Triple bottom line and life-cycle cost assessments of sustainable resource management in Boston, MA

Abstract

Urban planners today are facing a multitude of problems with the prevailing paradigm of development. Apart from being hydrologically unbalanced, and operating on a ""fast-conveyance"" premise, large cities suffer from high levels of greenhouse gas emissions and inefficient management of resources. Realizing the need for a different paradigm of development, this study examines the feasibility of a new urban management approaches based on the concepts of ""Total Hydrologic Balance"" and ""Sustainability"". Water conservation and reuse, energy conservation, vegetated roofs, decentralized water management in semi-autonomous urban clusters, and integrated resource management were investigated in multiple configurations and assessed for benefits on a ""Triple Bottom Line"" basis. Green roofs were studied for water retention, runoff reduction and building insulation and were found to be effective in reducing runoff from the one-year storm. However, for larger design storms there's a need to couple green roofs with other tools that reduce directly connected impervious areas. For water reclamation, facilities using biological nutrient removal and yielding a high quality reusable effluent were proposed inside the urban ecoblocks with their cost estimated from construction curves. Water and energy conservation were thoroughly dealt with and broken down to direct and indirect ways to conserve, while proposing low flow fixtures and energy efficient appliances with no or minimal additional cost. Anaerobic digestion of sludge and heat extraction from wastewater were also considered as renewable sources of energy. A ""Life-Cycle Cost Analysis"" was also used in order to determine the economic viability and applicability of each proposed alternative. Such analysis revealed that sustainable management is feasible for different scales of cluster and various land use compositions. Alternatives centered on water management or green roofs only were not feasible on their own while comprehensive alternatives using a holistic approach and plans incorporating energy conservation were the most beneficial. Land use and population density were analyzed for their effects on the different scenarios. The results suggested that the payback period was not much affected by those parameters while the net present worth showed it highest values at 55-70% developed land cover and a population density in the range of 6000-9000 persons/km2.