J. Pezdič, G. Vižintin, N. Gerič, T. Verbovšek University of Ljubljana

1. Dependence between Exploitation, Recharge and Pollution Sensitivity of the Deep Aquifers: Case Study in Pomurje, Slovenia J. Pezdič, G. Vižintin, N. Gerič, T. Verbovšek University of Ljubljana NTF, Department of Geology, Slovenia

2. Scope • Integrated and sustainable water resources management focused to mass and energy transport during the exploitation of deep aquifers. • Geochemical and stable isotope composition of thermal waters of selected deep wells in SW part of Pannonian basin in Slovenia. • The cascade treatment of available energy and mass capacities, with possible uses of thermal water in the studied region.

3. Location and geology • Q – Quaternary alluvial deposits • Pl – Pliocene clastic sediments (gravel, sand, silt, clay and tuff) • M – Miocene clastic sediments and poorly consolidated rocks • Pz – Paleozoic low grade metamorphic schists

4. Structure

5. Reservoir parameters • Thermal gradient: very high, between 45 and 80 °C/1000 m. • Water temperature: between 9 °C (mean annual T) up to 73 °C. • Geothermal waterreservoir: • Miocene sandstones with medium permeability (800 – 1200 m). • Fractured heterogeneous Mesozoic carbonates with great permeability and high mineralization(2000 – 5000 m). Water temperature from these reservoirs is high (120 – 230 °C) and it is not exploited jet. • Precipitation: 700 to 900 mm/year (low compared to other parts of Slovenia) • Hydraulic conductivity: 10-5m/s to 10-4m/s for “Mura formation” (upper part of Tertiary sediments). • Thickness of permeable strata: from 20 to 80 meters (from electrical log).

6. Methodology • Chemical and isotope (O, H, C) analyses from six deep wells in years 1994 - 2004. • Long-term aquifer tests on a series of geothermal wells (Do-1g, Do-3g, Le-1g, Le-2g) around sampling area. • Mathematical flow modeling for defining the ground water flow balance of deep multi layer aquifers.

7. ResultsReservoir recharge • The capacity of the water flow in the system depends on the hydraulic gradient and the porosity of the stratigraphic layers. The reservoirs with large volume and mainly low permeability of sediments limit fluid circulation. • Water in upper aquifer is drained intensively to the pumped area, with velocity around 6.3x10-6 m/s (based on isotopic 18O and dissolved sulphate data in ten years period). • Recent MODFLOW-based numerical modeling gives similar conclusions.

8. ResultsGeochemical and isotope composition • The water’s 18O varies from -4.68 to -12.45 ‰ (up to +0.85 ‰ (SMOW) for the deep strata with Miocene formation water). • The isotope composition of CO2 exhibits the range of 13C from -2.21 to -10.77 ‰ (PDB) and of 18O from -7.0 to -18.3 ‰ (SMOW) (Fritz et al., 1980; Pezdič, 1991; Pezdičet al., 2004). • Water from all wells is thermo-mineral, of type Na-Cl-HCO3-.

9. ResultsGeochemical and isotope composition • Water from geothermal wells Mt-1, Mt-4 and Mt-5 contains much higher values of organic substances than the water from other three wells, also these wells are deeper, with lower discharge and with higher mineralization (Gerič et al., 2004). There are also higher values of S, CH4, CO2 and CaCO3. • Higher values of CO2 cause easier water outflow by "gas uplifting".

10. Use of energy Energy from the thermal system of wells is used in steps: • room heating (56-73 °C) • swimming pools water (35-42 °C) • greenhouse facilities (42 °C). • The output water temperature is around 30 °C. Alternatives or extensive usage of spared geothermal water energy are being studied. The reserves of geothermal water in this area are "endless" by recent exploitation as the Termal 1 aquifer is filled in wide area of Eastern Alps.

11. Possible further use of geothermal water and gases Cascade treatment of energy: • The hottest water (up to 73 °C) can be used in two ways; during the winter for heating directly or with heat pumps. During the summer it can be used in reverse process of heat exchange by cooling using the special heat pumps. The system could also be used in greenhouses, where excess energy is acquired from thermal water. • In second step the water with temperature around 35 °C could be used for fish farms or mushroom production. • In the final step, water with temperature 15-25 °C has still enough energy to be used in series of heat pumps. • Carbon dioxide could be used for better plant growth in greenhouses. CaCO3 precipitationin the pipes could be prevented or slowed down keeping CO2 in the water. • Short treatment in geothermal water from well Mt-2 has been proven as curable for "Psoriasis" illness, with very good positive results.

12. Conclusions • Current analyses are focused to numerical modeling (flow prediction) to estimate the available energy at the Moravske Toplice system, based on the hydrogeochemical sampling results and hydrogeological knowledge of interesting area. • Pumping rates (60 l/s) in Mura formation are for now in the ranges which permit the formation’s multi-layer system to be renewed with water from catchment’s areas. • Hydraulic stability noticed in Mura formation may be not the case for the multi-layers aquifer system in Lendava and Murska Sobota formation. • The geothermal energy sourcefrom Moravske Toplice should be used properly to avoid environmental damages and to keep the thermal aquifer in balance. • Finally, the optimum use of energy during all seasons of the year can be acquired by cascade treatment use, which is already being partly used at the moment.

13. Thank you for your attention!