The Long Term 2 Enhanced Surface Water Treatment Rules, know as LT2ESWTR was promulgated in 2006 obligating large drinking water utilities to comply with the rules by 2012. The rule was designed to prevent cryptosporidium, a difficult to kill pathogen from entering the drinking water supply. An incident in Milwaukee resulted in thousands of people becoming ill and others to die. It was considered a serious threat that was not treated by the standard disinfection method of chlorination.
The AWWA has reported on both the monitoring results and treatment methodologies employed by these utilities in the August issue of the associations journal.
The LT2ESWTR required utilities to first monitor their water for the presence of cryptosporidium. Based on these results, utilities were placed in bins associated with the observation of cryptosporidium being in present in the source water. The more pathogen found, the more aggressively the utility had to treat its water. Reservoirs ad lakes showed the lowest occurrence with 3.2% of samples showing the organism while rivers and other flowing water sources showed up to 11% of samples with the pathogen. The average was about 6.4% of all surface water sources had the organism.
If utilities fell into the higher risk bins, i.e. they observed higher levels of cryptosporidium, they were required to use EPA methods referred to the microbial tool box. Utilities assigned in the higher risk bins used a variety of methods to treat the water. These methods begin at the water source where plans to control the watershed are intended to prevent the organisms from entering the source water. Various filtration methods were employed by the utilities to filter out the organisms. Finally, some utilities upgraded their disinfection processes to inactivate the organism. One of the more popular methods was ultraviolet light or UV.
Unfortunately, the AWWA survey only looked at 38 utilities with 24 actually reporting results. So the study did not provide good statistical information on how the various methods are being used. For example, the particular utilities contacted had not used ozone, although ozone is used to control cryptosporidium, especially were water temperature is higher and their are other reasons for using ozone. For example, in reservoirs and lakes, algae can create significant taste and odor challenges for a water utility while also having to deal with cryptosporidium. So employing ozone water treatment in these cases can provide both taste and odor removal as well as pathogen reduction.
The Milwaukee outbreak lead to a detailed study of the drinking water systems in this country that use surface water. A well designed plan involving considerable public comment resulted in an enhancement of the safety of drinking water. Although the process took over a decade, the results will be enjoyed for many years to come.