The Hows and Whys of Landfill Entombment
Abstract
Investigations at Robins Air Force Base in Georgia identified an existing closed hazardous landfill as the source for active seeps of contamination into a stormwater channel. The landfill, closed in the mid- 1960's, was used for general refuse disposal, laboratory chemical disposal, and fire protection training. Volatile organics, semi-volatile organics, pesticides and priority pollutant metals had high concentrations in soils and groundwater samples. Ground-penetrating radar was used to establish landfill boundaries since limited historical records were available. Soil borings confirmed underlying low permeability clay layers and high permeability sand lenses. The unknown composition of the refuse, high concentrations of pollutants, environmental hazards and costs associated with removal led to the selection of complete encapsulation (entombment) of the landfill. Design of the entombment included a perimeter soil-bentonite cutoff wall, a two component barrier with a multi-layered cap, and leachate and methane gas collection. The underlying clay layer has a low laboratory permeability, below 1x10(exp -7) cm/sec. The two component barrier consists of a bentonite mat and HDPE flexible membrane liner. This system was selected from alternative barrier designs for use as the low permeability infiltration barrier to meet RCRA requirements which state that the cap permeability must be less than or equal to the underlying soil. Long-term permeability and compatibility testing of bentonite mixtures for the cutoff wall with landfill leachate resulted in poor performance of certain bentonites. This led to selection of a sole source bentonite mixture. With entombment, leachate generation is expected to be minimal. However, leachate collection wells are provided to maintain an inward groundwater gradient within the cutoff wall and provide a way to measure excess infiltration from a cover breach or failure.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1996
- Accession Number
- ADP017710
Entities
People
- Elizabeth Williford
- William P. Gilman