So long as the landfill hasn't been dumped in on top of 20 ft. of bog, has had a good time to settle, and you're using a raft, you should be ok. Whether or not the stream would be affected would surely be determined by the material in the landfill.
Have you an engineer or architect working on your behalf while the build is ongoing, if not it might be something worth considering.
I could well be wrong but I wouldn't have thought that a developer subcontracting the work to others would not be able to get homebond, but the cost might particularly if they are developing on a small scale.