The successful widespread commercialization of aquifer thermal energy storage (ATES) in the United States will depend on the effectiveness with which the experiences gained from early full-scale systems are used as guides in the design, installation and operation of future projects. One such early system from which both anecdotal and quantitative information is available is the Mid-Island Postal Facility in Melville, New York. At this facility, built in the mid-1980s, an ATES system has been integrated with the building's central heating and cooling plant. “Cold” wells are charged with water that is cooled during the winter by heat pump and closed circuit cooler operation. Water from these cold wells is then used to meet the facility's cooling load during the summer, before being pumped back into the ground at “Warm” wells. Dehumidification during summer operation is accomplished by a liquid desiccant system that uses propane boilers to provide a heat source for desiccant regeneration. This system will also add water to the air during periods of low humidity. This paper provides an overview of the project, and describes the analysis being performed to assess energy and economic merits of this innovative system.