One has to wonder why it is that the county has determined that it needs "to review potential health hazards from coal trains that may run through the county en route to new Northwest export terminals." [Coal clash: Multnomah County to examine health hazards from coal dust and diesel].
It will be interesting just what the review will entail. Look - both the coal and disesel issues have been studied and studied - for years. A quick Google or Bing check will provide the researcher with a wealth of material. It would seem - a little to my surprise - that there is little opposition to harmful effects of either.
See this from BSNF: Coal Dust Frequently Asked Questions. It is a self interest assessment, but one can easily surmise that the real issue is not the elimination of either coal or the train carrying the coal - it will be in making the transportation of coal as safe and harmless as possible.
And see this from EPA: EPA Cuts Diesel Locomotive and Vessel Pollution. The point being that diesel locomotive pollution is not a new subject nor has it been ignored by the government.
If the county wants to join in the opposition - just say so. There seems little need for a separate review or the costs needed for it.