A modular underdrain system is disclosed. The modular underdrain system may comprise an intermediate modular component having a first peripheral side including a first mating portion and a second peripheral side including a second mating portion. The first peripheral side may comprise at least one transfer orifice. An intermediate plate member is disposed intermediate the first peripheral side and the second peripheral side along a width dimension. The intermediate plate member may comprise a metering pipe opening. A metering pipe may be sized to be positioned within the metering pipe opening.