If the well is dry you are drilling deeper, if the well is not making water like it use to it could just be screen is clogged with minerals like iron or calcium and would need a chemical treatment to open the screen along.  

I'm based in Beaumont & have a similar background in engineering and work in the chemical industry as well.

Sometimes just draining the pool is enough to solve some chemical issues.

My initial thought is to clean with a mold killing chemical and then watch it.

All of the experts tell me if a house was treated with chemicals more than say 20-30 years ago it is unlikely you will ever have termites again because of the chemical that was used.I guess they are talking about Chlordane. 

Concern susceptible to harsh chemical cleaners if used by tenants. 

I am talking about a very beefy manual with extreme details on how to handle a certain situation.Here is an example of what I mean by Standard Operating Procedure, this example is one I wrote for a Maintenance Request:1.0  Maintenance Requests1.1  Clogged Toilet1.1.1  When the resident informs the Maintenance Manager (MM) of a clogged toilet, perform the following:1.1.2  Inform resident to first utilize the plunger and remind them to not ever use drain-o or any chemical product.

Around me it goes for $4 for a one pound box or $10 for a 4.5 pound box.There is also a "TSP Substitute" which is a different chemical that doesn't work as well. 

I have a friend who runs a company doing this so I borrowed his equipment for the cost of filters and chemicals (about $1000).  

I also went with a synthetic roofing underlayment that is supposed to be stronger than the traditional 15# felt.