The challenges of going remote

In recent years, advances in technology have radically improved the quality and reliability of remote environmental monitoring; Neill Cornwell examines some of the key challenges and explains how they are being overcome. In comparison with laboratory analysis, environmental monitoring in the field represents a greater challenge because of the number of extra variables that a changing environment delivers. Traditionally, the most common method for monitoring remote sites would be to take spot samples or to install an automatic sampler and to analyse samples in a laboratory. This enables the measurement of a wide variety of parameters to a high degree of accuracy, but high levels of precision are pointless unless the samples are truly representative and laboratory analysis necessarily incurs a significant delay between sampling and the provision of results. The labour costs involved with sampling also weigh heavily against this option, so there has been a long-standing demand for remote monitoring equipment that is able to provide accurate, reliable, continuous data. In contrast with spot samples, such data would enable the monitoring of trends and the identification of events or peaks. Over the last few decades multiparameter water quality monitoring ‘sondes’ have been developed that employ low-power sensors with an internal datalogger and batteries to measure and log water quality continuously. However, in contrast with say, remote automatic weather stations, water quality monitoring has presented an array of further challenges.  All of the main challenges to remote monitoring result in a requirement for a site visit – to recalibrate, repair or clean sensors, or to collect data or provide a new source of power. Such visits can be time-consuming and costly, especially for the more remote sites. In addition, the health and safety implications can be significant at remote sites; often necessitating more than one member of staff. Recalibration Many water quality sensors employ an electrochemical method to perform a measurement and are therefore prone to drift and require regular recalibration. Instrument manufacturers have therefore sought to develop new technologies that maximise the period between calibrations or eliminate this requirement entirely. For example, the latest optical dissolved oxygen sensors can be deployed for up to 12 months without recalibration. The development of smart sensors has also made a major contribution to the reduction in time necessary for field service operations. Smart sensors retain their own calibration so that they can be quickly and simply swapped in the field. Also, multiple and simultaneous same sensor calibrations will help to reduce calibration uncertainties, technician time and the amount of calibration solution required. In addition, smart sensor systems indicate their health status and provide alarms if they drift from specification. The introduction of wet-mate sensor connectors has also helped to reduce the likelihood of data corruption or loss. The latest sondes also communicate wirelessly; employing Bluetooth to avoid the need for cables and simplify operations in the field. Biofouling When water monitoring equipment is installed for an extended period, particularly in slow-moving or stagnant water, it is inevitable that biological materials will accumulate on those parts of the instrument that are submerged. This biofouling will include sediment and the growth of biofilms of bacteria and other biological materials such as algae, weed and organisms such as snails, molluscs, barnacles etc. Some manufacturers have therefore developed technologies that overcome the biofouling challenge. For example, some of the latest water quality monitoring sondes employ construction materials such as titanium, copper-alloy and a single wiper to help inhibit biofouling. Power Many remote monitoring locations do not have mains power available, so external 12 volt systems (often supported by solar panels) are necessary to run the monitoring instrumentation and outstation. Manufacturers of remote monitoring equipment therefore focus heavily on the development of low-power electronics. Intelligent logging can also help to reduce power demand, by recording at a reduced frequency when readings are ‘normal’ and increasing the data resolution when pre-set trigger points are reached. Data collection The most useful data is (near) real-time; providing users with instantaneous information on specific environmental conditions and events. However, remote sites often lack communications infrastructure, and physical obstructions such as hills, buildings and trees may hinder the potential for radio communication. Nevertheless, technology has advanced considerably in recent years and a wide range of options now exist (satellite, radio, GSM, GPRS, Bluetooth, internet, cable etc.) so that data collection capability can be designed to meet the specific needs of each application, and by connecting with the internet (hosting in the ‘cloud’) data can be made available to large numbers of users. In addition to automated reporting capability, monitoring stations are now able to detect pre-set conditions and issue alarms by email and/or sms.   In summary, for most remote monitoring applications, the objective is to ensure the availability of real-time, accurate, reliable data, whilst maximising the time interval between service visits. However, in the following case study at Sellafield, the monitoring challenges are magnified by the presence of high levels of radiation, which substantially increase the problems and costs involved with water quality monitoring. However, as explained below, recent advances in technology have also simplified and improved monitoring in what must be one of the most hostile environments imaginable. Case Study – monitoring nuclear waste legacy storage ponds Following a rigorous assessment period, EXO water quality monitoring sondes are being deployed in nuclear waste legacy storage ponds at the Sellafield nuclear reprocessing site in Cumbria, UK. One of the major challenges facing Sellafield is the safe decommissioning of the First Generation Magnox Storage Pond (FGMSP), a nuclear fuel storage facility that was originally built in the 1950s and 1960s as part of the UK’s expanding nuclear programme to receive and store, cool irradiated Magnox fuel prior to reprocessing. In the 1970s a lengthy shutdown at the Magnox Reprocessing Plant, combined with increased throughput of fuel due to electricity shortages, spent fuel to be stored in the pond for longer than the designed period which led to increased fuel corrosion and radiation levels. [caption id="attachment_38772" align="alignleft" width="200"] Image supplied courtesy of Sellafield Ltd[/caption] Over the years the pond has accumulated significant quantities of waste materials, sludges from corrosion of fuel cladding, skips of fuel, and fuel fragments and other debris which has blown into the pond. Standing above ground, this 5m deep open pond holding some 14,000 cubic metres of contaminated water (approximately the size of two Olympic swimming pools) is considered a decommissioning priority. To assist with future retrievals, a detailed knowledge of the facility’s inventory through visual inspection of the pond is needed. Despite high levels of radioactivity, this open pond appears to intermittently bloom with a range of microorganisms that cloud the water, reducing visibility and hampering inspection and retrieval operations. Sellafield is the company responsible for safely delivering decommissioning, reprocessing and nuclear waste management activities on behalf of the Nuclear Decommissioning Authority (NDA), and a project team led by Xavier Poteau has specific responsibility for transferring monitoring technologies to the FGMSP pond. Water passing through the pond reaches the Sellafield Ion Exchange Effluent Plant (SIXEP) which removes radioactivity from liquid feeds from a number of plants across the Sellafield site. The plant settles out and filters solids using a carbonation process to neutralise the alkaline pond water and then employs ion exchange to remove radionuclides. Water samples are routinely collected from the pond for laboratory analysis, and analytical data is reported to the Environment Agency and the NDA. In addition to this regulatory requirement, water quality data is also required to inform efficient operation of SIXEP and to ensure that legacy fuel is stored in optimal conditions. For example, the water is caustic dosed to maintain a pH of around 11.5 which reduces the speed of nuclear fuel degradation. As a result of physical restrictions, it has only been possible to take water samples from specific locations around the edge of the pond and, being radioactive, routine samples have to be limited to about 100ml to be within laboratories guidelines. Sampling is also an arduous, time-consuming process; two people have to be involved and each sampler has to wear a pvc suit and facemask, two pairs of pvc waterproof gloves and a pair of Kevlar gloves to ensure that the gloves are not accidentally punctured. The samplers are also only allowed to be close to the pond for a limited time. Instrumentation might appear to be the obvious solution, but again, there are several challenges, not least of which is that gamma spectrum analysis has to be conducted on a sample in a lab. In addition, electrical instruments often fail in a radioactive environment, so the general assumption is that they will do so, unless proven otherwise. Continuous monitoring probes, similar to those employed by the water industry, are not feasible because of the wiring that would be required. However, portable instruments offer the potential to reduce the volume and frequency of water sampling. The EXO2 sondes are multiparameter 6-port water quality monitors that have been developed for remote, long-term monitoring applications. They have been designed to be lightweight and rugged, with internal batteries and datalogging capability, operating on extremely low power and incorporating a range of features that minimise maintenance requirements and avoid biofouling. For example: wet-mateable connectors resist corrosion; components are isolated to prevent short-circuits; welded housings and double o-rings prevent leaks, and high-impact plastic and titanium resists impact damage. Smart sensors are easily interchangeable and users are able to select the sensors that best meet their needs. The FGMSP project team, for example, uses sensors for pH, temperature, conductivity, turbidity, fDOM (Fluorescent Dissolved Organic Matter – a surrogate for Coloured DOM), Blue-green Algae and Chlorophyll. Initially, the FGMSP project team trialled an older version of the multiparameter water quality monitoring sondes. “This enabled us to assess the quality of the sensors and demonstrate that they were able to operate well in a radioactive environment,” said Technical Specialist Marcus Coupe. “The launch of the EXO was of great interest to us because, with Bluetooth communications and smart sensors that retain their calibration data, the EXO offered an opportunity to dramatically reduce time spent at the pond. “The snap-on probes are calibrated in the laboratory and can then be quickly and simply swapped with those that have been deployed on a sonde. This means that the main part of the sonde can be left onsite while the sensors are swapped, and the Bluetooth comms enable us to collect 18,600 sets of data in less than 20 minutes.” Commenting further on the success of the trials, Xavier Poteau said: “It has been common experience in the nuclear industry to have to apply significant adaptations to electrical equipment, so that it is able to function correctly in a radioactive environment, and this can incur a heavy cost and time penalty. However, these sondes have performed very well ‘off the shelf’ which is a sign of good design.” In addition to normal water quality monitoring work, the FGMSP project team has deployed a sonde with a submersible remotely operated vehicle (ROV). This enabled the team to monitor water quality at previously unachievable locations. “Any loss of visibility in the pond can potentially cause a significant risk to operations within the legacy ponds, as well as potentially slowing down future retrievals, so the ability to deploy a sonde with a ROV offers a valuable insight into understanding the challenge, and moves us from single point sampling to a more 3D-like data stream,” said Coupe. The data from the FGMSP sondes compare favourably with the results of laboratory analysis, so Poteau believes “a high level of confidence is being established in the EXO data and this means that we will be able to reduce the amount of sampling that we undertake, which will save a great deal of time, hassle and money. “I strongly believe that our experience could be beneficial to the wider audience as well as the nuclear industry.” The Sellafield case study exemplifies the advantages that technological developments have delivered to the field of remote environmental monitoring. The overall objective is to deliver the data that people need, when they need it and where they need it, in a way that minimises capital and operational costs. The development of smart sensors, intelligent loggers, low power electronics, extended deployment technologies and high-speed/low-cost communications has radically improved the quality and reliability of data and opened up a new world of opportunity for environmental monitoring, which is extremely exciting because better environmental data informs better environmental decisions. Author Neill Cornwell, Xylem Analytics Contact www.xylemanalytics.co.uk (+44) 1462 673581