| When raw water is treated with chlorine to protect against potentially harmful microbes, chemical byproducts are formed as the chlroine reacts with organic precursors in the raw water. Some of these byproducts pose health risks and are themselves regulated by the federal and state governments. The two classes of disinfection byproducts that are currently regulated are triholamethanes (THMs) and haloacetic acids (HAAs). These byproducts are of concern because they have been shown to increase rates of cancer and birth defects in laboratory animals and are classified as probably human carcinogens. In 2004, Cuesta was required for the first time to monitor the levels of both of these byproduct classes. While our water was in compliance for HAAs, it contained THM's well over the maximum contaminant level (MCL) of 80 parts per billion (ppb). Until recently, this was true for every quarterly DPB test. |
| Cuesta attemped to reduce THM formation by improving raw water quality to lower the concentraion of organic precursors. This chiefly involved trying to improve algea control and the timing of moving water from one reservoir to another. Thes efforst proved unsuccessful and in the fall of 2006, the California Department of Health Services (now the Department of Public health, or DPH) required that Cuesta enter into a mitigation agreement for THM levels. As part of this agreement, Cuesta contracted with Water Quality & Treatment Solutions to evaluate alternatives to mitigate THMs. Several treatment alternatives were evaluated, with cost being an importnat consideration. The only method evaluated that tests showed was likely to be successful was a switch to chloramine as an alternative disinfectant. Chloramine is a combination of chlorine and ammonia and results in fewer THMs because it is slower to react with precursors than is free chlorine. Cuesta signed an agreement with DPH to install a chloramine disinfection system in December of 2007. |
| About a year of engineering evaluation followed, during which time another treatment alternative, aeration, came to the attention of the public works staff and the board of directors. The most prevelent THM, chloroform, is relatively volatile. Aeration aims to reduce chloroform and other volatile THMs by partitioning them out of the water and into the air. Aeration has the potential advantages of being simpler to employ and avoids changing the chemicals used as a distribution system disinfectant. In the winter of 2009, the Guild initaited an evaluation of aeration. There are few facilities in the country that are using aeration as a DPB mitigation method, so there were many uncertainties about whether it would be an effective method with our particlar raw water, disinfection needs and distribution system. As a result, DPH required that the Guild continue apace with its plans to implement a switch to chloramine as a disinfectant. |
| By midsummer of 2009, aeration was showing signs of being an effective treatment method for THM's. although levels of HAAs were sometimes elevated. In the fall of 2009, DPH agreed to postpone implementation of chloramine disinfection and to allow the Guild a year long formal evaluation period for aeration. A critcal issue was whether HAA levels could be kept down along with THM levels. In the second quarter of 2010, the Guild came into regulatory complaince for THM levels for the first time since it came under regulation for DPB levels. HAA levels have also stayed in compliance. We hope for continued success as we move into the second half of the year long evaluation period. |
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