The invention is a three stage wastewater treatment system having a first tank, a second tank and a third tank, all in fluid communication and forming a unitary structure. The first and second tanks are nested, where the first tank is the innermost tank. The first tank has a clarifier structure disposed therein separating the interior of the first tank into a quiescent zone and an aeration zone. Positioned in the aeration zone is at least one air injector positioned. The treatment system is covered, and is generally buried (but can be used above ground).