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

在英国，处理固体废物的通常方法是填埋。我们有2万多个垃圾场，其中包含60亿吨垃圾，现在已经满了。垃圾填埋场会造成严重的环境问题，特别是当雨水或溪流中的水进入并与废物混合形成一种称为“渗滤液”的液体时。如果渗滤液泄漏到环境中，它会污染地下水和地表水，破坏生态系统并污染饮用水。现代垃圾填埋场是封闭系统，有时被称为“干坟墓”。塑料薄膜排列在底部和侧面，以控制渗滤液渗出的量。封顶减少了进入的降雨量，从而减少了渗滤液的形成。形成的渗滤液被保留在基地，在那里可以收集和处理。在填埋场停止填埋后，它被覆盖并进入一个被称为“善后”的管理阶段。在事后处理期间，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期处理周期以几个世纪为单位。在这段时间里，工程控制系统必须保持工作状态，同时还有主动的环境控制系统，用于气体和渗滤液的提取或处理。延长的护理期会给运营商、监管机构和社会带来问题，而且在可持续性方面是不可接受的。荷兰的一个独特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其带出后处理。该项目还旨在确保未来的渗滤液排放量将永远处于可接受的低水平，而不需要任何人为干预。如果该项目成功，它将为垃圾填埋后处理带来更具可持续性和成本效益的方法。我们的研究旨在提供支撑该项目所需的一些科学知识。它将在de Kragge垃圾填埋场进行，在那里，运营商将通过废物再循环渗滤液和水。这将把污染物冲到渗滤液中，然后在垃圾填埋场外进行处理。这种处理方法的成功与否取决于水或渗滤液如何流经垃圾填埋场。如果流量分布均匀，废物将比优先流动路径允许液体绕过一些废物更均匀地冲洗。（这就是为什么有时仍然可以读到在垃圾填埋场埋了40年的报纸的原因）。优先流道的间距至关重要。我们计算出，如果流动路径之间的距离小于0.5米，污染物将迅速从废物中扩散出来，大约10年内就可以进行清理。距离超过1米的流动路径可能会限制废物中污染物的释放，从而在所有污染物被清除之前，可以安全地将垃圾填埋场带出。我们的研究将集中在了解垃圾填埋场内液体流动的性质和流动路径，以及它们对垃圾填埋场清理的影响。我们将安装监测系统，该系统可以在大约0.5米的尺度上区分在优先流动路径上发生的流动和在垃圾填埋场的不饱和区域内更均匀地发生的流动。化学示踪剂将被注入该运营商的渗滤液再循环系统，我们将监测其在废物中的流动情况。在解释了示踪剂数据之后，我们将开发并验证一套不同的模型，用于跟踪污染物的流动并描述垃圾填埋场的清理。我们将针对新数据测试一系列模型概念，以确定最有效的模型概念。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世界各地的冲水工程和废物储存库管理提供科学依据。

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.