This Environmental Assessment (EA) documents an analysis conducted by the Bureau of Reclamation to evaluate the effects of a proposal to (1) use manual, mechanical, and herbicide methods to control undesirable terrestrial and aquatic weeds; (2) use toxicants, shooting, and non-lethal methods to control problem/nuisance burrowing mammals; and (3) manual and commercially available pesticides and baits to control rodents and spiders in facilities and on lands managed by Reclamation on the Alamosa Field Division, Colorado. The purpose of the proposed action is to protect structures and facilities, provide for public safety, and enhance the health and safety of Reclamation employees, contractors, and cooperators. Proposed pest management objectives, strategies, methods, mitigations and best management practices, and an herbicide safety and spill plan, standing operating procedures for hantavirus, and control requirements for problem/nuisance burrowing mammals are documented in an Integrated Pest Management Plan, which is available for public review.