We are routinely asked the following question: “Do you do soil testing and site evaluation?” Often this is the sole question posed in an e-mail or during an initial telephone enquiry in relation to a potentially contaminated site.
This simple question masks a degree of complexity, as soil is a stratified vertically and spatially heterogeneous mix of inorganic and organic components in a highly complex matrix. Further complications can include historical or current anthropogenic inputs or physical disruption. All these factors need to be taken into account when designing the sampling scheme and putting the test results into context.
The study of soils, i.e. soil science, comprises a broad range of scientific disciplines, including chemistry, physics, geology, mineralogy, hydrology, and increasingly biology and genomic techniques. Its aim is to quantifying the soil matrix, i.e. its chemical and physical constituents, as well as increasingly to understand the complex relationships between the various physical components and the soil biota.
Contaminated land assessment
Within the United Kingdom (UK) the responsibility for environmental management and contaminated land are held by the Environment Agency and Scottish Environment Protection Agency, as described within the Environment Act 1995.
A site can be investigated for a variety of reasons, e.g. change in ownership where a buyer wishes to ascertain the scope of any contamination and land value, change in land use, regulatory agency requirement and ascertain remediation costs.
A typical programme of investigation can constitute up to four main components or phases, as detailed below.
Phase I – preliminary risk assessment This phase does not require site sampling or analysis, but typically a site visit is undertaken. The aim of the preliminary risk assessment, or desk study, is to identify any potential sources of contamination from either current or historical activities. Information is obtained from a wide variety of sources, including current information, previous owners, industrial activities, historical maps, hydrology, geology, documented pollution incidents, previous planning permissions, and licensing applications.
To detect connections between sources of pollution, pathways and receptors, potential receptors are identified:
- Human habitation
- Natural water systems – lakes, rivers and aquifers
- Other water systems – canals, ponds and ecological systems
Where the site contains potential evidence of pollution pathways a Phase II investigation can be warranted to quantify the risk.
Phase II – intrusive site investigation This phase does require site sampling and analysis. A sampling programme is devised depending on the potential contaminants and pathways identified during the Phase I desk study.
The scale and complexity of the sampling programme will reflect the size and heterogeneity of the site, including:
- Possible sources of pollution, e.g. identified point sources as compared to widespread background pollutants
- Underlying hydrology e.g. depth to water table or groundwater, complexity of surface water features, geology
- Age of potential pollutants
- Probable environmental fate
Specific contaminants will be addressed based on the likelihood of being present, as determined during the Phase I study. Some analyses may be undertaken in-situ using appropriate methodology or equipment, e.g. hand held portable devices for determining concentrations of contaminants.
Other analyses will require specialist methodologies or instrumentation within a laboratory setting.
Specific details of current good practice in relation to investigating contaminated land are within BS 10175:2011+A1:2013 – Investigation of potentially contaminated sites, code of practice. Details of investigating ground gas are covered in BS 8576:2013 Guidance on investigations for ground gas – permanent gases and Volatile Organic Compounds (VOCs).
Once analytical data are obtained, it is then possible to make risk estimates at the generic level. Generic risk assessment models, such as the Contaminated Land Risk Assessment (CLEA) model and other similar models are often used to estimate potential harm to receptors. This is especially the case where the land use is to be changed, e.g. from derelict to residential, and estimates of exposures to receptors need to be made.
At the generic level, these models tend to use information on measured concentrations of contaminants in soils to estimate exposure of vulnerable receptors to these contaminants. The models may cover exposure pathways such as ingestion of dust and soil, as well as uptake by garden vegetables that are subsequently consumed. Final estimates of exposure are then compared to agreed ‘safe’ levels of exposure. Where estimated exposures exceed ‘safe’ levels, site-specific risk assessment may then be carried out.
Phase III – site remediation Based on the data obtained during both the Phase I desk study and Phase II site investigation, a thorough site history would have been identified with pollutant, pathway receptor vectors identified and quantified. Phase III implements any agreed remediation plan. At this stage considerable liaison with regulatory bodies, local councils and residents’ associations are typical.
The remediation plan may use a variety of techniques, depending on the pollutants present, to remediate the site to the agreed standard. Soil remediation techniques are well documented and constantly evolving from the simple to complex, e.g. excavate and dispose in appropriate landfill, in-situ remediation using extractants, and solidification/stabilisation.
Phase IV – site validation Phase IV site validation ensures the identified risks associated with a site have been remediated to agreed concentrations and thus no longer pose a significant threat to receptors. This typically involves validation sampling and analysis, the scope of which would be agreed during the planning of the site remediation to ensure the validation process is thorough and robust.
Soil survey Where the soil is relatively undisturbed, more generic soil classifications can be used to identify similar soils and aid in mapping. Surprisingly, the UK has three distinct soil classification systems developed to facilitate mapping and to best represent the range of soils found in the component parts of the UK. Soil classification is often seen as an academic pursuit, so countries often develop systems to assess land and its capability to support agriculture or forestry as a means of disseminating soils information. The Scottish Land Capability for Agriculture (LCA) classifies land into one of seven categories (Bibby et al , 1982) and is often used to value land prior to sale and advise on development and planning. Class 1 land has the greatest cropping flexibility and Class 7 is of limited agricultural value. Data once only available as maps are now available digitally and are accessible online e.g. www.soils-scotland.gov.uk/data/lca250k.
When making a soil map, soil surveyors typically assess a landscape, taking into account aspect, slope, relief, vegetation and anthropogenic influence, e.g. agriculture, to visualise the wide range of factors that influence the soil. Soil pits are dug at appropriate locations where detailed inspections can be made and along with auger borings, a detailed picture of the underlying soil and its characteristics can be made. Once the map is made, additional soil samples are often taken to characterise the soil. This generally involves sampling the soil by soil horizon, i.e. the natural layers that develop in a soil. Bulk samples, composite samples or soil cores can all be taken to provide data on a wide range of soil properties.
Soil survey and sampling has been undertaken on a national scale for many years in many different countries. For example the National Soils Inventory of Scotland (NSIS1) sampled Scotland’s soils across a 10 km grid from 1978 through to 1987, with a second sampling programme (NSIS2) taking place from 2007 through to 2010 using a 20 km grid. The selected profiles to characterise the soil map units numbered around 10,000 profiles and around 50,000 samples from the soil horizons. The analytical data from these samples are stored in a soils database and the actual physical sample is stored in the National Soil Archive of Scotland, both held at the James Hutton Institute. This archive provides a valuable repository for one of a nation’s greatest assets, its soils.
Soil samples ought to be analysed using appropriate methodology for the determinant in question at reputable analytical facilities. Due to the complex nature of soils historically a multitude of analysis methodologies exist, often specific to the main soil types encountered in a particular country.
Within the UK the British Standards Institution (BSI) is responsible for organising stakeholders with the relevant expertise to develop formal standards within Technical Committees. BSI is a member of the Comité Européen de Normalisation (CEN) which promotes harmonisation of standards across Europe. Global harmonisation of standards is promoted by the International Organization for Standardization (ISO), of which BSI is a member.
Standardisation promotes the exchange of goods and services and reduces the likelihood of misinterpretation if stated explicitly in contractual agreements.
More information on BSI and standards can be found at: www.bsigroup.com/ More information on CEN and standards can be found at: www.cen.eu/Pages/default.aspx More information on ISO and standards can be found at: www.iso.org/iso/home.htm
Laboratory soil testing
Laboratories undertaking soil analysis can be accredited under various accreditation schemes pertaining to specific standards. Within the UK the United Kingdom Accreditation Service (UKAS) routinely assess laboratories to ensure they meet and maintain specific standards. Those laboratories undertaking testing and calibration, for example, are assessed against ISO 17025 ‘General requirements for the competence of testing and calibration laboratories’. Other accreditation standards are also available, for example, ‘Monitoring emissions to air, land and water’ (MCERTS), as developed by the UK Environment Agency (EA).
Lists of laboratories meeting specific standards are publicly available via the UKAS website: www.ukas.org/testing/singlesearch.asp
Laboratories can be searched based on a variety of input parameters, for example, location, type of laboratory and the type of test required.
ISO 17025 is a comprehensive standard assessing a broad range of laboratory activities, including staff training records, instrumental maintenance and performance checks, laboratory environmental conditions, analytical methods, and quality control including reference materials, data recording and provision of reports.
The standard is continuously evolving to ensure integrity is maintained. Recent developments describe the concept of ‘deviating samples’. Samples that are not sampled or stored properly can be described as deviating under current quality assurance systems, e.g. ISO/IEC 17025:2005.
Examples of scenarios in which a sample could be described as deviating include:
- Stored at incorrect temperature
- Stored in inappropriate containers
- Insufficient sample data, e.g. date and time
- Cross contaminated
- Microbiologically compromised
UKAS document TPS 63 ‘UKAS Policy on Deviating Samples’ discusses deviating samples in depth.
It is imperative, therefore, that samples are sampled, stored and transported appropriately. The receiving laboratory has a duty to report any samples it suspects of deviating from the standard.
Certified reference materials
Certified reference materials (CRMs) are available from a variety of sources. Soil material typically has values attributed to specific determinants after analysis using specified methods from a range of reputable laboratories. Data obtained are statistically analysed to provide a certified value with a confidence limit applied.
These materials are available for purchase for a wide variety of determinants and matrices, including multiple soil types.
The Laboratory of the Government Chemist (LGC) standards provide a range of standards available for purchase: www.lgcstandards.com/epages/LGC.sf
Laboratories often validate internal reference materials for routine use using CRMs. Samples can be accompanied, therefore, by internal reference material of known determinant values through the analysis procedure and play an integral part of a robust quality control system.
Reputable laboratories participate in inter-laboratory or proficiency testing trials to constantly test their procedures and methods and ensure the data obtained is comparable with other laboratories. It is an integral part of a through quality assurance system and a prerequisite for many accreditation schemes.
Typically a sample of unknown origin is sent to participating laboratories. Specified determinants are calculated and the data reported. The data for all of the participating laboratories are statistically analysed and the laboratory is assessed using a z-score. The z-score is an indication of the participating laboratory’s score as compared to the mean value from all participating laboratories. Typically z scores of <2 are accepted, 2-3 is marginable and >3 requires investigation. Where scores fall outside the acceptable criteria for a specific determinant, the laboratory typically instigates an investigation to determine if there has been a failure in protocols and determines any corrective action that is deemed appropriate.
Inter-laboratory trials are available for a wide range of matrices and determinants, e.g. the LGC organise ‘Aquacheck’ and ‘Contest’ proficiency testing schemes.
Soil testing and land evaluation not only deal with a complex and highly variable matrix, but require input from a broad multi-disciplinary science base. Legislation, accreditation and new methodologies are increasingly dictating and influencing soil testing.
Effective, efficient and accurate data requires input from site investigation, planning, soil sampling strategies, correct storage, transportation, method identification and analysis by reputable laboratories.
Simple questions so often require complex answers, and “Do you do soil testing and land evaluation?’’ is no different.
Published: 27th May 2015 in AWE International