Mass (and volume) murder. How to compute the "body" count?February 6, 2011 7:39 AM   Subscribe

Help me write yet another science fiction story. I need to figure out the environmental damage resulting from an accidental sewage spill.

As a part-time writer of science fiction, I occasionally ask the Hive Mind’s help with technical matters. This has worked out well for me in the past -- here and
here being two examples that resulted in story sales. I’ve got a new one in the works and have set myself a problem I can’t solve because I lack some specialized knowledge. And I don't even know where to go looking for it.

The main plot point concerns the accidental release of (say) 100 gallons of raw sewage and chemicals onto the ground in Bucks County, PA, during June in an unspecified future year by a flying nightclub that has set down in a field to provide an evening’s entertainment. The release is from the club’s waste tanks. Environmental regulations have become so strict by this future time that huge fines and even jail sentences can be levied by officials from a government agency I call The Environmental Protection Task Force.

Fines and so forth are partly based on the amount of damage caused. So, my question: How many organisms (and for bonus points, what kinds of organisms: nematodes, microbes, earthworms, etc) would such a spill be likely to kill? The spill is not noticed for an hour and a half. Also, is there a way to roughly compute the volume of earth/dirt/soil affected? I want my sinister agents to be capable of figuring the volume of dirt and the “death toll” on the spot based on soil consistency, rate of seepage, and so on.

posted by Guy_Inamonkeysuit to Science & Nature (13 answers total)

I think you would need to be more specific about the chemicals involved. Raw sewage isn't the most toxic stuff, really, as long as you don't drink it and the quantity is limited -- it makes a fine fertilizer, for example, and has been applied to fields for thousands of years. The real issue (again, ignoring the chemicals part of this) is going to be risk to humans in terms of oral/fecal contact, risk to a local stream if too much raw sewage gets dumped in at once (but that will take a lot more than 100 gallons to have any real effect), and of course the aesthetic damage of a stinky mess.

Having said all that, there might of course be an initial kill of some soil organisms, but again that would be balanced by being followed by a later "bloom" as the nutrients in the sewage get filtered, absorbed, and processed by soil organisms and plants. Remember that a septic tank is putting that same stuff (minus the solids which get pumped out every year or so) out through the drain field just under the ground surface.

So does it have to be sewage? Or can it be a chemical or fuel oil spill, which will much more drastically impact a patch of ground?
posted by Forktine at 8:05 AM on February 6, 2011

Response by poster: I was wondering about that (sewage versus chemicals), as it seems as if the chemical spill would be better for my purposes. I'd like the release to be pretty toxic. It doesn't necessarily have to be sewage. Perhaps think of it as the noxious brew inside a porta-potty...?
posted by Guy_Inamonkeysuit at 8:11 AM on February 6, 2011

Rocket fuel is pretty damn toxic. The EPA just announced it's going to regulate perchlorate, one ingredient, but I know there are even more dramatically toxic compoments too. Maybe your flying nightclub dumped a tank in the field?

For an even more nuanced futuristic legal regime, you might want to look up the current law about discharging pollutants from ships into the ocean. Seems like in a flying nightclub future, this law would be amended to cover aircraft. You might also want to research CERCLA, the main federal environmental law, which already provides for some pretty stiff liability, in theory anyway. There is also federal criminal liability for pollution, but I'm not sure of the basis. Try googling "Libby, Montana," which was the center of a big criminal environmental case about asbestos mining.
posted by yarly at 8:29 AM on February 6, 2011

Response by poster: Thanks, yarly. The club's using gas turbines, I think, not rockets. Still, that's an angle I hadn't thought of.
posted by Guy_Inamonkeysuit at 8:52 AM on February 6, 2011

100 gallons of waste sewage might drown some worms the same way as 100 gallons of water. Not sure if that is what you are looking for. Generally sewage is not good to drink but is not really harmful in the way that chemicals are harmful.

If I were you I'd extrapolate an actual event to a future as you see it. Then you don't have to really guess. Take for example the equivalent of a Gulf oil spill in this future world or something similar. It isn't hard to find many examples by searching Google news.
posted by JJ86 at 9:20 AM on February 6, 2011

I think it'd be entertaining if there were huge fines and jail sentences for spilling plain old gasoline/diesel/kerosene/etc. It's got plenty of nasties, but there's only so much we can do in this day and age to keep it from getting everywhere, when every gas station on every corner has/had leaky tanks, and there are people who still think these chemicals make a good weed killer.
posted by gueneverey at 9:37 AM on February 6, 2011

What if your nightclub clientele was using a lot of exotic drugs, which appeared in their excreta, and then went on to... I don't know, soil organisms on X doesn't seem that dramatic. Or what if there was an airborne illness that drifted downwind and infected the residents of a small town? Or what if something filtered into somebody's well?

As for area, it's roughly 400 liters of fluid; assume 5cm depth when it spreads out, since it's sewage, and you've got 8000 square centimeters of surface affected. That's a square 90cm on a side, which (converting back to Imperial...) is about 38 inches. Gosh, that's not so big, is it?
posted by richyoung at 9:43 AM on February 6, 2011

Response by poster: It may not be so big, but that's still a substantial kill. According to my research, in just one pound of soil, there are more than 460 billion organisms; in a cubic yard of soil, something like 740 trillion.
posted by Guy_Inamonkeysuit at 9:46 AM on February 6, 2011

Rich's math is off. 400 liters is 400,000 cubic centimeters, which at a 5cm depth would cover an area of 80,000 square centimeters, meaning a rectangle about 2.8 meters on a side or a circular area 3.2 meters across. Also, that's the volume of the spill itself. Soaked in, it would affect a much, much larger area.
posted by jon1270 at 10:10 AM on February 6, 2011

Unless it is rocket fuel or diesel or something nasty like that, it isn't going to kill those trillions of organisms. The sewage might drown a few, but it will also feed billions more. Fuel oil, however, could leave that patch of ground pretty sterile if it was given time to soak in. It isn't hard to find out the impacts and costs of remediation, either -- you can end up needing to dig out the contaminated soil, try and trace groundwater plumes, and have downstream fish and wildlife kills.

But that's if it's nasty stuff; sewage alone won't do it.
posted by Forktine at 10:11 AM on February 6, 2011

I agree w/Forktine that it hardly makes sense to think of sewage purely in terms of what it might kill, since it contains all sorts of nutrients that would actually benefit other organisms. But then, maybe the senselessness of it fits your story idea nicely, given that the EPTF agents are supposed to be sinister?
posted by jon1270 at 10:18 AM on February 6, 2011

Best answer: So here's probably more than your require, but it's Sunday morning and I'm just finishing my coffee.

A 1 to 1-1/2 hour release time isn't very much for a spill to do anything, but there are a bunch of factors you can tweak to get the spill to do what your story needs. The key ones are:

1. the physical morphology of the site, how close water courses are, what the soil type is, where the water table is;

2. the land use, are you in farmland, a residential area or an old industrial park;

3. the physical and chemical characteristics of the wastes spilled. Important factors include how easily it dissolves, how much will evaporate, it's viscosity and density.

Soil type is one thing your agents who deal with the spill are going to be very interested in. There are no standard "types" for soil, general descriptors yes, but specific types, not really. It's conceivable to think that this might come in the next twenty years of so, particularly for regulators. I've been in a couple of meetings where this has been discussed. Your agents might want to refer to something like "eco-system type 12B", for example to describe a certain micro-system of organisms and soil types. As I say, nothing exists as a standard terminology here now, so feel free to make up something as you need it.

Physical morphology, what the site looks like, is key. If the spill happens in the middle of a field, it will not have a large effect. A couple hundred gallons isn't very big and penetration in 1 to 1.5 hours would be small for moderate-viscosity sewage. Current technology would be to scoop and bag, remove the affected soil, maybe a few tonnes worth and everything would be over. Land spills on the surface are typically very limited in extent, maybe a few hundred square yards, going at most a yard or two in to the soil, not deep enough to be a ground water concern. Soil is very absorbent. The features that will make this into a spill that would get people excited are access to a water course or loose soil/gravel over a high groundwater table.

Water is the key to mobilizing a spill. Wastes spilled into a stream can go tens of miles in a single night, and potentially effect many, many people and ecosystems. If you want a big impact, with lots of potential damage to ecosystems and people, have the stuff leak into a lake or a stream. Terms: water floating on the surface will be called a "slick", wastes moving in the water, dissolved in the water will be called a "plume". Slicks will travel more slowly (a few miles) than plumes (tens of miles).

As I said above, soil transport of your waste plume will be very limited in 1 to 1.5 hours, but moving water can transport the spill a very long way. Groundwater contamination into artesian flow, underground rivers, will be more limited in scope than surface water spreading, perhaps only a half-mile or maybe two, but won't be visible. If you want a slow burning problem with people getting mysteriously sick at various times, ground-water contamination is the way to go. In groundwater, they'd call the contamination a plume.

The chemical and physical properties of the spilled material are also pretty important to how big this will end up. I'll give you a few examples.

The spill of a high-viscosity material that isn't very water soluble, like heavy or residual fuel oil will be minimal in extent if spilled in soil in 90 minutes. Spills onto water can be a real problem, but ground water won't be a concern. Spill containment is effective and can be used in this scenario.

Low viscosity, insoluble materials like kerosene or gasoline can penetrate down to the water table and spread in an artesian system. Speed and how much equipment is available for earth-moving is pretty critical here. If they catch it early enough, your responders may be able to dig out the area fast enough to stop larger contamination. If they don't catch it early enough or if they don't have the equipment, the spill plume can reach the groundwater and spread over a fairly large area, possibly several hundreds of yards, perhaps even a mile or two, without much remedy possible (at least with current technology). At that point, the agents are looking at a months-long (perhaps years-long) clean-up effort. Spills into water of these materials are even more exciting. Spill containment has to be deployed very quickly to be effective and transport can be miles or tens of miles. Weather is very important factor for on-water spills. Damages can run, in the current day, into the millions because of the large areas affected. Non-soluble materials tend to linger in the environment and can easily cause long-term impacts in an ecosystem.

Low viscosity, highly water-soluble spills, like alcohols or ammonia, are the worst case, in terms of spill area. They penetrate quickly though most soils and would be the first kinds of materials to reach groundwater. Plumes of solubles are much larger than those of insolubles and you could see effects miles away after even 90 minutes with high artesian flows. Spills of solubles into water are a common cause of mass kills. A soluble plume travels not on the surface of the water like most insolubles do, but through the water. This can cause a front of toxicity travelling at above the speed of the current (speed = current + rate of diffusion). These sorts of spills are effectively impossible to contain. These sorts of spills tend to cause a "short, sharp shock", high inital impact, but generally no lasting effects. There are certainly exceptions, like metal toxins for example.

Toxicity and effects can take many forms. The common one most people think about is acute toxicity---poisoning leading to immediate death. More subtle are sublethal effects which render a damaged ecosystem less productive. These often take the form of impairment to juvenile development or reproductive dysfunction. Endocrine disruption is one of these failure modes, but hardly the only one. Secondary effects are also something to worry about. A common problem in water systems is reduction of oxygen, either by chemical degradation or by biological breakdown of the contaminant. Your agents might need to refer to chemical oxygen demand (COD) or biological oxygen demand (BOD). Oxygen depletion can cause kills even with non-toxic spill products. This is one of the major concerns with sewage spills. Finally, there are concerns of non-chemical dangers, mostly things like bad bacteria or viruses getting into water supplies. Your agents may also need to be concerned about nano-particles and even nano-technology escaping too.

Land use is important because that ties into how bad the spill is judged to be. Under most current legal regimes, there's some segregation between industrial lands, residential lands and parkland/natural reserves, in roughly increasing order of requirements. This will be very important to your assessors, as it determines the levels of fines/penalties they can impose. A spill on an old industrial site with no residential use nearby is going to be much less of a fine than a spill into a sensitive ecological reserve that's been designated a National Wildlife Reserve or A UNESCO Heritage site, for example. If you want to ratchet up the penalties, make the spill transport into a designated ecologically-sensitive area or near a school, for example. Even today, affecting a site like that could put fines for a spill of that size you propose potentially into the millions.

As to the question of figuring out the organisms present, your agents will have an "ecological sensitivity map" (that's the current phrase) for what the receiving environment will have in terms of what lives there. This is an atlas which lists areas where sensitive organisms live ("resources" in current parlance) as well as the eco-system type (see soil discussion above). This is the info that they would use to determine what organisms had been affected by the spill. Even today these environmental sensitivity atlases are fairly comprehensive. It's not hard to imagine that they would have earthworm and soil microcosm data fifty years from now.

The process for assessing damage is what your agents are going to concern themselves with. The over-arching framework today is called "natural resource damage assessment" (NRDA) in the US, though different terms are used in other parts of the world. NRDA is specific to current US federal regulation. The phrase "damage assessment" is common though. A particular bit of terminology, particular to oil spills, but increasingly used for all spills is "shoreline clean-up assessment technique" (SCAT---yes, we talk about SCAT teams and SCATing constantly on spills), which is used to assess damage (and clean-up progress) on shorelines. Shorelines are very important as that's a usual endpoint for spilled materials, fouled debris and dead organisms.

Damage assessment is multiple things: inspecting (and measuring) the sites in person, sampling and measuring the environment with instruments, and finally modelling the spill on computer to predict future impacts and to hindcast the spill so that you can confirm that what you think happened is consistent with the physical and chemical and biological evidence.

Finally rocket fuels: The most common are hydrocarbons, kerosene and napthas. These are moderately toxic, low-viscosity, non-soluble materials. More exotic fuels include hydrazine/MMH/UDMH. These are very nasty compounds that are highly water soluble and quite toxic. Alcholols, methanol and ethanol, are sometimes used by hobbyists. Both are water soluble and low-viscosity. Methanol is quite nasty, ethanol less so. Aluminum fuels (!) wouldn't be a concern for most spills unless they're in some exotic form. Most aluminum compounds would not be very toxic anyway.

So there's a big brain dump. Sorry if it was more than you were looking for. Feel free to memail me if you have more questions, or I can answer here.
posted by Anonymous 5\$ Sockpuppet at 10:27 AM on February 6, 2011 [4 favorites]

Response by poster: Well, thanks to everyone, and I'll probably use bits from all answers -- but Anonymous 5\$ Sockpuppet has the winning entry. I'll let everyone know how the story turns out. Thanks to Forktine for suggesting rocket fuel, Can't use that but the fuel for the turbines should be nasty enough if I tweak circumstances a bit.
posted by Guy_Inamonkeysuit at 8:54 AM on February 7, 2011