Raw Water Tank Replacement Capital Improvement Project

The City’s existing 170,000-gallon raw water storage tank is too small to buffer changes and/or interruptions in flow from the raw water pump station (RWPS) located at the base of Shasta Dam. The City’s 2016 Water Master Plan (WMP) recommended the existing raw water tank be replaced with a new 1.6-million-gallon (MG) tank.

When the Centimudi Water Storage Tank (currently in design) is put into service, the two existing finished water (FW) tanks located on the north side of the water treatment plant (WTP) can be demolished. Both tanks have reached or exceeded their useful service lives. The new raw water tank will be constructed on the north side of the water treatment plant (WTP).

There is a long list of benefits in upgrading the undersized 150,000-gallon raw water tank to a 1.6 million gallon tank. These benefits include more storage capacity during emergency situations when the water treatment plant (WTP) or raw water pump station (RWPS) are down due to fires, snow storms, lightning strikes, power outages, equipment/infrastructure failures  etc.. The RWPS is owned and maintained by the U.S. Department of the Interior’s Bureau of Reclamation (USBR) and is aging and unreliable. USBR is in the process of designing and upgrading the old RWPS contingent on the City of Shasta Lake constructing a new 1.6 million gallon raw water storage tank.

The 10-year Water Master Plan completed in 2016 for the City of Shasta Lake identified the need for a new 1.6-million-gallon (MG) raw water storage tank which could change the way the Shasta Dam Pumping Plant currently operates. Also, a new 2.45 MG potable water storage tank is proposed on Forest Service land and is in the environmental review and approval process. Completion of this project is expected in 2026. Once this project is complete, the two older potable tanks will be demolished and replaced with the new 1.6 MG raw water storage tank.

Currently the pumping plant feeds a 150,000-gallon raw water storage tank with a combination of 5 pumps ranging in horsepower (HP) from 125 to 400. The limited size of the raw water tank requires the pumping plant to modulate flows leading to excessive stop starts. The current plan is to install new motors and VFDs on the existing pumps to modulate flows and provide a “soft start”. The 150,000-gallon RW storage tank will be replaced with a much larger 1.6-million-gallon capacity tank within the next 8 years. The larger raw water tank will allow for greater flexibility in pumping plant operations reducing and perhaps eliminating the need for modulation. The larger raw water storage tank will not be available for 7-10 years and the pumping plant will need to operate with the constraints of the smaller 160,000 gallons tank until the new tank is constructed in spite of the increasing water needs/demands. Flows to the raw water storage tank are expected to increase in the future and range from 2,200 acre-feet per year to 4,480 acre-feet per year.

 According to the 2017 Pace Engineering (PACE) report, “the typical pump combinations (Pumps 1, 2, and 3 and Pumps 1, 2, and 5) generally operate “way out” on their respective pump curves, meaning the pumps operate beyond the Best Efficiency Point and oftentimes beyond the manufacturer’s rated curve. Pumps operate beyond the POR as described in HI 9.6.3 -Rotodynamic Pumps Guideline for Operating Regions (2017), according to the PACE report.

The consideration is to size the pumping plant (pumps and motors) to operate with the 1.6 MG storage tank that is to be constructed within the next 8 to 10 years. This would minimize future equipment modifications once the larger storage tank is erected. This consideration may improve the long-term efficiency and maintenance costs of the pumping plant.