Larubia my heart goes out to the family of your grandchild and you. It rends my heart when children suffer so.
There are several Superfund sites in Delaware that are affecting the ground water. Sussex county is just one area. Each site has it's own issue. A couple contaminants, PFOA and PFOS are a discovery of the not too distant past that are suspect for various maladies.
Sadly those chemicals, and I suspect others, were not tested for by the Safe Water Drinking Act of 1974.
It's hard without certainty to point a finger at the exact cause for many illnesses but water is a common vector.
If those billions of dollars were spread (without sticky fingers), to all municipalities in need, it won't go very far.
Ironically and perhaps you already know, the Dupont Company paid penalties for PFOA and PFOS pollution.