Evaluating coagulating systems for use as invasive barriers in the subsurface

Batch and column test methods were developed and applied in the laboratory to study the reduction in hydraulic conductivity (K) of porous media injected with coagulants that form barriers to flow and contaminant migration. Coagulum formation is achieved as the carboxyl groups of long, hydrolyzed polymer chains are cross-linked by the coagulant cations; the K of the porous medium is reduced as this coagulum is formed in and plugs the pore space. Laboratory methods for the subsurface injection of the polymer and coagulant were developed and subsequent column tests were conducted to demonstrate the ability of the selected coagulating system to reduce the K of coarse, unconsolidated material. Results for the specific coagulating system examined indicate that coagulum formation is virtually instantaneous and that additional reductions in K are more efficiently achieved by increasing polymer concentrations. These laboratory results represent a lower bound on the effectiveness of the selected coagulating system in reducing the K of the natural subsurface due to incomplete mixing of coagulants in the test column from very slow injection rates and the use of a coarse test sand that is more difficult to plug with coagulum than finer, poorly sorted materials. Reductions in K of up to five orders of magnitude have been reported for similar materials and indicate the potential application of invasive barriers to control the subsurface flow in waste management or groundwater remediation scenarios.

Duke Scholars

Author J. Jeffrey Peirce Civil and Environmental Engineering