Relationship of regional water quality to aquifer thermal energy storage

Abstract

Aquifer thermal energy storage (ATES) involves injection and withdrawal of temperature-conditioned water into and from a permeable water-bearing formation. The purpose of this study was to assess ground-water quality and associated geologic characteristics as they may affect the feasibility of ATES system development in any hydrologic region. It was determined that seven physical and chemical mechanisms may decrease system efficiency: particulate plugging, chemical precipitation, clay mineral dispersion, piping corrosion, aquifer disaggregation, mineral oxidation, and proliferation of biota. Factors affecting ground-water chemistry are pressure, temperature, pH, ion exchange, evaporation/transpiration, and commingling with diverse waters. Modeling with the MINTEQ code showed three potential reactions: precipitation of calcium carbonate at raised temperature; solution of silica at raised temperature followed by precipitation at reduced temperature; and oxidation/precipitation of iron compounds. Ameliorative chemical procedures are available. Low concentrations of solutes are generally favorable for ATES. Near-surface waters in high precipitation regions are low in salinity. Ground water recharged from fresh surface waters also has reduced salinity. Rocks least likely to react with ground water are siliceous sandstones, regoliths, and metamorphic rocks. Limestone, dolomite, shale, and basalt contain reactive minerals. Intrusive rocks may yield alkalis, alkaline earths, and iron by hydrolysis of feldspathic and ferromagnesian minerals.more » On the basis of known aquifer hydrology, current population trends, escalating energy costs, and climate, 10 US water-resources regions are candidates for selected exploration and development. All are characterized by extensive silica-rich aquifers.« less