SFPUC Southeast Plant Primary & Secondary Clarifier Replacement

Location: San Francisco, CA

Owner: San Francisco Public Utilities Commission

Contract: $25.8 Million

Role: General Contractor

Delivery Method: Design-Bid-Build

Result and Benefit to Client

Despite multi-layered critical issues that arose after construction started, the $25.8-million Southeast Water Pollution Control Plant Primary & Secondary Clarifier Upgrades project was delivered on schedule and $2.25 million under the City’s revised budget after they added tasks to the original scope of work. With focus on successful outcome and an innovative mindset, Monterey Mechanical resolved every management and technical issue that arose. Excellent partnering with the City and County of San Francisco and key subcontractors was a key component of successful project management.

Project Description

Constructed in 1952, the aging infrastructure of the City and County of San Francisco’s Southeast Water Pollution Control Plant (SEP) required upgrades. The SEP is the City’s primary treatment plant handling approximately 80% of the wastewater from the eastern two-thirds of San Francisco’s residents. The maximum treatment plant capacity is 250 million US gallons per day, with the average daily dry weather flow of 60 million US gallons. Monterey Mechanical was contracted by the City and County of San Francisco (the City)/San Francisco Public Utilities Commission (SFPUC) to upgrade the mechanical, structural, electrical components at the primary and secondary sedimentation tanks (clarifiers) to ensure operational reliability, seismic requirements, and compliance with regulations for liquid treatment. Major upgrades to the primary sedimentation tanks included replacing key mechanical and electrical equipment and addressing structural repairs to the concrete, tanks, and influent channel; and installation of covers for the primary sedimentation tanks and ventilation system. Similar upgrades were required for the secondary clarifiers including replacing key equipment and retrofitting eight secondary clarifiers, and structural repairs including concrete repairs and coating.

Challenges | Solutions

1.     Partnering with the City to Overcome an At-Risk Schedule for First Dry Season

Challenge: The contract allowed two secondary clarifiers to be taken offline during a four-month dry season (June-September), but before taking a unit offline, any new equipment had to be onsite. With the contract starting mid-March 2016, there was a substantial hurdle to overcome with only 10 weeks to the start of the dry season when work could begin, and a substantial amount of pre-construction tasks to accomplish.

Solution: Monterey Mechanical devised a solution that enabled taking the first units offline three weeks prior to the first day of the 2016 dry season and start demolition of the old equipment prior to the arrival of the new equipment. This allowed a jump start on the concrete repair, coating work of the tank walls, and demolition of old equipment. Partnering efforts resulted in an improved procurement process enabling a shortened two-week review and approval for submittals. As a result, the new equipment arrived as demolition of the old equipment was removed and we immediately started installation of the new equipment that began arriving mid-July, just six weeks after the start of the dry weather season.

2.     Innovative Solution for Unworkable Requirement for Odor Control Cover Replacement

Challenge: The contract stated that the membrane covers for the odor control system could only be removed/replaced when the tank was offline during the four-month dry season. This requirement was not feasible because when the tanks were offline, it was extensive repair work on the tanks was the most critical.

Solution: To avoid this limitation of repair work, Monterey Mechanical proposed setting up special barricades around the openings while the tanks were online to allow continuous replacement of the covers over a 9-month period. This resulted in successful installation of new membrane covers to contain odors.

3.     Mentoring LBE Subcontractors to Ensure Safety Requirements Were Met

Challenge: The contract required 20% of work be performed by Local Business Enterprises (LBEs). Many of these small firms do not have knowledge of safety requirements. One specific example is that some of the LBEs we teamed with did not know about the safety regulations for confined-space, proper fall protection, or lockout/tagout requirements.

Solution: To avoid safety issues, Monterey Mechanical mentored the LBEs providing instructions on our stringent safety program. We conducted Tool Box Meetings and helped the LBE staff fill out Job Hazard Analysis Plans prior to beginning work. Work was monitored to ensure it met both quality/safety requirements. As a result, there were no recordable safety issues or lost time incidents.

4.     Innovative Solution to Resolve Impractical Restrictions for Influent Channel Repairs

Challenge: Online 24/365, needed repairs to the large influent channel repairs included injecting cracks with epoxy and repairing/coating concrete surfaces with polyurethane. The contract stated the channel could only be shut down for repairs one eight-hour period during a process plant shut down, which occurred only once per month. Also, the work would have to be performed during the four-month dry season, which translated into 32 hours to complete all the work, which was insufficient.

Solution: Monterey Mechanical proposed an alternate plan to install a bulkhead in the influent channel that would allow a portion of the channel to be taken offline while the other portion remained online, with the bulkhead acting as a temporary channel shut off. The solution enabled repair over a 10-week period versus the insufficient 32 hours.

5.     Quick Revision to Workplan after Announcement that Access Road would be Closing

Challenge: The two-year repair schedule was put in jeopardy when during the first six months the City announced that the access road needed for access by large cranes and forklifts would be closed due to construction at an adjacent $300-million project. The road was needed to access the influent channel to make repairs, and the utility/electrical rooms to replace equipment. Complicating the issue, the City asked us to complete 100% of the influent channel work the first 2016 dry weather season versus 50% during the 2016 dry season and 50% during the 2017 dry season. Layered on these two complications, the City asked us to complete installation of the new equipment in the utility/electrical rooms prior to March 2017—six months ahead of schedule.

Solution: Monterey Mechanical devised a plan to complete the first half of the influent channel coating work during the 2016 dry weather season and relocate the bulkhead and complete the other half of the influent channel during the first month of the 2016 wet weather since we it was predicted the wet season would be delayed due to El Nino. As a result, all work on the influent channel and utility room equipment replacement was completed before the road closed.

6.     Resolution for Unworkable Repair Window for Primary Sedimentation Tanks and Secondary Tanks

Challenge: The contract stated that only one primary sedimentation tank could be drained and worked on at a time, and only four tanks could be taken offline during any annual four-month dry season. With only a four-month window, and with each tank requiring more than a month to complete, it was not possible to complete the repair on all tanks, because after repair each tank had to be put back online and run for 14 days to prove it was functional and reliable prior to taking the next tank off line. Complicating an already-complicated situation was the upcoming road closure. We were simultaneously facing this same challenge with the secondary clarifier tanks with the contract stating that only take two secondary tanks could be taken down in an annual dry season, and only one secondary clarifier tank could be taken down in the wet season. The first four months of the 21-month contract were allotted for engineering and fabrication, with each tank requiring four months from start to finish. So even if four of the eight tanks were completed in both the 2016 and 2017 dry weather seasons, that still left four tanks to finish during the wet season, and there was only a total of nine wet season months. With every task on the critical path, there was to cushion on the schedule.

Solution: Monterey Mechanical proposed taking all four tanks off line simultaneously which would enable efficient sequencing of specially craft-subcontractors work by rotating them from tank to tank. We moved subcontractors in unison from one tank to the next until all tanks were functionally tested and put online at the same time, while concurrently performing the 14-day test. We also proposed working on one primary sedimentation tank at a time during the wet weather season to complete this scope of work ahead of schedule. We proposed a contingency plan in the event of high flows during the wet season where the City would give us a two-hour notice to remove personnel and tools from the tank if the City needed the capacity of the tank we had taken out of service. The City’s approval of our proposed solution enabled us to work on one secondary tank at a time during the wet weather season without needing to place the tank online during an unplanned event, and work on two secondary clarifier tanks during the wet weather season, with the restriction that we could only take one secondary clarifier tank offline on the north group and only one secondary clarifier tank off on the south group. This solution enabled completion of this work on schedule.

7.     Innovative Solution to Resolve Unfeasible Requirement for Electrical Gear Replacement

Challenge: A major portion of the project was to replace the aging electrical equipment in the Motor Control Centers (MCC) that provides electrical power to all the motors throughout the plant. Specifications called for a new MCC to be built in the same location as the existing MCC. Unfortunately, the contract also required all MCC equipment to be powered and operational at all times, which would be impossible while replacing and commissioning new electrical gear in a new MCC. The initial solution was to build a temporary MCC to keep the plant operations powered while equipment in the old/existing MCC was replaced, however building a temporary MCC would require that each piece of equipment go through a process shutdown and that the power conductors and controls be moved from the old MCC to the temporary MCC one piece at time, which would have taken several weeks. The problem, understandably, was that no one wanted to pay for the costly temporary structure, so the City offered to alter the stipulation from 0 shutdown hours to 10 shutdown hours to switch out all the equipment, a process that required several weeks to complete at a minimum.

Solution: Monterey Mechanical proposed mounting the new MCC back-to-back against the existing MCC. This solution was much less expensive than the initial solution to install a temporary MCC, and also required only relocating minor pieces of electrical equipment to make room for the new MCC line up, which minimized interruptions to the plants process. The result was that all equipment in the MCC—which included 16 secondary clarifiers, PLCs, air compressors, and RAS pump systems—was replaced on time and without any interruptions to the plant operation.

8.     Innovative Solution to Repair Air System without Shutdown while Escalating Schedule due to Pending Road Closure

Challenge: The contract required the replacement of the aging compressed instrument air system, and also stipulated that the air system had to be online at all times to keep the plant running, meaning we had to keep one of the two existing units in operation at all times. This was an issue because if the instrument air system is shut down, all the pneumatic-controlled actuators throughout the plant stop operating and will shut down plant. Trying to operate the system on one unit made the plant vulnerable without a backup. To further complicate the issue, the setup of compressors, dryers, and air storage tanks didn’t lend itself to being run with 50 percent of the equipment removed. And because of the upcoming road closure, we were asked to escalate the schedule for this task, despite the yet unresolved issue and need to complete the change out of the system before the road closure.

Solution: To solve both issues, Monterey Mechanical proposed building a temporary air system to bypass the existing system. Rather than trying to keep half of the existing air system in service, we built a secondary temporary system that allowed us to demolish the existing system and install the new equipment, complete all functional testing and startup services, and bring the new system on line in a shorter duration than previously planned. Once the new system was online, we could remove the temporary system. The proposed solution was a success and we were able to install the new instrument air system without interruption to plant operations or shutting the plant down, and we completed it before the access road was closed.

9.     Quick Workaround Solution to Resolve Oversight in Specifications for Sludge Pump VFDs

Challenge: The Motor Control Centers (MCC) were engineered on the contract drawings, however, after the project started plant operators realized the drawings overlooked a critical fact—the sludge pumps needed to be on VFD drives instead of soft starters. Delayed decisions by the City caused the procurement of the MCCs to be behind by several months.

Solution: Monterey Mechanical proposed providing the VFDs the operations group wanted but locating them in separate enclosures. This solution started the procurement process while the VFDs were designed and built in a separate enclosure. This solution resulted in completion of installation prior to closure of the access road.

Environmental Sensitivity/Mitigation

While focusing on safe and successful project execution and delivery, Monterey Mechanical was mindful of reducing impacts on the environment and the surrounding neighborhoods.

Discharge to the Bay: The most serious environmental challenge was maintaining the plant’s federal effluent discharge quality requirements while taking portions of the plant out of service for the repair. To meet federal discharge requirements, Monterey Mechanical assured all new equipment was properly tested for performance and reliability before placing it into service, and plant operators were given extensive training on the new equipment. After equipment was tested, Monterey Mechanical worked with operations to schedule a precise time/duration for connection of new equipment.

Storm Water Prevention Plan: Monterey Mechanical developed a Storm Water Pollution Prevention Plan (SWPP) to ensure no dust migrated from the construction site into the surrounding neighborhoods or silt entered any of the tributaries to the bay. We assigned a fulltime Qualified SWPP Practitioner to the project to ensure that the plan was monitored and executed to prevent any unwanted discharge of construction materials.

Odor Control: Monterey Mechanical performed work in a manner to ensure foul air was not released.

Recycling: All the steel from the existing secondary clarifiers, and primary tanks, as well as the existing aluminum covers that were on top of the primary tanks, was hauled to a metal recycler. Demolished concrete and asphalt was sent to local recyclers to be crushed for future construction.

Noise: Monterey Mechanical worked develop a schedule for work to be performed during normal business hours to avoid work at night that would potentially disturb the surrounding community.