This dissertation considers the epistemic problem of adapting expert knowledge to an established political goal. Its particular focus is the failure of scientific and technical experts in different fields to effectively communicate across their disciplinary boundaries in order to provide coherent advice. The information needed to meet the goals of environmental policy is rarely limited to the domain of any individual scientific discipline or technical field. Each discipline has its own technical language, experimental procedures, problem solving strategies, exemplars, scale of application, factors that are included in models, factors which are considered exogenous to models, and background assumptions -- all elements of what might be termed the 'cognitive map' of a discipline. Because experts produce knowledge within the context of their field's cognitive map, and these cognitive maps vary greatly between disciplines, there are significant epistemological difficulties involved in the provision of interdisciplinary expertise for policy purposes. Using the Clean Water Act as a case study, I will argue that these epistemic divisions between different disciplines are an important part of the reason why a group of technical advisors who are honest, competent, attempt to be objective, and have similar goals for the policy can still manage to fail to communicate, or even to have productive disagreements about the technical advice they provide to lawmakers. I will also explore the extent to which a philosophy of epistemic mediation might be possible; making some suggestions of how philosophers of science might help not only to clarify but also to bridge some of the divides between disciplinary fields of expertise.