Leachate movement from unlined landfills in fractured rock

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Sheppard, D.S.; Zhan, X.; Rait, G.; Chague-Goff, C. 1999 Leachate movement from unlined landfills in fractured rock. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences science report 99/07 72 p.

Abstract: The potential for landfill leachates to flow through fractured basement rock below unlined landfills needs to be assessed for monitoring and design purposes. In this demonstration study, the geological structures with the potential to carry the water were mapped in two landfills and the leachate flow rates and directions were modelled using the computer routines FRAC3DV. A sampling and chemical analytical programme was conducted in order to be able to differentiate the composition of waters affected by landfill leachates from those derived from Wellington greywacke. A result was that leachate is anticipated to flow through the fractures in the basement rock at quite high rates (>5m/day), and that the leachate must be expected to appear in groundwaters and surface waters both downstream and in adjacent valleys, within the design lives of the landfills. The result will allow the better siting of monitoring wells, and could be used to improve the design of landfills and groundwater monitoring systems in such terranes. Chemical analysis for the major components in the waters showed that two measures, alkalinity and bromide, are characteristically elevated in waters affected by landfill leachate. (auth)