Carbon and Water Resource Management for Water Distribution Systems

Water distribution systems (WDS) worldwide face increasing challenges as population growth strains a limited water supply in many areas. In the United States, existing water infrastructure systems require significant investments to refurbish an aging stock of assets. Much of this investment is required in drinking water transmission and distribution, where a substantial amount of material and economic inputs are lost as a result of pipeline leaks. With growing worldwide concern for reducing environmental impacts of the built environment, infrastructure investment on the scale of WDSs must be accurately assessed for potential unintended consequences. U.S. water infrastructure systems have already been identified as a major consumer of energy: it is estimated that 13% of the total U.S. electricity demand is consumed by water-related energy use./nThe existing literature on environmental assessment of WDSs does not provide a comprehensive, detailed picture of the total impacts of utilities. The current body of knowledge either omits common WDS elements or focuses on solving theoretical design problems. This research provides a framework for the most comprehensive greenhouse-gas (GHG) emission assessment of U.S. WDSs with the most accurate data available. This research presents opportunities for incorporating environmental metrics into asset management, a popular management strategy used by utility managers worldwide. The major contributors to emissions in WDSs are identified, and cost-effective solutions for reducing GHG emissions are recommended. A major opportunity in cost-effective GHG reduction lies in effectively reducing distribution losses from leaks in pipelines. This dissertation provides a model, tool, and analysis solutions that help communicate the GHG emissions associated with leaks and the related economic costs for reducing these leaks./nThis dissertation employs life-cycle assessment (LCA) in determining the GHG footprint of a WDS. LCA is a commonly used, holistic environmental assessment method. Products and processes are analyzed from "cradle to grave" which implies that all supply chain entities, both upstream and downstream, are included in the assessment. This research uses hybrid LCA methods to reduce uncertainty in providing the most accurate assessment possible./nThe study focuses on four major elements of a WDS: water storage, pipes, water wells, and pumping. These entities, namely water storage, water wells, and booster pumps, have never been analyzed at this level of detail in previous research. Each element is separately analyzed for GHG contributions to a drinking water utility's footprint. Whenever possible, the most relevant LCA data are used in creating the overall model. This represents a WDS LCA with better data than have previously been used in any of the existing literature, which often omits infrastructure aspects or reuses inaccurate data from previous work./nThe scope of work includes material production, construction, operation, and maintenance of a case study U.S. WDS. Material production includes all supply chain entities involved in delivering materials for use in the WDS. Construction involves all equipment use and temporary materials used in the assembly and installation of the WDS elements. Operation and maintenance encompasses all emissions that result from inputs related to the delivery of drinking water to customers after construction is completed. Determining the GHG emissions of leaks in distribution and transmission is a major facet of the operation and maintenance assessment. A tool is developed to calculate pipe replacement scheduling based on GHG emissions from leaks./nThe LCA results are based on a case study for a distribution system utility located in the Western United States. The case study utility draws all water from a large, pristine aquifer and pumps this water to storage tanks at higher elevations to create a gravity fed system. It has no dedicated transmission lines, and the high pressure spikes from pumping with a small operating budget have created a WDS that loses 40% of pumped and treated water in distribution./nThe LCA results show that pumping energy contributes the majority to the case study utility's GHG footprint, accounting for 84% of the total emissions. Losses, the majority of which are assumed to be leaks by the case study utility, contribute 40% to this number. Piping materials (6%) and maintenance (5%) are the next largest contributors to the total GHG emissions for a 50-year analysis period. Projections for growth show that decarbonization of the local electricity mix and reducing distribution losses could significantly reduce GHG emissions despite service growth for the case study utility. Assessing water storage options showed that concrete reservoirs had significantly higher impacts than steel tanks on a storage capacity basis./nAs distribution losses from leaks were found to contribute significantly to the GHG footprint, this research developed a "breakeven" tool to give utilities an environmental perspective on pipe replacement scheduling. The tool's results show that accrued GHG emissions quickly matched the emissions that would result from construction and material inputs from replacing the pipe, even for modest leak increase rates. These results are in stark contrast to the case study utility's current replacement schedule, which operates on a 300-year cycle due to economic constraints./nTo give the breakeven tool results more context, this dissertation uses the utility's reported pipe replacement costs to compare GHG emissions and economic costs for different leak scenarios. This comparison effectively allows utility representatives to visualize the costs of potential GHG emission savings by reducing leaks. For the case study utility's inputs, avoiding GHG emissions through pipe replacement was revealed to be cost effective./nAlthough the case study utility has unique aspects uncommon to many U.S. WDSs, such as the high loss volume and low treatment inputs, the LCA model assesses other materials and processes that can be applied to GHG assessments of other WDSs. The new LCA data sources reduce uncertainty for future applications. This research provides evidence that WDSs can cost-effectively reduce their GHG footprint, and that the entirety of WDS infrastructure can be targeted for GHG reductions by policy makers./nThe GHG intensities of drinking water and cost effectiveness of GHG savings through leak reduction were estimated for California and Texas. These scenario analyses showed that values vary with different regions based on the treatment and pumping requirements, and that there are diminishing returns for GHG savings in leak reduction. Still, the economic cost of avoiding emissions through leak reduction was determined to be an extremely cost-effective option for carbon abatement when compared to other infrastructure solutions, such as renewable energy options.

Advisor: Horvath, Arpad