Missable achievement.
This is cumulative through playthroughs, so if you miss it on the first one, you can go back and add to your total just by returning to the beach.
The first three fireworks (essentially roman candles) are in the beach area at the beginning of the game, near the fire.
The fourth and fifth are in the upper sewers (the second part of the game) in the area of the wishing well. You can find it marked on the map you'll come across shortly after you enter the sewer. Basically, as you go into the sewer system and follow it around, when you get to the first actually fork where you can go in multiple directions, turn left (toward the overturned shopping cart) and follow the path until you see a hole in the wall followed by a chamber with a bucket hanging through a hole in the ceiling (the bottom of the well). The last two fireworks are on the platform near the bucket.