The Long Read: Biggins Wood Site – Cheriton – Part 1

Two geo-technical reports regarding the Biggins Wood site (Cheriton) – owned by Shepway District Council (SDC) have been produced. The first in Oct 2010 and the second in Sept 2014. The second does not show up in the planning application – Y13/0024/SH.

There is Methane, a known explosive gas, at fifteen times the typical maximum values and seventeen times the typical value for carbon dioxide, a known poisonous gas  according to both reports.  It is considered that the Biggins Wood site from a gas point of view, should be classified as Amber 1 site according to the second report and the National Housing Building Council technical advice must be followed.

The soil and gases can be re-mediated – rid it of hazardous waste and pollutants and Environment Specialists who work with land which is contaminated have informed us that “any site is remediable, if you throw enough money at it.” And at SDC’s Cabinet held on the 31st May 2017, (agenda item 83 ) the budget estimates to be thrown at Biggins Wood is £131,000 before any tender or work begins on developing the site.

In the budget estimates at point two, it states:

Both issues were addressed in geotechnical reports at the pre-planning feasibility stage, and a brief summary of the existing reports was provided by Idom Meerebrook after our purchase.

The brief summary provided by idom meerebrook to Andy Jarrett (pictured) is dated the 27 March 2015. This information tell us then that SDC must have bought the land prior to March 27th 2015. However, the land registry says otherwise. It tells us that SDC officially became the Landowners on the 21st Dec 2016. The facts; which have been wholly provided and produced by SDC, contradict each other. So did SDC purchase the site prior to Dec 2016, but not register it, until Dec 2016? We’ll leave you to draw your own conclusions.

Back To School

Co2 is poisonous and Methane is explosive. These are the known side effects of the two gases.

Carbon Dioxide (CO2 )
Carbon Dioxide is toxic, odourless and colourless, and in high concentrations can result in asphyxiation. The gas is formed by the oxidation of carbon compounds such as that which occurs in landfill sites. When CO2 levels reach a concentration of 3%, symptoms of headaches and shortness of breath will occur; these become severe at 5%, and at 7 – 10% will cause suffocation.

Methane (CH4 )
An odourless flammable gas that is explosive when released into the atmosphere at levels as low as 5%, and exposed to a source of ignition. Methane is formed where there is below-ground degradation of organic substances e.g. landfill sites, sewage treatment areas, mining operations and peat bogs. Two boreholes in the central part of the site (WS115 and WS122) recorded some variable concentrations of methane; a maximum concentration of 4.7% having been recorded.

The 2014 report goes onto say

• It is therefore considered that gas protection measures suitable for an Amber 1 site should be incorporated into all the proposed residential properties on the site. This should include a ventilated sub floor along with a suitable gas resistant membrane sealed within the floor slab and across any wall cavity. All service penetrations must be suitably sealed.

Methane & Co2 are known greenhouse gas emissions and contribute to global warming. SDC have stated it will mitigate and reduce greenhouse gas emissions in its local plan at page 334 where it states

• National planning policy and legislation requires us to work to mitigate climate change, mainly by reducing our greenhouse gas emissions and promoting sustainability.

Yet all the while the site continues to release harmful greenhouse gases into the atmosphere in its current state. This is due to two important factors Rainfall (Precipitation) & Atmospheric Pressure. (The same is true for Princes Parade as it too was a former landfill site)

Rainfall

Rainfall or precipitation impacts on ground gas concentrations, as high levels of rainfall cause a noticeable rise in the groundwater table. This in turn reduces the available pore space in which methane and carbon dioxide can exist in a gaseous state. Some proportion of the gases will dissolve, although this will be slight. The rise in water table will lead to a marked increase in concentration of ground gases and an associated increase in release of gases to atmosphere.

This change in volume of the water table can also occur as a result of changing barometric pressure. The combination of these factors results in precipitation providing the greatest external influence on ground gas emission rates.
A rise in water table level due to precipitation increases pressure in soil pore spaces, and thus increasing the flow of ground gases into the atmosphere.

Another effect of precipitation – (especially in clay-rich soil – which Biggin Wood sits on) would be a temporary sealing of the ground surface, either trapping ground gases within the ground or causing emissions of ground gases in a different location(it migrates), ie neighbours gardens, Harcourt Primary School.

Where the ground gas is trapped, generation is likely to continue at the same rate, which will result in increased gas pressure. Further, if prolonged sealing occurs, aerobic conditions may become anaerobic, causing increased methane generation. When the surface dries out, release of ground gases may occur at a faster rate until a state closer to equilibrium is reached.

Atmospheric Pressure

Barometric pressure (measured in millibars, mb) has a key impact on the state of ground gas and is considered to be the second largest influencing factor. At lower pressures, the ground gas will expand, resulting in increased emission rates as the gases increase in volume. Conversely, rising pressure will cause air to flow into the ground, diluting ground gas concentrations.

Barometric pressure also has an influence on gas solubility, with high pressures producing a greater solubility of many gases. On the other hand, low pressures result in these gases being released from water, providing the potential for release of large volumes of ground gases to atmosphere and/or into structures. It should be noted that the rate of change of pressure is the key driving force, with a swift drop over a small pressure range having the potential to produce a greater concentrations and flow rates of ground gases than a gradual drop over a greater pressure range.
The moisture content of the soil has an impact on the magnitude of this pressure effect.

Where soil is dry, the response in relation to pressure changes is swift. However, where the soil is damp or saturated, the barometric pressure changes will be muted to some extent. Time delays of up to 24 hours have been observed.

So as weather is a continuous feature and pressure is constantly rising and falling, the site is continuously releasing gas into the atmosphere; which rather goes against what SDC state at page 334 regarding greenhouse gases.

Of course, the gases can be re-mediated and there are companies such as the A Proctor Group Ltd, who sale to the rescue and can provided membranes to create barriers and ventilation systems to allow the gas to be emitted into the atmosphere. The sale costs will be an added cost to the overall development of the site. The 2014 report states the elevated concentrations of ground gases beneath the site can be re-mediated by the provision of ventilated sub floor void and correctly installed gas resistant membrane and present a significant likelihood in the severity of risk across the whole site concerning methane and carbon dioxide levels.

The Soil

Laboratory testing of the soil on the Biggins Wood site has recorded the made ground soils to contain concentrations of heavy metals and PAH compounds above screening values for a residential land use and these soils are considered to pose a risk where residential end users of the southern part of the site may come into contact with them.

The analysis of the soil laboratory test results taken from the Biggins Wood site indicates that the made ground soils contain concentrations of lead above the screening value for a residential land use and may pose a significant risk where these soils remain in areas where end users of this part of the site may come into contact with the soils i.e. gardens and soft landscaping areas.

The analysis of he soil laboratory tests taken from the Biggins Wood site indicates that a number of Polycyclic Aromatic Hydrocarbon (PAH) compounds are present within the made ground soils at concentrations significantly above the relevant screening values for the residential land use. As with the concentrations of heavy metals, these may pose a significant risk where the soils remain in areas where end users of this part of the site may come into contact with the soils i.e. gardens and soft landscaping areas.

In the 2010 report it stresses elevated levels of arsenic. By the time the 2014 report is written up and presented to the former owner, the arsenic disappears. It is not explained how this has happened within the four years between the reports.

Also, the soil is contaminated in the area shaded in red (below). The approximate extent of Made Ground Soils at the site that should be considered to be hazardous waste for disposal purposes. So those lorries will be coming and going, regardless. And look how close the land is to the neighbours who live in Charles Crescent and Elventon Close and Harcourt Primary School.

Google Maps

To remediate the Metal and PAH compound contaminated made ground soils across the site means, the developer will need to remove of all made ground soils or placement of 600mm of verified cover soils over a geotextile within all private garden areas.Removal of all made ground soils or placement of 300mm of verified cover soils over geotextile within all soft landscaping areas. So over half the site approximately.

How much will it cost to dig out the soil, or buy it in and raise the level of the soil across a 10.75 acre site?

How much will the membrane/s cost.

How many lorries in and out, bringing, or taking soil from or to the Biggins Wood site?

How much will that cost?

And what about the increased traffic emissions, next to a school with children known to have asthma? Their environment and the community environment will be affected and this cannot be sensibly ignored.

Remedial measures are considered to be necessary to reduce the potential risk to end users of both parts of the site to an acceptable level. Within the residential development area remedial works proposed encompass the inclusion of gas protection measures to the ground floors of houses and the provision of clean cover soils to areas of soft landscaping and gardens. For the commercial development area, whilst provision of clean cover soils is not required, there remains a requirement for provision of gas protection measures within ground floors.

So across the whole Biggins Wood site a gas membrane will be needed. That’s 10.75 acres or 4.35 hectares. What will the cost of this be to any developer?

Yes, the soil and gas emissions can be dealt with, yes soil will have to be removed and yes there will be a cost to any developer, with all this extra work which will have to be done. Is this why the former owner of Biggins Wood Homes Limited, (owned by Ravensbourne Holdings Ltd – Luxembourg) didn’t build? And do remember he was a multi-millionaire, who had the cash to throw at the extra costs of remediating the soil and the gas issue.

The risk  and severity of harm due to the gases is considered to be severe/high by both reports.

The 2014 report makes it clear that the likelihood of harm is likely to arise to a designated receptor from an identified hazard. Realisation of the risk is likely to present a substantial liability. Urgent investigation (if not undertaken already) is required and remedial works may be necessary in the short term and are likely over the long term.

Three years after the issue of this report, there has not been any Urgent Investigation undertaken. Why would fully qualified site investigators state that it was “urgent”, there must have been and must still remain significant risks which cannot be sensibly ignored.

The likelihood there is a pollution linkage and all the elements are present and in the right place, which means that it is probable that an event will occur. Circumstances are such that an event is not inevitable, but possible in the short term and likely over the long term.

The severity of the contaminants on the site are known to be Severe and Moderate this will cause both short term (acute) and (chronic) risk to human health likely to result in “significant harm” as defined by the Environmental Protection Act 1990, Part IIA.

Pollution of sensitive water resources (note: Water Resources Act contains no scope for considering significance of pollution). A significant change in a particular ecosystem or organism forming part of such ecosystem.

So the risk, the likelihood of the risk and the severity of the risk means that overall, there are risks which cannot be sensibly ignored having regard to the nature and gravity of the feared harm in the particular case of the Biggins Wood site.

As the environmental specialists who work with contaminated land on a daily basis and are fully qualified to give an opinion on the matter have stated to us:

• “any site is remediable, if you throw enough money at it.”

But who will foot this bill, the local taxpayer , via SDC and the developer? Or just a developer alone? Any self-respecting voter would want to know.

Finally,  the former owner Adrian Kirby who has appeared on the Sunday Times Rich List with an estimated £65m fortune. Why didn’t he develop it? Was it the cost and the risk factors perchance.

 

The Shepwayvox Team