Phase 1 Desk Study

Comprises a Preliminary Risk Assessment report usually in relation to the development of a site, often required by Local Authorities to sign off planning conditions. A Phase 1 Desk Study will compile a variety of published information upon a sites historical, geological, hydrological and environmental settings. Upon completion, the report will identify any potential contamination or ground related hazards that pose a risk to human health, controlled waters, structures , services and vegetation.

A Walkover Survey is most commonly included within the Phase 1 Desk Study, which is a physical visit to the site, whereby a thorough visual assessment is undertaken to confirm and help assess areas identified during the desk study that may highlight potential zones of contamination.

Following both the Desk Study and Walkover Survey a Conceptual Site Model (CSM) can be developed.

Ground Investigation

An intrusive method of investigation which obtains the soil, rock and groundwater parameters/ profiles below the surface. This enables a detailed understanding of the engineering behaviour of the ground and geotechnical hazards related to different soil and rock types. GDGES can design and undertake a site specific Ground Investigation to adhere with the client’s project and indeed any other regulatory body, Local Authority etc.

Ground Investigation Methods

There are a number of different GI methods used in the industry, each of which have their own advantages and limitations. The method used will be influenced by the proposed development, anticipated geology, site location and  client requirements . Some examples of different Ground Investigation methods are:

• Cable Percussion Boreholes
• Window/Windowless Sampling
• Rotary Drilling (Rotary Core & Open Hole Drilling)
• Dynamic Probing
• Continuous Flight Auger
• Trial Pitting (Hand Dug & Machine Excavated)

Following the Ground Investigation an interpretative Geotechnical/Ground Investigation Report can be produced.

Geotechnical Foundation Design

GDGES can provide Geotechnical Foundation Design Reports for new foundations, ranging from small extensions to larger commercial and mixed-use developments.

Each project will be site specific and an appropriate Ground Investigation method will be chosen to suit this in order to acquire the necessary information in relation to the underlying geology and hydrology of the development site.

In-Situ Testing from the Ground Investigation in addition to Laboratory Testing and monitoring will further enhance the capabilities of selecting an appropriate design. Some examples of different Foundation Designs could include: 

• Strip Footings/Foundations
• Pad Foundations
• Raft Foundations
• Piled Foundations

Environmental & Geotechnical Testing

A comprehensive range of both Contamination and Geotechnical Testing is provided here at GDGES with associated reporting. We also use accredited UKAS/MCERTS laboratories.

During various phases of development, Contamination Testing may be considered necessary for a number of purposes including due diligence, as part of the sign off process for planning conditions from Local Authorities, for a Phase 2 Ground Investigation, licensed Waste Removal from the development site in addition to Validation Reporting.

Most commonly, when testing for Contamination in soils we have a standard suite we follow, these include:

• Metals
• Speciated Polycyclic Aromatic Hydrocarbons (PAH)
• Banded Petroleum Hydrocarbons (TPH CWG)
• Total Monohydric Phenols
• Soluble Sulphate and pH value
• Total Cyanide
• Total Organic Carbon (TOC)

Other Contamination Testing we can provide includes:

• Asbestos Identification and Quantification
• Volatile Organic Compounds (VOCs)
• Semi-Volatile Organic Compounds (SVOCs)
• Benzene/ethylbenzene/toluene/xylene (BTEX suite)
• Pesticides
• Waste Acceptance Criteria (WAC Testing)
• Topsoil Classification

Geotechnical Testing

This can include both Classification and Performance tests on the given Soils/Rock. GDGES can provide Geotechnical Testing such as:

• Bulk Density Test
• Dry Density Moisture Content
• Moisture Content – plastic and liquid limit
• Particle Size Distribution
• California Bearing Ratio Test (CBR)
• Oedometer Consolidation Test
• Permeability Test
• Quick Undrained Triaxial Testing
• Point Load Strength Index
• Moisture Content Bulk Density of Rock
• Uniaxial Compressive Strength
• Saturation Moisture Content (Chalk)
• Porosity (Chalk)
• Intact Dry Density (Chalk)

Gas & Groundwater Monitoring

A variety of  gases may occur in the ground either from contaminated landfill sites, historical infilled ground, petroleum hydrocarbon spills or can be present in a natural form, for examples in peat deposits or existing coal measures.

It is important to know that landfill gas and even natural gases can enter buildings through migration pathways in the sub surface and consequently build up to toxic and sometimes explosive concentrations. If detected, these risks should be mitigated and considered before any new development is undertaken.

A Desk Study will often identify within the Conceptual Site Model (CSM) if potential sources of ground gas are near a site, in this instance a Ground Gas Risk Assessment will be required alongside a site specific monitoring programme. Usually, installation of ground-gas monitoring standpipes will be included as part of the Ground Investigation if deemed necessary for the particular site. The main gases analysed as part of the monitoring programme include Methane, Carbon Dioxide, Oxygen in addition to Gas Flow Rate, Atmospheric Pressure and the Groundwater Level.

Groundwater monitoring often complements gas monitoring and the two are undertaken simultaneously, it is essential to geotechnical design and a detailed groundwater monitoring programme ensures efficient foundation design, making real world savings when designing for slope stability, retaining structures and both shallow and deep foundations.

Soakaway Testing

A Soakaway Test measures how quickly and efficiently water is able to infiltrate through a given soil or rock type. Soakaways are an effective method of storing excess water/surface water runoff and controlling the infiltration of water into the surrounding soil.

Soakaways are one of the most common types of SUDS (Sustainable Urban Drainage Systems) for developments which are not close to main sewage systems and help mitigate the risk of surface water flooding.

GDGES can provide Soakaway Testing in accordance with BRE Digest 365, which is the most common method of undertaking a soakaway/percolation test. The procedure is carried out whereby a trial pit is dug using an excavator which mimics the soakaway, it is then filled with water and recordings taken at specific time intervals detailing the water level drop. This process is repeated a total of three times. The time taken for the water level to fall from 75% to 25% can then be used to calculate the soil infiltration rate, which then allows a soakaway design to be drawn up.