It means you have no way to install a septic system. Septic systems are fairly common in Chapel Hill and require a leach bed. When waste leaves the home it goes through several chambers to be broken down and then the liquid eventually "leaches out" to the ground. If the lot doesn't perk, the waste liquid will not trickle down into the soil to be further filtered. Unless you can tie into a public sewer you will not be able to build on the lot.
There are some alternatives such as "irrigation" type that spray rather than leach. However, it is more difficult to get a permit and could be risky. Also, when you purchase a home with a septic system, you should request the septic map from the county and confirm that there is a septic repair area in case the leach bed fails in the future.
Triangle & Coast Realty
it depends on the size of the lot, if it is eight acres or bigger, you have some options. But a smaller lot creates problems that you probably do not want to deal with - if you have other choices.
Let me know if I can be of assistance if you are heading up our way from Florida.
All the best,
Reg Morgan, Broker, GRI, CRP
Coldwell Banker HPW
Check out my blog at http://www.ChapelHillRealEstateSearch.com
I have considerable experience with new home construction, and land acquisition and would be happy to assist you if you're looking to purchase here in the Chapel Hill area. You may contact me directly through my profile here on Trulia.