In Genesis 8:8, this signifies what people in the church have in them, the word ground being used because this is a person's first stage in becoming a church.Later, the face of the ground being dried up in Genesis 8:13 signifies regeneration when falsities no longer appeared.

(Reference: Arcana Coelestia 898, Genesis 13)

In Exodus 15:8, this signifies falsities gathered together. Waters normally signify truths, but in this case, where they were blocking the escape of the Children of Israel from slavery and signify the opposite: falsities.

(Reference: Arcana Coelestia 8286)