DOTGOV is a Web crawl of the .gov US government websites, and was used by the TREC Web track 2002-2004. It can be obtained from the University of Glasgow. The topics and qrels are available from the TREC website:
Indexing the DOTGOV collection is easy with Terrier. No terrier.properties are required to be altered from the default created by trec_setup. If you wish URLs in your index, then set the following properties:
trec.collection.class=TRECWebCollection indexer.meta.forward.keys=docno,url indexer.meta.forward.keylens=26,256
See the Terrier documentation on Web-based Terrier to see how to build a Web search engine for this collection.