Improved water quality for disinfection by-products in Calistoga’s drinking water
Over the last few months the city issued two notifications because certain disinfection byproducts exceeded limits established by the Department of Water Resources – Division of Drinking Water. Disinfection byproducts are common byproducts from chlorine reacting with naturally occurring organics in the water during the disinfection treatment process.
Trihalomethanes, or THMs, and haloacetic acids, or HAAs, are measured monthly and a four quarter average is determined for compliance monitoring. The limit for THMs is 80 parts per million (ppm) and the limit for HAAs is 60 ppm.
Despite those exceedances, Public Works staff routinely works to reduce the amount of disinfection by-products in Calistoga’s drinking water. The department is in regular communication with the State Water Resources Control Board—Division of Drinking Water, and engaged the services of a specialist in water chemistry and selected an outside consultant in the water treatment industry to assist the city in identifying economical measures for the removal and/or reduction of disinfection by-products.
To access the effectiveness of its efforts, the city took additional samples in December and January at the sampling sites near the Calistoga Public Library and on Greenwood Avenue at Grant Street. In December, samples from the Library site showed THM results were 28.3 ppm and HAAs were 44.3 ppm. The same month, samples at the Greenwood Avenue location showed THMs were 54 ppm and HAAs were 50 ppm – all under the state limit.
For January 2018, at the Greenwood Avenue site the THMs were 30 ppm and HAAs were 37 ppm, again below the state limit.
The reduction in disinfection by-products over the past two months is encouraging, officials said, and demonstrates efforts have resulted in the reduction of the formation of disinfection by-products. However, because the city is required to use the test results from the prior three quarters, it is possible that the city’s four quarter running average may again be above the state limit, said Mike Kirn, public works director.
“If that is the case, the city would be required to issue another notice of exceedance. Please be assured the city is doing everything it can to improve water quality and we appreciate your patience. If you have any questions please call us at 707-942-2828.”