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We are trying to deindex a large quantity of pages on our site and want to know what the best practice for doing that is. For reference, the reason we are looking for methods that could help us speed it up is we have about 500,000 URLs that we want deindexed because of mis-formatted HTML code and google indexed them much faster than it is taking to unindex them unfortunately. We don't want to risk clogging up our limited crawl log/budget by submitting a sitemap of URLs that have "noindex" on them as a hack for deindexing. Although theoretically that should work, we are looking for white hat methods that are faster than "being patient and waiting it out", since that would likely take months if not years with Google's current crawl rate of our site.

We own a large wiki site which allows people to make articles about their business and other things that Wikipedia would prohibit. To make our site more rich and expand the pages people can link to on their pages, we scraped between 1-2 million pages from the english wikipedia, pages such as “Los Angeles, CA” and “United States” etc. We’ve been getting a steady supply of organic backlinks from users who create their own pages and cite their wikis on their website, in news etc. However, starting 2 months ago our organic traffic has started slowly decaying as if we have received some kind of algorithmic penalty. What could it be? Could it be dupe content from the wikipedia pages we imported and indexed? Could it be some kind of algo from the Penguin update? We are just very confused why our organic search traffic would begin to drop at all since every day we have organic users making quality pages, some of whom organically backlink their articles on their own website and these obviously add up over time.