Groundwater transport in fractured bedrock Case studies from Talvivaara and Yara mines, Finland

Transcription

1 Groundwater transport in fractured bedrock Case studies from Talvivaara and Yara mines, Finland Antti Pasanen Anu Eskelinen, Jouni Lerssi, Heikki Forss, Taija Huotari, Pekka Forsman, Marja Liisa Räisänen, Nina Hendriksson, Samrit Luoma, Tiina Kaipainen, Kaisa Turunen, Arto Pullinen Geological Survey of Finland Anniina Kittilä, ETH Zurich Taija Lahtinen, City of Kokkola Kimmo Hentinen, Sweco Finland 1

2 Introduction (Very) brief stratigraphy of Finland Quaternary Precambrian crystalline bedrock Gap for 1.5 to 3.5 Ga Harri Kutvonen/ GTK

3 Motivation Bedrock groundwater was studied poorly in Finnish mines, even though, it is important for water management The effect of groundwater to general water balance was poorly understood in mining operations Transport of contamination underground was not considered an issue To develop inexpensive, but robust, methodology to study bedrock groundwater using existing methods Environmental and groundwater studies were considered as cost not investment in mining operations 31 Antti Pasanen MNDP/METS 2018

4 Introduction case Talvivaara Talvivaara mine (Currently Terrafame) utilizes polymetallic black schist ore Metal extraction by bioheapleaching Main product is nickel (planned 50 ktpa) By products are zinc (planned 90 ktpa), copper (15 ktpa) and cobalt (1,8 ktpa) Talvivaara gypsum pond leaks in 2012 and 2013 posed a threat to groundwater 4 Antti Pasanen MNDP/METS 2018, Madrid

5 Aim of the study Study the potential pollution and effects caused by the gypsum pond leaks in sediment and bedrock groundwater Study the formation of concentrations in groundwater Study the potential groundwater transport routes and directions Estimate the potential hazard to nature and humans 5 Antti Pasanen MNDP/METS 2018, Madrid Yle

6 Aim of the study Based on preliminary investigation the study was focused on Identifying preferential groundwater flow paths in bedrock Pinpointing suitable coring sites Measuring the hydraulic conductivities and heads Interpreting the groundwater flow patterns in bedrock Geochemistry of groundwater and selected surface- and process waters In addition isotopic composition of water and groundwater flow patterns in sediments were studied 6 Antti Pasanen MNDP/METS 2018, Madrid

7 Study site Factory area Gypsum ponds Open pit Talvivaara gypsum pond area 7 Primary heap leaching Fracture zones Bedrock GW observation Sediment GW observation Surface water obervation Sediment GW flow direction

8 Methods Aerogeophysical and DEM data Estimation of the thickness of overburden Lineament study Geophysical methods Gravimetric Magnetic Refraction seismic Electrical resistivity tomography (ERT) Ground penetrating radar (GPR) 8 Antti Pasanen MNDP/METS 2018, Madrid

9 Methods Drilling and logging new wells 8 bedrock wells and 5 sediment groundwater observation wells Slug tests in 4 bedrock wells Average linear groundwater velocities in bedrock Water geochemistry and isotope analyzes In total 29 sampling sites, and 42 samples, Field measurements (ph, temperature, redox potential, electrical conductivity, dissolved oxygen and field alkalinity) Laboratory analyzes (dissolved and total concentration of elements, ferrous iron (fe2+), TOC, DOC, anions, solids content and alkalinity) Isotope analyses (18O/16O, 2H /1H, 86, 87Sr; 234, 235, 238U, 32, 34S; 204, 206, 207, 208Pb low concentration) 9 Antti Pasanen/IAH 2014 Marrakech, Morocco

10 Results Talvivaara, Electrical resistivity tomography profile 2 Wetland, Peatbog Wetland, Peatbog Possible fracture zone 10 Antti Pasanen MNDP/METS 2018, Madrid Wetland, Peatbog Unfractured bedrock Fracture zone?

11 Results Elevation (m asl) Talvivaara, seismic profile 40 Bedrock velocity (m/s) Bedrock surface GW table Ground surface Distance (m) 11 Antti Pasanen MNDP/METS 2018, Madrid

12 Results Drilling FID5 12 Antti Pasanen MNDP/METS 2018, Madrid

13 FID 0 Gypsum ponds Open pit P7 FID Esityksen nimi / Tekijä Primary heap leaching

14 Results Background Black schist P1 and P7 FID Antti Pasanen MNDP/METS 2018, Madrid Others P7 P1 Open pit and wastewater Open pit Gypsum pond Gypsum pond

15 δ2h (, VSMOW) δ2h (, VSMOW) Results Surface Bedrock groundwater Gw backgroun d FID28 FID0 waterp7 FMWL FID0 FID27P7 FMWL FID3 FID28 KorteKA FID0 FID5 P7 P4 FID5 FID2 Gipsum bond; bedrock gw8 Gw background Surface water Gipsum bond; surface water ,2-14,0-13,8-13,6-13,4-13,2-13,0-12,8-12, δ18o (, VSMOW) δ18o (, VSMOW)

16 Results FID 0 Kartta P7?? FID 28?? 16 Esityksen nimi / Tekijä

17 Summary Pinpointing the coring sites and sampling locations is crucial when studying hydraulic connections and transport in crystalline bedrock groundwater Similar traces of chemical contamination in P7 and FID 28 indicate possible long term seepage from primary heap and transport in bedrock groundwater through fracture zone Isotopic composition of water (δ18o, δ2h) supports this interpretation Isotopic composition (δ18o, δ2h) suggests a hydraulic connection and water flow from FID 0 to P7 Chemical analyses do not indicate the connection between the observation points Fracture zones can act as preferential flow paths in bedrock and can be significant in transporting contamination outside the mining area 17 Antti Pasanen MNDP/METS 2018, Madrid

18 Case Yara Introduction case Yara Aim of the project was to develop a quantitative water balance prediction tool for mine sites WSFS surface water model (Finnish Environmental Institute SYKE) Three layer FeFlow groundwater model One direction coupling, surface water model GW model In addition to case Talvivaara methodology: VLF-R was used as main geophysical method for fracture identification One year long groundwater surface monitoring campaign 181Antti Pasanen MNDP/METS 2018

19 VLF-R 191Antti Pasanen MNDP/METS 2018 Case Yara

20 Rate budget model Top of model 201Antti Pasanen MNDP/METS 2018 Top of bedrock Case Yara Bottom of model

21 Thank you! Talvivaara Mining Plc, Yara Finland Oy and TEKES is thanked for their support. Talvivaara Mining Plc