The drought has led to an increase of THMs, which can cause cancer, in the East Bay’s drinking water.

For the last few days, crews from the East Bay Municipal Utility District have been flushing water from a Berkeley Hills reservoir as one step towards removing water that contains cancer-causing compounds.

EBMUD workers on Thursday pumped water from the Berkeley View reservoir near Grizzly Peak and flushed it into a storm drain on Wilson Circle, where it will travel to the Bay. Crews have been pumping 90,000 to 120,000 gallons the last few days to flush the lines that serve about 2,100 homes in the hills.

The flushing started after quarterly sampling revealed that water in two of EBMUD’s 16 sites, including one in Berkeley, at 1431 Summit Rd., and one in Orinda, contained more trihalomethanes, or THMs, than is considered safe. THMs are byproducts of the process used to treat water. They are created when chlorine used to treat water reacts with molecules formed by the breakdown of leaves, brush and other organic matter in water. The “maximum contaminant level” for THMs for any location is 80 parts per billion, and in the second quarter of 2017, those two reservoirs reached that level, according to the district.

“Although the district is currently in compliance with the regulatory standard, these elevated levels are a cause for concern from a public-health perspective,” Michael J. Wallis, EBMUD’s director of operation and maintenance, wrote in a June 8 memo that was distributed to the board of directors.

Despite the cautionary tone of the memo, this is not an emergency and customers should not be unduly alarmed, said Andrea Pook, a senior public information representative for EBMUD. EBMUD’s water is safe to drink, she said. However, pregnant and immunocompromised individuals should consult their doctor, she added.

“That is our number one commitment, to protect public health and to make sure we are providing the best quality water we can,” said Pook. “We don’t want to take any risks.”

The law requires EBMUD and other agencies to issue a public notice if THM levels reach 80 parts per billion four quarters in a row, she said. A singular reading like the ones for the Berkeley Hills and Orinda reservoirs does not trigger public notice, although the district is taking steps to correct the problem, she said.

In general, EBMUD has twice as strict standards for its water quality than that required by the state or federal government, said Pook. Still, the district is above its own internal goals of only having THM levels at 40 PPBs, she said. The system-wide average is now 58 PPB, according to the memo.

“We are committed to bringing those numbers down,” said Pook.

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The drought and water conservation are two contributing factors to the highest rise in THMs the water district has seen in 20 years, according to Pook and the memo.

The heavy rains of this past winter flushed years of debris into EBMUD’s primary source of water, the Pardee Reservoir located in the Sierra Nevada foothills about 30 miles northeast of Stockton, she said. In previous years there had not been enough rain to do that.

EBMUD treated the water with chlorine, which reacted with the organic debris to form THMs. Further complicating matters was the fact that customers cut back their water consumption during the drought, which meant there was less water going through the pipes and flushing out THMs.

See EBMUD’s tips on what to do if your water has been flushed. See its FAQs about THMs, or disinfection byproducts.

Warmer weather also speeds up the chemical reactions that help chlorine form THMs. Both NASA and the National Oceanic and Atmospheric Administration have reported that the planet has experienced record-breaking heat the past three years, according to the memo. Normally, THM levels decrease in the colder winter months; this has not happened the past two years, according to the memo.

EBMUD is taking several steps to dilute the THMs. It has been flushing the Orinda reservoir area for the past few weeks and has just moved into Berkeley. The crews release enough water to send three feet of water per second through the pipes, which scours the pipes.

“Flushing removes sediment and mineral deposits, and helps maintain a chlorine residual within the distribution system to ensure the delivery of high-quality water to customers,” said Pook.

The district has stopped using 40 distribution reservoirs, which has had the effect of moving water through the system faster, according to the memo. It has also reduced the use of chlorine as well as chloramine, which is used locally, in some cases.

To fully address the issue, EBMUD will have to spend millions of dollars in the next decade or so to build pre-treatment facilities that will remove organic material with carbon filtering. The district might also consider filtering the water in the Pardee Reservoir through carbon, said Pook. These long-term approaches are at least five to 10 years off, however.

This issue comes as the EBMUD board of directors is poised to increase water rates by 9.25% this year, and another 9% in 2018.

The proposed increases are earmarked for infrastructure improvements, and to make up for revenue declines linked to lower than projected water use during the recent drought, said Jenesse Miller, an EBMUD spokesperson.

EBMUD was formed in 1923 and now serves 1.4 million people throughout Contra Costa and Alameda counties.

Frances Dinkelspiel is co-founder and executive editor of Berkeleyside.