CHUCK NEWELL: Well, we're going to wrap up talking about monitoring and discuss how you analyze and present all this MNA data. DAVE ADAMSON: And today we're really talking about fairly simple calculations in data presentations. We're going to talk more about computer models and more sophisticated data analysis in upcoming lectures. Let's start with LOEs, the lines of evidence for monitored natural attenuation. CHUCK NEWELL: OK, well here's line of evidence one, and these things have been out there a long time, but there's really-- the first one is historical contaminant reduction, and this is this contaminant mass reduction monitoring data versus time. And sort of the why is I shrink therefore I am sort of with respect of Voltaire. What is you want to demonstrate to directly that you have this decreasing trend, and then when do you do it? You always do it. So line of evidence two? DAVE ADAMSON: A line of evidence two is hydrogeologic, or geochemical data, or even rate calculations, and you're doing this because you need to know more than just it's decreasing. You sort of need to know why. Most of these are indirect methods to demonstrate that degradation is occurring, and when do you do it? Most of the time. CHUCK NEWELL: OK, now, Dave, just a note about the calculation of rates. I always say this should be under line of evidence one-- is it's really just processing your primary data, but it's listed under line of evidence two. I was on two different sort of groups who were putting together protocols, but what I thought was a very logical slight adjustment where you put the grades under line of evidence one, it went unheard. DAVE ADAMSON: So you're saying you went unheard. I'm really sorry to hear about that, but for now, I think we'll keep it under line of evidence two. CHUCK NEWELL: OK, well, let's go to line of evidence three. These are these field or microcosm studies. You use it when you need to know a little bit more than what you have with line of evidence one, line of evidence two. It's a direct method to demonstrate some particular process that you're interested or want to confirm, but for many of our conventional contaminants, it's pretty rarely used, right, Dave? DAVE ADAMSON: Yeah, it is. CHUCK NEWELL: OK, so thinking about all this stuff, here's a philosophical question-- another one about these line of evidence. Let's say you have a confirmed degradation product like cis-1,2-dichlorethane in your plume. You know it's produced by the bacteria, and it's not from one of your original sources. Is that line of evidence one or line of evidence two? DAVE ADAMSON: Well, I think I've seen it categorized as either. I think it's sort of a direct evidence, so, I mean, really is should be under line of evidence one in my opinion. CHUCK NEWELL: OK, line of evidence one. We'll put it in there. OK, well, let's keep going, and we're now going to sort of talk about this primary line of evidence. It's morphed a little bit to demonstrating historical mass destruction plus demonstrating plume stability. In some of our training, we present some of these thoughts about this plume stability. So what are we doing here? We're trying to define is that plume-- is it stable? Is it shrinking, or is it expanding? So how do we do this? DAVE ADAMSON: Well, we're essentially just evaluating that historical concentration measurement in groundwater. That c versus t data that you plot up can give you a lot of valuable information for line of evidence one. CHUCK NEWELL: OK, and then we say, when do you do it? Always do this when you have sufficient data. You can't do it with just one or two sample events. You want to have enough of the information that's really out there and do all this stuff. So now let's look at some of the common graphical treatments for line of evidence one. DAVE ADAMSON: OK, so on the left is a plume map over time with different plume outlines for different years. It looks like this guy is shrinking pretty rapidly. Chuck, does it go to 0 very often? CHUCK NEWELL: Well, that's a pretty interesting question. The answer is that in these plumathon studies or these multiple site studies that were done in 1990-- they identified plumes as being, well, expanding, or they're stable, or they're shrinking, but most interestingly they said some of these plumes were exhausted. And I talked to David Rice, the lead author of the study that developed this four bucket framework, and he said there were these hydrocarbon plumes that seemed to get low concentrations like a 10 part per billion average plume concentration, and they just seemed to sit there. They didn't actually go to 0. We seem to see the same long tail phenomenon at chlorinated solvent sites, so maybe the plume that we're looking here on the left-- maybe it will stop shrinking and then hover in this exhausted footprint for a while. Hard to know. DAVE ADAMSON: OK, well on the right is a concentration versus time graph, but different times for different years. Just another graphical way to present line of evidence one, the primary line of evidence. OK, well those are two great graphs. How about two more? CHUCK NEWELL: OK, so here's just some other ways to think about this, and there's other ways to demonstrate plume loss, and mass loss, and plume stability. Method one, concentration versus distance-- so we talked about that. Then a method two is concentration versus time. The first thing-- the key thing here is you just look at this, and you do this qualitatively-- that, yes, concentrations are declining over time, and yes, the plume concentration decline is getting farther away from the source. DAVE ADAMSON: But you also use these data to calculate rates, right? CHUCK NEWELL: That's right. So we touched on that in the last lecture, but here again are some excerpts from the US EPA issue paper about calculating monitored natural attenuation rates. And we discuss in this particular document that you can do this with either concentration on that y-axis or with mass discharge, but the key point here is that there are two main kind of rates, and they're apples and oranges. You don't want to get them confused. Concentration versus time graph on the top right-- that's really more of the rate of source attenuation, or how fast the NAPL is being depleted or the rate of back diffusion is going down. So it tells you a little bit about how long the plume will be there-- its duration. DAVE ADAMSON: So the concentration versus distance rate really speaks to the degradation rate actually being observed in the plume. Now, Chuck, you have an example of a more complicated application of concentration versus distance, right? CHUCK NEWELL: Now let's look at this one. Here we have an excerpt from some guidance from the Texas Risk Reduction Program-- their monitored natural attenuation guidance, and it tells you how to use a concentration versus distance graph to derive or develop these attenuation action levels, ADLs, which are really like a glide path to see if you're on the right path for doing monitored natural attenuation. Three different steps here for this graphical method-- number one is you're going to plot your actual data, concentration versus distances, as whisker plots everywhere where you have a monitoring well. That shows your actual range of these historical concentrations, so those black whiskers are different points. DAVE ADAMSON: OK, well then your next step is sort of get that orange or red line that's there. That's your AAL line, and it's pretty simple. You're just connecting on the left hand side your max concentration, your source concentration to basically your PCL concentration, your protective concentration limit at that POE, that point of exposure. CHUCK NEWELL: OK, then at each point there-- each monitoring well that you're going to develop an ALL-- those are those squares-- those orange squares, and you don't want to exceed that number. And if your monitoring data starts to creep up, and you get above there, hey, you've got to figure out why isn't your prediction that monitored natural attenuation is working? Why is it going off course? Do you need a new conceptual model? Was there a new release? But that's what this thing-- it gets you on this glide path. So now let's go into was some graphics for line of evidence two-- how you demonstrate geochemical conditions. DAVE ADAMSON: OK, well here's an example we're basically mapping electron acceptors inside and outside of a containment plume. The blue line is a BTEX benzene plume at a gas station site, and the red shows a high dissolved oxygen area, and the yellow is depleted dissolved oxygen area, so areas below a one microgram per liter level. CHUCK NEWELL: Right. DAVE ADAMSON: Milligram per liter level, excuse me. CHUCK NEWELL: Got it, OK. So by showing this dissolved oxygen, this hole that's out there, you can show that the aerobes have used the dissolved oxygen that was there to consume the contaminant, and you typically do this by showing holes for sulfate, and then for nitrate, and for any-- and you also show production of ferrous iron and methane, which are reaction byproducts that sort of accumulate inside this plume area. DAVE ADAMSON: And so this is for BTEX. You can do this for chlorinated solvents, as well, right? CHUCK NEWELL: That's right, but it's a little different. The underlying reason is different. Showing the oxygen, nitrate, and sulfate depletion at a hydrocarbon site demonstrates that the hydrocarbon compounds are actually being degraded, but at chlorinated solvent sites, the oxygen, the nitrate, and sulfate are competing electron acceptors for some of the reactions that you like. What you're trying to show is that they're out of the way so these dechlorinating reactions can proceed. So right now they only proceed if there's this really deep anaerobic zones, and the oxygen, and the nitrate, and much of the sulfate is gone. So Dave, what do you think? What are the most important electron acceptors when we're doing these types of graphs? DAVE ADAMSON: Well, I think nitrated might be the least important, and I think you can learn a lot just by looking at dissolved oxygen, or ORP maybe, and methane, but at some sites, I also know that sulfate and iron can be really important. So it's a little bit like choosing which one of your children you like the best. CHUCK NEWELL: Well, it's hard to say, but I think I'll just say I love them all equally. DAVE ADAMSON: Very diplomatic answer. Let's change slides here maybe. Here we've got another example then of geochemical mapping-- geochemical conditions overlaid with contaminant plumes. So we've got a graphic showing a dissolved oxygen hole in the middle of the BTEX plume, but we've got distance from the source, then, on that x-axis. So we're showing is as it sort of progress down gradient. And you want to see the same type of a hole for nitrate, and sulfate, and maybe for ferrous iron you'd see sort of a mountain in the middle and very low or non-detect concentrations of those things outside of the plume, right? CHUCK NEWELL: Right. OK, well let's wrap this up, and we'll go through there. We showed you some key graphics like plume size versus time, concentration versus distance, concentration versus time plots. DAVE ADAMSON: Yeah, so if you're showing a source well castration versus time, for example, that's basically representing the attenuation in the source. CHUCK NEWELL: Right. And then concentration versus distance shows that attenuation in the plume once the contaminants have left the source. DAVE ADAMSON: And then the last thing we looked at is sort of plotting geochemical parameters and using that to sort of understand where degradation is occurring.
