The water for Rancho Murieta comes from the Cosumnes River at Granlees Dam and pumped into Calero, Chesbro and Clementia Reservoirs from November 1st until May 31st of each year. These Reservoirs work as large settlement basins before the water is transferred to the Water Treatment Plant.
In 1978, a 1.5 million gallons per day (mgd) capacity Water Treatment Plant was constructed to meet the increased demands of development and upgraded treatment requirements of the time. In 1987, a duplicate plant with 2.0 mgd capacity was constructed. The treatment processes comprised of coagulation, sedimentation, followed by filtration and finally disinfection. Both of these plants were retrofitted in 1995 to meet the new Surface Water Treatment Rules with the installation of dual media filtration utilizing sand and anthracite coal. The existing plants have generally operated well and provided a reliable operational capacity of 1.5 mgd and 2.0 mgd respectively with a total capacity of 3.5 mgd.
The current demands are again increasing and the District is anticipating additional community growth, including the construction of a new hotel and residential units. These demands have been met with the expansion of the water treatment plant with the installation of an ultrafiltration membrane system in the old Plant 1 sedimentation basin and filter building.
The current estimated build-out maximum day demand for the entire treatment plant is 6.0 mgd taking into water conservation efforts, greater use of reclaimed water and less growth than originally planned. Plant 1 has a capacity of 4.0 mgd and Plant 2 has a capacity of 2.0 mgd.
Treatment System Upgrade
The retrofit and expansion of the existing water treatment plant includes some new influent piping through self-cleaning screens. The purpose of the screening process is to remove large objects from the water as it enters the plant through a 16-inch inlet pipe from the District’s Chesbro Reservoir. Objects such as fish, leaves, and debris are screened out by a mesh size of 1/64 inch (400 microns) stainless steel screens. Also modified were the Plant 1 flash mixer and flocculation basins to be able to accommodate the higher flows.
In place of a section of the old sedimentation basins, new membrane tanks with GE Zeeweed V4 1000 ultrafiltration submerged membranes were installed. The membranes remain submerged in the basins and water is drawn through them by vacuum pumps. The strained water then flows into a newly expanded chlorine contact channel which runs underneath Plant 1 for disinfection. Other new improvements include new pumps for permeate, reject, and backwashing; new membrane cleaning chemicals (sodium hypochlorite, citric acid, hydrochloric acid and sodium bisulfite) and new chemical storage and feed systems for use; A plate settler will be used to clarify waste from the backwash, maintenance, and recovery cleans and recycles that calcified water back to the head of the plant, with concentrated solids being sent to waste; New flow paced chemical feed systems; Two new treated water booster pumps were added to pump the treated water out to the distribution system; Modifications were also made to increase the size of one of the drying beds that receives the underdrain sludge from the plate settler.
The system utilizes ultrafiltration cassettes with a capacity of 2.0 MGD each (3 treatment trains total) at a total maximum daily production capacity of 4.0 mgd, to produce potable water for the distribution and use in Rancho Murieta. The total capacity is not 6.0 mgd as one unit is typically in a cleaning mode while the other two are operating. The membranes have a nominal pore size of 0.02 microns small enough to filter out most bacteria and viruses. (see table below)
The system has multiple computer systems integrated with monitoring and controls, with water quality and system integrity alarms set up to call out/alert staff to warning issues as well shut down the facility or individual treatment trains if water quality requirements are exceeded.
Water Filtration Types vs. Size of Common Contaminents