This manual presents a procedure for the design of land treatment systems. Slow rate, rapid infiltration, and overland flow processes for the treatment of municipal wastewaters are given emphasis. The basic unit operations and unit processes are discussed in detail, and the design concepts and criteria are presented. The manual includes design examples as well as actual case study descriptions of operational systems. Information on planning and field investigations is presented along with the process design criteria for both large and small scale systems. (Author/BB)