Life cycle assessment of the City of Atlanta, Georgia’s centralized water system

Abstract

The main goal of this study was to conduct a life cycle assessment (LCA) for the City of Atlanta’s (CoA) centralized water system in order to understand the sources of the largest environmental impacts in the system. The boundaries of the water system we studied included the water supply system, the wastewater collection and treatment system, and the stormwater collection system. The CoA has separate wastewater and stormwater collection systems; therefore, they are considered separately. We defined the functional unit (FU) of our study to be 1 m3 of water distributed to the point-of-use, and our scope includes infrastructure construction and decommissioning in addition to system operation. We used the US Life Cycle Inventory (USLCI) and ecoinvent databases to inventory all emissions and resource use. We determined the major impacts of the water system and the sources that create these impacts using TRACI v2.1, which is the life cycle impact assessment (LCIA) methodology developed for North America by the Environmental Protection Agency (EPA). In addition, a method to evaluate the impact of freshwater consumption on ecosystem was used in this study because it is excluded in TRACI v2.1. The four major impacts of the CoA’s centralized water system were carcinogenic effects, ecotoxicity, non-carcinogenic effects, and eutrophication; respectively, they contribute 62, 8, 6, and 5 % of the average impacts of a US resident per year (2008) for the annual water use of a single-family home resident. Notably, the input which causes 68 % of the carcinogenic effects, which has the largest normalized impact, was from infrastructure construction which is often ignored in the literature. Freshwater consumption had a relatively low impact, with an evaporative water loss of 0.23 m3 per FU and a moderate level of water stress on the middle Chattahoochee River Basin; however, the impact of freshwater consumption would rapidly increase with population growth due to increased water consumption and expansion of the impervious area in the CoA. This study is distinctly different from other LCA studies because it includes infrastructure construction, which was a major contributor to the water system’s environmental impacts. Our results suggest that infrastructure construction should be considered in LCA studies for centralized water systems. It is worth noting, however, that European datasets were used to determine emissions and resource use related to infrastructure. Results would be more accurate if inventory datasets for US infrastructure were available.