Image courtesy of Modus Eundi
Don't look now, Angelenos, but city officials have just announced the startling discovery of unusually high levels of bromate, a suspected carcinogen, in two reservoirs. But it's not necessarily what you think: The bromate formed in sunlit water when chlorine spontaneously oxidized bromide from the groundwater. The city will have to drain around 600m gallons - the equivalent of a day's supply - from the Silver Lake and Elysian reservoirs. The measured bromate levels were 68 parts per billion (ppb) and 106 ppb, respectively; water suppliers are typically required to keep levels below 10 ppb.
Bromide, a natural component of most water supplies, tends to be oxidized to bromate when drinking water undergoes ozone disinfection; treatment plans that use this process are thus required to test for bromate levels before distributing the water. In this case, however, the bromide was oxidized in the reservoirs following the treatment process. Currently, neither state nor federal regulations require testing for bromate in water post-treatment.This finding only came to light when a Department of Water & Power (DWP) laboratory did some tests for a commercial customer. "There is very sparse information available for the type of drinking-water scenario facing us," said Pankaj Parekh, LADWP's head of water quality compliance, who noted that his staff scientists are still studying what exactly happened in the reservoirs.
Though slightly unusual, LADWP is hardly unique in storing drinking water in large, exposed reservoirs. Its monitoring activities recently identified two other reservoirs with high bromate levels - both in San Diego County. Rufus B. Howell, chief of California's Department of Public Health (CDPH) Division of Drinking Water & Environmental Management, recommended that bromate monitoring "be expanded to cover certain additional facilities not utilizing ozone disinfectant."
Officials from the EPA have indicated that they too may establish new monitoring guidelines if they determine that this problem could be replicated at other reservoirs nationwide.
Via ::Chemical & Engineering News: Bromate in Los Angeles Water (news website)