Underdrain block for filter media system

An underdrain block for a filter media system comprising an air backwash and a water backwash system, the underdrain block comprising:

• a top wall, the top wall defining a plurality of air and water discharge holes;
• a bottom wall, and two side walls connecting the top wall to the bottom wall, the side walls have an inner surface and an outer surface, wherein the distance between the outer surfaces of the side walls is within a range of from approximately 12 inches to approximately 24 inches and the height of the underdrain block is within a range of approximately 7 inches to approximately 9 inches;
• a plurality of interior walls defining a first primary lateral and a second primary lateral, the interior walls further defining a first secondary lateral and a second secondary lateral, the secondary laterals separated from the primary laterals by one or more lateral separation walls, the lateral separation walls having an upper portion and a lower portion, the upper portion of the lateral separation walls defining a plurality of air distribution orifices, the lower portion of the lateral separation walls defining a plurality of water distribution orifices;
• the lower portion of the lateral separation wall perpendicular to the bottom wall, the upper portion of the lateral separation wall slanted at an angle within the range of between approximately 120.degree. to 125.degree.;
• and
• a center separation wall extending between the top wall and the bottom wall, the center separation wall separating the first primary lateral from the second primary lateral and the center separation wall further separating the first secondary lateral from the second secondary lateral, the center wall comprising a thickness that is divisible so that the underdrain block is separable into two usable half-sized blocks.