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Due to a lack of reliable data and research on what should be defined as Final Storage Quality, little is known about the real time needed to reach final storage quality for a landfill. In addition, even within the regulatory bodies the concept of final storage quality is poorly understood. A paper presented at the UK Waste2004 conference by O. Hjelmar and J.B. Hansen of DHI Water and Environment, gives us some guidance when it provides us with a case a study. They tell us that their results indicate that even with a relatively high leachate production rate corresponding to a very abnormally high infiltration of 33 % of the precipitation, final storage quality is hardly achieved in 30 years. Very low concentrations have been reached for some components while others remain of concern. So, this explain why so few have given thought to exactly how one might define final storage capacity in term of each contaminant in an old landfill site leachate. This leads all old landfill owners to feel that maybe they are being neglected. They don't see why a more sophisticated investigation of the time needed to reach final storage quality for landfills containing MSW residues has not yet been carried out. After all, they would like to have a much better idea for how long their old landfill will continue to be a liability. The eventual achievement of final storage quality (FSQ) at a landfill, i.e. a situation where active environmental protection measures are no longer necessary and the leachate is acceptable in the surrounding environment, is certainly embodied in the regulations. When a landfill is closed and the surface is restored these days the owner/operator/licence holder must provide a site closure plan. However, acceptance of the closure plan by the regulator does not imply anything with regard to the time post-closure when the regulator will cease to regulate the site under its environmental permit or licence. As we have already stated, the concept behind FSQ is not very well defined. In principle, it refers to the quality which will be attained by the waste in any landfill at some time in the future. The intention of the concept is to define when protective measures and maintenance are no longer necessary to ensure that the leachate produced is fully acceptable in the surrounding environment. Presumably, within the principle, at FSQ there will be no landfill gas present and the atmosphere within the landfill will be fully aerobic. It is generally assumed that the processes of decomposition which occur within all landfills (e.g. biodegradation, leaching, chemical reactions, mineral changes) and subsequent removal of dissolved components with the leachate by flushing, will eventually lead to the attainment of the

FSQ. The safest definition of FSQ would be that the waste has reached a stage which ensures that the concentration in the leachate does exceed a value, which is acceptable in the surrounding groundwater or any adjacent surface water without any dilution or attenuation. This is also a definition, which is very difficult to fulfil. Other, more realistic, definitions could be based on the flux of contaminants and incorporate a geologically stable long-term measure to reduce the rate of infiltration and/or take dilution and attenuation processes in the immediate vicinity of the landfill into account. The latter would be in line with the principles applied in the setting of the criteria for acceptance of waste at landfills in the EU (Hjelmar and Holm, 2004). When determining whether or not FSQ has been reached, it is important to know if the concentration of a component in question can be trusted not to increase significantly at any point in the future. Whereas observations such as those described in their paper may serve as useful indicators in this respect, predictions of future longer-term behaviour, especially those based on external factors, would need to be supported by sophisticated hydro-geochemical equilibrium calculations. The accuracy of the water balance calculations as an average for the period of time considered will be important. Knowing the water flux from the water balance calculations, for some of the parameters a first impression of the time to FSQ may be obtained. That is by comparing the concentration of a contaminant in the leachate to the acceptable concentration in the groundwater or surface water adjacent to the landfill, or at some point downstream of the waste mass, the number of volumes of flushing required can be roughly guaged, and from this the very approximate time scale deduced. It is an enlightened and specific goal of Danish landfilling policy that a landfill should reach FSQ within a period of 30 years. Unfortunately, few other nations have yet appreciated (or been willing to accept) the longevity of the environmental hazard of modern landfills. In effect the result is entombed waste in current sanitary landfills which will inevitably generate biogas and leachate when physical barriers fail in the future, allowing for the first time the intrusion of moisture into the waste mass. This is a contradiction of the precepts of the sustainability concept. The current regulations for diversion of organic materials away from landfills will help, but do not fully address this, although in principle they should help. Throughout the landfilling nations, with notably only one or two exceptions, and despite the obvious need for changes, and the importance of reaching FSQ in the shortest possible time, there is generally very little political will to fund and support any research in this area.

Steve Evans has written more about Final Storage Quality and Landfill. Visit his Waste, Landfill and Resource Management website.

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What is Final Storage Quality For a Landfill