NOVELTY - Self regulating treatment of wastewater and contaminated groundwater involves constructing treatment zone (1) having top (13), and bottom (3) portions, inlet (9), outlet (11), unit for introducing exogenous treatment agents and unit for removing accumulated solids; establishing within zone an aqueous zone colonized with bacteria; allowing mixed microbial population to become established in presence of water to be treated and floating non-aqueous liquid electron donor; directing water to inlet; generating treated water in the treatment zone; and directing treated water to outlet.    USE - For treatment of wastewater and contaminated groundwater (claimed) to the resolution of waste-water from coal and other mines, coal yards, runoff from chemical operations, and any other semi-permanent or permanent point source.    ADVANTAGE - The method is specific for the contaminants to be treated, long lasting, requires infrequent attention, stable and requires irregular addition of inexpensive, readily available, easy to handle biochemical energy sources. The electron donor/nutrient for the bacteria are biodegradable and are relatively inexpensive. High purity is not required. The oils float as a separate phase on the water being treated and degrade slowly to provide a steady nutritional source for the bacteria. The method prevents migration of bacteria and nutrients away from the treatment zone; concentrates precipitated and accumulated solids in a collection zone to limit clogging of the system and which is stable over extended periods of time. The method requires minimum maintenance.    DETAILED DESCRIPTION - Self regulating treatment of wastewater and contaminated groundwater involves evaluating characteristics of water to be treated; constructing treatment zone (1) having defined dimensions, top (13) and bottom (3) portions, inlet (9), outlet (11), unit for introducing exogenous treatment agents and unit for removing accumulated solids; establishing within treatment zone an aqueous zone colonized with bacteria selected for treatment of water; allowing mixed microbial population to become established in presence of water to be treated and floating non-aqueous liquid electron donor; directing water to inlet; generating treated water in the treatment zone; and directing treated water to outlet.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic of a generic treatment system.    treatment zone (1)    bottom (3)    inlet (9)    outlet (11)    top. (13)