We have a company that maintained the chemicals and cleans the pool.

The only reason I could see doing that is if there were some kind of toxic chemical in the wood but if it was just a normal flood with non-toxic water, you don't need to worry about that.  

I know you don't have the toxic chemicals etc.

This includes the heat treatment and in most cases a chemical and powder treatment.

As far as drugs, I would deal with it in a non-curable breach of contract section such as: Non-Curable Breach of Agreement: Any of the following events will be deemed a non-curable breach of this Lease; (a) Police raid upon your Premises; (b) Your arrest for possession/sale/storage of any narcotic/controlled substance/chemical or herbal contraband in or about the Premises; (c) Failure topermit Owner's entry to the Premises following receipt of adequate notice; (d) Failure to cooperate with Owner or any pest controller/fumigator/exterminator following receipt of notice of such services; (e) Defaults by you causing Owner to serve more than two notices to pay or quit, in any twelve (12) month period; (f) A misrepresentation on your Rental Application; (g) Delivery of any security door/gate key to anyone not party to this Lease.

My sister went there once, she said there were mosquitos or horseflies as big as small cars, and some truck drove down the beach a few times a day spraying clouds of chemicals to kill them.I can't get that picture out of my head.

It didn't hold up well and it was highly toxic due to all the formaldehyde and other chemicals used in the curing process.

Many clothes are polyester/synthetic that do not readily support mold growth. 

Trucking, construction of drilling pads, pipe, testing, drilling mud, chemicals, casing, etc. 

I wouldn't risk having major chemicals in a place I had to reside or rent out.