ERS have completed the remediation of perchloroethylene (PCE) contaminated soils and groundwater at a former tannery near Kinghorn, Fife.
The Site
The groundwater in shallow bedrock at this site in Fife was contaminated with perchloroethylene (PCE) associated with a former degreaser building when the site was used as a in a tannery in the past.
Prior to ERS’ involvement, a 5-year programme of monitored natural attenuation had been undertaken. However, as the site had been recently earmarked for a housing development, active remediation was required to expediate treatment.
Proposed Remediation Strategy and Further Investigation
ERS proposed a strategy at tender stage based on the injection of reagents into the groundwater to degrade contaminants in-situ. Following acceptance of the remediation strategy by the regulator (SEPA), ERS’ first step was to gather further data to complement previous site investigation data and confirm the proposed design.
Six new boreholes were drilled into rock and installed with standpipes suitable both for groundwater sample collection and to support subsequent in-situ treatment, helping minimise costs.
Groundwater monitoring and sampling from the new boreholes showed that concentrations of chlorinated solvents in groundwater were locally significantly higher than anticipated and suggested the possibility of residual dense non-aqueous phase liquid (DNAPL) onsite.
ERS then undertook a short phase of shallow soils investigation to identify any relict structures, tanks or grossly impacted soils which could host DNAPL above the shallow fractured bedrock and may compromise the groundwater treatment. These works exposed some grossly contaminated soils which were removed. The works also identified that the footprint of the degreaser building was slightly offset compared to historical plans and, therefore, the injection grid was adjusted accordingly.
Impacts of Coronavirus
Just before in-situ remediation works could start onsite, the UK went into lockdown due to the Covid-19 pandemic. In Scotland, this meant the closure of construction sites - this reduced the time available for remediation works on the site by 20%!
Once construction sites were allowed to reopen in the summer of 2020, with new social distancing, regular Covid-19 testing and other safety measures in place, our team set about implementing ERS’ in-situ remediation strategy.
In-Situ Remediation
ERS’ strategy involved both in-situ chemical reduction (ISCR) and enhanced reductive dechlorination (ERD). This was achieved by injecting a combination of reagents comprising zero valent iron (ZVI) and a organic carbon source and electron donor. In addition, a PCE degrading mixed microbial culture was also introduced to drive anaerobic reductive dechlorination, as our in-house qPCR testing had shown low levels of chlorinated solvent degrading bacteria on the site.
Reagent injection was undertaken by ERS’ in-house team and equipment using inflatable packers and injection pumps.
All works, including drilling, were undertaken under ERS’ Mobile Plant License with associated strict controls of noise, dust and other emissions to the environment.
Monitoring Remediation Progress
Following injection, ERS monitored treatment progress via in-situ measurement of field parameters gathered using low flow sampling techniques, laboratory analysis of volatile organics, chloride and dissolved ethene to check reduction in concentrations, and in-house qPCR analysis to check on relevant microbial community members.
The Results
Comparison of before and after concentrations in groundwater samples showed a 96% reduction in overall contaminant mass at the site. Furthermore, additional checks showed redox conditions were still supportive of reductive dechlorination and qPCR analysis confirmed the presence of bacteria capable of full contaminant breakdown. This meant that the already low contamination levels would continue to decrease further at the site into the future.
Thanks to some hard work from the team, ERS was able to submit the works verification report within the Client’s original timescale, despite the delays caused by the construction sites shutdown. The report was accepted by the regulators, the injection wells were subsequently decommissioned, and the client was able to commence development of the site on time!
Following on from this successful groundwater remediation, the Client commissioned ERS to undertake further remediation on another part of the wider site: looking for an old underground tank associated with former candle works and removing it along with the surrounding contaminated soils.
