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Lessalt Water Treatment Plant Upgrade

Project Summary

As part of the Hollister Urban Area Water & Wastewater Master Plan (HUAMP), the Lessalt Water Treatment Plant  underwent a significant upgrade in 2014. Built in 2002 as a joint project between Sunnyslope and the City of Hollister, the plant was struggling to meet certain California Division of Drinking Water regulations that had been increased since its original design and construction. San Benito County Water District (SBCWD) participated in the project since it is a member agency of the HUAMP and the raw water supplier for Lessalt. For their financial participation, SBCWD became the owner of the plant though Sunnyslope staff still operate and maintain it. 


After requesting and evaluating proposals from various design engineering firms, Kennedy/Jenks Consultants was selected. Due to the limited size of the site and the existing treatment plant structure and piping, the designers had to be creative to fit all the new treatment process equipment and piping. After extensive pilot testing and analysis, it was decided to add Greensand and Granular Activated Carbon filters upstream of the original micro filtration membrane portion of the plant. These filters effectively remove the manganese and organic carbon that had been causing regulatory issues. Also, changes were made to increase the maximum peak capacity of the plant from 1.75 million gallons per day (MGD) to 2.5 MGD. A new booster pump station was also designed to send the water into distribution system and to the customers.


After the design and specifications were completed, the project went out to bid and was awarded to Specialty Construction Inc. They regraded the site and built retaining walls to create the space for the new Greensand and Granular Activated Carbon filters. Piping and valving was installed to and from the filters for normal operation, back washing, exchanging the filter media, surface washes, and other operations. A new 130,000 gallon treated water tank was constructed of welded steel to hold the water before it is pumped into the distribution system. The booster pump station was built to send water into either or both of Sunnyslope's pressure zones. A new 16" pipeline was installed in Fairview Road to connect Lessalt to Sunnyslope's higher pressure zone. Finally, remote monitoring and controls were programmed so operators can run the plant even from offsite.