Abstract: A grinder pump assembly includes at least one grinder pump stage that has a diffuser and an impeller. The grinder pump assembly also includes a diffuser cap that includes cap contact surfaces. The impeller includes a plurality of upper vanes and lower vanes. The diffuser includes a plurality of lower contact surfaces, a plurality of diffuser vanes and plurality of upper contact surfaces. The upper vanes of the impeller are configured to rotate in proximity with the lower contact surfaces on the diffuser. The lower vanes of the impeller are configured to rotate in proximity with the cap contact surfaces. Multiple grinder pump stages may be used within a single grinder pump assembly.