The 200,000-gallon Relief Hill Road Storage Tank (the only major storage component in the WCWD system for treated water) currently experiences substantial seasonal overflow. As part of the original design, an altitude valve to control flow into the tank was installed. The altitude valve was to open when tank water levels dropped and close when the tank was full. However, operational experience has shown that the altitude valve is inadequate for the differential head to open or close until the storage tank is approximately half empty. The differential head is inadequate because the water treatment plant and the tank are too close in elevation. Therefore, there is not sufficient pilot pressure to open the altitude valve until the storage tank is dangerously low.
A needs assessment will be performed which clarifies the operational characteristics of the system and identifies a reasonable and cost-effective design and operational solution for the system. Based on this assessment, a final design will be identified and the appropriate system installed.
Current Status (September 2016)
The complete Level-Control Altitude Valve Improvements will be complete by December 2016.
The need to coordinate the design of the #10 Project –Relief Hill Road Flow Control Pressure System Improvements, as well as Project #13 – Downtown Leak Detection and Repair, has complicated the design decision-making process for this project element, as the infrastructure and system performance are closely interrelated. The original concept of simply installing an altitude valve is proving to be both too simplistic and not fully responsive to the operational needs and characteristics of the plant and distribution system (especially in light of the outcomes of the hydraulic modeling accomplished for Project # 10 – Relief Hill Road Pressure Improvements).
The current strategy emerging from the design team is focused on installation of a SCADA system to address the connectivity between the tank, the other components of the distribution system on Relief Hill Road and Downtown, and the water treatment plant in a more holistic fashion.
The use of SCADA as a solution will also address: water treatment plant operational issues associated with the pipe occasionally running dry at both ends of the service area; and, allowing for quick response to unexpected operational issues resulting from both planned and unexpected low flows, internal operational failure, chlorine counts and other dynamics. Finally, the use of SCADA allows for monitoring via an electronic system that enables adjustments without an operator being present at the plant. This is especially important in light of the commute time to the facility by the OM, the lack of an onsite T-3 operator, and the hazardous winter weather road conditions.
The contract to complete design of this system has been let and the design process is underway. Minor alterations to the existing treatment plant structure will be required to accommodate the SCADA system, such as but not limited to: creating a small insulated room within the plant to protect equipment from extreme heat and cold, installation of a generator to ensure that the system runs reliably during power outages and some rewiring and reconfiguring of internal power sources and phone lines, as well as possible installation of a dish system to assist in internet reliability. Additionally, the water tank will need some modifications to accommodate the SCADA system, including a solar electrical system to provide the power needs of the system, as well as a full inspection and cleaning of the tank by a certified tank maintenance firm.
City of Nevada City
Bryan McAlister, City Engineer, (530) 265-2496 x126, firstname.lastname@example.org
Measurable Physical Benefits