In this remediation webinar we are pleased to have with us as a special guest speaker Mr. Matthew J. Valentine, P.G., LRS, Vice President/Project Manager at Woodard & Curran. Mr. Valentine is also joined by Mr. Barry Poling, Central Regional Manager at REGENESIS. This presentation is a case study of a site in South Carolina contaminated with TCE, where PlumeStop® Liquid Activated Carbon™ was selected to remediate the 1,700 foot TCE plume. Mr. Valentine and Mr. Poling discuss the proces from the pilot study to the full scale implementation, covering why PlumeStop was selected, the conceptual site model, and the remediation results to date. Questions from the live audience during the webinar are also addressed.
Dane: Today’s presentation will focus on Accelerated Biodegradation of Chlorinated Contaminants Using In-Situ Liquid Activated Carbon. With that, I’d like to introduce our presenter for today. We are pleased to have with us Mr. Matthew Valentine, Vice President and Project Manager at Woodard & Curran. Mr. Valentine has over 26 years of professional experience in geology, hydrogeology, and geotechnical engineering projects. For the past 16 years, he has managed a wide variety of project ranging from environmental assessment and geotechnical investigations to feasibility and corrective measures studies.
He has conducted, supervised and managed subsurface explorations, remedial investigation, and site characterizations at numerous contaminated sites. We also have with us today Mr. Barry Poling, Central Regional Manager here at Regenesis. He has 15 years of experience in the environmental industry including extensive experience in Phase I and Phase II site assessment remediation, and industrial compliance. He provides senior leadership in the areas of remediation design, strategy, and business development. All right, that concludes our introduction. So now all hand things over to Matt to get it started.
Matt: Thanks, Dane, I appreciate the introduction. I appreciate everyone for attending the webinar. This is a case study of a site that our company’s been working on for over 20 years. We became involved in the site shortly after the RCRA Facility Assessment was completed in the early ‘90s.
The first thing I’d like to go over is just an outline of the presentation. And let you know that there’ll be a project summary that I’m going to review. And a little bit about the site background and description of the site or the pilot study and the results of that pilot study. And then, the remedial design that we went through with the help from Regenesis, the full-scale remedial action that we implemented, and some preliminary results that we found based on the initial performance monitoring that we’ve completed.Click Here To Read Full Transcript
So the project summary, the site is located in South Carolina. The stratigraphy consists of Coastal Plain sediments that are primarily composed of really anything from clay through sand and even some course sand units. The target zone for our remedial action is primarily comprised of a sandy clay and it does have some sand stringers and if that created its own issues and we’ll talk about those later on.
We conducted a remedial turns evaluation for the downgradient portion of the blue, which is going to be the focus of this talk and we recommended accelerated biodegradation using PlumeStop, which is a Liquid Activated Carbon. The pilot test was conducted using an injection of the carbon with a controlled-release electron donor, which is HRC and I think most of you folks have heard of that before. We also injected by a bioaugmentation culture known as BDI to help enhance the reductive dechlorination process.
The pilot test results demonstrated that the cVOCs decreased the concentrations in two wells from 98.7% to 100%. Based on the pilot test results, we went through a full-scale remedial design and then implemented that design using injection barriers. And for that full-scale of implementation, the performance monitoring is ongoing.
So a little bit about at the background of the site, it’s a former manufacturing facility that began operations in the 1950s. And actually it was a different type of manufacturing that started back way in 1930s.
There are the RCRA Facility Assessment was completed in 1989 and it identified 44 different SWMUs and 3 areas of concern. The RCRA consent order was issued in 1998, which prompted the RFI to work to begin. We completed the RFI in 2007, and submitted the report to the agencies, and then that report was ultimately approved in 2010.
Just wanted to highlight the site plan for everyone and to show that the general area of the plant itself not intended to read every little point, every little word on this slide but the general area of the plan is about 60 acres and to the north-northeast is a landfill area that’s also part of the site. Our focus is down here in AOC-1, and this’ll be what we’re going to focus on for this presentation in the area downgradient of AOC 1.
Continuing on with the background, we conducted several rounds of source area treatment. In 2010, we did a Nanoscale zero-valent injection, an iron injection and pilot test. And that test and application had limited success so we continue to do work at the site. In 2014, we did another full-scale application using 3DMe, HRC, and BDI. And we’re still in the process of evaluating those results but the preliminary results look pretty good.
In 2014, we conducted the remedial alternatives evaluation for the downgradient area. In late 2014, we conducted the pilot test so we’re going to be talking about. In 2015, we completed the remedial design based on the successful results of the pilot test with a goal to reduce contaminant concentrations within the downgradient plume and limit further migration of that plume. In late 2015 and January 2016, we implemented the full-scale design of the remedy.
So next I just kind of wanted to go through the conceptual site model of the site itself. Here’s an aerial view of the site and you can see the plant itself, the landfill area to the northeast, and what will show here, so that’s the facility.
The source area is actually a degreasing unit that was found in the building here and this is really what defines AOC 1. The plume we found extends about 1700 feet from that source area down through basically fields there’s a railroad here. And what we found throughout all of our investigations was that groundwater flow through this area averages about 60 feet per year with the contaminant transport velocity of about 30 feet per year or half of that.
One of the interesting features of the site is immediately downgradient of the plume, there is a small residential area. Everyone in that residential area is on public water and the city itself does have an ordinance for groundwater use. They’re not allowed to use groundwater. They’re required to be hooked up to the municipal supply.
Okay, next I wanted to show a cross-section through AOC1, to the left the northwest this would be the source area, and then groundwater flow is also from the left to the right. There are three units of interest to the site. Unit 1 consists primarily of silt and sands and it extends from about 5 feet below the ground surface down to 20 feet. The average horizontal hydraulic conductivity of that unit is about five to six feet per day and there is very strong downward vertical gradient.
Unit 2, which is present about 25 to 45 feet below ground surfaces you can see here, and you’re not intended again to read all of the notes on this section. I just wanted to show that the sediments are basically flat line and generally this is the zone that we’re interested in. That zone is primarily composed of sandy clay unit with sand stringers, as I mentioned previously. The average horizontal hydraulic conductivity of that unit is lower. It only about two to three feet per day and in that unit there’s only a slight downward vertical gradient. But as I mentioned, about 90% of the Contaminant Mass is found in this unit.
We also have a unit 4 present from about 60 to 80 feet below the ground surface that consists primarily of fine sands that are partially cemented. The average hydraulic conductivity horizontally is three to four feet per day in that unit.
And you might ask yourself, “Where is unit 3?” Well, there is no unit 3 in this portion of the site. Unit 3 is a discontinuous shell hash unit that just isn’t present in AOC 1, but it is present throughout the rest of the site.
Next, I wanted to go through some of the pre-remedial design work that we did. This just shows, actually it’s broken into two slides, that shows the cross section that I just showed and the green lines located here and here represent two of the five delineation boring transects that we did.
We prepared a work plan to describe this work, submitted it to the agencies for review and approval. Each of the green lines represent delineation borings that we did across the transect of the plume. We collected both soil and groundwater samples continuously about the boring themselves were about on 50 foot spacing. They helped really to delineate the width from the plume.
So the next, this is a continuation of that same zone. This is what defines the downgradient area and we did three additional transects throughout across the plume. The results of the pre-remedial design investigation helped us locate additional wells that we installed. And these wells are used for performance monitoring. It helped us update the conceptual site model, particularly with plume width and plume length and it also served as a basis for recommending the pilot studies that we completed.
This slide shows the entire site and colored contour map. You can see the source area is pretty obvious here. This shows the work before we did the source area treatment. What I like for you to pay attention to is that the red box down here. This is where we focused our pilot study and in two wells in particular. Well BL-55 represented a mid-plume location that had total cVOC concentrations anywhere from 6 to 12 ppm. The next location that we did our pilot test was BL-59 and this was near the edge of the plume, the leading edge, and concentrations of cVOC at that location vary from about 10 to 20 parts per billion.
So I just want to show a general view of what the area looks like. Previously, this looked a lot like the background where we had forested land but about two to three years before we did our work in this area, they clear-cut the area and you can see what was left. It did create many issues when it came to access. And there are some areas, that we’ll talk about later, further down that became quite swampy.
This slide shows a blow-up of each of the two pilot study areas. The first being BL-55, where we had higher concentrations, once again, and in that location we use 10 injection points. We injected just under 1900 gallons of PlumeStop, 300 pounds of HRC and nine liters of BDI. And you can see the general orientation of the borings and how they were laid out. Down near the leading edge of the plume at BL-59, 12 injection points were used, a little over 1900 gallons of PlumeStop, again 300 pounds of HRC and 9 liters of BDI.
With that I wanted to hand it over to Barry Polling. He is going to tell you a little bit about what PlumeStop is and some of the other work that they did during the pilot test that really helped for its success. Barry…
Barry: All right, thanks Matt. Yeah, so what is PlumeStop? I’m gonna give you a short answer to this question but if you’re attending this webinar and you have attended some of our webinars in the past, we went into pretty extensive detail about the development of this technology, the results, and where we currently are. If you haven’t seen those webinars, they are available on our website, which will provide you with a much broader explanation.
So generally speaking, PlumeStop is about bioremediation technology designed to rapidly achieve low groundwater remedial targets and to show sustained reductions. The designed intent of this technology was to develop a flowable dispersible sorbent that can be injected into the ground and to sort of contaminants to it but allow those contaminants to remain biodegradable for degradation.
We looked at a lot of different things, including activated carbon, which is the class of technology that we keyed then on. We looked at powdered activated carbon. The challenge with powdered activated carbon by itself was that it’s not flowable and it’s very difficult to get into the subsurface. If you go back to what Matt showed earlier, this is a sandy clay site, sick plume, big area. The idea of injecting the powdered activated carbon into a plume like that is just, the logistics, it’s challenging.
So with that came the development of PlumeStop. And with PlumeStop, what we did is powdered activated carbon and we [inaudible 00:15:42] it down about 1-2 microns in size. So to put that into perspective, 1-2 micron is about the same size as bacteria or clay particles. That carbon is then suspended in a proprietary organic polymer, which creates what the tagline is, which is a Liquid Activated Carbon. It looks a lot like what you see in this image and it’s flowable can be injected under low pressures. At this particular site we were averaging under 30 PSI across the entire area so that gives you a sense of what we were able to do in a clay sand formation. If you want to go to the next slide, Matt, we’ll talk a little bit about some of the strategy and our involvement out there.
So you know Matt mentioned earlier about pre-remedial design investigation. He showed some information on that. They did some extensive analysis to answer a couple questions. First question was how thick is this plume? You know that the early investigation said it was 20-foot thick and was 1700 feet long. The question going into it was is really 20-foot thick and then in their pre-remedial design investigation, they looked at that on macro scale and determine that it was. When we came into our pilot test, we wanted to go and hone in on a macro scale and see if our investigation correlated with their pre-remedial design investigation within the specific pilot test treatment area.
And to do that design verification, as we’d like to call it, we did two things. First, we did continuous soil cores with the goal of trying to identify mass flux zones. Okay, and as part of the mass flux zone identification, we did analytical sampling, vertical profiles sampling on about a one-foot interval, and then we also did what we like to call Settling Tubes. Settling Tubes are used to assist in determining the percentage of fines and course material particles within a particular sample. And then, we’re also looking at sand sizes and sorting.
And on this next slide you’ll see some specific samples collected from within this treatment zone. These samples range from 24 feet to 27 feet. And really what we’re looking for here is mass flux zones. We’re trying to see on micro scale: Are there areas that have more sand than others? Are there other areas with more clays than others? And then we go back and correlate that with the vertical profile sampling that was done to see if is it truly, to answer that beginning question, is a truly 20-foot thick.
So the result of our efforts was that it correlated with the pre-remedial design investigation. The plume was truly 20-foot thick and there were many micro fractures and small sand stringers that were discontinuous throughout the zone, and which served as the transport zones within the aquifer.
Matt: Okay thank you, Barry. I think one of the interesting parts of this project were the areas in which we were working, as I’ve showed earlier, what the landscape looked like. Our first pilot test area was again around awhile called BL-55-II. It’s actually located behind the truck. And it’s located right off of a roadway. So the access for this location was actually very good, We had no issues with access and all that changed when we move to our second location but moving on, whether that was good during this event.
We collected baseline concentrations of baseline samples and what we found at the first location, the baseline concentrations were on the order of about 12 ppm of TCE. We conducted the pilot test and collected performance monitoring samples. Six months post-injection of the pilot test, the TCE was completely degraded the only thing left was cis-1, 2- DCE at a concentration of 375 ppb.
After 12 months, we saw the cis bump up a little bit up to 1100 ppb. And we’ll be talking a little bit further about that later. But the overall results were 97% and 90% reduction of the total cVOC sat this location in six and twelve months, respectively. The other things we noted where the indicator parameters were very positive in indicating that the degradation process was ongoing.
This next slide just shows a graphical depiction of that you could see starting back in 2012 when we first put this well and we’ve collected samples and was basically a migrating plume you can see the increasing concentrations before we did our pilot test. The green line represents the pilot test injections and you can see what happened within one month, the concentrations drops dramatically. After six months as we mentioned we had 375 ppb of cis-1, 2 and then 1100 after approximately one year. You can see here also the blue represents the TCE concentrations and the red represents the total cVOCs, which in this case is primarily cis-1, 2.
Then we move down to BL-59. Right before we move down to this location we got about three to four inches of rain of course, and making access to this location is next to impossible. Fortunately, we worked with our drilling contractor and Regenesis field folks and they were terrific in implementing the pilot. We ended up using timber mats after trying several different ways to access the area. The timber mats proved to be the most successful way of getting to these locations.
The baseline concentrations of BL-59, as you could see, we did have a little bit of cis-1, 2-DCE about 90 ppb and the TCE with around 12 ppb, much lower representing the leading edge of the plume. After we did the injections the performance monitoring results, after one month, showed non-detect of all see cVOCs, which was sustained through 12 months or 100% reduction of the cVOCs. The indicator parameters at this location we’re close to the baseline concentrations and we didn’t see much change in that but that’s likely due to the fact that the initial cVOCs concentrations were solo at this location.
Once again here’s another graph just showing there what we’re discussing graphically. So you could see the concentrations total cVOCs up to over 20. We did our injections, they drop down to ND and they sustain that for over a year.
So based on those results, I’m sorry I want to go through the concentrations in a tabular format so that you can see it. And Barry wanted to run through one of the notations that we saw as far as the results of the cVOCs and particularly the cis-1,2 at the BL-55 location. Barry…
Barry: Yeah, thanks Matt. So really the goal of this is to predict the question that may rise, which is: What about cis production? Couple main points I want to make. First off, funded from a biodegradation standpoint, this is a reductive dechlorination project. We put in HRC. We put in by BDI and we are promoting reductive dechlorination through this process.
And to add to that, a couple weeks ago, we did another webinar, which was on reductive dechlorination and ERD. And we did a multi-site review and we were trying to establish some trends, see what what’s expected at a ERD site. Couple things that we noticed in that evaluation of the data is that, you know, on average, we’re seeing about 2X to 3X increase with peak cis concentrations as compared to your parent product is a TCE or DCE.
So, for instance , if you have 10 ppm TCE, you would expect up to a 20 to 30 ppm of cis at peak, and that peaks cis formation, you know, in our data has been hitting between six months and one year. So we are right or right in that wheelhouse from its timing perspective but what you don’t see it this site is cis two to three times greater than TCE.
So while we are seeing some cis production is very muted compared to what we would expect under a traditional ERD. The reason for that is the PlumeStop and that the degradation process is occurring. PlumeStop is making it more efficient. And, you know, I still tell clients, if you think about it the ERD is occurring under the veil of PlumeStop, they’re just not seeing everything in the water. And, you know, my colleague always likes to say that this peak is think Alleghenies and not Himalayas. And that we’re seeing much shorter peaks with PlumeStop-promoted ERD projects.
Matt: Thanks, Barry. So moving on, after the success of the pilot test we conducted remedial design and what the design consisted of was three injection barriers through the transect the plume at varying distances from the source. Each of these barriers was 400 feet long. And we worked with Regenesis to determine many things as far as the design goes but particularly the injection point spacing, the dosage amounts and the product volumes. And honestly, we have to say, that that working with Regenesis was a very great process. They performed, they really showed their worth during this phase the investigation and we’ll get into a little bit more detail about the design here shortly.
We also worked with the off-site landowners on access issues. After our experience at BL-59, we realized that we were going to only be able to access that area if we were to build a road through that to get down to the third barrier, which I’ll show you here shortly. It was through a swamp and that was no easy process. It ended up taking us quite a bit longer just to get the road in than we had originally anticipated.
We discussed this approach with the regulatory agencies and submitted a remedial action work plan, which they reviewed and approved. Therefore, we proceeded implementing the work plan and that work was just conducted from November of 2015. We completed the full-scale application in January of 2016.
Here’s a picture of the full-scale design as we had originally laid it out. You can see the plume and the contours that make up the plume again the source area and the three transect barriers that we designed: one near the leading edge of the plume, one mid plume and one about 300 feet downgradient of the source area. I’ll show a blow-up of each of those sections now.
Barrier Design-1 which is the one closest to the source area consisted of 59 injection points, 21,000 gallons of PlumeStop, 270 gallons of HRC, and 48 liters of BDI. It included a single row of injection points across the entire width of the plume and then a second row of points throughout the core of the plume. And there were different dosage amounts and product volumes that were injected in these two different barrier rows.
The mid-plume barrier or Barrier-2 was also 400 feet long. It consisted of 50 injection points, 22,000 gallons of PlumeStop, 180 gallons of HRC, and 40 liters of BDI. And it was a very similar design as the first barrier, where we had one single row of injection points across the entire width of the plume and the second row of injection points throughout the core or this area.
The third barrier was a little different than the first two. The concentrations are obviously much lower. It again extends 400 feet across the plume. It had 50 injection points, 10,000 gallons of PlumeStop, 100 gallons of HRC and no BDI was injected along these points. The reason for that was that we saw some degradation of the TCE down at this location. We did see some cis 1 and 2 and that was really the first place we saw that throughout the entire plume. That may be related to the fact that it’s located in a swamp and swamp may be providing some recharge that has higher TOC values and what we saw further upgradient.
This is a slide showing the completed remedial action. What I’d like to draw your attention to is the blow-ups of each of the three areas. This first one was the one closest to the site or barrier area one, again, mid-plume, barrier area two, and leading-edge plume, barrier area three. And you can see the roads that we installed to access those areas.
We did have challenges, two in particular for this remedial action. First, obviously, as we’ve been talking, the swampy timbered area and just getting access down to barrier area three that added a significant amount of time. The second challenge that we weren’t expecting was the difficulty that we had in product delivery at barrier area one.
We started at barrier area three and completed that those injections and barrier area two without really any problem injecting the required volumes into those injection points. We got to barrier area one, we were able to inject into the core of the plume. But then as we moved out further to the flanks of the plume, it became much harder, and there were fewer sand stringers which required us to inject more volume into fewer points in this location. And you can see on the blow up there are fewer points is particularly on the west end of this barrier.
The other thing I’d like you to pay attention to are the three wells that we’re gonna use and talk about to evaluate the performance of the remediation in the three areas. The most upgradient barrier we’re going to be looking at BL-22, the second barrier area, BL-62, and the third barrier area, BL-59. We conducted performance monitoring. We’ve completed the three and six-month events and there’s a one-month post-injection events planned for January of 2017.
Again the three wells that we’re going to look at and talk about here BL-22, BL-62 and BL-59 and the reason we’re looking at those particular wells are because they are located what we consider to be the zone of influence of the injections. Other wells, based on the ground water flow, which is very slow, aren’t really representative of what’s going on or the result of the injections.
So looking at BL-22, we started with an initial concentration of almost 17 ppm. And you can see that breakdown. And then after three months, all that was left was 448 ppb of TCE and no daughter products. That’s a 97% reduction in three months. After 6 months, all the TCE was gone. We had very low concentrations of some of the daughter products and 98% reduction after six months.
BL-62 is located on one of the flanks and not in the core of the plume near the second barrier so we had lower initial starting cVOC concentrations. After three months, again, everything was destroyed, 100% reduction, and then those reductions persisted at 12 months after post-injection. BL-59 was one of our pilot study wells and you know our initial concentrations were low because we have conducted the pilot test there. And basically, what we were doing here is to showing that 21 months, post injection of the pilot, we still were able to sustain 100% reduction of the cVOCs. The other thing to note was many of the indicator parameters showed positive signs of ongoing degradation.
So just summarizing what we’ve talked about so far, PlumeStop was used in both pilot test and full -scale applications at this site to treat the downgradient portion of the long narrow cVOC plume, 1700 feet. The pilot test results indicated are very rapid and sustained degradation of the cVOC in groundwater. The post-injection performance monitoring of the pilot resulted in 90% to 100% reduction of cVOCs. And the concentrations of those cVOCs were fairly significant in mid plume.
Based on the success of the pilot test, PlumeStop was also used in full-scale implementation utilizing three injection barriers that were 400-feet long on each. Preliminary performance monitoring that was conducted as part of the full-scale implementation indicated contaminant concentrations reductions of 98% and 100% for the wells that were located within the zone of influence of the injections. The indicator parameters are again showing positive signs that that degradation process is ongoing. One year performance monitoring event will be taking place in January and we will allow for evaluation of the remedial progress of the injections at other locations that are further downgradient of the injection area.
That concludes this portion of our presentation and we are more than happy to go through questions.
Barry: All right. Thanks, Matt. So let’s see here. I’m gonna walk through a few questions that have been posted. First few questions are just project related. Did you have any problems getting regulatory approval with PlumeStop in, say, South Carolina?
Matt: We did not. They were very receptive to just about everything we did and in particular the UIC process went very smooth and they were extremely easy to work with and had no issues.
Barry: Okay good. For the injection, did you use injection wells or injection points or direct push?
Matt: Yes, for the pilot, is that what you mean?
Barry: For the pilot and the scale…
Matt: Yes. We use direct push. We use those. We did consider using injection points, permanent injection points, but in this environment it’s just as easy to go in with the DPT and it turned out to be very successful.
Barry: Okay, I know you hit on this earlier map but I see a couple questions here so, is the source area being addressed and if so with why and how’s it going?
Matt: Yeah, I did touch on that originally back in 2010. We had done a fair bit of work in the source area which culminated in a pilot test using zero-valent iron we injected in the pilot and it showed positive results. So we implemented a full-scale injection using that product and it was marginally successful. It did shrink the plume a little bit. We found out that additional work needed done.
So in 2014, we contracted with Regenesis and used a combination of 3DMe, HRC and BDI in a little larger treatment area that extended under the building and that seemed to be quite successful. We’re in the process of performance monitoring to evaluate those results but we’re seeing to date is some contraction of the plume, particularly at the leading edge and along the sides of the treatments zone, which is what we’re expecting. So those wells in the source area will also be included in the January 2017 sampling event and we will be able to further evaluate the performance of that work.
Barry: Okay, great. Is the downgradient residential area concerned for vapor intrusion?
Matt: It’s not. And the reason being, our unit that we’re most concerned with…well, first of all, the plumes not there yet. It is a concern, I mean, it would be a concern had that had the plume continue to migrate. But what we have is our zone of concern is located from 25 to 45 feet below the ground surface and as I mentioned in when we were looking at that cross-section there is a zone of cleaner water in unit one that extends from 5 to 25 feet below the ground surface so that that keeps vapor intrusion from becoming an issue.
Barry: Okay. Okay and how long did the full-scale application take to implement?
Matt: It took a little over two months to complete I believe we probably could’ve knocked two weeks off of that time frame had we not had the access issues. We had particularly at barrier three. And then I’d say we had additional delays related to the injection problems that we encountered barrier one when we were having difficulty injecting the product at that tighter clay in that portion of the formation.
Barry: Okay, all right, and in the low-lying swampy area what types of special actions were needed to work in there?
Matt: Well, yeah we talked about that. I got to show some nice pictures of what we were dealing with. So initially when we were doing the pilot and we encountered what became a huge swamp. We tried many things we tried bringing in gravel with your textile, plywood many different things and what we ultimately found that that worked was just use of timber mats. So it did extend the amount of time, but once we were able to get the mats and procure them and move them around, it ended up being a…that’s what we used.
And for the full-scale, we, you know knowing what we learned from the pilot, we knew we had to put a road in and that’s what we ultimately did and then that that made it much simpler to get to the locations.
Barry: Okay and a continuation to that, someone asked, was this swamp or a wetland? Were there any wetland issues regulatory issues you entered?
Matt: They weren’t. And it’s only a swampy area because it does dry out. You know most of the year, it’s just when you get large rain events, it drains. I mean, it lays there but it takes a little bit of time to drain but ultimately it does dry out.
Barry: Okay, good. Okay, I touched on this when what injection pressures were you experiencing during the works. I’ll take that one.
Generally, we were less than 30 psi throughout the majority of the project. And had a couple areas where we peaked up over that at certain depth intervals, but it was very intermittent, so generally speaking, less than 30 psi.
So you mentioned that you had some trouble injecting at barrier one what sort of trouble and how do you work around that?
Matt: Well, that that goes on to the injection pressure that we had. They were significantly higher in barrier area one and we attributed that to just the fact that there were fewer sand stringers that were there to accept the product as we were injecting. It was interesting, you know, after the experience of barriers two and three, where we had no problems at all.
We weren’t it and we got up to barrier area one and just encountered this tighter formation and so with the use of higher injection pressures, we were able to inject the product that was required at each of the areas, that being the core, and then the outer portions and the flanks of the plume. On that western side, as we showed, we weren’t able to get all the points in, so what we ended up doing was injecting say double the volume and maybe half the points that were required. So we did get all the volume in it just wasn’t in each of the points that that we had originally planned on.
Barry: Okay good. Okay, this questions for me and that I noted that cis production was lower with PlumeStop than ERD, but it was still increasing as a last data point, what do we think is occurring here?
You know, as I mentioned, in most of our data were seeing peak cis and vinyl concentration that six months to a year, post-injection. So there’s that is there the potentially could go up a little bit from where it’s currently at 1 ppm. I think that could occur, but I were close to that number. I really feel like we’ve reached our peak levels and then we’re going to start seeing on down.
And is that breakthroughs a rebound? You know I wouldn’t call it rebound. There’s a mass transfer phenomenon with carbon in general that there’s a greater affinity to sort of TCE than their at cis. So one thing to remember, this is a barrier, it’s a pilot test and there this upgradient parent mass continuing to flux through.
And so as a flux through and there’s a equilibrium between absorption and degradation, you can see…We think that’s why we’re seeing the 1 ppm at cis. But if it’s a standard ERD approach, we would expect 20 ppm at cis or more. So there’s a lot on there or it’s being degraded rapidly.
Another question that’s for me, and I’ve seen this question in many forms, it’s vinyl chloride. Why haven’t you seen vinyl chloride? You’re correct that we haven’t seen monochloride at the site. We have seen ethane and a few the samples in certain areas. So that is there.
The geochemical parameters support reductive dechlorination. So we’re confident with the fact that the end product is being developed and geochemistry is correct. We’re seeing sulfate reduction all those sorts of things you want to see.
We’re confident that we’re seeing complete degradation so the question where is the vinyl chloride, there’s two possible scenarios there? One, it’s being degraded more rapidly than then it is being released into the water, so you’re not seeing it in the water. The other is that it’s just sort on the carbon so never actually releases from the carbon it goes completely through that degradation process without seeing them. And we’ve seen that on other sites as well most of the PlumeStop and ERD sites that I’ve reviewed, daughter product production is muted compared to ERD alone, yet the geochemistry looks very similar.
All right. Okay so, we’re there any underground utility challenges at the site?
Matt: There were not. There is one sewer line that runs down through the area but it wasn’t in the area where we were doing our injections so we, after having it defined, and we had that the local utility come out and confirm its location. We really didn’t have any issues with that at all.
Barry: Okay, here’s another good one pH. What about the pH in the groundwater? And I’ll take that Matt.
In that one of the earlier slides Matt showed, we did shows the pH did in one of the wells. We saw pH drop below 6. In our experience, biodegradation rates may slow significantly at a pH below 6. In this scenario we believe that the pH drop was temporary and likely due to an influx of organic acids released from the HRC in that localized area basically into the well. And we expect that to stabilize overtime. We believe this because it again if you look at the geochemistry we have solid evidence to support the biodegradation is occurring and that your ratios to TCE impact DCE in parent are there. So in this case, pH has not been a challenge thus far.
All right, so I’ve got a good question kind of wrap up question here for you Matt. What’s next for the project?
Matt: That is a good question. We consider the remedial action that was done in both the source area and at least the downgrading area as being the final remedial action for the AOC-1 plume. Obviously, we’ll be evaluating the source area and if additional work needs done there, that will probably be the next thing that needs to be done. But on a site-wide basis, we are in the process of conducting a risk assessment for the entire site. And then depending on the results of that risk assessment, we may be conducting some form of limited corrective majors.
We’re actually in the process of evaluating that right now and in the short term we will be conducting some additional groundwater monitoring, probably on a quarterly basis for at least another year or two to evaluate the success of the remedial action in AOC-1. But we feel the rest of the site of the other two AOC’s and all the other SWMUs have been adequately addressed and we expect them to move forward through the risk assessment and we’ll have to see what happens beyond that.
Barry: Okay, good. See one final question here I think I can pick off really quick. It’s, understand that the liquid activated carbon was injected via direct push, could you inject it through permanent injection wells? So short answer yes. You absolutely could and we’ve done that. Typically, it’s cost-benefit, But, yeah, short answer, yes it can be injected through permanent injection wells.