David A. Reckhow
The disinfection of drinking water with chlorine was implemented as early as 1908 in an effort to inactivate water borne pathogens. However, chlorine reacts with naturally occurring organic' matter in water to form a host of chlorination byproducts. The possible detrimental health effects from exposure to these byproducts lead to the development offederal regulations for disinfection byproducts (DBPs) in drinking water. Most recently, standards were reduced to 80 ug/L for trihalomethanes, and 60 ug/L for haloacetic acids. The drinking water supplied by the Massachusetts Water Resources Authority (MWRA) has approached and sometimes exceeded the concern level at a few locations in the distribution system at some point in time. For this reason, the utility has focused on finding methods to lower DBPs in their system without additional treatment. Without a filtration plant, the Authority has turned to reduction of DBP precursor levels from their principal water sources, the Quabbin and Wachusett Reservoirs, as a possible control option. This in turn necessitates extensive knowledge of the origin and nature of natural organic matter (NOM) in their watersheds. The main objective of this research was to evaluate the sources of NOM and DBP precursors in the tributaries of the Wachusett Reservoir in an effort to understand the critical processes governing DBP precursor formation. Spatial, temporal and seasonal TOC, UV A and DBP precursor levels were measured for eight principal tributaries of the reservoir. The data set was used in order to better understand relationships between water quality parameters and to possibly link the impacts of land use, temperature and discharge conditious to organic carbon levels in the watershed. Also, laboratory leaching and biodegradation studies were conducted using leaves from several tree species collected from the watershed. These studies were intended to improve the understanding of the biological alteration of organic carbon from plant materials. The basic organic water quality of the major Wachusett tributaries is very similar in nature, with an average TOe of 5.0 +/- 1.6 mg/L and an average SUY A of 3.6 +/- 0.5 Llmg-m. On average, DOC accounted for 96% of TOe. In addition, DOC correlated very well with UY absorbance at 254 nm (? = 0.94), reflecting the consistent aromatic nature of the NOM sources. Analysis of the entire data set showed that the relationship between discharge and TOe, SUY A, specific THM, DRAA and THAA formation potential was statistically significant. Both DOC and SUY A increased with an increase in discharge, while specific DBP formation potential decreased. Visual inspection of the data set revealed that long residence times and possible enhanced biological activity during warm temperatures may result in the degradation of DBP precursor material. Rain events showed that NOM flushed from upper soil horizons during periods of high discharge are a significant source ofDBP precursor material.