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Hollister Industrial Wastewater Treatment Plant

Sunnyslope Water District has a contract with the City of Hollister and San Benito Foods - Neil Jones Foods Company to operate the Hollister Industrial Wastewater Treatment Plant on the western side of Hollister. 

From July through September, San Benito Foods operates its tomato canning facility in Hollister and discharges the industrial wastewater from the canning process to the Industrial Wastewater Treatment Plant. 

Treatment Process


From San Benito Food's tomato canning facilities near downtown Hollister, industrial wastewater gravity flows through a large pipe to the headworks of the Industrial Wastewater Treatment Plant at the western end of South Street. 


At the headworks, wastewater passes through a mechanical grinder which pulverizes any tomato scraps or other solid debris. The wastewater is also tested for pH, Dissolved Oxygen (DO), salinity, and several other key factors for the treatment process. It is also metered to determine the exact wastewater flow into the treatment facility. From the headworks, wastewater then flows into Pond 1 where it is treated.


From the headworks, wastewater enters the treatment pond through one of four inlet structures. The pond is divided into three distinct sections by baffle curtains running through the pond. Initially, water enters section 1A where 18 aerators mix the wastewater to increase the dissolved oxygen (DO) of the water. It is important that the wastewater has a high DO to promote the growth of aerobic microbes which break down and consume the organic matter and tomato waste. This process does not cause the odors or bad smells often associated with wastewater as long as enough oxygen is in the water to support the aerobic microbes. 

Highly aerated wastewater then enters section 1B where four smaller aerators maintain the DO while the solids settle out of the water and form a sludge at the bottom of the pond. During the off season, that sludge is dredged, treated, and properly disposed of at a landfill or as fertilizer for agriculture.

Water enters section 1C at the southern end of the pond, then must travel all the way back to the northern end where it is pumped out after being fully treated. In section 1C are four final polishing aerators.


Fully treated wastewater is pumped form the treatment pond by the effluent pump. A portion of the water can be diverted back to the pond inlets to repeat the whole process for additional treatment. Clean treated water that meets regulatory standards is then directed into one of four percolation basins for disposal. The water soaks into the ground and replenishes the local groundwater.