It’s perpendicular to the floor, but the front edge of the wall is angled maybe 20 degrees.
I would also recommend getting an engineer to look at it. They’re not expensive. I’d say less than $100 to get one to have a look. Especially if there’s no drawings involved.
That chimney has to weigh an awful lot, and its pressure is on the other side of that buttress half-wall. No way, no how would I remove that wall without a structural engineer saying it’s OK.
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…might specify for a long run of basement wall, especially where there is concern about soil movement.
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I thought that there was soil on the other side of the wall, like it was either a split basement, or else a full basement with poured stairs coming down into it. If that was the case and there were poured walls on the other side of the door as “bulkheads”, that would buttress the wall from leaning out, not necessarily from leaning in. We have very active soil in this area here and things like that are not uncommon.
If there isn’t soil on the other side of that long wall then I would be mistaken, but that was how I read the description.
I really think she’ll need an Engineer on-site to tell her, and if they want a building permit for the removal they’ll likely require one anyhow.
I would have that wall down by now. But that’s me. I’m also likely to be rebuilding it after finding out it’s necessary purpose. ZenBeam might have the right idea with the chimney. Cracks could have shownup after the chimney was completed, so the wall may have been built to add a safety factor. I have seen problems from chimneys settling after building. Also, the flue from the stove runs through a narrow section of the wall. Perhaps that flue, and maybe the whole chimney was added later.
Anyway, my approach would be to try and locate the previous owners, or builders to ask about it. Your neighbors may have some idea how to do that, or know something about the wall if they’ve been around long enough. As someone else mentioned, there should be as-built plans on file with your municipality, along with a history of any permits issued for additional work.
That’s what I immediately saw in that exterior picture. You have a chimney sitting on the ground outside that wall. Kind of a big piece of the puzzle don’t you think?
Here are my thoughts. I won’t be using “maybe” or “could [del]of[/del] have” but it’s all my own guesswork. I worked remodel construction for years know a bit of engineering regarding loads and thrusts. That being said I’m not an engineer, nor giving advice, Ceci n’est pas une pipe, et c.
It’s a buttress and as such is structural. The slope on the outside edge is a big clue. This is typical of concrete buttresses, as seen here orhere. The other clue is that the chimney is made of brick and is a free-standing structure, although it’s on the same foundation pour of the house. You can see the brick facing in your first picture where the flues pass through the foundation walls. The floor heating system was original (and how nice that must be in Maine!) as was the wood stove. The wood stove’s presence is why the form bolts weren’t cut off: Why bother trying to get in there if you don’t have to?
So my big guess is a post construction change was made necessitating the buttress, since Renee has pointed out that the buttress was not part of the original pour. It also has that “Washington Monument” look to it with the difference in concrete colors showings two batches of trough mixed concrete were needed. The change was that the owner added the stone facing to the chimney afterwards. That stone facing would nearly double the weight of the chimney and put the chimney support out of code. The buttress was engineered to take the additional side thrust of the increased weight and everyone went home happy.
Just my theory, of course. I had fun looking at the pictures and speculating. My brother works for a post-construction damage contractor. I think I’ll have to run this by him. I’m dieing to see how this turns out.
I still don’t think it is structural 
I’m pretty sure that a chimney foundation is cast with the building foundation. The reason being is that otherwise you would have to prepare the fill for the chimney footing after backfilling the house foundation - seems cheaper and easier to just form it with the house foundation on the undisturbed soil.
So, for that wall to be a buttress, it would mean that it is preventing the foundation wall from tipping inward.
For the foundation wall to tip inward, it would need to pull the doorway bulkhead in with it, including all the soil sitting on the bulkhead wall footing. Since the chimney is resting on a footing cast with the building footing, the chimney and all the soil sitting on its footing would need to move, too.
What I am getting at is that there is far more mass on the soil side of the wall to counteract any soil pressure trying to tip the wall over.
Yeah, my theory for the scenario may be a little far-fetched (but I had fun thinking it up:)) but I have no doubt that thing is structural. You just don’t make pony walls out of reinforced concrete. You build them out of lumber and shoot them into the foundation. Like I said though, this is a fun thread. 
I think that’s the key point here - in this day and age, no one spends the money making an unnecessary wall like this unless there was a really good reason for it and there was no cheaper way to accomplish the task. Given the house was built in 2009, the OP ought to be glad they even spent the money on concrete for the foundation. 
This actually is the only theory that really makes sense to me.
Una, this house is custom built and has several random upgrades, some pretty expensive (hot water to the outdoor spigots, custom inset cabinets in the kitchen, etc). Apparently they over-reached, though, we got it as a short sale.
I have never heard of this. Any idea why?
ETA: Hot tub? Outdoor showers?
both those are good reasons.
washing car. having warmer water to wash garden produce at harvest time in chilly autumn (for people far north enough).
I still don’t think it is structural
Here’s another reason I don’t think it is structural: it was cast after the rest of the concrete walls.
That means it is sitting on a measly 6" footing (the basement floor slab).
If it was done as an afterthought (too heavy chimney) it would require its own footing.
if it was a vertical load like a post it would require a footing. as a buttress maybe not.
i’ve seen add-on buttresses in concrete and stone done on floors without footings. buttresses in ground would require footings.
This makes sense if you’re imagining normal soil with a moderate water content.
If you instead consider soil after there’s been six inches of rain over the coarse of two or three days in the spring, so that the ground is saturated with water, that stairwell may be essentially floating in the ground, applying upward pressure on the wall, rather than holding it from moving. Water saturated soil won’t pull on the stairwell, holding the wall from moving.
The footings may have essentially mud on them, with mud able to come in from below the footing, so that the soil on the footings isn’t helping keep the wall vertical either.
This is when a buttress will be important.
But the stairway footing is at the same level as the foundation wall footing.
I guess we could assume that the stairway was poured in a stepped manner, but that seems unlikely because the form work would be complicated and expensive to produce.
I don’t know, but if I was concerned with the strength of the foundation wall, I would certainly pour the interior wall to the same height. I would also specify a footing be placed, since any horizontal load will be transfered to a moment load which will become a vertical load.
Nope, doesn’t make sense. My take is that it was added to keep the furnace area separate from the doorway. If you have the material at hand, throwing up a small concrete wall should be amazingly cheap.
I was assuming that it’s something like a precast concrete stairwell, and attached to the wall.
Is the door an opening or does the wall stop and start on each side of the doorway? From the photo it appears the exterior wall stops at the doorway, and if so the half wall is likely a buttress to prevent the exterior wall from pushing inward. If the wall isn’t connected (or even if it only has a small amount of concrete wall connecting it) this is a weak point and likely caused some after construction concerns. (Also–do the joists sit on the exterior wall or are they framed into it–it is really difficult to tell from that photo but that looks like a strange detail there)
In my opinion as an Architect they likely were getting some slight cracking or pressure/warping of the joists that run into this wall and just added this wall to alleviate that pressure.
No one spends money on a wall that isn’t needed in my experience. You can get rid of it but you need to get an engineer or architect in to help you find a solution.