Burns & McDonnell completed a detailed evaluation of the City of Gillette's wastewater treatment facilities — including the collection system and wastewater treatment plant — and final design and construction administration of the recommended improvements.
The project was named the 2007 Project of the Year by the American Public Works Assocation, Rocky Mountain Chapter.
During the evaluation phase, a collection system model was prepared and, based on growth projections; a collection system capital improvements plan was prepared. The existing 3.85-million-gallon-per-day (MGD) wastewater treatment plant was evaluated based on projected flows, projected waste loads and anticipated future National Pollution Discharge Elimination System effluent limits, including more stringent ammonia nitrogen and total residual chlorine limits.
- Preliminary treatment system
- Primary treatment system
- Secondary treatment system
- Effluent disinfection system
- Solids processing and handling system
- Anaerobic digester gas handling system
- Plant power system
- Collection system and treatment plant telemetry system
In addition to specific treatment plant processes, other policy and management issues were evaluated; including wastewater system staffing and additional effluent reuse alternatives. Based on the detailed evaluations, an overall capital improvements plan was formulated along with an implementation schedule. The major improvements included expansion of the secondary treatment system, installation of ultraviolet (UV) light disinfection, construction of mechanical dewatering facilities, incorporation of iron salt addition for digester gas cleaning, and upgrading the existing telemetry and control system. The improvements resulted in a facility rated for 5.2 MGD (maximum month flow).
Construction on the $13.2 million project began in August 2005 and was completed in the Spring of 2007. The major capital improvements included:
- Remodeling the existing administration building to facilitate staff needs
- Installation of aluminum dome covers on the two existing primary clarifiers
- Construction of two additional aeration basins and one secondary clarifier at the secondary treatment system
- Modifying and automating the existing oxygen supply system
- Installation of a UV light effluent disinfection system to replace the existing chlorine gas system
- Anaerobic digester gas handling system modifications
- Modifying the existing chlorine building to provide liquid sodium hypochlorite storage and feed equipment (for effluent disinfection backup and filamentous growth minimization)
- Construction of a new centrifuge dewatering system to enhance the composting operation and minimize biosolids beneficial reuse costs
- Installation of a ferric chloride/ferrous chloride chemical storage and feed system to assist in odor minimization and to reduce historically observed high levels of hydrogen sulfide in the anaerobic digester biogas
- A complete SCADA system upgrade
- Construction of a new collection system/maintenance building to house large city vehicles and implements
- A new on-site sewage lift station to handle flow from the Sleepy Hollow interceptor sewer
- Other treatment facility, mechanical, electrical and site improvements
To ensure that the city maintained control over major equipment selection, the project included direct procurement of the centrifuge equipment and the UV light disinfection equipment.
All improvements were designed in-house by Burns & McDonnell. The project was funded through the State Revolving Fund loan program. The construction firm of Garney Wyoming built the improvements, and the project was completed in March 2007.