title: Effect of tunnel excavation on source and mixing of groundwater in a coastal granitoidic fracture network.
abstract: The aim of this study was to assess how the excavation of the Äspö Hard Rock Laboratory tunnel has impacted on sources and mixing of groundwater in fractured crystalline (granitoidic) bedrock. The tunnel is 3600 m long and extends to a depth of 460 m at a coastal site in Boreal Europe. The study builds on a unique data set consisting of 1117 observations on chloride and δ(18)O of groundwater collected from a total of 356 packed-off fractures between 1987 and 2011. On the basis of the values of these two variables in selected source waters, a classification system was developed to relate the groundwater observations to source and postinfiltration mixing phenomena. The results show that the groundwater has multiple sources and a complex history of transport and mixing, and is composed of at least glacial water, marine water, recent meteoric water, and an old saline water. The tunnel excavation has had a large impact on flow, sources, and mixing of the groundwater. Important phenomena include upflow of deep-lying saline water, extensive intrusion of current Baltic Sea water, and substantial temporal variability of chloride and δ(18)O in many fractures.
authors.affiliation: Linnæus University, School of Natural Sciences, Barlastgatan 11, SE-391 82 Kalmar, Sweden. frederic.mathurin@lnu.se
authors.forename: Frédéric A
authors.initials: FA
authors.lastname: Mathurin
authors.forename: Mats E
authors.initials: ME
authors.lastname: Åström
authors.forename: Marcus
authors.initials: M
authors.lastname: Laaksoharju
authors.forename: Birgitta E
authors.initials: BE
authors.lastname: Kalinowski
authors.forename: Eva-Lena
authors.initials: EL
authors.lastname: Tullborg
mesh_terms: D002712:Chlorides / Q000032:analysis; D004784:Environmental Monitoring; D005060:Europe; D060587:Groundwater / Q000032:analysis*; D010100:Oxygen / Q000032:analysis; D010103:Oxygen Isotopes / Q000032:analysis; D012822:Silicon Dioxide / Q000737:chemistry*; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis
chemical_list: D002712:Chlorides; D010103:Oxygen Isotopes; D014874:Water Pollutants, Chemical; C007886:granite; D012822:Silicon Dioxide; D010100:Oxygen