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从断裂含水层系统抽取的地下水供应钻孔中常见的问题，例如英格兰东南部的白垩。管理这种高浊度事件的策略包括混合或过滤水，或暂时关闭受影响的井或井眼隔离井段，这每年要花费水务公司及其客户数百万英镑的十分之一。虽然浊度的来源可能不同，但浊度峰值的发生通常与长时间降雨或强风暴事件后快速流过裂缝的地下水有关。这种高浊度事件的发生目前还无法预测，这给供水公司带来了严重的财务风险，并限制了现有地下水资源的可靠性。该项目旨在开发一种井内监测系统，用于连续观察井内裂缝流入并评估其与浊度事件的联系。该系统基于主动分布式温度传感（a - dts）技术，该技术使用安装在井眼中的光纤电缆，在环境温度条件下连续监测井眼内的温度变化，并响应由加热电缆内金属芯引起的热脉冲。因此，该项目将：论证了A-DTS技术在地下水钻孔压裂流量量化中的适用性。这将包括在一系列条件下测试不同的技术设置和监测策略，并验证a - dts技术与传统非连续井眼表征方法的结果。开发基于连续a - dts的裂缝流量和浊度变化早期预警系统。因此，在对裂缝流动的长期（12个月）连续监测中，还将监测井眼内不同深度的浊度和电导率（EC）。3. 通过开发和应用数值模拟工具来模拟地下水（和悬浮颗粒）在不同的操作和气象条件下流经地下，从而确定井眼浑浊的危险区。这将允许描绘最可能的水和颗粒路径，并绘制最有可能将颗粒和浑浊输送到所调查钻孔的风险区域。这项研究的成果将通过提供新的工具来识别和描述现有供水井基础设施内部和周围的浑浊风险区域，从而直接使供水公司受益。这将为风险改善措施的设计和实施提供信息，也将影响对新地下水供应钻孔的位置、设计和操作的决定。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浑浊事件发生前调整其基础设施的运作，从而减少对其运营和供水基础设施的整体影响，从而为运营商及其客户节省成本。本项目开发的建模工具将支持划定地下水污染危险区，从而不仅影响水资源基础设施的管理，而且影响地面基础设施的设计、管理和运营。此外，该技术在评估盐渍化风险方面也有潜在的应用（例如，通过识别和划定供应钻孔内和周围的风险区域），以及检测水力压裂作业对地下水流动状况的可能影响（例如，通过识别现有钻孔内的流动状况变化/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，裂缝性含水层

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