passenger footwell front and rear soaked

[bionic]

pulled up the carpet the other day as i was going to be running a few wires and sound deadening but i came across a soaked underlay i have asked a few people on the group page on facebook but i haven't really got any help that can put me towards the correct path

i have removed the trim by the wiper blades to find the drain plug is free as seen in pic below



as for checking under the battery im struggling to think what could be under there as its in its own tray thats above the gearbox...

can anyone point me in the right direction please as its putting my build on hold as i need to remove all the existing deadening to better quality stuff and also add more deadening to the car

its a 2007 b6 passat

thanks for your time