Sunday, February 27, 2011

Our graywater system

We now drain all our graywater to the yard: kitchen sink, bathroom sink, bathtub, and washing machine.

Washing Machine

I set up the washing machine a few weeks ago, using Oasis Design's "laundry to landscape" method, which relies on the pump of the washing machine to move the water. This allows us to send the water slightly uphill, into our backyard "shrub thicket" of blueberries and serviceberries, where a gravity-fed system couldn't reach.

PE Pipe Exiting Garage
Our washing machine drain pipe wasn't the right size or type to use a barb to transition directly to the 1" polyethylene (PE) pipe. So, I used large-ish hose clamps (metal ring with a screw that ratchets the clamp smaller and smaller as you tighten the screw) to attach the washing machine drainpipe to a rubber tube we had around, which then attaches to the PE pipe. We placed the washing machine against the south wall of the garage, where I drilled a hole just large enough for the pipe to exit the garage. I included a vertical piece 6' tall to allow proper venting and as an overflow escape if something clogs the pipe. This prevents burning out the washing machine pump.

Pipe Layout
The pipe extends about 10' due south from the garage wall, then takes a 90 degree turn to the west before running another 30'. I drilled 1/4" holes into the bottom of the pipe every 2' or so. We'll use stumps and logs to pin the pipe into place, preventing the chickens from moving it around.

This pipe doesn't work perfectly yet. Despite my efforts to raise up the path next to the garage wall (see the bare dirt in the first picture above), the pipe still dips down before heading gradually upslope to the discharge points. This means most of the water exits through the first couple of holes, and that the last bits of water stagnate in the low spot by the garage wall. I may reconfigure the setup so the pipe still dips to cross the path, but then immediately jumps up and anchors to the black locust trunk visible in the picture above. That would allow a continuous feed downhill to all the discharge points, giving a fairly even irrigation pattern. I can add a joint or cleanout valve or something at the garage wall low point to remove crud that builds up, or drain the hose before hard freezes.

Sinks & bathtub

The rest of the house drains feed a mini constructed wetland in the front yard, which lies slightly below the house, allowing gravity fed flows. If we didn't have to worry about house resale, we could have done what Oasis Design calls "radical plumbing", just piping each drain directly to the outside with one 1" polyethylene pipe for each drain. In that scenario we wouldn't need any vents or p-traps or larger pipe, since we wouldn't have a connection to the sewer system. However, we're including a plumbing valve under the house so that the graywater can be sent either to the wetland or to the sewer, so we needed to use standard 1.5" ABS pipe complete with vents to the roof.

The wetland resides in an old fiberglass jacuzzi I got for free from craigslist years ago, about 6'x4'x3'. I plugged up all the holes in the tub using rubber patches and 100% silicone caulk. In 2007 or 2008, I dug a big hole in the front yard, just across the main path running by the north edge of our house, and buried the hot tub pretty close to level, but making sure it tipped slightly away from the house, so the overflow would drain into the adjoining garden bed. I made the top of the tub level with the path, or perhaps even slightly lower. Over the years we've built the paths up several more inches, so the tub is now uncomfortably low. Back then, I wanted to make sure we could gravity feed from the house drains into the tub, and we did not yet have plans to lift the house. Had I known then we'd wind up raising the house 3', I'd have made the tub higher. Woulda saved me some digging, too!

Original wetland, marble slate overflow, & hole dug for new bath tub

Molded dirt and marble slate for overflow
We put a few inches of dirt into the bottom of the tub, and planted it with cattails, rushes, wapato, and tule. For a couple of years, we just dumped graywater directly into the tub from 5 gallon buckets placed under the kitchen and bathroom sinks. We had no access to the underside of the house, so no way to use the bathtub graywater.

At some point I buried a bath tub (again, free from craigslist) to receive the overflow from the wetland. I leveled the new bath tub to overflow away from the house again, to keep moving any excess water further into the garden bed area. I tried to strategically compact dirt to control the wetland overflow location, and to use a scrap piece of marble slate to catch the water and carry it down to the new tub. Unfortunately, lots of water seeped through the dirt and was lost to the soil in the surrounding paths. The marble slate wasn't quite long enough to properly reach between the tubs, so we lost yet more water. All in all, probably 20% or less of the input water made it into the second tub.

Furthermore, the water in the wetland stagnated somewhat, smelling a bit nasty when we pulled it up from the bottom of the tub. When we poured graywater into the tub, it followed the path of least resistance, mostly across the surface of the tub straight to the overflow area. So we were concerned that the plants weren't having a chance to purify the water much. We decided to follow the method described in Toby Hemenway's Gaia's Garden, and fill the wetland with gravel and baffles. The rocks in conjunction with the oygenating plant roots supposedly help create a combination of aerobic and anaerobic sites for microorganisms to live, eating the other microorganisms and solids coming in with the graywater.

Our friend Nat loaned us a concrete mixer, and helped me make a run with his trailer to buy half a cubic yard of 3/4" gravel. We held a work party and used the mixer to wash off the rocks, to minimize the dirt we'd be introducing into the system. (Dirt will eventually clog up the spaces between the gravel and dramatically slow the water flow through the wetland.) We placed a vertical inlet pipe into the end closest to the house, and another vertical pipe near the overflow area; both pipes have many holes drilled into them to allow water flow. We placed larger river rock (~1.5"-3", a byproduct of my excavations under our house) around those pipes. I based this decision on the literature I read; I think it helps with allowing optimal water flow, or perhaps it helps trap the gunk coming in from the house without clogging up the smaller rocks?

We filled the rest of the tub with the smaller gravel, building up vertical baffles using sturdy scrap plastic (mostly square lids from 4 gallon buckets). The baffles force the water to take a long, circuitous route right, then left, then right, then left through the wetland, giving the plant roots the most time possible to clean the water before it finally overflows at the far right edge of the tub.

Current setup - second tub in background
The drain pipe from the house will enter into the vertical inlet pipe (foreground), dropping the graywater to exit through the drilled holes and begin its journey through the wetland. I still have to finalize the plumbing under the house, so the pipe into the wetland temporarily discharges onto the surface (smear of goop at lower left), rather than into the inlet pipe. I installed the second vertical pipe near the overflow area (not visible, as it extends only 2" above the surface) to allow insertion of a siphoning hose; supposedly it helps the plant roots penetrate deeper down if you drain all the water out now and then. I've only tried once to siphon the water, with partial success; I dropped the water level by maybe 6", but couldn't get more than that to work. Partly I ran into difficulty starting the siphon without getting my mouth all over a graywater-smeared pipe; some sort of mechanical suction device may help with this. Finally, we replanted the old cattails, tule, and rushes, and topped everything with some wood chip mulch.

Ready to install pond liner scraps for new overflow
A few months ago, I fixed the overflow setup, by replacing the marble slate with some scrap pond liner from our ecoroof project. Now most of the overflow makes it down into the second tub.

I assume in the winter, with the wetland plants dormant, we get very little treatment, so I'm careful not to use the water from the second tub for anything where contamination may cause problems. In the summer I feel comfortable using the water to irrigate, rinse roots, wash my hands, etc. However, we haven't done any water quality testing, which would be necessary to establish how well the wetland actually treats the water.


Nat West said...

Norris, you should check on the washer drain hose to barb fitting frequently especially until you get a handle on how much crud is catching on the inside of the hose, at the barb. That kind of barb-in-a-tube isn't allowed in plumbing code because of buildup. The better solution is an (expensive) "Fernco" rubber hub. They're remarkably expensive new.

Norris said...

Hey Nat,

Thanks for the tip. No crud at all so far at the barb. I had looked for a Fernco, but didn't find one of the right size. Maybe I didn't look hard enough, or needed to go to a plumbing supply store instead of a general hardware store.

I'm going to try posting a question about this to the Oasis Design forum, but registration seems to be broken right now. I'm curious whether anyone who's been using this design for a while has seen crud build-up.