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How to seal a pond or constructed wetland

Chicks in swamp

Our greywater swamp became a much more pressing problem last week as the grasses and clovers began to go dormant.  In the summer, actively growing vegetation pushes an astonishing amount of water from the soil up into the air via transpiration, but once the weather cools and plants slow down, the ground is on a trend toward increasing wetness.  While our chicks love hunting for bugs in the greywater effluent, we stopped going out the back door because it was just too swampy.  I guess it's time to put greywater management on the list!

After some brainstorming, Mark and I agreed that a constructed wetland was the way to go.  But what would it look like?  I thought you might enjoy seeing what goes through  my head when I'm thinking about a design like this:

Constructed wetland design

In case you can't read my scrawl, the big questions pertained to lining.  Should we line the wetland at all, and if so with what?

As we know from experience, our clay soil will create a boggy spot where the greywater comes out even without a liner.  Assuming you're not cleaning up something really toxic (in which case, a liner is recommended to keep the toxins from leaching into the groundwater), the only real reason to line a constructed wetland is to keep the soil from drying up during the summer.  However, a liner does have benefits --- it allows real wetland plants to take hold over a large area, and can even be used to create a pool of clean water at the end of the wetland for irrigation or frog habitat.

If we do decide to line the wetland, there are three options:

  • Purchase a pond liner.  If we went for the high quality version, that would be pricey --- $266.
  • Compact clay soil.  Mainstream folks tend to rent mechanized compacters to mash wet clay around under pressure and create a nearly impenetrable liner.
  • Gley the pond.  You can read my post about gleying here.  (Using pigs to seal a pond is a method of gleying.)

Of course you know which option appeals to me, but our little wetland is nowhere near big enough to make it worthwhile to raise pigs just to seal it, and the area is at the same time too big to haul in enough manure to gley without animals.  I'm wondering how much stomping around in boots would be required to compact the soil, and whether chickens can be used to gley ponds.  Ideas?

Our chicken waterer is the POOP-free alternative to traditional, filthy waterers.


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Could you borrow a pig for a short time?
Comment by Irma Wed Oct 10 09:22:20 2012
EPA

Anna, have you seen the EPA going after folks for doing stuff like this over the last 4 years? It's scary. The EPA has even claimed they have the power to classify a property a "wet lands" if it has puddles after a rain. The most prominent story on this abuse of power is out of Idaho where a couple bought a piece of ground with the intention of building a house on it. The EPA had them tied up for years. The EPA even went to far as to say the couple had NO LEGAL RIGHT to challenge the EPA ruling! It took a Supreme Court case to allow the challenge to be made. Our government is out of control!

http://www.washingtonpost.com/politics/supreme-court-allows-idaho-couple-to-challenge-epa-on-wetlands-ruling/2012/03/21/gIQAFgdsRS_story.html

Comment by Heath Wed Oct 10 09:43:26 2012

I don't think you really would need to seal it, based on what I read on your blog every year- rain, rain, and rain in your clay soil...

One thing I found from our first greywater system and my rice paddy is that they seal themselves pretty well given enough time. All the bits of food rinsed off plates, any oils or grease, and soaps contribute to an organic slime that will slowly grow out away from the pipe (and clog your infiltration medium). Rainwater will add some fines to the system. Basically all raindrops were once a mote of dust- it adds up over time. Also, the greywater plants will die and contribute to the mix.

In Japan, the rice farmers till their flooded paddies with rototillers. It compacts the base, and stirs up the top 10cm or so to settle out naturally, thus leaving a thick layer of clay on the top. And every year the irrigation water to flood the paddy deposits just a touch of new mud washed out of the mountains. I get growth of about 1mm/year in clay and silt from the input water to my paddy. I think two people stomping around in boots after a good rain would make a pretty tight seal.

If you have a problem with it percolating too fast, you could just bury a few buckets to their rims. They wouldn't drain dry like the rest of the basin, and you could contain the planting of vigorous spreaders in one area (cattails for example)

Comment by Eric in Japan Wed Oct 10 10:25:24 2012
We have a greywater pond that has been in place 27 years....initially we used some cheap black plastic to line it. The weight of the water against the plastic and a buildup of sediment have sealed it nicely.
Comment by Anonymous Wed Oct 10 11:50:34 2012

Irma --- I'm afraid the space is too small to even make it worthwhile to set up the infrastructure (fencing, etc.) for a rental pig. :-)

Heath --- There's a big difference between a man-made area where water ends up puddling and a real wetland. I'm actually very much in favor of protecting the latter (even if it only looks like a puddle to the untrained eye), and of turning our man-made area into as much like a natural wetland as possible. But I'm a treehugger. :-)

Eric --- Awesome data! I really appreciate you doing the experimentation so we can just follow your lead. You've pretty much sold me on your method --- just digging out a spot for the water to pond, and maybe adding some buckets of cattails to get things started. Thanks!

Anonymous --- That seems to support Eric's data --- that just adding the water can naturally gley the wetland. I hope it works!

Comment by anna Wed Oct 10 15:21:48 2012

I've been pondering using bathtubs to construct a greywater system.

The only practical place for us to run our greywater is down the border of our property (the house is close to the fenceline), and it's not wide enough to do something in-ground. I also don't want to risk it overflowing or leaching into our neighbour's paddock. But a series of bathtubs would fit nicely.

Comment by Darren (Green Change) Wed Oct 10 18:06:46 2012

I recall John Wells on the Field Lab blog hauling in Benonite (sp?) to seal a dam he built on a creek... Not sure what all that involves or if it is even practical.

My OTHER job is installing/repairing septic systems... Occasionally we dig lagoons and have never worried about sealing them, like Eric says they will naturally with the constant saturation. I brought one up to code recently that had been let go and had completely dried up during the summer drought... When we were digging it out it went from dust on the surface to so much mud underneath our machines were getting stuck. After a couple more feet we hit moderately dry soil again!

Comment by Phil Wed Oct 10 22:30:18 2012

Darren --- I got bogged down on bathtubs when I realized that my capacity estimates were way off on my drawing above. I was figuring on just filling the bathtubs with water, but of course they'd already be full of gravel, sand, and/or dirt to grow plants, so I'd actually need a lot more of them.

But in a place like Australia where water is presumably scarce, it might be worthwhile. Also, I'm pouring all of my roof water in as well, which you probably wouldn't be doing. I'll look forward to seeing what you do on your blog!

Phil --- Bentonite is a kind of powdered clay that folks often send into cracks in dams to try to get it to reseal. I don't hear much about people using it to seal a whole pond in the first place, but they might.

Interesting story about your lagoons! What part of the country do you live in?

Comment by anna Thu Oct 11 07:19:45 2012
Too small for pigs? Try an American Guinea Hog. If anyone in your area has feeders available they'd be a good fit. You can keep one on garden scraps, cracked eggs, and pasture. He could seal your pond for a season and provide 50-100 lbs of meat and the best lard you ever cooked with! They are easy to keep in with hog panels or hotwire, and small enough to tackle for a home butchering job.
Comment by Karen Mon Oct 15 10:43:20 2012
Karen --- We actually may try a couple of pigs in the spring, but not for this project. Just the fencing alone would be too much hassle for such a small area.
Comment by anna Mon Oct 15 12:21:22 2012

One very unique homestead, $1,500 per acre, the opportunity of a lifetime