The chemistry of the reactions between chlorine and the organic materials present in water is complex and, although extensively studied, poorly understood. Disinfection by-products or trihalomethanes (THMs) are formed in drinking water primarily as a result of the chlorination process to kill pathogenic organisms. THMs are halogenated aliphatic hydrocarbon compounds with the general formula CHX3, where X represents a halogen, which may be fluorine, chlorine, bromine, or iodine, or combinations thereof. The total THMs in drinking water is composed of chloroform (CHCl3), bromodichloromethane (CH2BrCl) or dichlorobromomethane (CHBrCl2) (BDCM), dibromochloromethane or chlorodibromomethane (CHClBr2) (DBCM), and bromoform (CHBr3). The Environmental Protection Agency (EPA) limits the maximal annual average level of total THM’s (TTHM) to not exceed 80 ppb. At heightened level, THM have been proven to have carcinogenic effects.
Baltimore’s water supply relies on surface water from rainfall and snowmelt, collected and stored in reservoirs outside the city. Three major impoundments (the Liberty, Loch Raven, and Prettyboy Reservoirs) derive water from two water sources (Gunpowder and Patapsco Watersheds) and one river (the Susquehanna). Water from the Liberty reservoir and upstream sources is treated at the Ashburton Water Filtration Plant, while water from Loch Raven and Prettyboy reservoirs is treated at the Montebello plant. Finished water samples were collected from these two water filtration plants to investigate the concentrations of by-products of the chlorination process. Following EPA’s recent protocol, Gas Chromatography-Mass Spectroscopy (GC-MS) was used to determine the total trihalomethanes (TTHMs) of chlorination disinfection.
Results/Conclusions
Analysis of the total THMs at the two filtration plants over a two year period (2015 and 2016) revealed that for 2015 the average TTHM at Ashburton was 48 ppb and at Montebello 53 ppb. In 2016, Ashburton averaged at 41 ppb and Montebello averaged 44 ppb. These levels are below the maximum allowable limits set by the EPA. Based on the present findings, chlorination disinfection by-products in Baltimore’s water system are not a threat to public health. The study will continue to analyze 2017 and 2018 water samples to confirm the findings.