Improving yields from vertical landfill wells through better design, installation and maintenance

Abstract

A review of published investigations and groundwater well installation practice has established what factors are known to affect the performance of vertical wells: the design and installation of the well, the low hydraulic conductivity of waste and the physical and microbial clogging of the filter pack and well screen.  Down-well CCTV surveys and exhumations have shown that chemical precipitations are also common, often completely coating the well screen and closing all slots, though precipitates were generally only present in the gas zone, above the leachate table, where the closure of slots will not attribute to well losses.  Smearing of ground waste and cover soils around the borehole was observed in exhumed wells drilled using a rotary barrel-auger. Over time, sediments and waste pieces may be washed into the well and will be a function of the flow velocity and the pumping regime.  Accumulations of material will reduce the effective drawdown in the well.  Field trials have demonstrated that removing the material using development techniques has an adverse effect on performance due to the invasion of soils into the filter pack.  When designing new wells for use in a landfill, a compromise may have to be made between a design that limits well losses, a design that prevents fine-grained material from being washed into the well, and one that is not prone to microbial clogging.  Rules used in the groundwater industry for selecting filter packs and well screens, may, therefore, not be suitable for landfill wells, though where sulphate reducing processes are the dominant degradation mechanism, fine-grained filters can be used.  If a well does become clogged with deposited sediments, then well development techniques should be avoided.</p