Abstract

The United States Environmental Protection Agency along with local agencies commonly grant exemptions to the ban on land disposal of hazardous wastes when the operators claim injected wastes will be structurally, hydrologically, and stratigraphically isolated from freshwater aquifers for at least 10,000 years. Major factors in the prediction of this prolonged isolation include the physical characteristics of the formation that is receiving the waste. Some of these physical characteristics, such as porosity and permeability, directly affect the ability of the reservoir aquifer to store injected waste. Injection of liquid waste into deep aquifers can cause unforeseen chemical or physical changes to the waste or the aquifer.

By using a dynamic flow-through reaction vessel, cores of the injected formation were subjected to simulated subsurface conditions. Nonionic surfactant solutions, designed to imitate hazardous waste, were injected into these cores, and resulting changes in permeability were measured. Preliminary laboratory tests show that surfactants flowing through laboratory simulations of deeply buried aquifers (1800 m) for as little as three days will form gel-like substances that cause a substantial loss of permeability.

The amount of exposure of the surfactant to the sediment appears to be the main factor in this gel formation. Temperature and the presence of brine have a minimal effect on the permeability loss. The duration of injection, the concentration of the injected organic chemical, and the confining pressure all regulate the amount of grain/surfactant interaction and thus are major factors in the amount of permeability loss.