You can enter a zip code or location and get an idea of the amount of waste being produced in your community. Your question is not easy to answer because the National Park Service does not have a national policy on this. It is up to the individual parks to weigh the advantages and disadvantages on road clearing and deicing. If the park is closed in the winter then obviously no road clearing takes place. Other parks such as Yellowstone are open but they don't clear the roads.
Some places use only sand or ash and no chemicals at all.
If you want to know what a specific park's policy is you will have to contact the park directly. The Fish and Wildlife Service has 21 units with this designation and the Forest Service has 88. You will have to contact one of these agencies if you wish to report a violation. The National Park Service does have some information that has been translated to other languages. The results will contain listings of all documents that have been translated into the referenced language that are currently posted on the NPS ParkNet web site.