Site investigation
With respect to the redevelopment of land, our geoenvironmental reports typically include:
- A geotechnical assessment – including the derivation of pragmatic foundation solutions, the assessment of slope stability etc
- An assessment of land contamination – including potential risks to both human health and controlled waters
- Consideration of hazardous gas issues – including landfill gas, radon and mines gas
- A mining risk assessment in accordance with Coal Authority guidance
- Design of appropriate site preparatory (and where necessary remediation) earthworks
Ground conditions can be investigated by a number of techniques; those most commonly used by Lithos include:
- Machine excavated trial pits
- Cable percussive (shell & auger) boreholes
- Window or windowless sampling boreholes
- Rotary boreholes
Ground investigation typically includes:
- Exploratory holes excavated by appropriate techniques, to appropriate depths, and at appropriate spacings
- Appropriate in-situ tests
- Detailed description of the ground encountered
- Retrieval of representative soil and groundwater samples
A sufficient number of soil samples are collected from each exploratory hole at regular intervals to allow selected laboratory testing (contaminant and geotechnical) to be performed.
Soakaways provide a way to dispose of stormwater run-off from buildings and paved areas to ground, rather than to public sewer or watercourse.
Soakaways must store the immediate stormwater run-off and allow for its infiltration into the adjacent soil sufficiently quickly to provide the necessary capacity to receive waters from a subsequent storm. The time taken for discharge depends upon the soakaway size, and permeability of the ground in which it is built.
Lithos undertake soakaway tests in general accordance with BRE Digest 365 “Soakaway Design”. A trial pit is part-filled with water from a bowser and allowed to drain to near empty. Each test can take up to 5 hours, but it is generally possible to complete about 6 tests in a day.
We are able to review existing data (including previous site investigation reports) and identify potential environmental liabilities associated with ownership of a site. Such work is usually undertaken in order to inform prospective purchasers and funders of a proposed acquisition. In essence, our report provides a due diligence environmental audit with respect to ground-related issues.
Our report might include a description of current operations, although it is not a compliance audit (i.e. an assessment of whether or not the company is in compliance with applicable UK environmental legislation), nor is it intended to review the site’s Environmental Management System.
A preliminary investigation (desk study or Phase 1 report) includes the following works:
- An assessment of the land use history
- Determination of the site’s environmental setting (by reference to geology, mining/quarrying, risks associated with hazardous gas (including radon, landfill gas, mines gas etc), proximity to landfilled ground, proximity to COMAH or explosive sites, hydrology, flood risk, and hydrogeology)
- Site walkover and inspection
- Assessment of anticipated ground conditions, including potential contaminants
- Assessment of anticipated foundation and engineering issues associated with redevelopment for a residential end-use
- Preparation of a conceptual ground model and design of an appropriate ground investigation
Primary aims of the desk study are to identify key ground-related issues that may affect the site, thereby enabling the design and costing of an appropriate intrusive ground investigation.
For small scale development, a desk study may be all that is required to satisfy the Local Planning Authority; especially where the site has not been subject to any potentially contaminating previous uses.
A desk study might also enable “ballpark” assessment of abnormal redevelopment costs associated with the ground.
A conceptual site model (CSM) is often summarised in a drawing that shows a cross-section through the ground, identifying potential geotechnical and contamination hazards. The CSM is initially prepared after review of geological maps, environmental data, historical plans etc, and is subsequently refined in light of data obtained during a ground investigation.
In the context of land contamination, there are three essential elements to any risk: (1) a contaminant source, (2) a receptor (eg controlled water or people), and (3) a pathway linking the (1) and (2). Risk can only exist where all three elements combine to create a pollutant linkage. Risk assessment requires the formulation of a CSM which supports the identification and assessment of pollutant linkages.
Mining risk assessment
In July 2011, the Coal Authority (CA) formalised their requirements in relation to planning applications and introduced some new terminology relating to Coal Mining Development Areas.
The CA have defined specific Coal Mining Development Areas and Low Risk Areas. The former are areas, based upon CA records, where potential land stability and other safety risks associated with former coal mining activities are likely to be greatest. They include, for example, areas of known or suspected shallow coal mining, recorded mine entries and areas of former surface mining. The CA is now a statutory consultee for any planning application within a High Risk Area.
Lithos have completed many desk-based risk assessments, which include an examination of the mining report together with published geological maps, geological technical reports\memoirs, any available borehole logs, and any available mine abandonment plans.
A mining risk assessment would normally be included in the broader geoenvironmental Desk Study (or Phase 1) report required by planning applications for all developments other than minor domestic extensions.
Wherever possible we will avoid recommending further intrusive investigation (rotary boreholes), and also provide pragmatic advice, most notably with respect to a suitable foundation solution.
Where necessary Lithos undertake intrusive investigations to determine whether or not old mineworkings actually pose a significant risk to surface stability.
