The performance of a leach field in processing waste water is maintained or
improved by a control system in which one or more selected parameter in a
waste water conduit, or in the influence zone of the conduit, is measured,
compared to a set point(s), and one or more variable is manipulated. For
example, gas composition, gas pressure, water level and water content are
measured; waste water flow, heating, air flow and air composition are
changed. In one mode of operation the manipulated variable is
qualitatively different from the parameter being measured.
