Alignment sheet vs. as-built survey: how to read pipeline drawings
Every ROW file has both documents in it somewhere, and every new tech or landowner outreach rep eventually asks which one to trust. They answer different questions. The alignment sheet shows what the design called for; the as-built shows what crews put in the ground. Reading them against each other is how you catch the gap between the two.
What the alignment sheet shows
The alignment sheet is the design document. It's drawn before construction, usually at a scale like 1"=200', and it lays out the proposed centerline, station numbers, angle points, the width of the permanent and temporary easement, and often the names of the landowners of record at the time the right-of-way was acquired. Valve sites, tap locations, and road or waterway crossings show up as planned features, not surveyed ones.
Treat the alignment sheet as intent. It tells you where the pipe was supposed to go and what the legal easement width was supposed to be on paper. It's the document you pull when you need the original easement width, the parcel owner of record, or the station number for a call-in location. It is not a record of what got built, and construction crews deviate from the design line more often than most new hires expect, for reasons ranging from rock to a wet crossing to a landowner refusing a particular tree line.
What the as-built survey shows
The as-built is the record of what actually went into the ground. A survey crew walks or flies the line after construction, or during it, and ties the pipe's real location, depth of cover at key points, weld numbers, and the real location of valves, casings, and crossings back to state plane coordinates. If the contractor had to bend the line 15 feet to miss a boulder field, the as-built shows the bend. The alignment sheet, unless someone went back and redlined it, still shows the straight run.
This is the document you want when you're answering a one-call locate, scoping a dig-in investigation, or trying to figure out whether a new fence post sits over the pipe or over bare easement. Depth of cover numbers on an as-built are specific to the survey date, which matters more than it sounds like it should. Cover changes. Erosion, grading, a neighbor's pond project, all of it moves soil around a pipe that hasn't moved an inch.
Where the two documents disagree, and why it matters
The gap between the alignment sheet and the as-built is rarely dramatic. A few feet here, a station number that shifted at a tie-in, a crossing that moved downstream of where the sheet shows it. But that gap is exactly where encroachment problems hide. A landowner building a pole barn measures off the alignment sheet's platted easement line because that's the document in the county record or the one a title company handed them. The actual pipe, per the as-built, runs ten feet closer to where they're about to set footings.
Pull both documents before you walk a stretch, not just the one your field book happens to have in it. If the alignment sheet gives you the legal easement width and the as-built gives you the pipe's actual location within that easement, you need both numbers to say with any confidence whether a structure, a culvert, or a fence line is a real problem or just close enough to watch.
A quick way to check both against each other
Start with the station numbers. The as-built carries the same stationing as the alignment sheet across a bend in the centerline, so matching stations gives you a clean anchor before you start comparing offsets. From there, check crossing locations. Those are the features most likely to have moved during construction, and the ones most likely to sit near something a landowner wants to build on later. If the two documents don't reconcile at a given station, that's a spot for a field tie, not a guess.
None of this tells you when a new fence or a new foundation footer shows up on your corridor between the walks your patrol schedule allows for. Pipeline Encroachment flags new structures and excavations inside the right-of-way from recent imagery, on a cadence that doesn't wait for the next scheduled patrol to pass that mile again.