Phase 1 and Phase 2 Land Quality Assessments

Anyone involved in commercial property transactions should ask themselves whether the property has environmental liabilities attached to it.

One of the main potential liabilities for brownfield sites is contaminated land which could be acting as a source of pollution to controlled waters, or which could represent a hazard to humans, animals, plants and buildings.

Almost all brownfield sites are likely to have a history of some contaminating activities but the extent to which these sites still represent a high risk to the environment is dependent on several factors including:

• the extent to which there remains a source of contamination on the site;
• the degree to which the source contaminants are physically and chemically mobile;
• the geological and hydro-geological characteristics of the ground at the site and in the vicinity;
• the presence of man-made pathways, such as pipelines and service trenches, which could provide a route for the migration of contaminants.
• the sensitivity of the surrounding environment to the effects of contamination.

The most cost-effective way to assess potential liabilities from contaminated land is to undertake a phased risk assessment, commencing with a desk study and, if appropriate, proceeding to field investigations.

The "Phase 1" investigation is a desk based review of relevant information which:

• identifies possible contaminant sources from an investigation of historical activities on or adjacent to the site;
• determines the local environmental sensitivity based on a review of the solid and drift geology and the groundwater and surface water characteristics;
• identifies the potentially vulnerable groups, collectively known as “receptors”, that could be harmed by the identified contaminating substances on the site;
• culminates in a preliminary environmental risk assessment which will point the way for any field investigations.

A good phase 1 investigation can save substantial sums in unnecessary or poorly targeted field investigations.  On the other hand, a superficial phase 1 investigation can result in an erroneous assessment of risk, which can lead to costly surprises in due course.

A “Phase 2” contaminated land investigation is an intrusive field investigation in which soil and water samples are collected for chemical analysis.

The main purpose of a phase 2 investigation is to verify, refine or eliminate the potential environmental risks identified in an earlier phase 1 desk study.  The investigation should also be sufficient to identify the need for, and extent of any remedial works needed to reduce environmental risks to acceptable levels.

Phase 2 investigations are strongly recommended in circumstances where potential contamination has been identified and there is a high risk of harm to human, animal or plant health, or of pollution being caused to groundwater, surface water or the marine environment.

Field Investigation techniques

The investigation techniques used in phase 2 investigations depend on the nature of the site and the underlying geology.  A typical investigation may involve the excavation or drilling of exploratory holes by a combination of trial pitting and boreholes.

Trial pits can be a very cost-effective form of investigation and can provide excellent visual and olfactory evidence to an investigator.  The main disadvantage with trial pits is that their depth is limited to the reach of the excavator, which is typically between 4 and 5 metres.  Where there is ingress of groundwater however, this also limits the practical depth as the trial pit can become unstable.  It is also usually impossible to see the ground below the water table. In spite of these disadvantages however, trial pits, used in conjunction with other methods, are a very effective method of investigation.

Boreholes are required when it is necessary to explore to greater depths than can be achieved by trial pitting. They are particularly needed when it is necessary to investigate groundwater or landfill gas.

In general, there are two types of borehole: cable percussion boreholes and rotary boreholes.
Cable percussion boreholes are less expensive than rotary boreholes but are suitable only for drilling into deposits above the rock head, such as made ground or Drift deposits.  When it is necessary to drill into rock, rotary drilling is required.  This is the case when the water table is in rock and samples of groundwater are required.

Laboratory analysis

The method of analysis for particular substances is an important factor as different methods produce different detection limits.   We always use laboratories that are experienced in dealing with contaminated soils and water and we involve the analytical chemist in the preparation of schedules of analysis for the collected samples.

Interpretation of results

It has to be remembered that a phase 2 investigation is based on sampling techniques so the immediate question to resolve is: to what extent do the results represent the conditions in the site as a whole?  This question should always be considered using statistical techniques to determine the type of sampling distribution and to assess confidence intervals.  It is also possible to estimate the mean concentration of a substance, to a stated level of confidence, from limited sample data using established statistical techniques.

It is also necessary in the interpretation stage to re-visit the conceptual model developed in the phase 1 assessment in order to verify or amend assumptions. (The conceptual model is a description of sources of contaminants, sensitive receptors that could be harmed by them, and the means by which the two could come into contact).

The interpretation stage should conclude with a risk assessment, (unless the report is required for purely factual purposes, as is the case with site condition reports for permits under the Pollution, Prevention and Control Regulations 2000), which indicates the means by which unacceptable risks can be mitigated.