meyn, persson, leander swim20 vulnerability assessment of groundwater aquifers during the...
TRANSCRIPT
Meyn, Persson, Leander SWIM20
Vulnerability Assessment of Groundwater Aquifers during
the Construction of the Citytunnel in Malmö, Sweden
Alina Meyn, Kenneth M Persson and Bo Leander
SWECO, Malmö & Lund university, LundSweden
Meyn, Persson, Leander SWIM20
The Citytunnel Project
• Citytunneln is a rail project • Three new train stations• 17 km new track; 6 km two
parallel tunnels with single tracks below Malmö; 4.5 km bored, 1.5 km cut and cover construction
• Appr cost: 1 B EURO; Ready 2011
Meyn, Persson, Leander SWIM20
Meyn, Persson, Leander SWIM20
Three aquifers
Meyn, Persson, Leander SWIM20
Meyn, Persson, Leander SWIM20
Meyn, Persson, Leander SWIM20
Vertical distribution of hydrological flow zones
Zone Hydro-
logical unitGeological formation
Geological subdivisions Thick-ness(m)
A Soil unconfined
aquiferBarrier 1
Quaternary soils
FillPeat material
Postglacial depositsUpper moraine Glacial sediments
Under moraine
2-52-3
I Upper limestone
aquifer
Copenhagen limestone
Cop. Limestone 3-8
IIBarrier 2
Low permeable
layer
Top layer of Bryozoan limestone 35
III Lower limestone
aquiferBarrier
Bryozoane limestone
.
More compressed Bryozoan limestone.
1050
Meyn, Persson, Leander SWIM20
Meyn, Persson, Leander SWIM20
Meyn, Persson, Leander SWIM20
mm/year Mm3/year
Precipitation 675 106
Evapotranspiration 545 86
Groundwater recharge
130 +20
Pumping for Malmö city
-6,6
Groundwater runoff 15
Pumping for Citytunneln
15,48
Re-infiltration 13,24 netto -2,24
Leakage to limestone 20 2,9
Netto 11,1
Water balance
Meyn, Persson, Leander SWIM20
Meyn, Persson, Leander SWIM20
Meyn, Persson, Leander SWIM20
Actual pumping at Malmö C and Triangeln (September 2005 - March 2008)
DaysAverage m3/hour
Accum.m3
Mm3/year
Triangeln Pump 907 125 2,7 1,09
Reinfiltration. 883 132 2,99111%
1,24
Tapwater 582 28 0,41 0,26
Discharge to harbour
601,0 0,13
Netto: 0,29 0,15
MC Pump 777 342 6,4 3,00
Reinfiltration. 777 264 4,9577%
2,32
Netto: -1,4 -0,68
Netto: -1,2 -0,53
Qpump 2,7 Mm3 for 907 days,or 1,09 Mm3 peryear. Allowed Qpump 400m3/hour not reached. Max 125m3/hour
Meyn, Persson, Leander SWIM20
Meyn, Persson, Leander SWIM20
Meyn, Persson, Leander SWIM20
Meyn, Persson, Leander SWIM20
Meyn, Persson, Leander SWIM20
Meyn, Persson, Leander SWIM20
Meyn, Persson, Leander SWIM20
Conclusions
• Three main hydrological units: unconfined soil aquifer, upper limestone aquifer and lower limestone aquifer
• Separated by barriers. • Hydrological properties, location close
to the Sound and low topographic gradient make the aquifers vulnerable to salt water intrusion.
Meyn, Persson, Leander SWIM20
Conclusions
• During undisturbed (i.e. no contractors present) conditions, flushing of all aquifers takes place
• Highest chloride content observed in areas with lowest permeability
Meyn, Persson, Leander SWIM20
Conclusions
• At some points of Malmö Central station area Cl > than in present seawater
• Hydraulic contact with relict saltwater over fissures.
• Upconing (pumping for heating and cooling)
Meyn, Persson, Leander SWIM20
Conclusions
• Citytunnel Project follows strictly the Environmental Permit
• Re-infiltration exceed pumping rate at Triangeln
• Reached 80% of pumped water at Malmö C. • No visible changes in chloride content of
the groundwater at Malmö C area and Triangeln
• Some dilution of Cl due to re-infiltration with tapwater at Triangeln
• Increase of chloride content at Kung Oskars street.
Meyn, Persson, Leander SWIM20
Conclusions
• Some flushing / ion exchange at Triangeln Station area
• No visible changes in Malmö Central area
• Some saltwater intrusion process in Kung Oskar street area.
Meyn, Persson, Leander SWIM20
Conclusion
• Citytunnel Group managed in general to preserve groundwater level
• Flushing/dilution at Triangeln station area.
• Some very high horizontal and vertical permeability could still cause salt water intrusion, even if hydraulic head were minimal
Meyn, Persson, Leander SWIM20
Thank you
Questions, anyone?