The United States Air Force (USAF) operates the Aerospace Data Facility (ADF) at Buckley Air National Guard Base (ANGB), located in Aurora, Colorado. USAF proposes to modify the ADF to provide additional secure, permanent office and computer operations space. Modification is needed to provide response capability to USAF directives requiring the expansion of ADF's mission and to provide permanent work space for staff currently located in temporary trailers. ADF is a space tracking and data processing center completely contained within the perimeter fence of Buckley ANGB and located approximately 12 miles east of Denver, Colorado. Main features of the ADF include an operations building (Building 401), radomes housing receiving antennae, a chiller plant, a power plant housing emergency power diesel generators, temporary office trailers, warehouses and other storage facilities, and a recreation complex. USAF is proposing to add approximately 150,000 square feet to Building 401. This expansion would provide permanent office space for approximately 500 employees, currently located in trailers adjacent to Building 401, and additional computer operations space. Utility modifications proposed to support the addition include adding two 2,500- kilowatt emergency generators to the existing power plant; two 1,000-ton-capacity chillers to the existing chiller plant; tree cooling tower cells adjacent to existing cooling towers; and miscellaneous additions and modifications to integrate additions with existing facilities. Construction, scheduled to begin in late spring 1993, would last approximately 18 months. Cost for the Proposed Action has been estimated at $40,000,000.