Environmental assessment of the potential effects of aquifer thermal energy storage systems on microorganisms in groundwater

Abstract

SUMMARYThe primary objective of this study was to evaluate the potential environmental effects (both adverse and beneficial) of aquifer thermal energy storage (ATES) technology pertaining to microbial communities indigenous to subsurface environments (i .e., aquifers) and the propagation, movement, and potential release of pathogenic microorganisms (specifical ly, Legionel la) within ATES systems. Seasonal storage of thermal energy in aquifers shows great promise to reduce peak demand; reduce electric utility load problems; contribute to establishing favorable economics for district heating and cooling systems; and reduce pol 1 ution from extraction, refining, and combustion of fossi 1 fuels. However, concerns that the widespread implementation of this technology may have adverse effects on biological systems indigenous to aquifers, as well as he1 p to propagate and re1 ease pathogenic organisms that enter these envi ronments need to be resolved.Groundwaters are habitat to an abundant and diverse microbial population. The activities of these organisms are important to the removal of a variety of hazardous wastes. However, these organisms have only recently been studied, and their full importance is not known at this time. The growth and activity of microorganisms indigenous to aquifers are governed by a variety of environmental factors including: the porosity of the aquifer nutrient avai 1 abi 1 i ty oxidation-reduction conditions PH temperature the adsorption of microorganisms to subsurface particles. Perturbations, due to the implementation of ATES technology, can locally alter these physicochemical factors which can, to an unknown degree, affect the growth and activities of microorganisms inhabiting aquifers.Of the environmental factors 1 isted above, groundwater temperature a1 terations caused by injection of heated or cooled waters during the operation of ATES systems have the greatest potential for altering the types and activities of native microbial communities. Microorganisms, depending on the species, have specific temperature ranges that allow for their growth. If the use of ATES systems alters the temperature of an aquifer beyond the range that supports growth, microbial activity will become dormant or cease. Other ATES-related alterations that can cause changes in the microbial ecology of aquifers include groundwater chemistry (e.g., pH, Eh, solubi 1 ity of minerals) and changes in physical characteristics (e.g., adsorptive to subsurface particles, hydraul ic conductivity). However, the true impact of such changes in the microbial ecology and activity can not yet be assessed. Experience with ATES in other countries, as well as in the U.S., has not indicated major impacts; however, intensive monitoring programs have not been conducted in conjunction with the operation of most systems.In addition to indigenous microbial populations, allochthonous organisms (i .e., organisms foreign to that environment) can survive and grow in aquifers. A1 lochthonous microorganisms detrimental to human health (i .e., ...

Seasonal Thermal Energy Storage Program: Progress summary for the period April 1986 through March 1988

“…Thus, their complete role in the subsurface ecosystem is uncertain. The activity of indigenous subsurface microorganisms is subject to a number of environmental factors (Hicks and Stewart 1988) including:…”