1.) What caused the toxic waste to begin being pushed to the surface?
The Blizzard of 1977 caused the "bathtub effect" on the canal. With all the winter snow, rain, etc. caused an early spring and an early thaw, and all the water was forced underneath the canal from this clay pit to the top and it started oozing out of the top of the canal.
2.) What are some of the health hazards associated with the chemicals dumped there?
There were over 400 chemicals found there. Including lead, arsenic, lindane, a variety of other pesticides, benzene, and many more. Many of these cause cancer, some of them cause liver problems, liver disease, many of them cause central nervous system problems and some of them cause birth defects.
3.) Besides humans how are other parts of the ecosystem affected by this?
The chemicals flowed to a nearby set of creeks. The chemicals had made there way underground to the creeks. The EPA wanted to dredge the creek.