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The DWP has decided to dump all the water in Silver Lake and the Elysian reservoir because of unusually high traces of the carcinogen bromate, which formed in the water due to a chemical reaction between sunlight, chlorine and the bromide in groundwater. "This is the first time an occurrence like this has ever been observed," says a DWP information sheet. The reservoirs were taken out of service when the contamination was detected in October, but now the decision has been reached to empty the reservoirs. The effect on water supplies will be minimal, the DWP says, even though 600 million gallons will mostly be dumped into the Los Angeles River. Here's a Times story and a letter from the state Department of Public Health. The DWP release follows in full.
Snapshot
The LADWP recently discovered bromate at unusually high levels in Silver Lake and Elysian reservoirs, which are part of the LADWP water distribution system. The level of bromate in the reservoirs, if allowed to continue and be served to our customers, could result in the Department exceeding the acceptable drinking water standard. As a result, the reservoirs were immediately isolated and the water contained in them is not being served to our customers. There is no immediate health risk. The Department is working closely with the California Department of Public Health to investigate the problem and has since changed its operations to prevent a repeat of its occurrence. All water being served to our customers continues to meet all public health standards. The water contained in the reservoirs will be used only for non-potable purposes; the remainder will be disposed.
Background
Upon notification from a laboratory performing tests for one of our commercial customers, LADWP water quality staff confirmed the presence of unacceptably high level of bromate in Silver Lake and Elysian reservoirs. As a result, water system personnel immediately removed the reservoirs from service. Water quality staff also immediately tested the other three open distribution reservoirs for bromate. Those tests came back negative.
The LADWP tests for bromate along with hundreds of other chemical constituents in accordance with California Department of Public Health testing protocols. It is a known carcinogen, with adverse health effects possible only after long-term exposure and testing standards and protocols are set by state and federal authorities. Bromate is known by public health officials and water quality experts to form in public water systems when water containing naturally occurring bromide is purified using ozone, a method typically used at filtration plants. Since it can form as part of the purification process, it is known as a "disinfection by-product". In the case of Silver Lake and Elysian reservoirs, which are filled with water treated at the LA Aqueduct filtration plant, bromate formed unexpectedly when the water in the reservoir combined with groundwater, was treated with chlorine, and exposed to sunlight. This is the first time an occurrence like this has ever been observed. In response, staff moved swiftly to isolate the reservoirs. In fact, LADWP was commended by the California Department of Public Health for its quick action (see attached) and all steps have been undertaken in consultation with the Health Department.
Removing the reservoirs from service has had no adverse impact on water supply due to lower seasonal demand during the fall and winter months. This flexibility has allowed water quality and water operations staff the time to understand how this unprecedented formation occurred, change operations to prevent a recurrence, and evaluate all options for remediation, including whether the water in the reservoirs could be filtered or treated to acceptable drinking water standards.
After a thorough review of all available technology, and in consultation with LADWP General Manager David Nahai, the Department feels it is in the best interest of the public to identify only non-potable uses for the water contained in the reservoirs and to dispose of the remainder. This course of action is recommended in an abundance of caution, cognizant of the importance of customer confidence in the safety of our drinking water. Staff plans on spending additional time evaluating the feasibility of methods to beneficially use the water and will proceed with draining in early 2008. After draining the reservoirs the LADWP will take the opportunity to thoroughly clean both before returning them to service. This action is expected to take 3 - 4 months, with the reservoirs returning to service in time to ensure system flexibility during the higher demand summer months.
The LADWP will outreach to neighbors living in the vicinity of the reservoirs to inform them of our plans and keep them apprised of our progress. We will also remain in close consultation with the affected City Council district Members, their staff and area Neighborhood Councils.