A FLOW PUMP SYSTEM FOR ASSESSING CLAY BARRIER-PERMEANT COMPATIBILITY

This paper presents the performance, reliability, and features of a hy draulic conductivity, k, testing equipment specially designed and fabr icated for clay barrier-permeant compatibility studies. The key compon ent of the equipment is a flow or infusion/withdrawal pump that is use d to deliver a constant and continuous flow of permeant at some prescr ibed rate through two stainless steel syringes to a soil specimen. The pump has a switch that allows the motor direction to be changed to al low one syringe to empty while the other is filling. This provides an uninterrupted flow of permeant to the specimen, unlike most traditiona l testing equipment that requires complete stoppage of permeation in o rder to provide a fresh supply of permeant. In some cases, re-establis hment 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 rubbe r 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 liquid s and redox-sensitive permeants such as acid mine drainage. Furthermor e, this cell is connected to a back pressure supply to decrease the ti me required for the pressure to return to its original value after swi tching 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 scree n. 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 AM D did not change k, it may have dissolved some primary soil minerals s uch as calcite and dolomite, which in turn buffered the pH of the effl uent from a specimen permeated with more than ten pore volumes of AMD.