Biophysical remediation of petroleum hydrocarbon contaminated soil in Yorkshire
Our industrial past has left us with a large number of brownfield sites, many of which contain elevated concentrations of contaminants in the soil and groundwater. These substances pose potentially significant human health risks as well as impacting on groundwater, surface water, and flora and fauna.
ECG committee member James Lymer from the engineering and environmental consultancy firm, Wardell Armstrong LLP, describes some of the regulatory and practical considerations of cleaning-up contaminated land in the UK.
Contaminated land legislation
In the UK, new policy initiatives and various pieces of specific legislation for dealing with contaminated land have been introduced since the 1990 Environmental Protection Act.
Part II(a) of the Environmental Protection Act 1990 Part II(a) of the Environmental Protection Act 1990 was introduced under Section 57 of the Environment Act 1995 and came into effect in England and Scotland in 2000 and Wales in 2001.
Under Part II(a), the statutory definition of contaminated land is:
Part II(a) was extended in 2006 to include radioactivity in England and Wales, but this currently only applies to human exposure to radioactivity.
Local Authorities Local Authorities are responsible for the inspection of contaminated land and for ensuring remediation is undertaken where necessary. Local Authorities also maintain a Public Register detailing the regulatory actions that they have implemented. The Environment Agency has a complementary role with specific responsibilities such as acting as the enforcing Authority for designated special sites. Planning Contaminated land is also a consideration within the Local Authority planning system. When planning permission is sought for the development of a site that is considered to be potentially contaminated, the local planning authority will take this into account and may require investigative work to be completed by the applicant. Developers (applicants) often commission specialist environmental consultants to conduct contaminated land investigations on their behalf. The resulting assessment of these investigations can then be submitted with the planning application to the Local Authority for approval that the site is suitable for the proposed use.
Planning permission may be granted on condition that the site is remediated to the satisfaction of the Local Authority depending on the results of any investigation. New planning guidance (PPS23) was launched in November 2004, and this includes an Annex 2 which gives more detailed guidance about development on land affected by contamination.
The main difference between Part II(a) and PPS23 is that under the planning system, risks have to be assessed based upon the new or intended use of the land, rather than on the existing use, which was a criterion in the Part II(a) regime. For more information on the regulation of contaminated land, refer to Defra Circular 01/2006 and Planning Policy Statement 23 (see references for details).
Contaminated land investigation
Source-pathway-receptor models A key tool in the investigation and assessment of potentially contaminated land is deriving and updating a conceptual model through various phases of work. A risk assessment of the source-pathway-receptor linkages identified in the conceptual model can then be performed. A typical conceptual model is shown in Figure 1.
ECG committee member James Lymer from the engineering and environmental consultancy firm, Wardell Armstrong LLP, describes some of the regulatory and practical considerations of cleaning-up contaminated land in the UK.
Contaminated land legislation
In the UK, new policy initiatives and various pieces of specific legislation for dealing with contaminated land have been introduced since the 1990 Environmental Protection Act.
Part II(a) of the Environmental Protection Act 1990 Part II(a) of the Environmental Protection Act 1990 was introduced under Section 57 of the Environment Act 1995 and came into effect in England and Scotland in 2000 and Wales in 2001.
Under Part II(a), the statutory definition of contaminated land is:
- land which appears to the Local Authority in whose area it is situated to be in such a condition, by reason of substances in, on or under the land, that:
- significant harm is being caused or there is a significant possibility of such harm being caused; or
- pollution of controlled waters is being, or is likely to be, caused.
Part II(a) was extended in 2006 to include radioactivity in England and Wales, but this currently only applies to human exposure to radioactivity.
Local Authorities Local Authorities are responsible for the inspection of contaminated land and for ensuring remediation is undertaken where necessary. Local Authorities also maintain a Public Register detailing the regulatory actions that they have implemented. The Environment Agency has a complementary role with specific responsibilities such as acting as the enforcing Authority for designated special sites. Planning Contaminated land is also a consideration within the Local Authority planning system. When planning permission is sought for the development of a site that is considered to be potentially contaminated, the local planning authority will take this into account and may require investigative work to be completed by the applicant. Developers (applicants) often commission specialist environmental consultants to conduct contaminated land investigations on their behalf. The resulting assessment of these investigations can then be submitted with the planning application to the Local Authority for approval that the site is suitable for the proposed use.
Planning permission may be granted on condition that the site is remediated to the satisfaction of the Local Authority depending on the results of any investigation. New planning guidance (PPS23) was launched in November 2004, and this includes an Annex 2 which gives more detailed guidance about development on land affected by contamination.
The main difference between Part II(a) and PPS23 is that under the planning system, risks have to be assessed based upon the new or intended use of the land, rather than on the existing use, which was a criterion in the Part II(a) regime. For more information on the regulation of contaminated land, refer to Defra Circular 01/2006 and Planning Policy Statement 23 (see references for details).
Contaminated land investigation
Source-pathway-receptor models A key tool in the investigation and assessment of potentially contaminated land is deriving and updating a conceptual model through various phases of work. A risk assessment of the source-pathway-receptor linkages identified in the conceptual model can then be performed. A typical conceptual model is shown in Figure 1.
Regulation of contaminated land sites An important factor for safeguarding human health is the proposed use of the brownfield site. The redevelopment of land for residential purposes is more sensitive than development for commercial use. Local Authorities have regulatory responsibility for the protection of human health from exposure to possible contaminated land sites. The Environment Agency is responsible for the regulation of groundwater and surface water protection by ensuring that there are no discharges of contaminants into groundwater or surface water.
The risk assessment process A Phase I (Desk Study) involves the identification of potential sources of contamination, pathways and receptors by assessment of desk based information such as historical plans, geological maps and industrial profiles. A qualitative risk assessment is then performed for the site based on the conceptual model. |
Where the Phase I Desk Study identifies potentially significant source-pathway-receptor linkages, then a Phase II (Site Investigation) may be carried out to provide quantitative information on the contaminant source, to assess pathways and the risk to the receptors as part of a Generic Quantitative Risk Assessment (GQRA). Phase II involves obtaining soil and/or groundwater samples and submitting them for chemical analysis. Soil and rock samples are obtained by the drilling or excavation of the ground.
Contaminant concentrations in soil and groundwater are compared with available generic assessment criteria and if concentrations are particularly elevated, then a Detailed Quantitative Risk Assessment (DQRA) can be performed. A DQRA involves the use of computer models to derive site specific assessment criteria for comparison with contaminant concentrations.
Contaminant concentrations in soil and groundwater are compared with available generic assessment criteria and if concentrations are particularly elevated, then a Detailed Quantitative Risk Assessment (DQRA) can be performed. A DQRA involves the use of computer models to derive site specific assessment criteria for comparison with contaminant concentrations.
Remediation
Remediation is usually required when the results of the GQRA or DQRA indicate that contaminant concentrations pose a significant risk to critical receptors. Remediation may involve:
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Plates 1 and 2 illustrate a contaminated land site, which is currently undergoing remediation.
Petroleum hydrocarbons
In the UK, oil or petroleum hydrocarbons are considered to be significant contaminants in soil and groundwater systems, particularly as elevated concentrations may pose a risk to human health and the environment. Hydrocarbon contamination is frequently encountered in site investigations at brownfield locations.
Petroleum hydrocarbons (or TPH as they are commonly referred to) comprise a range of organic compounds (alkenes, alkanes, BTEX and PAHs). With this complexity, several methods of classification of TPH in groundwater and soil have been developed.
The Total Petroleum Hydrocarbon Criteria Working Group (TPHCWG) approach derived during the 1990s is a commonly used classification method for TPH. In this approach, petroleum hydrocarbons are divided into aromatic and aliphatic hydrocarbon fractions between C5-C35 and then further divided into a total of 13 fractions. The fractions are based on the fate and transport properties of the compounds which differ for aromatic and aliphatic compounds.
Petroleum hydrocarbons
In the UK, oil or petroleum hydrocarbons are considered to be significant contaminants in soil and groundwater systems, particularly as elevated concentrations may pose a risk to human health and the environment. Hydrocarbon contamination is frequently encountered in site investigations at brownfield locations.
Petroleum hydrocarbons (or TPH as they are commonly referred to) comprise a range of organic compounds (alkenes, alkanes, BTEX and PAHs). With this complexity, several methods of classification of TPH in groundwater and soil have been developed.
The Total Petroleum Hydrocarbon Criteria Working Group (TPHCWG) approach derived during the 1990s is a commonly used classification method for TPH. In this approach, petroleum hydrocarbons are divided into aromatic and aliphatic hydrocarbon fractions between C5-C35 and then further divided into a total of 13 fractions. The fractions are based on the fate and transport properties of the compounds which differ for aromatic and aliphatic compounds.
An example of an assessment and the remediation of a brownfield site
Assessment Wardell Armstrong LLP in Sheffield was commissioned to assess TPH contamination in soil and groundwater at a site in North Yorkshire. It was discovered that a significant spill of TPH had occurred in the past and was most likely sourced from on-site storage containers. Samples obtained from the site indicated elevated concentrations of TPH of aromatic fraction C21-C35; up to 35,000mg/kg in soil and 21,000mg/l in groundwater. As these concentrations were considered to pose a risk to human health, a remedial target of 9,000mg/kg for aromatic C21-C35 in soil was generated. A Detailed Quantitative Risk Assessment revealed no significant risk to groundwater but there was a potential risk to human health.
Remediation: soil
Ex situ bioremediation was considered a cost-effective and appropriate measure to reduce the TPH soil concentration and also the risk to any future occupiers of the proposed land use. Ex situ biophysical remediation is a commonly used technique in the UK, and in this case windrow turning was employed to meet the remedial target of 9,000mg/kg.
Windrow turning (a term borrowed from a composting technique in agriculture) involves the mechanical excavation of TPH-contaminated soil and placement into thick layers or heaps. Regular mechanical turning and tilling of the heaps is then carried out to improve the aeration of the soil. Naturally occurring micro-organisms in the soil facilitate biodegradation of the petroleum hydrocarbons and thereby reduce the source concentrations to a site specific remedial target.
Remediation: groundwater Groundwater samples containing significantly elevated concentrations of TPH were considered to contain mainly free product. It was agreed that as part of the proposed remedial work, any TPH free product and groundwater encountered was to be pumped out of the excavation and treated by passing the mixture through an oil/water separator followed by a granular activated carbon filter. The separated TPH free product was disposed off site at a suitable facility.
Summary The site was found to be contaminated with aromatic hydrocarbon fraction C21-35 in soil and groundwater. Results from the DQRA indicated that the elevated concentrations posed a risk to human health. A remedial target of 9,000mg/kg was agreed and then achieved within 3 months using ex situ bioremediation with windrow turning.
Soil and groundwater samples taken during the remediation period were used to validate that the remedial target had been met as part of a validation report which was agreed by the Local Authority. The Planning Condition was then discharged for the commercial development.
JAMES LYMER
Wardell Armstrong LLP, Unit 4
Newton Business Centre, Newton Chambers Road, Thorncliffe Park, Chapeltown Sheffield S35 2PH
References
Defra Circular 01/2006, Environmental Protection Act 1990: Part 2A, Contaminated Land, September 2006, Crown Copyright. http://www.defra.gov.uk/environment/land/contaminated/pdf/circular01-2006.pdf
Planning Policy Statement 23: Planning and Pollution Control, 2004, Crown Copyright http://www.communities.gov.uk/publications/planningandbuilding/planningpolicystatement23
Total Petroleum Hydrocarbon Criteria Working Group: Volume 5. Human Health Risk Based Evaluation of Petroleum Release Sites: Implementing the Working Group Approach, June 1999. http://www.aehs.com/publications/catalog/contents/tph.htm
Assessment Wardell Armstrong LLP in Sheffield was commissioned to assess TPH contamination in soil and groundwater at a site in North Yorkshire. It was discovered that a significant spill of TPH had occurred in the past and was most likely sourced from on-site storage containers. Samples obtained from the site indicated elevated concentrations of TPH of aromatic fraction C21-C35; up to 35,000mg/kg in soil and 21,000mg/l in groundwater. As these concentrations were considered to pose a risk to human health, a remedial target of 9,000mg/kg for aromatic C21-C35 in soil was generated. A Detailed Quantitative Risk Assessment revealed no significant risk to groundwater but there was a potential risk to human health.
Remediation: soil
Ex situ bioremediation was considered a cost-effective and appropriate measure to reduce the TPH soil concentration and also the risk to any future occupiers of the proposed land use. Ex situ biophysical remediation is a commonly used technique in the UK, and in this case windrow turning was employed to meet the remedial target of 9,000mg/kg.
Windrow turning (a term borrowed from a composting technique in agriculture) involves the mechanical excavation of TPH-contaminated soil and placement into thick layers or heaps. Regular mechanical turning and tilling of the heaps is then carried out to improve the aeration of the soil. Naturally occurring micro-organisms in the soil facilitate biodegradation of the petroleum hydrocarbons and thereby reduce the source concentrations to a site specific remedial target.
Remediation: groundwater Groundwater samples containing significantly elevated concentrations of TPH were considered to contain mainly free product. It was agreed that as part of the proposed remedial work, any TPH free product and groundwater encountered was to be pumped out of the excavation and treated by passing the mixture through an oil/water separator followed by a granular activated carbon filter. The separated TPH free product was disposed off site at a suitable facility.
Summary The site was found to be contaminated with aromatic hydrocarbon fraction C21-35 in soil and groundwater. Results from the DQRA indicated that the elevated concentrations posed a risk to human health. A remedial target of 9,000mg/kg was agreed and then achieved within 3 months using ex situ bioremediation with windrow turning.
Soil and groundwater samples taken during the remediation period were used to validate that the remedial target had been met as part of a validation report which was agreed by the Local Authority. The Planning Condition was then discharged for the commercial development.
JAMES LYMER
Wardell Armstrong LLP, Unit 4
Newton Business Centre, Newton Chambers Road, Thorncliffe Park, Chapeltown Sheffield S35 2PH
References
Defra Circular 01/2006, Environmental Protection Act 1990: Part 2A, Contaminated Land, September 2006, Crown Copyright. http://www.defra.gov.uk/environment/land/contaminated/pdf/circular01-2006.pdf
Planning Policy Statement 23: Planning and Pollution Control, 2004, Crown Copyright http://www.communities.gov.uk/publications/planningandbuilding/planningpolicystatement23
Total Petroleum Hydrocarbon Criteria Working Group: Volume 5. Human Health Risk Based Evaluation of Petroleum Release Sites: Implementing the Working Group Approach, June 1999. http://www.aehs.com/publications/catalog/contents/tph.htm