Underground rain downspout advice!

Hello guys,

really not sure if this is the right place to post this as it is not directly related to indoor plumbing but here it goes!

So our condo building has rain gutters that have been located directly on top of our driveway's slope (about 25degrees) and as a result the water constantly discharges in front of our garage doors and pools there. Not good IMO but im not an expert.

Last week we met and I proposed to install underground downspout extensions to re-route there rain gutters and discharge into the ground far away from the foundations and driveway.

What we've done: We bought 4in plain PVC pipe and fittings, dug a trench from the aluminum rain gutter to about 15-20ft away from the building, then dug a hole at the end of the trench (about 18in diameter by 24in deep) and filled with 3/4 gravel. The trench is about 10in deep.

We put a 90degree elbow at the beginning of the drain line with a rectangular gutter adapter to 4in round pipe, then at the other end of the drain line we put a T with a female threaded adaopter on top and a screwed cap (for future cleanup if we need). The cap barely protrudes from the grass so lawnmowers wont hit it.

While digging the seepage pit, we noticed that past the first 7-8 inches, its pure clay. I mean it felt like wax almost. We didnt worry about it too much but after all was done and buried, I tested the drainage with a garden hose, at full capacity for about 2-3 minutes and we filled the pit and pipe. Water seeps slowly in the ground and it takes a good 10 minutes for the pit to appear entirely drained (not sure as there's no way to tell from above ground).

I am wondering if this drainage setup will work? The building roof's is equipped with 4 gutters (one on each corner) and the building is approx. 40ftx80ft.

I fear the seepage pits doesnt keep up (because of the clay), fills up until the 90deg elbow and then overflows against the foundations...

We have to repeat the same on the building fronts next week so I'd like to do it better if need be or at least confirm this will work before we repeat the same somewhere else..

All right! Thanks!!!

Untill you know for sure, you might open the clean outs so if it backs up it will be away from the building. Is there no city storm sewer system you can pipe to?

Hey nealtw

No as far as I know there's no city storm sewer anywhere close... You are right, I may leave the end cap open (or maybe drill two small holes for overflow? so if it overflows, it will be away from the building..

Do you think I should dig deeper/larger for the next drain?

If it’s the type of clay you describe it will act like a pond and just hold water. Making it larger won’t buy you much as it will fill up and then you will be back to the same condition. If you have any grade away from the building the idea is to follow the grade until you are far enough away from the building and then let it discharge out on to the lawn. If you don’t have the grade needed the next best thing would be to use solid pipe as you did for maybe 10 feet and then switch to perforated pipe and lay that in the soil above the clay and back fill that with gravel. I like to fill it with gravel right to the surface and eventually grass will grow over it. sometimes when you need to get grass right away I have used gravel then a layer of straw and then an inch or two of soil. The only thing you have to get rid of the water is the top soil getting down in that waxy clay will just hold water and you are wasting money on the stone.
I would guess a leach line with 20 foot of the perforated drain pipe is where I would start.

My first impression is that your "dry well" is not big enough for the roof runoff volume. That dry well holds just over one gallon. Not enough.

I suggest you "go big or go home." Here is a solution ....

1. Buy a round 55 gallon drum or (easier) a large round plastic trash can
2. Drill a lot of 1" holes to facilitate seepage from the can.
3. Run your PVC drain line into the side of the can about 4" from the top so you can bury it along its run
4. Optional - wrap the can with one layer of landscape cloth to keep soil out of the can
5. Dig a much bigger hole in the ground.
6. Drop the can in the hole. Fill can with gravel. You can fill the perimeter around the can with gravel too. You can mount the can to grade, leaving the gravel exposed OR set it below grade and grow grass on it.
7. Enjoy your good work

both guys are essentially right. The hole has to be bigger, and the soil around it should be modified to allow better drainage. A friend just had some similar work done and the contractor was going to add gypsum to the soil. I'm curious whether the gypsum is granular or powder, or whatever. I wasn't there when he did the work so if anybody knows, please post it.
The other method is to redirect surface drainage to the curb. Hopefully there are storm drains in the street.

A large 55 gallon drum full of holes and filled with gravel and then filled in around it with gravel is going to be the same thing as a big hole filled with gravel.

The water first needs a place to go and then it needs a method to dissipate. It can soak or leach into the surrounding soil or it can evaporate or it can be drained far enough away that it can join in with some other system to take it away like a storm drain or even a road side ditch. If your soil is clay it will dissipate down very slowly.

I would rather dig a 10 inch deep ditch by hand 50 feet than a 4 foot wide hole 4 foot deep.

Most new building around here have to have storm water retention off of any surface that is not water absorbing. So basically buildings and drive and parking areas that are paved. The retention pond or underground water holding has to absorb the average storm and then let it leach away slowly. When they are connected to storm drains it’s only as an overflow for emergency rainfall.

Thanks guys for the ideas and advices!! Exactly what I was looking for.

I like the idea of a large shallow hole (or better, large and deep hole) that will be able to contain significant amounts of water then let seep slowly... Since its clay, I assume the more surface area water has to dissipate the better..

This weekend I will pull the grass over the dry well, remove the gravel, cut the PCV pipe, remove the T, dig much bigger then proceed with CallMeVilla's suggestion.

There are no drains or any runoff lines, or anything else close to the drain. If I dig deeper, this may sound like a stupid question but can I hit something or cause soil problems? for example, if I dig 4 feet deep?

BTW this is in the back of the building just adjacent to a highway.

slownsteady said:

both guys are essentially right. The hole has to be bigger, and the soil around it should be modified to allow better drainage. A friend just had some similar work done and the contractor was going to add gypsum to the soil. I'm curious whether the gypsum is granular or powder, or whatever. I wasn't there when he did the work so if anybody knows, please post it.
The other method is to redirect surface drainage to the curb. Hopefully there are storm drains in the street.

Click to expand...

Gypsum makes the clay clump together when it’s worked into the soil. The sticky paste clay forms little clay balls that let water and plant roots take hold. A lot of the time they add sand to amend the soil with gypsum. I knew an old guy that put drywall scraps along with sand on a clay field he had by the dump truck loads. The paper broke down over time with rain and snow after he worked it in with a rotovator. He ended up with some nice soil. The stuff they add to soil I believe is more of a powdered product.

Worthwhile to rent a hole digger? I have time to dig by hand but if I will run into rocks and harder ground, I may be better off renting a machine and get it done ASAP..

first; the highway has to have accommodations for runoff. Maybe you can tap into that somehow. Second; I have to assume by your user name that this is a condo community, so there may be many units with similar problems. A backhoe / excavator makes quick work of this and you guys can do several holes in a day. Third and most important; you can hit almost any kind of utility when you dig. Call before you dig.

Rent a light electric jack hammer (40 pounds) and it will make the job faster, easier .... trust me you will like this. Its MANLY and efficient.
I would put down a tarp for the excess dirt. This protects your grass until you can re-use or dispose of the dirt.

Invite a buddy or two for the fun .... Think Tom Sawyer and the fence whitewash project. Heck Neal would do it for beer ! Bud would expect dinner, wine and soft music.

I hope you brought enough for everybody.............

Does this building have a below grade basement?

we have run into this around here. we call it yazoo clay i have seen this done before with pretty good results.

you need to spread the water out over a wide area, so that it will perc. into the soil
if not, it will just make a mud hole