Wastewater/Recycled Water Pump Station
Design: April 2014 – December 2016
Construction: January 2017 – September 2019
Cost: $13.5 MM
This project will save millions of gallons of potable water each year, protects our coastal aquifers from seawater intrusion, provides an economical alternative to using potable water for industrial processes, and reduces the amount of (treated) sewage we release into the ocean—all while making beneficial reuse of an underappreciated, untapped resource: Los Angeles’ raw wastewater.
West Basin can provide this bounty of recycled water by taking treated secondary effluent from the nearby Hyperion Water Reclamation Plant (HTP) and treating it with state-of-the-art micro-filtration, reverse osmosis, and UV disinfection processes. In doing so, WBMWD essentially takes plain municipal wastewater and makes it cleaner than the water we drink at home! And they plan to make even more if they could find a way to reliably deliver even more of HTP’s secondary effluent.
As with any recycled water purveyor, maintaining capacity is critical for WBMWD, as their contractual obligations require that they deliver recycled water at all times—and if WBMWD doesn’t have enough, they are obligated to furnish precious and expensive potable water in its stead. This obligation represents a substantial financial risk for the District and in general, requires maximum reliability for all WBMWD’s recycled water facilities.
In addition, the existing pump station was fed by a single power source without provisions for emergency power or a redundant power feed. Construction would require tapping into wetted, pressurized facilities and messy underground construction on a busy arterial road. Complex treatment processes at HTP, the largest wastewater treatment plant in the Western United States, and ECL would need to be protected at all times during construction, and the sheer number of stakeholders made communication and coordination challenges.
Now, imagine designing a facility meant to meet these challenges and house three (3) large, 800 hp, 4,160V pumps within a 24’ L x 18’ W project site—a footprint just larger than two parking spots. Just for good measure, add the complexity of a deep excavation constrained by tidally influenced groundwater.
To overcome this challenge, LEE + RO developed a custom shoring solution that incorporated Giken Silent Pile Technology, ground improvement (grout injection), a sealed cofferdam, and a conventional tremie slab to seal off the excavation and make construction possible. It’s a tight fit, L+R developed a pump station layout that has space for three pumps, associated valves, and large diameter suction and discharge pipe headers.
The existing HSEPS was powered by a single 34.5 kV feeder from LADWP, without a redundant feed or onsite emergency power. L+R conducted an alternative analysis and determined that the installation a 3,000 kW diesel-powered generator with an automatic transfer switch provided better value and increased reliability to the District than adding a redundant LADPW feed. In addition to emergency power, L+R also designed modern power distribution, motor control infrastructure, and proprietary, software-driven pump control to increase efficiency, reliability and pump service life.
Prior to construction, many wondered how we would approach the technical challenge of tying in HSEPS’ suction piping because it required a high-stakes connection to the existing HTP secondary effluent channel, a 60” pressure pipeline. Any mistakes during tie-in would result in a catastrophic spill of secondary effluent and result in major damage to the facility. As such, L+R’s approach to this work was an abundance of caution and attention to detail and centered around the use of highly qualified construction divers and welders, inserted into the pipe at low flow to make the necessary cuts and welds for the connection of the pumps’ new suction piping. A combination of high-level coordination, detailed construction drawings and specifications meant that this high-risk portion of the work went smoothly, without drama.
LEE + RO began developing alternatives that would not only meet RWQCB’s new nitrogen limits, but also deliver value to the City. LEE + RO selected an activated sludge oxidation ditch with anoxic zone as this treatment process would be able to meet the limits while providing a high level of reliability and ease of operation for City staff. Additional facilities included a new circular secondary clarifier, aerobic digesters, sludge drying beds, percolation/evaporation ponds, and improved power distribution and emergency standby power.
LEE + RO completely reimagined and redesigned the project in less than six months so that the City could keep up with its rapid growth and RWQCB’s regulatory requirements. The project resulted in excellent effluent quality and nitrogen removal, and the process is still in operation today.
In 2007, the RWQCB instituted new discharge limits on the City’s treatment plant. Total nitrogen which had no previous limit, was set to 8 mg/L. At the time, typical performance of the AIPS was 50 mg/L and North Activated Sludge System was 35 mg/L. The RWQCB’s changes meant that the older activated sludge system that the City was operating could no longer operate in compliance.
Midway through design, LEE + RO was tasked with determining the best approach to meet these new limits while minimizing the City’s capital outlay.
LEE + RO determined that the most appropriate and cost-effective approach was to convert the current activated sludge system to a Simultaneous Nitrification/Denitrification (SNdN) process. By carefully controlling oxygen transfer within the existing oxidation ditch, the SNdN process could do with one tank what other systems accomplish using multiple tanks. This innovative process modification delivered huge value to the City. With the SNdN modification coming in at 15% of the cost of a new Oxidation Ditch, saving the City more than $6 million in capital costs.
In 2010, the City’s WQCF needed improvements to their solids handling facilities. In locations like Patterson, where land is plentiful, sludge drying beds offer a low-cost, low-maintenance solution for treatment plants that need to dewater their wastewater solids. However, factors like the weather (especially during the cold/wet winter months) and the City’s growing size increased solids production, and the City found that solar-based dewatering was no longer sustainable.
LEE + RO was asked to develop and analyze numerous alternatives for mechanical dewatering, including high-speed centrifuges, belt filter presses, and screw presses.
To meet aggressive regulatory deadlines set by RWQCB, successful project delivery would require a fast-track approach. After quickly analyzing alternatives during preliminary design, the City selected skid-mounted, high-speed centrifuges for dewatering. Skid-mounted design greatly accelerates both design and construction because the time-consuming work of coordinating numerous pieces of equipment to operate in concert was handled by the equipment vendor. LEE + RO developed a final design for the centrifuge facility in five weeks and construction was completed in 12 months. Patterson and LEE + RO went from project conceptualization, preliminary and final design, and construction/startup in less than 30 months.
In 2015, the City retained LEE + RO for emergency assistance to develop solutions that could be quickly implemented to fix a hydraulic bottleneck at the WQCF which significantly reduced the peak wet weather capacity of the treatment plant.
The concern was that that heavy “El Niño” rains would result in significant inflow/inflation resulting in a spill at the treatment plant or flooding throughout the collection system. To complicate matters further, the construction constraints were just as daunting: re-configuring the piping inside of the existing process facilities would be difficult since the subsequent downstream process was a 1,000,000-gallon process tank, with no means of isolation. This would require either emptying the existing process tank, a lengthy, complicated, and costly affair that would require the restart of the biological process; or developing an alternate method to provide hydraulic isolation of this tank.
LEE + RO elected to keep the 20-foot deep tank online and used construction divers to install a temporary isolation plug. Divers inserted a 2-foot diameter plug into the tank inlet which lay submerged under 10 feet of wastewater. The inserted plug provided temporary hydraulic isolation which enabled the replacement of the upstream bottleneck. This creative solution avoided a biological restart of the 1,000,000-gallon tank and the resulting outcome for the City:
In 2018, LEE + RO was tasked with designing the second phase of upgrades to the City’s original oxidation ditch for additional treatment capacity.
Expand on the solution devised in 2005 to meet WQCFs new requirements by relying on well-timed, modular additions to the treatment process.
LEE + RO designed a 100,000-gallon anoxic system that increased the system’s ability to remove nitrogen and make both of Patterson’s existing oxidation ditches operate similarly. The upgrade also included mechanical replacement of the system’s two 40-foot diameter circular clarifiers and reconfiguration of the piping at the distribution structure, activated sludge pump station and effluent pump station, which performs better than the SASTS built in 2005. The result: nitrogen removal by 50%, and the kind of process improvements extended the service life of WQCF’s secondary treatment process for another 15 years.