Took me forever to finally solve the problem. The issue was both that I was using a Union All rather than a join and that I had duplicate records in my dimension table resulting in duplication of the output. I cleaned up the data source and used the following code:

SELECT

,b.[PBCat]

,a.[Station]

,a.[Facility]

,a.[CC]

,a.[Office]

,a.[BOC]

,a.[BOCName]

,left(a.[Appro],4) as [Appro]

,a.[FY]

,a.[Obs]

,a.[FTE]

,a.[Month]

FROM [BudgetFormulation].[dbo].[ObjectClass] a

Left Join [BudgetFormulation].[dbo].[DIMObject] b

On a.[BOC]=b.[BOC4]