Phase 1 Geotechnical and Geoenvironmental Assessment (Desk Study)

Site Investigation

Geology, Hydrogeology and Hydrology

Flood Risk Assessment

Archival Mapping and Historical Land Use

Mining and landfill identification

Radon Risk Assessment

Potential Contamination

Munitions and Unexploded Ordnance

Environmental Constraints

Conceptual Site Modelling

Geoenvironmental and Geotechnical Risk Assessment

 

The aim of the Phase 1 Geoenvironmental Assessment is to identify and assess the potential geotechnical and geoenvironmental (contamination) hazards on the site.  Since all sites are different it is important to identify the scope and purpose of the desk study.  This will include who commissioned the work, the development proposals, the relevant procedures followed and the objectives.  Any issues specifically should also be noted if these might normally be expected as part of the desk study. 

Site Description 

The site description should define the exact extent of the site.  This should include a site address, grid reference and elevation.  The boundaries and topography of the site should be defined. 

A site inspection should always be carried out, not only of the site itself but the immediate surrounding area.  This will include information not apparent from any maps and describe what currently occupies the site i.e. buildings, hardstanding, watercourses, vegetation, trees and any particular features.  The type and distribution of vegetation can indicate soil and groundwater conditions and note should be made of any invasive plants such as Japanese Knotweed and Giant Hogweed.  Adjacent features and land-use should be reported if there are likely to be an impact on the development.  It is not uncommon for features such as tanks to be known about, but be unrecorded.

The walkover should note any potential sources of contamination and geotechnical hazards such as slopes, excavations, landslipping, ground subsidence, soft ground or desiccated/shrinkable soils. 

All structures on the site should be inspected both internally and externally for any evidence of structural damage such as tilting, cracking or chemical attack.  Any evidence of underground features should be noted.  Where practical, local residents can often give valuable information, although caution should be used in respect of “peoples’ memories”.  Local place names can give useful indications of former uses, e.g. Gas Works Lane, Water Lane, Tannery Road etc.

A photographic record of the site and specific features of the site should be included with the report. 

Site History               

The past history of the site and the surrounding areas is extremely important to assessing the likelihood of contamination or geotechnical hazards.  Historical Ordnance Survey maps date back to the mid 19th Century and often specify the actual industrial use of particular sites or buildings.  They may show area of quarrying or infilling as well as indicate where buried obstructions such as underground tanks or old foundations can be expected.  As described as above, experience interpretation place names or terms such as “pickle” alongside anecdotal evidence are all important to this. 

The influence or impact of off-site past industrial use will depend upon the type industry concerned, the underlying geology and the topography.  However, normally consideration should be given to any such features within a 250m radius of the site (or further where appropriate), as having the potential to affect the site. 

Historical maps are available from libraries and also commercial providers such as GroundSure or Envirocheck.  It is the latter which provide a cost effective method of obtaining maps and include the ability to superimpose current site boundaries on older maps.  Issues regarding possible breaches of copyright are also avoided by using licensed products.  

It should be remembered that historical maps only provide a snapshot in time and care must be taken with interpreting what may have occurred in the intervening years.  For example a quarry may be shown on one map and infilled on the next.  However in the intervening period it could have expanded prior to infilling.  Similarly, industrial uses may not always be recorded and many military or sensitive uses, have been omitted from maps of the period. 

Other sources of information may include the ubiquitous internet search, historical aerial photographs.  It may be necessary to additionally search the libraries of Local Authorities and Local History departments. 

Geology and Mining               

The geology of the site should be recorded by reference to published geological maps.  These such maps most commonly exist at 1:50,000 (I inch to 1 mile) and 1:10,000 (6 inch to 1 mile).  The British Geological Survey Geo-Index also provides existing ground investigation records including logs and reports.  It should be noted that these records can relate not only to the surrounding areas but may also comprise previous investigation of the site itself.  The information on the geological maps can also be supplemented with British Geological Survey technical reports, flood risk appraisals and memoirs. 

The bedrock geology and overlying superficial deposits should both be reported, together with any geological faults that may affect the site.  An explanation of the likely ground conditions should be given together with any other mapped geological features. 

Mining Areas 

In former coalfield areas, the maps may not always record the presence of coal workings.  The likelihood of shallow mineworkings affecting surface stability should be established in conjunction with a Coal Authority report.  Such reports also record areas that have been affected by extraction of brine, which is particularly prevalent in the Cheshire area. 

Hydrogeology and Flooding 

The assessment should also include the hydrogeology of the site, in particular as to whether the site lies on a Principal Aquifer and /or Source Protection Zone, which are both susceptible to pollution of groundwater.  Flood risk data is continually being updated by the Environment Agency and Local Authority. 

The presence of surface water features and drainage should be described and the overall risks of flooding to the site should be determined, primary with reference to the Environment Agency flood map data and Local Authority commissioned Strategic Flood Risk Assessments.

Any groundwater or surface water abstraction points ‘downstream’ of the site, in particular any potable (drinking water) abstraction points should be recorded as this may have liability implications should the development site be causing pollution. 

Environmental Setting 

This addresses the question as to whether a site poses an actual environmental risk or is at some external risk from pollution will be determined by its environmental setting.  This will in turn depend upon the site’s topography, geology, hydrogeology and hydrology amongst other site specific considerations. 

It is necessary to consider other potential sources of contamination such as pollution control licenses, discharge consents, hazardous sites (COMAH, NIHHIS), pollution incidents, landfills, waste treatment sites, and past and current industrial sites.

As a general point, current industrial operations rarely provide a risk of pollution to a site.  Invariably pollution has been caused by historical activities and processes which were often deemed normal practice in the past, but are considered unacceptable today.  In this regard, the past history is invariably the more significant in respect of possible ground pollution. 

The site should be considered in relation to any designated environmentally sensitive sites such as Special Areas of Conservation, Special Protection Areas, Nature Reserves and Sites of Special Scientific Interest.  In particular could contamination on the site be affecting such sensitive areas whether these are on or adjacent to the study site. 

Data relating to current industrial licensing, consents and the like, together with relating information relating to environmentally sensitive sites is typically available through commercial data suppliers.  As with the historical maps, this is usually a cost effective method of obtaining this data. 

For both the historical maps and datasets, there is usually little or no interpretation of the information and it is essential that this interpretation is carried out by an experienced and qualified individuals.  Automated risk assessments do not include appraisal by qualified staff and should always be viewed with caution and this method is not usually acceptable to Regulators.  A real life example of this was a contaminated former petrol filling station site recorded as having no past industrial use.  The historical maps never recorded the site as a filling station, nor did the environmental data.  However the walkover quickly identified former bases for pumps and filling points for underground storage tanks (USTs).  

Radon 

The need to incorporate Radon Protection Measures should be determined by reference to risk maps produced by the Health Protection Agency.  Such information is also usually included within commercially available datasets. 

Environmental Risk Assessment and Conceptual Site Model 

A quantitative health and environmental risk assessment should be carried out as part of the assessment.  The process of risk assessment is set out in Part IIA of the Environment Protection Act 1990 and amended in subsequent legislation.

 The Act introduces the concept of a pollution linkage.  This linkage consists of a pollution (contaminative) source or hazard and a receptor, together with an established pathway between the two.  For land to be contaminated, a pollution linkage (hazard-pathway-receptor) must exist.  This forms a so-called 'conceptual model' of the site.

 

 

 

It is also worth mentioning our sister site on leaseback property

Search Results