Re: Gas Works
 
Orr, David
1977    Philadelphia as Industrial Archaeological Artifact: a Case Study.
Historical      Archaeology 11:3-14
 
There are general, above-ground treatments of gas and light plants in
 
Stott, Peter
1984    Industrial Archaeology of Boston Proper.  MIT Press, Cambridge, MA
 
Oliver Evans Chapter of the Society for Industrial Archeology
1990    Workshop of the World: A Selective Guide to the Industrial Archeology of
Philadelphia.  The Oliver Evans Press, Wallingford, PA.
 
You should also check (if available) the British journal "Industrial
Archaeology," and the US journal "IA: the Journal of the Society for Industrial
Archaeology."
 
I hope that you have taken into account the fact that gas production often
produced toxic byproducts that remain in the soil.