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Designing a dry well for yard drainage

Post in 'DIY and General non-hearth advice' started by Badfish740, Mar 24, 2014.

  1. Badfish740

    Badfish740 Minister of Fire

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    The back corner of my yard has always been a problem. My entire 1/4 acre lot is a gentle slope toward the southwestern corner. This coupled with a layer of heavy clay right underneath the topsoil makes for a swamp that only dries out in the dead of summer. Since I have neighbors behind and on both sides I can't dig a ditch to drain it, so I'm contemplating an underground retention basin or dry well to give the water somewhere to go below the surface and then hopefully, slowly dissipate into the ground. Here is what the spot looks like now.

    Looking south:
    [​IMG]

    Looking west-the hole you see is about 2' deep, dug with a hand auger. I wanted to try to get a feel for the soil. After about 8" of topsoil it's nothing but nasty red clay with bits of rock mixed in. I couldn't get any further with the hand digger after 24". As you can also see, my next door neighbor has a 10x10 shed on a slab right in the same area-curiously he has no drainage issue on his side at all. The neighbor directly behind me does, but his property slopes to a drainage ditch along the road in his front yard so at least he has that option.

    [​IMG]

    Looking southeast toward the rest of the yard-you can see the change in the grass which corresponds with the level of wetness in the ground. Basically the wet area is where it's perpetually green:

    [​IMG]

    As you can see its basically a mudpit. Its impossible to mow (I usually go in there with the weedeater) and its pretty much unusable. The dog loves it of course :p Anyway, I'd like to reclaim it by eventually putting down a layer of stone and moving the firepit, picnic table, etc...back there, but until the drainage issue is addressed, I can't do anything. Here's the plan:

    Basically I'm planning on creating a large volume of space underground so that the water can percolate down through the topsoil and a layer of rock, into six barrels. My hope is that the volume will be large enough so that after a good rain the topsoil will be dry, and the water will have drained down into the barrels below, where it can slowly work it's way into the soil.

    I'd first start by renting a small excavator and digging a pit in the back corner of the yard, about 7' long, by 5' wide, by 5' deep. Once the pit is dug, I'll line the bottom and sides with landscaping fabric. This will keep water from washing dirt into the rock and clogging it. After lining the pit with fabric, a 6" layer of 3/4" washed stone would be spread on the bottom. On top of the stone bed, six 55 gallon polyethylene drums would be placed in two rows of three. The drums would be perforated with 1/4" holes on the tops, bottoms, and sides with the goal being to create as many openings as possible without seriously weakening the drum structurally. Once the drums are placed, the hole will be backfilled with 3/4" washed stone so that the drums are surrounded on the top bottom and sides by a 6" layer of stone. Once 6" of stone is placed on top of the drums, the stone would be covered with landscaping fabric, topsoil, and sod. Here's a crude rendering I came up with:

    [​IMG]

    My gut tells me it will work, but I'm putting it out for a sanity check. The one caveat I think of is that I'll have to treat it like a septic tank/field and never drive over it, but I don't usually take the truck back that far in the yard anyway, and as I said, the plan is to make it an outdoor picnic area long term. People around here commonly use poly barrels as drywells for their downspouts, and underground protected from UV rays they should last forever. Thoughts?

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  2. razerface

    razerface Minister of Fire

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    be easier to haul in some dirt,,,grade out the low spot. Does not look like it would take much.

    You drain it on top to the neighbors,,,his drainage will take it from there.
    Looks simple from here! :)
    Last edited: Mar 24, 2014
    Swedishchef and Joful like this.
  3. Highbeam

    Highbeam Minister of Fire

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    You are making a mistake. Do not proceed with your plan.

    The clay soils prevent water from ever soaking in and going away. By digging a hole you are not providing opportunity for infiltration but instead creating a bathtub for water to accumulate. Would make a great place for a fish pond. That is another option if you insist on digging.

    Instead, fill the hole. Letting this water runoff downgrade as it is doing right now. Thing is, right now, before it can runoff downgrade it has to fill your current shallow bath tub. You will not be increasing the runoff, just eliminating the bath tub.

    If you had dug down and found free draining sand or gravel then things would be different and your test hole wouldn't be full of water. Your test hole is proof that creating a bigger hole will just provide storage for more water and will not make the water go away.

    Fill the low spot.
    Joful, midwestcoast and ironpony like this.
  4. Badfish740

    Badfish740 Minister of Fire

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    Is it worth going to more trouble to dig deeper and see if there is indeed sand or gravel? The hole I dug is barely two feet deep. If I were to proceed with this plan I'd be digging down at least 5'. If I were to hit sand or gravel at four feet, this would work, correct?

    Let's say on the other hand I'm sitting on top of 25' of clay and there is no feasible way to drain the area via a dry well. What do I have hauled in? "Clean fill" and then spread topsoil over it with some sod?
  5. ironpony

    ironpony Minister of Fire

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    yes and yes. Highbeam is spot on.
  6. billb3

    billb3 Minister of Fire

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    You might be better off trying to find a spot in the yard with no clay t drain it off to and have your dry well there.
    Do your own little perc test filling a hole with water to see how long it takes to drain.
    If you don't find at least a draining layer in that clay you really haven't gained anything.
    Even with the barrels.

    How much of that roof shed is draining into your yard ?

    You can't drain into someone else's yard here.
    I asked my neighbor to turn his shed drains sideways rather than have the long pipes dumping his shed roof onto my property and he told me he could do anything he wanted and to go f myself. Town inspector showed up and gave him 30 days to put in dry wells on his shed. Had to pull a permit and be inspected. Haven't had a pond in the yard since.
  7. Highbeam

    Highbeam Minister of Fire

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    Often, that clay layer can be 80 feet deep before you hit another soil type. I wouldn't chase it much farther than you have but if you had a thin clay lense and were able to break through to good free draining material under it then you certainly could use that as an infiltration well. The risk with this is that you are introducing surface junk like dog crap into a perviously protected layer of groundwater. Maybe that bothers you, maybe not.

    I would tend to fill the hole with something pretty similar to the surrounding soils to encourage water to keep on moving overland. If you filled it with clean gravel then the water would still accumlate there but you wouldn't see it, it might not heal up as quickly. Just be sure that it is not a clean (washed) material like drain rock, you want the fines.

    Ah, draining water onto your neighbors. I think you, and even Bill, will find that you are not only allowed but required to allow surface runoff to continue as it did in nature. Just as you can't redirect runoff onto a dry neighbor, you also can't redirect runoff away from a wetland. The idea is to minimize your effect on the natural condition. Filling a hole in clay will not increase the runoff. Once that hole is full of water, each drop of water that enters is forced out of the other end. You are typically required to disperse concentrated runoff so that when it crosses the property line it is in the same state as it would be naturally. That's what happened with the shed, he hadn't dispersed his concentrated runoff which takes quite a distance.
  8. Highbeam

    Highbeam Minister of Fire

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    With those small lots and close neighbors I would just get 2 yards of material in my pickup truck. Dump it, spread it out quickly, and seed it on a Saturday and hope it's enough. If not, do another load in a few weeks. This is small scale landscaping, not filling your property. Some people have beauty bark dumped on their lots, you're having a small delivery of top soil placed there.

    And yes, I get 2 cubic yards of gravel loaded into my pickup at a time. It's a one ton. You might not have a one ton so it might take a couple of trips.
  9. ewdudley

    ewdudley Minister of Fire

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    Tile off with perforated tile 18-24" deep into a 6-8 ft deep well and pump out from there, assuming you have someplace appropriate to discharge it. It works in the Netherlands.
    Last edited: Mar 30, 2014
  10. osagebow

    osagebow Minister of Fire

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    I agree with filling it, but you might check a geologic map of your area. I have heavy clay, but it's on top of fractured sandstone. A small drywell of culvert tile drains my whole yard. French drains running everywhere into it.
  11. granpajohn

    granpajohn Minister of Fire

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    If you want to do that, use this. (Click the green button and follow the directions):

    http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm

    ETA: It's free even though you use a shopping cart.
    SCS became NRCS and stopped publishing paper book soil surveys, thus requiring the use of this web tool by everyone. Long story.
    Last edited: Mar 24, 2014
  12. homebrewz

    homebrewz Minister of Fire

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    Geologic maps and soil maps tend to be pretty general and are good for areas of 100 acres or more. I think you would get more information by talking to any neighbors that have been there a long time, as they may remember some basements being dug if the neighborhood is recent. As said above, it could be a clay lens or it could be much thicker than that. Any soil outcrops nearby can help too where you can look at the strata. I like the perk test idea as it might give you clues as to what the strata is like without a lot of effort.
  13. semipro

    semipro Minister of Fire

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    The soil maps won't likely be of much help for the reasons homebrewz mentioned.
    You're not on septic are you? Looks like the kind of neighborhood to have sewers but thought I'd check.
    If it were my place I'd consider a nice planting bed there with wet loving plants like canus. The evapotranspiration from the plants will dewater the soil.
    Last edited: Mar 25, 2014
  14. Highbeam

    Highbeam Minister of Fire

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    I have had the opposite experience with soil survey data. I have been absolutely freaking amazed at how precise and accurate the information is. Down to the foot. I'm in "the business" and work with soil information all the time, we depend on the soil survey data before trusting a site dug test pit. It is freakishly amazing that this level of soils data has been available for so many decades. I don't know how they did it. I own a large piece of vacant land in a remote area. Undeveloped. The soil survey was accurate within feet of soil changes.
  15. M1sterM

    M1sterM Member

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    2 CY of stone is about 2.25-2.5 tons (TONS). Must be quite the "one-ton" truck.
  16. razerface

    razerface Minister of Fire

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    "1 ton" truck,,,,does not mean it will haul 1 ton. It is rated for more then 1 ton,,depending on the weight of the truck.

    he is talking dirt, not stone
    Last edited: Mar 25, 2014
    UMainah likes this.
  17. Highbeam

    Highbeam Minister of Fire

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    As you know, the "ton" designations on pickups have long been bogus. For as short as my gravel trips have been, I make sure that there is a healthy inch or so before the factory suspension bottoms out. Tires at 80 psi are not overly squatted either. My rated cargo capacity is only 2500#. Hand unloading 2 CY of gravel is about all I want to do in one day.

    Oh and you might be surprised to know that those slide in campers you see are often well over 4000 lbs these days. In a one ton truck if you're lucky, usually 3/4 tons.
  18. M1sterM

    M1sterM Member

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    I know. Some duellies are rated up to about 3 tons of payload, but still wouldn't want to put more than 2.5 tons or so in the bed. It was a tongue-in-cheek comment.
  19. Butcher

    Butcher Minister of Fire

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    Looks like a good spot for a raised bed veggie garden.
    billb3 likes this.
  20. razerface

    razerface Minister of Fire

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    if he raises it,,,,won't be wet any more.
  21. jebatty

    jebatty Minister of Fire

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    Take advantage of the wet area, it is an asset, not a liability. Raised garden, rain water garden, plant things that like wetness and enjoy the view, the options while not endless all are very attractive and much better than trying to beat Mother Nature. She loves you, love her back.
  22. Badfish740

    Badfish740 Minister of Fire

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    Thanks for all the responses! One of the things I love about this forum is that it teaches me how much I don't know about something. I've looked at the soils reports, investigated a few of the methods suggested, and I think I might have found a solution which is kind of a hybrid between putting in a rock filled drywell and just filling the area in with dirt. I found a thread on another forum from someone who had a similar issue. Here's the solution:

    Cover the entire area in landscaping fabric (in my case, about a 25' x 50' area), spread a layer of 4" crushed stone, then a layer of 2", another layer of fabric, then 3/4". The idea is that water will still collect in the area as it does now, but that it will be under a 12" layer of rock with two layers of fabric to keep mud from pumping up through the rock. I think it's worth a shot at least.
  23. razerface

    razerface Minister of Fire

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    your numbers do not add up.

    If you put a 4" layer and then a 2" layer of stone,,,???? That equals a 6" layer. then fabric and another 3/4. That equals 6 3/4,,, not 12.

    I must not understand what you are trying to do. If you fill and grade, there is no mud to pump up. I think you are making it more difficult for yourself then it has to be,,,but have fun!.
    Last edited: Mar 26, 2014
  24. JustWood

    JustWood Minister of Fire

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    I have a 1000 gallon cistern/tank that collects water from a spring behind my shop. It's there to wash vehicles/equipment and fire prevention. Was going to just tile it into a nearby creek but had the tank laying around so I made good use of it.
    Marked it as it's at grade and had the fire chief over to show him where it was in case of a fire at my place.
    Might be worth looking into . Might see some savings on your homeowners also if the fire dept is aware of it. Savings over time may pay for the installation.
  25. granpajohn

    granpajohn Minister of Fire

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    I believe those numbers are the stone sizes; not the layer thickness

    http://www.laurelsandandstone.com/products.html

    Caution with crusher run (CR-6 etc), it is compactible (amazingly so). Don't drive on it or it becomes rather impervious, like a driveway. Don't worry though; tell your aggregate dealer what you're doing and he'll help.
    Badfish740 likes this.

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