alternatives being considered for an earth retention cutoff wall adjacent to a water supply reservoir include both secant pile walls and bentonite slurry walls. the ground conditions are residual soils and weathered to decomposed rock occasionally hard solid rock in very irregular profiles. we feel the slurry wall would have to be hydrofraise, but need to hear your experience on the cost effectiveness of the equipment mobilization for 300 lineal meters project. thank you for your input.