Integrated remediation of a mixed pesticides TPH and VOC plume at a former industrial site
This video explains the in situ remediation of significant groundwater contamination with petroleum hydrocarbons, VOCs and a mix of organochlorine pesticides, including pentachlorophenol, Lindane and Dieldrin. Watch the video to find out how Soilfix worked closely with REGENESIS to design and implement multiple in situ approaches, delivering a successful remediation solution to the FTSE100 client and their consultant Ramboll. Video length: 7m 08s
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Located in the south east of England, an industrial site had been occupied by a timber yard, incinerator, fuel storage tanks and a saw mill. In the 1980s, these were demolished and the site use changed to light commercial and a car park for a FTSE 100 Company. In later years, it was decided that the site should be prepared for redevelopment and due diligence site investigation was carried out by Ramboll Environment and Health UK.
This identified significant contamination of soil and shallow groundwater with a wide range of contaminants: petroleum hydrocarbons, volatile organic compounds including BTEX, trimethylbenzene, and a mix of organochlorine pesticides, including pentachlorophenol, Lindane and Dieldrin. Modelling by Ramboll confirmed an unacceptable risk to the surrounding sensitive receptors, as well as an unacceptable human health risks to potential future site users.
Soilfix, a multi-disciplinary contaminated land remediation contractor, was asked to provide a fast-track, remedial solution. Steve Jackson, Soilfix: “We were approached by our client, a FTSE100 company, and their consultant Ramboll, with whom we’ve worked a lot before, to help them address their lease surrender process, because the site had soil and groundwater contamination and their lease required them to address that contamination to the satisfaction of the regulators.”
Steve Jackson, Soilfix: “We carry out a range of soil and groundwater treatments and enabling works for the developers and land companies, to help them prepare sites for redevelopment and also for industrial clients to help them manage their environmental liabilities or surrender their leases.”
Soilfix originally looked at the site at the remediation options appraisal stage, and realised that a range of approaches would be required to address the groundwater contamination problem. So we contacted REGENESIS to come up with some collective ideas how to best address the problem.
Steve Jackson, Soilfix: In conjunction with removing the main source of the contamination, the underground storage tank and the surrounding unsaturated zone and soils, REGENESIS proposed a combined in situ remediation approach, using a combination of RegenOx® initially, to lower the hydrocarbon loading and compounds such as Pentachlorophenol, in advance of injecting PlumeStop® to act as a reactive treatment zone. The strategy proposed a number of injection wells that we could also use for further characterisation in terms of contaminant concentrations, groundwater flow and so on.
Tim Blake, Soilfix: “Once we got to the site, it was discovered that the geology was more variable than anticipated, with some areas experiencing low permeability. Steve Jackson, Soilfix: “We were getting some daylighting issues from the remediation wells. What we found was the depth of the terrace gravels was very variable and shallow in parts of the site. And also we thought that the permeable lenses were quite discreet. To overcome the challenge, REGENESIS quickly proposed to switch the approach for the primary saturated zone treatment.”
Rhys Goddard, REGENESIS: “After discussions with Soilfix we were able to adjust the design. We used a mix of PersulfOx® in areas where the ground conditions were more challenging, and RegenOx in areas where we knew there were underground services present.” RegenOx is an ISCO technology specifically designed to be compatible with all types of underground services.
Steve Jackson, Soilfix: “REGENESIS also proposed hydraulic conductivity profiling, which is an in situ technique which is not widely applied, which we thought was a really good idea, to better understand and characterise the injection zone for more permeable lenses that we could target with the chemical oxidation and also the subsequent PlumeStop injection. The mapping by the HCP testing, it did work really well.”
REGENESIS carried out the in situ chemical oxidation treatment in fixed wells, on an injection grid of 4 by 4m spacing. What we found with the persulfate injection, the PersulfOx, was that we achieved significant reductions in the higher concentrations of TPH, Pentachlorophenol and other organics, which reduced the loading overall in advance of the PlumeStop injection.
Second Phase Treatment
We are now entering the second phase of the groundwater treatment of the site, which is the injection of PlumeStop. In this second part of the groundwater remediation works, PlumeStop was injected across the treatment area supported by ORC-Advanced® in selected locations to adsorb and enhance the natural attenuation of the remaining pesticides and petroleum hydrocarbon concentrations in the groundwater.
Rhys Goddard, REGENESIS: We’re injecting plumestop from 1.5m down to 3.5 meters below ground level (BGL) in 0.3m intervals. In selected areas we’re then injecting ORC Advanced from 3.5m back up to 1.5 meter BGL in 0.5m intervals. This ‘top down, bottom up’ treatment approach allows us to complete the work more efficiently and saves us time. This was important on this project, as there were strict deadlines to adhere to.
Steve Jackson, Soilfix: “The projects was a great success, not only did we meet the betterment based objectives that we agreed with the client’s consultant Ramboll, for many of the contaminants we ended up meeting the stringent criteria that were originally derived by the risk assessment. So, this enabled timely reporting and the client surrendered their lease on their programme. We felt this was largely down to the project team approach that we took with REGENESIS, from conception through to validation and completion of the project in conjunction with Ramboll.”
“One of the things I was most pleased with about the project was – I’m always one for using new innovative technologies and giving them a go. So to use PlumeStop for the first time, for it to work so effectively was really pleasing to me, in spite of how challenging the project was.”
Feedback from Ramboll and their client, they were delighted with how the project performed. “They both appreciated how tight the timescales were to carry out the remediation works and then carry out groundwater verification in a very tight period, but they were very pleased to surrender their lease.”