[dad911]

They likely have an easement through the property, should be marked on current plot plans. In nj, we can also get a copy from local county clerks office. They can (and probably will) install more lines in that easement, you cannot dig, install structures, or cross with heavy equipment.

We have developed a few properties with pipelines and easements. Pipeline co will have to approve plans, won't allow placement of anything over the easement, and if you want to cross the easement (in our case, electric and natural gas service lines) they had to be in conduit, encased by concrete, and go beneath the pipeline. They have made us either mound soil or place concrete pads over their easement for construction equipment to cross.

I've seen them anywhere from 24" to 12' deep. And every 6-7 years, around here anyway, they dig and install another pipe, along side the existing lines.