I believe he was asking whether the chemicals such as clorine from the pool water would leach into the pond. (and not about using the pool as a pond). The answer is no, unless you are pumping the pool water into your backyard.
It all depend on the pool plumbing. When changing water in our pool for maintenance, the water is simply pump into the city drainage. And thus absolutely no water (cl2) get mixed in with the surrounding soil.
When building a pond, you can either use pond liner or cement the floor which would also prevent any unwanted chemicals leaching into your pond water.
Rohn