Hey guys,My name is Ali, and I am a Chemical/Systems Engineer. 

A licensed exterminator charges at least $500 per unit for treating a 3 bedroom unit (for one treatment and follow up 3 weeks later), or more (some charge $750 per 3 bedroom unit with 1 initial and 2 follow-up chemical treatments). 

Now residual amounts of chemicals will very very difficult to conclude the source...if you do test be ready to put some money forth. 

Did they dump chemicals?

try some Muriatic acid ( wear goggles, rubber chemical gloves and a mask) you can find this at local hardware store or mason supply. this is used to clean brick. if you are inside, open windows and ventilate the room, this is some strong smelling stuff. just follow the directions on the container.

I'm a Chemical Engineer by study and have recently transitioned to a Sourcing Analyst role over the past year and really enjoy what I do now.

I am a chemical plant inspection and play with real-estate on the side. 

I am a 2014 graduate of Ohio State with a degree in Chemical Engineering. 

We are only about half developed and situated to take advantage of Houston's downtown and Med Center, UTMB in Galveston, and the Houston Ship Channel and Bayport chemical compounds.

It has something to do with the highly chemical conditions that stay in the dry walls.