Looking at rates that might be associated with these reactions,
we can rely on a great paper that came out in water research in 2011,
where they compiled a lot of these things and again,
we're talking primarily about a fairly limited number of compounds.
So they were looking at trichloroethane as well as chloroethane.
They did a great job of putting sort of what they saw for sort of rate constants.
They even converted them into half life for those half life people.
So they listed them here in some of the products, and
temperatures that are associated with those.
>> So thumbs up for me.
It has a lot of information.
Some of those papers from 1959,
but where are some of the ranges that we're seeing in that table?
>> Yeah, so TCA in this case, we're looking at half-life
somewhere around the order of one to 10 years in this case.
So pretty reasonable half-life in this case.
The one thing that you might want to be aware of, though,
in this case is that TCA is actually relatively biodegradable.
So, if you want to do a comparison between this abiotic hydrolysis rate and
biodegradation, maybe about an order magnitude or
even two orders of magnitude which you see in difference of this rates.
The biodegradation is generally faster in these cases.
>> But the biodegradation only occurs under that certain sites or
some sites where there's no biodegradation, right?
>> Yeah. And then a lot of these cases one
to ten years in terms of half life might be relevant for
what your needs are in terms of the viability of natural attenuation.
So, not to dismiss that the hydrolysis rates are actually relevant here.
>> So that's cool, but now let's talk about temperature.
How does it affect it?
>> Well, these are chemical reactions.
So if you have a higher temperature, you're going to proceed at a faster rate.
And this follows the Arrhenius equation, and just take a look at this.
If you see your term there with the T, the temperature term.
If you increase that,
you're going to increase the k associated with that reaction.
>> And I'm a sort of a fan of history of science and
I like reading up about some of this stuff.
And Arrhenius Equation is a key thing that we use a lot in our business thinking
about how temperature might affect these rates.
Turns out this guy is a Swedish chemist around the turn,
around the 1900 time period.
He was one of the first guys besides this equation,
thinking about how enzymes worked, how reactions worked,
identified the potential for global warming from the burning of coal.
But he's been on it in a 1900 time frame was that he's in Sweden and
global warming would be a great thing.
>> No, well we're in a little different place now, but good to know.
>> But we still use this formula for the future.
>> Yeah, and in this case, just remember if the temperature increases,
k is also going to increase.
So, one way to look at this sort of temperate dependence of these rates is to
plot a bunch of data.
So, this is a pretty standard [INAUDIBLE] plot in this nice paper,
looking at hydrolysis of TCA.
And so in this plot here, we've got the natural log of the rate coefficient
the hydrolysis rate coefficient associated with these various temperatures.
So as you're moving front the bottom right to the upper left,
you're seeing an increase in temperature associated with an increase in rate.
>> Okay, now this is one of my least favorite types of way to
express temperature.
This is one over temperature in degrees kelvin.
What does this mean in real life in terms of
how much temperature change will increase the rates or change the rates?
Well, one way to look at it is sort of, you might see a cold weather site,
a cold run water might be something like 10 degrees Celsius and
a hot maybe in a warmer climate you might see something like 25 degree Celsius.
The rate increase associated with that sort of the very matter temperature
changes is 16 time increased in the hydrolysis rate coefficient.
So pretty significant.
>> That's a lot and that's the increase in the rate of insinuation.
I think some folks are actually gone to TCA sites and try to heat them
up just a little bit to get it to 25 degrees increase that hydrolysis rate.
>> Mm-hm.
>> Mm-hm.
So is this process relevant at you site, at person's site?
>> Well let's take a look at some of the.
Some of the key factors here.
Basically if you're at a TCA site you see it disappearing.
You look for 1,1-DCE and acetic acid as products.
And you can use the ratio of those things maybe even to help you
estimate the age of the release.
Particularly at sites where the conditions might not be favorable for biodegradation.
>> A little tough to do in some cases, a lot of other factors in there that
whole dating thing can be tough but there are papers about how to try to do it.
>> Yeah, and it's relying on that it's a predictable reaction,
that you may be able to actually know what those rate coefficients are with some
>> Some degree of uncertainty.
>> It's a lot of unknowns in that dating stuff.
>> Yeah.
Rates are significant, and in a lot of cases from natural attenuation,
because we're talking about releases that may have occurred decades ago, so
if you half-lives in the one to ten year range, you might have seen
quite a bit of degradation of related, just the hydrolysis.