Meyn, Persson, Leander SWIM20 Vulnerability Assessment of Groundwater Aquifers during the...

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


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


Three aquifers


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


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


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


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.


Conclusions

• During undisturbed (i.e. no contractors present) conditions, flushing of all aquifers takes place

• Highest chloride content observed in areas with lowest permeability


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)


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.


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.


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


Thank you

Questions, anyone?

Meyn, Persson, Leander SWIM20 Vulnerability Assessment of Groundwater Aquifers during the...

Documents

Transcript of Meyn, Persson, Leander SWIM20 Vulnerability Assessment of Groundwater Aquifers during the...