Groundwater transport in fractured bedrock –Case studies from Talvivaara and Yara mines, Finland
Antti Pasanen ([email protected])
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
24. 4. 20181
Introduction(Very) brief stratigraphy of Finland
Harri Kutvonen/ GTK
Precambrian crystalline bedrock
Quaternary
Gap for 1.5 to 3.5 Ga
Motivation
Antti Pasanen MNDP/METS 201831
• 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
Antti Pasanen MNDP/METS 2018, Madrid4
• 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
Introduction case Talvivaara
24. 4. 2018
Case Talvivaara
Antti Pasanen MNDP/METS 2018, Madrid5
• 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
Aim of the study
24. 4. 2018 Yle 14.10.2013
Case Talvivaara
Antti Pasanen MNDP/METS 2018, Madrid6
• 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
Aim of the study
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7
Study site
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Gypsum ponds
Open pit
Primary heap
leaching
Factory area
Fracture zonesBedrock GW observationSediment GW observationSurface water obervationSediment GW flow direction
Talvivaara gypsum pond area
Case Talvivaara
Antti Pasanen MNDP/METS 2018, Madrid8
• 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)
Methods
24. 4. 2018
Case Talvivaara
Antti Pasanen/IAH 2014 Marrakech, Morocco9
• 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)
Methods
24. 4. 2018
Case Talvivaara
Antti Pasanen MNDP/METS 2018, Madrid10
Results
24. 4. 2018
Talvivaara, Electrical resistivity tomography profile 2
Possible fracture zone Fracture zone?
Wetland, Peatbog Wetland, PeatbogWetland, Peatbog
Unfractured bedrock
Case Talvivaara
Antti Pasanen MNDP/METS 2018, Madrid11
Results
24. 4. 2018
Talvivaara, seismic profile 40
Bedr
ock
velo
city
(m/s
)El
evat
ion
(m a
sl)
Distance (m)
Bedrock surfaceGW tableGround surface
Case Talvivaara
Antti Pasanen MNDP/METS 2018, Madrid12
• Drilling FID5
Results
24. 4. 2018
Case Talvivaara
Esityksen nimi / Tekijä1324. 4. 2018
FID 28
P7
FID 0Gypsum ponds Open pit
Primary heap
leaching
Case Talvivaara
Antti Pasanen MNDP/METS 2018, Madrid14
Results
24. 4. 2018
Open pit and wastewater
Gypsum pond
Case Talvivaara
Background Black schist
P1 and P7 Others Open pit and wastewater
Gypsum pond
Open pit
P1FID 28
P7
Results
-15 -14 -13 -12 -11 -10 -9 -8 -7-105
-100
-95
-90
-85
-80
-75
-70
-65
-60
FMWL
FID28
FID0
P7
P4
FID5
Gipsum bond; bedrock gw
Gw background
Surface water
Gipsum bond; surface water
δ18O (‰, VSMOW)
δ2H
(‰
, VS
MO
W)
Surface water
-14,2 -14,0 -13,8 -13,6 -13,4 -13,2 -13,0 -12,8 -12,6-104
-102
-100
-98
-96
-94
-92
-90Gw backgroundFID28P7FMWLFID0FID27FID3KorteKAFID5
δ18O (‰, VSMOW)
δ2H
(‰
, VS
MO
W)
FID28
FID0
P7
Bedrock groundwater
Case Talvivaara
Esityksen nimi / Tekijä16
• Kartta
Results
24. 4. 2018
FID 28
P7
FID 0
?
?
?
?
Case Talvivaara
Antti Pasanen MNDP/METS 2018, Madrid17
• 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
Summary
24. 4. 2018
Case Talvivaara
Introduction case Yara
Antti Pasanen MNDP/METS 2018181
• 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
Case Yara
VLF-R
Antti Pasanen MNDP/METS 2018191
Case Yara
Rate budget model
Antti Pasanen MNDP/METS 2018201
Case YaraTop of model Top of bedrock Bottom of model
Thank you!
• Talvivaara Mining Plc, Yara Finland Oy and TEKES is thanked for their support.
© Talvivaara Mining Plc