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I own a family house that used to until about 20 years ago have a sewage collector pit in use. It has been abandoned for about 20 years now. It has concrete walls and roofing and gravel on the bottom. It was never disinfected or treated in any way.

My question is whether it is safe to go down inside the pit or it could be infectious?

EDIT: My intention is to use it to dispose of plant matter.

EDIT2:

  1. I originally asked this question after I went in because I was afraid it might be infectious (since it was storing human poop for many years before sitting empty for 20). Gases accumulating never occured to me, which was stupid of me, but now I know, since many responses and comments pointed it out. This is something I will take into account and make sure everyone who might ever want to do anything with the pit does too. The pit itself is structurally sound, there is no chance anyone in the next 50 years will ever fall into it by accident or anything like that.

  2. The plant matter too I already put in when I submitted this question, since, as I've written above, it has not occured to me this could pose a danger (that's why my question was originally about the infection risk). So it was a done deed, not an actual decision I took after being aware of the possible issues. A very important additional info is that this 'plant matter' is actually half rotten (as in brown rot) dry wood, it is not something that will vigorously decompose and produce a lot of gases very quickly. Another important aspect is that this pit is safely closed (though it has a grill covered opening with a diameter of about 15 cms on its roof that exits into the garden so it is very definitely not a hermetically closed space) and there is literally no chance anyone ever going inside without taking precautions. I know because it's either me, or someone I might sell the house to, but if I sell it I will most definitely tell them about the pit and the possible accumulation of CO2 and the precautions they need to take. Also, I highly doubt I will ever descend as I really have nothing to do there, I just went down once (before putting anything there and before asking this question) because I was curious and, as it turns out, stupid.

Benjamin Márkus
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    Is it well ventilated? – Andrew Morton May 04 '21 at 11:48
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    "sewage collector pit" is this the same as a [septic system](https://www.epa.gov/septic/types-septic-systems)? – FreeMan May 04 '21 at 11:55
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    Would be concerned about having enough air to breath in the pit, depending on depth. Have a rope and someone to pull you out. Infection risk is usually for open cuts in skin. Would not be on my top ten places to enter, except for repairing. – crip659 May 04 '21 at 12:05
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    What is your reason for going in the pit? – MonkeyZeus May 04 '21 at 12:10
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    Don't go down there unless you get a confined space blower and vent the pit for 20 minutes first. – JACK May 04 '21 at 12:29
  • It is properly ventilated, it has a large hole on its roof and another one of smaller diameter. My reason to go in is that I intend to use it to dispose of plant matter from my garden I cannot put elsewhere. – Benjamin Márkus May 04 '21 at 12:38
  • Why not use a compost bin? Many designs from small to large. – crip659 May 04 '21 at 13:15
  • I use a compost as well but I have no room for another one. – Benjamin Márkus May 04 '21 at 13:16
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    Keep it sealed (maintain the lid properly) and it's a perfect way to dispose of bodies. [or so I've heard] :-) :-) – Carl Witthoft May 04 '21 at 17:53
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    It might be properly ventilated for sewage purposes but unless it's properly circulated for breathing purposes then you will die. – MonkeyZeus May 05 '21 at 11:42
  • I believe the term for this is a '[cesspool](https://srcontracting.com/cesspool-vs-septic-tank/)' which might help you find more information. – JimmyJames May 05 '21 at 13:22
  • @CaiusJard infectiousness and toxicity are separate issues. As far as the toxic byproducts of decomposition are concerned, concentration is everything. Most decomposition doesn't occur in environments where its byproducts can accumulate like they can in a septic tank. – Will May 06 '21 at 11:06
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    The danger isn't from the former contents - if poop remained infectious for 20+ years then the entire planet would be infectious, considering how many hundreds of thousands of years of pooping (and dying, and rotting away etc) all the creatures on earth have done – Caius Jard May 06 '21 at 11:25

1 Answers1

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Do not enter the pit.

Without proper ventilation, old septic tanks (and this sounds not enough different to matter) are prone to collect gasses that will kill you (without you noticing. And the people who go in to try and help you, until one is smart enough to use a self-contained breathing apparatus to recover the bodies that died before them.)

It should have been filled with gravel to prevent access (and deaths) when it was decommissioned.

Direct link to top result for septic pits with vegetation killing people.

Ecnerwal
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    See also: https://diy.stackexchange.com/a/91102/18078 – Ecnerwal May 04 '21 at 12:34
  • I think it is properly ventilated, it has one large opening on its roof and another one of smaller diameter. What kind of gases can build up? – Benjamin Márkus May 04 '21 at 12:40
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    Well, then, the answer linked in the comment above applies **precisely** to your planned use. Without a blower, it's not ventilated. The one linked there killed 3 people with grass clippings. I've edited to put the link in this answer as well. Debatable if it's really methane as the newspaper claims or just bad reporting (CO2 collects more easily, since it's heavier than air - methane is lighter than air.) – Ecnerwal May 04 '21 at 12:43
  • Yes, that link is very useful. I will not go in unless using a blower first. – Benjamin Márkus May 04 '21 at 12:49
  • Would also have a second or more person/s(not in pit) holding a rope tied to you, in case. – crip659 May 04 '21 at 13:17
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    Totally agree with Ecnerwal. CO2 is heavier than air and will accumulate in the pit. Like Ecnerwal said, it should have been filled with gravel and capped off. – George Anderson May 04 '21 at 15:27
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    Also, "plant matter" needs oxygen to decompose. in a mostly sealed bit, you'll create an anaerobic sludge that neither God nor man would ever want to touch. – George Anderson May 04 '21 at 15:30
  • It's not sealed that much, plenty of oxygen will be able to go in, I highly doubt it would become an anaerobic environment. CO2 will accumulate for sure, but nobody will go down for years I will make sure of that. In a few years it should be fine - but I will do every precaution that has been recommended here before going down after the plant matter has decomposed. – Benjamin Márkus May 04 '21 at 18:43
  • I do not intend to use it regularly, just this one time I will put a huge amount in I really cannot put anywhere else and leave it be as long as it's needed. – Benjamin Márkus May 04 '21 at 18:49
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    Upon doing a bit of reading it seems it will become somewhat anaerobic. The possible disadvantages are smell because of H2S and the mentioned build up of CO2. Should the former happen, I intend to take care of it by filling up the pit with water, which will also push out any hazardous gases. The latter I will take care of 1) by not entering, 2) if I must I will ventilate it very thoroughly. – Benjamin Márkus May 04 '21 at 19:45
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    @BenjaminMárkus If you did that, you'd playing with a potential death trap. Drop the idea and fill the pit in. Even if you will always remember to take suitable safety precautions, someone else blundering into it won't know too. Is having a giant compost pit really worth the chance of killing somebody?!?! – Dan Is Fiddling By Firelight May 04 '21 at 21:21
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    @BenjaminMárkus do you not have a landfill nearby that will accept green waste? Rent a trailer for a day and make a few trips if necessary, it's not free but it's much less likely to kill you or someone else – llama May 04 '21 at 22:22
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    A rather more [comprehensive list](https://inspectapedia.com/septic/Septic_Tank_Accident_Prevention.php) of septic accidents. – J... May 04 '21 at 23:03
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    Yeah, really. Confined spaces tend to pile up bodies of rescuers. Some of the worst tragedies out there, aside from electrical drownings. One rescuer knew about the risk but had to take off the air tank to climb through the hatch... was unable to get it back on in time. Anyway, 20 year old homo sapien guano is pretty good fertilizer. I would simply demolish the whole thing and recover the fertilizer. – Harper - Reinstate Monica May 04 '21 at 23:56
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    @BenjaminMárkus Even if you don't care about your own safety, having a death trap like this on your property is a liability *nightmare*. You could be held liable for someone else entering it and getting hurt/killed. Until you get this filled in, you should probably also post [warning](https://www.inkace.com/ansi-vert-danger-breathing-apparatus-sign/) [signs](https://www.mysafetysign.com/carbon-dioxide-cause-suffocation-ventilate-entering-sign/sku-s2-0814) of some sort. – bta May 05 '21 at 00:03
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    @BenjaminMárkus Why are you ignoring the warnings that we have given you? We have given you one very simple precaution that you need to take: do not enter the pit. You do not know how to make the pit safe to enter. If you think that you *do* know how to make the pit safe to enter, then there is one thing that you ***absolutely must*** do, and that is to write down your plan and then take it to an expert on hazardous confined spaces (perhaps the fire department, I don't know). If you don't have an expert telling you that your plan is safe, then **your plan is not safe**. – Tanner Swett May 05 '21 at 12:17
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    @BenjaminMárkus Please keep in mind that if you do this wrong, you may kill not only yourself but several of your loved ones. It has happened before and it will happen again. – Tanner Swett May 05 '21 at 12:19
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    @BenjaminMárkus everything you are saying/planning sounds incredibly stupid and completely unnecessary. Just find another solution that doesn't include a deathtrap. – eps May 05 '21 at 14:58
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    A community or commercial composting operation will in most cases be very happy to accept green matter for free, and will turn it into useful compost. Community ones may even exchange some compost for the green matter. Commercial ones are happy to have it to cut the food waste with. – Ecnerwal May 05 '21 at 15:02
  • Thank you for all the reflections. I appreciate and will follow all precautions mentioned. I do not agree this is a 'death trap' or anything of the sort any more than everything around your house that has the potential to kill you if you are acting stupid is a 'death trap'. Nobody will do anything with that pit for the next 20 years as was the case for the previous 20 years. I am absolutely, 100% sure of that. No need for all this drama, in my opinion. – Benjamin Márkus May 05 '21 at 18:41
  • One additional detail: it is not fresh green clippings or anything like that I put in, but mostly rotten, fallen wood branches and twigs that have been raked from an area of my garden, and a few mostly rotten logs that have been sitting, drying and rotting outside for years. The moisture content of the whole setup is way below and the carbon content (in terms of C/N ratio) is way above than the ratio needed for a proper anaerobic decomposition process. No need to worry this much, I'm not stupid. – Benjamin Márkus May 05 '21 at 18:44
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    don't go near it. don't speculate what will be in 20 years. animals, children. I bought a house with foundations dating back to 1890. cesspool was empty, looked clean, most of the "ceiling" had been removed. I was not aware it had a second floor below connected with a pipe. nobody was. I have no own memory of climbing down, and woke up next day in hospital. also, one of my grand-grandparents reportedly died in an abandoned pit in the countrside. have it filled up. – dlatikay May 05 '21 at 20:47
  • Oh god, I'm starting to regret I even asked this question. Let's put it this way: is putting dry wood into a cellar dangerous? I wonder how many of you would call _that_ a 'death trap' and the sort you've brought up. It is essentially the same situation. Putting this way the answer is: yes, it could be, take care of proper ventilation before entering. Which, as I've written down about 10 times now, I will. Structurally it sound as a nuclear bunker, noone is going to accidentally fall in. All is fine, please trust my judgement, I understand what I am doing. – Benjamin Márkus May 05 '21 at 20:59
  • Most of the feedback is to some imaginary monster version of the actual situation I am in and tried to describe, this might explain the nature of my responses. But there is no way anybody will believe me here so I'm kinda giving up. – Benjamin Márkus May 05 '21 at 21:55
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    @BenjaminMárkus based on the edits you added to the question since the above exchange you're lucky to be alive already. You entered an environment you had no way of knowing would be any different from the multiple cases of tanks that kill people each year, and you still think the warnings you've received represent "some imaginary monster". You clearly lack the competency to evaluate risks of the kind you're playing with, and your misplaced confidence will be very little mitigation if you "give up" and wind up culpable for the deaths of others. – Will May 06 '21 at 10:59
  • This is an issue with large ships btw, if you go down in a non ventilated area you may pass out and die. Watch this: https://www.youtube.com/watch?v=uNVj_JpZia8 same problem – Thomas May 06 '21 at 17:20