The individual concerned has been sent a PM, as is normal practise, outlining what changes had to be made with the permission of the Admin team and why. This incident resulted in players being barely able to move at all within sight of the relevant chunk. This severely hampered the playing of others. In such a case, the Admin team will take whatever steps are required to restore the world and/or server to a state where people can participate. In this case, this meant modifying someone's constructions. In others, it may mean returning to a backup from the previous day or disabling a mod. This may mean that some things are lost by the players' affected. Where judged reasonable by the Admin team, players are compensated.
The OP was very general because we believe many things may have contributed to the lag and believe it best to advise all players what not to do so that we won't have a repeat of tonight. The players who assisted us did not enjoy having to spend a couple of hours creeping forward so as to solve the problem. There was no such thing as an easy fix tonight for anyone.
So yes, there was a quarry full of water, but there were also problems with various machinery, as stipulated in the OP. We understand that players are setting up in the FTB city as their base of operations, but they must remember that others play nearby. We ask players to please consider this when constructing on your plot. You may wish to have a ongoing, self-sufficient plot of land, but that may not be reasonable in such a location or within a multi-player environment.