The current configuration of the hydraulic/pneudraulic repair facility at Hill Air Force Base (AFB) is restricted in the types of weapon systems it supports and the amount of work that can be accomplished there. Hill AFB requires a facility that would accommodate increased workload capacity and adapt to changes in workload mix. The project involves constructing a two-story addition (10,000 square feet per floor) on the north side of Building 503. The addition will be outfitted with state-of-the-art equipment and the repair process and layout will be transformed in accordance with lean manufacturing concepts. Following federal regulations, this Environmental Assessment (EA) has been designed and written to do the following: (1) provide the Air Force with sufficient information to make informed reasoned decisions concerning the construction of the Two-Story Addition to Building 503, and (2) inform members of the affected and interested public of this project so that they may express their opinions to the Air Force. The document has been developed and organized to provide the reader with sufficient information to understand the issues to be addressed, the environment in which these issues arise, and the social and environmental consequences of these actions. The chapters are written so that nontechnical readers can understand the potential environmental consequences of each of the alternatives. The findings of this environmental assessment indicate that the Proposed Action to construct a two-story addition on the north side of Building 503 will not have significant adverse effects on the human environment or any of the environmental resources as described in the environmental assessment. Therefore, it is concluded that the issuance of a Finding of No Significant Impact is justified.