Headworks, Dryden Box & Influent Flume Improvements
City of Modesto, California

The $17 million Headworks and Dryden Box Project at the City of Modesto’s Primary Sutter Avenue treatment plant is currently under construction by general contractor, C. Overaa & Co. The project involves constructing numerous buried junction structures tying into existing pipelines, installation of several hundred feet of large diameter pipe, new process equipment, odor control improvements, and major electrical improvements that include replacing motor control centers and upgrading control systems with PLCs to improve remote automated control via the existing SCADA system.

The work includes pumped bypasses, shutdowns, temporary systems, tie-ins, and startups requiring manipulation of existing system valves and gates to test the new system in a loop prior to incorporation into the process with small windows of opportunity for testing and confirming reliability. The junction structures require control of groundwater and complicated shoring systems to construct the structures, and temporary bypasses to demolish existing piping within the new tie-in structures, while minimizing impacts to the operation of the existing treatment plant processes. The project started in November 2018 and is scheduled to be completed on or before November 2020.

The City’s goals included to minimize disruption to the daily domestic sewer treatment process while making the upgrades to the sewer treatment facility during the allotted seasonal construction windows. The City also wants to complete upgrades to the Can Seg pump station (Pumping Plant No. 3) including startup and commissioning prior to start of canning season on July 1st.

West Yost provides Construction Management and Inspection (CM&I) services including correspondence/document control, Submittal & RFI review and coordination, and as-built updates. West Yost conducts weekly progress meetings, coordinates Methods of Procedure (MOP) review meetings prior to shutdown/tie-in milestones and bypass events, and daily coordination with plant Operations and Maintenance staff to minimize disruption to the daily treatment process. West Yost also provides daily construction inspection (quality assurance) including coordinating materials testing and special inspection services on an as-needed basis, startup coordination & oversight, monthly schedule review, monthly payment application review and payment recommendation, review and negotiation of Potential Change Orders (PCOs), monthly reports summarizing construction activities and issues, claim and dispute resolution, and weekly review of permit/environmental compliance.
West Yost meets the City’s goals through rigorous review of the CPM Baseline Schedule and frequent coordination (Methods of Procedure review) meetings with the client and contractor to schedule shutdowns, bypasses, tie-ins, etc. to minimize disruption to daily treatment processes. West Yost is in daily communication with City Operations & Maintenance staff to discuss concerns.

An abandoned structure was encountered that encroaches on the proposed Junction Box that spans the entire depth of the 40-foot-deep excavation. In order to construct the new Junction Box, the structure would require demo to the full extent of the excavation, which would result in a change order with an order of magnitude of approximately $300,000. Working with the Contractor and the Design Engineer, we were able to avoid demolishing the abandoned structure and minimize additional costs created by the unforeseen condition by deleting construction of the new Junction Box and tie-in the new 84-in. line to the north wall of the existing Junction Box. In addition, the abandoned structure was utilized as shoring in lieu of the proposed driven sheet piles resulting in additional cost savings.

The original SCADA integrator (HSQ) named in the specifications due to the proprietary SCADA program they provide and maintain City-wide, posed a challenge creating a situation where the first critical project milestone of getting Pumping Plant No. 3 on line before Can Seg season started on July 1st would potentially not be met. The project named integrator was unresponsive to status check-ins by the Electrical & Instrumentation subcontractors and not meeting intermediate goals. West Yost worked with the City and Design Engineer to implement an industry standardized SCADA system, leading to replacement of the proprietary SCADA program and integrator, resulting in a credit of $200,000 in addition to meeting the July 1st deadline.