Gehan Homes Environmental Hazard Spring Texas

I live behind a newly built Gehan Home in Benders Landing Estates in Spring, TX.  In January 2015 I witnessed the crew pumping what appeared to be a truck load of a white powdery substance into the ground prior to pouring the foundation.  It was extremely wet and muddy after days of rain.  It was also very windy and pillowy clouds of the substance drifted to my yard for days.  My patio and entire back yard were covered in the substance.  Days later both my husband and I became ill with upper respiratory illnesses.  Within weeks my trees started to look sick.  Since then, we have had to remove 10 very large trees which succcumbed to blight and disease.  I believe they became weakened by the substance.  Don't home builders have a responsibility to to use potentially toxic materials in a way that does not affect waterways, trees and nearby residents?