Quantifying macroscopic flow and transport in the unsaturated zone to address the long-term contaminant burden of waste repositories.

在英国，管理固体废物的通常方式是填埋。我们有20,000多个地点，包含60亿吨废物，现在已经满了。垃圾填埋场可能会造成严重的环境问题，特别是当水(来自雨水或溪流)进入垃圾并与垃圾混合形成一种称为渗滤液的液体时。如果渗滤液泄漏到环境中，可能会污染地下水和地表水，破坏生态系统，污染饮用水。现代垃圾填埋场是围堵系统，有时被称为“干坟墓”。塑料薄膜排列在底部和侧面，以控制渗滤液的渗出量。盖子可以减少进入的降雨量，从而减少渗滤液的形成。最终形成的渗滤液被保留在基地，在那里可以收集和处理。在一个地点停止填埋后，它被覆盖并进入被称为“善后护理”的管理阶段。在善后护理期间，只要渗滤液存在污染危险，就需要收集和处理。不幸的是，现代垃圾填埋场的后续保养期是以世纪为单位的。工程设计的围堵系统必须在这段时间内一直保持工作，同时还要有主动的环境控制系统，用于气体和渗滤液的提取或处理。延长善后保养期会给运营商、监管机构和社会带来问题，在可持续性方面是不可接受的。荷兰有一个独特的项目，旨在迅速改善三个示范垃圾填埋场的渗滤液质量，以便在未来十年内将它们带离善后护理。该项目还旨在确保未来渗滤液的排放量将达到可接受的低水平--永远不需要任何人为干预。如果该项目成功，它将带来更可持续和更具成本效益的垃圾填埋后处理方法。我们的研究旨在提供一些支持该项目所需的科学知识。这项工作将在德克拉格垃圾填埋场进行，运营商将在那里将渗滤液和水通过废物进行再循环。这将把污染物冲出渗滤液，然后在垃圾填埋场外进行处理。这类处理的成功取决于水或渗滤液如何流经垃圾填埋场。如果流量均匀分布，垃圾的冲洗将比优先流动路径允许液体绕过一些垃圾时更均匀。(这就是为什么有时仍然可以阅读被埋在垃圾填埋场40年的报纸)。优先流动路径的间距至关重要。我们计算出，如果流动路径的间距小于0.5米，污染物将以足够快的速度从垃圾中扩散出来，以便在大约10年内进行清理。相距超过1米的流动路径可能会限制废物中污染物的释放，以至于在所有污染物被清除之前，垃圾填埋场可以安全地离开。我们的研究将集中于了解垃圾填埋场内液体流动和流动路径的性质，以及它们对垃圾填埋场清理工作的影响。我们会在约0.5米的范围内安装监测系统，以区分优先流向堆填区的水流和在堆填区非饱和区内较为均匀的水流。化学示踪剂将被注入操作员的渗滤液再循环系统，我们将监测它们在废物中的流动。在解释示踪剂数据之后，我们将开发和验证一套不同的模型，这些模型跟踪污染物的流动并描述垃圾填埋场的清理。我们将根据我们的新数据测试一系列模型概念，以确定哪些模型概念效果最好。然后，这些将为了解荷兰垃圾填埋场冲洗项目的绩效和评估任何剩余风险提供一个框架。这些模型还将为优化冲厕工程和世界各地废物库的管理提供科学基础。

The usual way of managing solid waste in the UK has been landfill. We have more than 20,000 sites, containing 6 billion tonnes of waste, which are now full up. Landfills can cause major environmental problems, especially when water (from rain or streams) gets in and mixes with the waste to form a liquid called 'leachate'. If leachate escapes into the environment it can pollute ground and surface water, damage eco-systems and contaminate drinking water.Modern landfill sites are containment systems, sometimes called 'dry tombs'. Plastic membranes line the base and the sides to control how much leachate seeps out. A cap reduces the amount of rainfall entering to reduce how much leachate is formed. Leachate which does form is retained at the base, where it can be collected and treated.After landfilling at a site has stopped, it is covered and enters a management phase known as 'aftercare'. During aftercare, leachate needs to be collected and treated for as long as it presents a pollution hazard. Unfortunately, aftercare periods for modern landfills are measured in centuries. The engineered containment system has to keep working for all this time, along with active environmental control systems for gas and leachate extraction or treatment. Extended aftercare periods cause problems for operators, regulators and society, and are unacceptable in terms of sustainability.A unique project in the Netherlands aims to rapidly improve leachate quality at three demonstration landfills so that they can be brought out of aftercare within the next decade. The project also aims to ensure that future emissions of leachate will be acceptably low - for ever, without any human intervention. If the project succeeds, it will lead to much more sustainable and cost effective methods for landfill aftercare.Our research aims to provide some of the science required to underpin the project. It will be undertaken at the de Kragge landfill, where the operator will recirculate leachate and water through the waste. This will flush contaminants out into the leachate, which will then be treated outside the landfill. The success of this type of treatment depends on how the water or leachate flows through the landfill. If the flow is evenly distributed, the waste will be flushed more uniformly than if preferential flow paths allow the liquid to bypass some of the waste. (This is why it is sometimes possible still to read newspapers that have been buried in a landfill for 40 years). The spacing of preferential flow paths is critical. We calculate that if the flow paths are less than 0.5 m apart, contaminants will diffuse out of the waste fast enough to allow clean-up within about a decade. Flow paths that are more than 1 m apart are likely to limit the release of contaminant from the waste to the extent that a landfill might safely be brought out of aftercare before all the contaminant has been removed.Our research will focus on understanding the nature of liquid flow and flow paths within the landfill, and their influence on landfill clean-up. We will install monitoring systems that can differentiate, at a scale of about 0.5 m, between flow occurring in preferential flow paths and flow occurring more evenly within the unsaturated zone of the landfill. Chemical tracers will be injected into the operator's leachate recirculation system, and we will monitor their flow through the waste. After interpreting the tracer data, we will develop and verify a suite of different models that track flow of contaminants and describe landfill clean-up. We will test a range of model concepts against our new data, to identify those that work best. These will then provide a framework for understanding the performance of the Dutch landfill flushing project and for evaluating any residual risks. The models will also provide a scientific basis for optimising the engineering of flushing, and the management of waste repositories worldwide.