Ground contamination
A detailed review of environmental, geological, hydrogeological, cartographic and recent historical public records, carried out as part of due diligence relating to the purchase of a house in 2009 in Upper Brents, which borders the proposed development site, showed that the land was previously used for brick earth extraction and was subsequently backfilled with waste.
There was little information on the waste composition except that it is likely to be local and both industrial and domestic waste. Contamination problems have been recorded and a note on one of the Registers of Landfill says the site was used for ‘difficult wastes’, usually meaning contaminated material.
There does not seem to be any current site investigation apart from a few reference boreholes and maps by the Geological Survey or Environment Agency. Since the site has been randomly excavated and randomly backfilled with a random selection of waste materials there will be large variations. Because of these uncertainties, conventional representative sampling is not possible, and all the waste material would need examination and testing for contaminating content. Any predictions will be just a guess unless a detailed investigation is carried out. The lack of a sufficiently detailed survey could be regarded as negligent. A decision on the site feasibility therefore requires a detailed site investigation of the waste fill extent and composition.
Clearance, reprofiling and construction carry risks of contamination of the aquifer lying in the chalk strata below the site, drawn on by the Shepherd Neame Brewery.
Surface water drainage into the mixed waste may become contaminated and hence soakaways are unlikely to be acceptable, and some other means of disposal is required.
It is highly concerning that the Kent County Council’s Minerals and Waste Planning Policy Team submission does not acknowledge the unknown nature of the backfilled materials and the likelihood of ground contamination.
For further details see section 2, page 8
2. Ground contamination
2.1 Geotechnical & Hydrogeological Aspects
In 2009 a detailed collection of all the available environmental, geological, hydrogeological, cartographic and recent historical public records was carried out by Envirocheck (Landmark Information Gp. - Order No 28259928-1-1 ref 0123 29-6-2009).
This archive survey was done as part of the due diligence checks for the purchase of a house at 101 Upper Brents on the border of the current proposed Ham Farm development. The survey was considered necessary because of the extensive workings and flooding known to have occurred previously. The survey covered an area within a minimum radius of 1000m from the house, which includes the proposed Ham Farm Development.
The records show intermittent sand and gravel deposits and clayey silt (brick earth) deposits over chalk. This description is a summary with other (sometimes cemented) deposits present. The brick earth had been extensively extracted between about 1890 and 1920/1930
Temporary railways, lagoons and temporary structures are shown on the Ordinance Survey drawings at various dates. The depth of the brick earth excavations is not given but it would usually be above the local water table to allow working. It is likely a thin brick earth cover to the chalk would have been left in place at the base of the excavations to reduce water flow (partly tidal) into the site. The excavations have been backfilled with waste to an unknown depth and a thin clay or silty clay cover provided. Grass and crops are grown on the cover.
There was little information on the waste composition except that it is likely to be local and both industrial and domestic waste. Contamination problems have been recorded and a note on one of the Registers of Landfill says the site was used for ‘difficult wastes’.
site is generally within 500 to 1000m from Shepherd Neame Brewery, which is understood to use well water from the Chalk aquifer which extends widely and goes beneath the proposed landfill development as well as the Brewery. The Brewery is one of the oldest in the UK and supports a wide variety of employment in Faversham and the surrounding area. The risk of the Ham Farm development is that the works might cause the release of sufficient contamination to the aquifer to prevent or discredit brewery operations.
2.2 Site Investigation
There does not seem to be any current site investigation apart from a few reference boreholes and maps by the Geological Survey or Environment Agency (listed in the Envirocheck Report). Since the site has been randomly excavated and randomly backfilled with a random selection of waste materials there will be large variations.
Site investigation must necessarily involve excavating into the mixed waste to determine the extent, whether the remaining cover to the chalk is sufficient, and the type and proportion of the contaminants. The mixed waste material is placed randomly and to variable unknown depths and hence conventional representative sampling is not possible and all the waste material would need examination and testing for contaminating content. Any predictions will be just a guess unless a detailed investigation is carried out. The lack of a sufficiently detailed survey could be regarded as negligent. A decision on the site feasibility therefore requires a detailed site investigation of the waste fill extent and composition.
2.3 Construction
2.3 Construction
The process of construction would require removal of contaminated waste. As conventional representative sampling is not possible all the waste material would need examination and testing for contaminating content. Any predictions will be just a guess unless a detailed investigation is carried out. The lack of a sufficiently detailed survey could be regarded as negligent. A decision on construction feasibility therefore requires a detailed site investigation of the waste fill extent and composition.
Where a brownfield site is backfilled with domestic waste of this age it usually consists of ash and inert materials. It can be excavated, examined and tested for limited contamination which can be removed and the site material reconstituted to a condition and density suitable for new construction. Where a similar site is backfilled with randomly mixed industrial and domestic waste and the industrial waste is considered to be ‘difficult,’ usually meaning contaminated, there is no reliable procedure for restoring the site apart from removing the contaminants which may be extensive. However, excavation to sort and find such contamination will tend to damage drums, containers, sacks, etc and release contamination with no means of recovery.
In the circumstances as described it would seem appropriate to leave the waste tip areas undisturbed as green field allowing the Brewery and the relevant authorities to check regularly for contamination plumes at the boundaries and to be able to gain immediate access to carry out remedial works if necessary.
2.4 Other Matters
Should it be decided to proceed after considering the site investigation and contamination other reservations are as follows:
Piled Foundations
The irregular depth of the original excavation leaves an irregular depth of backfill. The backfill, however it is treated, will settle by different amounts over different time periods of many years. This means that structures are usually built on piles drilled down to the Chalk which do not settle significantly. A variable gap will develop between the base of the structure and the filled material below. This needs special detailing and special service connections to avoid fractured sewers, water supply or gas supply pipes below or adjacent to the structure, often in positions difficult to access. The services may need piling to avoid fracture and may need special pipe materials and connections because of the chemical content of the industrial waste.
Full venting is likely to be required because of gases produced by the waste.
Surface water drainage into the mixed waste may become contaminated and hence soakaways are unlikely to be acceptable, and some other means of disposal is required.
D W Cox PhD MSc BSc MICE FGS CEng 37 Upper Brents ME13 7DL
18 February 2024
The Kent County Council's Minerals and Waste Planning Policy Team submission (22 May 2023)
The submission states that the application site is not within 250 metres of any safeguarded mineral or waste facility, and thus would not have to be considered against the safeguarding exemption provisions of Policy DM 8: Safeguarding Minerals Management, Transportation, Production and Waste Management Facilities of the adopted Kent Minerals and Waste Local Plan 3013-30 (Early Partial Review 2020).
The submission further states that 'The applicant has prepared a Mineral Resource Assessment to address the need to investigate if there are any grounds to invoke an exemption from the presumption to safeguard the mineral resources of the application site from sterilisation by the proposed development.'
This clearly does not acknowledge the unknown nature of the backfill material and the likelihood, as detailed in the above information above, that the ground is contaminated.
