Restrict human and pet traffic to the contaminated area. Place stakes around the circumference of the contaminated ground and use bright tape or string to keep people out.
Call your local university extension office or EPA official. Their contact information can be found online or through your municipalities local government office.
Show the contaminated area to the extension agent or EPA official. Let them have access to the results of any soil tests that have been done to the contaminated area. Follow any additional instructions they give you to minimize further contamination.