Design and construction of the barrier system for the Halton Landfill

Abstract

Considerations related to the design of the Halton Landfill as a "hydraulic trap" are summarized together with the research that was conducted to support the design concept. The interrelationship between hydrogeology and the engineered design is examined. Laboratory experiments demonstrated that there can be diffusion away from a source, even with significant inward velocity. Existing theory was found to provide a good prediction of the observed concentration profile in these experiments. It is also shown that a pressurized air pocket below the clay effectively acts as a zero-flux boundary and hence, with respect to migration of chloride, could be conservatively neglected in the impact assessment. The results of the impact calculations predict only a small increase in chloride concentration in the receptor aquifer while there is negligible predicted impact due to organic contaminants. The landfill was designed and constructed with a granular "sub-liner contingency layer" (SLCL) beneath the compacted liner. The operation of this layer is discussed. Finally, the construction of the compacted clayey liner with a hydraulic conductivity of 1 × 10-8 cm/s is documented.Key words: landfill, hydraulic containment, liner, field case, construction.

Effect of filter–separators on the clogging of leachate collection systems

“…Unlike in the sand layer of the graded granular F/S design and the nonwoven GTF/S, there would need to be a very substantial buildup of clog material in the large voids of the sacrificial gravel layer above the geotextile before there was a sufficient reduction in the hydraulic conductivity to impact on the lateral flow capacity to leachate collection pipes. A design configuration that would allow leachate to enter a manhole from both above and below the geotextile layer has been described in Rowe et al (2000c).…”

“…The nonwoven geotextile reduces clogging in both configurations considered (i.e., between the waste and gravel and within the gravel layer), but its location within the gravel layer resulted in the greatest treatment of the leachate as it percolated through the system (as evident by the biofilm that accumulated above the geotextile) and the least clogging of the underlying saturated gravel layers. These results suggest that if used in this type of configuration, there should be more unsaturated gravel between the saturated zone and the geotextile to minimize interaction and maximize the thickness of gravel available for leachate flow; an example of such a design, adopted in the Halton Landfill, has been described by Rowe et al (2000c). At the time of writing, the Halton design has been working very effectively in the field for 11 years.…”

Containment Criterion for Contaminant Isolation by Cutoff Walls

“…The concentration at the inside and outside faces of the wall was fixed a priori in the analytic solution. It is possible to fix both the Darcy flux and the contaminant concentration at the outside face of the wall under controlled laboratory conditions (see, for example, Rowe et al 2000). Similar conditions have been invoked in the back‐analysis of solute profiles that have evolved over geologic time scales (for example, Desaulniers et al 1986).…”

The performance of a laboratory facility for evaluating the structural response of small-diameter buried pipes

“…Here, the pipe was placed within a 600 mm deep layer of uniform coarse gravel to simulate the drainage layer. Crushed (40-50 mm) dolomitic limestone, similar to that used at a number of Ontario (Canada) landfills (e.g., Rowe et al 1993Rowe et al , 2000, was used as the backfill material. This material is a poorly graded coarse gravel (GP) and consists of large angular particles with 70% finer than the 51 mm sieve size and only 8% finer than 38 mm.…”

“…This silty clay till of low plasticity (liquid limit of 24% and plastic limit of 14%) was placed at a water content near the plastic limit (corresponding to 2-4% wet of optimum, which is standard practice for placing a compacted clay liner; e.g., see Rowe et al 1995) and an average bulk density of 2100 kg/m 3 . This till was from the Halton landfill site and its use as a liner has been described by Rowe et al (1993Rowe et al ( , 2000.…”