Experts and BHG readers answer.
evergreen shrubs - dying
Arborvitae is indeed not very tolerant of wet soils. If the damage is occurring over winter, it may be because the soil drains poorly and the roots suffocate. If the drainage on the site can't be improved, you might try installing a berm and growing the trees at the top of the berm to raise their roots out of the wettest soil. Or you could grow another type of plant that better tolerates wet soils. Unfortunately few evergreens tolerate wet soil conditions.