Prince William Landfill Keeps Moving Forward

Prince William Landfill is right off Dumfries Road in Manassas, VA and has operated at this location since 1972 when it was merely the county dump. Today the landfill encompasses 1,000 acres, receives a little under 1,000 tons/day of household trash, and has extensive environmental controls.

The oldest section of the landfill contains 57 acres that were closed in 1991 when the state law that regulates landfills (HB 1205) went into effect. That area has undergone retrofit with liners and leachate and landfill gas collection systems to protect the environment in an ongoing effort to manage the problems we created in the past. The newer section of the landfill was designed to comply with modern environmental regulations and sustainable practices.

Today Prince William County Landfill is engineered and built as a series of cells. The cells include liners of plastic membranes and watertight geo-synthetic clay liner fabric on the bottom of the cells along with a leachate collection system. At the end of each day, earth covers the trash deposited in the cell, to keep animals away, improve aesthetics- cut down on the smell. When a cell is full it is capped to prevent (or at least limit) the rain that percolates through the landfill and covered in soil.

In 2025 Cell 3B was opened and Phase II capping took place. The area capped was filled, compacted and covered with a lining and soil suitable for grass to grow and stabilize the slope. Phase I was capped about 10 years earlier. Prince William Landfill has operated for half a century.  Landfill gas is generated during the natural process of bacterial decomposition of organic material contained in the trash buried in the landfill. Landfill gas is approximately forty to sixty percent methane, with the remainder being mostly carbon dioxide. Landfill gas also contains varying amounts of nitrogen, oxygen, water vapor, sulfur, and other contaminants. The gases produced within the landfill are either collected and flared off or used. The landfill gas cannot be allowed to build up in the landfill because of the explosive potential. 

Landfill gas is a renewable energy source. Landfill gas that is used to produce energy does not have to be flared and wasted. In 1998 the County formed a partnership with NEO Prince William to install a landfill gas collection system and a 1.9 MW energy recover facility which was a two-engine turbine that burned the gas to make electricity that was sold to NOVEC, the local electric cooperative. The 1.9 MW energy recovery system was utilizing less than 25% of the currently available landfill gas for energy recovery. Any excess gas was being flared.

OPAL Fuels, previously known as FORTISTAR who acquired NEO, continued to collect the landfill gas (LFG) and generate electricity using onsite engines, expanding the system over the years. The initial two 16-cylinder CAD engines were added to in 2013. A new building was built to house three additional larger 20-cylinder engines. The five engines consumed approximately half of the gas produced by the Landfill by turning turbines to produce 6.7 megawatts (MW) of electricity. To handle the other half of the gas produced, the Landfill has been using flares to destroy the methane for several years.

In September 2021, the board of county supervisors voted unanimously to allow OPAL Fuels to retire its generators and design and install a renewable natural gas production facility at the landfill. OPAL Fuels would provide capital and operate the facility,  but share the profits with Prince William County. In addition, air emissions would be reduced. The new RNG facility eliminates combustion of LFG in the flares and the engine facility, instead converting the LFG to consumer-grade RNG with a 95% conversion efficiency. Also, it was anticipated that revenue to the country would increase.

from PW Landfill

At full output, the RNG facility will produce approximately 12.4 million gas gallon equivalents (GGE) of RNG per year which will be used as vehicle fuel or to provide energy to homes and businesses. The end use of the RNG off-site will create additional environmental benefits by replacing fossil fuels. The profit share for the Electricity Generation Plant was about $250,000 annually. The profit share for the RNG Plant will be a minimum of $400,000 annually and can be upwards of $1 million, depending on the price of natural gas and the volume of gas sold. Natural gas prices are volatile.

The transition at the landfill from electricity generation to renewable natural gas (RNG) production was finished in early 2024, marking a shift from on-site power turbines to a high-efficiency processing facility. This change is a key part of the county's Eco-Park vision, which aims to convert the landfill into a hub for multiple renewable energy sources, including solar.

The 10MW electrical transmission lines and interconnects to NOVEC previously used by the 6.7 MW gas plant simplifies the process for solar integration. This existing infrastructure can now be used to feed solar-generated power back into the grid NOVEC. The county's long-term plan for the Eco-Park includes installing solar panels on sections of the landfill that have reached capacity and been capped. By shifting gas processing to a smaller, more efficient footprint, more surface area becomes available for solar arrays.