Homepage 2019 » Forums » Water Sustainability » graywater treatment on a slope

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    Hello all,

    I’m thinking that on our site it would be really difficult to use greywater because we have rocky soil that leads water to drain right through rather quickly AND we’re on a pretty steep slope. . .I suppose we could dig into the hillside to try to make a mulch pit for watering fruit trees (if we can find a place where soil will drain at the right speed!). But then I’m worried about whether that would cause us to lose stability in the slope. . . and the slope ends in a retaining wall. . .

    Has anyone used greywater on a slope???



    Greywater needs live organic matter, or it isn’t filtered or broken down adequately before joining the groundwater.

    I would probably make a depressed basin, fill partly with compost, then mulch. You basically then have a mulch basin. both mulch and compost should hold the water pretty well, which will help give it time to break down before infiltration. Any clay on site?

    Of course, this basin would have to be a kind of terrace, or gravity will pull it sideways down the slope.




    What exactly are you concerned about in regard to using greywater on a steep slope?

    In general, whenever you plant a tree on a slope you want to create a bit of a micro terrace for the tree.

    If you’re concerned about water moving downhill too fast for the tree to absorb it, you can try digging a swale uphill from the tree. (here’s a drawinghere's a drawing to show what I mean)

    You might also be concerned about erosion- that is definitely something to consider when you change how water moves down a slope, particularly if you’re causing any disturbance to the soil through planting, building, etc., so try to minimize disturbance to native soil first. Adding mulch is a good idea. Perhaps most important, you can reduce the danger of your greywater eroding the hillside by releasing the water slowly, with as little force as possible. For example, you could filter it, store it, and release it from your storage tank very slowly, maybe through a drip hose.

    Note that if you do any storage with greywater (other than in a pond I suppose), the general wisdom is that you need to filter it first to remove any organic matter.

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