The Borie Well Field is a vital groundwater supply source for the Cheyenne Board of Public Utilities (Cheyenne BOPU) supplying up to 4.3 mgd (3,000 gpm) of high-quality drinking water as a supplement to the City’s main surface water supply. This groundwater was contaminated with tricholorethene (TCE) during the 1960s from the FE Warren Atlas Missile Site 4. Over approximately the past ten years, TCE levels in these production wells have been increasing, with several wells exceeding the EPA’s Maximum Contaminant Level of 5 ug/l (ppb). The USACE, Omaha District, was tasked with providing treatment of this water supply for the Cheyenne BOPU. Due to the urgency of providing remediation, the USACE decided a design-build contract with one firm responsible from pre-design through start-up and operational (up to 4 years) would better facilitate meeting the timeline (15 months) of providing a facility with an ultimate capacity of 8.6 mgd.
In March of 2009, McMillen Jacobs was awarded this project providing the complete design, permitting, construction, and annual operation and maintenance services for the new facility. Our unique company structure of in-house engineering and self-performing construction provided the USACE with a single firm, who would be responsible for the entire project. We provided the Corps with a value-engineering proposal to locate the new plant at a higher location, a half-mile from the RFP location, where gravity flow could be used. The location allowed the USACE to eliminate construction of a 400 hp treated, groundwater pump station, saving them significant capital and O&M costs (more than $60,000 per year).
The facility utilizes four units of air-stripping technology thru a low-profile tray system, each treating 1,000 gpm (1.4 mgd). The units are fed by an innovative hydraulic influent flow split structure which provides for perfect gravity flow-splitting of the influent water to whichever units are operating. This allowed for the elimination of four influent flow-modulating valve-and-meter systems and greatly simplified PLC programming requirements. One critical result of this design was that the new facility was reliable and simple enough that it could operate “unmanned” continuously (24/7).
McMillen Jacobs designed and installed more than 2,800 linear feet of new HDPE pipe ranging in size from 12″ to 48″. Due to the pipeline being installed at an existing water treatment facility, there were multiple ties into existing underground pipelines required where connection types and sizes were unknown until uncovered. Underground utilities also posed issues throughout the pipeline installation. McMillen Jacobs excavated, moved, and compacted 9000 yds of material to construct new building pad for a new 4600 sf pre-engineered metal building. Concrete foundation, stem walls, floors, diversion structure, and effluent split structure. Our project team installed four air stripper units inside the new building with associated mechanical piping, electrical conduit and control panels, and complete building ventilation and civil works. All of the local county and state agency coordination had to occur efficiently and simultaneously with the final design phase of the project.
2012 Oregon ACEC Engineering Excellence Honor Recognition