On Thursday morning, a day after historic hail-and-rain storms pounded Sonora and nearby communities, Joe Marshall went down to the basement of his home on Stewart Street to figure out how to deal with 4 feet of hail.

It looked like a blizzard had somehow inundated his low-lying home’s lower level. He had a crew of three helpers with him, trying to clear the white stuff out.

Hailstones remained piled up a couple feet deep in places outside his home, but the challenge for Marshall and scores of other residents and business people in downtown Sonora was the same: cleaning up in the wake of a whopper storm stronger than any gully washer seen here in more than two decades.

Rob Cole, a neighbor, used a neon orange toboggan to drag the hail into the backyard. Justin Hiner and Wes Kanawyer used big-blade shovels to hurl mounds outside.

Marshall said he was so stunned and surprised by the ferocity of the Wednesday storm that he didn’t even notice the hailstones until about 9 p.m. Wednesday, seven hours after the brunt of the storm began easing up.

As of Thursday morning, he and his helpers still hadn’t figured how all the hail got in, but they all agreed the intense flooding and runoff followed gravity to settle in a low spot shared by Marshall’s home, the Tuolumne County Probation Office parking lot and the Sonora AT&T central telecommunications center.

“The hail dumping changed the drainage,” Cole said.

“Water finds the weak spots,” Hiner said.

Cleaning up

All along Stewart and Washington streets, residents and business owners cleaned up Thursday, digging out driveways and basements still loaded with hailstones, airing out flooded hotel rooms, scraping up mud with shovels, mopping up and sanitizing with bleach.

Powerful thunderstorms towering as tall as 40,000 vertical feet lined up and stalled and reformed and hit the same narrow corridor again and again between noon and 3 p.m., with the heaviest, strongest system letting loose about 2 p.m., Craig Shoemaker, a National Weather Service meteorologist said. He estimated it was a 25-year storm event.

The storms delivered at least 2 inches of rain in about two hours, and that’s not counting layers of hailstones that came down first, inches deep in places all over downtown Sonora. The hail combined with intense rainfall and runoff to overwhelm Sonora’s storm drain system, which dates in places to the late 1800s, City Administrator Tim Miller and City Engineer Jerry Fuccillo said Thursday.

“Parts of the system are rock-lined tunnels with iron doors,” Fuccillo said. “Sonora Creek, its drainage basin is especially susceptible to real high-intensity, short-duration storms like we had Wednesday. I’d say it was a one-in-500 years storm. A 100-year storm is 1.15 inches per hour, by Caltrans standards.”

May 1996 storm ‘very similar’

Whether it was a 500-year storm or a 25-year storm, it’s been almost 23 years since a storm pumped Sonora Creek up to levels high enough to wash over the creekside deck outside the old Wagon Wheel Restaurant and inundate the lower Save Mart just downstream from Coffill Park and South Green Street. Fuccillo said Wednesday’s storms and May 16, 1996, storms and flash floods were very similar.

Eight inches of runoff rushed through lower Save Mart in May 1996, carrying paper goods out of the store and washing down the front steps, The Union Democrat reported. Other major storms that compared in intensity to Wednesday’s storms happened in December 1996-January 1997 and in November 2002, when flooding caused more than $100,000 damage at Sonora Carpet Mart alone, but neither of those incidents matched the chaos in Sonora in May 1996 and March 2019.

This time around, the path of the storm was still evident Thursday at El Arroyo, the creekside reincarnation of the old Water Wheel, at Rodeway Inn and at lower Save Mart. El Arroyo was still closed, with public entrances and exits locked and interior doorways open, and a strong smell of bleach at the front entrance on Washington. A supervisor for the new business said he was too busy to talk but assured El Arroyo will be open Friday.

Workers with big-blade shovels scraped mud and debris into piles Thursday in the Rodeway Inn parking lot, and most of the lower-level rooms’ doors were open to allow drying out from flooding that entered every ground-floor room on Wednesday. Staff at Sonora Inn said the owner for both establishments, Jeff Michels, did not want any employees to talk to news media. Michels declined to comment.

Lower Save Mart was open for business Thursday, one day after closing due to flooding in the back of the business that’s most vulnerable to Sonora Creek when it rises up high enough. The flooding caused very little damage in the store’s back room, and it caused no damage whatsoever to the building itself, Victoria Castro, a Modesto-based spokesperson for Save Mart, said Thursday.

‘Restaurant and flood decon’

Asked if Tuolumne County public health has any guidelines or requirements for restaurants that experience flooding, including any particular cleanup requirements, Robert Bernstein, the county health officer, referred questions to Rob Kostlivy, the county Environmental Health director, who responded, “We use the FDA guidelines for cleanup.”

Asked for details, Kostlivy provided a link labeled “Restaurant and flood decon” that led to a U.S. Food and Drug Administration web page titled “Restaurants and Grocers Reopening After Hurricanes and Flooding.”

Urban flooding like Wednesday’s incident in Sonora can carry all kinds of chemicals and synthetic materials, as well as potential health concerns. Federal FDA guidelines for post-flooding include recommendations such as before reopening, restaurateurs and grocers “should conduct a complete self-inspection to ensure that normal operations can be resumed safely and without compromising food safety.”

Establishments required to cease operations in an emergency and those affected by a natural disaster “should not re-open until authorization is granted by the local or state regulatory authority,” according to the federal FDA.

Decontamination and sanitization procedures include chemical sanitization such as chlorine bleach, at a concentration of 1 tablespoon of bleach in 1 gallon of potable water, should be used on all equipment and structural surfaces that are salvageable.

“When you decontaminate, do so in a manner that eliminates any harmful microorganisms, chemical residues, or filth that could pose a food safety risk,” federal FDA guidelines state.

TUD: ‘No spills’

Tuolumne Utilities District staff used sandbags and other flood-fighting methods to prevent wastewater spillage at the TUD Sonora Wastewater Treatment Plant, Ed Pattison, the TUD general manager, said Thursday.

“Yesterday’s epic storms, yeah those were torrential downpours,” Pattison said. “It was all hands on deck at TUD. We were very concerned about possible wastewater spills. Staff efforts using sand bags and other protection measures, we were able to keep storm waters and reroute those torrential flows around the plant, and protect it from that wave of flows that passed by.”