There is some information on the EPA website about the Mansfield Trail Dump.
Without knowing where you are looking I can't say with any certainty that you are in a contaminated area. Have you spoken to your Realtor, Attorney, Title Company, etc? Have you read the seller's discosure to see if there is anything there?
If you are not working with a Realtor I would be happy to have a discussion on the subject, but without knowing where the subject property is I can't answer the question fully.