Professional Engineer George Gilbert provides an inside glimpse of a rare occurrence in Kentucky – an 8-acre landfill slide – and how the potential disaster was effectively mitigated and managed.
At around 10 a.m. on Sept. 4, 2013 the owner of the Big Run Municipal Solid Waste Landfill near Ashland, KY., reported a solid waste slide. About 800,000 tons of municipal solid waste slid from its disposal location to an area extending some 400 feet off the landfill plastic liner and clay. The total slide was about 20 feet deep and consisted of about 8 acres. The amount of waste represented about one year’s worth of disposal effort.
Here’s how things looked immediately after the slide (see below).
Note the large wall of garbage (left). Compare this to the size of the person at the toe of the slide area (look for the small figure in the yellow vest, center right). In this photo taken by Rodney Maze, facility personnel were constructing a leachate (waste juice) collection system after the slide.
Landfill Manager Mike Vossmer and staff noticed a bulging in the lower waste mass before it happened. “I pulled everyone off the lower waste footprint and pond areas just in case,” said Vossmer.
The remediation efforts avoided further environmental damage through cooperation between the landfill owner, the owner’s consulting engineers, the Environmental Response Team (ERT), and the Division of Waste Management (DWM). ERT and DWM are part of the Kentucky Department for Environmental Protection. As a result of this collaborative teamwork, things were on track for a safe cleanup and restoration of the landfill monitoring systems.
The DWM’s Morehead Regional Office received the call and Karen Hall, waste supervisor, and Rodney Maze, an environmental inspector and ERT member, responded (ERT consists mainly of inspectors, who volunteer to respond to environmental and natural disasters on and off-hours duty). Their main concern was the affect of the mass movement on environmental monitoring systems, fire potential and the impact on residences. The waste covered nine downhill groundwater monitoring wells and one underdrain system along the northeast portion of the slide area. ERT personnel issued an “emergency directive” at 7 p.m. that first evening to abate the release and restore the environment, specifically to:
- Monitor the slide for further movement;
- Construct a containment structure;
- Daily sample and analyze the sediment pond water discharge; and
- Prevent off-site odors.
“After quickly finding out that no one was hurt, my immediate concern was directing the facility to monitor the slide for movement; containment of leachate and surface water; and preparing for fire potential from the exposed waste by requiring an access for fire fighting equipment,” said Maze.
ERT brought their mobile command post to the site to better manage the emergency phase of the incident.
On Sept. 6, Solid Waste Branch Manger Ron Gruzesky arrived and met with ERT, the landfill owner, and the three engineering companies hired by the landfill: Kenvirons, Cornerstone, and Civil and Engineering Consultants. At that and subsequent meetings, a plan to move forward was established:
First: Cover the exposed waste in the slide to cut down on odors and mitigate fire potential. Two of the engineering companies had previous experience with another waste slide in other states, and noted that fire could break out with the waste exposed to the air. It would take too long to excavate pathways and place soil over the wastes, so it was decided to spray a temporary liquid cover onto the waste that quickly cured into a solid. Soon after, the operator’s contractor began replacing cover soil. The owner also coordinated with the local fire department to plan contingency responses.
Second: Complete construction of the temporary containment berm to catch any surface water run-off or leachate emerging from under the wastes. Pump the trapped water into the leachate tanks.
Third: Reinstall the downgradient monitoring well “nest” to be sampled within 30 days. Continue surface water discharge monitoring by the pond below the landfill. Set up air monitoring stations.
Fourth: Evaluate the liner, leachate collection system and gas collection network for any damage that must be repaired.
Finally: Submit a forensic or after-the-fact report on what caused the garbage slide and a design on measures to prevent a reoccurrence.
Surveying several points on the waste mass determined that the slide had stopped moving. Work then began in earnest on mitigating the slide and establishing environmental monitoring points. The landfill owner conducted daily meetings with ERT, the construction contractor Ryan, and its engineering consultants. The Solid Waste Branch, including Gruzesky, attended meetings as needed.
ERT declared the emergency response over on Sept. 27, 2013. Big Run Landfill submitted a check for the cost of the response, which was $30,864.
Once the emergency phase of the incident ended, members of the Morehead Regional Office and Solid Waste Branch maintained contact with the landfill owner to continue remediation.
On March 20, 2014, the landfill owner submitted the “Landfill Forensic Investigation and Remedial Design” by Civil and Environmental Consultants Inc.
The report concluded that:
- “Soft spots” of wet material and excess pore pressure, or when a particle of municipal solid waste feels like it is underwater, contributed to the failure;
- The soft spots occurred along the soil cover placed between Cell 1 (former waste disposal area) and Cell 7 (later disposal area) when the soil did not allow the water to drain;
- Periods of high rainfall during several months contributed to soft spots;
Differences in municipal solid waste types led to differences in water absorption contributing to the soft spots; and
- Most of the landfill bottom liner was undamaged, except for about 0.25 acres in the corner of the newer disposal cell.
In other words, the water had no place to go down, so it went sideways and took the garbage along.
The cabinet agrees with the major conclusions of the report. Acceptance of wet industrial sludge in a short period probably contributed to the differences in waste properties allowing the soft spots.
The report also recommended constructing a soil or stone berm to provide slope stability. The berm will start at the bottom of the landfill, be 35 feet high at its deepest point and cover over four acres on top of the landfill cap. The soil or rock weighs around 140 pounds per cubic foot, compared to wet garbage at about 72 pounds per cubic foot. The much heavier berm will hold the waste in place.
The landfill owner repaired the 0.25-acre liner damaged by the slide (right) and submitted the repair report on April 1.
The owner has moved the waste back into the disposal cell, allowing the rock berm project to be started and provide slope stability. The owner sampled and analyzed air, surface water and groundwater monitoring during waste relocation.
There have been no detected impacts to the environment from the slide.
The author of this story, George Gilbert, is a professional engineer and works for the Kentucky Division of Waste Management. He can be reached at 502-564-6716 or George.Gilbert@ky.gov.