South San Joaquin Irrigation District may invest $1.2 million in a backup generator to assure that a PG&E wildfire power cutoff — or another prolonged power outage — doesn’t impact the district’s ability to treat drinking water.

There are 220,000 residents in Manteca, Lathrop and Tracy that rely on SSJID for domestic water.

The Nick C. DeGroot Water Treatment Plant near Woodward Reservoir was constructed with a 500-kW, 480V diesel generator.

The generator was never intended to function as a backup power supply capable of allowing water to be treated and delivered. The main purpose is for life and safety services (emergency lighting, fire pump, gate access etc.)

The system that SSJID has that sends water to cities is gravity flow and has water storage tanks at various points along the way including at the treatment plant.

The storage tanks, though, have capacity only to take care of needs in terms of hours.

A prolonged outage such at one that PG&E may trigger that can last 72 hours or more would basically cut off the supply of water to the three cities.

Other emergencies could trigger power loss at the treatment plant including blackouts.

On a hot August day in 1996 the Western Power Blackout occurred during an intense heat spell where many areas throughout the western United States — including Manteca — were dealing with temperatures flirting with the 110-degree mark.

Power was knocked out to more than 4 million people in California and Oregon. Some had power restored with minutes. Others, including the 42,000 people living in Manteca at the time, were without power for 12 hours.

As the power outage dragged on and the mercury soared people sought relief by going outside and letting their kids turn on sprinklers and hoses to cool down.

Given Manteca relied 100 percent on well water at the time and only a few wells had backup generators, water pressure started plummeting.

Manteca firefighters realized a potential disaster was in the making in the terms of combatting a fire. Manteca Police dispatched officers to drive down streets using public address systems to tell people to turn off sprinklers.

What happened in 1996 is nothing compared to the prospects of PG&E’s plan to cutting off electricity to Manteca and nearby cities for up to five days whenever severe wildfire conditions exist in areas in the foothills and Sierra that are served by the same transmission lines that power valley communities.

There are more than twice as many Manteca residents today.

And while some city wells used in tandem with surface water from SSJID emergency have backup generators, the city would not be able to pump and treat enough water at well heads to serve its needs in a prolonged outage.

The board meets at 9 a.m. today to consider the project.

If approved, it will take 72 weeks to get a generator in place large enough to power the water treatment plant’s first phase water treatment production capacity.

To contact Dennis Wyatt, email dwyatt@mantecabulletin.com