North Marin Water District must pay a $12,000 fine for discharging chlorinated water into its main reservoir last year. The district, which provides water to customers in Novato, Point Reyes Station, Inverness Park and Olema, was recharging Stafford Lake with treated water from the Russian River in early 2021 when, regulators allege, it accidentally allowed water with high residual chlorine levels to flow into the reservoir for up to four consecutive days. Chlorine-treated water is toxic to fish, but the district found no impacts on the lake’s aquatic life.
After a public comment period ending Sep. 12, the San Francisco Bay Regional Water Quality Control Board plans to assess its fine: $3,000 for each of the days it reported violations of the National Pollutant Discharge Elimination System. North Marin wrote to the water board earlier this month accepting the fine but pointing out that the regulators had extrapolated the highest sample level of chlorine found on one day—1.2 milligrams per liter, over 11 times the legal limit—to the preceding three days. At its regular meeting on Sept. 6, the district’s board will decide whether to pay or dispute the fine.
“Part of me wants to fight it because there was only one day where some samples indicated we may have had a problem, and yet they’re hitting us up for four days,” said Tony Williams, the district’s general manager. “They took the highest value and said that it was on all four days.” But he said the $12,000, the minimum allowable penalty, likely wasn’t worth fighting.
According to Mr. Williams, the discharge was an indirect result of the drought. The district rarely makes use of its unusual capacity to “backfeed” Stafford Lake by reversing the flow of a distribution line and sending treated drinking water purchased from Sonoma County Water Agency into the reservoir. Ordinarily, the line pumps raw water from the reservoir to the treatment facility. The backfeeding operation is reserved for severe drought conditions and the district has only done it seven times since 1988.
Last February, N.M.W.D. operators saw a chance to recharge the unusually low water levels by pumping millions of gallons from the Russian River, already treated with a chlorine-based disinfectant, through the distribution system and into their own reservoir to bank for use in the dry season. To meet state requirements, the district had to use a chemical compound to dechlorinate the water to approved levels for streams and lakes. Though the water would have been safe for humans to drink, high concentrations of chlorine can be lethal to fish, attacking their gill tissue. Goldfish owners are told not to fill their tanks with tap water for the same reason.
When North Marin operators returned to work at 6 a.m. on Monday, March 1, an employee noticed that a sample tap line used to test dechlorinated water was sputtering. The employee took two grab samples that showed chlorine concentrations well over the regulatory limit—first by a factor of eight, then 11 times higher than the limit. The water board took the highest sample and applied it to the weekend before and the previous Friday. During those four days, 15.6 million gallons of treated water flowed into the reservoir, equivalent to about 3 percent of its capacity, though it’s impossible to know precisely how much of that water was overly chlorinated.
N.M.W.D.’s operators were accustomed to using a chemical called calcium thiosulfate to dechlorinate water on the infrequent occasions when the district backfeeds into the lake or flushes its distribution lines. But because of pandemic-related supply chain problems, they had to order sodium bisulfite, which has a slower reaction rate. The water board attributed the mistake to N.M.W.D. employees’ lack of experience with the new chemical, but Mr. Williams said that was not the only factor, arguing the tests taken at the sample line may not have been representative and were potentially taken inconsistently.
In response to the discharge, operators installed a new sample line the same day and alerted the regional water board. The district also updated its dosing procedure for the dechlorination chemical and replaced its old chlorine analyzer, which took samples once a minute, with a more reliable device that monitors levels constantly.
The water board’s estimation that highly chlorinated water entered the reservoir on all four days errs on the side of caution, and N.M.W.D. appeared to avoid the worst impacts of such a discharge. After fixing the sample line and revising the testing procedures, all the district’s tests showed less than one tenth of one milligram of residual chlorine per liter of dechlorinated water.
The district’s own biological assessment, performed the same day, found nothing amiss. The water wasn’t discolored or visibly polluted, and the five western pond turtles observed near the reservoir’s spillway “exhibited normal behavior and appeared healthy,” a district report said. Because the discharge occurred in winter, when Novato Creek is flowing vigorously and N.M.W.D. isn’t required to release reservoir water to fortify it, the chlorinated water was contained within Stafford Lake.
“The bottom line, just to emphasize,” Mr. Williams said, “there’s no environmental damage that has been documented, or that we observed.”
But Gordon Bennett, president of the Inverness nonprofit Save our Seashore and onetime opponent of N.M.W.D.’s Gallagher well project, said the instantaneous impacts on aquatic life could have been serious and difficult to notice after the fact. The accident was “compounded by carelessness,” he said, and the water board should have fined the district more harshly.
“It’s like someone going out to Stafford Lake Park and shooting a dozen shorebirds which are then eaten by scavengers,” Mr. Bennett said. “Four days later, a biologist surveys the entire lake and finds no dead birds, but plenty of live ones, and so concludes that there were ‘no adverse impacts’ from the shooting. Tell that to the dozen dead birds that were shot.”
In 2015, N.M.W.D. paid a $38,000 fine to the water board after a treated water tank overflowed the previous year, sloshing 204,000 gallons of chlorine-treated drinking water into an unnamed tributary of Vineyard Creek in Novato. That water contained more than six times the legal limit of residual chlorine.