Regulatory Control of Groundwater Contamination by Hazardous Waste Disposal Wells: An Engineering Perspective

Abstract

ABSTRACT A major cause of ground water pollution by hazardous industrial chemical waste disposal wells is a leaky well casing. The detection of such leaks and prompt action to correct them is an important element of the federal Underground Injection Control (UIC) program for ground water protection. Two methods have been in use for casing leak detection in the conventional well with tubing set in a packer: one based on monitoring the volume (level) of liquid in the annulus; the other on monitoring the pressure ("annulus pressure") of a pressurized gas "cap" artificially imposed over the liquid in the closed well annulus. Obviously, annulus liquid volume monitoring relates casing leaks directly to liquid volume loss, while annulus pressure monitoring equates the same indirectly with the resulting gas pressure decline. However, relating loss in liquid volume to gas cap pressure decline is based on the presumption of isothermal conditions and the absence of gas-liquid interaction within the annulus. As neither condition obtains in the well environment, the reliability of the annulus pressure monitoring method which is now a primary federal requirement appears to be in serious doubt. The need, for a re-evaluation of the regulatory status of annulus pressure monitoring for casing integrity and for a technically sound alternative method is thus apparent. It is shown that annulus liquid level monitoring is possibly the simplest and most practical method for monitoring casing leaks. Imposition of a pressurized gas cap can enhance the rate of liquid leakage and thereby increase the sensitivity of the monitoring process.