Tests are conducted at 16 locations throughout EBMUD’s service area every quarter. For calendar year 2019, THM concentrations ranged from 29 parts per billion (ppb) to 65 ppb. All sites were well below the Maximum Contaminant Level (MCL) of 80 ppb. The MCL is applied to the average of all four quarterly samples; it was developed to limit long-term exposure to THMs while balancing the need to disinfect water to protect the public from disease-causing pathogens.