Capping the I-95 Landfill

Capping the I-95 Municipal Landfill

When a landfill reaches capacity, which it eventually does, it is usually capped to ensure that rainfall will not infiltrate the surface. The leaching of rainwater through the landfill could cause contamination of the groundwater and nearby surface waters.

Landfill Capping

VLDPE cap being placed at the I-95 Landfill: General Information

Although the EPA and the Commonwealth of Virginia did not require that the I-95 Landfill be capped with a geomembrane system, the County determined that such a system should be used on portions of the facility in order to minimize the potential for any environmental hazard.

Topsoil was placed over the very low density polyethylene (VLDPE) liner, and this vegetative layer was fertilized with composted sewage sludge. Soil excavated during the construction of the Washington Metrorail transit system provided additional topsoil and regrading material, and reduced capping costs.

Steep slopes and varying topography required that the landfill use a textured liner to prevent slippage of the overlying soil.

The natural decomposition process which occurs in landfills produces gas. The gas is primarily composed of methane and carbon dioxide.

An extensive collection utilization system has been installed at the site so that the gas can be used.

The cost for the first two phases of landfill closure (130 acres) was approximately $175,000 per acre. The closure projects at the I-95 Landfill Complex have involved many engineers from the County, as well as outside consulting firms and contractors.

Innovative Efforts for Cost Reductions

In addition to using earth from the Metro system's construction and composted sludge to fertilize the topsoil, normally unusable screenings from a nearby quarry were incorporated into the drainage system. As a result of these recycling efforts, Fairfax County was able to save $1.6 million. The cost saving efforts and the environmental concerns of the designers and engineers earned a nomination by the American Academy of Environmental Engineers for the 1994 Excellence in Engineering Award, Design Category.

A capping in process

Cap being placed at the I-95 Landfill: An Excellent Achievement

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