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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


• 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


• 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

24. 4. 2018

7

Study site

24. 4. 2018

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


• 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


Results

24. 4. 2018

Talvivaara, Electrical resistivity tomography profile 2

Possible fracture zone Fracture zone?

Wetland, Peatbog Wetland, PeatbogWetland, Peatbog

Unfractured bedrock

Case Talvivaara


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


• 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


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


• 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


• 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


Case Yara

Rate budget model


Case YaraTop of model Top of bedrock Bottom of model

groundwater transport in fractured bedrock – case studies ... · nina hendriksson, samrit luoma,...

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