Test Driving a Project Delivery Hybrid: An Evaluation of Design-Assist

To keep pace with the 2005/2006 housing boom, the City of Roseville, CA, required an expansion to its Pleasant Grove Wastewater Treatment Plant (WWTP) that would increase the existing secondary treatment processes and provide new primary and solids treatment processes. During the expansion design, the City found that an aeration upgrade was required immediately to address an increased loading projection. The aeration upgrade required adding eight aeration motors to each of the existing three oxidation ditches for a total of 1,260 horsepower. After sizing and selection of the mechanical equipment, the majority of the remaining work was electrical. At the 30 percent design, the aeration upgrade design was separated from the expansion project and became an independent project to be constructed immediately.Design-build was the initial choice for this project due to the need for an accelerated schedule. In 2007, however, contractors and engineers were back-logged with projects. Due to the significant wiring and a prenegotiated mechanical package, it appeared to be a project that would result in a high design risk and a low fee for the engineer. Consequently, a delivery analysis was conducted. Due to the risk-return factors, the City elected a delivery option not well known to the wastewater industry, design-assist.