The operation, maintenance, and construction of underground structures require a huge amount of energy and generate a significant amount of greenhouse gases (GHG) (Hendrickson 2000). The energy and GHG are generated from the process of extracting raw materials, producing and manufacturing new materials, transporting materials to sites, and installing materials (Junnila et al. 2006). Energy conservation and control of GHG are critical to ensure energy security for future generations and to alleviate the impact of climate change. This paper presents a new approach of Enterprise Carbon Accounting for underground infrastructure. The method is based on categorization depending on the size of the organization and its assets. Categorization of similar buildings and assets are averaged and analyzed as a unit. Outliers and averages of each type are then examined for causes, correlations, and future solutions. The proposed method will establish a carbon emission and energy use baseline for the large scale agency that owns and operates underground infrastructure.