Three cities in Stanislaus recycle wastewater for farmland. Will Riverbank join them?
Riverbank is looking at upgrading its sewage plant to produce water clean enough for crops.
The city would join three others in Stanislaus County that recycle water from kitchen and bathroom drains for use on farms. Modesto, Ceres and Turlock send their highly treated effluent to the Del Puerto Water District on the West Side.
Riverbank would sell its water to farmers just to the north, possibly including some in the South San Joaquin Irrigation District.
It would not be a huge boost to the supply for SSJID, whose sources are much more abundant than Del Puerto’s. But it could help Riverbank pay for sewage treatment upgrades likely to be required by the state, with or without the irrigation element.
The City Council discussed the results of a study on the idea June 8. The consultants will add public comments to the final version to be sent to the State Water Resources Control Board. It granted $150,000 for the research.
The council will meet again on the issue after the state agency accepts the study, likely by late July, City Manager Sean Scully said. It could then decide whether to undertake further planning, including where and how the recycled water is delivered.
The cost could be about $70 million based on one of the likelier options for enhancing treatment and delivering water to farms. The funding could include sewer rate increases, fees on developers, and state and federal grants, along with the income from farmers. Completion is at least four years off.
The study was done by the national engineering firm of Brown and Caldwell, along with Kjeldsen, Sinnock and Neudeck, based in Stockton and West Sacramento.
Water recycling has emerged as cities face higher standards for sewage treatment and many farmers struggle to secure long-term supplies.
The city of Oakdale has upgraded its treatment enough to supply cropland. A means for distributing this water has not been designed or funded.
Plant lies along river’s edge
The Riverbank treatment plant lies at the north end of town, along the Stanislaus River. The process starts with screening of solids, which go to a landfill near Manteca. The remaining wastewater goes into ponds where oxygen is added. It then moves to other ponds where some of the water evaporates and some seeps into the ground. The state board regulates the process to guard against pollution.
Using the wastewater on crops would require Riverbank to add filtration and disinfection to the process. The city would also have to install storage tanks for the cleansed water and a means of getting it to farmers.
One option is pipelines directly to farmers in a zone just north of the city but outside the SSJID boundary. Another is a pipeline to a district canal, where the water would be mixed with the main supply from the river.
The study estimated that the project could yield 2,550 acre-feet of irrigation water. That’s less than 1% of the 300,000 acre-feet that SSJID can take from New Melones Reservoir each year.
The consultants projected a recycled water price of $39 per acre-foot to start. A typical SSJID farmer pays $9 per acre-foot this year.
The study said the direct piping option is more likely, at least in the near future. A key benefit for farmers: The water would arrive under pressure, allowing it to go right into sprinklers and drip irrigation lines. This would save them the cost of pumping groundwater.
A spokesperson for SSJID could not be reached for comment. The study said district leaders “expressed that they may be open to partnership with the City of Riverbank for receiving recycled water.”
‘Working exactly as planned’ in Del Puerto
The Del Puerto system started operating in 2018 with water from the sewage treatment plant for Modesto and Ceres. Turlock added its wastewater last year.
The farmers do not directly use this supply. Rather, the cities discharge the wastewater into the San Joaquin River, and Del Puerto withdraws an equal volume from the Delta-Mendota Canal, which is fed by the river.
The project now provides about 27,000 of the 100,000 or so acre-feet of demand in the district, General Manager Anthea Hansen said. The volume could reach as much as 60,000 acre-feet as the city populations grow.
“It’s working exactly as planned,” Hansen said. “The cities have been great partners.”
Del Puerto covered the $82 million construction cost. The district has about 45,000 farmland acres straddling Interstate 5 from Vernalis to Santa Nella.
It had been getting all of its water from the federal Central Valley Project, but that has declined sharply due to drought and Delta fish protections.
In the especially dry 2021, the allotment is zero for Del Puerto and other West Side districts lacking senior water rights. Hansen said her farmers are getting by with the recycled water, wells and storage from previous years.
