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RESTORATION OF DISTRESSED SECONDARY MONITORING SYSTEM
AT A HAZARDOUS WASTE LANDFILL – REPAIR IMPLEMENTATION
James J. Parsons, P.E.
NTH Consultants, Ltd
Jenghwa Lyang, Ph.D., P.E.
NTH Consultants, Ltd
Distressed secondary riser pipes were discovered at a hazardous waste disposal facility during routine sampling. The riser pipes extended from a secondary sump, up a 10-foot high (vertical) intracell berm, turn 45 degrees through the primary clay and 80 mil geomembrane liner, and extend vertically through approximately 120 feet of hazardous waste to the surface. Video inspection of the 8-inch to 12-inch diameter riser pipes revealed that at four riser locations, the field-fabricated elbows had partially buckled. At one riser location, the vertical portion of the pipe buckled at two points.
Investigation of the distressed riser pipes led to a unique and challenging repair approach.
Wayne Disposal, Inc., a subsidiary of EQ The Environmental Quality Company, owns
and operates the Site No.2 disposal facility in Belleville, Michigan. The site comprises
approximately 400 acres and has landfilled municipal solid waste, industrial hazardous
waste, and commingled waste. Current operations include disposal of hazardous waste
and waste regulated by the Toxic Substances Control Act (TSCA). The balance of the
disposal areas is closed. The facility is currently licensed to landfill 11 million cubic
yards of hazardous/TSCA waste.
Master Cell VI is the current active disposal area. The 34-acre cell consists of five
subcells designated as A-North, A-South, B, C and D. These cells were constructed
during the late 1980’s and early 1990’s with a typical double composite liner system
that includes from the bottom up: a 60 mil secondary HDPE geomembrane liner, one to
three layers of secondary drainage net, geotextile, a 5-foot compacted clay liner, an 80
mil primary HDPE geomembrane liner, 12-inch peastone leachate storage layer,
geotextile, 12-inch granular drainage layer and a geotextile separation layer.
A network of perforated 6-inch diameter DR 7.3 HDPE pipe comprises the primary
leachate collection system.
The secondary leak detection system for subcell D includes a sump and a DR 17 HDPE
riser pipe that extends along, and is fully supported by, the sideslope of the cell to
ground surface. Each of the remaining subcells incorporates a secondary sump and a
DR 17 HDPE riser pipe (Fig.1) that extends approximately 10 vertical feet along a 2
vertical to 1 horizontal slope, then turns within the primary compacted clay layer and
extends vertically through approximately 120 feet of waste.
Figure 1. - Typical secondary sump and riser See PDF
DR 17 HDPE riser pipe (Fig.1) that extends approximately 10 vertical feet along a 2
vertical to 1 horizontal slope, then turns within the primary compacted clay layer and
extends vertically through approximately 120 feet of waste.
The vertical portion of the riser pipe is sleeved with a second pipe at a point
approximately 10-feet above the primary liner (Fig. 2). The sleeve was designed to
reduce downdrag forces imposed upon the riser pipe as waste settlement occurred.
Figure 2. - Protective outer sleeve for riser pipe See PDF
In 2002, a vertical expansion of Master Cell VI was constructed. The vertical
expansion, designated as subcell E, overfills the existing subcells and extends to the
north over the adjacent closed Master Cell V.
The operating permit for the facility requires liquid in the secondary sump to be
sampled and pumped dry on a quarterly basis. Water accumulating in the sump is
primarily consolidation water from the compacted clay liner and has historically been
free of contaminants that may indicate a leak in the primary liner system. Early in
2003, during routine sampling of the secondary sump in subcell B, the pump became
stuck during extraction. The pump was eventually retrieved, however the outer pump
shield remained inside the riser pipe. In addition, difficulty was encountered extracting
the pump from the A-North riser pipe.
Camera inspection of the riser at subcell B was initiated to locate and determine means
of retrieving the outer pump shield. A 4-inch diameter pan-and-tilt camera was
lowered into the riser pipe and revealed significant deformation of the pipe wall in the
field-fabricated elbow within the primary compacted clay liner (Fig. 3). The magnitude
of the deformations prevented camera inspection past the elbow.
Figure 3. - Distressed elbow in Subcell B riser See PDF
Because difficulty was encountered during extraction of the pump from the riser at A-North, this pipe was
also inspected using the 4-inch camera. At a depth of approximately 57 feet below the
waste surface, the vertical portion of the riser pipe was severely buckled (Fig. 4).
Again, this condition prevented camera inspection below the buckled section.
All of the risers were subsequently video inspected using a 1-inch diameter push
camera to depths of at least 120 feet. At A-North, a second buckled section was
observed approximately five feet below the first. Deformation of the elbow was also
noted. At subcells A-South, B and C, deformation within the elbows was noted but no
buckling of the vertical riser pipe was observed. The riser pipe for subcell D, which is
the only riser fully supported on the cell sideslope, was undamaged. In addition to the
four distressed secondary risers, a primary cleanout riser, critical to the leachate
collection system, was damaged.
The impact to the facility operations of potential total failure of the secondary risers
could be enormous. Without the ability to sample and test the liquids in the secondary
sump, the facility would loose the ability to demonstrate that the liner system has no leaks. Compliance and regulatory
constraints could force the facility to severely limit or cease operations.
Evaluation of the secondary leak detection riser pipes in Master Cell VI was initiated.
The evaluation included a detailed survey of the damaged risers, collection of record
photographs, survey notes, inspection reports and other data, as well as structural
analysis of the pipe to determine the cause of failure.
The survey included measurements of the depths to each deformation and comparison
to record survey data. Original construction reports, photographs and surveys were
reviewed and collated with measured data and original design calculations. In most
cases historic survey data indicated that the horizontal location of the riser pipe at the
current waste surface varied from the location of the initial dike penetration
significantly, in some cases as much as 50 horizontal feet through the entire 120 foot
depth. An observation of the inspection videotapes confirmed sweeps and angular
offsets from vertical throughout the lengths of pipes, particularly at welded joints.
Historical photographs from the project records revealed a construction sequence that
included fabrication of the HDPE riser pipe from the sloped section of the intra-cell
berm, through the elbow, and the first vertical section of pipe, before the compacted
clay layer had been constructed. This sequence made adequate backfilling and
structural support below the elbow very difficult, if not impossible. Figure 5 shows this
sequence at the tie-in between subcell A-North and subcell D.
Figure 5. – A-North riser at tie-in to sub-cell D See PDF
Figure 6 shows the loose condition of the bedding soil at the reducer and elbow
sections.
Other data evaluated included soil boring information and shallow test pits excavated
around one of the risers. The original design specified the placement of sand bedding
around the vertical portions of the outer protective sleeves, extending around the pipe
diameter for 5 feet. The sand bedding was intended to assist in limiting downdrag
forces as well as to provide a buffer against waste placement in direct contact with the
outer protective pipe. Boring information revealed that the sand bedding was not in
place throughout the entire length of the riser. In addition, test pits excavations
revealed buried drums in direct contact with the protective sleeve.
Figure 6. - Condition of bedding soil around elbow See PDF
Structural analysis of the HDPE riser pipes and outer sleeves to resist the forces imposed by lateral
and vertical pressures was completed based on ASTM F1759 – Design of HDPE
Manholes for Subsurface Applications. Historic settlement data from settlement plates
installed in late 2000 and estimates of settlement based on standard penetration test of
the waste were used in the analysis. Settlement analysis suggest that the total waste
settlement could be highly differential, varying significantly from place to place and
could be as high as 10 to 15 percent under fills of 100 feet or more.
Results of the analysis indicated that the long-term strain in the waste fill could exceed
the critical buckling strain of the outer protective sleeves and that the outer sleeves
were likely to buckle from waste down drag forces alone at depths of about 50 feet or
greater. Load transfer to the inner pipe can occur because the outer sleeve deforms
downward from down drag forces and come in contact with the inner pipe at points of
angular offset from vertical.
Axial buckling of the inner riser pipe was evaluated for the condition where down drag
forces are transferred to the inner pipe installed at an angular offset of 30 degrees from
vertical. This condition imposed both an axial load component and a bending load
component on the inner pipe. The axial load component was evaluated using ASTM
F1759 and the bending component was analyzed using a solution for a beam on an
elastic foundation (Hetenyi, 1946). The results showed that the inner riser pipes could
fail in axial buckling if down drag forces were transferred to them.
In general, the results of the evaluation concluded that possible poor backfilling below
the elbow, lack of sand bedding around the pipe and angular offsets from vertical likely
contributed to transfer of down drag forces to the inner pipe causing buckling failure.
Other installation defects, such as equipment impact damage or poor waste placement
techniques, may have caused or contributed to the observed distress in the pipe.
How do you repair a distressed pipe that terminates in a sump over 120 feet below the
surface of a hazardous waste landfill? To answer this, numerous methods were
thoroughly evaluated, including:
- Open excavation;
- Sliplining with a smaller pipe and use of micro pumps;
- Pipe bursting technologies;
- Braced excavations;
- Micro-tunneling;
- Directional drilling;
- Conventional tunneling below the landfill
- Internal re-rounding of the pipe followed by structural polymer reinforcing; and
- Drilled access shafts to the sump with complete riser replacement.
The evaluation of the repair methods considered several design challenges. Regulatory
oversight by the Michigan Department of Environmental Quality (MDEQ) and the US
Environmental Protection Agency (EPA) would require regulatory approval.
Environmental impacts also needed to be considered. Any repair undertaken must be
environmentally protective and could not impact the environmentally sensitive
secondary leak detection system. Any contamination of the secondary leak detection
system could potentially be construed as a leak in the landfill liner system.
The most straightforward solution, and potentially the least costly, was open excavation
to the distressed elbows and a direct repair of the riser pipes. This method was not
considered desirable because it would require relocation of over 500,000 cubic yards of
hazardous waste. Not only was there insufficient permitted area to relocate the waste
to, but also would potentially expose the environment to airborne contaminants and
undesirable odors. Further, this method would nearly completely disrupt regular site
operations.
Cost and risk analysis was completed for most of the options. Three options were
considered viable; insertion of a smaller diameter “slipline” pipe with reinforcement of
the damaged sections, internal re-rounding with structural reinforcement, and drilling of
access shafts for a direct replacement of the damaged sections.
Preliminary evaluation of the slipline option determined that the configuration of the
damaged elbow sections combined with length, diameter and capacity of available
pumps, prevented this option. Further, the damaged vertical section of the riser at
subcell A-North eventually closed completely, preventing even a 1-inch diameter
camera to pass. Internal rerounding technology had never been attempted in this
application and would require redesign of conventional rerounding equipment and
modifications to normal procedures. Drilled access shafts would allow complete
replacement of the damaged risers, but required breaching the primary synthetic and
clay liners. The owner elected to proceed with development of the rerounding option to
occur concurrently with the design of drilled access shafts.
Internal pipe re-rounding is a technology typically applied to horizontal PVC pipe with
two-way access. That is, the equipment is inserted into a manhole and is pulled through
a length of pipe from a second manhole. To apply this technology to rerounding of the
HDPE riser pipes in a vertical orientation with only one-way access limited use of this
technology. A contractor was located who had successfully applied rerounding
techniques to vertically oriented HDPE pipes.
After several months of research, bench scale trials and equipment modifications, field
trials were begun in early 2004 (Fig.7). Field trials successfully rerounded one of the
upper deformations of the riser pipe at sub-cell A-North, but failed to make the turn
through the deformed elbow section. After numerous unsuccessful attempts at
rerounding, the technology was ultimately abandoned. The shaft accessed repair method became the focus of the repair design effort.
Figure 7. - Field trials of rerounder See PDF
A shaft-accessed repair involved numerous design challenges. The concept would
requires:
- Drilling through over 120 feet of hazardous waste;
- Accurately excavating to the end of the secondary riser pipes that terminate within a 3-foot by 5-foot sump;
- Put personnel in the shaft to hand excavate through the last 5-feet of hazardous waste;
- Breach the primary 80 mil HDPE geomembrane liner;
- Hand excavate through 5-feet of compacted clay liner;
- Complete the above work at the lowest point in the cell;
- Control leachate and secondary consolidation water;
- Prevent contamination of the secondary leak detection system.
Additional challenges with logistics also needed to be addressed. Regulatory approval
was needed to cut a 7-foot diameter hole in the primary containment liner near the low
points of the subcells. Drilling a shaft would also require a crane with over 120 feet of
boom to be in place on top of the landfill. Because of the proximity to an adjacent
major airport, the crane would infringe on FAA and airport management airspace,
thereby requiring FAA approvals. And finally, we needed to identify an appropriate contractor to implement the work.
After several meetings with the Environmental Protection Agency, the Michigan
Department of Environmental Quality and airport management staff, the draft work
plan and conceptual design was approved. With regulatory approval in place, the
project team moved forward with addressing the remaining challenges.
Due to the construction complexities and specialty sub-contractor needs of the
conceptual repairs, the contractor was solicited early in the final design phase of the
project. This allowed the contractor and major subcontractors to
provide input as the final design was developed. Working as a single team, the Owner,
designer and contractor provided valuable input in preparation of the final design. Of
primary concern to all parties was the safe execution of work. To this end, the
contractor developed a comprehensive Health and Safety Plan to guide each step of the
work.
Figure 8. – Design of shaft access to secondary sump See PDF
The final repair design was packaged in such a way that a drawing, detailed
construction sequence, Quality Assurance requirements, and Health and Safety
requirements for each of the anticipated 17 major tasks was presented on it’s own sheet
relating specifically to that task. This system would allow the team to have easy reference to all pertinent information based upon the current task in progress.
Construction of the first access shaft was begun for repair of the primary cleanout riser
in March of 2006 (Fig 9). This location did not require a breach of the primary liner
and would serve as a “dry run” for subsequent shafts.
Figure 9. – Shaft excavation at Cleanout D-14 See PDF
The shaft was successfully extended through 120 feet of waste and intercepted the
leachate collection pipe on the primary geomenbrane liner, where a new cleanout riser
was installed to the top of the waste (Fig. 10).
Figure 10. – Leachate collection pipe within shaft at D-14 See PDF
During the shaft design process and even through the start of construction, the design
team, including the contractor, had continued to explore options that would avoid the
need for penetration of the primary synthetic and clay liners with a shaft. The team had
worked extensively with several pump manufacturers to develop or modify a pump that
could fit within a small diameter “slipline” pipe and was short enough to extend past
the deformed elbows and capable of lifting liquid over 130 feet (air lift pumps could
not be used since sampling of the liquid for volatiles was required). As the shaft at
cleanout D-14 was being excavated, the perseverance paid off; a pump manufacturer
was able modify a newly developed pump that met the needs of the project.
A piston driven pump with an outside diameter of 1½-inches, flexible enough to pass
through the deformed elbows and capable of lifting the secondary liquid over 130 feet
made the “slipline” a viable option again for the secondary risers at sub-cells A-South,
B and C. “Sliplining” the distressed secondary risers would avoid the need for
breaching the primary liner. With an expedited regulatory approval, the team went
forward with an appropriate design. The collapse of the vertical portion of the riser at
sub-cell A-North initially was thought to require the use of a shaft accessed repair.
The “slipline” repair methodology included installing 1-inch to 4-inch diameter pipe
(the lower 5-feet perforated) inside of the existing 8-inch to 12-inch secondary riser
pipes. The annual space was then filled with filter sand to an elevation approximately 5
feet below the damaged elbow sections. A thin “choke” layer of fine sand was placed
on the filter sand. High strength, low shrinkage grout was then placed as internal
reinforcement through the elbow and to a point approximately 10-feet above the elbow.
Because of the limited annular space and the need to assure complete filling of the pipe,
as much as 17 cubic feet of filter and choke sand were added one cup at a time through
a tremie pipe, washed into place by adding water (Fig. 11).
Figure 11. –Filter sand placement in Riser B See PDF
Water added during the filters and placement operation was pumped out from the bottom to assist settlement of the
sand through the elbow and into the storage pipes within the sump.
With cleanout ability restored at cleanout D-14 and pumping capability restored from
secondary risers at sub-cells A-South, B and C, attention was turned to the last
remaining secondary riser at sub-cell A-North. At A-North a complete collapse of the
vertical riser pipe at a depth of 57 feet below waste surface prevented insertion of a
“slipline” pipe. The collapse had also prevented inspection of the deformed lower
elbows for over one year, so the condition below the total collapse was unknown.
The decision was made to combine the two successful repair approaches previously
used. Install an access shaft to the 57-foot depth, remove the damaged section of pipe,
extend the remaining pipe back to waste surface, then install a “slipline” pipe and the
piston pump. The first challenge was accurately targeting the shaft location. An
inclinometer was used to determine the exact horizontal and vertical location of the
collapsed section of pipe. Because the pipe was known to be at roughly a 30 degree
angle from vertical, a 9-foot diameter access shaft was selected to provide working
room to complete the repair, including butt-fusion welding of a new DR 17 riser pipe to
the existing riser, and sweep the new section of pipe back to vertical (Fig. 12).
Figure 12 –Access shaft plan at sub-cell A-North See PDF
The 9-foot diameter shaft was extended to the collapsed section of the existing riser (Fig. 13), the damaged pipe was removed,
and the new vertical riser pipe was installed to waste surface.
Figure 13 –Hand excavation around sub-cell A-North collapsed riser pipe See PDF
Once access was restored, video inspection of the lower elbow was completed and
revealed that additional deformation of the elbow section had occurred. In fact,
difficulty was encountered extending the 1-inch diameter push camera through the
elbow. Insertion of several pipes, ranging in diameter from 3-inch down to 1-inch, was
attempted. Only the 1-inch diameter pipe could be inserted full depth into the
secondary sump. Since the piston pump casing was 1½-inch diameter without a
“slipline” pipe, a further redesign of the pumping system was needed.
The pump manufacturer fitted the pump foot valve with a ½-inch diameter suction tube
and tested the modified pumping system. Trials showed that the liquid could be lifted
through the suction tube the expected 26 vertical feet to the pump foot valve where it
was ultimately pumped to the waste surface.
To “slipline” the secondary riser at A-North, a 3-inch diameter DR11 pipe was used.
The lower 50 feet was reduced to a 1-inch diameter DR11 pipe with the lower 5-feet
perforated section. This allowed the 3-inch diameter pipe to be supported above the
deformed elbow and the 1-inch diameter pipe to extend full depth into the sump. The
1½-inch diameter piston pump with 49 feet of suction tube was then threaded into the
“slipline” assembly. As with the other slipline repairs, the annular space between the
existing 8-inch diameter secondary pipe and the 1-inch diameter “slipline” pipe was
filled with filter sand. The deformed elbow was then reinforced with high strength
grout. The assemblies as constructed are shown in Figure 14. Upon completion,
pumping capability was restored at the secondary sump at a rate of approximately one
gallon per minute. This rate is sufficient to pump the secondary sump dry in a single
shift and restored sampling capability at sub-cell A-North.
Figure 14 – “Slipline” at sub-cell A-North secondary riser pipe See PDF
Failure of riser pipes extending vertically from secondary leak detection sumps could
be disastrous to a landfill owner/operator. This paper has presented a case study of a
project that restored pumping and sampling capability to a hazardous waste landfill
with four distressed secondary risers and one distressed leachate collection system
cleanout riser under over 120 feet of hazardous waste. The authors have presented a
condensed progression of events that lead to a comprehensive repair design that
included excavation through the primary geomembrane and primary clay liners of a
hazardous waste landfill.
Diligence on the part of the owner to continue to explore and develop all available
options, even as construction began, lead to a non-intrusive repair solution that was
preferable to all parties, including the regulatory agencies involved.
The authors would like to thank the management of Wayne Disposal, Inc. for allowing this case study to be shared. Particular thanks go to Mr. Kerry Durnen, P.E. Director of
Operations for Wayne Disposal, Inc. Site No. 2. His attention to detail, willingness to
support “out of the box” approaches, and genuine desire to do the right thing blurred
the line between client and consultant.
Parsons, J., Lyang, J., and Durnen, K (2006) “Restoration Of Distressed Secondary
Monitoring System At A Hazardous Waste Landfill” Proceedings of the ASCE 4th
Forensics Conference, Cleveland, OH
Simpson Gumpertz & Heger Inc. (2004) Report “Investigation of Distress in Secondary
Riser Pipes, Master Cell VI, Wayne Disposal, Inc., Landfill No. 2, Belleville,
Michigan”. Prepared for NTH Consultants, Ltd.
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