title: Temperature change affected groundwater quality in a confined marine aquifer during long-term heating and cooling.
abstract: Global warming and urbanization together with development of subsurface infrastructures (e.g. subways, shopping complexes, sewage systems, and Ground Source Heat Pump (GSHP) systems) will likely cause a rapid increase in the temperature of relatively shallow groundwater reservoirs (subsurface thermal pollution). However, potential effects of a subsurface temperature change on groundwater quality due to changed physical, chemical, and microbial processes have received little attention. We therefore investigated changes in 34 groundwater quality parameters during a 13-month enhanced-heating period, followed by 14 months of natural or enhanced cooling in a confined marine aquifer at around 17 m depth on the Saitama University campus, Japan. A full-scale GSHP test facility consisting of a 50 m deep U-tube for circulating the heat-carrying fluid and four monitoring wells at 1, 2, 5, and 10 m from the U-tube were installed, and groundwater quality was monitored every 1-2 weeks. Rapid changes in the groundwater level in the area, especially during the summer, prevented accurate analyses of temperature effects using a single-well time series. Instead, Dual-Well Analysis (DWA) was applied, comparing variations in subsurface temperature and groundwater chemical concentrations between the thermally-disturbed well and a non-affected reference well. Using the 1 m distant well (temperature increase up to 7 °C) and the 10 m distant well (non-temperature-affected), the DWA showed an approximately linear relationships for eight components (B, Si, Li, dissolved organic carbon (DOC), Mg(2+), NH4(+), Na(+), and K(+)) during the combined 27 months of heating and cooling, suggesting changes in concentration between 4% and 31% for a temperature change of 7 °C.
authors.affiliation: Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama, 338-8570, Japan. Electronic address: saitou@mail.saitama-u.ac.jp.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Saito
authors.affiliation: Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8567, Japan.
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Hamamoto
authors.affiliation: Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama, 338-8570, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ueki
authors.affiliation: Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama, 338-8570, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Ohkubo
authors.affiliation: Department of Civil Engineering, Aalborg University, Sofiendalsvej 11, 9200, Aalborg SV, Denmark.
authors.forename: Per
authors.initials: P
authors.lastname: Moldrup
authors.affiliation: Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama, 338-8570, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Kawamoto
authors.affiliation: Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama, 338-8570, Japan.
authors.forename: Toshiko
authors.initials: T
authors.lastname: Komatsu
mesh_terms: D004784:Environmental Monitoring; D060587:Groundwater / Q000737:chemistry*; D007564:Japan; D012621:Seasons; D013696:Temperature; D060753:Water Quality
keywords: Confined marine aquifer; Dual-Well Analysis (DWA); Ground Source Heat Pump (GSHP) systems; Groundwater quality; Long-term heating and cooling; Subsurface thermal pollution