TY - JOUR
T1 - Scale deposits in tunnel drainage systems – A study on fabrics and formation mechanisms
AU - Eichinger, Stefanie
AU - Boch, Ronny
AU - Leis, Albrecht
AU - Koraimann, Guenther
AU - Grengg, Cyrill
AU - Domberger, Gunnar
AU - Nachtnebel, Manfred
AU - Schwab, Christian
AU - Dietzel, Martin
PY - 2020
Y1 - 2020
N2 - Rapid deposition of chemical sediments, particularly calcium carbonate, is a widespread phenomenon in tunnel constructions, which can significantly disturb water draining. The removal of the scale deposits in the drainage setting is labor and cost intensive. Prediction or prevention of these unwanted scale deposits are challenging and require detailed knowledge on their site-specific source, formation mechanisms and environmental dependencies. This case study combines a mineralogical, (micro)structural, isotopic, microbiological, and hydrochemical approach to understand the formation of scale deposits in an Austrian motorway tunnel. Chemical and isotopic results revealed that all investigated solutions originate from a distinct local aquifer. High pH (11), indicative high alkaline element concentrations (Na 26 mg/l; K 67 mg/l), originated from concrete leaching, and a strong supersaturation in respect to calcite (SI > 1) are representative for the environmental setting of scaling type 1. This type is characterized by the formation of calcite, aragonite, and rarely documented dypingite (Mg5(CO3)4(OH)2*5H2O), and yields in a highly porous material showing minor indications of microbial presence. In contrast, scale deposits of type 2 are strongly microbially influenced, yielding dense and layered mineral deposits, typically consisting of calcite. The corresponding aqueous solution revealed elevated Mg concentration (38 mg/l) and a high molar Mg/Ca ratio (0.8). Scale deposits containing distinct aragonite precipitates next to calcite, mostly growing in pore spaces of the scale fabric, are accounted as type 3. Therein, dypingite is always growing on top of aragonite needles, indicative for prior CaCO3 precipitation. The composition of corresponding solutions shows the highest Mg/Ca ratio (1.1). Scale type 4 is characterized as a compact deposit consisting entirely of calcite. Its corresponding solution exhibits a molar Mg/Ca ratio of 0.6. From the obtained data sets a conceptual model was developed describing the distinct operative and (micro)environmental conditions responsible for the distinct diversity of scale deposits.
AB - Rapid deposition of chemical sediments, particularly calcium carbonate, is a widespread phenomenon in tunnel constructions, which can significantly disturb water draining. The removal of the scale deposits in the drainage setting is labor and cost intensive. Prediction or prevention of these unwanted scale deposits are challenging and require detailed knowledge on their site-specific source, formation mechanisms and environmental dependencies. This case study combines a mineralogical, (micro)structural, isotopic, microbiological, and hydrochemical approach to understand the formation of scale deposits in an Austrian motorway tunnel. Chemical and isotopic results revealed that all investigated solutions originate from a distinct local aquifer. High pH (11), indicative high alkaline element concentrations (Na 26 mg/l; K 67 mg/l), originated from concrete leaching, and a strong supersaturation in respect to calcite (SI > 1) are representative for the environmental setting of scaling type 1. This type is characterized by the formation of calcite, aragonite, and rarely documented dypingite (Mg5(CO3)4(OH)2*5H2O), and yields in a highly porous material showing minor indications of microbial presence. In contrast, scale deposits of type 2 are strongly microbially influenced, yielding dense and layered mineral deposits, typically consisting of calcite. The corresponding aqueous solution revealed elevated Mg concentration (38 mg/l) and a high molar Mg/Ca ratio (0.8). Scale deposits containing distinct aragonite precipitates next to calcite, mostly growing in pore spaces of the scale fabric, are accounted as type 3. Therein, dypingite is always growing on top of aragonite needles, indicative for prior CaCO3 precipitation. The composition of corresponding solutions shows the highest Mg/Ca ratio (1.1). Scale type 4 is characterized as a compact deposit consisting entirely of calcite. Its corresponding solution exhibits a molar Mg/Ca ratio of 0.6. From the obtained data sets a conceptual model was developed describing the distinct operative and (micro)environmental conditions responsible for the distinct diversity of scale deposits.
KW - Calcite
KW - Drainage system
KW - Dypingite
KW - Gallionella ferruginea
KW - Scale deposit
KW - Tunnel
UR - http://www.scopus.com/inward/record.url?scp=85079860957&partnerID=8YFLogxK
U2 - 10.1016/j.scitotenv.2020.137140
DO - 10.1016/j.scitotenv.2020.137140
M3 - Article
C2 - 32088488
AN - SCOPUS:85079860957
SN - 0048-9697
VL - 718
JO - Science of the Total Environment
JF - Science of the Total Environment
M1 - 137140
ER -