Duplicate content is harmful.

You have a very good site. And you have good keyword combination and getting good traffic from your keywords though if you use the same content for more than one page than it is very harmful for your site, Duplicate contains occurs many problems. It's something you want to avoid as much as possible. In this, people have reported their pages disappearing completely from the search results because of duplicate content. Drupal is a very friendly with SEO. It contains Modules and Files are available for such a problem.
Example
robots .txt File-
In this if we have two pages with the same content than by this file we can say search engine to ignore that page. For that we have to just write
Disallow: /node/
after this any content that's only accessible from a /node/ URL will no longer get indexed by search engines.