That can be a real hassle. I’ve been getting that for about a month on my iPhone 5s. The only solution I have found is to disbale JavaScript if you want to view the page (Drudge), or if it happens with a specific article from a site (I see this a lot).
On your iPad got to Setting>Safari>Advanced>JavaScript. Toggle it off to read or access the site without the popup.
Sometimes when you get the popup on one page it will happen several times for the same ad on different websites ad nauseum.
To get rid of the annoyance, got to Settings>Safari>Clear History and Website Data.
Of course this will erase your browser history and log you out of all sites, but it gets rid of the problem.
This is less of a popup and more of a script within the webpage that hijacks the page. Popup blocker will not kill this off. If you are on a Mac, you can set up a white list that redirects these kinds of sites into a black hole in your laptop so you never see them, but not on mobile or tablet devices that are locked down.
Remember to turn JavaScript back on once you’ve read what you need to or your browsing experience will be rather limited.
Hope this helps, and good luck.
DISABLE JAVASCRIPT
Javascript is enabled in each browser settings menu. Safari and most browsers have it enabled as default. Brave is default off.