Environ Earth Sci (2010) 60:703–713 DOI 10.1007/s12665-009-0208-0

ORIGINAL ARTICLE

Hydrogeological and thermal characterization of shallow aquifers in the plain sector of Piemonte region (NW Italy): implications for groundwater heat pumps diffusion Stefano Lo Russo Æ Massimo Vincenzo Civita

Received: 19 January 2009 / Accepted: 15 June 2009 / Published online: 30 June 2009 Ó Springer-Verlag 2009

Abstract The low annual and seasonal variability of the shallow groundwater temperature in the alluvial plain aquifers of the Piemonte region (NW Italy) confirmed the potentiality of the low-enthalpy open-loop groundwater heat pumps (GWHP) diffusion to contribute to the reduction of regional greenhouse gas emissions. The distribution of mean groundwater temperatures ranged from a minimum of 10.3°C to a maximum of 17.9°C with a mean of 14.0°C. Differences among diverse areas were slight according with the modest variations in the general climatic condition. Like the air, temperature distribution of the shallow groundwater temperatures is generally similar to topographic elevations in reverse manner. Higher temperature values recorded were typical of summer months (June, July). On the opposite lower values were measured in January and February. No significant difference phase (time) difference between air and groundwater temperature appeared in the data analysis. Besides air-temperature influence (seasonal variability) seemed strictly connected to the depth to groundwater in the measure point and it was negligible when the value was over 9.5 m. For the application of the open-loop systems, extensive examinations of the hydrogeological local conditions should be conducted at site scale and groundwater heat transport modelling should be developed. Keywords Groundwater temperature
Geothermal energy
Heat pumps
Monitoring
Piemonte

S. Lo Russo (&)
M. V. Civita Dipartimento di Ingegneria del Territorio, dell’Ambiente e delle Geotecnologie, Politecnico di Torino, C.so Duca degli Abruzzi, 24, 10129 Torino, Italy e-mail: [email protected]

Introduction Remarkable increases in energy demands for domestic, agricultural, and industrial sectors have required impressive consumption of non-renewable resources, which resulted in many environmental pollution problems, global warming, and rapid depletion of the fossil fuels in twenty-first century (Sheffield 1997). Consequently, renewable and clean energy sources were essentially required to combat climate change while increasing security of supply. Solar energy, wind power, tidal power, biomass energy, waste energy, and geothermal heat emerged as alternative to fossil fuels and it was expected that use of these energy sources would reduce CO2 emissions into air, rate of global warming, and relevant environmental pollution (IEA 2006). The adopted EU Energy Efficiency Action Plan contains measures to increase the level of renewable energy to achieve the key goals of (1) reducing EU global primary energy use by 20% by 2020 and (2) dropping its worldwide greenhouse gas (GHG) contributions to a level that would limit the global temperature increase to 2°C compared to preindustrial status (EC 2006). However, current energy policies—that accounts for 80% of all EU’s GHG emissions—and traditional transport development would mean EU CO2 emissions would increase by around 5% by 2030 and global emissions would rise by not sustainable 55% (EC 2007a). Moreover, Europe is becoming increasingly dependent on imported hydrocarbons and with ‘‘business as usual’’ the EU’s energy import dependence will jump from 50% of total EU energy consumption today to 65% in 2030. Reliance on imports of gas and oil is expected to increase from 57 to 84% by 2030, and from 82 to 93% by 2030, respectively, resulting in political and economic risks (IEA 2006).

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With limited domestic energy sources, and no nuclear plants, Italy is highly dependent on energy imports. The country has proven crude oil reserves of 0.7 billion barrels; however, the domestic production of approximately 100,000 barrels per day meets only a limited amount of domestic consumption. In the last decade, the declining production from Italy’s natural gas fields and the increases in domestic consumption have increased the country’s reliance upon gas imports, which arrive mainly by pipelines. Natural gas, renewable sources, and solid fuels are gradually replacing oil in electricity generation. Final energy consumption has been increasing, while industry remains the most energy-consuming sector. Energy intensity value (150) is below the EU average (182), while CO2 emission per capita (7,731 kg/cap) and intensity (2.2 t CO2/toe1) are slightly above EU average (8,180 kg/cap and 2.4 t CO2/toe, respectively). Despite strong growth in sectors, such as onshore wind, biogas, and biodiesel, Italy is far from the targets set at both the national and European level. Focusing on national production of heat and cold from renewable energy sources between 1997 and 2004 biomass is by far the main contributor with a share of over 92% of total (from 1,994 to 2,393 ktoe). Solar heat has grown significantly from 7 to 18 ktoe, although its contribution is negligible. Geothermal heat has decreased over the same period by an average rate of 2% decreasing from 213 ktoe in 1994 to 181 ktoe in 2004 (EC 2007b; EC 2007c). To revert this trend, several actions by public administrations and private stakeholders took place in some Italian region based on the searching of clean and renewable energy resources and the industrial development of correlated technologies. The successful implementation of very low-enthalpy geothermal (T \ 50°C) open-loop groundwater heat pumps (GWHP) for heating and cooling buildings in several European countries has stimulated the investigation of the thermal and productive characteristics of the plain aquifers in the overall Piemonte region. These widespread systems can be frequently located near potential users (below and near buildings) and therefore no regional thermal energy transport infrastructure is required. GWHP typically withdraws groundwater to provide heat. In the winter, the GWHP extracts heat from the water to provide space heating. With reversible heat pumps, the heat-transfer process can be reversed in the summer and the groundwater absorbs heat from the living or working space and cools the air. Actually, the GWHP’s are suited to regions with extended shallow aquifers, from which it is relatively easy and not very expensive to extract groundwater (Drijver and Willemsen 2001).

1

toe = tonne (1,000 kg) of oil equivalent.

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There are three types of commonly used open-loop systems. Direct open-loop heat pumps, where the water is passed directly through the heat exchangers of the heat pump, are largely used for residential and very small commercial applications (Rafferty 2001). This system is most suitably applied where low-salinity groundwaters are available, because the direct use of high-salinity waters can cause scaling, i.e., the deposition of mineral scales in pipes, valves and/or heat exchangers (PDEP 1996). Standing column systems (SCW) are used in locations where groundwater wells do not produce sufficient water for a conventional open-loop system and where water quality is also good. In SCW systems, groundwater is re-circulated from one end of the column well (static water level) to the heat pump, and back to the other end (bottom) of the deep bore. Usually, only one well is required for conventional buildings; larger projects may have several wells in parallel. SCW systems can be thought of as a cross between closed-loop earth-coupled systems and open-loop groundwater source systems. The indirect open-loop systems generally involve a heat exchanger between the building loop and the groundwater, which eliminates exposure of any building components to groundwater (Rafferty 2001). Generally, a highly productive, shallow (within 30 m of surface) aquifer would favour successful and efficient functioning of the GWHP (Clauser 1997, Drijver and Willemsen 2001, Karagiorgas et al. 2003, Sanner et al. 2003, Zhao et al. 2003, Marcic 2004, Lee and Hahn 2006). The most important consideration in GWHP design is to obtain a plentiful amount of groundwater with a very stable temperature. This study is aimed to highlight the hydrogeological potential for the Piemonte regional territory to supply clean energy by the diffusion of these technologies and therefore contribute to reducing GHG emissions starting from the regional analysis of (1) the hydrogeological plain setting and (2) the spatial distribution and temporal variability of the shallow groundwater temperature.

Materials and methods Climate conditions in Piemonte region The stronger effects of physical space on climate in Piemonte are linked to the nature of the mountains. No influence is exerted by latitude variation, due to the little north–south extension of territory (2° 200 of difference in latitude). From outside, the most important effects are linked to the continental nature of the middle Po valley, the humidity coming from the Mediterranean, and north-west Atlantic currents; these three factors determine pluviometric-thermal conditions in the easternmost part of the

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plain, and the higher humidity of Maritime Alps, the Ligurian Apennines, and high mountains (Biancotti et al. 1998). Due to the high differences in level, air masses directed towards north-west and coming from south and east are subject to sudden upward motions. Adiabatic expansion causes condensation and precipitations: the piedmont area is subject to heavy and frequent rainfalls. The precipitation gradient grows according to height along ridges; in thalwegs the higher humidity of proximal and distal valley tracts alternates with more xeric conditions of central areas. Here steppe-like conditions can also be reached, with a rich Mediterranean flora and precipitation less than 600 mm/ year. The interval in which average annual air temperatures are included ranges from 13.2°C of Novara (162 m amsl) (plain sector) to negative values over 2,000 m height. Average annual temperature decreases regularly with height except for some situations where deviations linked to local conditions are observed. In the plain areas, the average monthly temperature exceeds 10°C from April to October, while in mountain zones above 500 m the period with average monthly temperatures exceeding 10°C shortens progressively and it becomes 0°C above 2,000 m height. Values higher than 5°C are recorded from March to November up to 800 m height. Values higher than 7°C are recorded from March until October–November in plain areas below 500 m height; at higher altitudes, the period shortens while shifting to summer months. The coolest month at all altitudes is January while the warmest is always July. The highest average monthly temperatures, about 24°C, are observed in the large cities (Alessandria, Asti, Novara and Torino); these values decrease to 8°C around 2,300 m height. The observed limit between the plain and mountains corresponds to the isodiaphore of 21°C. Geology and hydrogeology Piemonte region continental plain area is fully bordered by the arcuate orogenic belt of the Western Alps (crystalline and carbonate rocks), which is morphologically connected by extensive alluvial and morainic fan (see Fig. 1). The alpine range continues north-east with the central segment of the chain, and the south-east with the Ligurian Apennines. The Western Alps are a thick-skinned thrust belt formed by the subduction of the European Plate beneath the Adriatic Plate that began in the Late Cretaceous. Final collision and nappe staking took place in the Late Eocene (Coward and Dietrich 1989; Gebauer 1999; Vezzosi et al. 2004). The Alpine orogenic wedge was the result of a complex geodynamic process due to plate convergence, characterized by mainly ‘‘horizontal displacements’’

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involving lithosphere oceanic subduction followed by continental collision (Polino et al. 1990). The post-collisional, ‘‘late-Alpine’’ (Pliocene to Recent; Hunziker and Martinotti 1987) history of the chain is mainly dominated by ‘‘vertical movements’’ (either uplift or subsidence), due to both active tectonics and isostatic rebound (Debelmas 1986; Cadoppi et al. 2007). The mountain area, which is carved by valleys transversal to the direction of the main structures and converge towards the region barycentre showed relief energy growing from SW to NE. In the southern sector of Piemonte, the transition from the plain to the Apennines is gradual, being characterized by the intermediate presence of hilly terrigenous sectors (Monferrato and Langhe) belonging to the Piedmontese Tertiary basin. The plain area covers 9,349.6 km2 (36.8% of the total surface area of 25,392 km2). The stratigraphic relationships among the various continental units in the region are the results of different exogenous processes linked to Quaternary glacial and alluvial dynamics. The overall thickness of sediments is also strictly dependent on the morphostructural setting of folded and faulted tertiary marine substrate and vary from hundreds of meters in SW part (Cuneo) to few meters near Monferrato hills in the central sector of the region. Generally, these units are lithologically represented by coarse gravel and sandy sediments (locally cemented) with limited amounts of thick clayey–loamy horizons related to lacustrine facies. Tertiary substrate is mostly constituted by marls and sandstones. Well developed drainage patterns characterize the alpine valleys. Small flood plains along alpine rivers are present in the main valleys in the mountain sector. Po and Tanaro rivers are the main draining watercourses of the region. Continental sediments generally show high to medium primary hydraulic conductivity with horizontal and vertical variations linked to stratigraphic settings. An unconfined high-productivity aquifer connected to the surface water drainage network is found across the entire Piemonte plain and in the major valleys in the mountain sector. Usually groundwater flux direction in the shallow aquifer follows the topographic trend at a regional scale. Deviations are due to local conditions. Confined productive aquifers are also widespread; they represent the main regional source of water for human consumption. Crystalline and terrigenous rocks shows low to very low primary permeability with no considerable aquifer. Some significant water circulation is found only in fractured zones and in carbonates. Springs in mountain sector are supplied generally by detritus aquifer covering crystalline bedrock or carbonate structures. These diffuse, high quality water resources are usually used for human consumption in mountain villages. Thermal (55–70°C) springs exist only in rare geological circumstances in the southern part of the region (Vinadio,

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Fig. 1 Hydrogeologic map of Piemonte and distribution of the regional groundwater monitoring stations (modified after Civita et al. (2004))

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Valdieri, Acqui Terme); they have been used since Roman times, mainly as thermal spas. A few less important hot springs occur in other parts of the Alpine chain, linked to particular local tectonic settings, but energy recovery from these resources could have only local significance. On other hand, geological bodies and groundwater in the Piemonte plain could represent an important source of clean geothermal energy through the widespread implementation of GWHP technology. The regional plain shallow aquifers are separated by hydrogeological boundaries in 14 different planning areas defined in the Water Protection Plan (WPP) (Regione Piemonte 2007). The ground depth of the separation surface between unconfined and deep aquifers was determined by the analysis of over 2,000 boreholes data and an isobaths map was produced on the whole plain (see Fig. 2). The vertical separation between the unconfined and deeper confined aquifers varies from a few meters to several tens of meters depending on local hydrogeological conditions. Deep, high-quality groundwater bodies are legally preserved for human consumption. To avoid potential alteration of the deeper aquifer, they should not be intersected by the wells to be used to operate the GWHP plant. Moreover, GWHP could be used only with shallow groundwater. Nevertheless, where the local hydrogeological conditions are such that no confined aquifer is present below the water table or the top of the confined aquifer is below 60 m depth, it may be appropriate to consider 60 m as the maximum depth for injecting GWHP discharges. Groundwater planning and monitoring network in Piemonte According with the EU Water Framework Directive principles (EC 2000) the regional Water Protection Plan (WPP) (Regione Piemonte 2007) adopted comprehensive planning actions both for surface and groundwater for the main 34 river basins of the region. Restrictions to specific discharges and withdrawals as well as detailed land use provisions were locally defined for each basin and jointed with an investments program for sewerage and depuration infrastructures and eco-compatible agricultural practices. At the beginning of 1990s an intense program of groundwater monitoring connected with water planning actions started at a regional level. The PRISMAS, PRISMAS II, and TANARO groundwater monitoring projects were developed by the regional authority to cover the whole plain sector and several hundreds of monitoring points were analysed, classified, and selected. The network consistency at the end of 2007 was 446 points for water table and 211 points for deep confined aquifers.

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According with national law, each monitoring point was checked by the regional environment protection agency (ARPA) at least twice a year and water temperature, electrical conductivity, and water level were measured directly on site. Water samples were collected and analysed in laboratories to control the main chemical parameters and identify eventual pollution. Data were used to verify trends in hazardous substances (nitrates, phosphorous, etc.) and to define planning actions and restrictions in land management. After validation data were released to the public. The chemical analyses showed a strong geographical and temporal variability in water quality, and identified some chemical pollution phenomena probably linked to urban and industrial areas. Occasionally, nitrates and phosphates, as well as agricultural runoff, were also present in shallow groundwaters of rural areas (Regione Piemonte 2007). In general, though, water quality at the regional scale is still good enough to be used without the need for secondary exchangers in the heat pump systems. In exceptional cases (i.e., in the more polluted sites), groundwater quality is unsuitable to be used directly and secondary exchangers are recommended. This technical option would significantly affect both the capital and running costs of the heat pump plant. For this reason, the characteristics of a prospective site (including water chemistry) should be carefully studied before choosing the heating system in order to verify the real economic benefit of installing a GWHP system. Considering all legal and hydrogeological constraints and focusing on potentiality of GWHP use, only shallow aquifers monitoring data were analysed in this study. The main 14 groundwater areas were considered for clustering and basic statistical analysis. 414 water table monitoring points were selected according with the accountability of available temperature data collected from 2000 to 2005. For each measured point the data set mean temperature value was computed. Seasonal variability of temperature was checked also in terms of SD and compared with the mean depth to groundwater in the monitoring station. Mean temperature values were aggregated in the proper groundwater area and the mean area value and SD was determined (see Table 1). To evaluate the hydro-geothermal energy potential that might be exploited by the use of GWHP systems in the shallow aquifer across the entire plain, the shallow groundwater temperature data were used in combination with the hydraulic parameters extracted from the regional database on pumping tests carried out in productive Piemonte wells (shallow aquifers) since 1990 (Regione Piemonte 2007). Note that temperature-monitoring network points did not coincide with the wells where the pumping tests were conducted (see Table 1).

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Fig. 2 Water table potentiometric surface with the isobaths of the shallow aquifer bottom in the plain sector of the region

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Results and discussion Groundwater temperature distribution and productivity characteristics Distribution of mean groundwater temperatures for the shallow aquifer is shown in Table 1. The mean groundwater temperature ranged from 10.3°C minimum to 17.9°C maximum with a mean of 14.0°C at a regional level. Differences among diverse areas were slight according to the modest variations in the general climatic condition in the plain area at a regional level. Like air temperature distribution, shallow groundwater temperatures are generally similar to topographic elevations in a reverse manner and the lowest mean temperature recorded in PA8 area, near mountain southern sector, and the highest in PA3 proximal to the central lower part of the plain seemed connected to this factor. Higher temperature values recorded in the data set were typical of summer measures (June, July) in all areas considered. Conversely, lower values were recorded in January and February. No significant phase (time) difference between air and groundwater temperature appeared in the data analysis (Bundschuh 1993). Besides this air-temperature influence (seasonal variability) seemed strictly connected to the depth to groundwater in the measure point. Very slight temperature variations between different seasons (SD \ 10% data set mean value) were recorded when the value was over 9.5 m. This phenomenon could be explicated by the atmospheric heat transfer ability of the upper soils limited to a few meters. There also exists sporadic values not explained by the abovementioned simple factors. In this case, local artificial conditions, including land use, surface vegetation, groundwater pumping wells near monitoring station, and hydrogeological condition (buried rivers, lakes, etc.) may be potential sources for the anomalies (Hahn et al. 2004) and explained also the absence of preferential axis or zonation in the mean temperature contour map (see Fig. 3). Interpolation was performed by the Inverse Distance Weighting (IDW) method. On a regional scale, the aquifer is generally characterized by high productivity (average specific capacity: 13.5 L s-1 m-1) and good saturated thickness (average: 23 m). Geographical variations in those parameters are mainly due to specific hydrogeological local conditions (depth to groundwater, aquifer storavity, depth to impermeable clayey layers, etc.). Monitoring geographical density The density of the groundwater temperature-monitoring network is far from the optimal target represented by one

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measurement point per 10 km2; only area PA14 (Fig. 1) could be considered sufficiently covered by the network. The pumping test data are similarly patchy: low densities are due to the scarcity of productive wells in areas (e.g. PA1 and PA3) characterized by shallow depth to groundwater (\1–4 m), while higher values are typical of areas (e.g. PA6, PA7 and PA8) with many wells used for irrigation and a deeper (25–30 m) water table. The high productivity and the relative stability of the groundwater temperature confirm the hypothesis that the shallow aquifers are regionally suitable for installing GWHP plants. High values of transmissivity and saturated thickness ensure good heat dispersion in a restricted area around the injection wells. Therefore, thermal interference between wells will be limited, and one could design heat pump systems in such a way that changes in aquifer temperatures near injection wells are as high as 10°C. Well-designed GWHP systems could optimize thermal energy extraction from the aquifers without causing undue environmental effects. Against this, uncertainty linked to the long-term environmental effects is currently the main constraint on the wide implementation of GWHP systems in Piemonte. Quite apart from building design considerations, the lack of data about the actual behaviour of the plain aquifer under the thermal stress connected to the injection of warmer or cooler groundwater represents the main difficulty to answer for researchers and developers. Therefore, it is prudent to start the incentives to the GWHP diffusion with an initial (i.e., 1–2 years) experimental phase aimed to collect subsurface data directly on test-sites by suitable temperature groundwater monitoring network around the plants. Such information would be quite useful to support adequate numerical modelling studies. This would assist in the correct evaluation of the subsurface environmental effects and acquisition of information about subsoil thermal parameters (West et al. 2007) that would be needed when developing technical guidelines for the wide implementation of the technology at a regional scale.

Conclusions Focusing on the GWHP, the groundwater temperatures trend and the productivity characteristics of the shallow aquifers in the alluvial plain of the Piemonte region were examined. Low temperature geothermal energy (shallow groundwater) is widespread in the plain sector of the region and could be utilized extensively. According with the requirements of hydraulic productivity and stability of groundwater temperature to reach high efficiency of system design

123

123

1173.2

110.7

9349.6

Pianura Novarese

Pianura Biellese

Pianura Vercellese

Anfiteatro morenico di Ivrea

Pianura Canavese

Pianura Torinese

Pianura Pinerolese

Pianura Cuneese

Pianura Cuneese in destra Stura di Demonte

Altopiano di Poirino e colline Astigiane

AstigianoAlessandrino occidentale

Pianura Alessandrina orientale

Pianura Casalese

Fondovalle Tanaro

Piemonte plain

PA1

PA2

PA3

PA4

PA5

PA6

PA7

PA8

PA9

PA10

PA11

PA12

PA13

PA14

Total

223.9

582.5

669.6

414

13

13

52

33

11

39

523.5

896.1

42

34

12

10

15

60

38

42

Number of temperature monitoring wells

0.44

1.17

0.58

0.89

0.49

0.12

0.74

0.38

0.49

0.14

0.22

0.34

0.58

0.70

0.36

Monitoring density ratio (Number of monitoring wells/ 10 km2)

3079

82

97

341

220

120

256

241

300

90

85

104

483

359

301

Total number of measurements

17.9

16.4

15.9

15.1

15.8

15.6

15.8

16.4

16.6

15.6

16.7

15.9

17.9

16.8

17.0

10.3

13.1

15.2

12.3

11.3

13.3

11.5

10.3

12.2

13.4

13.0

12.4

12.3

12.6

11.6

7.6

3.3

0.7

2.8

4.5

2.3

4.3

6.1

4.4

2.2

3.7

3.5

5.6

4.2

5.4

Maximum Minimum Maximum (°C) (°C) variation (Max– Min) (°C)

Shallow groundwater temperature data set

1117.0

693.8

888.0

453.4

440.6

1031.9

545.4

Surface (km2)

Planning Area area (PA) code

14.0

14.7

15.5

13.3

13.2

14.2

13.5

13.7

13.7

14.1

14.6

14.0

15.0

14.2

13.6

1.2

0.9

0.2

0.6

1.0

0.7

1.0

1.3

1.0

0.8

1.1

1.0

1.1

0.9

1.3

4

8

82

23

71

28

249

315

177

11

15

7

6

22

17/01/ 14/11/ 1018 2000 2005

09/10/ 01/04/ 2001 2005

21/03/ 13/10/ 2001 2004

22/03/ 01/04/ 2001 2005

12/03/ 01/04/ 2001 2005

22/05/ 27/10/ 2000 2005

15/03/ 31/03/ 2001 2005

26/03/ 17/03/ 2001 2005

28/04/ 29/09/ 2000 2005

27/04/ 24/10/ 2000 2005

18/04/ 25/10/ 2000 2005

04/05/ 26/10/ 2000 2005

03/02/ 27/10/ 2000 2005

03/02/ 17/10/ 2000 2005

17/01/ 14/11/ 2000 2005

SD Starting Ending Number of Mean pumping data groundwater (°C) data analysis analysis tests temperature (°C)

1.09

0.36

0.36

1.41

0.34

0.79

0.53

2.23

4.54

1.99

0.24

0.34

0.07

0.11

0.19

Density ratio (Number of pumping tests/ 10 km2)

Pumping tests data set

13.5

9.8

7.5

8.6

5.9

13.5

10.8

14.3

16.9

11.1

10.6

10.0

1.4

6.4

8.5

Mean specific capacity (L
s-1 m-1)

23

21

22

20

24

23

17

21

27

19

14

21

19

16

34

1.4 9 10-2

1.3 9 10-2

1.4 9 10-2

8.6 9 10-3

5.9 9 10-3

1.3 9 10-2

1.1 9 10-2

1.4 9 10-2

1.7 9 10-2

1.1 9 10-2

1.1 9 10-2

1.0 9 10-2

1.7 9 10-2

1.4 9 10-3

8.5 9 10-3

Mean Mean saturated transmissivity thickness (m2 s-1) (m)

Table 1 Summary of temperature data for shallow aquifers derived by the regional monitoring network (2000–2005 studies) and hydraulic parameters derived by pumping tests conducted since 1990

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Fig. 3 Distribution of the mean groundwater temperatures in the plain shallow aquifers

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and system maintenance in GWHP plants shallow aquifers showed good characteristics and potentiality. Frequent fluctuation (not seasonal) of the groundwater temperature greatly reduces efficiency of GWHPs because all the system engineering parameters such as size of heat pumps, powers of well pumps and compressors, specifications of piping connections, and types of heat exchangers are usually optimized to a given constant temperature (Rafferty 1998). So it is most desirable that the groundwater temperature is constant for a certain period (e.g., 3–4 months, heating mode for winter or cooling mode for summer) for stable energy gain and consistent system performance. Fortunately, the shallow groundwater temperatures are rather constant for the summer or winter seasons and also considering annual periods and this element confirms that a strong implementation of GWHP could be considered suitable in the overall plain. Geothermal heat pumps require a relatively large initial investment, with small annual operation costs thereafter (Lund 1996). Respecting traditional cooling and warming systems recent applications of GWHP technology in NW Italy showed that the time needed to restore initial major investments costs is proportional in reverse manner to the dimension and importance of the plants. Furthermore, constant growing of oil and fuels costs encourage this technology also by reducing time to recover initial major investments respecting traditional plants. Future diffusion of GWHP could be favoured by the great number of existing groundwater wells used for various purposes throughout the region that could limit additional installation costs especially for small buildings. The potential use of open-loop groundwater heat pumps is being actively considered. In all cases for practical application of the open-loop systems, extensive examination of the local hydrogeological conditions and the potential environmental changes should be conducted at site scale and modelling should be developed. In this way, an opportune software resource is represented by the finiteelement FEFLOWÒ package developed by Diersch (2005). Due to the great amount of shallow groundwater bodies in the plain sector, deep confined aquifers should be still preserved for human consumption. Geographical distribution analysis showed that technical and economic efforts should be made by public authority to implement the monitoring network and reduce the lack of information about groundwater temperature at a regional level. New GWHP installations should provide data to increase public data base without additional costs for administration and the regulatory framework should be adapted in that sense. Acknowledgments This study was partly supported by the Water Planning Department of the Piemonte region.

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