What Do I Do With This Sludge? A Wetland Restoration Report and Plea for Advice.

This fall, we completed (mostly) a wetland restoration project I’ve been trying to finish for more than a decade.  A beautiful clearwater meandering stream runs through our Platte River Prairies south of Wood River, Nebraska.  At one point, however, the stream enters the remnants of a sand and gravel mining operation from early last century.  What was left after the gravel extraction was a long lake with big piles of spoil sand all around it.  Before our restoration project began, the stream dumped into one end of the lake and flowed out the other.  While the lake had good fishing in it, it didn’t meet some of our real objectives for the site, including shallow wetland plant communities, and habitat for migratory birds, freshwater mussels, and other wetland animals.

In 2001, in partnership with the US Fish and Wildlife Service’s Partners for Wildlife Program and Ducks Unlimited, we restored the west half of the lake to a meandering stream channel and backwater wetlands.  The west half was the easy and cheap half because the lake was relatively shallow (6 feet and less) and there were big piles of sand right along the edge.  The project essentially consisted of pushing those sand piles into the lake with a bulldozer and using an excavator to create new stream channels. 

The results of that initial effort were encouraging.  We had excellent establishment of wetland and wet meadow plants from our seeding after the construction was done, and the area is heavily used by many wetland wildlife species, including shorebirds and waterfowl, river otters, beaver, muskrats, and many others. 

A photo of a backwater wetland within the west half of our sandpit restoration, ten years after construction and seeding. The water is no deeper than about 2 feet in any location.

Unfortunately, the relatively higher cost of restoring the second half of the lake (the wider and deeper portion) kept us from completing the rest of the project until this fall.  Once again, our partners were the Fish and Wildlife Service and Ducks Unlimited.  This time, the restoration process was essentially the same as the first phase, except that much of the sand to fill in the deeper portion of the lake had to be hauled from further away (from along the edges of what we’d restored earlier).  We recreated several stream channels and adjacent wetlands, and – except for a few finishing touches and one little issue - the site is done and ready for seed.

The right side of his photo shows a portion of the west (first) half of the project, completed in 2001. On the left, we pulled sand from piles that were still remaining after that 2001 phase, and hauled it to the east to help fill in the deeper portions of the lake this year.

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Jonas Davis (left) and Andrew Rieschick (right) with Ducks Unlimited inspect a portion of the new construction, including a nearly-completed shallow stream channel that was designed to function as a wetland slough in low water, and carry streamflow under high water conditions.

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This panoramic of the nearly-completed east half of the project consists of multiple images stitched together.

Unfortunately, it turns out that when you fill a lake with sand, the organic matter on the bottom of that lake gets displaced by the fill sand, rather than just covered up by it.  Eventually, when the lake is nearly full of sand, that organic matter becomes concentrated in the little sliver of lake that is yet to be filled in.  The consistency of that saturated, gooey organic matter (sludge) is essentially the same as mucky quicksand.  Oh, and it smells pretty bad too. 

Here's what the sludge looked like when we were nearly done filling the east lake. It was essentially a long trench, filled with slimy, goopy sludge - up to 8 or 10 feet deep. It'd make a great castle moat, but isn't really what we wanted (or safe) for a wetland.

Dealing with this kind of sludge when filling small irrigation pits and other small bodies of water is commonplace for wetland restoration folks (I’m told) but no one around here has ever seen the volume of sludge that we now have at our restoration site.  Lucky us!  So what do we do now? 

We didn’t feel like we could leave the sludge in place, mainly because there are clearly some safety risks involved with leaving a long channel filled with 10 feet of quicksand-like sludge in the middle of a wetland restoration project.  Our immediate solution was to use an excavator to remove the sludge and a bulldozer to spread it out over a large area of the adjacent low-lying sandy soil.  We hoped it would dry out enough we could then deal with it in some way.  At the present time, we have an acre or two of 8-12 inch deep goop on top of sand along one edge of our new stream channel. 

Here's what the sludge looked like right after it was spread out. It covers about 2 acres of the land adjacent to the new stream channel. It's dried out more since then, but is still wet on the bottom. Anyone want to buy some goo?

So, now what?  After considerable discussion, we figure we have at least two choices:

1.) Leave the sludge in place, disk it smooth after it dries sufficiently (it’s getting fairly dry already) and broadcast wetland and wet prairie seed over the top.  One big question about this option is whether or not plants can grow in that organic matter – not knowing what kind of nitrogen concentration (or other chemical issues) we might have to deal with.  The second, more important question, is what the long term consistency of that organic matter will be like, assuming plants grow in it.  The sludge is sitting on sand that will be frequently flooded whenever the stream rises or groundwater comes up during wet seasons.  Thus, the sludge – though drying now – will resaturate fairly frequently.  Will it always be a sloppy mess that people and animals will struggle to walk through?  Or will the roots of the newly established plants mesh together sufficiently that they will “stabilize” the area fairly well?

2.) Remove at least some/most of the sludge and haul it somewhere else.  We could then disk the remaining organic matter into the sand and seed it – with confidence that we could establish a good wet prairie/wetland plant community on the site.  There are several options for how we could remove and haul the material.  We also have a few options for where to take it – including a neighboring farmer, who would be happy to incorporate it into his sandy cropfield…as long as he doesn’t have to pay for it. 

Unfortunately, removing the material is a little logistically complicated (we’d need a track loader that could move through the existing sludge and wet sand without getting stuck, trucks that could haul the material – potentially big manure spreader/dump trucks, and something to spread out and/or incorporate the material at its new location.)  It’s also heavy on cost, and we’re a little light on cash.

This is where you, helpful reader, come in.  I’m hoping that among the wide array of people who read this blog, or to whom this particular post is forwarded – by helpful readers – someone has dealt with a similar situation and can give me some good advice.  I’m going to be collecting some of the organic matter this week, and will do some greenhouse trials to see if wetland seed will grow in it.  That should help answer part of the question about potentially leaving the material in place.  Beyond that, I am really at a loss. 

Help and advice are welcome.  Good-natured ribbing will be grudgingly tolerated.

Thanks in advance.

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About Chris Helzer

Chris Helzer is an ecologist and Eastern Nebraska Program Director for The Nature Conservancy. He supervises the management and restoration of approximately 4,000 acres of land in central and eastern Nebraska - primarily along the central Platte River. Chris is also the author of "The Ecology and Management of Prairies in the Central United States", published by the University of Iowa Press.
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25 Responses to What Do I Do With This Sludge? A Wetland Restoration Report and Plea for Advice.

  1. Tami says:

    I don’t know how close this project is to yours since the investigators were ADDING biosolids to a wetland restoration, but perhaps you could contact the principals for advice about vegetation establishment:

    http://faculty.washington.edu/clh/wet.html

  2. John Hughes says:

    Chris,

    I’m not sure if the logistics of the site would permit cropping, but planting a nitrogen-dependent annual crop such as corn or wheat on the sludge might be an effective way to remediate the site. This should have the effect of removing excess nutrients during the harvesting process, but it all depends if cropping the site is even feasible; if it isn’t, I would advocate your second option, as I think you will have some significant invasive species issues if you leave the sludge in place. Hope this helps, and good luck!

  3. Dan Staehr says:

    Is there a possibility of “composting” the sludge in some way by piling it up and adding drier organic matter to it? Or just covering it over with dry organic matter in some way to get a different consistency?

  4. Michael Scullin says:

    When I was stationed in California long ago I saw what I can only describe as a “subterranean moldboard plow” which was used to overturn the salty upper portion of the irrigated fields and to bring up unsalty soil from a couple feet down. Inasmuch as you have only an acre or two to mix, were it possible to get such a device in Nebraska it might serve to mix the goo with the sand and create a more “palatable” substrate on which to grow – what? Spartina? Willows? Or whatever. Lots of luck.

    • James McGee says:

      Chris, I would look up the succession of old beaver dams. It seems to me your problem is comparible to what is left over after beavers abandon their dam.

      Most chemical companies deal with their sludge by burning it. This reduces the sludge to a small amount of ash, but it requires lots of coal. For the chemical companies it is more economical to buy the coal and reduce the volume they need to landfill. After burning the
      sludge, they then only have to landfill the remaining ash. Municipalities aerate large tanks maintained at warm temperatures to digest their sludge waste. What is left over is then spread on farm field or sold as milorganite.

      I would think the cheapest thing to do is leave the sludge where you have put it and let it slowly oxidize over time. If low nitrogen proves to be an issue then you could always add fertilizer to speed up the process.

      Probably the best way to dry the sludge out and get oxygen deeper is to get plants growing on it. I do not know what plants would be good for this process. I believe they often use poplar. It will be interesting to see how your experiments turn out. Maybe your wetland plants will grow better on the sludge.

      If all fails, you could dig a hole in the uplands and bury the stuff.

      James

  5. David says:

    Chris,

    Is the organic soil a natural component of the ecosystem you are trying to restore? If not, I would get rid of it as it could preclude you from ever getting to your final endpoint goal due to undesirable system feedbacks. If you feel that you can live with it and are only concerned about establishing a plant community and the battle with invasives, as opposed to hydrological concerns, I think I would just grass it in and hay it once a year after waterfowl nesting season. Removing biomass from the site will reduce the phosphorus levels and help feed your cows. Another option would be to plant a food plot for waterfowl. The DU guys could help you here! I do not think I would mess around with trying to establish a native plant community. At least not right away, too many other priorities. I know of many sites where the site manager removed high organic matter (for building shallow ponds) and spread it over their uplands thinking they would just plant it to prairie. Well, these areas still haunt them today in the battle to get to the desired plant community.

    David

    • James McGee says:

      David, What do you mean by undesirable system feedbacks? I completely agree that soil should not be altered if possible. Spreading pond sludge on an upland site would be a disaster. In this case, I would suggest your friend skim off as much amendment as possible to restore the original soil profile. At a local nature preserve a misguided ecologist had construction crews remove soil from the top of a ridge because it blocked the view of the Nature Center. Despite planting quality prairie plants in this location, each year it is mainly dominated by dogbane and other unconservative species. It’s too bad this Nature Center can no longer restore the soil to the site.

      James

      • David says:

        James,

        Sorry, I was not very clear. We try to look at an ecosystem as a control system and typically refer to the relationship of it major system functions as feedbacks (negative or positive). When presented with a new site and given the endpoint ecological goal, we look at these system relationships and try to identify which ones are reinforcing our endpoint ecological goal and which ones are driving us away from our endpoint ecological goal. The idea is to get the system right before diving into the detailed management practices. And if there are system feedbacks that cannot be corrected, it helps us set proper expectations for the site owner so they know up front what the limitations are. So items like hydrology, nutrient loading, existing plant communities, etc. are commonly looked at. It is perhaps a simple way at looking at things and we are always limited by our lack of knowledge, but it has served us well.

        In Chris’s case, I was thinking that phosphorus may be an issue with water quality? It certainly has been an issue for us. We also believe phosphorus is a positive reinforcement for reed canary grass.

        Hope this helps! Got to head out now. Today’s agenda is buckthorn control. Speaking of undesirable feedbacks! Are buckthorn leaves are high in nitrogen which is bad for oak woodland/savanna plant communities? I suspect it is true but hard to prove. As is the common belief that buckthorn is allelopathic.

        David

  6. This is a guess but I suspect bringing it to the surface and allowing it to dry will alter it considerably. The difference being what I assume were anaerobic conditions in the lake and aerobic conditions on the surface.

    I heard reference to something similar here last week. When Mississippi River backwater areas are dredged to enhance overwintering habitat for fish, sometimes the dredge material is a really fine sediment with lots of organic matter, something the locals call “Loon S—”.

  7. Orvin Bontrager says:

    Smooth the sludge out enough to plant an annual oats crop in very early spring. This will give early cover and allow one to see what other plant species emerge from the sludge. Cut the oats for hay or allow to mature to provide cover next summer and erosion control. If many undesirable species emerge with the oats, one can control them with glyphosate.

    Over seed with the desired seed mixture after the oats are mature or hayed or wait until next fall to seed. I doubt if there is much nitrate-nitrogen remaining in the sludge. There will be some nitrogen mineralization from the high organic matter. That’s OK. Chemicals won’t be a problem, they are broken down and degraded by now.

    Utilize this as a demonstration of a more diverse environment while incorporating high organic matter soils in the landscape.

    • Chris Helzer says:

      That makes good sense, Orvin. I’ll see what my greenhouse trial shows too – hopefully that’ll give me a feel for any invasives that might want to show up, as well as establishment potential for my good plants. Thanks for the input.

  8. James C. Trager says:

    Soil testing and seed bank analysis of the sludge should tell you about the possible vegetation trajectory of this material. But, barring either of these, then plant oats as Orvin suggests, or some other non-invasive annual to give you an idea about fertility characteristics and weediness. It seems it would be better to know about these before plowing the matrial into the sandy substrate, but it also might indicate this sort of mixing may be just the thing to get this restoration going.
    Can you tell us a bit more about what is the predicted wetness and hydrology of the restoration?

    • Chris Helzer says:

      Ok, here is some more information about the hydrology/wetness of the site. Overall, the site is a stream and a series of floodplain wetlands. The stream, in this stretch anyway, maintains fairly constant flow, even in dry periods – it’s got strong groundwater inputs. The long length of the stream, though, also makes it pretty flashy when there are heavy rains within 20-30 miles west of us. When that happens, the entire floodplain can be covered by a couple feet of water – or more. We have some pretty good-sized sandbars formed when that happens.

      The area where the sludge is currently spread out is probably right at the average groundwater level, so the sand beneath it will almost always be wet. This makes me think the bottom of the sludge layer will also be wet much of the time, but there will also be periods where the entire depth of it should dry out. The wetness of the site will make it difficult to get equipment like tractors into the area, so mowing and other mechanical treatments might be tricky, or at least would require us to get some equipment other than our tractor to do the job.

      Let me know if there are other facts/opinions I can give you! Thanks for all the great replies so far.

      • James McGee says:

        Chris, Given your description of the location of this sludge, I would suggest removing it immediately. It is likely a flood will soon wash this sediment to a down stream location. This could cause it to smothering high quality vegetation or stream beds. The Nature Conservancy would potentially be liable for the very expensive clean up/mitigation costs.

        James

  9. Kris Lepine says:

    Hopefully you get a better soil texture to work with after ripping/disking/tilliing the sludge into the sand. After mixing the sludge in, if weeds are a concern after seeding, I suggest adding sterile wheatgrass (Regreen) to your native seed mix. The wheatgrass will quickly germinate and create a sod layer that will stabilize the sludge soil and help prevent weeds from colonizing. The wheatgrass will also help hold the native seed in place. The wheatgrass will die off the following year and vegetation will transition to the native species. I have had good luck with this approach in floodplain wetlands in Washington state.

  10. James McGee says:

    Another idea to mitigate the potential for the sand and silt to move off site would be to temporarily install silt screens. This is typically required for construction projects.

  11. Cyndi Trail says:

    I suggest you contact Dr. Bragg (University of Nebraska at Omaha, Biology Dept. phone 402-554-2641). A few years back, he organized restoration of a prairie stream just west of Omaha where there were three silted-in farm ponds. I believe he had to deal with the same issue, because the largest pond (well over an acre) was a few inches of water over deep anaerobic sludge.

  12. Melanie Thompson says:

    I don’t know if this would help, but my father-in-law lives near Wisner, NE and has started dredging out swine lagoons using a huge backhoe, bulldozer, etc. The stuff he pulls out is tested for composition (minerals, elements, what-have-you) and then is SOLD to farmers for them to incorporate into their fields. If the nitrate content is high and micronutrients are present, I think that possibly you might have a viable product to be sold to area farmers. If you want to talk to my father-in-law about what he’s doing, I know he would be happy to pass along any tips or thoughts on the process that he’s using.

    • Chris Helzer says:

      Thanks Melanie. I’ve had a neighboring farmer express interest in it here too. The logistics of getting it from us to him are still up in the air, and the question of whether/how any money would trade hands is an unanswered question too… I think I’ll see what the results from my little wetland plant germination test are and then go from there. If our neighbor can use it and we can get it to him cheaply, that might work out well.

      thanks for the response!

  13. Peter Dunwiddie says:

    I’d be surprised if there isn’t a fairly substantial seedbank of some kind already in the sludge. Whether they are species you would want to have growing all over there is another question. And whether they would even germinate and grow in their happy newly relocated home also remains to be seen – things you might be able to get a hint about with your greenhouse experiments.
    The decision seems to come down to – is this sludge a problem, an asset, or just a smelly inconvenience (you could say the same about a lot of things in life)? If you conclude it’s a problem, then getting rid of it will be necessary. I generally opt for the cheap solutions (within reason), so try the Tom Sawyer approach and convince someone that it’s so precious to them they should pay you for it, or at least let them haul it away for free. If neither of those approaches work, you might try a few things to see just how fast you can make it disappear on its own. There are various ways to encourage the oxidation of organic matter – peat farmers are discovering them daily. And if none of this works and it’s going to have to stay where it is, various of the stabilization suggestions others have made sound promising. “If life gives you lemons, make… an oatfield?”

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