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Overhauling Vallejo’s Wastewater Infrastructure with the Mare Island Pump Station 3W Effluent Bypass Project

The Vallejo Flood & Wastewater District (VFWD) is responsible for safely treating 6 billion gallons of raw sewage each year. Its 450 miles of sewer pipes and 40 pump stations are utilized 24 hours a day and must be continually maintained or replaced. The VFWD serves a total area of approximately 28 square miles, covering the City of Vallejo, adjacent unincorporated areas, and Mare Island. The VFWD has proposed constructing several new facilities to replace the existing wastewater treatment plant (WWTP) and rehabilitate other existing facilities with aging equipment at its WWTP.

VFWD contracted Myers & Sons Construction (Myers & Sons) out of Sacramento to build a new Mare Island treated effluent pump station (MIPS) and associated chlorine contact tank (CCT)-D adjacent to the existing CCT-C. When complete, the new configuration will allow VFWD to treat and discharge more recycled water for its customers. This project will also allow for the decommissioning of the existing MIPS.

Specifically, the contract calls for a new pile-supported structure that consists of a new Mare Island Pump Station and Chlorine Contact Tank D. There will also be a pile-supported addition to the existing Chlorine Contact Tank C, a pile-supported electrical duct bank to tie the controls of the new CCT-D, and CCT-C upgrades into an existing adjacent electrical building. Additionally, installations include a pile-supported transformer, a pile-supported electrical vault, construction of a new outfall pipeline and associated Mare Island Valve Vault, a new temporary electrical control building, VFDs for the plant return pump station, new chlorination and dechlorination pipelines, associated electrical duct banks, and other general site improvements. To make room for this work, Myers & Sons was contracted to demolish an existing Confined Space Training Facility and an existing switchgear facility. The contract also calls for a complete overhaul of the existing south biotower. This work includes the removal of the tower’s existing aluminum cover, the removal and replacement of existing media, the removal and replacement of its rotary distributor drive, adding a VFD, other upgrades to the electrical system, and adding a catwalk. The complete list of the work can be reviewed in detail at https:// www.vallejowastewaterplans.com/ jobs/873/details/mips-3w-effluentbypass-project.

Robert Barton is the Project Manager overseeing the Vallejo Mare Island Pump Station (MIPS) 3W Effluent Bypass Project for Myers & Sons. “We began mobilizing our equipment and crews on March 1, 2023, and are contracted to have everything completed by January 2026. One of the first things we focused on was the demolition of existing equipment and structures, such as the old switchgear pad, bollards, and a pre-existing confined space training structure. Next, our crews began potholing various areas throughout the site, along with utilizing ground-penetrating radar to locate existing utilities,” says Barton. “This project started up slowly, but we were kept busy with several separate service contracts that included concrete and asphalt improvements through the WWTP, the replacement of tide control gates off of HWY 37, and the servicing of a pump station at Tubbs Island off of Highway 37.”

Myers & Sons is self performing much of the work on this $40 million pump station project, including all of the underground earthwork, cast-in place concrete, mechanical and underground piping, demolition and modifications to existing components, construction of all new structures and replacement of media at the south biotower. Condon-Johnson & Associates were subcontracted for the installation of 167 precast piles throughout the entire jobsite. “Condon-Johnson utilized a 210-ton crane with a 169-foot-tall pile driving cage to install the precast concrete piles to depths up to 144 feet below the bottom of planned excavation,” says Barton. “We then started the process of having our subcontractor, Blue Iron, install sheet piles around the perimeter of the entire excavation site due to the fact that we are digging down 22 ½ feet in young bay mud in limited real estate for the contract excavation. As of November 17th, we have removed around 5,000 cubic yards of material and have around another 5,000 cubic yards to go. Once the sheet piles were in place, we began excavating down five to six feet before having Blue Iron back on site to install a set of reinforcing struts, brackets, and walers for the sheet piles. We then excavate the next five to six feet, have Blue Iron reinforce, and repeat the process. This is a four stage excavation over the entire footprint, and we are beginning our third stage today.”

Myers & Sons began the excavation with a Cat 352 excavator that would fill a dump truck in just three scoops but has since switched to using two John Deere long-reach excavators and two labor crews for the sheet pile work and to do the rest of the excavation. “The first five feet of the excavation were suitable for reuse as cement-treated subgrade; we trucked this dirt across the road to our staging area for later use. The rest of the material in the excavation is young bay mud that we exported offsite to a local duck club for use in levee improvements,” continues Barton. “Once we are at the bottom of the 22 ½ foot deep sheet-piled excavation, we will install the cement-treated subgrade for the new CCT. Our subcontractor, Griffin Soil, will bring in their batch plant truck, and our crews will load the first five feet of previously excavated material into the truck for mixing. We will mix in a 16% cement addition by weight to be poured as slurry into the back of Myers’ supplied concrete pump truck. We will then pour and finish the cement-treated material to form a four-feet section of stabilized subgrade over the entire footprint of the excavation for the new CCT. Once the new cement-treated soil gets up to design strength, we can remove the bottom and middle sheet pile reinforcement. Next, we perform the concrete slab on grade for the entire structure. Once that concrete slab on grade is at design strength, we can remove the top sheet pile reinforcement and move on to the concrete walls and decks. We are estimated to pour around 2,500 yards of concrete in all for this structure.”

Barton explains that the young bay mud has a PI of 50 and is at a 40% moisture content right now, with the optimum being around 18%. “This jobsite is said to sink as much as 14 inches every ten years, and that makes sense because we ran into an asphalt pavement section around 4 ½ feet deep in our excavation that may have been part of an old parking lot,” says Barton. “We were expecting to be dewatering at around 20 gallons per minute, and in preparation, we set up several dewatering wells and sump pumps that flow into a Baker settling tank, into a filtration system, and then back into the WWTP’s storm drainage system. What we are currently experiencing is more like half a gallon per minute – a flow rate that is less than your typical water faucet at one’s home. We think it’s due to the high waterretaining ability of the young bay mud and the fact that our excavation is sheet piled.”

Barton points out that one of the main challenges on this project is just how linear the jobsite is in the sense that nothing can really go forward until the new CCT and Mare Island Pump Station is poured out and backfilled. “The new approximately 150-foot by 70- foot cast-in-place chlorine contract tank and mare island pump station will be poured out by September 2024. After everything is backfilled, we will remove the sheet piles and begin installing the mechanical equipment for the CCT,” continues Barton. “The mechanical equipment includes a large pump station on top, chlorine agitation equipment, and other flow control equipment that will allow the facility to treat an estimated additional 10 million gallons per day. Once all the equipment is operational, we can start making preparations to commission the entire new structure.” According to Barton, building the new chlorine contact tank and the Mare Island pump station structure is around 70 percent of the contract. “Once the structure is complete, four pipelines will be installed from one structure to the next so that they will work together and equalize, and then around 800 feet of 30-to-42-inch HDPE pipe will be placed. Additionally, two 400-FT 8-inch schedule 80 PVC pipelines with two PVC hoses going through each pipeline. The two PVC hoses are necessary to convey chlorination (SHC) and dechlorination (SBS) chemicals from the existing storage facilities onsite. Chemical leak prevention is of paramount importance, so this pipeline is constructed with a redundant PVC hose in each pipeline. In the event of a leak, the liquid chemicals would drain to a nearby containment manhole, and the plant will know to immediately switch to the redundant PVC hosing and then replace the now defunct PVC hose,” says Barton. “We will also install welded steel pipe at diameters of 36 to 42 inches in 50-to-60-foot sections at depths of 8 to 16 feet between the new CCT and the existing adjacent CCT. This will require more sheet pile shoring. We then still have another 1,800 linear feet of duct banks, which are essentially buried electrical conduit. Pipelines will be backfilled with a specialty lava rock, which is less dense to prevent sinking, and duct banks will be encased with red concrete.” In addition to the primary job of constructing a new pump station and installing hundreds of feet of pipeline, Myers & Sons was also tasked with removing the circular aluminum roof of one of the biotowers and will then gut and replace the internal components. “We utilized a 350-ton crane to remove the aerobic bacterial treatment tank cover, which was then demolished and scrapped. We are also removing all of the plastic 2-foot by 2-foot media boxes and replacing them with new media,” says Barton.

The Vallejo Mare Island Pump Station (MIPS) 3W Effluent Bypass Project is a diverse project with several features, parts, and components. To perform all of the various tasks, Myers & Sons must have the right equipment for each specific job application. “We own and maintain many of the larger pieces of equipment that are used regularly on our jobsites. When it
comes to some of the more compact or specialty pieces of machinery, we turn to equipment distributors like Sonsray Rentals. For this particular job, we have rented several machines, including a Case wheel loader for moving the spoils to the laydown yard, and two Skyjack telehandlers for general handling of all construction materials around this compact jobsite. We originally rented these machines, but just recently purchased one of the Skyjack telehandlers from Sonsray Rentals,” says Barton. “We work with John Johnson from Sonsray Rentals and have rented so many different pieces of equipment from them over the years. This includes mini excavators, skip loaders, wheel loaders, telehandlers, and so much more. When I call John, he gets back to me within 30 minutes and always goes above and beyond to get us what we need, no matter what the timeframe or circumstance. For instance, I had an emergency response project back in March for the City of Richmond at a wastewater treatment plant. They called us on a Monday, and by Wednesday, we were putting in a 20 MGD pump bypass, and I had to get a forked wheel loader right away. John did not have one available, but he went out of his way to get it to me within the next hour from another source. John and Sonsray Rentals are always resourceful and responsive. Even when they won’t profit personally, John and Sonsray Rentals are there to keep us happy and moving forward profitably. Sonsray Rentals is definitely one of our go-to rental companies.”

The purpose of this and other wastewater treatment facility projects is to replace critical aging infrastructure that is beyond its useful service life. The Vallejo Mare Island Pump Station (MIPS) 3W Effluent Bypass Project will increase energy efficiency, operational flexibility, and redundancy, improve environmental compliance reporting, and prevent unauthorized raw wastewater discharges to the San Francisco Bay. For more information on Vallejo Wastewater Flood District, go to www.wastewater.org.