For the past few years from roughly August to December, the Goleta Water District has faced concentrations of trihalomethanes, or THMs, above federal regulations within the water distribution network. The effects of THMs include skin, lung, and eye irritation as well as increased cancer risks. High concentrations have been observed in parts of, not all, of the water distribution network, with some concentrations twice as high as the federal standard. Although the link has not been confirmed, persons connected to the water supply have issued complaints to the water district due to skin, eye, and lung irritation attributable to contact with the water. Where are the THMs in our water coming from, what are the current/future community health risks, and what is the Goleta Water District doing about them?

Sources: THMs are naturally occurring compounds but are typically at concentrations far below those of concern to human and environmental health because they are formed in the presence of organic matter and chlorine. When humans treat water with chlorine, we can increase the amount of THMs produced if there is organic carbon in the water. Chlorine is important for us to use to kill harmful bacteria in our water supply. Thus, it is important for water treatment districts to filter out the carbon to prevent THMs from forming in the presence of higher concentrations of chlorine.

In Goleta we have high natural concentrations of organic carbon in our water, especially at the end of summer when plants start to die off and introduce organic matter to our water supply. The high THMs in Goleta drinking water are thus coming from the organic matter in our water supply and the chlorine with which we treat our water. In the presence of sufficient organic matter and chlorine, the formation of THMs increases the longer the water is held within pipes after treatment.

Community Health Risks: Short-term effects of THMs include skin, eye, and lung irritation. Also, similar to sun exposure, the more you are exposed to the compounds, the higher your cancer risks. Eliminating THMs from the water supply is not easy, although organic matter can be filtered, once THMs form, we cannot filter them with currently available technology. Thus, it is important to have good filters for organic matter at the treatment plant. But due to the high concentrations of organic matter in Goleta, filtering sufficient organic matter is difficult.

Current Water District Efforts: To work to reduce immediate health risks, the district flushed the system, reduced post treatment retention time (limiting the time THMs could form), and reduced the chlorination of the water as allowable to maintain compliance with other water quality criteria. With these efforts, concentrations of THMs still remained at levels above federal criteria and residents still had complaints during the final quarter of the year.

In 2018, the district will install an aeration system to work to off-gas THMs in the water supply, perform more frequent flushing of water in the system, and work to reduce the residence time of water post treatment. For the mid to long term, the district is pursuing funding for an air stripping facility to off-gas THMs and to purchase alternative water treatment methods that either reduce organic matter concentrations or the need for chlorine. The projected timeline for new treatment technologies that would provide the best assurance for lower THMs is five years.

Bottom Line: THMs will likely continue to be an issue in the Goleta Water District for the next few years. Users may have a high variety of THM concentrations which are dependent on the residence time of the water and the fluctuating organic matter concentrations. Many users will likely have negligible effects while some may experience the aforementioned symptoms.

If experiencing irritation from the water, notably between August-December, minimize contact and try to use neighbor or friend water supplies if they are not experiencing adverse effects. The Goleta Water District is actively combating the issue but with funding, construction, and supply constraints, may not be able to bring levels to recommended concentrations prior to implementing major changes to the treatment plant, for which the estimated timeline is five years.

Nicol Parker is a PhD student at the Bren School of Environmental Science and Management at UCSB studying the fate and transport of contaminants.


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