Pre Purchase Audit of a Converted Observatory, Trelleck, Monmouth, NP25

Case Study Reference: CS22-05-02

Planning Authority: Monmouthshire County Council

Planning Reference:

Synopsis:

During the sale of the dwelling (former observatory) pre purchase sales indicated the site was located on a landfill which caused the sale to fall through. In order to support the sale Demeter Environmental were commissioned to prepare reports to provide additional information on the risks associated with the landfill.

The first stage of the work was to prepare a Phase I desk study report in order to determine if the site has the potential to be impacted by elevated levels of contamination, and to determine the source as well as the likelihood of the risk occurring.

A desk study determines what issues relating to historical contamination may affect the site, this is undertaken by reviewing the site history using a combination of O.S. maps, aerial, plates and street level imagery, a review of data held by regulatory bodies (Environment Agency, local authority, BGS etc.) as well as a site walkover survey.

The history of the site and surrounds were researched using a combination of Ordnance Survey (O.S.) maps, street level imagery and aerial plates, this revealed the site was occupied by a quarry from the 1938 map until the 1971 map when a refuse tip was identified on the site.

By 1990 an observatory weas present on the north western boundary. A number of quarries and a landfill were noted in close proximity to the site.

Street level imagery revealed the area of the site adjacent to the road was wooded.

The planning history of the site was reviewed as part of the desk based research and the reports associated with the previous application were located and studied, no previous applications were noted.

The published geological maps identified the site as being in an area where no drift soils were recorded, the bedrock was given as the Quartz Conglomerate Formation (interbedded sandstone and conglomerate). The borehole section sheets published by the BGS were reviewed and no borehole in close proximity to the site were available hence no further information on ground conditions could be obtained.

Prior to the works a trial trench was excavated on the site, the path of the trench was overlain alongside the location of the refuse tip and quarry to determine if any landfilled material was to be expected, evidence of bottles were noted in the spoil heaps.

Data provided by regulatory bodies confirmed the presence of a quarry and a refuse heap on the site as well as three quarries and a covered reservoir in close proximity to the site. The boundaries of the landfill on the maps provided by the regulatory bodies did not match the boundaries on the O.S. maps.

 

On completion of the desk based research a site reconnaissance
visit was undertaken in order to obtain further information on the potential sources identified in the desk based research and to identify any other potential sources. The walkover survey confirmed the site was occupied bya single story dwelling, which was a former observatory. The area along the south western boundary was wooded with landscaping on the reminder of the site and a vegetable patch close to the dwelling.

Once the walkover survey was completed a qualitative risk assessment was undertaken on the potential sources of contamination identified in the desk study report in order to determine if any warranted further investigation, this concluded that the refuse tip on the site as well as the landfills in close proximity to the site posed a potential risk and further works to reduce the uncertainty were required.

In order to install gas monitoring wells and to delineate the area of the refuse tip / quarry a site investigation comprising of a number of syanmic sampling boreholes was undertaken, as part of the investigation samples of the soils from the refuse tip were taken and subject to broad range analysis to assess if site soils posed a risk to human health.

The chemical analysis indicated that site soils were impacted by a number of contaminants, whist the impacted soils were within the made ground a spatial analysis indicated the majority of the impacted soils were below 0.3mbgl indicting a capping layer had been placed on the tip.

It was concluded that whilst the site was not ‘suitable for use’ it was unlikely to meet the legal definition of contaminated land’ and remediation was advised on any area used to grow produce.

In order to provide further information samples of the soil from the vegetable path were taken and subject to chemic al analysis, this confirmed the spoils in this area were suitable for use on the site.

Ground gas monitoring confirmed the presence of carbon dioxide at concentrations greater than 5%, positive flows were not recorded in any of the visits, spot monitoring within the building did not record any ground gases. Based on the data it was concluded that the risk form ground gases was negligible.