Material Facts - where are they?

We all know we have to know the product we sell.  We also have to love the product we sell in order to be successful.  There is a neighborhood down the road that is behind a school.  Is it my favorite neighborhood? no.  Are the values doing well? yes.  Is it a nice location? yes  On up the road from the neighborhood is a landfill.  Not right next door but on up the road three quarters of a mile or so.  The landfill has been there since 1993 and is visable from the road no matter which end of the road you come in on. My question is how far out is that a material fact?  

There are two nice neighborhoods directly across the street from the landfill.  They have not suffered in property values at all!  In fact both neighborhoods have new construction phases going on in them and they are well established neighborhoods.  There is also a new neighborhood being built in front of the landfill (directly under the high tension lines) and is flourishing!

I ask this question because I had a client who got upset that she is "right next to the dump."  Long story, short.  She is finding another home but I am not sure where this falls with regards to liability.  Now I am curious.  My client had five properties (including two fully treed buffer zones) between her home and the property owned by the landfill company.  That property owned by the landfill company was attached to the property being currently used for the landfill but was newly acquired acreage.  The new acreage wasn't expected to be worked into the landfill for another five to ten years.  As well, much of the newly acquired land was intended as buffer for the active portion of the landfill.  It was unusable due to water flowing through it.  Before she signed any contracts we quizzed the on site agent at length regarding the lands around the neighborhood.  He insisted it was all privately owned. And didn't know of any plans for any of it and couldn't make any promises.  

I have since heard from another agent that she had a client get out of a new construction contract over two miles away from the landfill.  They were even made aware of the location of the landfill beforehand and later changed their minds anyway!

I don't want to misrepresent any of my clients but how far out do we go? We also have a speedway in Concord.  Lowes Motor Speedway, you may have heard of it.  Now, a motor speedway is loud!!  I live in Harrisburg around six miles away and I hear the track twice a year during the races.  I disclose the track to all clients by driving by and having discussions about race weeks, noise, and traffic.

When i checked with the NC licensing board for some more definitive answers about material facts I couldn't get much.  If something isn't an environmental hazard and it isn't adverse to the property (failing property values, etc.) then there isn't a material fact. I have always disclosed the landfill to the neighborhoods across the street from it but do I really need to go out a three mile radius?  Five mile radius?  Any ideas?