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

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

The project is aligned directly to the NERC Environmental Risks to Infrastructure Programme (ERIIP), in particular Theme 1: Identifying, understanding and quantifying environmental risks to the infrastructure system and Theme 3: Dealing with uncertainty in design, operational and investment decisions.

Project outputs will have a direct impact on changes to the operation and management of groundwater resource infrastructure, including the assessments of asset integrity to enable infrastructure operators to identify and focus at the most vulnerable zones and enable preventative action or interventions (see letters of support). A-DTS based innovative monitoring technologies will for the first time allow to identify and characterise sub-surface risk zones critical to the operation of groundwater production infrastructure and thus, inform the design and implementation of risk amelioration measures (e.g. temporary or permanent packering of risk zones in existing borehole infrastructure as well as of locations, design and operation of new groundwater supply boreholes. The continuous borehole A-DTS developed in this project will provide involved industry stakeholders with early warning of turbidity impacts to groundwater based drinking water production and supply infrastructure and drinking water quality, avoiding or reducing disruption to infrastructure.

In addition, the fluid flow and heat transport modelling tools developed in this project will impact procedures for designation of surface risk zones for groundwater contamination and thus not only have a highly valuable impact on water resource infrastructure but also on surface infrastructure design, management and operations. The innovative monitoring project is designed to inform standards of groundwater abstraction infrastructure and to provide end-users in water industries with operational guidance for enhancing infrastructural resilience to environmental hazards.

In addition to the assessment of storm and groundwork engineering driven turbidity events, the developed innovative A-DTS technology will provide substantial advancement to the assessment of salinization risks and potential impacts of hydraulic fracking operations on unintended increase in fracture flows. The involvement of UKWIR (UK Water Industry Research Ltd) will support the facilitation of the project outputs at a national and international level.

The innovative monitoring technologies developed and applied throughout this project will benefit the project partners by improving the security and resiliency of water resource infrastructure, securing safe drinking water supply while optimising production operations and reducing infrastructure failure and thus, financial losses.
The positive impact of the project will be measured by the successful implementation of an early warning system in infrastructure operations, which will secure more resilient water supply systems with reduced down-time, infrastructure repair costs and financial losses.

The project partners will benefit from improved predictions of the utilisation of infrastructure assets and water resource available. Therefore the impact of integrating the developed innovative A-DTS fracture flow monitoring technology can be measured by improved predictions of turbidity spikes in abstraction boreholes and subsequently, either its avoidance of reduced impact on infrastructure and financial assets.

We expect the developed technology to benefit not only the main project partners but a wider range od water companies and underground resource businesses and hence, measure the impact of the project also by the uptake of the developed technologies by other industry sectors, including those with a focus on subsurface energy resources and in particular unconventional oil, gas and geothermal energy companies.