Water Resour Manage (2011) 25:3277–3299DOI 10.1007/s11269-011-9855-5

Water Concession Principles for Geothermal Aquifersin the Mura-Zala Basin, NE Slovenia

Nina Rman · Andrej Lapanje · Joerg Prestor

Received: 31 March 2010 / Accepted: 22 May 2011 /Published online: 10 June 2011© Springer Science+Business Media B.V. 2011

Abstract Demand for thermal water in the Mura-Zala basin, situated betweenSlovenia, Austria, Hungary and Croatia, is constantly increasing, with the sandygeothermal aquifer within the Neogene Mura formation being the most exploited.During the water concession granting process various problems were identified,together with the need for elaboration of the uniform concession granting prin-ciples. The latter were devised according to the specific hydrogeological settingsand field inspection of 23 geothermal wells, performed through use of an adaptedmethodology. The inspection revealed changes in wells performance, low efficiencyof energy abstraction and a lack of reinjection. The acquired information was appliedto the development of particular principles, including the six key indicators. Firstly, aunified and integrated operational monitoring programme must be established, andupgraded by a national surveillance monitoring. Secondly, an application of the bestavailable techniques is proposed. Stimulation of energetic and balneology efficiencyis also needed, with recharge and reinjection conditions evaluated and applied wherepossible. Limited or full water concessions could be granted based on their fulfilmentthen. This continuous step-by-step approach should enable the implementation ofadequate measures to meet the standards required for the thermal groundwaterbodies according to the EU water framework directions.

Keywords Water rights · Thermal water management · Geothermal well ·Operational monitoring · Sedimentary basin aquifer · Pannonian basin

N. Rman (B) · A. Lapanje · J. PrestorGeološki zavod Slovenije (Geological Survey of Slovenia), Dimiceva ulica 14,1000 Ljubljana, Sloveniae-mail: nina.rman@geo-zs.si

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1 Introduction

Management of geothermal resources is a complex task in Slovenia, with responsibil-ity partitioned between the government departments of water, energy and mineralresources. Although their action plans should work together to achieve a sustainableand effective development of geothermal resources, this is not the case. Implementa-tion of the Water Framework Directive (WFD; European Union 2000) has increasedthe number of water rights granted for a variety of utilization types in Sloveniaduring the last 10 years. However, the objective of attaining a good qualitative andquantitative status of thermal groundwater bodies appears to be endangered by thediscrepancies between current legislation and actions of the users. A brief history ofthis problem is described in the following paragraph.

All thermal water facilities were defined as a socialised property before theSlovenia’s independence in 1991. After, a transition of the socio-economic systemfrom socialism to capitalism took place and public property became private. Waterrights were granted as water permits on the basis of utilization facilities ownership,regardless of the status of geothermal resources. This happened between 1991 and2002, when the new Water Act according to the WFD (European Union 2000)was implemented. After 2002, all thermal water users were obliged to apply forconcessions during the following 2 years. The idea was that the existing water permitsshould be converted into concessions together with the new applications of as-yetnon-registered thermal water users. The granting process for geothermal aquifersin NE Slovenia started in 2006. However, local hydrogeological conditions meantthat the individual treatment was not possible, and many of the required data werenot available. In addition, some legislative problems occurred. Given the paucity ofliterature on the subject (Anonymous 1980; Crane 1991), the question of solving theimplementation of water rights in an objective manner remained. Beside, no timelimits were set for the granting procedure as it is a discretionary right of the State.Most of the activities ceased until 2008, when the Geological Survey of Sloveniabegan a geothermal utilisation screening in the Slovenian part of the Mura-Zalabasin in cooperation with the Ministry of the Environment and Spatial Planning. Astime passed, the Mining and the Water Act proved quite harmonious with activitiesassociated with the granting process subsequently slowly increasing.

At the beginning of this study, numerous administrative, legislative and scientificquestions connected to the granting activities arose. The work started with theidentification of expected problems as presented in the following Section 2. Thereview indicated that hydrogeological structure is of great importance thereforeit is discussed in Section 3. Moving on, more practical actions are consideredin a proper evaluation of the active, inactive and potential thermal water users.Consequently, methodology for field inspection of geothermal wells was developedand is presented in Section 4. It was applied to 23 wells of 12 thermal water users.The obtained results form a firm basis for a multiple-approach overview of both theusers and the wells. The best practice is identified or newly defined in Section 5. Thefindings are summarised within the newly developed principles for granting waterconcessions, which are presented in Section 6. We believe that the implementationof the proposed principles represents a scientifically-justified tool with which a goodthermal groundwater body status in NE Slovenia can be achieved according to theWFD (European Union 2000).

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2 Identification of Concession Granting Process Problems

Following the presented objectives, the first issue is to identify the current statusof the inspected geothermal aquifers and expected problems associated with theconcession granting process. The lack of precise geoscientific data is a direct conse-quence of poor monitoring application in Slovenia. As already stated, the geothermalaquifers exploitation is regulated by two ministries and legislations. The Ministry ofthe Environment and Spatial Planning manages the utilization via the Water Act(Anonymous 2002) and thermal water concessions. These users are predominantlythermal resorts and health centres that discharge waste water into the environment.The Ministry of the Economy manages the mineral resources via the Mining Act(Anonymous 1999, 2010) and mineral concessions, and the geothermal energy isadministratively defined as a mineral resource. These users are obliged to exploitgeothermal energy in doublet systems (i.e. water abstraction and reinjection). Theunclear relationship between these two legislative bodies complicates the legalsettings of concession decrees, with investors often applying for mining concessionsbut failing to set up geothermal doublets. A non-operating reinjection well is thecase with the district heating system in Lendava, and inexistent in the greenhouseheating system in Dobrovnik. The two Acts were in principle coordinated after2008. The users with mineral concessions are obliged to follow both legislations(mutual responsibility) and perform the production monitoring since then. It wasalso decided that all users abstracting water from the same aquifer are to beprocessed under the same requirements and concessions granted simultaneously.The only remaining problem is a lack of precedent cases, which would stimulatethe distribution of responsibility in this joint water concession granting procedure.We suggest that these shortfalls are amended by the Mining and Water legislationthroughout the strategic document and technical regulations as presented in thispaper.

Besides this rather political conflict, some discrepancies between the users in NESlovenia were also identified. Abandoned oil and gas boreholes were used to abstractthermal water at the beginning of spa resorts development, while boreholes drilledprimarily for geothermal purposes prevail only from the late 1980s. In the lattercase, users own the wells, while in the earlier examples this is not necessarily thefact. Due to this problem difficulties occurred when applying for water concessions,as no official agreement between the owners and the users exists. Therefore untilthe ownership and management issues are settled no concession application couldbe elaborated. It was attempted to overcome these disagreements in this study byexcluding the unofficial and unwritten distribution of water rights between the userson a first-come-first-served basis.

The third inconvenience is governed by the geological structure of NE Slovenia,positioned as it is on the western margin of the Pannonian basin, with the Mura-Zalabasin extending SW-NE (Fig. 3). Hydrogeological characteristics of the latter basinare described in detail in the following section. However, an emphasis on the needfor uniform treatment of the existing and potential new users can be given now, asthe same Tertiary aquifers are exploited for different direct-use purposes throughoutthe entire area of the basin. The overexploitation has already been identified in theMura formation aquifer in Murska Sobota (Kralj and Kralj 2000a; Kralj et al. 2009)and Radenci (Pezdic 2003).

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The research had to surpass a regional approach since the transboundary assess-ment and management of geothermal aquifers is conditional on the transboundarycharacter of water-bearing layers. The Republic of Slovenia has already identifiedand established a number of transboundary expert commissions which deal mostlywith cross-border surface water issues. The Slovenian-Austrian Mura commissionhas discussed a geothermal well drilled in Korovci in 2008, and prescribed a pumpingtest controlled by both sides a precedent case of this kind (Schmid 2010). A similarneed for transboundary management has also been recognised by some surfaceand shallow groundwater management authorities in the Balkans and SouthernEurope (Stevanovic 2008). The Mura-Zala basin is politically divided among fourcountries: Slovenia, Austria, Hungary and Croatia. The transboundary character ofgeothermal aquifers was first identified by the collaborative TRANSTHERMALproject (Götzl et al. 2008) between Slovenia and Austria, followed by the T-JAMproject (Nádor and Lapanje 2010; Rman et al. 2011) between Slovenia and Hungaryand supplementary work by the TRANSENERGY project (Szocs et al. 2010). Thispaper focuses on the Slovenian thermal water users only, as the Slovene governmentis currently in the process of granting water concessions. However, the proposedapproach is applicable world-wide and no major problems are expected with itstransmission to other countries.

The presented issues indicate the necessity of conducting a systematic and uniformresearch regarding all thermal water users in the inspected area, regardless of theirnatural, historical, legislative and transboundary affairs. After these problems wereidentified, a special attention was paid towards the site-specific field inspection ofusers. A similar approach has been taken by Hermans (2010), who investigatedtransfer of water policies between different countries. He also started with therecognition of local needs and problems, derived from interviews with local keyplayers. The necessity of joint expert and public cooperation in the transboundaryproblem identification, analysis and resolution has been previously described byMylopoulos et al. (2008). Their integrated methodology and tool system whichuses a similar bottom-up planning approach on an international, national and locallevel stands as a good example. We presume that this is also the case for transferof our methodology to other countries in the future, although we recognise thatdiscrepancies may arise and different approaches to some issues may be required(Ma et al. 2008).

3 Hydrogeological Setting of the Research Area

This investigation focused on the extension of the Mura-Zala sedimentary basinin NE Slovenia (Fig. 3), where the flatlands of the Mura River floodplain aresurrounded by the Slovenske gorice and Goricko hills (a few hundred metres higher).This area is currently exploited by 19 active geothermal wells, with three inactiveand one potentially active reinjection well also included in the investigation (Fig. 1).These 23 wells are used by 12 companies, whose operating information was acquiredin 2008 (Table 1). In addition to these wells, several abandoned oil and gas boreholesare present in the area (Vižintin et al. 2008) which could potentially be modified forthermal water abstraction or serve as monitoring wells.

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Fig. 1 Location of the investigated geothermal wells in NE Slovenia, their current production statusand prevailing captured geothermal aquifer (cross-section is shown in Fig. 2)

The Mura-Zala sedimentary basin, extending from NE Slovenia to westernHungary, is associated with the extensive Pannonian sedimentary basin (Fodor et al.2002). The Palaeozoic metamorphic basement is divided into several structural unitsextending NW-SE. The metamorphic rocks contain negligible quantities of thermalwater (Kralj 2001), although fissured metamorphic basement aquifers (according toHochstein 1988) are exploited in Benedikt and Maribor. The two locations werenot included in this research as they represent different aquifer systems. Narrowpatches of fissured and karstified Mesozoic carbonates with some thermal water andwellhead temperatures of between 80◦C and 150◦C have been identified in Korovci,Strukovci, Pecarovci, Ljutomer and Murski Gozd, but no exploitation is yet applied.

The pre-Tertiary sequence is covered by the Neogene clastic rocks which weredeposited in marine, brackish and freshwater environments and whose permeablelayers follow the geological stratification (Žlebnik 1978). These water-bearing layersrepresent the most important regional sedimentary basin (according to Hochstein

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Table 1 Inspected geothermal wells in NE Slovenia

Well Locality Well manager Drilling purpose Water use

Do-1/67 Dobrovnik Municipality Oil and gas No useof Dobrovnik research

Do-3g/05 Dobrovnik Ocean Orchids d.o.o. Geothermal Greenhouse heatingFi-14/57 Beltinci Municipality Oil and gas No use

of Beltinci researchLe-1g/97 Lendava Terme Lendava d.o.o. Geothermal BalneologyLe-2g/94 Lendava Nafta Geoterm d.o.o. Geothermal District heatingLe-3g/08 Lendava Nafta Geoterm d.o.o. Reinjection No useMo-1/58/73 Mala Nedelja Segrap, d.o.o. Oil and gas Balneology

researchMo-2g/08 Mala Nedelja Segrap, d.o.o. Geothermal Balneology & heatingMt-1/60 Moravske Naravni park Terme Oil and gas Balneology & heating

Toplice 3000 d.o.o. researchMt-4/74 Moravske Naravni park Terme Geothermal Balneology & heating

Toplice 3000 d.o.o.Mt-5/82 Moravske Naravni park Terme Geothermal Balneology & heating

Toplice 3000 d.o.o.Mt-6/82 Moravske Naravni park Terme Geothermal Balneology

Toplice 3000 d.o.o.Mt-7/93 Moravske Naravni park Terme Geothermal Balneology

Toplice 3000 d.o.o.Mt-8g/06 Moravske Pocitek-užitek d.o.o. Geothermal Balneology & heating

ToplicePt-20/49 Petišovci Terme Lendava d.o.o. Oil and gas Balneology

researchPt-74/50 Petišovci Terme Lendava, d.o.o. Oil and gas Balneology

researchSOB-1/87 Murska Sobota Komunala Murska Geothermal District heating

Sobota d.o.o.SOB-2/88 Murska Sobota Zvezda - Diana d.o.o. Geothermal Balneology & heatingT-4/88 Radenci Zdravilišce Geothermal Balneology

Radenci d.o.o.T-5/03 Radenci Zdravilišce Geothermal No use

Radenci d.o.o.Ve-1/57 Banovci Terme Banovci Oil and gas Balneology & heating

researchVe-2/57 Banovci Terme Banovci Oil and gas Balneology

researchVe-3/91 Banovci Terme Banovci Geothermal Balneology & heating

1988) geothermal aquifers in Slovenia (Fig. 2). The Neogene aquifers are in generalconfined (Lapanje 2006), although to the north-west, where they are in contact withthe Quaternary aquifers or where the sand and sandstone layers outcrop, the un-confined characteristics are observed. Nevertheless, the confined nature grows moreevident with distance from the potential recharge area, and moreover the piezometricheads between different formation aquifers most probably do not coincide. Artificialconnection between the aquifers is distinctive in wells that exploit more than oneaquifer what has already been proven in three wells. The only natural outflow fromthe Neogene aquifers has been identified in Radenci, where the fracture zones enable

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Fig. 2 Schematic cross-section of the hydrogeological units in the Mura-Zala basin in the NW-SEdirection

inflow of large quantities of mineral water (cooled thermomineral water) that hasbeen exploited for more than a century.

The lowermost Neogene rocks form the Špilje and Haloze formation aquifer(Jelen et al. 2006), previously known as the Murska Sobota aquifer (Kralj and Kralj2000b), which is of the Carpatian to Lower Pannonian age. The water-bearing layersare a few tens of metres thick, with rather low porosity and permeability due tocompaction and cementation. Fissured porosity of sandstone and breccia prevails,with oil and gas traces often found in permeable layers isolated in half-trenches. TheLendava formation aquifer of the Pannonian age (Jelen et al. 2006) is situated abovethe Špilje & Haloze formation. Its rather thin turbiditic sandstone deposits are oflow porosity and permeability, and do not represent a very important geothermalaquifer. The Mura formation aquifer of the Pannonian to Pontian age (Jelen et al.2006) is deposited above and produces thermal water of temperatures up to 65◦C.This intergranular aquifer of the sandy part of the deltaic system is made of up toone hundred metre thick intercalations of sand in silt and clay. The sandy layers areinterconnected, exhibit good porosity (up to 30%), hydraulic conductivity (in therange of 10−5 to 10−6 m/s) and momentary yields of up to 60 l/s. Some of the wellsin this aquifer have already been proven to be hydraulically connected (Kralj 2001;Pezdic et al. 2006). The water demand is constantly increasing in the latter aquifer,mostly due to the absence of technological problems such as degassing or scaling.The presented Neogene aquifers are the main subjects of this research.

The Miocene aquifers are often covered by the sandy and gravely PliocenePtuj formation (Jelen et al. 2006) geothermal aquifer, separated from them bythick layers of clay. It shows similar hydrogeological characteristics to the Muraformation aquifer, but it is considerably thinner and the thermal water tends tobe less mineralised and colder due to its shallower position. Geothermal wells thatexploit this aquifer were excluded from this research. However, two are active in Ptujand already indicate overexploitation. Above the Neogene aquifers, the Pliocene-Quaternary and Quaternary alluvial aquifers occur under the water table conditions.Highly permeable gravel is deposited in a few tens of metres thick layer. Fresh

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groundwater flows in the NW-SE direction and is hydraulically connected to theMura River.

The Slovenian groundwater bodies (GWB) were delineated and characterisedaccording to WFD (European Union 2000) and Slovenian regulation in 2005(Anonymous 2005b). Their extent was determined according to porosity and lithol-ogy boundaries, productivity, spatial delineation, catchment basin boundaries, flowlines, interstream boundaries, junctions with large affluents, recovering and poten-tial use boundaries (water protection areas), tracer experiment results, as well asboundaries of significant pressures. The latest hydrogeological map (1:250,000) wasused as a cartographic basis for their delineation, being elaborated by implementingthe international recommendations and standard legend as proposed by the IAH(Struckmeier and Margat 1995).

The Slovenian groundwater bodies are currently delineated only by surfaceboundaries. The thermal groundwater body of the Mura-Zala basin (Fig. 3) hasbeen identified and characterised within the six groundwater bodies (the Sloveneabbreviation is VTPodV): 4018 Goricko, 4016 Murska kotlina and 4017 VzhodneSlovenske gorice in the Mura River basin, and 3015 Zahodne Slovenske gorice, 3012Dravska kotlina and 3014 Haloze and Dravinjske gorice in the Drava River basin.The identified geothermal aquifer types in the Mura-Zala basin include the follow-ing: geothermal aquifers in the deeper Neogene sediments and Pre-Tertiary carbon-ate or metamorphic basement rocks; aquifers in the shallower Neogene sedimentswith fresh or thermal water; alluvial fresh water aquifers in the Mura and DravaRiver plains of the Quaternary age. The thermal groundwater body of the Mura-Zala

Fig. 3 Delineation of the water bodies in NE Slovenia in 2010

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basin has not yet been delineated in the third dimension, but only significant changesin stratification have been noticed. All thermal groundwater bodies are being delin-eated progressively as part of the actual water concession granting procedure for theindividual user.

4 Field Inspection Methodology

It was attempted to overcome problems and hydrogeological factors governing thewater concession granting process in NE Slovenia via the development of a clear,systematic and objective methodology for distribution of the water rights, regardlessof the historic, ownership, legal or transboundary issues. In the first phase, screeningof site-specific data was performed through the field examination of 23 geothermalwells (Table 1) of the 12 users. The applied methodology included interviewswith the well’s and exploitation system’s maintenance staff, visual inspection ofwellheads and direct use systems, field measurements of water temperature, leveland yields, and an overview of hydrogeological reports. Valuable technical, hydroge-ological, production, monitoring and waste water management data were compiled inthis way.

4.1 General Well Status

Technical data consisted of the well’s location, manager, drilling purpose, direction,depth, wellhead and direct use system status. These data were grouped in order torecognise poor maintenance and to identify possible risk factors.

4.2 Hydrogeological Data

Information regarding the exploited formations, screening depths, performed pump-ing and interference tests and performance changes was gathered here. The inter-pretation was carried out by grouping wells which exploit the same formations,identifying their characteristics and analysing pumping tests results.

4.3 Exploitation Characteristics

This included data associated with the water utilization, mode of operation (perma-nent/temporary), exploitation characteristics (outflow/pumping, pump type, capac-ity, depth), annual production (2007, 2008, submitted in water concession) and wastewater management. The results were analysed by individual aquifers and as a whole.

4.4 Operational Monitoring

Observed operational monitoring parameters were: presence, location, type andrecording characteristics of the installed pressure, water level and temperaturetransducers; flow meters; outflow valves at the wellhead that enable in-situ chemicalsampling and date of the last chemical analysis. Waste water monitoring data werealso included in this dataset, with observations made as to how its treatment wasperformed and whether the quantity and quality of the emitted water was monitored.

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4.5 Energetic and Balneological Efficiency

A distinction between energetic and balneological efficiency of thermal water utiliza-tion was made. The difference between used and available heat energy (Eq. 1) wasevaluated in the first case.

Ei = Vaa · 4.18kJ

kgK�T, (1)

where Ei, Vaa and �T are the used or available annual heat energy, average annualproduced thermal water and temperature difference, respectively. For the usedheat energy, difference between the wellhead temperature and that of the outletwaste water was taken. For the available heat energy, the outlet water temperaturewas assumed to be 12◦C, as this is defined in already granted concession decrees(Anonymous 2004, 2008). The energetic efficiency was calculated by Eq. 2.

η = Twellhead − Toutlet

Twellhead − 12◦C, (2)

where Twellhead and Toutlet correspond to the aforementioned parameters.Different combinations of annual produced thermal water, annual number of

bathers and swimming pool volumes were checked for the balneological efficiencyin order to obtain representative estimates.

5 Field Inspection Results and Discussion

Accurate interpretation of the obtained data should lead to a comprehensive assess-ment of current state of the thermal water availability and its users.

5.1 General Well Status

The observed geothermal wells are located in the Slovenske gorice hills and the MuraRiver plain. Eight were drilled for oil and gas research, 14 are geothermal and 1 is apotential reinjection well. Only 3 are deviated and all are shallower than 2 km.

Wellheads in shafts and above-ground are mostly well maintained, as poor mainte-nance was identified only in three cases. Older pipe work is constructed of iron, whileat newer wells plastics prevail. The pipeline is poorly isolated in both cases. Calcitescaling occurs in four wells. The problem is mitigated by the injection of inhibitorsinto three wells, while at the fourth the separated CO2 gas is captured and returnedinto the water in order to adjust its pH value and prevent scaling. If the wellheadoutflow valves are positioned before the degassing unit, quality chemical samplingis enabled. Unfortunately, only 17 of the 23 wells have such valves installed. Theexploitation system is only rarely based on the principles of cascade use. The emittedwater still has a rather high temperature (approximately 30◦C) at which it could beused for another purpose.

5.2 Hydrogeological Data

The inspected geothermal wells exploit quartz sand or sandstone water-bearing lay-ers (Table 2). More specifically, the Mura formation aquifer is tapped by eight wells,

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Table 2 Hydrogeological properties of the inspected geothermal wells in NE Slovenia

Well Screened Prevailing Multiple Hydraulicinterval productive aquifers connection(m bWHD) aquifer tapped between wells

Do-1/67 931–1874 Mura formation sand No Do-1/67 & Do-3g/05Do-3g/05 1022–1570 Mura formation sand No Do-1/67 & Do-3g/05Fi-14/57 1046–1881 Mura formation sand Yes no testingLe-1g/97 735–1458 Mura formation sand Yes no testingLe-2g/94 813–1493 Mura formation sand Yes Le-2g/94 & Le-3g/08Le-3g/08 720–1216 Mura formation sand Yes Le-2g/94 & Le-3g/08Mo-1/58/73 845–1107 Mura formation sand No Mo-1/58/73 & Mo-2g/08Mo-2g/08 893–1513 Mura formation sand Yes Mo-1/58/73 & Mo-2g/08Mt-1/60 1115–1234 Špilje & Haloze f. sandstone Yes not provenMt-4/74 1176–1263 Špilje & Haloze f. sandstone No Mt-4/74 & Mt-5/82Mt-5/82 1090–1246 Špilje & Haloze f. sandstone Yes Mt-4/74 & Mt-5/82Mt-6/82 720–974 Mura formation sand No Mt-6/82 & Mt-7/93Mt-7/93 751–985 Mura formation sand No Mt-6/82 & Mt-7/93Mt-8g/06 651–906 Mura formation sand No no testingPt-20/49 817–909 Mura formation sand Yes Pt-20/49 & Pt-74/50Pt-74/50 701–833 Mura formation sand No Pt-20/49 & Pt-74/50SOB-1/87 550–870 Mura formation sand Yes SOB-1/87 & SOB-2/88SOB-2/88 601–848 Mura formation sand Yes SOB-1/87 & SOB-2/88T-4/88 400–542 Špilje & Haloze f. sandstone No no testingT-5/03 705–792 Špilje & Haloze f. sandstone No no testingVe-1/57 1252–1363 Mura formation sand No Ve-1/57 & Ve-2/57 & Ve-3/91Ve-2/57 1175–1570 Lendava formation sandstone Yes Ve-1/57 & Ve-2/57 & Ve-3/91Ve-3/91 1111–1467 Mura formation sand Yes Ve-1/57 & Ve-2/57 & Ve-3/91

nine tap both the Mura and Lendava formation aquifers, one mostly Lendava, threemostly Špilje and Haloze, and two wells tap water from the Lendava plus Špilje &Haloze formation aquifers. Screening depths range from 400 to 1,880 m below theground, depending mainly on well location.

The conducted study has confirmed the assumption that some wells tap resourcesfrom multiple aquifers. This is not only a management problem since it is in a conflictwith WFD (European Union 2000) incentives, but also creates certain hydrologicaldifficulties. Free water flow between different water-bearing layers in a single wellhas already been observed in two wells in Murska Sobota (Kralj et al. 2009) and inone in Lendava. Based on our research, in-well flow might occur in 12 wells; in twobetween the Špilje and Haloze and Lendava formation aquifers, and in ten betweenthe Lendava and Mura formation aquifers.

Pumping and/or outflow tests were performed at all wells, but in 65% theylasted less than 30 days, while in 9% no data regarding their duration is available.Interference tests were completed at fifteen wells that predominantly exploit theMura formation aquifer and indicated that the screened layers are hydraulicallyconnected.

Well’s yield depends on its technical specifications and the respective aquifer’shydraulic conditions. These data were gathered from the hydrogeological reportsfor water concession applications. The wells tapping the Mura formation aquiferhave recommended yields of 4–35 l/s, but short-term yields can reach 60 l/s in some

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places. The Lendava formation aquifer has much less favourable hydraulic conditionsand therefore the recommended average yield is below 2 l/s per well, while theshort-term maximum is 4 l/s. The Špilje and Haloze formation aquifers have highervalues; 2–10 l/s for short-term exploitation and 2–4 l/s on average. The reported op-timum and maximum abstraction rates are usually determined only via the technicalspecifications and short pumping tests. This results in overestimated quantities of theavailable thermal water for an individual user, as the figure is actually limited bythe aquifer’s volume and interference between the wells. Moreover, no numericalestimation of the total available thermal water volume in geothermal aquifers inthe Mura-Zala basin is currently available. It is ascertained that these aquifers arealready overexploited as changes in wells are obvious (Table 3, column 3). However,it is not yet possible to discuss any specific figures. In order to do so, pumping testsshould be performed systematically and following the required standards (ISO 2003).Besides, the recommended newly applied annual monitoring interpretation shouldeventually provide a reliable estimation of the available thermal water.

Geothermal aquifers utilization can become more sustainable if reinjection iscarried out. There were some efforts to introduce reinjection practices into the Muraformation aquifer before 2000, but only small quantities of the abstracted water wereinjected into the well Mt-7 for a limited period of time (personal communication).Now, the well is used for production. Although the reinjection is already a legalobligation for two users who claim to exploit geothermal energy and following theMining Act, it is not applied in practice. A reinjection well in Lendava should receive

Table 3 Exploitation characteristics of the inspected geothermal wells in NE Slovenia

Well Production Production Max. water Max. momentarymethod changes temperature (◦C) yield (l/s)

Do-1/67 Inactive Yes 55 14Do-3g/05 Pumping Yes 61 60Fi-14/57 Inactive No 61 25Le-1g/97 Pumping Yes 62 18Le-2g/94 Pumping Yes 66 50Le-3g/08 Inactive (reinjection) No 60 −50Mo-1/58/73 Pumping Yes 43 6Mo-2g/08 Pumping No 50 6Mt-1/60 Natural outflow Yes 75 5Mt-4/74 Natural outflow Yes 75 4Mt-5/82 Natural outflow Yes 72 16Mt-6/82 Pumping Yes 61 64Mt-7/93 Pumping Yes 56 26Mt-8g/06 Pumping Yes 58 25Pt-20/49 Pumping Yes 52 12Pt-74/50 Pumping Yes 45 13SOB-1/87 Pumping Yes 51 25SOB-2/88 Pumping Yes 51 22T-4/88 Natural outflow Yes 40 10T-5/03 Inactive No 52 4Ve-1/57 Pumping No 63 5Ve-2/57 Pumping Yes 68 5Ve-3/91 Pumping Yes 62 13

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waste water from the district heating system, but it does not operate. In the secondcase, the reinjection well which should receive waste water from the greenhouseheating system is not even drilled. However, it must be kept in mind that the thermalwater used in open systems, such as swimming pools etc., cannot be returned toaquifers due to its altered chemical and microbiological composition, and so thereinjection can never be total for these users.

5.3 Exploitation Characteristics

The hydraulic data have confirmed that the Mura formation aquifer is and will bethe most exploited geothermal aquifer in the region. This investigation included11 geothermal wells that are permanently in operation, eight of which are activeonly in winter, three inactive and one reinjection well (Table 3). Only four activewells produce water by natural outflow via thermal- and/or gas-lift, while pumpingis required in the remaining ones. Depth of the installed pumps varies between 36and 158 m below the wellhead. As the highest abstracted thermal water temperatureis 75◦C, the exploitation systems are designed for direct use. Space and/or waterheating combined with balneological use of the cooled thermal water (swimmingpools, therapeutic use) prevails, while only the latter is rare (Table 1).

The maintenance staff reported changes in 10 wells. Additionally, they wererecognised via a comparison of the measured parameters as reported by differentpumping tests in eight wells. Changes are usually expressed as lower yields, lower dy-namic water levels, lower water temperatures and changes in chemical compositionof the thermal water. Unfortunately, the changes are not continuously monitoredtherefore a systematic data interpretation is hard to apply. If we presume that thetechnical specifications remain unchanged since their installation, the changes inoperation can only be a result of hydraulic changes in aquifers and/or greater demandfor thermal water abstraction. These reasons indicate that only unified manage-ment of all users exploiting the same geothermal aquifers in the Mura-Zala basin isreasonable.

Changes in geothermal aquifers can with certainty be attributed to the increasedthermal water demand which has risen rapidly in the last few years (Fig. 4). Theabstracted volume rose by more than 0.5 million cubic meter from 2007 to 2008, whenit exceeded two million cubic meters. The growth mostly affects the Mura formationaquifer. Deeper aquifers are not subjected to such large changes because the waterhas high mineralization and lots of gas, and therefore is much harder to use.

Two parameters can be used for future forecasts. The projected production after2008 is a predicted value with which users expressed their near-future plans. Incontrast, the quantities submitted in the water concession applications are officiallyreported values. These quantities differ by almost a million cubic meter. One of thereasons for this is that a new well has been drilled and put through a testing phase, sowater concession has not yet been asked for. Another reason is that a few new users,who do not plan to use thermal water in the very near future, are still asking for waterconcessions. Moreover, some existing users applied for much higher quantities in theconcessions than they plan to actually exploit in the future. In general, the thermalwater abstraction rose by one third from 2007 to 2008, from 1.55 to 2.17 million cubicmeters and is expected to rise further to over four million cubic meters. If all waterconcessions are granted unconditionally, the total abstraction could rise to over 5.2

3290 N. Rman et al.

Fig. 4 Thermal water abstraction in 2007, 2008 and the expected in future

million cubic meters per year, of which the Mura formation aquifer will contributemore than 90%.

Together with the rising production, the volume of waste water has simultaneouslyincreased. However, it should be stated that direct use systems installed in NESlovenia differ. In greenhouses and spatial heating systems, thermal water is isolatedfrom the surroundings and only its heat is used. In contrast, cascade use is commonin thermal resorts. There, thermal water is first used for space and water heating,and afterwards to fill swimming pools—either as pure thermal water or mixed withcold fresh water before being released into pools. As a consequence, both theunmixed and the mixed water are being released into the environment. Most wastewater is not treated specifically before it is emitted to streams which eventuallyrecharge the River Mura. The average annual emitted waste water temperature isbetween 27◦C and 30◦C, the latter being the legally allowed maximum in Slovenia(Anonymous 2005a). Only one user cools waste water to 15◦C. This is achieved byheating rainwater, which is later used for watering plants.

5.4 Operational Monitoring

Results of the investigation show that the operational monitoring is only rarely satis-factorily managed. Discrepancies between the demand for automatically performedand constantly recording monitoring and the actually installed systems can be seenin Table 4. The computer-managed systems usually support the display of presentvalues, but recording is often not carried out and therefore no long-term analysis ofparameters can be made. Since all four inactive wells do not have any permanentlyinstalled monitoring equipment, they are excluded from Table 4.

Groundwater level and temperature transducers are not installed in almost half ofthe wells, with these parameters monitored and recorded only in the newer. Olderwells tend to have analogue pressure and temperature probes at the wellheads, whichdisplay only momentary values. Water temperature is often measured digitally in

Water Concession Principles for Geothermal Aquifers 3291

Table 4 Installed monitoringdevices in the activegeothermal wells

Monitored Not measured Measured, Measured,parameters not stored stored

Groundwater level 11 6 2Wellhead pressure 3 16 0Temperature 10 7 2

(in well/at wellhead)Temperature 4 8 7

(in engine room)Water yield 4 7 8

the engine room, where recording also takes place. In terms of water yield from theindividual wells, two issues were observed: one well does not have any flow metersinstalled, while another three are jointly measured by a single meter and thus noindividual values are available. For the remaining 15 wells cumulative values areavailable, but momentary measurements are recorded for only eight of them.

Chemical analysis of pure thermal water is rarely undertaken on an annual basis.Very poor data are available for four wells, where the last chemical analyses werecarried out more than 12 years ago. Chemical analyses of the remaining 11 wereundertaken in the last 3 years, and for the other four in the last 8 years.

Current monitoring, performed and controlled by the users themselves, is mostlyunsatisfactory. Failures of the installed monitoring devices are a commonplace,which results in unwanted additional costs and permanent loss of valuable data.Failures are mainly caused by the elevated water temperatures and salinity, CO2 gaseruptions, scaling or other mechanical problems. All of this indicates that an area-wide evaluation of the geothermal aquifers using only the existing monitoring data isnot feasible.

5.5 Energetic and Balneological Efficiency

Heat from thermal water is obtained in three ways by users in NE Slovenia: by plateheat exchangers (68%), heat pumps (11%) or systems combining both (16%). Inaddition, water from one well is used only in swimming pools. The total installedcapacity of the 23 wells was 87 GWht in 2007, with an energetic efficiency of 65%,and 119.3 GWht at 66% efficiency in 2008. Comparison of the available and usedheat energy, calculated separately for different utilization, is presented in Table 5.

Table 5 Used and available heat energy of thermal water in NE Slovenia in 2007 and 2008

Use of thermal water Used energy Available energy Average energetic

TJ/year kWh/m3 TJ/year kWh/m3 efficiency %

Balneology 2007 2.5 13 5.3 31 48Balneology 2008 17.6 17 30.5 35 58Heating 2007 24.8 39 32.0 55 78Heating 2008 77.3 39 101.9 56 76Balneology & Heating 2007 175.6 35 275.6 56 64Balneology & Heating 2008 187.0 34 297.1 55 632007 Total 202.9 32 312.9 50 652008 Total 281.9 30 429.5 49 66

3292 N. Rman et al.

Table 6 Balneologicalefficiency parameters in 2007

Thermal Bathers per Bathers per Availableresort pool volume abstracted water thermal water

Person/year/m3 Person/year/m3 m3/person/day

Segrap 21.4 1.6 3.8Radenci 198.8 16.0 0.1Banovci 61.1 1.6 0.6Terme 3000 79.6 0.6 1.7Pocitek-užitek 53.8 0.8 1.3Zvezda-Diana 96.7 1.0 1.0Lendava 145.6 1.0 1.0

The results show that the energetic efficiency of above 75% is achieved wherethe water is used for space and/or water heating only. A rather low efficiency rateis observed in places where it is used for balneological purposes only. The energeticefficiency for individual wells varies from 27% to 94%, with a mean of around 65%.The most important parameter controlling it is the temperature of waste water. Theefficiency cannot improve as long as it stays around 30◦C.

When estimating the balneological efficiency a comparison between the thermalresorts was made as shown in Table 6. As precise data on average annual batherswere available only for 2007, the annual thermal water abstraction and swimmingpool volume in 2007 were used to calculate the following ratios.

Thermal resorts usually use water for both heating and bathing, and thus it isnot currently possible to make realistic estimations of the balneological efficiency interms of the reported parameters. More representative indicators could be obtainedif additional data on utilization were available, such as swimming pool temperaturesand actual yields. A value of 10 m3 of water per person per day (Anonymous 2003)is defined as the minimum limit for pool water not to require disinfection in theSlovenian legislation. Because this value is lower in all inspected cases, the usersare obliged to disinfect their water. We suggest that this parameter is used also toestimate the balneological efficiency.

6 Water Concession Granting Principles

Information acquired in this study was applied in determination of six key indicatorsrepresenting the assessment criteria for water concession granting process, regardlessof the utilization type. Firstly, the operational monitoring which should as soon aspossible be upgraded by a national surveillance monitoring is proposed. It should befollowed by an application of the best available techniques for thermal water abstrac-tion and utilization. In addition, the energetic and balneological efficiencies mustbe at least as high as suggested. The reinjection potential should be evaluated andreinjection applied where possible. Last but not least, the operational and nationalsurveillance monitoring results should serve as an input data for a comprehensiveassessment of recharge and trends, elaborated annually by numerical modellingtechniques involving water flow, heat and transport simulations. Based on annualverification of the presented indicators, temporary or long-term water rights shouldbe granted and re-distributed when necessary.

Water Concession Principles for Geothermal Aquifers 3293

6.1 Operational Monitoring

The first and most important key indicator is a mandatory, unified and integratedoperational monitoring. It has to be implemented by the user and consist of thecontinuous recording of groundwater level or wellhead pressure, water temperature,yield and chemical composition or conductivity (Axelsson and Gunnlaugsson 2000).The latter can be checked by annual chemical analysis, but only if the variationof chemical composition is not presumed. Chemical sampling and its interpretationshould follow the Groundwater Daughter Directive (European Union 2006). Wherereinjection takes place, the required measurements should be also performed atthe reinjection wells. The monitoring results should be interpreted annually, byindividual users and on a regional scale. These data should eventually be combinedwith results derived from the newly established national surveillance monitoring ofthe deep geothermal aquifers. It is proposed that this should become an obligation forboth the users and the state since the data obtained in terms of the abstracted thermalwater, changes in aquifers and regionally available thermal water will be used to assistin distribution of the hydrogeologically acceptable thermal water concessions.

In order to monitor aquifer changes, systematic build-up tests are recommendedalthough different approaches can be taken. In the transboundary Lower Bayern–Upper Austrian Molasse basin (Büttner et al. 2002), wells are shut every Tuesday at4 p.m. for 15 min. The recovered wellhead pressure or groundwater levels are mea-sured then. Weekly values are averaged to monthly and graphical trends are observed.The alternative is to measure the difference in ground water level 15 min before andafter the well is closed. Vižintin et al. (2008) proposed that build-up tests should be un-dertaken annually, with producing wells shut for 6 h. Whichever approach is agreedupon and used in Slovenia, its continuous execution and interpretation are essential.

6.2 Best Available Technology

Encouragement of best available technology application is proposed, as this willhave a direct impact on decreasing the need for thermal water, increasing efficiency,mitigation of potential system failures as well as diminishing environmental pollu-tion. Appropriately managed geothermal wells should have well-maintained well-heads which are isolated and protected from unfavourable weather conditions andunauthorised persons. Materials installed in and above the well should be inert foraggressive water/gas mixtures and higher temperatures, while scaling problems couldbe effectively mitigated by injecting inhibitors. Installation should avoid areas ofgas or water leaks and include the placement of a water release valve before thedegassing unit at the wellhead. If pumping is required, computer-managed frequencypumps are recommended. Exploitation system should be based on the principles ofcascade use, computerised and controlled as much as possible. Supporting technical,lithological, hydrogeological and chemical documentation should be well-kept andregularly updated.

6.3 Energetic Efficiency

Only one user cools thermal water to 15◦C, which is a little higher than the mean an-nual air temperature (12◦C), but this should be repeated by others. Higher energetic

3294 N. Rman et al.

efficiency should lead to lower thermal water abstraction as well as lower thermaland chemical pollution of the surface streams into which waste water is emitted. Toindicate a good energetic efficiency, a value of at least 70% usage of the availableenergy should be reached, with most wells already achieving levels of around 65%.This means that if the wellhead temperature is 60◦C, the emitted waste watershould have a maximum of 26.4◦C, while if the wellhead temperature is 40◦C, thetemperature should be below 20.4◦C.

6.4 Balneological Efficiency

The only indicator of balneological efficiency that could be derived from the reportedutilization parameters is the volume of available pure thermal water used in swim-ming pools. A value of 10 m3 per bather per day, which is the limit above which thepool water does not need to be disinfected, should not be exceeded by anyone whouses thermal water for swimming or balneology.

6.5 Feasibility of Reinjection

A few issues must be addressed with respect to the feasibility of reinjection. Thereinjection operated in Moravske Toplice for a limited period of time (as mentionedin Section 5.2). Therefore it is not expected to be difficult to apply at otherlocations characterised by similar hydrogeological conditions, such as Lendava andDobrovnik. Where closed thermal water exploitation systems are used, all water canbe returned into the aquifer—although probably more than one reinjection well willbe required. Only non-treated thermal water from open systems can be returned intothe aquifer therefore fewer reinjection wells will be needed in this case. Secondly,reinjection wells represent a large investment cost, which is not currently feasiblefrom a user’s point of view as exploitation problems are not severe. Indeed, eventhough the reinjection is already a legal requirement for two users following theMining Act, it is not applied.

From our point of view, the reinjection should be required for all users utilisingnon-treated thermal water as it has a relevant positive effect to aquifer’s hydraulicconditions and environmental pollution mitigation. Current users should be given alimited period of time for its implementation, while new users should establish thesystem before production. This should be based on numerical simulations and cost-benefit analyses, but poor economic conditions should not be used as an excuse forinactivity.

6.6 Recharge of Geothermal Aquifers and Numerical Modelling

The need for reinjection is partly conditioned by the natural recharge of geothermalaquifers. Estimation of the latter is heavily dependent on the quality and availabilityof regional hydrogeological data which are rather poor, as discussed in Sections 5.3and 5.4. Better estimates should be obtained when the national surveillance moni-toring programme is implemented by the Slovene Environmental Agency (ARSO),which will combine data from the operational and national monitoring. Newly drilleddeep geothermal wells at optimum locations can be used for national monitoringwhen made, although a scenario involving a combination of the existing and re-drilled

Water Concession Principles for Geothermal Aquifers 3295

abandoned oil and gas boreholes is much more feasible. Annual data should beanalysed at least every 3–5 years, as in this period trends should become evident(Goldbrunner et al. 2007). Until a regional numerical model of the Mura-Zala basinis established, this monitoring scheme and analysis should represent a sufficient toolfor supervision and adjustment of the granted concessions.

As soon as sufficient monitoring data for the Mura-Zala basin are available, anationally managed regional numerical model of flow and heat transfer in geother-mal aquifers should be established. Simulation results should enable estimation ofthe available thermal water reserves in individual aquifers, which will furthermorerepresent an expert basis for redistribution of water concessions. As such, themodel should be integrated and continuously re-evaluated in order to manage thegeothermal aquifers in a sustainable way. National guidelines for geothermal wellsshould also be prepared, in which uniform instructions for construction, operationand closing of a geothermal well are discussed, as outlined by Büttner et al. (2002).

6.7 Principles of Water Concession Granting

Problems and special circumstances arising during the concession granting processwere discussed in the previous sections together with the proposed concession require-ments. In this section it will be demonstrated how the distribution of water rightsshould be conducted. Based on the Water Act, the users must not deteriorate the ex-isting quantitative and qualitative conditions of each individual groundwater body.As already mentioned in Section 5.3, the thermal water demand outlined in submittedconcession applications is at least twice the current abstracted value. As a conse-quence, changes in geothermal aquifers are likely to occur and thus the water conces-sions should be issued in such a manner that rapid identification of changes is possible.

We propose that each geothermal well for which any kind of water concessionis granted has to satisfy the six key indicators, as outlined in Section 6. However,more than just these numerical indicators are required. We believe that from timeto time the implementation and ef fectiveness of the granting policy process should bechecked and adjusted as recommended by De Stefano (2010). Fulfilment of the sixkey indicators should be evaluated annually for all concessioners, together with theregional numerical simulation of geothermal aquifers. This should be followed bythe adjustment of granted water concessions if necessary (Fig. 5). If fully performingsite-specific operational monitoring has not been established and operating for aperiod of 1 year, no new capture of thermal water should be allowed. Until themonitoring is implemented, only reinjection research may be conducted. In any case,the abstraction exceeding the available reserves is not allowed, with each aquiferformation treated individually.

Existing thermal water users are recommended to be granted an adjustment periodof 1 year from the date of issuing a temporary water concession for demandedquantity, to fulfil the requirements of the latter. Until then, and especially not beforethe results of the 1-year fully performing operational monitoring of all users showgood aquifer conditions, no increase in thermal water abstraction (exceeding currentlevels of water exploitation) should be allowed.

New thermal water users should fulfil all the above requirements before theproduction starts. The submitted quantity should be abstracted in the first year ofproduction and for this test period a temporary water concession should be issued.

3296 N. Rman et al.

Fig. 5 Water concession granting procedure scheme

If annual evaluation of the six key indicators shows good geothermal aquiferconditions, a long-term concession for tested quantity can be issued. For any increasein quantities or changes in other requirements, a 1-year temporary water concessionshould be granted in order to acquire information as to their impact on the aquifer.

In contrast, if any of the requirements is not reached or negative impacts onthe geothermal aquifer are identified, the responsible user should be ascertained.His water rights should be reduced or cancelled and a new 1-year temporary waterconcession for reduced quantity issued. If the responsible user is not detected, allusers in the potential influential area should be treated in the latter way, and ifneeded, issued with proportionally diminished water rights.

We are aware that a time period of 1 year as defined in temporary water con-cessions is, hydrogeologically speaking, not sufficient to make founded judgements.However, we believe that the proposed annual evaluation demanded for all waterconcessionaires, encourages continuous annual control over the fulfilment of thepresented requirements. Therewith the longer the time interval of observation thebetter the time series of monitored data, numerical modelling simulation resultsand predictions will be. This continuous supervision will enable early recognitionof changes and give time to undertake proper measures to mitigate them.

7 Conclusions

The review of the measures required for the water concession granting process pre-sented here has shown that it is possible to conduct a granting procedure disregardinggeological, historical, legislative and transboundary issues that may occur. Six key

Water Concession Principles for Geothermal Aquifers 3297

indicators have been outlined which can be used collectively as an objective tool forwater rights distribution, and may serve as minimum performance requirements. Wepropose that operational and national monitoring, best available technology, analysisof energetic and balneological efficiency, reinjection feasibility and aquifer rechargeare adopted as basic numerical indicators for the evaluation of geothermal aquifersin the Mura-Zala sedimentary basin. If their implementation is checked annuallyand granted water concessions accordingly adjusted, these activities should enableefficient control over the thermal water availability. As a result, early measureshelping to diminish any possible negative impact on the aquifers could be taken.These actions should help to meet the standards required for thermal groundwaterbodies according to WFD (European Union 2000). We propose that all geothermalresources are managed by the concordant actions of the Water and the Energysectors, and controlled by the national Environmental Agency.

The proposed actions were submitted to the Ministry of the Environment andSpatial Planning, and are in the implementation phase. However, from a hydroge-ological point of view this is not enough. As already argued in this paper, a stronghydrogeological presumption exists that the Neogene geothermal aquifers in theMura-Zala basin extend into Austria, Hungary and Croatia. Despite the fact that thetransboundary effects have not yet been thoroughly investigated, it can be assumedthat simultaneous investigation and actions are required in all countries in order tosustain the health of these thermal groundwater bodies in the future.

Acknowledgements This research was financed by the Ministry of the Environment and SpatialPlanning (contract no. 2511-08-200084) and the investigated thermal water users.

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