A Progressive Solution for the Nation’s Largest Wastewater Treatment Plant 

Solving for Overflow Situations on an Accelerated Timeline

Under most conditions, the GLWA’s wastewater treatment plant uses the 18-foot diameter Detroit River Outfall (DRO) to discharge plant effluent to the Detroit River, allowing the proper time for treated plant effluent to mix with a disin­fect­ing chlorine solution and dechlo­ri­nat­ing sulfur dioxide solution to meet NPDES permit require­ments. During wet weather, however—when total flows swell from 600 million gallons per day (mgd) to 1,700 mgd—the utility relies on the Rouge River Outfall (RRO) to discharge a combination of secondary and primary effluent. Unfor­tu­nately, the RRO lacks the necessary disin­fec­tion capa­bil­i­ties as are provided for the DRO.

Given the delay in achieving disin­fec­tion of all discharges, GLWA determined that they needed to adopt an innovative progressive design-build delivery approach to meet the MDEQ’s accelerated schedule following a February 1, 2016 contract start. Adherence to this timeline required the 60% design to be completed by November 1, 2016 in order to obtain the Michigan Act 451, Part 41 Construc­tion Permit and complete nego­ti­a­tions of the project guaranteed maximum price by January 2017. This alternative delivery construc­tion schedule also required 100% plans and spec­i­fi­ca­tions for the first construc­tion package by April 2017, all design packages completed by November 2017, and substantial completion of the facility by April 1, 2019.

A progressive design-build project approach—the first for GLWA—included the development of a large physical model of the complex outfall system to ensure that disin­fec­tion contact times could be achieved and that the system controls would function properly.  Project specifics required:

• Modi­fi­ca­tions to existing gate and conduit systems
• Instal­la­tion of chemical injection points, including baffle walls, flow meters and diffuser systems throughout
• Full instal­la­tion of a new chemical building, which includes a whole new ovation control system
• Complete underground process yard piping and electrical duct bank throughout the existing system
• Startup, training and operational assistance

Technical Superiority and a Proven Partnership 

CDM Smith’s wastewater process engineers have been instru­men­tal in chlorine opti­miza­tion throughout GLWA’s system for the past 15 years, including the design of several regional Combined Sewer Overflow (CSO) pumping, treatment, and control facilities. This extensive on-site experience helped them understand system flows and intricacies to best integrate the RRO disin­fec­tion into GLWA’s existing operation. 

Armed with knowledge of the system’s inner workings, engineers began RRO improve­ments by performing detailed inves­ti­ga­tions into the outfall channel conditions and developing a detailed compu­ta­tional fluid dynamics (CFD) system model to estimate appropriate contact times. The model included a total of 15 million finite elements to represent the channel system, the flow of effluent between different inflow points, chemical diffusers, and discharge to both the DRO and RRO. 

Design-Build Benefits for Unforeseen Project Challenges 
As the largest single-site facility in the country, GLWA’s facility contained substantial utilities, many of which were not completely documented. As part of the project scope, CDM Smith was tasked with examining the four parallel 1,700-foot-long 15x15 foot conduits that provide the necessary contact time for RRO disin­fec­tion. Because some of these conduits had not been used for over 40 years, and others had been in constant use without inspection, CDM Smith provided on-site inspections using a Remotely Operated Vehicle (ROV) and dive team. This work identified several issues that needed to be addressed, primarily an 8-foot-deep sediment buildup along the length of two conduits. The sediment was tested, dewatered and disposed of in accordance with regulatory require­ments and permit deadlines, which required close coor­di­na­tion with GLWA staff to ensure that all safety precautions were met and activities did not conflict with daily plant operations. 

CDM Smith's construction team was able to partner with local and qualified subcontractors to help throughout the length of the design-build process, creating accurate estimates, addressing constructability concerns, and adhering to a schedule that accurately portrayed the project timeline. This allowed both designers and builders the chance to discuss operability issues and maximize system integration once construction was underway.

Constant collab­o­ra­tion through a forward-thinking progressive design-build approach helped ensure that cost impli­ca­tions, constructabil­ity and design specifics were fully understood. And ultimately, GLWA will be able to safeguard their water quality and increase efficiency by making use of recent advances in technology, as well as provide increased envi­ron­men­tal protection and employee safety.