Background/Objectives. Enhanced Reductive Dechlorination was selected to treat a site in Belgium contaminated with chlorinated solvents (PCE and degradation products). The contamination has migrated to a depth of 80 m with the highest concentrations in the upper 50 m. The geology consists of a permeable sandy aquifer until 35 m underlain by a more silty, less permeable layer until 50 m. The plume in the upper aquifer is 200 m wide and 400 m long. There is limited space to install and maintain the wells because of the buildings and infrastructure present.
Approach/Activities. In order to deliver the reagents to promote the reductive dechlorination cost effectively a recirculation system with injection and extraction wells was proposed. A pilot test to demonstrate complete dechlorination and to determine hydraulic parameters like radius of influence and injection capacity was performed. Eight injection wells and 4 extraction wells were installed on the site and groundwater was recirculated without aboveground treatment. Additionally, the following innovative adaptions were evaluated during pilot testing:
• Measures were taken to limit biofouling of the system as fouling can significantly influence remediation performance and increase remediation costs. A first measure was to decrease TOC concentrations to very low levels (25-50 mg/L). Additionally, a weak acid carbon donor was selected as a carbon source. The dosing of low amounts of acid can limit fouling in the system and the immediate surroundings of the injection wells. Testing is required to evaluate whether these adaptions would lead to sufficient degradation.
• The possibility to gain heat and cold from the recirculated water was evaluated. The gained energy can be used to heat or cool buildings (aquifer thermal energy storage or ATES). The current study is the first study in Belgium for combination of ATES and remediation. The cold and heat demands from different buildings on the site were evaluated and potential scenarios for combination with remediation were calculated.
Results/Lessons Learned. The pilot test ran for 5 months during which 30.000 m³ of water was recirculated . Complete dechlorination to ethene was demonstrated and no significant well fouling was observed. This has important implications as maintenance costs for the system are significantly reduced and the system can be operated more continuously.
With respect to the energy study, several scenarios indicated that a significant reduction of the site energy costs could be achieved by using the energy of the pumped water of the remediation project.
In the presentation the results of the pilot test with respect to degradation and clogging will be presented together with the results from the energy study.
Shale gas development, in particular hydraulic fracturing, is a contentious issue. Those opposed to shale gas argue that the risks to the environment are not fully understood, are potentially too great and that the entire activity further challenges our ability to meet climate change targets. Those on the other side of the argument suggest that greater gas capacity is needed to meet demand and ensure a secure and affordable energy supply, and that the risks associated with shale gas development are generally well understood due to a mature oil and gas sector. The risks and arguments are complex and it is easy for stakeholders and decision makers to become lost in the uncertainty, thus leading to potential misunderstanding or ignorance about the issues. By way of case study, this presentation will discuss the application of environmental risk assessment (ERA) as a tool for communicating risk and uncertainty between different sectors (e.g. industry, government, the public). We show that completion of a fit-for-purpose ERA supports decision processes by making explicit the risks and thus enabling operator and regulator to align regulation and risk management strategies in a transparent manner. This presentation will discuss the benefits of this process with reference to a range of environmental issues (e.g. fugitive emissions, wastewater) in the context of sustainability and perception.
While the number of installed Aquifer Thermal Energy Systems (ATES) has been growing rapidly in some European countries, the implementation of such systems is still a niche market in Denmark. One of the reasons for the slow development in Denmark is the widespread and well-developed district heating (DH) systems found in almost every city and town throughout the country. Building owners are obligated to connect to the DH system even if they would prefer an individual heating and cooling system based on groundwater. Another reason for the slow development is that all drinking water supply in Denmark is based on groundwater, and protection of our drinking water resource has the highest priority – for good reasons. This means that ATES must be thoroughly designed and documented before installation and commissioning. The purpose of this presentation is to show that the ATES technology can implemented without risk in areas of groundwater interests and even in areas with known groundwater pollutions.
In 2011 Geo was asked to perform feasibility studies and authority applications work for two separate ATES systems. The two systems are located in areas of drinking water interest, and close to known groundwater pollutions already threatening the quality of the groundwater resource. In both cases abstraction of drinking water takes place from the same aquifer as the ATES systems would utilize for seasonal storage of heating and cooling.
An international data warehouse with a huge demand of cooling energy is interested in making savings on their consumption of electricity used for operating conventional chillers. The data warehouse is placed within 1500 m from the nearest drinking water wells and less than 500 m from a site heavily polluted with chlorinated solvents. The risk of causing an accelerated mobilization of the pollution made the local authorities very concerned and cautious towards granting permission for an ATES system in the area. For this reason detailed ground investigations and modelling was needed in the design phase in order to point out the optimum location of the ATES wells and thus minimizing any risk of worsening the groundwater pollution. On a voluntary basis the data warehouse agreed to let the ATES system function as a remediation system if a critical breakthrough of pollution is observed in the future. For this reason the system is being prepared for not only cooling purposes, but also groundwater remediation should it be needed.
A large Danish university is constantly on the lookout for reducing the carbon footprint of the campus by taking advantages of renewable energy whenever possible. A large ATES system is one of many solution for reducing the overall energy consumption at campus and could function as an add-on to the new large cooling central being installed. The ATES system can also serve as a large energy storage supplying heat pumps with energy during the winter season. The university is placed within 2000 m from three large drinking water well fields and less than 300 m from one of the largest known groundwater pollutions in Denmark. The pollution is already spread to the groundwater aquifer and therefore it is extremely important that the ATES system does not affect the plume of chlorinated solvents in a negative way. On the contrary, the ATES system should be designed in such a way that it will have the opposite effect and actually prevent or limit the natural groundwater flow in spreading the plume towards the downstream water wells. In fact the university has made a declaration of intent with the authorities to find out how both parties can install two neighboring groundwater systems (ATES and remediation) with the aim of creating a win-win situation.
Both cases show how and why it is possible to install and run even large ATES systems in restricted areas without affecting the groundwater resource and the local water supply in the area. At the same time both two cases also shows that ATES systems, if properly designed, can be used as a technology to limit or prevent groundwater pollutions in spreading further, and as such actually serve a purpose beyond providing renewable heating and cooling.
1. Introduction
Low enthalpy geothermal energy is currently one of the cutting-edge topics in scientific community and public debate. Nowadays the number of installations is increasingly growing in NW Italy and doubtless advantages are more and more recognized by the public. At the same time, new concerns are arising for uncontrolled management of new installations that could negatively affect existing geothermal systems, chemical and microbiological equilibria and water wells production. Particular awareness for regional management of subsurface is thus needed by means of developing correct planning and monitoring strategies. Specific attention for geothermal application should be focused on densely urbanised areas due to the intense thermal footprint induced by human activities, as well as the presence of extensive and concurrent subsurface exploitation. Previous studies revealed that extensive thermal anomalies can be found in shallow and sometimes deep aquifers of groundwater bodies beneath urban areas; moreover, medium-sized centres can have similarities with megacities in subsurface thermal behaviour (Taniguchi et al. 2007; Zhu e al. 2010; Menberg et al. 2013). Piedmont Region represents an interesting case study because geological and hydrogeological surveys mark favourable conditions for low enthalpy geothermal exploitation. A shallow and permeable aquifer with relevant thickness is present and observed groundwater temperatures range from 13 to 15°C (ARPA 2009). In such conditions GWHP and BHE systems are prone to be installed both in cooling and heating mode. The present study aims to give a qualitative assessment of thermal trend in Piedmont shallow subsurface with a specific focus on urban and sub-urban area of Turin, describing preliminary outcomes from new surveys and assessing preliminary considerations about the sustainable use of the investigated aquifer.
2. Study area and methods
Turin and its neighbourhoods are settled in a glacial-alluvial plain enclosed by Ivrea Morenic Amphitheatre (north), Western Alps (west) and Turin Hill (east) with 2124 km2 of areal extent and ~1.5 million units population. The mean annual air temperature ranges between 11 and 13,6°C from the mountains towards Turin urban area. The shallow aquifer, largely exploited for non-drinkable purposes, is constituted by coarse sands and gravels. Two surveys involved this water body in spring and autumn (the second still ongoing) on 45 observation points. The observation point consisted in monitoring wells owned by public authorities and private with depths ranging from 13 to 50 m and average screened thickness of approximately 14 m. Points were chosen in urban and rural contexts in order to quantify both the background temperatures and the potentially urban-affected thermal trend. Downhole thermal logs were performed beneath water table level with increasing distances between two measurements. Before data processing a preliminary evaluation of the eligibility of observation points was performed in order to exclude non-significant measurements. Mean temperatures for each observation well were calculated averaging the downhole measurements.
3. Thermal trend
Temperatures show a variability of values that reaches differences up to 3-5 °C from the beneath water table level to aquifer bottom, where values are close to the mean annual air temperature. In those wells where the length of thermal log is adequate, a depth below which temperature variation is stable can be identified and it ranges between 10 and 40 m b.g.l.. The areal distribution of groundwater temperatures reveals an inhomogeneous pattern. The highest concentration of warmer temperatures is located within Turin urban area, where the range is approximately 14-20 °C. Warmest anomalies occur in correspondence of the eastern side of Turin and the maximum is represented by 19.69 °C. In rural areas temperatures decrease by 1-2°C, reaching the minimum of ~9°C near Lanzo Valley (20 km NW from Turin). Other positive anomalies outside the main urban area seem to be isolated and do not form well defined clusters. It is likely that a great part of variability is due to local anthropic and geological factors.
4. Conclusions
The presented data give preliminary qualitative information about the subsurface thermal trend in Turin province, where the highest concentration of warmer temperatures were detected in Turin urban area. Further analysis is ongoing in order to better indentify single inputs, such as local hydrogeological and anthropic factors, that are expected to affect the variability of groundwater temperatures. The lack of integrated and updated thermal surveys, as well as the deficiency of a urban-focused monitoring network, represents intrinsic obstacles for large-scale surveys. For future sustainable geothermal exploitation of shallow groundwater bodies in Turin province, stakeholders should then take into account the improvement of subsurface management and monitoring networks.
References
ARPA (2009) Indagine geotermometrica sui piezometri della rete di monitoraggio quantitativa regionale Resoconto delle attività svolte. http://www.arpa.piemonte.it/approfondimenti/temi-ambientali/acqua/acque-sotterranee/Relazionegeotermometria2009.pdf
Menberg K, Bayer P, Zosseder K, Rumohr S, Blum P Subsurface urban heat islands in German cities. Sci Total Environ 2013;442;123-133.
Taniguchi M, Uemura T, Jago-on K. Combined effects of urbanization and global warming on subsurface temperature in four Asian cities. Vadose Zone J 2007;6:591–6.
Zhu K, Blum P, Ferguson G, Balke K-D, Bayer P. The geothermal potential of urban heat islands. Environ Res Lett 2010;5:044002.
The Dutch subsurface is increasingly used for an expanding array of functions. These functions are often conflicting. Different subsurface activities are competing for the right to use the valuable subsurface. Wild West urges for order!
Groundwater is an essential part of the subsurface. Groundwater management is considered to be complex, partly as a result of its invisibility and because of the fact that effects of actions will often arise at a different time or place. In The Netherlands, groundwater management is complexly organized. Groundwater management has long been an aspect of various legislation, and carried out by various authorities. Only recently acknowledgement has arisen that groundwater management requires an integral view. The lack of coordination in groundwater management or in use of the subsurface can lead to detrimental effects. The Dutch past has brought forward many examples, such as desiccation of natural habitats and affection of the wooden piles underneath building foundations by rot as a result of low groundwater levels.
These examples stress the consideration of interrelationships whenever subsurface developments are planned. Firstly, to preserve the existing use of groundwater and the subsurface. Secondly, to prevent unwanted mixing of groundwater bodies. If carried out carefully, groundwater can be used in a sustainable way. Also, by constituting a thorough overview of interconnections, spatial development at the topsoil and in the subsurface can be applied to address autonomous issues or to combine challenges to mutual solutions. A relatively new initiative is the so called area oriented groundwater management. At first devised to help solve complex groundwater contamination issues, it also is very useful for considering the bigger picture of groundwater related issues.
Many initiatives help to further establish consistency in the complex matter of groundwater and subsurface management. Consistency between scales is an important issue. The European Groundwater Directive has helped to promote the awareness of interdependency of groundwater quality on a regional scale. The link to general water management has been made more evident. Recent shifts in legislative responsibilities concerning groundwater management, along with the arising awareness of climate change and the discussion on the exploration of shale gas deposits, have raised the general attention to groundwater management. The design of the National Structural Vision on the Subsurface (in Dutch abbreviated to “STRONG”) has furthermore accommodated the awareness of the connecting power of groundwater in the subsurface.
In Dutch spatial planning, groundwater management traditionally was a minor issue. Now all authorities are joined in the design of STRONG, which focuses on a sustainable and efficient usage of the subsurface, based on common challenges addressing subsurface and groundwater issues. Subsurface activities are facilitated, as long as detrimental effects are prevented. Groundwater is acknowledged as a very important factor, leading to the watersystem based approach as a foundation for STRONG.
This approach, based on the functioning of the watersystem, requires specific knowledge. This knowledge is available in The Netherlands, but spread over many authorities and institutions. Therefore it is hard to produce a comprehensive overview. Besides this, it is still not common practice to take into account the combined effect of various activities. It is essential to join forces and share knowledge to enforce this. Therefore, the national and regional authorities are cooperating in establishing a 3D spatial planning for the subsurface. Also at different regional scales many joint efforts arise to establish sustainable use of the subsurface.
In our article we advocate a sound combination of knowledge and abilities to bridge the insti-tutional gaps considering groundwater management rather than reorganizing the legislative structure. This requires a willingness on the government level of organizations to co-operate, some valiance on the management level to deal with uncertainty (goals may not lie within the formal tasks of their organizations and control is more loose than usual). And finally it all comes down to the ability of the workforce to combine knowledge and resources in an effec-tive way. Experience will show whether ground water governance would benefit from a reorganization. If so, spatial planning might even effect the legislative landscape of The Netherlands.