Thanks - the second plumber came today and said exactly the same thing. He seemed reasonably certain it couldn't be coming from our (inside-the-house) plumbing; said it appeared to be the kind of small PVC drain pipe used with downspouts and landscaping. In theory they could snake a camera, but he said that it is filled with mud so that won't be very efficient. So digging is our next step. I may also try to reach the individual listed on the sediment control plan (and monthly inspections report) for the construction next door, just to see if he might have spotted some intake point from that property.

Hi again - I spent some time yesterday digging, and found the other end of the pipe. It's about a foot away from the corner of the house, pretty close to where a gutter drain pipe is located. I know the gutters weren't connected to anything when we bought the house 12 years ago, so it must have been abandoned sometime before that.

But now the question is what should we do - should we just have our landscaping guys rip it out? It's all caked with dirt and mud from what I can see but obviously its presence is something of a problem, otherwise we wouldn't have the muddy spot at the other end. It's literally right below the surface of our lawn, so it wouldn't be too hard to extract it (except for a piece that runs under the fort part of our kids' swingset.

You make it sound as if there is not a source of water entering the pipe, so it can't be the cause of a wet condition at the other end. But originally, you say it's leaking, so there is some confusion. If the pipe is packed with mud, it doesn't sound like it can be a conduit for water. Since you have exposed both ends of the pipe and determined that it is not serving any function, you can remove it just to get it out of the way. Wherever it's not bothering anything, you can abandon and leave it in place, if that's an easier solution. If you can verify that it is not carrying water, the wet condition at the far end of the pipe must have another cause.

You're right, Yardvaark. It's still a bit of a mystery then I guess - why is there a muddy spot in the corner of the yard if the pipe is all packed with mud? It rained very hard last night and at 5pm today, there is still a puddle where the pipe ends (furthest from the house.) That would suggest it's serving as a conduit for some flows of water. To be safe, I think I'm going to call a company that installs this stuff professionally. We're just outside DC, where the hot humid weather is just beginning, and if I don't deal with this mud pit soon, the yard will be uninhabitable due to mosquitos.

Is it a low area where water collects and hangs out for a while? You might try to observe water flow during a rain and see if that indicates anything.

It's definitely the lowest point in the yard, but it's a pretty mild slope - maybe just a few inches at most. In 12 years, we've never had anything like the water pooling that's happening now, right where the pipe ends furthest from the house. The only real change is the monstrously large house going up next door - they're putting a 9,000 sqft house (with a basement) on a lot that previously held a 900 sqft house on a slab. But I can't say for certain that this is the cause. I have a waterproofing company coming to look tomorrow, and may ask our regular landscape/lawn guys for their take as well. I've been trying to post a couple of pictures here without any luck - may try from my phone.

Here are a couple of lousy photos

It being the lowest point in your yard meaning that it is the pathway for water to leave your yard. Being that there is construction next door, have they blocked the flow of water trying to exit your yard? On the other side of the fence should be an even lower elevation than in your yard and it should continue to get lower through the neighbor's yard until it leaves his yard through some other property (which could be public property.) Follow the path of drainage beginning where it leaves your yard and verify if it is the case.

Aargh! So here's the latest: The waterproofing/drainage guys visited today. They said it was possible that the pipe is perforated and is somehow channeling underground water to one spot at the lowest point in our yard. They said it's also possible that the water is actually coming from the property next door with the massive new build (which is on the opposite side of the property from where the water is collecting, at a much higher grade). Either way, all they can do is excavate the pipe and see what happens next. They suggested it would be wiser and cheaper to have a handyman or landscaping firm do that. I put in a call to our lawn guys in hopes that they can do that.

But what worries me is that the waterproofing guys said that if eliminating the pipe doesn't resolve the water pooling, any other solution is going to massively complicated and expensive (like, tens of thousands of dollars.) Our house is bounded on either side by other homes and by other homes behind us on a cul-de-sac, and there is only about an 8 foot side yard to direct any water out to the front of the street - and that slopes in the wrong direction. I feel a little sick about the whole thing.

Yaardvarck, you asked about the house directly behind our fence. Without specific measurements, my sense is that our muddy spot is in fact the lowest point between our yards. The previous owners installed a row of pine trees on their side of the fence to shield the views (which we appreciated since they had painted the house neon yellow.)

Do you see any other options for dealing with this? Spending thousands to dig up a pipe we didn't even know existed and doesn't appear to have a purpose seems painful, especially if that is not even likely to solve the water problem.

OK, sorry for that long post. Can I follow up with a couple of potentially really stupid ideas? (1) What if instead of digging out the entire pipe, we strategically drilled or cut holes in it so that it cannot direct water toward this low-lying corner of the yard (if indeed that is what is happening)? Obviously we'll pull the thing up if we need to, but I'm afraid that will involve uninstalling our kids' playset, since it runs right underneath it.

Or (2) is there any kind of simple regarding that would help, especially in protecting us from increased water drainage as a result of the installation of a very large waterproofed concrete basement next door? Note that their backyard is a full 15 feet higher than ours, so we can never fix that.

From everything you've said, I don't think that pipe is anything more than some old pipe abandoned and not the cause of the yard wetness.

You say that the natural flow of your yard is toward the back. This indicates that at some time and probably for a long time, beyond the back lot line was the escape route for excess rain water. You say that the property beyond the back line is much higher than the low point in your yard. Is this as a result of a recent change (with the new build or something else)? The neighbor cannot legally stop the natural flow of water coming from your yard. If they have, then they are at fault and you must get them to correct it. First, you need to make sure. (I gave you directions above.) If it is clear that the escape route for water is penned in by higher ground, do your best to figure out how it came to be that way .... is new construction creating the higher ground apparent?

If you have questions, it would be good if you can provide a photo that shows the higher ground beyond, taken from a distance that shows the context and from an angle that captures grade.

AS far as getting rid of the old pipe. Your kids play area isn't a problem. Cut the pipe off with a pvc pipe cutter-cost couple of bucks & found in sprinkler section of Home Depot. Cut pipe off on both sides of kids play area & just leave the other piece under the area, it's not hurting anything. If the pipe is close to the top, you said 6 in. down, not a big deal (just under the lawn) get a flat shovel, lift lawn up& flip over so lawn is against lawn & get it out of there. I could do it(& have) & remove the pipe. Then flip the lawn place in place. Pipe isn't going to make a difference as it's so small, lawn will be fine pushed back in place. Then spray the replaced lawn area to soak loose dirt in & will look same as it did. Drainage is a serious problem & you can't impede on other people's property, there are city or county laws on that. Why is a 15 ft. fence allowed? Can't believe that is legal anywhere. Is their basement poured or just dug & full of water. That happened to my son, neighbor's had dug, out full of water, son reported it & city made them pump it out as it was soaking into son's property. Neighbors can't change way water is to run off. Be sure they don't try to or you will be dealing with them later in court!

The previous owners that installed that pipe apparently wanted a drier yard, figured that diverting the rainwater from the roof to the property line would be the answer, and put in a pipe that somehow backed up with mud. When they realized it wasn't doing as planned, they disconnected it from the downspout and then conveniently failed to mention it in their seller's disclosure, figuring it would never be noticed.

The pipe is harmless. You can let it be. Especially if you don't plan to use the root space for trees or don't feel like wasting money removing it. If it were me, I would dig up the entire thing with a shovel over a series of weekends.

The water pooling up at the back of your property is an asset! By re-engineering the landscape for residences, the developers created the natural equivalent of a seasonal gulley at the back of your property. Plants love water. Trees love water. In nature, such a damp spot would quickly fill in with lush, water-loving vegetation: Red Maple, Sweet Gum, Birch, Willow, etc. There's rarely an amount of water too large that nature can't put to use. I think you're right to plant native, water-loving vegetation back there. Let the neighbors drain more water from their new McMansions onto your property. I would use every drop of it.