Min ht for fuel jet is 4000feetAGL
Don't know what country you're from but in Oz min height is 6000ft AGL. ATC have to keep other traffic clear of 1000ft above, 2000ft below and 1/2 mile laterally around the dump zone. Also no racetrack patterns for obvious reasons so if they were dumping for 45 mins, a big no go zone would have been used.