## 1 Introduction and Background  
Underground infrastructure primarily consists of sewer pipeline systems. The U.S. has approximately 1.2 million miles of water supply mains. Each mile of interstate highway typically has an equivalent length of sewer pipes. Over time, these systems can experience structural failures, blockages, and overflows. According to the United States Environmental Protection Agency (USEPA), there are 860 combined sewer systems across the country. Growing environmental and health concerns highlight the need for rehabilitation of these systems [1]. Pipeline renewal and replacement are essential to minimize external flow and address structural issues. The selection of an appropriate rehabilitation method involves considering pipe characteristics and soil and groundwater conditions, as these factors can influence structural integrity, installation, and overall performance of the sewer system. Excavation technologies (ETs) are the most commonly used method for sewer rehabilitation, involving trenching to install or replace pipes. They are expensive due to the removal and backfilling of soil. This leads to increased soil erosion, carbon emissions, and human toxicity. The carbon footprint of ETs is much higher than that of trenchless technologies [2]. These issues can be mitigated by adopting trenchless pipe rehabilitation techniques like cured-in-place pipe (CIPP), pipe bursting, and slip lining [3]. CIPP is a popular and innovative trenchless pipeline rehabilitation method, where a resin-saturated tube is inserted into the damaged pipe, then inflated and cured using hot water, steam, or UV light [4]. This technique reduces ground disruption and minimizes environmental impact [5; 6]. However, research has shown that the CIPP process can release harmful substances, such as styrene, which contribute to aquatic toxicity among other chemical pollutants that persist for over four weeks [7], indicating that CIPP also has environmental downsides. Both the CIPP and ET methods have distinct advantages and limitations. To better understand the type and quantity of emissions produced and select the most suitable method accordingly, it is crucial to evaluate and compare the emissions produced by both methods [8]. The carbon footprint represents the total greenhouse gas emissions resulting from human activities, primarily composed of carbon dioxide (CO\({}_{2}\)) but also including methane (CH\({}_{4}\)), nitrous oxide (N\({}_{2}\)O), black carbon (BC), and various fluorinated gases. While these other gases are present in smaller amounts, they significantly contribute to heat retention in the atmosphere. Calculating the carbon footprint is essential for addressing climate change, as it measures both direct and indirect CO\({}_{2}\) emissions associated with specific activities and throughout the life cycles of products or processes. This includes contributions from individuals, businesses, populations, and governments, necessitating a comprehensive accounting of all emissions [9]. To measure these contributions, an Ecological Impact Assessment (EIA) of CIPPs and ETs was conducted. EIA is a structured approach used to evaluate the environmental effects of a product, service, or process throughout its life cycle. This methodology supports compliance with environmental regulations and promotes sustainable decision-making. For this research, EIA was conducted using USEPA's TRACI 2.1 methodology, through SimaPro software. TRACI 2.1 (Tool for Reduction and Assessment of Chemicals and Other Environmental Impacts) is a framework developed by the USEPA to evaluate the environmental impacts of products, processes, and systems by providing characterization factors for Life Cycle Impact Assessment (LCIA) across multiple impact categories [4; 10]. By normalizing results against average annual impacts of U.S. or Canadian citizens, TRACI 2.1 enables meaningful comparisons across categories, facilitating informed decision-making for sustainability and environmental performance improvements.