I don't work at DTW
, I work at a smaller spoke city in State College, PA. We only get prop aircraft like Saab 340's, Dash-8's, and Jetstream-41's.
Our de-icing procedures are as follows.
1) Load the aircraft (passengers & baggage). We do not have jetways, which is one of the reasons we do not de-ice on the ramp as passengers would have to walk through the mess.
2) Engines are started, with the aide of a GPU. The aircraft taxis away from the terminal to the de-icing pad which is about 100 yards away. Engines are then shut-down.
3) The aircraft is de-iced on the pad.
4) After de-icing is complete, the GPU, which was towed over by a tug, is reconnected to the aircraft.
4) Engines are restarted and and the aircraft is now set to depart.
The deicing pad has a special drainage system that collects the deicing fluid. The glycol is then removed and recycled. This prevents it from running off into local streams. The Dept. of Environmental Protection has been on the airport's case a few times because they found traces of deicing fluid in local streams. We have unique geology in the area and sinkholes on the airport property. The problem was that runoff that contained some deicing fluid had gotten into the sinkholes which go directly into the groundwater and streams. The sinkholes have been filled with concrete to prevent pollution from the airport getting into them.
Part of the reason that propellor aircraft are deiced with the engines shut down it to deice the prop and to be able to get all the wing surfaces. A spinning propellor would make it more difficult to hit the leading edges and would also deflect a spray fluid all over the place. It just sounds like too risky a procedure. I'm never a big fan of being anywhere close to a spinning propellor. Disconnecting the GPU after engine-start is enough for me.