Union Sanitary District Share: Government Union Sanitary District Visit Website 5072 Benson Road Union City, CA 94587 (510) 477-7503 (510) 477-7501 (fax) About Map About Union Sanitary District operates a 33 million gallon per day wastewater treatment facility in Union City and provides collection, treatment and disposal services to a total population of over 347,000 What's Nearby? Distance: 5 10 15 20 25 50 mi.