Effective method to monitor and control water quality to blend groundwater in small quantities with the surface-water supplies and conform to all regulatory drinking water standards
The San Francisco Public Utilities Commission (SFPUC), the municipal water supply agency for the city and county of San Francisco, Calif., began mixing groundwater from a local aquifer with the city’s customary surface-water supply sources in April 2017. San Francisco had not used groundwater as a drinking water supply for more than 90 years. The planning, engineering design, and construction for this renewed groundwater use was accomplished under the San Francisco Groundwater Supply Project (SFGW Project), a part of the agency’s capital program to diversify the city’s drinking water supply sources and increase their reliability.
Due to differences in water quality between the groundwater and surface water, the SFGW Project opted to blend groundwater in small quantities with the surface-water supplies in two city reservoirs. This blending or mixing allows the city to continue to surpass all regulatory drinking water standards, as well as to ensure that changes in taste or odor are not noticed. A specialized project team developed and executed an online monitoring and control system to satisfy the project’s water quality requirements. The team includes SFPUC project management staff. The team members for the water quality control system included personnel from DTN Engineers, Kennedy/Jenks Consultants, and Tesco Controls.
Background
SFPUC is a purveyor to water retail customers in the city and county of San Francisco, as well as to 26 wholesale customers that serve Alameda, San Mateo, and Santa Clara counties in the greater Bay Area. From the mid-1930s until recently, SFPUC’s municipal supply came from the Hetch Hetchy Regional Water System, a system that combines the surface-water resources of the Hetch Hetchy Reservoir in the Sierra Nevada mountain range with five reservoirs in the Bay Area. On average, 85 percent of SFPUC’s water has been supplied by the Hetch Hetchy Reservoir, and the five Bay Area reservoirs have provided the remaining 15 percent.
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About the Authors
Diep Nguyen, P.E. is a Principal Engineer of DTN Engineers, Inc., and a licensed EE, CSE, and FPE in California. He is a Life Member of ISA and IEEE.
Jeff Gilman, P.E. was a SFPUC Senior Project Manager with more than 40 years of experience. He is a licensed geologist and hydrogeologist in California.
Todd Reynolds, P.E. is a Vice President of Kennedy/Jenks Consultants, a consulting engineering firm for environmental projects.
A.J. Cottengim is a Senior PLC Applications Engineer with Tesco Controls Inc., a system integrator and manufacturer headquartered in Sacramento, California.