Operations: The Oaks
6001 Olney-Laytonsville Road
(near Fieldcrest Road and Maryland Route 108)
Laytonsville, Maryland 20882
Oaks Landfill Operating History
The site is nearly 545 acres, with a waste disposal footprint of approximately 170 acres. The Oaks Landfill received mixed municipal solid waste from June 1982 until the County’s waste-to-energy facility, referred to as the Resource Recovery Facility, began operations in the spring of 1995. Once RRF operations began, the landfill received only ash residue and nonprocessible (non-burnable) materials until 1997.
As new cells were constructed, the landfill underwent several design changes to keep pace with changing environmental regulations. The first waste disposal area had a prepared soil floor and a leachate collection system consisting of perforated pipes in a herringbone configuration that collected a portion of the leachate.
The landfill was initially designed as an attenuation landfill. An attenuation landfill uses the natural filtering and bacterial cleansing characteristics of soils at the site to reduce the effects of landfill leachate.
Later, lined cells were built over the original landfill. The final cell was constructed with two feet of compacted clay in contact with an 80 mil High Density Polyethylene geomembrane liner, complete leachate collection drainage layer and a perimeter collection system (detail of modern
cell base liner design). It was designed to collect all leachate from the disposal cell. Intermediate cells included progressive advancements in the use of compacted clay and liner materials.
By the time it closed in 1997, the landfill had received approximately 7.0 million tons of waste. We completed the final capping construction for closure of the Oaks Landfill in early 2001. This work included the installation of a geosynthetic cap, stormwater riprap downchutes, leachate collection improvements, and a landfill gas collection system consisting of horizontal and vertical piping among other environmental control measures in accordance with Environmental Protection Agency (EPA) Subtitle D requirements of the Resource Conservation and Recovery Act (RCRA).
Other existing site infrastructure includes:
- internal access roads
- stormwater management/sediment control ponds
- groundwater/gas monitoring wells
- leachate manhole structures
- a leachate pretreatment plant and storage lagoons
- a maintenance building with office and warehouse space
- a landfill gas candlestick flare and blower building with a diesel powered backup engine.
Landfill Closure Construction
Final closure construction was completed in January 2001. Closure construction involved the placement of a multi-layered final cover over the waste.
This cover includes
- two feet of soil over existing waste
- a 40 mil synthetic geomembrane
- a geocomposite drainage layer which sits on the geomembrane
- two feet of final soil cover over the geocomposite
- the establishment of grass and vegetation on the surface (landfill cap
40 acres of the landfill were capped using a similar design with slightly different materials while the landfill was still operating.
Landfill Environmental Monitoring
Federal regulations require post-closure care and maintenance of the landfill for at least 30 years after closure. We will continue to collect and manage leachate and landfill gas and monitor ground water and surface water quality during the post-closure period. Low level ground water contamination was discovered in the northwest region of the site in 1990 while the landfill was operating. We addressed this problem by extending the public water system to serve the residents around the landfill.
The County's Department of Environmental Protection semi-annually monitors the ground water and surface water around the perimeter of the site and also checks perimeter wells for the presence of landfill gas.
Landfill Gas Management System
Historically, landfill gas was flared in an open flare. Landfill gas is generated at a rate of approximately 1,800 cubic feet per minute, or 2 million cubic feet per day. An initial attempt to develop a gas-to-electricity facility at the site was unsuccessful, although a leachate evaporation system was developed and operated with partial success. The former leachate evaporation system and equipment was decommissioned in June 2008.
Currently, the Oaks Landfill generates approximately 1,000 standard cubic feet per minute (scfm) of landfill gas, which is combusted at the existing landfill gas candlestick flare. The landfill gas consists of relatively equal percentages of methane and carbon dioxide that is generated naturally from anaerobic waste decomposition. Landfill gas is collected through a network of pipes in the landfill that are connected to a blower system that draws the gas from the fill area.
New Gas to Energy Facility (Future per MDE & County Permitting)
The new Landfill Gas to Energy (LFGE) Facility will take the landfill gas (35-40% methane) that previously went to a candlestick flare and beneficially use the methane content in a two-engine/electrical generator system (containerized Caterpillar 3520 and Jenbacher JGS 316 engines) to generate electricity. The LFGE Facility will be located adjacent to the existing Maintenance Building at the Oaks Landfill. It will be surrounded with a chain link fence with locking gates.
The new LFGE Facility will also incorporate a remote computer based system to detect if the facility shuts down and will have personnel that are on-call 24 hours a day, 7 days a week for system maintenance and repair.
The existing landfill gas candlestick flare will not be operational while the new LFGE is running; however, the flare will operate on an as needed basis to mitigate the potential for landfill gas migration if required.
Leachate Management System
The Oaks Landfill generates leachate, water that has come in contact with waste. Leachate originates from either moisture in the waste or rainwater that seeps through the soil cover and percolates through the waste before an area is permanently capped with a geomembrane (a thick synthetic plastic liner).
The Oaks Landfill manages and collects leachate through a system of pipes and drainage layers within the landfill. The collection system uses a series of pipes that flow via gravity and a pump force main on the facility's perimeter to convey the leachate to the primary pumping station. The leachate is then pumped into a single double-lined storage lagoon for holding.
Finally, the leachate is treated at the on-site Pretreatment Plant, pumped into another single double-lined storage lagoon, and truck-hauled to an approved Washington Suburban Sanitary Commission (WSSC) site for discharge into the sewer system at the Shady Grove Processing Facility and Transfer Station.