Hafler Land Surveying of Brevard, North Carolina
indicated the dam crest to be at approximately Elevation 2187 feet using a
1983 NGVD datum.
2. The above information does not include two add-on dikes completed in
1998 and 2000.

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Page 2 of 5
Two soil dikes were added to the landfill side of the dam crest in May 1998 and November 2000,
increasing the dam height by approximately 20 feet. The dam and dikes are considered to be stable in
terms of slope stability relative to the sinkhole. The sinkhole is believed to be a localized condition that
occurred on the inward side (i.e., on the landfill side) of the dam leaving considerable embankment on
the outward side of the dam to resist any changed lateral forces caused by the sinkhole.

Two large-diameter drainage pipes are located near the center of the dam where the sinkhole occurred.

• A 30-inch-diameter pipe is located at the base of the dam and connects the inward toe of the
dam to the outward toe of the dam. The 30-inch pipe was constructed using corrugated metal
pipe that was encased in concrete and sloped to convey stormwater and leachate from a
junction box at the inward toe of the dam to the Aerated Stabilization Basin (ASB), which is
adjacent to the toe of the dam. The original function of the 30-inch pipe was to drain leachate
from the landfill, drain runoff from the landfill surface (by way of a 48-inch diameter pipe that
connects to the 30-inch pipe), and drain discharging groundwater seepage from the landfill area.
Currently the 30-inch pipe drains water (believed to be mostly discharging groundwater) at an
average rate estimated to be approximately 40 gallons per minute (gpm). It is important that
the 30-inch pipe remain functional to avoid buildup of unwanted hydrostatic pressures in the
landfill, that could otherwise affect stability of the dam.
• A 48-inch-diameter pipe is located on the inward face of the dam and has been buried by sludge
since the mid-1990s. The 48-inch pipe was constructed using precast, reinforced concrete pipe
sections. A concrete slab was constructed on the inward dam face and was used to hold the 48-
inch pipe in-place with a system of stainless-steel wire ropes attached to the concrete slab
during sludge placement. The lower end of the 48-inch pipe terminates in the same concrete
junction box as does the 30-inch pipe. The primary purpose of the 48-inch pipe was to convey
stormwater and leachate from the surface of the Sludge Landfill during and after active waste
placement to the junction box at the inward toe of the dam, where drainage into and through
the 30-inch pipe to the ASB would occur. The above ground inlet to the 48-inch pipe is visible in
a riprapped drainage area that runs perpendicular to the dam crest. The inlet to the 48-inch pipe
no longer receives leachate or stormwater from the landfill surface. Figures 3, 4, and 5
(attached) show the approximate locations of the two drainage pipes and their spatial
relationship to each other.

The two dikes added to the dam crest were each approximately 10 feet tall and had cross-section
configurations similar to that shown on Figure 6 (attached). Both dikes were built on sludge that had
accumulated on the landfill side of the dam. The dikes were separated from the underlying sludge by
layers of geogrid, drainage stone, and geotextile fabric. Periodic horizontal and vertical surveys
completed for the dam and landfill indicate the dikes are settling due to consolidation of the sludge and
the sludge near the dam’s sloped inward face moving in a northern direction toward the center of the
landfill.

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August 4, 2022
Page 3 of 5
PHASE ONE INVESTIGATION OF THE SINKHOLE

To date, work completed for the sinkhole investigation consists of obtaining and examining
photographic views of the sinkhole, performing a survey of the landfill surface to identify other potential
sinkhole locations, and completing video and photographic inspection of the accessible portions of the
pipe interiors.

48-inch Reinforced Concrete Pipe (RCP)
This pipe is approximately 125 feet long, sloped at a 2 horizontal to 1 vertical, and is accessed from
the pipe inlet at the crest of the dam. Photographs of the interior of the 48-inch pipe showed
considerable presence of precipitated minerals and presence of debris that likely entered the pipe
through failed joints between sections of the pipe (see Figure 7, attached). Examination of the pipe
showed the intrusion of mineral precipitates starting at approximately 10 feet from the pipe
entrance and an apparent collapsed pipe section approximately 35 feet from the pipe entrance.
Further investigation of the 48-inch pipe was not possible beyond this point.
Based on conditions observed on July 20, 2022, the following preliminary findings for the 48-inch
pipe are offered:
• Mineral precipitates and pipe collapses similar to those shown on Figure 7 may be present
over much of the 48-inch pipe’s length.
• The mineral presence may be affected by the condition of the pipe at various depths.
• The 48-inch pipe collapse may have been caused by the two dikes that were added to the
dam. The dikes are settling inward in the direction of the landfill. The sludge around the
pipe(s) is compressible, has some adhesive strength, and may be causing horizontal and
vertical forces to be imparted onto the 48-inch pipe that could be sufficient to displace joints
between the pipe sections and cause the pipe wall to deform and buckle.
• The collapse of the 48-inch pipe is presently thought to be the cause of the sinkhole.
30-inch Corrugated Metal Pipe (CMP)
The 30-inch pipe that extends through the entire width of the dam, is approximately 330 feet long,
sloped at approximately 1 percent, and discharges at the toe of the dam into the ASB. Photographs
and video of the interior of the 30-inch pipe showed considerable buildup of debris in the pipe’s
invert, approximately 30 feet from the pipe’s opening (see Figure 8, attached). No investigation of
the pipe could be completed beyond approximately 45 feet from the pipe opening due to the soft
conditions of the debris in the pipe invert that were restrictive to camera insertion. The crown
portion of the 30-inch pipe that could be observed appeared in good condition. The portion of the
pipe invert that could be seen from the video effort also appeared in good condition.
A delta of soil and sludge debris is forming at the outfall of the 30-inch pipeline (see Figure 9,
attached). The delta suggests that a portion of the sediment and debris from the sinkhole was
washed out through the 30-inch pipe.

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August 4, 2022
Page 4 of 5
Aerial Survey
Landfill surface topography near the dam was surveyed on July 20, 2022 using drone aerial methods.
Figure 10 (attached) shows the July 20, 2022 topography overlain on an aerial photo of the landfill.
The sinkhole is clearly shown on Figure 10 as a series of concentric elevation contours. No other
area(s) of concentric elevation contours were identified from the aerial survey, suggesting no
apparent development of sinkhole(s) at other locations on the dam’s surface.
The July 2022 aerial survey included the landfill surface on the inward side of the dam. Comparison
of a March 2019 survey with the July 2022 survey showed that much of the landfill surface continues
to settle.
Safety Concerns
Warning tape is in place around the perimeter of the sinkhole for a lateral distance of at least 15
feet. Should enlargement or deepening of the sinkhole occur, the distance of the warning tape from
the sinkhole should be increased. Davidson River Village should continue to restrict access to the
landfill and make all authorized landfill site users aware of the sinkhole and its potential danger.

PHASE TWO INVESTIGATION OF THE SINKHOLE

Additional work is needed to develop a more complete understanding of the condition of the 30-inch
pipe and the concrete junction box, which both the 30-inch and 48-inch pipes are connected to.

For Phase Two of the investigation, it is recommended that the entire length of the 30-inch pipe be
cleaned by water-jetting in such a way as to wash any debris contained in the pipe outwards and into
the ASB. After cleaning, the 30-inch pipe will be videoed over its entire length to evaluate its condition
and any connection it may have to the sinkhole. If possible, the videoing will extend to the junction box
at the inward end of the 30-inch pipe such that the condition of the box interior can be visually
evaluated.

Phase Two will not involve any invasive work in or on the 48-inch pipe. Rather, work on the 48-inch pipe
will be predicated on the condition of the 30-inch pipe and that pipe’s ability to maintain its function
when work is performed on the 48-inch pipe. Once the Phase Two investigation has been completed, a
remedial action work plan will be prepared which will make recommendations relative to repair of the
30-inch pipe (if necessary), the fate of the 48-inch pipe, and backfilling the sinkhole.

COMMUNICATION WITH THE NC DEQ

The following communications with North Carolina Department of Environmental Quality (NC DEQ)
occurred following identification of the sinkhole.

• July 11, 2022, the Water Quality Section of the NC DEQ was informed of the sinkhole;
• July 14, 2022, NC DEQ asked to conduct a site inspection;
• Brett Laverty from the NC DEQ was on-site July 20, 2022, to observe the sinkhole investigation;
and
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August 4, 2022 
Page 5 of 5
Brett Laverty was given an update of the site and sinkhole on July 29, 2022 as per his request.
CLOSURE 
The above information was compiled for the Sludge Landfill in effort to evaluate the possible cause(s) 
for formation of a sinkhole near the crest of the dam that retains a portion of the Sludge Landfill and 
develop. Additional work is needed to develop a more complete understanding of the sinkhole and its 
effects on the dam, dikes, and existing piping. 
If there are any questions regarding the contents of this letter, please do not hesitate to contact me. 
Sincerely, 
SEVEE & MAHER ENGINEERS, INC.  
Matthew W. Muzzy, P.E. 
Principal/Sr. Geo‐Environmental Engineer 
Attachments:  Figures 
cc: Brett Laverty (NC DEQ) 
Jill Urey (Glatfelter) 
Mike Cody (DMC Remediation and Laboratory Consulting, LLC) 
Jack Garren
FIGURES
DWG:REV:LMN:CTB:
SME
SEVEE & MAHER
ENGINEERS7/27/2022
FIGURE 1
VIEW OF SINK HOLE
GLATFELTER SLUDGE LANDFILL
PISGAH FOREST, NORTH CAROLINA
SME-STDLMN20220720-UAV-SME-BASE
PHOTO TAKEN ON JULY 20, 2022
\\NSERVER\cfs\Phg\SludgeLandfill\Acad\20220720-UAV-SME-BASE.dwg, FIG 1, 7/27/2022 12:52:28 PM, jrl
DWG:REV:LMN:CTB:
SME
SEVEE & MAHER
ENGINEERS7/27/2022
FIGURE 2
VIEW OF SINK HOLE
GLATFELTER SLUDGE LANDFILL
PISGAH FOREST, NORTH CAROLINA
SME-STDLMN20220720-UAV-SME-BASE
PHOTO TAKEN ON JULY 20, 2022
\\NSERVER\cfs\Phg\SludgeLandfill\Acad\20220720-UAV-SME-BASE.dwg, FIG 2, 7/27/2022 12:52:39 PM, jrl
219521902186
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DWG:REV:LMN:CTB:
SME
SEVEE & MAHER
ENGINEERS
ENVIRONMENTAL CIVIL GEOTECHNICAL WATER COMPLIANCE
4 Blanchard Road, PO Box 85A, Cumberland, Maine 04021
Phone [phone] Fax [phone] smemaine.com
SME
SEVEE & MAHER
ENGINEERS
ENVIRONMENTAL CIVIL GEOTECHNICAL WATER COMPLIANCE
4 Blanchard Road, PO Box 85A, Cumberland, Maine 04021
Phone [phone] Fax [phone] smemaine.com
025 50 100 FEET
EX-TOPO SME-STD
FIGURE 3
EXISTING TOPOGRAPHY
GLATFELTER SLUDGE LANDFILL
PISGAH FOREST, NORTH CAROLINA
NOTES:
EXISTING AERIAL IMAGE FROM LOW ALTITUDE AERIAL PHOTOGRAMMETRIC MAPPING
PERFORMED BY SEVEE & MAHER ENGINEERS, INC. (SME) OF CUMBERLAND, MAINE,
DATED JULY 20, 2022. GROUND CONTROL ESTABLISHED USING AEROPOINTS.8/2/202220220720-UAV-SME-BASE NGRID
48" DIA INLET PIPE
30" DIA OUTLET PIPE
12" DIA DRAINAGE
PIPE FROM LANDFILL
CONCRETE STRUCTURE
SINK HOLE
PIPE LENGTH
UNKNOWN
\\NSERVER\cfs\Phg\SludgeLandfill\Acad\20220720-UAV-SME-BASE.dwg, FIG 3 LF&DAM TOPO, 8/2/2022 11:55:07 AM, jrl
DWG:REV:LMN:CTB:
SME
SEVEE & MAHER
ENGINEERS
ENVIRONMENTAL CIVIL GEOTECHNICAL WATER COMPLIANCE
4 Blanchard Road, PO Box 85A, Cumberland, Maine 04021
Phone [phone] Fax [phone] smemaine.com
SME
SEVEE & MAHER
ENGINEERS
ENVIRONMENTAL CIVIL GEOTECHNICAL WATER COMPLIANCE
4 Blanchard Road, PO Box 85A, Cumberland, Maine 04021
Phone [phone] Fax [phone] smemaine.comNASME-STD
FIGURE 4
RECORD DRAWING #R-200-E
GLATFELTER SLUDGE LANDFILL
PISGAH FOREST, NORTH CAROLINA
7/27/202220220720-UAV-SME-BASE
\\NSERVER\cfs\Phg\SludgeLandfill\Acad\20220720-UAV-SME-BASE.dwg, FIG 4, 7/27/2022 3:55:50 PM, jrl
DWG:REV:LMN:CTB:
SME
SEVEE & MAHER
ENGINEERS
ENVIRONMENTAL CIVIL GEOTECHNICAL WATER COMPLIANCE
4 Blanchard Road, PO Box 85A, Cumberland, Maine 04021
Phone [phone] Fax [phone] smemaine.com
SME
SEVEE & MAHER
ENGINEERS
ENVIRONMENTAL CIVIL GEOTECHNICAL WATER COMPLIANCE
4 Blanchard Road, PO Box 85A, Cumberland, Maine 04021
Phone [phone] Fax [phone] smemaine.comNASME-STD
FIGURE 5
RECORD DRAWING #R-216-E
GLATFELTER SLUDGE LANDFILL
PISGAH FOREST, NORTH CAROLINA
7/27/202220220720-UAV-SME-BASE
\\NSERVER\cfs\Phg\SludgeLandfill\Acad\20220720-UAV-SME-BASE.dwg, FIG 5, 7/27/2022 3:58:55 PM, jrl
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DWG:REV:LMN:CTB:
SME
SEVEE & MAHER
ENGINEERS
ENVIRONMENTAL CIVIL GEOTECHNICAL WATER COMPLIANCE
4 Blanchard Road, PO Box 85A, Cumberland, Maine 04021
Phone [phone] Fax [phone] smemaine.com
SME
SEVEE & MAHER
ENGINEERS
ENVIRONMENTAL CIVIL GEOTECHNICAL WATER COMPLIANCE
4 Blanchard Road, PO Box 85A, Cumberland, Maine 04021
Phone [phone] Fax [phone] smemaine.com8/2/202220220720-UAV-SME-BASE PLAN-PROF SME-STD
FIGURE 6
CROSS-SECTION OF
DAM AND SINK HOLE
GLATFELTER SLUDGE LANDFILL
PISGAH FOREST, NORTH CAROLINA
48" DIA INLET PIPE
30" DIA OUTLET PIPE
12" DIA DRAINAGE
PIPE FROM LANDFILL
CONCRETE STRUCTURE
010 20 40 FEET
PLAN
PROFILE
010 20 40 FEET
48" DIA INLET PIPE
30" DIA OUTLET PIPE
12" DIA DRAINAGE
PIPE FROM LANDFILL
CONCRETE STRUCTURE
DIKE NO. 2 (PRE SETTLEMENT)DIKE NO. 1 (PRE SETTLEMENT)
EXISTING GRADE (TYP)
SINK HOLE
SINK HOLE
EXPECTED COLLAPSED SOIL
PIPE LENGTH
UNKNOWN
PIPE LENGTH
UNKNOWN
NOTES:
EXISTING AERIAL IMAGE FROM LOW ALTITUDE AERIAL PHOTOGRAMMETRIC MAPPING
PERFORMED BY SEVEE & MAHER ENGINEERS, INC. (SME) OF CUMBERLAND, MAINE,
DATED JULY 20, 2022. GROUND CONTROL ESTABLISHED USING AEROPOINTS.
N
GRID\\NSERVER\cfs\Phg\SludgeLandfill\Acad\20220720-UAV-SME-BASE.dwg, FIG 6 PLAN-PROF, 8/2/2022 11:54:24 AM, jrl
DWG:REV:LMN:CTB:
SME
SEVEE & MAHER
ENGINEERS7/27/2022
FIGURE 7
INTERIOR OF 48" DIA PIPE
GLATFELTER SLUDGE LANDFILL
PISGAH FOREST, NORTH CAROLINA
SME-STDLMN20220720-UAV-SME-BASE
PHOTO TAKEN ON JULY 20, 2022
\\NSERVER\cfs\Phg\SludgeLandfill\Acad\20220720-UAV-SME-BASE.dwg, FIG 7, 7/27/2022 12:52:50 PM, jrl
DWG:REV:LMN:CTB:
SME
SEVEE & MAHER
ENGINEERS7/27/2022
FIGURE 8
INTERIOR OF 30" DIA PIPE
GLATFELTER SLUDGE LANDFILL
PISGAH FOREST, NORTH CAROLINA
SME-STDLMN20220720-UAV-SME-BASE
PHOTOS TAKEN ON JULY 20, 2022
30" DIA PIPE INTERIOR FROM PIPE INSPECTION30" DIA PIPE INTERIOR FROM END OF PIPE
\\NSERVER\cfs\Phg\SludgeLandfill\Acad\20220720-UAV-SME-BASE.dwg, FIG 8, 7/27/2022 12:52:58 PM, jrl
DWG:REV:LMN:CTB:
SME
SEVEE & MAHER
ENGINEERS7/27/2022
FIGURE 9
SOIL DELTA AT OUTLET OF 30" DIA PIPE
GLATFELTER SLUDGE LANDFILL
PISGAH FOREST, NORTH CAROLINA
SME-STDLMN20220720-UAV-SME-BASE
PHOTOS TAKEN ON JULY 20, 2022
SOIL DELTA AT OUTLET OF 30" DIA PIPEDEBRIS AT OUTLET OF 30" DIA PIPE
\\NSERVER\cfs\Phg\SludgeLandfill\Acad\20220720-UAV-SME-BASE.dwg, FIG 9, 7/27/2022 12:53:09 PM, jrl
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218621962
1
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1
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2194
2195
2194
DWG:REV:LMN:CTB:
SME
SEVEE & MAHER
ENGINEERS
ENVIRONMENTAL CIVIL GEOTECHNICAL WATER COMPLIANCE
4 Blanchard Road, PO Box 85A, Cumberland, Maine 04021
Phone [phone] Fax [phone] smemaine.com
SME
SEVEE & MAHER
ENGINEERS
ENVIRONMENTAL CIVIL GEOTECHNICAL WATER COMPLIANCE
4 Blanchard Road, PO Box 85A, Cumberland, Maine 04021
Phone [phone] Fax [phone] smemaine.com
010 20 40 FEET
3IN-DAM TOPO SME-STD
FIGURE 10
3" INTERVAL EXISTING TOPOGRAPHY
GLATFELTER SLUDGE LANDFILL
PISGAH FOREST, NORTH CAROLINA
NOTES:
EXISTING AERIAL IMAGE FROM LOW ALTITUDE AERIAL PHOTOGRAMMETRIC MAPPING
PERFORMED BY SEVEE & MAHER ENGINEERS, INC. (SME) OF CUMBERLAND, MAINE,
DATED JULY 20, 2022. GROUND CONTROL ESTABLISHED USING AEROPOINTS.7/27/202220220720-UAV-SME-BASE NGRIDSINK HOLE
\\NSERVER\cfs\Phg\SludgeLandfill\Acad\20220720-UAV-SME-BASE.dwg, FIG 10 DAM TOPO, 7/27/2022 3:59:41 PM, jrl