Reducing storm-induced contamination risks to water supply infrastructure by Active-Fibre-optic Distributed Temperature Sensing

地下水浊度超过饮用水上限是地下水供应井中常见的问题，这些井是从破裂的含水层系统中提取出来的，例如英格兰东南部的白垩岩。管理这种高浊度事件的策略包括混合或过滤水，或者暂时关闭受影响的油井或钻孔隔离井段，这每年会给自来水公司及其客户造成数十亿分之一英镑的损失。虽然浑浊度的来源可能不同，但浑浊度尖峰的出现通常与长时间降雨或强烈风暴事件后地下水通过裂缝的快速流动有关。目前无法预测这种高浊度事件的发生，这给自来水公司带来了严重的财务风险，并限制了可用地下水资源的可靠性。该项目旨在开发一种井内监测系统，用于连续观察井筒中的裂缝流入，并评估它们与浊度事件的联系。该系统基于有源分布式温度传感(A-DTS)技术，利用安装在钻孔中的光纤电缆，连续监测在环境温度条件下钻孔内温度的变化，并响应电缆内金属芯加热而产生的热脉冲。因此，该项目将：1.论证A-DTS技术在量化地下水钻孔原位裂隙流动方面的适用性。这将包括在一系列条件下测试不同的技术设置和监测战略，并对照传统的非连续井眼表征方法的结果验证A-DTS技术。开发基于连续A-DTS的裂缝流动和浊度变化预警系统。因此，在长期(12个月)的裂缝流连续监测中，还将监测井内不同深度的浊度和电导率(EC)。3.开发和应用数值模拟工具，在不同的运行和气象条件下模拟地下水(和悬浮颗粒)在地下的流动，以确定井眼浑浊的危险区域。这将允许划定最有可能的水和颗粒路径，并绘制最有可能向被调查的钻孔输送颗粒从而导致浑浊的风险区。这项研究的结果将为水务公司提供新的工具，以识别和描述现有供应井基础设施内和周围的浑浊风险区，从而直接受益于水务公司。这将为风险改善措施的设计和实施提供信息，并将影响对新地下水供应井的位置、设计和运行的决定。持续的A-DTS监测系统将为即将发生的浑浊事件提供早期预警，使水务公司有机会在事件发生前调整其基础设施的运行，从而减少对其运营和供应基础设施的整体影响，从而为运营商及其客户节省成本。该项目开发的建模工具将支持划定地下水污染风险区域，从而不仅对水资源基础设施的管理产生影响，而且对地表基础设施的设计、管理和运作产生影响。此外，该技术还具有潜在的应用于盐碱化风险的评估(例如，通过识别和划定供应孔及其周围的风险区)，以及用于检测水力压裂操作对地下水流动状况的可能影响(例如，通过识别流态变化/现有钻孔内的新裂缝)。关键词：浊度、风险、地下水供应、A-DTS、监测、预警系统、水务行业、客户、破裂含水层

Groundwater turbidity above the drinking water limit is a common problem in groundwater supply boreholes that abstract from fractured aquifer systems, such as the Chalk in South East England. Strategies for managing such high turbidity events include blending or filtering the water or temporarily shutting down affected wells or borehole isolating borehole sections, which costs water companies and their customers several 10th of Millions of Pounds every year. While the source of turbidity can vary, the occurrence of turbidity spikes is usually associated with fast groundwater flows through fractures following prolonged rainfall or intensive storm events. The occurrence of such high turbidity events can currently not be predicted, posing a severe financial risk to water companies and limiting the reliability of the available groundwater resource.This project aims to develop an in-borehole monitoring system for continuously observing fracture inflows in boreholes and assessing their linkage to turbidity events. The system is based on Active Distributed Temperature Sensing (A-DTS) technology which uses fibre-optic cables installed in boreholes to continuously monitor the temperature changes within boreholes under ambient temperature conditions and in response to heat pulses, induced by heating a metal core within the cable.The project will therefore:1. Demonstrate the suitability of A-DTS technology for quantifying in-situ fracture flow to groundwater boreholes. This will include testing different technological setups and monitoring strategies across a range of conditions and validating A-DTS technology against the results of traditional non-continuous borehole characterisation methods.2. Develop a continuous A-DTS based early warning system of changes in fracture flow and turbidity. Therefore, in long-term (12 month) continuous monitoring of fracture flows additionally turbidity and electrical conductivity (EC) at different depths within the borehole will be monitored. 3. Identify Risk Zones for Borehole Turbidity by developing and applying numerical modelling tools to simulate groundwater (and suspended particles) flow through the subsurface under variable operational and meteorological conditions. This will allow the delineation of the most likely water and particle pathways and the mapping of risk zones that are most likely to deliver particles, and hence turbidity, to the investigated boreholes.The outputs of this study will directly benefit water companies by providing novel tools for identifying and characterising turbidity risk zones within and around existing supply borehole infrastructure. This will inform the design and implementation of risk amelioration measures and will also influence decision on locations, design and operation of new groundwater supply boreholes. The continuous A-DTS monitoring system will provide early warning of imminent turbidity events, providing water companies with an opportunity to adjust operation of their infrastructure prior to the event and thereby reducing the overall impact on their operational and supply infrastructure, hence saving costs for the operators as well as their customers. Modelling tools developed in this project will support the delineation of risk zones for groundwater contamination and thus, not only impact on the management of water resource infrastructure but also on surface infrastructure design, management and operations. Furthermore, the technology also has potential applications in the assessment of salinisation risks (e.g. by identifying and delineating risk zones within and around supply boreholes) as well as for detecting possible impacts of hydraulic fracturing operations on the groundwater flow regime (e.g. through identification of flow regime changes/ new fractures within existing boreholes).Keywords: turbidity, risk, groundwater supply, A-DTS, monitoring, early warning system, water industry, customers, fractured aquifers