A hardhat, safety vest, and steel toed boots have been part of Titus Chen’s daily uniform lately. He has spent more time inside Sunset Reservoir than many of his colleagues, partnering with Dive Team guru John “JJ” Jordan to test operations, perform facilities inspection and plan improvements.
Sunset Reservoir, situated in San Francisco’s west side, is one of 10 drinking water reservoirs located in the City. Sunset Reservoir’s two basins impound 43% of the water delivered to San Francisco and serves approximately 30 percent of the City’s population. The SFPUC regularly empties these reservoirs of water to conduct inspection and maintenance work. This time, it was Sunset Reservoir South Basin’s turn and it has been empty for the past several months for cleaning, maintenance and inspection.
Chen, SFPUC Water Quality Engineer, has been testing reservoir operations, chemical feed equipment, and planning disinfection and startup activities in coordination with the City Distribution Division. On this day, he was collecting water samples from the ground water dispersion system inside the reservoir. The groundwater pipeline to Sunset Reservoir has been inactive for several months pending minor repairs to a pH adjustment station. The SFPUC conducted the test to confirm there were no signs of elevated turbidity or scouring inside the pipeline during startup of the groundwater well after a period of inactivity.
Chen described components in the reservoir that typically cannot be seen when the 90 million gallon basin is full.
The Solarbee mixers provide mixing, prevent thermal stratification, and reduce water age in the larger potable water storage reservoirs by drawing colder, denser waters from the bottom of the basin and spreading it across the water surface. The Solarbees are solar and battery powered, and run continuously, each moving up to 10,000 gallons per minute during optimal conditions while only using as much power as a lightbulb.
The groundwater pipe layout was designed using hydraulic modeling, with numerous openings and Tideflex valves to distribute water throughout the basin. The test also allowed SFPUC to observe the dispersion of groundwater throughout the basin via Tideflex (duckbill) valves.
Chen also explained that the main purpose of the basin being emptied is to clean and remove built-up sediment and inspect various areas. This includes refurbishing drainage valves and appurtenances. The SFPUC follows a 5-year reservoir cleaning schedule to remove sediment that can potentially degrade water quality, evaluate the condition of the reservoirs, and carry out repairs if necessary.
The SFPUC plans to place the South Basin back into service in late August following filling and disinfection. Approximately 3,500 gallons of sodium hypochlorite will be used during the disinfection to achieve a chlorine residual of two parts per million once the basin is full.