Combine the 3 cups sugar and 5 cups of the water in a saucepan. Bring to a boil and cook just until the sugar is dissolved. Cool completely.
In a large punch bowl, combine the cooled simple syrup, frozen grape juice, ginger ale, citric acid and remaining 4 1/2 cups water. Stir to combine, then add the crushed ice. Serve immediately.
Notes
from a family cookbook*citric acid can be found in most pharmacies or health food stores or online at Amazon.