Surgical Drilling: Design and Performance of an Improved Drill

A trickle-type water treatment filter bed formed in the ground for receiving water of a sewage plant and which absorption bed has a drain wall around its sides and which functions to prevent saturation of the absorption bed. The drain wall means for the absorption bed finds particular utility in soils of poor permeability. The drain walls have tile means located at a depth lower than the tile means in the absorption bed and the drain walls function to prevent surface water from running into the absorption bed thereby contributing to its saturation, and also functions to drain off excessive water in the absorption bed so as to permit the absorption bed to function in a proper manner.