Graduate Thesis Or Dissertation
Modeling Relationships between Climate, Source Water Quality and Disinfection Byproduct Formation and Speciation in Treated Drinking Water Public Deposited
Disinfection byproducts (DBPs) are formed in water treatment and in distribution systems when disinfectants, most commonly chlorine, react with organic matter and inorganic precursors, e.g. bromide. Reducing exposure to DBPs remains a concern for the national drinking water utility community, as some of them are of health concern. Currently, two class sums of DBPs, total trihalomethanes (TTHM) and five haloacetic acids (HAA5) are regulated under the Stage 2 D/DBP Rule. Changes in climate, as well as anthropogenic activities, can lead to increased DBP precursors, specifically total organic carbon (TOC) and bromide, which could force water utilities to make important and expensive decisions regarding treatment processes. Additionally, increased bromide can increase the formation of brominated DBPs, which are of greater health concern than their fully chlorinated counterparts.
The impact of climate on source water quality, particularly TOC and bromide concentration, and subsequent impact on a water treatment plant’s capacity to meet DBP regulations was evaluated at three sites. Source water TOC concentration was modeled with climate, temperature and precipitation, and land surface, soil moisture and vegetation, predictors using a local polynomial regression. A methodology was developed for determining site-specific source water TOC and bromide thresholds for Stage 2 D/DBP compliance. Thresholds were determined for the three sites; TOC thresholds varied monthly from 1.6-2.6 mg/L, 2.2-3.2 mg/L, and 2.2-4.2 mg/L and bromide thresholds for two sites was modeled using extreme value analysis with a peaks over threshold approach and a generalized Pareto distribution with temperature, precipitation and soil moisture covariates.
National occurrence of brominated DBP formation was assessed through analyzing trends for all nine haloacetic acids that include four unregulated haloacetic acids and for bromine incorporation factors (BIFs), along with spatial analysis for BIFs. Changes in HAA9 and in HAA5 occurrence before and after the D/DBP Rule implementation were compared to assess how regulatory changes have impacted unregulated brominated HAA species. For one case study location, BIFs were modeled using local polynomial regression with climate, temperature, and water quality covariates, the bromide-to-TOC ratio and UV254 absorbance.
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