2012 Best Project

Civil Works/Infrastructure Category

PAR 942 North Secondary Complex Improvements

Denver

Major improvements on the north side of Denver Metro Wastewater's Robert W. Hite Treatment Facility in north Denver included building a new wastewater process to treat centrate ammonia. That meant the project team had to modify aeration basins and secondary clarifiers to meet more stringent discharge regulations.

Crews built four centrate and return-activated sludge basins, each with a 700,000-gallon capacity. Centrate ammonia is a liquid by-product generated when solids are dewatered by centrifugation.

The activated sludge process uses centrate with high ammonia levels as a food source that re-aeration basins convert from ammonia to nitrate. Using the existing space, walls and piping resulted in the lowest per-unit treatment cost. The process provides nearly equal treatment capacity, but three aeration basins were able to be placed in one-third the volume.

Using existing facilities presented some challenges—much of the construction occurred inside a structure 20 ft below ground in a square city block area. Ultimately, treatment capacity was expanded with no increase in the plant's footprint.

The project was completed 13 months ahead of schedule, earning Garney Construction, the general contractor, a $960,000 early-completion bonus.

Key Players

Owner: Metro Wastewater Reclamation District, Denver

Engineer: Carollo Engineers, Broomfield, Colo.

General Contractor: Garney Construction, Littleton, Colo.

Entry submitted by Metro Wastewater Reclamation District