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, Lund Sweden

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

Three aquifers

Meyn, Persson, Leander SWIM20

Vertical distribution of hydrological flow zones Zone Hydro- logical unit Geological formation Geological subdivisionsThick- ness (m) A Soil unconfined aquifer Barrier 1 Quaternary soils Fill Peat material Postglacial deposits Upper moraine Glacial sediments Under moraine I Upper limestone aquifer Copenhagen limestone Cop. Limestone 3-8 II Barrier 2 Low permeable layer Top layer of Bryozoan limestone 35 III Lower limestone aquifer Barrier Bryozoane limestone. More compressed Bryozoan limestone

Meyn, Persson, Leander SWIM20

mm/yearMm 3 /year Precipitation Evapotranspiration54586 Groundwater recharge Pumping for Malmö city -6,6 Groundwater runoff15 Pumping for Citytunneln 15,48 Re-infiltration13,24 netto -2,24 Leakage to limestone202,9 Netto11,1 Water balance

Meyn, Persson, Leander SWIM20

Actual pumping at Malmö C and Triangeln (September March 2008) Days Average m 3 /hour Accum. m 3 Mm3/ year TriangelnPump ,72,71,09 Reinfiltration ,99 111% 1,24 Tapwater582280,410,26 Discharge to harbour 601,00,13 Netto:0,290,15 MCPump ,43,00 Reinfiltration ,95 77% 2,32 Netto:-1,4-0,68 Netto:-1,2-0,53 Qpump 2,7 Mm 3 for 907 days, or 1,09 Mm 3 per year. Allowed Qpump 400m 3 /hour not reached. Max 125m 3 /hour

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?