Preliminary (Desk Study) Investigation
A desk study is is an essential element of any investigation and is often required as part of a planning submission for most development.
Published geological and hydrogeological maps are examined to determine the environmental setting of the site, and historical maps dating back to 1850 enable the land use history of the site and adjacent area to be determined.
If the site is located in a former mining area, a mining risk assessment will be included with reference to Coal Authority mining reports, detailed geological maps and mine abandonment plans.
Historical maps may identify former uses of the site which may potentially have resulted in contamination of soils or groundwater. Where this is the case a preliminary contamination risk assessment will be undertaken to identify whether contamination is likely to affect the development.
IDG undertake a wide variety of intrusive investigations which are tailored to the site and client requirements. The form the investigation takes is dependent on the focus of the investigation.
Generally, and investigation is designed to achieve a number requirements which may include providing information for foundation design, soakaway design, soil or groundwater contamination assessment, ground-gas assessment, determine shallow mining risk, locate mine shafts or wells. More details are provided below.
Geotechnical site investigations are undertaken to characterise the engineering properties of the ground and to provide information to inform cost-effective foundation design.
Key information includes the nature, distibution and depth of Made Ground, the depth an stength of natural deposits capable of supporting structures, and the presence of depth of groundwater.
A variety of in-situ tests are undertaken while drilling boreholes and in addition samples are recovered for laboratory geotechnical testing. Boreholes are often installed with ground gas and groundwater wells to enable future monitoring.
Large areas of the central and northern parts of the UK are lie over former coal mining areas where mine workings and mine shafts may be present. For sites within the affected areas a mining desk study comprising a detailed geological and mining review can be undertaken to assess the risk to proposed development.
Where potentially workable seams of coal are identified to be present at shallow depth from which coal may have been extracted in the past, and intrusive mining investigation will be undertaken using rotary drill holes to determine the geological structure below the site and to determine whether mine workings are likely to be present, and if necessary, the measures required to treat the workings and shafts.
Hazardous Ground Gas Assessments
Where preliminary investigations identify potential sources of hazardous gas such as landfill sites, thick deposits of Made Ground, shallow mine workings, volatile contamination or peat deposits, the assessment of the risk to the development of hazardous gas may be required.
This may include monitoring for methane or carbon-dioxide from installed boreholes and the preparation of a gas risk assessment report.
From a planning perspective, a contamination assessment may be required if potential contaminative uses had been identified during the desk study. Such investigations are often conducted using either machine excavated trial pit, or using small tracked percussive drilling rigs (window sample drilling rigs).
Samples of both soil and ground water will be collected and sent to independed UKAS accredited laboratories for chemical testing.
Chemical test results are compared to generic or site specific criteria to assess the risk to human health or controlled waters.