## 5 Data Collection for GHG Emissions
### Carbon Footprint  
The carbon footprint (CF) is a measure of the total amount of GHG emissions, usually expressed in terms of CO\({}_{2}\) equivalents, that are produced during the year by an individual, organization, product, or process. These emissions fall into either direct or indirect categories. A direct emission is one that is under the control of an individual or entity. Examples include emissions from personal vehicle use or residential heating through the use of natural gas. Indirect emissions, in turn, are derived from activities that may be influenced by the individual--such as electricity consumption--where the usage, although controlled, would depend on the method of energy generation applied by the provider [4, 44].  
The framework for CF estimation in PI projects involves selecting GHGs, setting boundaries, and collecting emission data [31, 39]. GHG selection depends on the construction activity and guidelines. For example, ETs primarily emit CO\({}_{2}\), while some studies include all six Kyoto gases for a more comprehensive analysis [31, 45, 46]. A study in Indianapolis included CO\({}_{2}\) and CH\({}_{4}\) emissions in CF calculations [31, 47]. Boundary setting identifies the scope of CF estimation, which may include direct emissions and emissions from purchased energy (Tier I and Tier II) and other indirect emissions such as transportation and disposal (Tier III). Although Tier III is broader, it is generally excluded because of its complexity. In most studies, Tier I and Tier II are considered for practical estimation, while Tier III is reserved for advanced evaluations only [31, 39].  
CF can be categorized into basic CF, covering direct emissions and purchased energy, and full CF, which includes all direct and indirect emissions. Expanding CF estimation may provide deeper insights into sustainability efforts, though advancements in emissions tracking are necessary for accurate implementation [31; 39; 48]. The CF or carbon profile of a commodity or service comprises the summation of CO\({}_{2}\) and other GHG emissions, such as methane and nitrous oxide, over its entire life cycle. This includes stages like production, use, and disposal, measured in kilograms of CO\({}_{2}\) equivalents [4; 49]. In essence, a CF analysis captures more of the general environmental impact of activities or products.  
Comparative carbon emissions studies from various pipeline rehabilitation methods elevate trendless technologies as environmentally superior to ET. For example, one researched the CF for asbestos cement water main rehabilitation using CIPP and pipe bursting methods. The range of the emissions per 100 m of pipe calculated using NASTT, E-Calc, and NASTT BC was between 2.66 and 3.11 tons, showing the relatively low emissions of these trendless methods [4]. Similarly, the carbon footprint comparison of SP and PCCP on large-diameter water pipelines showed that SP had a 64% higher carbon footprint due to its energy-intensive manufacturing process, while PCCP produced greater emissions during transportation due to its weight [50]. Another study compared the carbon emissions of ET with trenchless tunnelling methods in rural settings. It quantified emissions from construction equipment and soil hauling along a 25-mile route in Texas. The results showed that trenchless methods generated significantly fewer emissions--887 tons of CO\({}_{2}\) compared to 5379 tons from ET--underscoring the environmental advantages of trenchless technologies in reducing carbon footprints [29]. These findings emphasize the importance of adopting sustainable methods to minimize the ecological impacts of pipeline infrastructure projects.