‘Virtual Curtain Wall’ provides protection from landfill gas
Innovative technology and techniques were recently utilised by Vertase, a UK specialist in the remediation of contaminated land, in order to tackle the potential risk of methane gas in the ground. The work was carried out at its latest residential project for joint clients George Wimpey and Persimmon Homes at Chequersfield in Welwyn Garden City.
In order to provide additional protection to the residential development site from the risk of methane gas emanating from a nearby landfill, Vertase considered conventional barrier methods before selecting an innovative “Virtual Curtain Wall” protection system. The curtain took only four weeks to install and cost £175,000.
Materials, including ash, bottles, metal, paper, shoes and brick as well as elevated concentrations of hydrocarbons and metals, were present at the landfill. Hydrocarbon contamination within soil and groundwater can present a potential source of methane, due to the breakdown of hydrocarbon chains creating lighter molecules that escape as vapours.
The “Virtual Curtain Wall” protection system comprises vent nodes that are driven into the ground using a method that minimises the amount of excavation required, making time saving efficiencies for the house builder. The vent nodes are connected to a geo-cellular collector duct system, wrapped in a membrane, with a vent stack and bollard featuring an inlet/outlet arrangement at calculated centres. The system utilises the forced dilution principle to create a zone of low pressure that attracts and dilutes ground gases to acceptable levels. This avoids the risk of ground gas or groundwater accumulation against membrane or bentonite barriers that is normally associated with the more traditional systems.
This type of gas cut off curtain has several site-specific advantages. The key factor is that installation minimises the possibility of potentially contaminated gas arising during construction.
In addition, groundwater control is not necessary and, because the vertical nodes are spaced intermittently along the length of the curtain, there is minimal impact on the local hydrogeology, and the effect is actually negligible in the long-term.
The curtain is vented through purpose-made stainless steel vents allowing fresh air in and the landfill gas to migrate to the surface.
Vertase has been instrumental in the evaluation, monitoring and assessment of the landfill gas from the start of the project, during construction, and through a long-term maintenance contract to evaluate the performance of this system.