Cleaning up the large number of groundwater contamination sites is a significant and complex environmental challenge. The environmental industry is continuously looking for remediation methods that are both effective and cost-efficient. Over the past 10 years there have been amazing, important developments in our understanding of key attenuation processes and technologies for evaluating natural attenuation processes, and a changing institutional perspective on when and where Monitored Natural Attenuation (MNA) may be applied. Despite these advances, restoring groundwater contaminated by anthropogenic sources to allow for unrestricted use continues to be a challenge. Because of a complex mix of physical, chemical, and biological constraints associated with active in-situ cleanup technologies, there has been a long standing focus on understanding natural processes that attenuate groundwater contaminant plumes. We will build upon basic environmental science and environmental engineering principles to discover how to best implement MNA as a viable treatment for groundwater contamination plumes. Additionally we will delve into the history behind and make predictions about the new directions for this technology. Any professional working in the environmental remediation industry will benefit from this in-depth study of MNA. We will use lectures, readings, and computational exercises to enhance our understanding and implementation of MNA. At the completion of this course, students will have updated understanding and practical tools that can be applied to all possible MNA sites.
Thermal Monitoring of Natural Source Zone Depletion (Thermal NSZD)
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來自 Rice University 的課程
Natural Attenuation of Groundwater Contaminants: New Paradigms, Technologies, and Applications
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New Directions for MNA
This final series of lectures will cover a mélange of interesting MNA topicsl We start with the brand new ESTCP BIOPIC tool, then talk about the broad universe of MNA that extends to a lot of different contaminant classes. Then some new developments in the LNAPL world: Natural Source Zone Depletion, both with conventional methods and a new method based on thermal monitoring. Then we talk a little bit about low threat closures and transition assessments, and end up with a brief conversation with the three instructors. And then you are done!
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Pedro AlvarezGeorge R. Brown Professor of Civil and Environmental Engineering
Department of Civil and Environmental Engineering
Charles NewellVice President
GSI Environmental Inc.
David AdamsonSenior Environmental Engineer
GSI Environmental Inc.
CHUCK NEWELL: OK, well, we've been doing a broad survey of several topics
this week, right?
But today, we're going to tunnel into one hot new technology
that Colorado State University and our company, GSI,
have been collaborating on.
DAVE ADAMSON: OK.
Well, what are some of the key topics we're going deal with, then?
CHUCK NEWELL: OK, a little bit of an esoteric mix here.
How about burning gasoline, compost piles, four seasons, thermocouples,
and the world wide web?
DAVE ADAMSON: That's a lot of words that don't seem to have any connection.
So how are you going to get them all together in this lecture?
CHUCK NEWELL: Well, I think I can do it.
Oh, but I forgot the one crown jewel word.
And that's the unit of heat, joules.
We're going to talk a lot about that as well.
DAVE ADAMSON: OK.
Well, let's move on.
Maybe let's review Natural Source Zone Depletion, NSZD, first.
CHUCK NEWELL: OK, so there was this whole idea of people
really go to these hydrocarbon sites and seeing these rates,
using things like carbon traps, or these dynamic chambers,
or these gradient methods.
What are some of the rates they're seeing out here?
DAVE ADAMSON: Yeah, again, we're seeing NSZD rates in the order of hundreds
to thousands of gallons per acre, per year.
So a lot of attenuation going on.
CHUCK NEWELL: OK.
And it's really this two-step process that's happening.
So if we go to this conceptual model, the yellow's where the LNAPL is.
This simplified drawing has it all in the saturated zone.
But down there, these anaerobic processes
are generating methane and CO2, and it's coming up
to the vados zone via this evolution process.
And then, what happens in that red zone there?
DAVE ADAMSON: That red zone is where you see your biological reaction going on,
in this case methane oxidation.
And so you're really seeing a lot of that being converted then to CO2.
CHUCK NEWELL: So think about the methanes coming up from below,
and then it gets in the vados zone.
You have oxygen coming in here.
And in the middle, there are these bacteria
who have been involving for millions of years
to degrade methane in the atmosphere, they can chop that stuff
and convert that methane to CO2.
And people have been measuring this carbon dioxide at the surface.
But wait, there's another way to do this.
And this is again an idea from Dr. Tom sale at Colorado State.
Emily Stockwell is the grad student.
But couldn't you measure the heat that's generated from this?
And so there are different ways to think about this.
But this whole technology is, let's not measure the gases, let's measure
the joules of heat that's generated by it.
So here, there are some different analogies.
And one is-- well, do you have a compost pile in your yard?
DAVE ADAMSON: I do-- I do.
I'm not sure I've ever seen it give off that much steam or anything like that.
CHUCK NEWELL: What's the temperature out there?
If you go out there in winter, what does it feel like?
DAVE ADAMSON: It's pretty warm out there, yeah.
I mean, you definitely have an elevated temperature because things are working.
CHUCK NEWELL: OK.
So the other part is all about sort of thermal dynamics.
I know you took that in your college career.
But if I have a gallon of gasoline, and I just set it on fire,
it releases, in this case, 45 kilojoules per gram, right?
Now, what if I take that same gallon gasoline
and I have bacteria degrade that?
How many joules of energy does that release?
DAVE ADAMSON: Well, in theory, that should be about the same,
give or take for the biomass that's formed.
CHUCK NEWELL: It's going to be slower, right?
But it's the same amount of energy.
So on the right-hand panel, we see some of this information, or this graphic.
We've got depth versus temperature.
The blue is the natural soil temperature at a clean zone.
But that red line starts showing at this one station.
Well, it's warmer by about one or two degrees centigrade.
Dave, where's that heat coming from?
The red is in that LNAPL zone.
DAVE ADAMSON: Yeah, that's that shift that's
tied to the LNAPL biodegradation.
CHUCK NEWELL: So you're seeing that signal.
So then, there are some complications that occur here, because, well, nature
is pretty complicated, right?
DAVE ADAMSON: Yeah.
CHUCK NEWELL: There are these four seasons of things that are happening.
So this is what you might see, generally, with the soil temperature.
The soil scientists know all about this.
There is a model called the Hillel model which predicts
this at any location at any time.
But in winter, what's happening with the red line there?
This is depth versus soil temperature, right?
DAVE ADAMSON: Yeah.
You're actually going to see colder temperatures at the surface
than you might see at depth.
CHUCK NEWELL: OK.
And then, the complete opposite in the summer, right ?
That at the very top there, that the blue line on the right,
that's this warm summer sun that's baking that soil.
It's warm on the surface, but then it gets colder down there.
DAVE ADAMSON: Yeah.
CHUCK NEWELL: So somehow you've got to remove that signal.
And the way that this idea is, if you have a background location,
and you have a location in the LNAPL, you subtract them out
to get this net temperature.
And that can lead to this way of calculating how much heat's
being generated through this thing.
So now let's go through some more ideas.
This is this conceptual model.
You have the cell LNAPL source that's coming up.
Real life, that's a two-step process, right, the methanogenesis and then
the methane oxidation.
But then it turns out most of the heat is actually
released in that second step.
But then, you've got surface heating and cooling,
you've got a geothermal gradient, you have groundwater flow.
But if you could draw a box around this, and instead of a mass balance,
you do a heat balance, you can figure out that rate.
And that's the key thing.
So here's sort of the installation that they conceived in here.
Dave, what's a thermal couple?
DAVE ADAMSON: Mhm.
A thermocouple is just a pretty easy way to measure the temperature
that you're seeing at depth.
And so there's a stick, and it's got these little points in there.
And then the way that this particular configuration
is developed by the guys at Colorado State goes to a box.
It's got a data logger, and it's got a cell phone,
and it's all powered by the solar panel.
And it can tell you the temperatures at these different locations.
Both the background location would look like this
and each point in the LNAPL zone would look something like this.
And here's what it looks like in actual real life.
There's the thermocouples on the left-- pretty small, pretty cheap, right?
DAVE ADAMSON: Yeah.
In this case, it's something that can be installed pretty easily.
You just put that stick in the ground with a direct push rig.
CHUCK NEWELL: Yeah.
So it's not a well.
It's actually just physically a stick or a rod.
And the direct push rig's in the middle.
And there's this completed station in there.
It's got the cell phone.
It's got the data logger on the right.
And then, every day it will send out these signals.
Here's the temperature.
And then, if you process it the correct way,
you can get this natural source zone depletion rate.
So here's just a picture of them working at a site.
In terms of looking at this stuff, we've got four different stations here,
lot going on in this particular figure.
But sort of the inset shows a ROST image of where LNAPL is, on the far left.
Most of it's on the saturated zone.
These guys, it's more distributed.
But the red is the higher temperature.
So this is a cross section going across an LNAPL zone.
And you see the blue line is the water table.
So where is most of the heat being generated here?
DAVE ADAMSON: Yeah, it's right above the water table.
It's in that unsaturated zone, that vados
zone where you're sort of seeing that transition between where
the methane's being released up into there and then been converted.
CHUCK NEWELL: So there's a little bit of heat
generated by the generation of the methane itself.
But it's where that methane gets burned or consume.
That's where most of this is.
I think they've actually got a movie from Emily Stockwell's
work, her master's thesis.
Let's look at this.
And this is different days that are out there.
And you can sort of see the red zone move up and down.
And there's different things happening.
Sometimes it's cold and warm in the atmosphere.
And you can see some of that.
But you can sort of get this sense that it's almost this big data thing, where
you're getting these temperatures every day,
and then you can sort of get this really good measure of all this stuff.
If you're measuring the fluxes, then you can sort of
understand what's happening with this natural source on depletion rate.
So let's move on.
The last piece of the puzzle here is you have all these temperatures.
How to analyze it?
DAVE ADAMSON: Mhm.
How do you get actual attenuation data rates out of that?
CHUCK NEWELL: And the thing is, you want not a temperature,
but you want a gallon per acre, per year.
DAVE ADAMSON: Right.
CHUCK NEWELL: So as part of this whole program, we've collaborated,
and we've come up with this particular web page.
It's called this, thermalnszd.com.
It's a sort of subscription-based web page
that people then would have these monitoring systems out there.
The data goes over the wireless to this web page.
And then this does all the calculations.
And as you can see this, in the end result,
as you can see the degradation at your site.
So here's just some more images.
You can go in there and look at the temperature versus depth profiles
on the left.
But then, the key thing here is that this particular site, since monitoring
began, 10,700 gallons of gasoline have been biodegraded based on that heat.
And in the past 30 days, it's 420 gallons per acre per year.
So real-time continuous monitoring of LNAPL.
So it's just something that's right on the horizon.
We've been working hard on it.
But it's something that we could think that may
have some pretty neat applications.
DAVE ADAMSON: Neat.
CHUCK NEWELL: OK, well, let's wrap up about this thermal NSZD,
the key points.
Number one is that the biodegradation of LNAPL generates heat.
DAVE ADAMSON: Yeah.
And then, if we can measure those subsurface temperatures,
we could basically get the rate of heat generation
and, ultimately, the rate of biodegradation.
CHUCK NEWELL: OK.
Field deployment, you're going to have several thermal couples
on an NSZD stick that goes down in there.
And on the surface, there is a little station
with the data logger and a wireless communication system.
DAVE ADAMSON: And then, there's this thermal NSZD
dashboard that's being developed.
It's basically a web-based subscription.
You can provide daily data downloads and continuous monitoring of NSZD rates.
CHUCK NEWELL: Cool.
