The last time San Luis Obispo ran critically short of water, the city pumped heavily from wells along Los Osos Valley Road.

The aquifer was so overtaxed by residents and farmers that the ground sank, resulting multi-million dollar lawsuit settlements over damaged businesses and homes.

Since the 1990s, the city has adopted a series of water measures — including rebates for more efficient fixtures, upgrading the sewer plant to deliver treated water to landscaping, and building a pipeline delivering water from Lake Nacimiento.

SLO no longer uses those wells for drinking water.

However, the Los Osos Valley Road area still faces issues with water.

As the Telegram-Tribune reported on March 31, 1989, the city was looking to tap water in that area when it discovered two contaminants — trichloroethlyne and tetrachlorethylene — in the local water supply.

San Luis Obispo Mayor Ron Dunin pours a ration of water at a City Hall during a meeting that took the first step toward water rationing during drought March 15, 1989. David Middlecamp [email protected]

The city was required to treat the water or blend it to use it for drinking at a cost of up to $450,000. The chemicals were said to disperse during sprinkler irrigation

The city is currently leading the Groundwater Enhancement Project, which it described as “an initiative to to ensure responsible use of groundwater in the San Luis Obispo Valley Groundwater Basin.”

“As a first step to improving groundwater quality,” the city said, it’s “conducting a characterization study to monitor a small plume of tetrachloroethylene (PCE), a chemical associated with dry cleaning and industrial operations, that was detected in the basin. “

You can learn more about the study’s findings at a public meeting at 5:30 p.m. on Wednesday, Nov. 16, at the Ludwick Assembly Room, 864 Santa Rosa St. in San Luis Obispo.

David Eddy wrote this story about sinking San Luis Obispo ground levels, published on March 1, 1991, in the Telegram-Tribune:

Subsidence cracks SLO homes

Several houses in a San Luis Obispo neighborhood are cracking because the ground is dropping out from underneath.

In recent months, many residents of the area near the corner of Los Osos Valley and Madonna roads have seen cracks form and continue to grow, and it’s got them wondering what’s going to happen to their homes.

“We don’t know how bad it’s going to get,” said Susan Leal, eying a quarter-inch crack in the kitchen floor of her Pereira Drive home.

The crack appeared less than six months ago, and now extends nearly the length of the floor. Another large crack runs through the ceiling.

“I’d repair it now,” said her husband Tony Leal, “but it might just keep on cracking.”

Susan Leal nodded, shrugged and then shook her head.

“Every day we get up and see how much farther it’s moved,” she said.

The Leals are by no means alone.

Just down the street, Susan Smith has found cracks in the walls and separations in the tiles in her bathroom floor.

Just before Christmas, she was cleaning her kitchen counter when she noticed it had separated about a half-inch from the wall.

And Smith too, said she is not alone.

“Everyone’s been talking about it being so bad,” she said, adding with a laugh: “My husband and I were going to put on buttons when we visited the neighbors saying ‘SLO Crack Patrol.’ ”

Not all the people who live in the area have had problems however. One-third of the people contacted said that although they were aware of their neighbors’ problems they hadn’t seen any cracks (or) other signs of shifting.

The Leals have no doubt about the cause of the problem. There’s so much water being pumped out of the aquifer below their house that the ground is sinking.

In fact the ground has dropped as much as 10 inches, said City Utilities Director Bill Hetland. The problem is known as subsidence, and is common in the San Joaquin Valley where farmers have pumped out huge amounts of water for crops.

But the problem is new to San Luis Obispo. That’s because far more water is being pumped out of the aquifer in the southern part of the city than ever before — and far more that the state Department of Water Resources considers safe.

Between 1941 and 1989, the city relied entirely on reservoirs for its water supply. When the reservoirs begin to run out, the city started pumping groundwater — 1,770 acre-feet in 1990.

An acre-foot is 325,000 gallons, or the amount necessary to cover an acre to a depth of 1 foot.

Sprinklers irrigate Dalidio property. Wells in the area was discovered to have chemicals TCE and PCE, photo published March 30, 1989. The solvents dispersed in sprinkling and were safe for agriculture but levels were too high for drinking water unless treated. David Middlecamp [email protected]

Farmers pumped out another 5,200 acre-feet last year, and rural residential well owners used another 978 acre-feet.

So although extractions averaged only 5,800 acre-feet per year during the 1980s, nearly 8,000 acre-feet was pumped out in 1990.

According to the state Department of Water Resources, the aquifer’s safe annual yield is only 2,250 acre-feet.

Businesses on Los Osos Valley Road near Highway 101, where most of the heavy-producing wells are located, were the first to feel something wrong. Windows separated from their moldings at one car dealership, and few have popped out. Business owners at Bear Valley Plaza couldn’t get their doors shut at night, and were forced to revert to chaining and padlocking doors.

Chef Em Bashore can no longer open her door all the way because of the ground subsidence Jan. 17, 1991. Due to drought the city of San Luis Obispo was pumping water near Los Osos Valley Road as well as farmers. When the ground in the area sank damaging businesses and houses lawsuits were filed David Middlecamp [email protected]

Em Bashore, the owner of Chef Em’s, said her ceiling hadn’t fallen in, as she feared in January. But she still has problems with ill-fitting doors.

“It’s just gradual,” she said. “There are still little things going wrong.”

Several business owners have mulled legal action because of the problem.

“Of course we’re concerned,” said Hetland. “We don’t want to get sued.”

But he’s not admitting the city is at fault. Hetland noted that most of the water is being pumped out by farmers, and in any case, he said the homeowner’s problems may not be entirely caused by pumping too much water out of the aquifer.

The clay soil in the area, Hetland said, normally contains a lot of moisture. When the soil dries out, as it does in an extended drought, it can compact, causing houses to sink.

“It’s not good soil to build on to start with,” he said.

Fred Potthast, a soils engineer for Pacific Geoscience, agreed that soil compaction could be the culprit.

Though Potthast said he could not comment specifically on the Los Osos Valley Road area, he is familiar with the adobe clay soils that are common throughout the county.

“The soils we have in this area are like a sponge,” he said. “They shrink when they’re dry and they expand when they’re wet.”

Normally, even during the summer, the soil may be dry on top but remains moist just a few inches down.

But because of the drought, the soil is drying at deeper levels.

“We’re seeing bone-dry soil as deep as 3, 4 or 5 feet,” he said.

When the soil dries out deep enough, the footings that hold the house in place begin to lose their support, said Potthast, and the house can begin to slip.

The problem can be taken care of by sinking the footings deeper or by running cables through the house’s foundation, but it’s not done on all houses.

“We’ve seen this problem from Paso Robles to Nipomo,” he said. “It’s happening a bunch.”

Leo Fedewa, a geologist for Cuesta Geotechnical, said to see how clay soil reacts to a drought, look at the dried out, cracked bottom of Laguna Lake.

But as to what is causing the problem in the Los Osos Valley Road homes, it’s impossible to say without doing more tests.

Potthast echoed those sentiments.

“You can’t put your finger on it and say it’s one thing.” he said. “It’s usually a combination.”

Hetland said city employees are closely monitoring the situation. Lately the ground has stopped sinking, as has the water table.

In addition, the city is negotiating with farmers with the idea of paying them to stop pumping so much water out of the aquifer. The city has little choice but to keep pumping — it doesn’t have another source of water.

“But if it’s just the drought drying out the ground, there’s nothing we can do,” said Hetland.

That’s little comfort to the Leals, who believe the problem is caused by too much pumping.

Related stories from San Luis Obispo Tribune

David Middlecamp is a photojournalist and third-generation Cal Poly graduate who has covered the Central Coast region since the 1980s. A career that began developing and printing black-and-white film now includes an FAA-certified drone pilot license. He also writes the history column “Photos from the Vault.”

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