What state is/was this? It sounds highly illegal and that person should be prosecuted. Make it have an impact by reporting them.
NY for example:
"Thus, for example, even a spill of a gallon of oil into a ditch is covered."
https://ag.ny.gov/environmental/oil-spill/oil-spills-homes-a...
California:
"California Penal Code 374.3 makes illegal dumping on public and private property punishable by a fine up to $10,000. Also, pursuant to Section 117555 of the California health and Safety Code, a person who dumps illegally is punishable by up to six months on jail."
https://pw.lacounty.gov/epd/illdump/penalty.cfm
Calcycle page on illegal dumping: