I told you to blow up gas canisters, and this big rack of them will open the wall to that stocked room near the entrance.
After the chaos of the escaped "loppers" is done, you'll have one more still locked up. His cell's back wall is breakable and leads to a secret stash. Open the cell, kill the baddie and break the wall.
Secret 3 and 4 here are connected and you need to do #3 to get to #4. When you reach the room with the well (water) in the center of the room, break the grate behind the pipes unde water. Swim through and up into some maintainance areas following ladders until you get to a valve. Turn the valve.
After #3 is done, there's water in some areas now. Drop down as shown and come up in the next room through a small opening for the secret goods.
