Webcor’s infrastructure resume continues to grow with the complex work our team’s delivering at the Biosolids Digester Facilities Project (BDFP), a Joint Venture with MWH Constructors for the San Francisco Public Utilities Commission (SFPUC). BDFP’s impressive scale and scope have gained significant attention from not only our industry peers but community leaders and stakeholders, who are beginning to realize the tangible benefits of the years of funding and planning efforts invested in this project.

The project comprises four focused teams delivering four building areas; Pre-treatment/Odor Control Building, Biosolids Digester Building, Dewatering/Load Out Building, and Ferric Chloride Storage/Pump Station Buildings..

Pre-treatment/Odor Control Building

The biosolids that come to the Pre-treatment/Odor Control Building are only partially processed. "It's more on the raw end of sewage," says Construction Manager Chase Corcorran. 

The building will hold over 80 pumps in its 30,000-square-foot basement, just part of the approximately 130,000-square-foot structure. "Some of the pumps are as big as 22 feet long and five feet wide," Chase says. "The building is very dense with equipment that receives the semi-raw waste and puts it into different parts of the treatment system."

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Of all the buildings in the project, the Pre-treatment/OdorControl Building is the only one with office space and architectural finishes. It is through this building that walking tours will be conducted. The project is the first of its type in the Western United States, and representatives of groups planning to build similar facilities will visit.

"There's a small living green roof, fancy ceilings, and viewing areas from which visitors can see the major operations below," Chase says. The fourth floor will be a penthouse with an all-glass face that looks out on the living roof. The basement, and the first three floors, on the other hand, will be filled to the brim with equipment and processes.

Work has brought the building back up to grade. MEP foundations are done, along with perimeter walls, the ground floor slab, and the next lift of the vertical structure. The main work of the building involves three massive funnel-shaped stainless steel cake storage hoppers. Each hopper features a 180-cubic-card funnel that stands one-and-a-half stories tall, occupying level one and the basement. "Assembled, each hopper is 80,000 pounds," Chase explains. "We have to get them into the building, set, and anchored before we pour the second-floor deck. This is the first major mechanical process we're setting in the building."

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Fabrication of the hoppers began seven months ago. The pieces were delivered to the site in three large pieces, with welding and prepping taking place on-site. The last was flown into place the week before Thanksgiving. 

Structure progress should be far enough by the year's end to start receiving the large piping. "All the work to install the pipe and conduit in the basement kicks off in January," says Chase, who adds that a Herculean effort will be required.

Biosolids Digester Building

Five digester tanks will occupy Building 610. "They're massive 1.7-million gallon reinforced concrete anaerobic digester tanks,"says Roman Navarro, assistant project manager. These 65-foot tanks will reside on the first floor and drop 40 feet into basement levels one and two. "They look almost like an ice cream cone, with the tank on the top and the cone tapering to the bottom below the first floor," Roman says.

The tanks are all pre-stressed concrete structures, each comprising six staggered pours for the core walls. "We started on tank 5 on the north-facing side of the project and worked our way down to tank 1," Roman says, adding that tanks 1-4 will act as the primary biosolid digesters while tank 5 will serve as storage.

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"DN Tanks, the contractor building the tanks, has an impressive wrapping machine," Roman says. The wrapping machine comes into play once all the core walls are placed. These wrapping machines sit on a curb on the exterior of the tanks and are attached to the center tower, which acts as bracing for the core walls and for the wrapping machine. Once the wrapping machine is installed, it rotates clockwise around the tank to blast the core walls, spray an initial layer of shotcrete, wrap the tank with a first layer of circumferential prestressing, spray the first layer of strand cover shotcrete, a second layer of circumferential prestressing, then spray the final layer of shotcrete, and wrap the tank in plastic wrap for curing.

"The Biosolids Digester Building is currently on its final round of shooting shotcrete on tank 3," Roman says. "We're working our way down to tanks 2 and 1. We have commenced liquid tightness testing starting at tank 5, which involves completely filling each tank and inspecting them for leaks under a full hydrostatic head. If any seepage is present, these locations are injected from the exterior of tanks to seal the leaks."

MEP buildout in the lower and upper basement levels is progressing well; the team has received deliveries on most of the major equipment in the basement levels. "The next major activity for building 610 will be building the covers for the tanks, external staircases, and the elevator at tank 3, which is set to start early next year," Roman explains.

Dewatering/Load Out Building

Ground was broken for the Dewatering/Load Out Building in July 2023, and since then, the project has been navigating a path marked by design modifications and the intricate process of onboarding a pivotal player: the Process Mechanical subcontractor. According to Project Manager Ruhi Thakur, delays in securing this essential subcontractor stem from funding availability anticipated in the middle of 2024 for the comprehensive process mechanical construction contract. Despite encountering challenges, the team is actively devising contingency plans (Plan Bs) to ensure adherence to the scheduled dates.

The design modifications revolve around the selection of the second named Storage and Loadout system, which is the heart of the Dewatering/Load Out Building’s processes -- a sophisticated combination of intricate conveyor systems and four large storage silos with the ability to discharge about 45,000 pounds from each of the two silos in one bay (a total of two bays). This system handles the transfer of dewatered biosolids from belt filter presses to the loadout trucks, which are responsible for shipping class A biosolids to diverse market resources.

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"In the complex world of heavy processes and plant construction, design changes pose considerable challenges, especially in a publicly hard-bid project," Ruhi says. "However, the team's ability to adapt and achieve milestones amid these challenges reflects their commitment to the project."

In a noteworthy development, the Dewatering/Load Out Building team had the opportunity to visit Denver in September to explore the city's main biosolids plant. MWH Constructors, Webcor's JV partner on the Biosolids Digester Facilities Project, played a pivotal role in the construction of the dewatering building and other facilities in the plant. The field trip, attended by three Webcor and three MWH team members, provided firsthand insights into the processes and lessons learned by the MWH Constructors team. (The travelers included MWH Constructors' Cecilia Gamboa, Jared Diller, and Kyle Gramlich, and from Webcor, Ruhi, Project Director Lisa Thomas, and Sr. Superintendent Stuart Chapman.)

The visit offered a glimpse into the intricate network of process pipes, resembling a complex array of spaghetti, which will eventually be installed in the Dewatering/Load Out Building. "The site visit to Metro Water Recovery in Denver was especially useful for the Webcor team members who've never built this type of project," says Project Director Lisa Thomas. "Having eyes on similar pieces of equipment to those that will be installed in our dewatering building helped us understand the complexity level around connection points, space constraints, and maintenance and operation.

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"We became less concerned about some items and much more concerned about others once we saw the actual installation," she says.  "Additionally, Kyle Gramlich, our MWH Constructors tour guide who worked on the Denver dewatering facility, provided commentary on lessons learned and pointed out issues that we would likely face with our building."

"We hadn't seen anything like it before. It was truly fascinating," Ruhi adds. The Denver trip broadened the team's understanding of the project and facilitated knowledge exchange and collaboration with industry peers.

Ferric Chloride Storage/Pump Station Buildings

The Ferric Chloride Storage/Pump Station Buildings consist of two new facilities for the Southeast Plant: Building 921, which will be the new W2 Pump Stations, and 913, which will house the new Ferric Chloride Storage Tanks. "921 and 913 are the smallest of the four major facilities on this plant, but they feed the two main components the other three facilities need to function: electricity and water," according to Sr. Superintendent Lili Fang.

The main electrical substations that power all the other facilities via a network of underground duct banks are located in one of the two facilities. There are three major categories of water within the Plant: W1,W2, and W3. W1 water is clean, potable water that the plant uses to feed water fountains and eye-wash stations. W2 waters are non-potable water that has been filtered but is still dirty. W3 water is very dirty. The main function of Building 921 will be to convert W3 water into W2 water through a series of disinfection processes using ultraviolet treatment so it can be circled back to the plant as part of the wastewater treatment process within Buildings 600, 610, and 615.

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Ferric Chloride is a highly corrosive chemical used as a flocculant and coagulant agent in sewage treatment. It helps smaller particles in wastewater clump together and promotes faster sedimentation of these large particles so they can be easily removed during the water treatment process. One facility will house the two Ferric chloride tanks that will store this chemical and feed it to the five digester tanks in the Biosolids Digester Building.

The Ferric Chloride Storage/Pump Station Buildings broke ground with make-ready work in June 2022; foundation and pile drilling started in January 2023. Structural concrete work will be completed by the end of this year, with all major equipment and piping installed by May 2024.

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"One of the most unique aspects of the 900 Area is the high percentage of LBE subcontractors we were able to sign up as prime subcontractors for the very first time," says Project Director Rowena Domingo. "Four main LBE trades provide foundation, plumbing, civil, and demo work. This is a good size work for these firms that pushes their capacity with support from the team to build them to work on future complex scopes."

The concrete sub also took on several LBEs, maximizing local hiring. The sub is mentoring those LBEs, Rowena explains. "There is also a good distribution of MWH and Webcor project management team that leans in on each other's technical strengths which continues to build camaraderie across the JV," she says.