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THE USE OF 3D GEOLOGICAL INFORMATION IN A LARGE MANAGED AQUIFER RECHARGE PROJECT Aki Artimo and Sami Saraperä Turku Region Water Ltd., Finland [email protected] Three-Dimensional Mapping Workshop, Oct. 8th 2011, Minneapolis, MN INTRODUCTION Artificially infiltrated groundwater will be produced for 300,000 inhabitants living in the Turku area at the end of this year. The infiltration water is obtained from the River Kokemäenjoki, 90 km north of Turku. Artificial infiltration takes place in the Virttaankangas Quaternary esker aquifer, 60 km north of Turku. The length of feeder pipelines (DN=1200 mm) is about 100 km. The cost of the project is 176,000,000 euros. BACKGROUND Precise control of the infiltrated water (i.e. flow paths and residence time in the aquifer) is important in the operation of the managed aquifer recharge (MAR) plant. The aquifer is not used merely to store the infiltrated river water, but also to enhance the quality of the water. The natural purification of the infiltrated water during the flow within the saturated zone of the aquifer is a crucial process for those artificial recharge plants operating in the Nordic countries. After its completion, the Virttaankangas managed aquifer recharge project will significantly increase the number of consumers using artificially recharged groundwater in Finland. BACKGROUND The main factors affecting the quality change of the artificially infiltrated groundwater are the composition of the soil material, hydraulic conductivity distribution within the esker aquifer and residence time of the infiltrated water. Even though the water quality change occurs beyond the MAR plant’s facilities, the operation can be controlled with the help of: - Measurements of hydraulic head changes - Water quality monitoring data - 3D hydrogeological model - Groundwater flow model - Tracers (natural isotopes, organic carbon and artificial tracers) TOOLS FOR THE PROJECT EXECUTION The 3D geological information database has been available during the construction of the MAR plant. Automated updating of the 3D hydrogeological and groundwater flow models has enabled the immediate use of the newest research information in the construction of the plant. In addition to basic sedimentological and hydrogeological information, the Virttaankangas 3D hydrogeological model has seen the introduction of geochemical, isotopic, and geophysical data into the 3D modeling workflow. Furthermore, the 3D hydrogeological model works as a structural basis for the 60-layer groundwater flow model. TOOLS FOR THE PROJECT EXECUTION Quantitative understanding GW flow models Hydrostratigraphical models Geological models Database development Simplified basin analysis approach. Modified from Sharpe et al. 2002 TOOLS FOR THE PROJECT EXECUTION Quantitative understanding (Aquifer management) Hydrogeochemical data Geophysical data Isotope data Drill hole data GW level measurements Tracer tests 3D Groundwater Flow Model 3D Geological information system (including time related data) Infiltrations and pumpings Sedimentological interpretations Integrated approach with constantly evolving and updating 3D models provides versatile tools for managed aquifer recharge. THE USE OF 3D GEOLOGICAL INFORMATION Geological information and 3D models have been used to solve, for example, legislative, constructional, and land-use related issues during the execution of the MAR project. Modeling tools were used to design the optimal layout and configuration of the infiltration pond and production well areas of the MAR plant. For example, locations of five previously planned infiltration areas were rejected due to discovery of morphologically undetectable kettle hole system underlying the infiltration areas restricting the flow of infiltrated water. Exact locations of the production wells were decided after a thorough examination of available sedimentological and hydrogeological data, which resulted in extremely high yields of the new production wells. As compared with the pre-3D plans for pumping well locations, the amount of wells needed for full scale production was almost reduced in half. Avg. pumping rate per well Previously built wells New wells 6,700 m3/d 5,000 m3/d 8,500 m3/d (Maximum yields of the new wells are higher than the used pumping rates.) Coarsest part of the esker THE USE OF 3D GEOLOGICAL INFORMATION Geological information system with the modeling tools provided the means to design and control the infiltrations and pumpings related to the one-year testing phase required in the environmental permits. According to those permits, the full scale production is only allowed to start after the results of the testing phase provide enough information of the controlled execution of full scale infiltration and pumping. During the one year testing phase the observed flow paths and residence times of the infiltrated water coincided extremely well with the groundwater flow simulations conducted prior to the testing phase. This was not the case when the earlier pre-3D plans for infiltration and pumping were simulated with the same flow model. Those plans would have resulted in a failure in the operation of the MAR plant. THE USE OF 3D GEOLOGICAL INFORMATION The groundwater flow model is the only tool that can be used to decide the exact infiltration and pumping rates for all the 19 infiltration ponds and 12 production wells so that the residence time of the infiltrated water in the aquifer is sufficient throughout the flow field. The groundwater flow simulations for full scale production will be conducted later this month. Modeling tools, tracer tests and the testing phase have shown that the influence of the artificial infiltration can only be observed in the coarsest part of the esker (glaciofluvial coarse unit). The ”glaciofluvial coarse” unit from the 3D hydrogeological model (left) and the corresponding gw flow model cells depicting the detailed variation of hydraulic conductivity within that unit (right). Flow of infiltrated water (5 days) Flow of infiltrated water (10 days) Flow of infiltrated water (5 weeks) Flow of infiltrated water (10 weeks) Flow of infiltrated water (15 weeks) Flow of infiltrated water (26 weeks) CONCLUSIONS All the investments in research have been less than 5 M€ (less than 3% of the total budget). The cost of one production well is about 100,000 €. Average pumping rate of the MAR plant’s production well is 6,700 m3/d, whereas the avg. yield of other water producers’ wells within the same esker area is 500 m3/d. The required one-year testing phase was successfully completed before the entire construction work of the project was completed. The cost of each day of delay in water production after the construction is completed is about 20,000 € due to the loan interests. The required production rates of the artificially infiltrated groundwater in this 176 M€ project would not have been achieved without the 3D geological information system and models.