Answer: Although evergreen, each fall these plants do show a certain amount of browning in the interior and the oldest foliage drops. This may well be what you are seeing, especially since they seem to have been healthy over the summer. For reassurance, and also just to make sure it is not a disease type problem causing the browning, you might want to take a few photos and consult with your county extension and/or professionally trained nursery staff to see what they think. Good luck with your arborvitae.
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