Sealing leaks which have developed in liquid surface impoundments with geomembrane liners may be difficult due to aged liner material. A technique utilizing electrophoresis which causes clay particles to be attracted toward leaks when an electric field is applied provides a cost-effective method for repair. This study presents an experimentally verified methodology to predict electrophoretic sealing of in-service geomembrane liners. The methodology includes a procedure to simulate axis-symmetric electrophoretic cake formation and a numerical technique to solve the electric field for voltage gradients. Path lines of solid particles are generated by superposing electrophoretic and Stokes' settling velocities. A numerical method to obtain a steady-state cake profile by conserving solids mass and an approach which uses path lines to simulate transient cake formation are described. For an initially uniform suspension, final and transient cake profiles are obtained under varying conditions. The effects of voltage difference, surface electrode size, and initial bentonite concentration on cake formation are discussed. In general, a higher Voltage difference or a wider surface electrode accelerates the cake formation process. For efficient cake formation, the surface electrode should be located close to the water surface over the leak. A comparison of theoretical predictions with previously obtained experimental data shows a reasonable agreement. The analysis presented in the study provides a relatively inexpensive and useful tool in the implentation of an in situ field operation.