Board Thread:Questions and Answers/@comment-24020883-20131025195606/@comment-13413401-20131025225758

Since you placed the Quarry over there, the blue lines appeared. This means that these chunks will be loaded, even if you go very far away from them. A similar effect can be created by placing a chunk loader.

To disable showing the blue lines, press F6 or F7 (i forget which one).