So one of the things that we wanted to try to look at
is what extent does sustained treatment occur at field sites?
And I'm going to go over some results from a ESTCP project.
This is a federally-funded project to evaluate
the performance of in situ treatment technologies
at a large number of sites.
And this is a 2015 project, so recently completed project.
As part of this, we're doing a big data study of regulatory reports,
of databases, and things where we could gather information on how
these types of technologies performed.
And you're doing this through gathering groundwater concentrations
within the treatment zone over long periods of time
and evaluating performance.
As part of this examination of sustained treatment,
we looked at that subset of sites, then, that have a long enough period
of post-treatment monitoring data to evaluate if sustained treatment is
actually happening at these sites.
And that was the case at 34 of these sites,
where you had three to 12 years of monitoring data
after the end of treatment.
So let's take a look at some of the results that came out of this study.
So these are 34 different sites that I'm going to show you the performance for.
And these are data that are showing what's
happening in the post-monitoring period based on the order of magnitude
reduction in concentration.
So there's two bars that are going to represent either site.
These are side-by-side bars.
And on the x-axis, we're going to show the data individually
for these 34 sites.
And the left bar for this first site is showing the concentration reduction
that was seen from before treatment to the first year
after the end of active treatment.
And the bar to the right of that one, then,
is showing the concentration reduction that occurred from before treatment
to at the very last year of the concentration record.
So the idea here is that sites that are undergoing sustained treatment
are showing evidence of sustained treatment.
You'd see a continued decrease in concentration
during that longer term period after the end of active treatment.
So you'd see these bars continue to go down, or in the better direction,
in these cases.
So that's an example of what happened here at this first site that's
shown up here on this chart.
So let's show some of the remainder of the data.
We basically saw a large number of these sites
that fell into this category of where you saw continued concentration
reduction after the end of the treatment period.
So these are evidence of sustained treatment.
He then saw a smaller subset of sites where basically there
was no change in concentration.
So these are stable situations where basically there
was no change in the concentration from the end of treatment
to the end of the concentration record.
And then finally, there were a small subset
of sites where you actually saw a decreased performance, or a worse
performance, such that at the end of the concentration record
that the concentration was actually slightly higher than it
was at the end of active treatment.
So in this case, the two on the left, the blue and the green bars,
are indicators to sustained treatment, while the ones on the right
are indicators that concentration did rebound
and that there was no evidence of sustained treatment.
So that was on a site-by-site basis.
Let's take a look, then, sort of looking at this again in a different way.
And we're going to use Mann-Kendall trend analysis.
So Mann-Kendall is a very popular nonparametric statistical test
for demonstrating whether there was an actual statistically significant trend
with, in this case, concentration data during the post-treatment period.
So we're going to look at those same sites.
This is 34 sites.
And based on Mann-Kendall, we saw that 89% of those 34 sites
fell into a decreasing, a probably decreasing, or a stable category.
So that's 89% of the sites that did demonstrate the sustained treatment
during the extended monitoring record.
And a much smaller subset, 11 of these, showed an increasing trend.
So that's on a site-by-site basis.
We're looking at each of those sites the number of wells that were in there.
And we did the similar breakdown on this and we got similar numbers.
So we're looking at 83% of the wells falling into that sustained treatment
category, while only 17% of the wells indicated an increasing trend where
there may have been a concentration rebound.
So the key point in this case is that sustained treatment
was indicated at the majority of the sites
and the wells that were included in this performance study.
And that can be very important in terms of managing expectations at these sites
and mitigating the chance that rebound, concentration rebound, would occur.
So the key points in this lecture, looking at both interfaces
and sustained treatment-- interfaces are common to environmental sites
and have increasingly been established as locations where
significant attenuation is occurring.
A sustained treatment is defined as enhanced or maintained
attenuation capacity within the treatment zone
even after the end of active treatment.
And sustained treatment may last for several years
at enhanced bioremediation sites and help prevent concentration rebound.
