Disinfection Byproduct (DBP) Formation and Mitigation Strategies in Drinking Water Systems
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Authors
Lacroix, Angelica
Issue Date
2024
Type
Dissertation
Language
en_US
Keywords
Aquifer Storage and Recovery , Disinfection Byproducts , Groundwater , Haloacetic Acids , Total Organic Carbon , Trihalomethanes
Alternative Title
Abstract
Aquifer Storage and Recovery (ASR) involves intentional and controlled storage of drinking water underground during periods of supply abundance and includes three distinct phases: injection, storage, and recovery. During the injection phase, excess drinking water from surface water sources such as rivers or lakes or highly purified recycled water to meet drinking water standards is considered as injectate. This water is injected into an underground aquifer where it is stored for later extraction. The aquifer acts as a natural reservoir, holding the water until such time when the stored water is recovered by pumping back to the surface. ASR programs play a pivotal role in addressing water quantity challenges, particularly in regions prone to drought and declining groundwater levels. While water managers focus on aquifer replenishment, continued formation of disinfection byproducts (DBPs) during water storage has the potential to compromise water quality by increasing the concentration of these compounds above the maximum contaminant levels (MCLs). There is limited information on reducing DBP formation in an active operating drinking water system practicing ASR, especially at full-scale. This research provides a comprehensive investigation to fill the gaps in knowledge including: 1) The effectiveness of two pretreatment methods prior to water injection: granular activated carbon (GAC) adsorption and chloramination with liquid ammonium sulfate (LAS) injection into injected drinking water and the resulting impacts on DBP formation during the storage and extraction phases; 2) DBP formation as a function of seasonality and speciation over an extended hold time using samples collected from different locations within a drinking water distribution system and definition of a total organic carbon (TOC) threshold which can cause DBP MCL compliance issues; and 3) The viability of prevention as a DBP control mitigation strategy, particularly when operating an ASR system where water will be stored at length. This research evaluated the upstream lake and reservoir source water characteristics and treatment plant DBP transformations to extract water quality variability insights. This research determined that wellhead pretreatment methods prior to injection utilizing GAC and LAS injection are both suitable alternatives for reducing DBP formation during aquifer storage and the costs are comparable when GAC is not replaced to maintain contaminant adsorptive capacity, but instead chlorine removal governs media exchange frequency. Additionally, a TOC threshold of 2.5 mg/L in the treatment plant finished water was determined to have the potential to exceed the regulatory maximum contaminant levels (MCLs) for both haloacetic acids (HAA5) and trihalomethanes (THMs) within the distribution system. While these findings represent significant contributions for DBP management downstream of the treatment facility, pretreatment of each wellhead would require significant capital investment and may not be necessary when TOC levels in the treatment plant finished water are less than the previously established critical value of 2.5 mg/L. Prevention as a DBP mitigation strategy was evaluated at the treatment plant and water supply levels and a statistically significant difference in the raw water TOC values was found between drought years (when the elevation of Lake Tahoe falls below the natural rim, 2.6 mg/L) and non-drought years (when water flows from Lake Tahoe into the Truckee River, 1.6 mg/L), with higher TOC values during drought periods.