I am building a small cottage on my heavily wooded and sloped land and need a way to dispose of my grey water. So far my plan is to use a trenching machine (thanks to a friend) and make a 2.5 ft trench on contour (or with a small slope) and fill 3/4 of the way with gravel and the remaining 1/4 with soil. Basically it would be an undergroundswale. It wouldn't freeze and I'm sure the trees and soil would readily absorb all the water and nutrients. I'm guessing we will put out about 50 gallons a day in grey water so if my leech line is about 150 ft long that should be ok right?
Hi Philip, looks like a good plan in outline. There are some things to consider, and I'll spell them out here:
How rapid is the soil infiltration rate? Rapid infiltration may mean that 3' of your 150' trench will be used, and the grey water will go straight to groundwater as pollution. Very slow infiltration may mean that your trench will fill up and overflow after a while, or in wet weather. In fact, if you're on the contour and it rains, what happens to all the water uphill - will that fill the swale?
How far down is the groundwater? If it's shallow, you may end up causing pollution even with that work.
Are there local legal guidelines that you need to follow? If so, then it could be tricky to sell your house or may be illegal to do what you propose. Certainly here in Ireland, the EPA Code of Practice (see www.wetlandsystems.ie/watertips.html) is the document that the council always refer back to. If it follows the Code, you're usually fine. If it doesn't, then you need to have permission; a really good reason that will yield permission, or else you may have to redo the job.
If all of the above is ok and you can still proceed, something you may consider is willow or an alternative biomass crop planted along the swale to soak up nutrients. Comfrey also works well as this puts down deep roots to capture nutrients. Orchard trees are another possibility if you're in an area that typically needs irrigation (here in Ireland I wouldn't use apple trees because the ground is already too wet for them in many areas).
If you can answer the above, I'll get back to you again
I would say the infiltration rate is not extremely high due to the high clay content of the soil here. Also it is worth mentioning that the soil is not very deep before the limestone is hit, about 3 ft. I am not concerned above the swale filling up excessively because it will be in a mature forest. The trees do a great job of slowing water down from hitting the ground and when it gets to the ground the roots and leaf litter help with quick infiltration etc.
What exactly is your definition of pollution? And what would you say are the differences between grey water coming out of a septic system and the grey water coming directly out of my future house? I was under the impression that I could basically eliminate the flush toilet and septic from my house but keep the leech line and there would not be much of a difference.
There are no legal guidelines for me to follow (I'm in the backwoods of Kentucky )
I didn't figure I needed a biomass crop because of the already existing trees. ?
Hi Philip, my definition of pollution in this context, is any material from your household grey water that may cause a deterioration in the quality of surfacewaters or groundwaters at or near your property. There's a surprising amount of contaminants in grey water - including suspended solids, nutrients, potential toxins and organics (which provide food to microorganisms, who then party and upset the balance of oxygen in streams and rivers).
Note that this is less problematic than mixed sewage, which contains all of the above and pathogens to boot. So, if you're designing a system that could feasibly handle all your septic tank effluent, then grey water will be happily dealt with.
If the swale is your only treatment method, then it's probably absolutely fine as long as you don't have specific regulatory requirements and as long as you dig it much shallower than you'd planned. If you've only got 3' of soil and you dig down 2.5'; that doesn't leave much for infiltration before it hits the limestone and potentially zips straight down into your groundwater.
Much better to dig down only 6" or so on the contour, and then build up over this area with gravel or brash-wood and a cover of soil. A ground-cover plastic sheet over the gravel will help to limit soil wishing down into it.