Members of the Northwest Division began mobilizing on March 15 for the $87 million City of Antioch Brackish Water Desalination Project, the first desalination plant project in the California Delta and only the second in the Bay Area. The project will allow the city to preserve its water rights and provide inhabitants with approximately 6 million gallons of potable water per day, despite increased quantities of brackish water in the San Joaquin River due to California’s revolving drought years and heavy agriculture irrigation demands.
The San Joaquin River water has higher salinity level as it approaches the Suisun Bay during summer season when raw water levels in the river are lower due to irrigation demands in the central valley. The higher demand for raw river water in the central valley allows sea water to travel further inland from the San Francisco Bay thru the Suisun Bay and into the San Joaquin Delta System.
To combat this increase in water salinity, the project team will add a Desalination Reverse Osmosis (RO) Treatment train to the existing Antioch Water Treatment Plant. The scope also includes construction of a new river pump station and intake structure with three 600 horsepower medium voltage vertical turbine pumps to take in water from the San Joaquin River into the plant, bypassing the plant’s reservoir with a bypass pipeline so that the cities reservoir is not contaminated by the brackish water.
On the intake side of the pump station, anchored into the riverbed, the team will install a coffer dam for the new submerged intake with automated self-cleaning fish screens and airburst system to protect the river species. On the shore side of the river the team will also excavate a 30-foot-deep shored excavation for the wet well and install and tie in a temporary 30” bypass pipe to the existing underground pipeline to maintain the existing intake and pump station during construction.
Once the water has been pumped to the plant, it will be run through traditional flocculation, sedimentation, filtration water treatment process, then through the reverse osmosis train. The RO trains are a series of high-pressure vessels with Membrane cubes loaded inside each of the hundreds of vessels. Brine created from the process will be transferred via a 4.3-mile pipeline to the nearby wastewater treatment plant—significantly better for the environment than the traditional method of direct discharge into the ocean sea floor.
Work inside Plant A includes the replacement of tube settler media inside the existing sedimentation basins and replacement of the filter media and under-drain systems in the existing filters, all of which is below grade and within existing structures.
To visit the City of Antioch’s website and read more about the project, click here.