Gas prices tumbled below $2 a gallon at several gas stations around the Tri-Cities.The lowest price per gallon at the pump was $1.77 at Mid-Columbia Grocery, 6409 Court St., in Pasco, according to GasBuddy.com on April 28. Gas at the Kennewick Costco was $1.89 a gallon.Benton County’s average is $2.09...