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JAN-FEB 2019

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40 INTECH JANUARY/FEBRUARY 2019 WWW.ISA.ORG SPECIAL SECTION flow in the transmission pipeline. l Connection point to the SFRWS transmission pipeline: point on transmission pipeline where chemi- cally treated groundwater from the well station is introduced. l Blending treatment zone: section in the transmission pipeline where the chemically treated groundwater and the surface water are mixed. The blending zones range between 400 and 580 feet, depending on the par- ticular conditions at the station. l Compliance sample point: where water quality samples are monitored for compliance, located downstream of the blending zone but upstream of the first customer turnout. l Distance to first customer turnout: a minimum of 100 feet from the com- pliance sample point for each well station to the first customer turnout. System water quality monitoring and control The water quality of the SFPUC blended water is monitored and controlled at each well station transmission line com- pliance point and as an overall system. Water quality analyzers and flow- me ters at each well station continuously monitor the system and calculate the blended water quality at the transmis- sion pipeline compliance points. Some water quality parameters, such as pH and chlorine residual, can be monitored in real time with online analyzers. Some parameters, such as chrome-6 and ni- trate levels, are calculated based on mass balance calculations for the system. The SCADA system monitors and cal- culates the combined water quality from multiple wells that contribute to a com - mon transmission pipeline. As the flow rates of surface water and groundwater change, the SCADA system adjusts the calculations to automatically update the calculated water quality parameters. Online analyzers for pH, conductivity, and chlorine residual also provide real- time feedback for adjustments to the well chemical feed systems. The SCADA system also generates alarms and auto - matically shuts down affected ground- water wells when the monitored or cal- culated water quality parameters exceed a predetermined set point. This ensures that the blended water quality will al - ways meet SFPUC's water quality ob- jectives to maintain high-quality, "good tasting" water for customers. Preliminary func- tional startup tests successfully showed that the online water quality and control system operates very effectively in moni- toring and control- ling the water quality for the ultimate pur- pose of delivering high-quality drink- ing water to the city of San Francisco res- W GSR-TIW SUTRO RESERVOIR SSPL SSPL SAPL3 SAPL3 CSPL2 CSPL2 CSPL2 SAPL2 SAPL2 HETCH HETCHY WATER OR FROM SVWTP W W W W W W W W GSR+HBW GSR-SBW GSR-CRW GSR-SRW GSR-LGW GSR-CBW SUNSET RESERVOIR TS6R TS2R BADEN PUMP STATION AND VALVE LOT FROM HTWTP FROM HTWTP HETCH HETCHY WATER OR FROM SVWTP HETCH HETCHY WATER OR FROM SVWTP LAKE MERCED PUMP STATION MERCED MANOR RESERVOIR SAN PEDRO VALVE LOT T64M T61M T63R T62R T60 GSR-MYW CSPL3 GSR-FHW TO CITY DISTRIBUTION SYSTEM UNIVERSITY MOUNT RESERVOIR Figure 5. Groundwater is also blended with imported surface water in the four major transmission pipelines to the city of San Francisco. Figure 6. Blending in the transmission pipeline is achieved and monitored before the first downstream customer

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