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.
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?
Peter Van Metre: 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 gauge
as to 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 results 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.
Barbara Mahler: We’re going to collect samples more frequently than we did the first time
around.
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: 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.
So we’re doing a much more controlled experiment than that.
We’re going to simulate runoff to try and see how toxic the runoff is and for how long.
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 an asphalt base as opposed to the coal-tar base.
Peter Van Metre: 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 concentrations
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.