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Isn't it the same as fertilizer by that point?
March 13, 2010 10:28 AM   Subscribe

Septic system question! How important is the last eighteen inches of pipe to the system's continued functioning? And can I grow crops there?

On our tiny farm we have a tiny greenhouse -- 10x20'. This is designed to accommodate two four-foot beds or tables along either side. So far we have just been using tables for starting seeds, but now we'd like to do a raised bed along the south half. We will need to line it with hardware cloth along the outside edges, extending the wall down into the ground 2 feet for rat-proofing, so I have been planning to dig down about 2 feet the whole way. I started this process and didn't get very far before I ran into the tail end of a ~4-inch perforated PCV pipe, which I assume is part of the septic system.

Picture here.

The part of the greenhouse in question is located at least 50 feet from the top of the septic system -- don't know what it's called -- the part where lid is, and the system can be accessed for cleaning etc.

I'm wondering two things. One, can I safely just saw through this last 18 inches or so of pipe and remove it so that I can line with hardware cloth as planned? Will this mess up the septic system? And two, can I then safely eat crops grown in a raised bed (adding probably 12 inches of topsoil) in this location? We hope to do greens and leeks etc in the winter and cucumbers, tomatoes, and melons in the summer, so ideally it would be both leaf crops and fruiting crops.

One thing we considered is to switch sides -- to put the seed-starting tables on the south side, the one we were planning to dig out, and the bed in the ground on the other side. But the north side has a large hedge about 15 feet away and gets less sun than the south side obviously, and I also would worry that the tables would then block sun to the bed. I'd rather have the bed on the south side if possible.
posted by librarina to Home & Garden (12 answers total)
 
"... One, can I safely just saw through this last 18 inches or so of pipe and remove it so that I can line with hardware cloth as planned? Will this mess up the septic system? ..."

If you've hit upon the closed end of the leach field (overflow) outlet pipe, which is what I actually think you've exposed, you probably don't want to disturb that. The point of a blocked end leach field pipe, is to provide a clean out point (for roto tool feed), later, when plant roots in your yard may have invaded your leach field pipes. If you just cut it off, grey water loaded with fecal coliform bacteria, may slowly seep into your greenhouse bed (and might still, depending on the relative horizontal percolation of your yard soil in the leach field, maximum rain, your water use habits, etc). Bad news, if you're planning to eat from that bed... I suppose you could dig up the last 10 feet or so of your leach field, and re-orient the pipe so that it doesn't impinge on your greenhouse, and so that you could install some sub-ground level hydro dam, to prevent leach field water, under the worst storm runoff situation, from reaching your sub-surface greenhouse bed. But that seems like a lot of work, and you might need to pull permits, depending on your jurisdiction, for alterations to your septic system.

Carefully repack soil around the pipe you've exposed, to the previous depth, and at least a foot on each side, and brace the re-packed soil on both sides with vertical pavers or tiles, staked deep into the ground with rebar. Put in your greenhouse bed, if you must have it, with a 2 foot "bump" in the middle, and be happy that you didn't have to spend a lot of money cleaning up a septic system issue, later.

But, in the long run, don't raise anything you plan to eat there, unless/until you prove that leach field runoff can never reach it, even in the worst downpours.
posted by paulsc at 11:10 AM on March 13, 2010 [2 favorites]


Yeah, we are in the Pacific Northwest so there is often a lot of rain. We try to be good about not using a lot of water -- efficient washing machine and dishwasher, etc. -- but we are better at it in the summer because the well runs dry if we aren't careful!

The end of the pipe is not capped, and I did not find any sign of it having been capped in the past (no plastic remnants in the soil around it).

Do plants take up bacteria though? It makes sense to me that they would take up like lead and such, but I don't really get how it would take up bacteria into the leaves or fruit. And if there is another foot of topsoil on top of the soil surface, is that enough buffer? I won't do root veggies in there.

If not enough buffer, how far away should I get from the end of this pipe? Should I not even consider growing anything downhill of the drain field at all?

Rearranging the whole thing seems like *way* too much work. Would probably rather just build another greenhouse somewhere uphill.
posted by librarina at 2:06 PM on March 13, 2010


If you don't have the septic system's original plans, it seems likely that the county, or whoever is responsible for permitting waste treatment there, does. I think it'd be worth hunting down those plans before you put too much work into anything, just in case this is unrelated to the septic system. (For example, could it be the end of a drain pipe behind a wall, etc.?)
posted by hattifattener at 2:18 PM on March 13, 2010


"... The end of the pipe is not capped, and I did not find any sign of it having been capped in the past (no plastic remnants in the soil around it). ..."

Either your bad luck, in that the installer didn't have a pipe cap on the truck the day he installed it, or, that local codes want the end of the leach field system open, so that excessive flows will produce identifiable "wet spots" in your leach field cover (lawn). I dunno, since I'm not a septic system contractor in the Pacific Northwest...

"... Do plants take up bacteria though? ..."

IANAPlantBiologist, either, but I do know that plants effectively take up, and respond to/suffer from viruses, if not bacteria, in soil.

"... Should I not even consider growing anything downhill of the drain field at all? ..."

Um, if I were feeding my family from that acreage, that would probably be my default, un-scientifically tested solution. Soil around houses is rarely tested or cultured for much. If the house roof runoff + local site rain + grade water loss/gain doesn't produce constant visible mold, or objectionable odors, on a frequent basis, most homeowners never bother to check their leach fields, until there is a plumbing problem.

You're trying to grow food, presumably for your family. Is there any higher standard for safety motivation?
posted by paulsc at 2:34 PM on March 13, 2010


Let's do some guessing. I think you have a two-chamber septic tank with a leach field of PVC pipe. If that is the set-up, you probably have more than one pipe in the leach field. As hattifattener has said, you may be able to find the plans for the leach field at your local Health Department offices. Those plans are probably quite general in nature, but will let you know if the entire garden area is atop the field, or if you have stumbled upon its very edge.

If this was my garden, I would not be cutting any of the pipes. I would trench around it for your wire mesh and put a plastic visqueen liner along the side of the mesh and over the top of the pipe to encourage any water that comes out of it to flow under and away from the garden. It will also help guard against roots growing into the pipes. Roots love septic run-off because it is high in nutrients. As you mentioned a raised bed, I would make it about 18 inches to two feet deep in the area over the visqueen, just to give any plant roots a little room to maneuver.

I would not be concerned about bacteria. First, the ground comes pre-loaded with it already. Second, unless you eat only hydroponically grown food, you are most likely already eating food that has been fertilized with some sort of manure. In certain countries near our borders, that fertilizer was probably not refined or processed to any degree. The main cause of food-borne illness is the failure to properly wash and cook it, not any uptake into the plants.
posted by Old Geezer at 2:56 PM on March 13, 2010


"... First, the ground comes pre-loaded with it already. ..."

That's a remarkably broad statement for all values of location and soil type that compromise "the ground," in the absence of laboratory test results specific to the site.

"... Second, unless you eat only hydroponically grown food, you are most likely already eating food that has been fertilized with some sort of manure. ..."

Big, big difference between oven sterilized manure mixes, and the untreated effluent of a home septic system + rainwater runoff + grade runoff. To say nothing, of course, of many, many variants of manure mix fertilizers, and their storage/mixing/pre-application treatment, or lack thereof, that might or might not be acceptable for food fertilizers in short loop nutrient situations.

"... The main cause of food-borne illness is the failure to properly wash and cook it, not any uptake into the plants."
posted by Old Geezer at 5:56 PM on March 13

Of course, if gardeners are actively working in areas of contaminated soil, it's pretty easy to transpose common soil bacteria to soon to be harvested plant surfaces, in the confines of a greenhouse...
posted by paulsc at 3:55 PM on March 13, 2010


Uh, yeah. Shitwater near food isn't a good plan, even if it is growing food. One well timed splash and shitwater is now in your lettuce. Or whatever.
posted by gjc at 4:39 PM on March 13, 2010


Well, I was back out there messing around again this afternoon, and, embarrassingly, found that that chunk of pipe only goes another inch or so beyond what's in the photo ... that is, it's not connected to anything else and not part of a system, just some buried trash.

I am now curious/worried about the whole thing, though, so I'll try to track down the map or plan of the system to see exactly where it lies.

I'll also get in touch with my county extension, I guess, regarding whether plants take up (pass on? harbor?) bacteria from the soil. I get the concern about surface contamination via water but since I'll be well above the ground -- more than 12 inches apparently -- and using imported topsoil, I'm less worried about that. Good point though about surface contamination via soil, paulsc. Thanks for the link to the testing site, too; for some reason it hadn't occurred to me to do that.

Does anyone know a rule of thumb and/or law regarding appropriate safe distance from the drain field? (I know this will depend on slope, ground water, etc.)

For reference, there is no standing water, soggy ground, bad smell, interesting flora or fauna, noticeably better growth in the area, or anything else indicating abnormal septic activity.
posted by librarina at 5:29 PM on March 13, 2010


You might see if you can call a septic guy to come out for a look around. I've had weird situations and people were willing to come out for free. And you probably need to know where/what the status of your septic system is.
posted by leahwrenn at 5:29 PM on March 13, 2010


paulsc writes "Big, big difference between oven sterilized manure mixes, and the untreated effluent of a home septic system + rainwater runoff + grade runoff. "

I've never heard of any farmer outside of those growing mushrooms oven sterilizing manure before spreading it over a field. They shovel it from the manure pile onto the spreader and have at it.

librarina writes "If not enough buffer, how far away should I get from the end of this pipe? Should I not even consider growing anything downhill of the drain field at all? "

You want to stay several feet and ideally around 30' away from any part of your septic field. This isn't so much about your plants becoming contaminated (after all kids are allowed to play on the grass over septic fields) but rather maintaining the health of your septic field. Plant roots and compaction are the two big concerns closely followed by excess water (from in your case irrigation). Around here we aren't allowed to put anything over either the field itself or a reserve area (if required). That includes stuff like garden sheds and hard surface patios.

If it was me I'd do actual raised beds exactly how you are doing seedlings now. There isn't any real need to have your plants in contact with the ground and having the beds higher will reduce the amount you have to bend over.

PS: that pipe looks to be only a few inches below grade which is extremely shallow for a septic field as the pipes are usually at least 18" down. Is it possible that pipe is a part of a french drain rather than a septic pipe? Is your green house in a low spot in your yard?
posted by Mitheral at 5:59 PM on March 13, 2010


To add to what Mitheral has said, those of us who actually farm have practical experience. The dairy down the road to the north of us sells manure by the truckload to the farmers down the road to the south of us. We simply use the manure from our own animals. None of us has ovens or sterilizing systems other than a compost pile and a spreader. I can guarantee you that if you are buying any produce out of season, you are buying it from countries that use manure without any ovens or sterilizers involved. It is a practice as old as agriculture.

I'm glad that the pipe in question is now a moot point. However, as Mitheral points out, it is not a health issue, but an issue of protecting the septic system from root invasion. If you are concerned about the location of your vegetable garden, contact your Agricultural Agent or Extension Service for advice. They have a wealth of information and training and it is all free.
posted by Old Geezer at 9:13 PM on March 13, 2010


Well, I asked the plant biologist that I live with, and she doesn't know of any micro├Ârganisms that will live in both humans and plants (but, she points out, that's not her specialty). This matches my general understanding of biology too. I have a hard time imagining there being a biological risk from growing food plants in the nutrient plume from your septic field. If you're dumping heavy metal salts or something into your tank, that would be a different matter.

As Mitheral says, people mostly worry about damaging the septic system, not the other way around. That said, putting animal manure on plants is safer than putting human manure on plants; and growing stuff near one family's runoff is safer than growing stuff near a city's combined runoff.

You could presumably take a groundwater sample and have it tested. Ideally do this a few times throughout the year (rainy season, dry season, after you have a lot of houseguests, etc). If you're growing stuff for sale rather than your own consumption this might be an even better idea.
posted by hattifattener at 11:09 PM on March 13, 2010


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