Volume 20, Issue 2 (June 1997)
A Flow Pump System for Assessing Clay Barrier-Permeant Compatibility
This paper presents the performance, reliability, and features of a hydraulic conductivity, k, testing equipment specially designed and fabricated for clay barrier-permeant compatibility studies. The key component of the equipment is a flow or infusion/withdrawal pump that is used to deliver a constant and continuous flow of permeant at some prescribed rate through two stainless steel syringes to a soil specimen. The pump has a switch that allows the motor direction to be changed to allow one syringe to empty while the other is filling. This provides an uninterrupted flow of permeant to the specimen, unlike most traditional testing equipment that requires complete stoppage of permeation in order to provide a fresh supply of permeant. In some cases, re-establishment of flow pressures can take a long time and therefore affect the attainment of chemical equilibrium and specimen volume changes during compatibility testing. A Plexiglas cell containing an inflatable rubber diaphragm is used in the present equipment as a permeant supply tank to prevent the exposure of the permeant to air, therefore making the equipment particularly suited for testing with volatile organic liquids and redox-sensitive permeants such as acid mine drainage. Furthermore, this cell is connected to a back pressure supply to decrease the time required for the pressure to return to its original value after switching gears. The advantage of the equipment includes a graphic-based data acquisition system that allows test parameters such as hydraulic gradient, hydraulic conductivity, volume change, and room temperature to be continuously monitored and displayed on a computer monitor screen. The performance and features of the equipment are demonstrated with a series of k-tests on clayey soil specimens permeated with water and then with acid mine drainage (AMD). The data indicated that, while AMD did not change k, it may have dissolved some primary soil minerals such as calcite and dolomite, which in turn buffered the pH of the effluent from a specimen permeated with more than ten pore volumes of AMD.