Former Joco Pit site in Borough Green

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Investigation of landfill gas contamination

All councils have a legal duty to inspect their areas for contaminated land. Where a council considers there is a reasonable possibility that land may be contaminated it should inspect the land to obtain sufficient information to decide whether or not it is contaminated.

Land at Tolsey Mead and Eaglestone Close is located on the former Joco Pit landfill site. The Council has monitored landfill gas there since 1991 when changes in legislation required the Waste Control Authority, in this case Kent County Council (KCC), to review redeveloped land which had been used for landfill in the preceding 30 years.

Initial borehole installation and monitoring was carried out jointly with KCC, however since then the Borough Council has continued to monitor landfill gas levels independently.

Having monitored since 1991, we now need to look more closely at this site as recent monitoring has shown a change in gas levels at one of our existing monitoring boreholes.

Need to investigate further

The Council makes its decisions about whether to investigate further or take action to remediate based on a consideration of the potential risk to human health and property from the possible contamination. This is called a risk assessment.

The Council appointed Leap Environmental Ltd to carry out a desktop study to ascertain the level of risk associated with the changes seen. Unfortunately there is inadequate data to complete the risk assessment. The Council now wishes to carry out further investigations to collect more gas data from across the site to confirm site wide conditions to enable a thorough and appropriate risk assessment to be made.

When monitoring began in 1991 eight boreholes were installed across the site as well as two just off site for control purposes. Unfortunately, over time a number of these have either become unusable or residents refused the Council access where they were located on private land. The works now planned will involve installing 8 new boreholes in order to assess a wider area of the site. This in turn will allow an accurate risk assessment for the site to be made. The works will involve an initial 3 month period of gas monitoring, including 1 month of continuous monitoring at 8 locations followed by 2 month of weekly spot monitoring.

Leap Environmental have been chosen to help us to do this. Our consultants are experts at risk assessment and they will collect information and provide a risk assessment that the council will consider when deciding whether the land is contaminated and if there really is an unacceptable level of risk.

We will only say it is contaminated if risk assessments show gas levels are causing an unacceptable risk to health.

Although these initial works are restricted to the former Joco Pit site comprising all properties on Tolsey Mead and Eaglestone Close (Zone 1) we have also written to residents of 2-18a Wye Road and 47a Annett’s Hall (Zone 2) as those properties directly adjoin the former Joco Pit.

We know that you will have a lot of questions and concerns and we've provided information on what we think would be residents' main concerns via:

Frequently Asked Questions tab (FAQs)

Two drop in sessions at Potters Mede on Wrotham Road are also planned for the following dates. Council officers and staff from Leap Environmental will be on hand to answer questions. Please joins us.

  • Tuesday 30 January between 6pm and 8pm
  • Thursday 1 February between 7pm and 9pm

Interim Report

An interim report, March 2018, provides a Preliminary Assessment based on results from the works completed to date. The report summaries findings from the site investigation including ground conditions, chemical test results from soil sampling completed and a summary of continuous gas monitoring data to date.

Final Report

A final report (with appendices A-D and appendices E-F), produced in June 2018 shows that results from this investigation have not demonstrated an unacceptable risk to human health from landfill gases with respect to Part 2A of the Environmental Protection Act 1990. The site has been assigned as low to very low risk. The report also outlines future recommended monitoring.

Following this report a letter was sent to all the households involved.

Additional Borehole Update

As recommended in Leap’s final report, an additional borehole was installed adjacent to BH2 (located in the turning pan of Tolsey Mead) on the 17 August 2018. This borehole is a dual installation designed to mimic the monitoring conditions in BH2, with both a shallow and deep standpipe. Low concentrations of petroleum hydrocarbons were recorded in the soils, however these did not exceed the assessment criteria. Gas monitoring results for methane were similar to those for BH2. Carbon dioxide concentrations were generally low. Read the full report.

Updated Gas and Soil Vapour Risk Assessment

Leap completed their monitoring programme in January 2019. The majority of the site including all residential properties is classified as very low to low risk, with BH2 and BH201 located in the road and not associated with any property, classified as moderate risk. The site is therefore not considered to pose a risk to residents. The council will continue to monitor the site on a monthly basis, and will review this frequency every 12 months. Read the full report along with appendices.

Further Information

If you have further questions then please email

You may find more information at the following websites.