## 4 Results
### Comparison of MICP Treatment Approaches
The LCSA results were also examined to identify environmental and economic \"hotspots\" (i.e., life cycle stage(s), process(es), and flow(s) with large contributions to one or several impact categories) [54]. Figure 6 shows that for Columns 1 and 2, the stimulation and cementation phases of MICP treatment are the primary contributors to impacts for all indicators, except eutrophication potential. Across these impact categories (and excluding eutrophication), the stimulation phase represents approximately 41% of total impacts for Column 1 and 48% of total impacts for Column 2. Similarly, the cementation phase is responsible for about 52% and 44% of total impacts for Column 1 and 2, respectively. For Column 3, most impacts stem from the cementation phase, which accounts for approximately 88% of total impacts. This is due to the large number of cementation injections required for the augmented column to meet the defined performance criterion (\(\Delta\)V\({}_{\text{std}}\) = 150 m/s). The bacterial cultivation and augmentation phases together represent between 0.1% and 15% of the total impacts. For all columns, the production of materials and energy is responsible for about 80% and 15% of total global warming potential, respectively. The remaining 5% of the global warming potential results from process emissions related to the generation of in situ nitrogen byproducts. Materials production accounts for over 99% of ecotoxicity, human toxicity, and ozone depletion potentials and over 73% for all other indicators, excluding eutrophication potential and life cycle cost. Eutrophication impacts for all three columns can be primarily attributed to process emissions, which represent approximately 79% to 82% of the total impact prior to rinsing and 37% to 61% after rinsing, with the balance largely stemming from materials production. Less than 1% of the eutrophication potential is caused by electricity consumption during pumping. Regarding economic impacts, materials account for 99.9% of the cost, while electricity use represents only 0.1%. The most impactful (and costly) materials are urea, calcium chloride, ammonium chloride, and sodium acetate, in descending order of impact. Urea production accounts for approximately 34% of total global warming potential and when considered along with MICP, process emissions is responsible for nearly 40% of the total global warming potential. Calcium chloride production represents about 20% of the total global warming potential due to the large quantities used. Though smaller quantities of ammonium chloride and ammonium sulfate are needed for MICP, the production of these chemicals is resource-intensive and environmentally impactful, requiring 38 MJ and 26 MJ of primary energy and emitting 2.4 kg and 1.9 kg CO\({}_{2}\) eq. per kilogram. Together, these materials comprise 85% to 91% of the total cost. The cost of urea alone accounts for 38% to 56% of the total cost; however, future assessments can use commercially sourced industrial grade chemicals, likely enabling further refinement of these estimates. While these results do not consider the impacts of effluent management, the volume of generated effluent (and thus impact/cost of effluent management) would likely be greatest for the augmented column, which required more cementation treatments to meet the defined performance criterion.