Peter Van Metre: Well, we’re out here today because two years ago we measured volatilization
of PAHs off of freshly applied coal-tar sealcoat and we found some extraordinarily high rates
and numbers.
So we want to verify those and we’re also at the same time sampling much more intensively
and with several other instruments that we didn’t have last time to try to do the best
job we possibly can to quantify this volatilization flux and see how important an air contaminant
it is.
Barbara Mahler: At the same time we’re going to be doing some run off experiments so we
can look at the potentially toxic effects of storm water runoff from recently seal coated
parking lots on aquatic biota.
Did Pete tell you some of the numbers we’ve gotten off these?
Jennifer Wilson: No, he was talking about it being some pretty nasty stuff though.
Barbara Mahler: Astronomical.
Jennifer Wilson: Really?
Peter Van Metre: Yeah, I think today we’re tying the all-time record for hundred degree
highs in Austin and tomorrow we’ll clearly break it.
Barbara Mahler: So this a simple field test to determine if it is the asphalt based sealcoat
or a coal-tar based sealcoat.
The coal-tar is not soluble in mineral spirits, which is what is in this jar.
So you can see it remain perfectly clear and there are little blobs of sealcoat down on
the bottom and there is no solution or dissolving or mixing.
The asphalt based product is soluble in mineral spirits.
So if it was the asphalt based product this would look like a cup of coffee and you wouldn’t
be able to see through it; you wouldn’t be able to see the individual blobs of sealcoat.
So it’s just a quick way to ensure that the product that they said they put down is
really what they put down.
Peter Van Metre: One more piece of foil after this too.
I want to five of them.
They come up easier than I thought.
Peter Van Metre: There’s the bottom.
It’s a little tin disk.
So this is good because we’ve never been able to know for sure just how much of this
stuff is on the pavement.
Not knowing that, we can’t make any mass calculations so we have to make an estimate
just based on the applicator rates, but we have no idea if they follow those guidelines
or if they would even know how much they’re putting out so now we can tell.
Today marks 69 days in a row in Austin that we’ve been over 100 degrees and here we
are at two in the afternoon on a black parking lot.
We’re out here because about eight years ago we were part of a group with us (USGS)
and the city of Austin that discovered that pavement sealcoat, the black stuff that you
see on the pavement behind us here, is a major source of a certain kind of contamination
in urban environments, PAHs or polycyclic aromatic hydrocarbons.
Being hydrologists in that when we first discovered this, we discovered it in runoff.
We did a study that’s kind of like what we are doing now.
Part of it where we had parking lots coated commercially with this product and then we
simulated runoff and we measured contaminant levels, PAH levels, in the runoff.
In that first study we found that they were very high, about 65 times higher in runoff
of coal-tar sealed parking lots, which is the main product type, the same product that
is behind us here, and runoff from unsealed parking lots.
Well we fast forward to two years ago, 2009, and we did a study out here where we moved
past the question of water quality to air because we know when this stuff is applied
you can smell it; it is a very strong odor.
That means it is volatilizing.
Barbara Mahler: There’s a little bit more to it than that.
In fact, as we were doing our runoff studies we would take scrapings, samples of the product
itself, of the dried material and what we noticed is that when you scraped up the dried
material and you measured the concentration it still had extremely high concentrations
of PAHs, but they weren’t as high as what was in the product itself.
So somewhere between when you put the product on the surface and when it dries and you scrape
it back off you’re losing some of those PAHs.
The question is are they going into the air and that made sense because we could smell
very strongly right now that there are PAHs being volatilized from the surface behind
us, but we wanted to measure how important this type of sealcoat might be to PAHs in
the atmosphere.
Peter Van Metre: Very true.
So this same patch of ground behind us, a 50 ft. by 50 ft. square area, was sealcoated
two years ago and we sampled air concentrations right on the surface with a thing called a
hat sampler that is a round steel disk that has a high volume air sampler at the center
and it samples the surface air layer.
We sampled concentrations about four feet off the surface with a second high volume
sampler.
With those two and with wind speed you can make an estimate of the total flux of PAHs
to the air, the total amount of volatilization.
What we found from that initial study in our first sample two-hours after the sealcoat
was applied was an extremely high concentration of PAHs in air and a really high volatilization
rate.
We’re back today because in that study we sampled relatively infrequently right after
sampling and spread over a whole year and we realized when we look at the result from
it that a whole lot of the action, a whole lot of the volatilization was happening in
the first few minutes or hours after application.
So we wanted to repeat the study and we’re also doing with the same method we used, we’ve
also got another USGS researcher Mike Majeski from California who has a set of tower samplers
that are the ones you see here with the little wind anemometer turning and then there is
another pole over to right of those with some hoses leading to it.
Those are a more traditional method for sampling air concentrations of contaminants and measuring
flux.
We are trying to compare two different methods here and verify the results we got the first
time we were out.
Barbara Mahler: We’re also going to collect samples more frequently than we did the first
time around.
The first time we collected samples one day and then four days and then two weeks after
sampling.
Here we’re going to collect samples; we collected samples as soon as the sealcoat
was laid down, two hours afterwards –
Peter Van Metre: One hour.
Barbara Mahler: One hour afterwards.
And then now, which is about four hours afterwards.
We’re going to collect another one tomorrow morning at 6:00 AM and another one tomorrow
afternoon.
So we’ll be able to have a much better description of what those PAH concentrations are in the
first few days after application.
Peter Van Metre: Then the other thing we’re doing that we have not done before and as
far as we know no one has done it the way we are, is there is a lot of evidence out
there that the runoff, if it does rain soon after the sealcoat is applied it is very toxic.
There have been two fish kills that we know of when it has rained within a day or so of
application of sealcoat, in the streams that those parking lots drained into.
There is one study that measured toxicity in runoff from a sealcoated parking lot when
it rained about a day after they sealcoated and found real high toxicity.
So we’re doing a much more controlled experiment than that.
We’re going to simulate runoff four hours after application, 12 hours, 24 hours, 48
hours, and 72 hours to try and see how toxic the runoff is and for how long of a curing
time is it before you get back to some fairly normal level of parking lot runoff as far
as that goes.
Barbara Mahler: Then we’re going to do all of these same types of sampling but we’re
going to do them in a few weeks on a surface that has been treated with a different type
of sealcoat, one that has asphalt based as opposed to the coal-tar based.
The big difference is that the coal-tar product contains 50,000-100,000 milligrams per kilogram
of PAHs and the asphalt based product contains about 50.
So there are about 1,000 times more PAHs in the coal-tar based product than in the asphalt
based product so we can compare volatilization and toxicity between these two product types.
Peter Van Metre: Yeah, that’s a really important point because the coal-tar product has now
been banned in Austin where we are, we had to get special permission to do this, and
in more than a dozen other US cities and in the State of Washington.
The obvious alternative is this asphalt based product.
So we also want to test it to see how environmentally friendly or safe it is.
Barbara Mahler: Yeah, it’s important to see how substantial the difference really
is from an environmental point of view between the two products.
Douglas Harned: So tell us about the night sample.
Peter Van Metre: About the night sample?
Douglas Harned: Why you’re out here in the middle of the night.
Peter Van Metre: We’re out here in the middle of the night because we want to sample at
certain time periods after the sealcoat has been applied.
This is 12 hours after so it happens to be 11:00 PM.
That’s because we are wondering how toxicity varies in runoff with time afterwards.
We want a sample at specific and pretty close time periods after the application of the
sealcoat; so this is 12 hours after.
The three major findings I would say of the studies of sealcoat, the first one is simply
that it has extremely high concentrations of PAHs and that’s in the product, it’s
in dust that’s swept off of the parking lot, it’s in runoff, it’s in air concentration
next to the parking lots.
So it’s just a really strong source of this group of contaminants.
Barbara Mahler: A second major finding is that it doesn’t stay where you put it.
Coal-tar sealcoat wears off.
You can see it on the parking lot around us.
You can see the asphalt through the sealcoat and that’s normal and that’s why applicators
recommend that you have it reapplied every three, four, or five years.
The question is where does it go?
We found that it comes off in storm water runoff, it gets tracked into people’s homes,
it ends up in storm water detention ponds, it ends up in our lakes and rivers, and it
ends up in the air.
So there are a number of different environmental compartments that are affected.
Peter Van Metre: To elaborate on one of the things that Barbara just mentioned is a major
finding is our studies of lake sediment chemistry around the United States have shown that concentrations
of PAHs have been increasing in urban lakes across the U.S. for the last 30 or 40 years
and that the dominant source of PAHs to those lakes is the coal-tar based pavement sealcoat.
5 PAH Long V3 (14:21 minutes)
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