What’s in the Water

Sweetwater Dam rises 200 feet from the floor of a rocky river gorge a few miles northeast of Bonita. The 136-year-old concrete and masonry dam holds back 28,000 acre-feet of water in Sweetwater Reservoir, a major source of drinking water in South San Diego County. 

The dam, and the reservoir, have been quiet fixtures of the Bonita and Spring Valley landscape for generations. These days, they’re drawing an unaccustomed amount of attention. 

Last week, I wrote about the unwelcome discovery of toxic industrial chemicals in Sweetwater Reservoir. If further testing confirms initial results, Sweetwater Authority, the government agency responsible for the dam and reservoir, could be required to install expensive new treatment systems to remove the chemicals. Water rates could rise to cover the anticipated cost of roughly $40 million. 

At the same time, the dam is showing its age and could require expensive repairs of its own. A recent engineering report found that one of the spillways that prevent the dam from overflowing has become dangerously dilapidated and either needs to be repaired or stopped up and abandoned. A full repair could cost roughly $24 million. 

South County's Sweetwater Dam on Tuesday, December 10, 2024. Photo by Zoë Meyers for Voice of San Diego

Last — but, for nearby residents, definitely not least — Sweetwater Authority is considering installing a floating solar panel array on one section of the reservoir as part of an effort to switch to renewable energy. Critics of the plan say it will mar a natural and recreational resource and could pollute the reservoir with toxic chemicals from solar panels or even droppings from birds that roost on the panels. 

Amid all that scrutiny, I wanted to look at the dam and the reservoir myself. Last week, I joined Sweetwater Authority General Manager Carlos Quintero and Justin Brazil, the water agency’s director of water quality, for a tour of Sweetwater Dam and the adjacent Robert A. Perdue treatment plant. The plant can treat up to 30 million gallons of water from the reservoir per day before funneling it to homes in Bonita and parts of Chula Vista. 

From a distance, the dam is an impressive wall of concrete rising from the bed of the Sweetwater River. Up close, the need for repairs is obvious. A walk across the top of the dam to its south side showed just how challenging it could be to address problems in the southernmost of the dam’s two spillways. 

Dam spillways act as release valves, funneling water out of the reservoir when major storms produce more runoff than the dam can handle. The Sweetwater Dam’s southern spillway is corroded in many places, with concrete that, even to my inexpert eye, appears unable to withstand the force of rushing stormwater. 

“We would probably have to demolish it and rebuild,” Quintero said when I asked what repairing the spillway could involve. One option the agency is considering is simply blocking the spillway and abandoning it. That would require fortifying the dam’s other spillway on the north side to handle a double share of water. Cheaper, but still costly. 

General Manager of Sweetwater Authority Carlos Quintero, left,

and Justin Brazil, Director of Water Quality, look onto the infrastructure

of an old spillway at the Sweetwater Dam on Tuesday, December 10, 2024.

Photo by Zoë Meyers for Voice of San Diego

The Perdue treatment plant could require repairs of its own. The day I visited, treatment operations had halted temporarily while workers installed an industrial-sized meter to measure water flow from the plant into the drinking water supply. 

While the plant idled, workers inspected the inside of a 10-million-gallon storage tank called the Clearwell, which holds treated water on its way to the drinking water system. Agency budget documents show that, depending on the results of inspections, the storage tank could require an expensive $42 million retrofit. 

“The Clearwell degrades over time,” Brazil said. “Maybe it’s in great shape. Or maybe it needs a minor patch-up. Or maybe we just need to keep monitoring. Or maybe we need to do something big.” Inspection results should be available “in one to two months,” he said. 

Both Brazil and Quintero took pains to emphasize that, regardless of possible pending infrastructure projects, water delivered by Sweetwater Authority remains safe to drink. 

“The number one part of my job is protecting public health and making sure treatment plants are always working,” Brazil said. “The troubleshooting is challenging but rewarding.” 

Solids rise to the surface of water through dissolved air flotation near the Sweetwater Dam on Tuesday, Dec. 10, 2024. Photo by Zoë Meyers for Voice of San Diego

Touring a water treatment plant mostly involves seeing everything you don’t want in your water. Brazil walked me and photojournalist Zoë Meyers through the Perdue plant, showing us how water is pumped from the reservoir and mixed with chemicals such as chlorine dioxide, ferric chloride and cationic polymer. The chemicals kill viruses and bacteria and cause solid particles to lump together and settle out of the water, making it clear. 

The surface of one 15-foot-deep tank was covered with a layer of unpleasant-smelling brown goo — the lumped-together solid particles, which float to the surface and are skimmed off into what Brazil called a “sludge pit.” 

Later treatment stages include filtering the water through a mesh of anthracite coal, adding chlorine and other chemicals and letting the water sit in the Clearwell to give the chemicals time to do their jobs. 

“We go through 600 pounds of chlorine in a week, on average,” Brazil said. Staff chemists routinely test water from various points throughout the delivery system in an in-house lab filled with test tubes, burners, sample jars, flasks and beakers. 

I can report that chemists have just as much Christmas spirit as the rest of us. Plant staff were in the midst of a holiday door-decorating contest. The door to the testing lab was covered top to bottom with a Santa Claus made of tissue paper and felt. Someone had the ingenious idea to use a small gold jewelry gift box to make Santa’s belt buckle. 

The most high-tech part of the operation is a control room down the hall from the lab where Sweetwater’s entire water system is monitored 24 hours a day via a bank of mounted computer screens that look like a miniature version of NASA’s mission control. At the touch of a button, plant operators can start and stop any piece of equipment throughout the agency’s sprawling network of pipes and pump stations. Brazil said the certification process to become a system operator takes up to three years. 

Brazil said running the plant, the dam, the reservoir and the rest of Sweetwater’s delivery system “keeps your mind busy” because ever-evolving rules, regulations and problems in the system “require you to rethink everything and keep current on the latest technology.” 

Still, he said, he loves his job, which he described as ensuring that “the general public doesn’t have to think about water.” 

Written by Jim Hinch | Dec. 17, 2024 | Voice of San Diego

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