Management practices have a direct impact on the cost of capital used for financing the operations and maintenance of existing infrastructure on a concurrent basis with planning and constructing new projects. This paper identifies best management practices that can improve credit rating, which in-turn theoretically lowers the interest paid on debt. As a result, these best management practices lower the weighted average cost of capital used to maintain existing assets on a concurrent basis with the construction of new infrastructure. As a practical example, this paper identifies the best management practices from the perspective of municipal credit rating agencies in the United States. The current research then constructs a deterministic integer programming model based on these best management practices. The deterministic model is part of multi-method model that will be mathematically embedded into a system dynamics model that can then be used as a facilities management plan. The facilities management plan aims at lowering the weighted average cost of capital for maintaining existing assets while planning and constructing new infrastructure. While the multi-method model is based on municipal credit rating in the U.S., the research goal is to nevertheless show how a system dynamics model is used to implement best management practices that are generally accepted as economically sustainable worldwide.