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20 000多个场地，含有60亿吨废物，这些废物现在已经满了。垃圾填埋场会造成严重的环境问题，特别是当水（来自雨水或溪流）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，污染饮用水。现代垃圾填埋场是一个封闭系统，有时被称为“干墓”。塑料膜衬在底座和侧面，以控制渗沥液的渗出量。一个盖子减少了进入的降雨量，以减少渗滤液的形成。形成的渗滤液会留在底部，以便收集和处理。在填埋场停止填埋后，渗滤液会被覆盖，并进入称为“善后”的管理阶段。在善后处理期间，只要沥出物具有污染危险，就需要对其进行收集和处理。不幸的是，现代垃圾填埋场的善后期是以世纪为单位的。工程控制系统必须保持工作所有这段时间，沿着积极的环境控制系统的气体和渗滤液提取或处理。延长后处理期会给运营商、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快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从后处理期中去除。该项目还旨在确保今后的渗滤液排放量将永远保持在可接受的低水平，而不需要任何人为干预。如果该项目成功，它将导致更可持续和更具成本效益的方法填埋场善后。我们的研究旨在提供一些所需的科学支持该项目。这项工作将在de Kragge垃圾填埋场进行，经营者将在那里使渗滤液和水通过废物再循环。这将把污染物冲入渗滤液，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过垃圾填埋场。如果流动均匀分布，则废物将比优先流动路径允许液体绕过一些废物时更均匀地被冲洗。(This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）。优先流动路径的间隔是关键的。我们计算，如果流动路径相距小于0.5米，污染物将扩散出废物的速度足够快，允许在大约十年内清理。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，填埋场可能会安全地被带出善后处理。我们的研究将集中在了解填埋场内液体流动和流动路径的性质，以及它们对填埋场清理的影响。我们将安装监测系统，以大约0.5米的尺度区分优先流动路径中发生的流动和填埋场非饱和区中更均匀发生的流动。化学示踪剂将注入运营商的渗滤液循环系统，我们将监测它们在废物中的流动。在解释示踪剂数据后，我们将开发和验证一套不同的模型，跟踪污染物的流动和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，以确定最有效的模型。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洗工程和全球废物储存库的管理提供科学依据。

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.