Treating Soil Flooded with Toxic Water

Hello everyone! A rental property where I was regenerating the soil to cultivate organic vegetables flooded due to its’ location after an especially wet rainy season. There was sitting water on the property for about two months (largely run-off from town, including overflow from local pit toilets…etc.). The water is finally receding, and I would like to have one more growing season while we finish out our lease, but I am nervous about planting in potentially contaminated soil. Any recommendations? Wait the standard 90-120 days until harvesting any vegetables to eat? Wait for the soil to dry and turn it before planting? Avoid it altogether? Thanks for your feedback!

Well, I’m not an expert on this, but my gut feeling tells me of two options:

  1. plant crops that don’t touch the ground
  2. separate vegetables from the ground by heavy mulching. That will also create a habitat for soil life to quickly break down contaminants.

That applies only if there aren’t any poisonous contaminants like heavy metals. Those would need to be taken care of by special plants… On the other hand, where we live, people don’t know/care about soil contamination at all. Stuff is planted right next to the highway and then sold…

Boy, I can sympathize with you, and I wish you all well :sunny: I wonder if some sort of remediation would work, like myco-remediation, which might do something about heavy metals, but I honestly don’t know. And, I wonder if it could touch any bacterial contamination. You might want to look into bio-remediation. :sunny:

@Roberto_Walle Robert, what do you think?

I hadn’t thought about the extra benefits of heavy mulching for this season, but that sounds like a great place to start! Especially for a fairly simple, short-term solution. Thanks!!

It’s really difficult to advise without soil tests, both chemical and microbial. A raised garden bed (layers of organic matter, compost) may be safer for this season

For heavy metals, a lot of them are chemically bound quite tightly to the soil. Cadmium may travel into the leaves of some plants, but lead won’t. For lead, it’s more likely consumed when veggies aren’t washed properly and soil is consumed directly. Do you know what sort of compounds are present, is it possible to get a soil test?

For microbial contamination, if human faeces are involved, there are all sorts of nasty things which might be present, google problems arising in areas which have open defecation for more details. It would be difficult to just wash it off, as the water may be contaminated also if the whole region was affected, and microbes are too small.

Overall either wait a year, or try raised beds, thick mulch, with high up plants like tomatoes, corn, don’t attempt lettuce/ salad greens.

Hello Kelly,
I have been following conversation on your posted topic. Soil test even testing the receding water would be very helpful. To start with or without soil or water test analysis, I would introduce Indigenous Micro-Organisms (IMO). I have found it very effective in environmental remediation and would be very good for soil reconditioning before planting and during crop growth.

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Ok, thanks! I’ll have to look into that.

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Thanks for your feedback! If it was soil I was going to need to work with long-term, I would definitely be doing soil tests…etc., but since we only have part of a year left to plant, and we are a fairly small organization, it’s tricky to know how much of our time/resources to put into regenerating the soil.

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I worked with farmers primarily on crop insurance matters both during and after two significant flood event in the western Iowa portion of the Missouri River Valley. Many of their fields were under water for up to three months. Once the water receded from their fields the two most pressing issues were removing or incorporating sand and regenerating the soil biology that was no longer active due to the anaerobic conditions from the extended time under water. Contaminates of various sorts were present and a concern to which I’m not qualified to address specifically. The following link is from Iowa State University on post flood management practices to restore the productive potential to fields that were flooded for extended time periods. Management Considerations for Post Flooding Soils | Integrated Crop Management

I would not spend money on tests myself. I don’t think they are really going to help you avert risk relative to the costs of the tests and not knowing what contaminants to test for. Most everything should be pretty diffused and natural systems have a way of breaking things down. I am curious about pit toilets though. Where do live? Mostly in the states pit toilets are a thing of the past. Did you mean those chemical toilets? Or are you in another country outside the US? I like raised beds because then you are likely to avoid much of the flooding in the future and it helps keep the microbes aerobic and mulching is a great idea for any garden and will help separate the blights in the ground from the crops. Use some bleach water to wash the first produce if there are really pit toilets around that could create unsanitary conditions for leafy vegetables such as lettuce and radishes that grow quickly. Once you have 2 months into production I don’t see how you have to worry much. Heavy metals are not likely going to be a problem. Generally, where those are a problem is on industrial sites and where people have had burn piles for garbage. Labeling the dates of food in the fridge and throwing it out on time and avoiding green potatoes and too much nutmeg or improper cooking of kidney beans are likely going to be more important relative to the risks you are going to encounter. Everything is about risk relative to other risks… Radon detection in your basement, sunscreen, balancing hormone levels in the body, exercise, etc. are often ignored and minimal risks are often trumped up.

This is super helpful! Thanks so much for your feedback!

Thanks so much for your feedback. We are located in Guatemala, so I’m almost positive that the floodwater would have included some level of sewage mixed in with it. A follow-up question for you… We are already working with raised beds (without a structure around them, just rows of planting beds that are raised about a foot higher than the paths around them). Some of them were entirely under water for a month or more, a few of them on the highest part of the property were not fully covered with water. Most of the beds already have hardy weeds which grew back quickly as the water receded. Some of the ones that stayed just above the floodwater still have celery, onions and some herbs that survived. Would you recommend turning the soil in the beds to expose more potentially harmful bacteria to the sun, or would you hand weed and avoid disturbing the soil, allowing the microorganisms to do the work of “cleaning” the soil?

I welcome others to comment here. There is “wisdom in a multitude of counselors” my dad would say based on Proverbs. I would harvest what you can harvest and wash with chlorine/bleach-water dilute mix and cooking as much reduce risk almost entirely. Here is what I do: Plant tomatoes in the highest beds because they will not tolerate residual water and also outside edges where they can get more wind flow and mulch there first as your #1 priority for thick mulch. Plant cabbage on the edges/sides of beds since they take up a lot of space and can fill between the beds and plant okra or kale just above the cabbage but plant them twice the normal spacing and tilt outward to 60 or 70 degrees when the plants start to crowd every other one so you can capture all the light entering the area between the beds. Weeds can be used as mulch if they have not gone to seed and you turn upside down ones prone to regrow. If you are entering a dry season put lots of organic matter in the planting hole (in situ-composting) and I add human urine as my fertilizer (around the outside edge of the OM filled planting station but not on the plant) if there is not a strong cultural rejection of this idea. I have use almost no manure, I have never made compost except in this method. As far as bang for buck with time I don’t find I need manure or prepared compost when I use this method and then you can focus on planting and planting and more planting instead of so much prep work. If this happens again plant vining winter squash/pumpkins in transplant cells (i.e. water bottles) and when water level is starting to recede plant them out on the edges of beds. They can grow sideways on the bed and then the vine can be moved to the waters edge and dirt can be placed on top so it can reroot. That way you are utilizing receding water to its maximum level and you can maximize the space used as the water recedes. You can even mound the soil up more when you do this to get an earlier start. Engage the church to sort out how to get more land into production in high value crops (most cases do not need to plant subsistence crops unless there is no market). Grow large quantities of the highest income vegetables on all the land you can find using this less labor intensive method. Eat the weeds that you can eat, and the #2 vegetables, take the #1s to the market and bring back from the market anything edible that they are throwing out to give to animals or for human consumption if it is still fit to eat. This system allows maximal income growth and allows income for hiring labor and procuring machinery and more land. When OM availability is low grow perennial legume plants and trees as intercrops for mulch and OM in the planting hole.

That is just a row of Okra or Kale around the outside edge of the bed and can plant something else in the center of the bed, preferably something that does not require a lot of airflow to minimize disease and is more shade tolerant.

Okay, I already have a planting plan, based on the needs of the ministry that we serve and what we can grow at our altitude/climate, but I am interested to try some in-situ composting. Thanks for the info!

Can you give us a report on what you finally did and how it worked out?

Hello! Yes, just note that I am working part-time and have limited training - I’m a good gardener, but not much of a scientist! However I’m happy to share what I did and my observations since then.

I waited until the dirt was fairly dry, then turned the soil in half of the raised garden rows, and hand-weeded the other half, because I wanted to compare the two methods for “starting over.” Since then, I haven’t noticed much of a difference between the two halves as far as productivity nor soil quality.

I did a chlorine shock-treatment in our hand-dug well, and I started by only planting slower-growing, non-root veggies such as swiss card and herbs and celery. Faster-growing plants such as spinach and lettuce I planted in a raised bed with dirt & compost I brought from a different location. I mulched everything heavily (with leaf mulch) to try to help avoid extra exposing the crops to any potentially lingering bacteria. About three months after the flood waters receded, I started planting root crops as well.

Overall, the soil didn’t seem as “rich” as it did before the flood, and even six months later I see a lot fewer earthworms, which is sad. But there is now a decent amount of life in the dirt, and good diversity of insects around. I have had more issues with some diseased chard, but that could be from any number of things. However, we are wrapping up our project at this property, because it is looking like it will flood again in a month or two, so I’m not investing much time into investigating the hows and whys anymore!

Well, if the area floods regularly, you could have done something chinampa-like… Natalie Topa has done this in the Nile basin in South Sudan.