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Information relating to Groundwater at the
Thor, Margate site
Thor Group Ltd is currently monitoring groundwater samples from boreholes on and around it's Margate Site as part of a decommissioning process.
Chemical manufacturing operations ceased in September 2005. The company has been working with the Environment Agency for a number of years to establish the extent of it's chemical footprint after 35 years of site activity.
Information from soil sampling and water testing is being gathered together to pin-point any chemical contamination that may have occurred over this period, in order to put a suitable remediation plan in place which will bring the site up to the required standards.
Three solvents have been identified in the groundwater - benzene, toluene and Aromasol (a mixture of aromatic hydrocarbons).
Solvent recovery and water purification processes have already begun and it is likely that this work will continue for a number of years to come.
History of Investigation
In early 2003 Thor Overseas Ltd undertook an intrusive site survey in support of it's application for IPPC permitting (a new licensing system for industrial processes overseen by the Environment Agency).
This involved testing the groundwater below the site and the soil around the site for any contamination by chemicals, in addition to assessing the historical processes and current uses of the site.
As a result of elevated levels of certain materials discovered during these tests, the company contacted the Environment Agency, Thanet District Council and the Water Authority in August 2003.
Since then regular meetings between these bodies, the Thor Management and Ecologia Environmental Services Ltd (contaminated ground specialists) have been held in order to:-
fully investigate the extent of the problem
regularly monitor the levels of contamination
plan and instigate the processes necessary to remediate the site.
Nature of Extent of the Contamination
The collection and analysis of an ongoing series of soil and water samples, from both within and beyond the site boundaries, has established that in addition to some minor contaminants there are significant levels of three solvents in the groundwater below the site.
These are individual substances benzene and toluene and a third mixed substance, Aromasol, which is a blend of many different solvent materials including tri-methyl benzene.
The chemical and physical properties of these substances are given in Appendix I.
Also established is the fact that the chemical plume in the groundwater below the site has migrated beyond the site boundary to the North. This direction is away from public water supply abstraction wells.
The full extent of the plume has not yet been determined but further works are in hand to do so.
The same three substances are also present in certain areas of soil within the site, along with compounds of mercury (also characterised in Appendix I).
Origin of the Solvent Spillage
The processes that generated the substances described above relate to the production activities carried out on site from 1973. The site is no longer operating so no further risk is posed.
The exact cause of the contamination is unknown but there are various possibilities such as physical spillage, overflowing of collection tanks or leaking pumps.
As production and storage of chemicals ceased on the site approximately four years ago, it is not considered as high a priority to establish the cause of the pollution as to locate the areas of contamination and to remediate the site.
Remediation of the Site
The removal of site buildings this year has made it possible to fully investigate the area. This will allow the development of a full remediation strategy for removing ground contaminants which is likely to include the removal and disposal of some soil.
These measures will commence in 2009.
Remediation of the groundwater by biological treatment began at pilot scale level in 2006 and has gradually been scaled up since then to the current level of 30 cubic metres per week. The treatment uses bacteria to break down the contaminants into carbon dioxide and water.
This process delivers the treated water to foul sewer and, because of the continuous pumping of groundwater, should prevent any further plume migration and perhaps retrieve some of the off-site plume.
The scaling-up of the process will continue until a sustainable treatment of groundwater is achieved. The likely duration of the water purification process is unknown at this stage.
THOR GROUP LTD.
Summary Report for Thor Chemicals 25th February 2008
The site is permitted to produce organic chemicals however manufacture ceased in 2005 and R&D activity ceased in December 2007. The permit remains in force until they surrender it but they would not be able to recommence any manufacturing without our permission.
We first became fully aware of the contamination in 2003 following investigative work done by Thor as part of their application for the PPC permit. Since then we have focused our efforts on understanding the nature of the contamination (which has involved extensive sampling) and reviewing Thor's proposals to remediate the groundwater.
Thor are currently voluntarily undertaking the investigation and remediation work on site. The current activities on site include
decommissioning of the buildings associated with R&D and manufacture
admin work in the offices
running a pilot scale treatment plant for the treatment of the groundwater.
investigative work associated with establishing the extent and nature of contamination
We do not consider the groundwater pollution to present an immediate risk to human health as the natural flow of groundwater is moving the plume of contaminants away from potable abstraction points. We are prioritising the work with groundwater remediation as this is the contamination that is most mobile.
The land contamination (which includes the mercury) is not considered an immediate risk to human health as
the site is not open to the public
the highest risk areas on the site are covered by concrete hard standing thereby reducing exposure to site staff and the risk of it transferring off site
the levels of soil contamination (including mercury concentrations) outside the boundary of the site are not considered significant
Remediating the contaminated land is the next priority but we have to ensure that any remediation does not mobilise the existing contamination causing it to spread off site.
As the site is no longer operational we have a reduced inspection frequency as there is little above ground to inspect. Our last site inspection was on the 5 August 2008. We anticipate that the next inspection would be in Quarter 2 of this year (Apr-May). Following our last inspection we have been in constant contact with Thor reviewing the plans, proposals and monitoring data that we have requested that they provide.
The outline plan going forward for the site
Thor is currently establishing the extent of the groundwater plume
We have requested that they provide the information associated with this in March
We are also reviewing their proposals for groundwater remediation and anticipate making a final decision on their proposals by the end of March when we have their latest monitoring data.
Thor will then need to obtain the relevant permissions to proceed with their plan
We will monitor the progress and effectiveness of the groundwater remediation.
We will also get Thor to progress the ground remediation to address the land contamination