Here is the description that the Southwest Area Type 1 Incident Management Team posted with the video on May 30, which is titled Tanker 40-Bae-146 Retardant Drop Whitewater-Baldy Fire:
Air Tanker puts down a line of fire retardant on Whitewater-Baldy Fire off of the 141 road. This drop was to help pretreat the north side of the road so fire crews could do their burn out on the south side of the road.
It’s not a great shot of the air tanker, but if you look carefully you can see two engines hanging below the right wing, which indicates that it IS the BAe-146 jet-powered Tanker 40.
I noticed that the lead plane was louder than the air tanker, which is very unusual — much less noisy than tankers with huge radial piston engines. BAe-146s are known for their relatively quiet operation, which enables the airliner to fly into some noise-restricted airports when others can’t.
Another thing I noticed was that the pilots were extremely accurate with their drop, placing the retardant right on the edge of the road, probably exactly where the firefighters wanted it.
Here is a bonus video from the Whitewater-Baldy fire, also posted by the Southwest Area Type 1 Incident Management Team. It was shot in the same general area, on the northeast side of the fire along Forest Road 141, May 28, 2012.