Phase 2 Investigation

When is this required?

On completion of the Phase 1 Environmental Report and if this indicates the potential for contamination to be a significant risk an intrusive investigation is required. We recommend preparing a Scope of Works document setting out in detail the nature of the investigation, the contaminants of concern and the methods to be deployed during the investigation so as to target the potential contaminants identified in the Phase 1 Environmental Report.

If the investigation is being undertaken for the discharge of planning conditions we recommend obtaining approval for the Phase 1 Environmental Report and Scope of Works before commencing the Phase 2 Investigation.

What does it involve?

The Phase 2 Investigation should be designed and undertaken to ascertain the presence, or otherwise, of contamination and its extent. This could be undertaken as a stand-alone exercise or cost effectively combined with a geotechnical investigation to provide information for foundation design.

For some projects soil samples from within the top 60cm, obtained by use of a hand auger, may be a completely adequate investigation. For others it may be necessary to undertake trial pits to physically inspect the ground and any fill material that has been placed on the site, or drill boreholes by mechanical means and instal standpipes to obtain groundwater samples or monitor for ground gases or vapours.

Soil, water or vapour samples will be taken for testing in a laboratory which has the appropriate certification: These may be taken from trial pits or boreholes or near surface samples collected by hand.

Investigation of former industrial estate

How much investigation is required?

This will depend on the size of the site and nature of the contamination and the proposed site use. The aim of the investigation is to ensure that sufficient information is gathered to enable a cost effective Remediation Strategy to be developed to make the site suitable for the proposed use. A well researched Phase 1 Environmental Report will enable the Phase 2 investigation to be targeted at the areas of concern and avoid unnecessary testing and investigation.

Longer term sampling or monitoring may be required for water courses and ground water or to monitor ground gases such as methane and carbon dioxide which may be migrating to the site from old landfills or natural deposits. It is important to recognise that the investigation may not be over in a day or two, monitoring for ground gas may require six visits at fortnightly intervals in order to be confident that the site has been correctly characterised.

Investigation Techniques

Soils

We use hand augers for obtaining samples, depending on the ground conditions these can penetrate several metres into the ground. Sometimes trial pits are the preferred option as they provide the opportunity for a visual inspection of the ground. Mechanically driven boreholes are used where samples are required from greater depths.

Surface and Groundwater

If there is a water course in the vicinity this may be sampled, typically down and then up-stream of the site, to determine if it is being impacted by the site.

Groundwater is generally sampled from standpipes installed in boreholes, with samples retrieved by pumping or in bailers.

Ground Gases

We monitor ground gases, methane, carbon dioxide and hydrogen sulphide, generally sampled from standpipes installed in boreholes. Where monitoring is required within a building, often a basement we can instal Vapor Pins®, these are an unobtrusive and cost effective means of measuring under-slab ground gases.

Gas measurement is taken using a GFM436 Multichannel Portable gas analyser connected via NyaFlow tubing to the stopcock valve of the monitoring well. The Gas Data GFM436 is an ATEX and MCERTS accredited handheld gas analyser.

The presence of hydrocarbons can affect methane readings. Using the Hexane channel on the gas monitor it is possible to determine if high methane readings are likely due to hydrocarbon interference.

Radon Gas

Radon is a colourless, tasteless, odourless gas at standard pressure and temperature, it is also radioactive. Breathing radon can increase your risk of developing lung cancer. There are maps available showing the general level of risk in parts of the UK. Basements are at greater risk than above ground structures in a similar location. Monitoring can be undertaken both prior to construction and within existing buildings.

Vapours

We monitor vapours generally from standpipes installed in boreholes. Where monitoring is required within a building, often a basement we can instal Vapor Pins®, these are an unobtrusive and cost effective means of facilitating the measuring under-slab vapours.

Vapour monitoring is carried out using a RAE system PID monitor with a 10.6eV lamp. The instrument is connected via inert tubing to the stopcock valve or Vapor Pin®.

If significant levels of vapours are detected a Silonite canister can be used to capture a vapour sample which can be tested in the laboratory for an appropriate suite of VOCs.

What happens if contamination is found?

If significant contamination is found, be it in the soil or groundwater in the form of ground gas or vapours a Remediation Strategy must be prepared.

Trial pits to investigate the capping and contents of an old landfill London Borough of Bexley