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 17m depth on the Saitama University campus, Japan. A full-scale GSHP test facility consisting of a 50m deep U-tube for circulating the heat-carrying fluid and four monitoring wells at 1, 2, 5, and 10m 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 1m distant well (temperature increase up to 7°C) and the 10m distant well (non-temperature-affected), the DWA showed an approximately linear relationships for eight components (B, Si, Li, dissolved organic carbon (DOC), Mg2+, 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.
a Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama, 338-8570, Japanidb Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8567, Japanid="aff3">c Department of Civil Engineering, Aalborg University, Sofiendalsvej 11, 9200, Aalborg SV, Denmark
Recommended Citation:
Takeshi Saitoa,,,et al. Temperature change affected groundwater quality in a confined marine aquifer during long-term heating and cooling[J]. water Research,2016-01-01,Volume 94