Public and private utilities selecting a wastewater treatment system face a difficult task in comparing the costs of treatment alternatives. Decisions about the type of treatment process to be employed are typically made very early in a project when the least amount of detailed information is available about a proposed design. Use of conceptual-level cost estimates has been the usual practice at the facility planning stage, and the accuracy of individual alternative cost estimates is typically given as + 50 to – 30 percent. This is an extremely low level of accuracy considering decisions must be made committing the utility to long term capital and O & M costs which can last for decades. These early project decisions are highly significant because the opportunity for saving costs declines as the project becomes committed to a process concept in predesign and design. Improvements in the methods for cost estimating at the facilities planning stage could yield better data for decisions and thus generous cost savings.