Chris,
WRT maintenance, usually the servient estate is tasked with mowing, debris removal, etc. What I was referring to is the fact that at some point, that pipe may leak, break or otherwise need to be dug up. The easement should allow for that, and should require the digger to repair the damage to the land rather than leaving a colossal mudhole full of backhoe tracks.
Be careful with corridor valuation theory, since you're valuing the damage to the servient estate, not the corridor. Search Lum for pipelines; I think there's an article that deals with a freshwater pipeline crossing someone's land, and it discusses theoretically expanding the tract to a marketable size, and using the unit market value of the theoretically expanded tract as the basis for valuing the easement. Again, though, you're not valuing an easement, so be careful. The "back door support" idea you had is the way I'd use it.
Steve Santora's right though. Both of these theories are pure sophistry. You can't get a true market value using either one of them, and they do ignore parcel size and HBU, at least in the abstract. The latter theory (theoretical expansion) simply plays "let's pretend." So it does recognize HBU and parcel size and geometry as market factors, but blithely ignores them without so much as a stated hypothetical condition. And that the courts have allowed the use of these theories does not, IMO, make them valid; just something you can get away with by appeal to authority.
What I was talking about WRT lot size: Is there a premium for larger lots in that S/D? Is there a penalty for smaller lots? Let's say the lot size is 100 x 119, with the last 19' take by the easement. Are there any 100 x 100 lots in the S/D? Do they sell for less than the 100 x 120 lots? If not, then you may not be able to demonstrate damage at all, especially if you add in the additional surface rights gained in the last 19', and subtract the routine mowing/maintenance that the HO would do anyway. Basically, if the buyers aren't paying a significant lot premium for that last 1900 sf of lot, then your buyer really hasn't lost anything.
But the counterargument is going to be that he bought a bigger lot on purpose, and now discovers that he's lost part of it. So what has been lost? He can fence it if he installs gates or removable panels across the easement. He can use it for recreation, doggie rest room, additional privacy buffer, or any other nonpermanent use. He can't dig in it or build a permanent structure on it. But he can put a skid-mounted portable building on it (unless prohibited by CC&R's). He'd mow it whether the easement was there or not, so I wouldn't count that as a burden.
Just how is this easement interfering with his quiet enjoyment? It offers no substantial hazard unless there's a helluva hydrostatic head in the line (900 psi or so.) BTW, what's the rear yard setback in that S/D? In some of my areas, R-1 zoning requires a 30' front, 15' side, and 25' rear setback. If the easement is in the setback zone, our hero's surface rights haven't been impaired at all.
