A method and apparatus for constructing a filter zone of an earthfill dam, in which the filter zone includes adjacent coarse and fine filter layers. The coarse and fine filter materials are discharged simultaneously from an earthmoving vehicle having an ejector body. The ejector body includes a longitudinal divider wall that maintains segregation of the materials during transport, and the materials are discharged through separate chute assemblies so as to place the materials in elongate, side-by-side berms. The ejector vehicle is followed by a dozer or other piece of equipment that grades both berms simultaneously. Each pass of the ejector vehicle and dozer thus forms a stratum of the filter zone. The passes are repeated to form a plurality of strata in overlying relationship such that the coarse particulate material forms the coarse filter portion of the filter zone and the fine material forms the fine filter portion of the zone.