Long-term monitoring of groundwater quality during in-situ artificial heating and natural cooling in the Arakawa Lowland near the Tokyo Metropolis, Japan
Abstract
Recently, subsurface temperature increases have been reported below several larger cities in the world. This phenomenon is likely induced by combined effects of global warming, urbanization, and rapid development of subsurface infrastructures including subways and underground shopping complexes. An increase in subsurface temperature may affect groundwater quality due to e.g. changes in chemical solubility, adsorption-desorption, and biochemical reaction rates. Despite this concern, few studies have investigated subsurface temperature effects on groundwater quality. In this study, long-term monitoring of groundwater quality during in-situ artificial heating and natural cooling was carried out over a period of seven years to evaluate effects of changing subsurface temperature on groundwater quality.
At an experimental site in the Arakawa Lowland near the Tokyo Metropolis of Japan, four deep (up to 50 m) groundwater monitoring wells were installed at 1 m, 2 m, 5 m, and 10 m distance from a 50-m deep, U-tube shaped heat source. The monitoring wells allowed groundwater sampling from both an unconfined and two confined aquifers. Long-term artificial heating and natural cooling experiments were repeatedly carried out together with high-temporal-resolution groundwater monitoring for the three aquifers. Results showed an increase in the concentrations of several chemical components such as arsenic, boron, silicon, potassium, and dissolved organic carbon simultaneously with a subsurface temperature increase. Oppositely, calcium and magnesium concentrations decreased with increasing subsurface temperature. All chemical concentrations returned to close to the original concentration levels after a subsequent subsurface temperature decrease to the original groundwater temperature, implying fully reversible chemical processes were taking place. Relationships between subsurface temperature and concentrations of groundwater chemical components were analyzed and approximate linear relations were obtained that will be useful for predicting effects of urban geothermal systems and subsurface warming on groundwater quality.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMGH41B1440S
- Keywords:
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- 0240 Public health;
- GEOHEALTHDE: 1831 Groundwater quality;
- HYDROLOGYDE: 1871 Surface water quality;
- HYDROLOGYDE: 1884 Water supply;
- HYDROLOGY