Further description:- United Kingdom  Soil and groundwater processes 

Glossary Entry:- United Kingdom  Soil and groundwater processes
Geo-environmental processes affecting the fate of contaminants in the subsurface 
Overview
 
    
A satisfactory understanding of soil and groundwater processes, and how they may affect the sources 
of contamination and the exposure of identified receptors, is a prerequisite for the risk assessment
and management of potentially-contaminated sites. Soil and ground water processes encompass:
contaminant hydrology, ecotoxicology, geochemistry, hydrogeology, microbiology, modelling.
Extensive scientific and technical information and guidance on soil and groundwater processes
is available in the UK.
1. General Approach
 
      
In the UK, well-designed site investigations will include suitable techniques and testing to 
indicate the basic soil and groundwater processes existing at a potentially contaminated site.
This will allow:
  • the identification of ground and groundwater conditions that can influence contaminant
    attenuation and migration;
  • the characterization of potential pathways in terms of migration and possible attenuation.
A wide range of factors influence the fate and transport of a contaminant once it has entered the
soil or groundwater. Thus, a multidisciplinary approach is needed to predicting or modelling the
behaviour of contaminants in the subsurface during detailed quanitative risk assessment or the
design of risk management/remediation options. This will require consideration and understanding
of a number of issues relating to the nature and prevailing conditions in the soils and groundwater
at the site being considered, including the geology, hydrogeology, hydrology, contaminant geochemistry,
geotechnics, ecotoxicology and microbiology.
Relevant soil and groundwater properties may include: Relevant contaminant physico-chemical properties may include:
  • Soil profile
  • Soil texture (relative proportions of sand, loam and clay)
  • Presence of mineral constituents such as clays, carbonates, phosphates, oxides and organic
    matter (expressed as the fraction of organic carbon foc)
  • Moisture content
  • Particle size distribution
  • Bulk dry density
  • Porosity (air-filled and water-filled)
  • Sorption capacity of the soil
  • pH and redox potential
  • Microbial populations
  • Elevation of water table
  • Groundwater flow direction
  • Hydraulic gradient
  • Hydraulic conductivity
  • Hydraulic dispersivity
  • Contaminant concentration
  • Chemical speciation e.g. the valency or oxidation state of a metal
  • Solubility in water (or other solvent if a non-aqueous free phase liquid is present)
  • Sorption (soil-water partition coefficient Kd and organic carbon-water partition coefficient
    Koc)
  • Octanol-water partition coefficient (Kow)
  • Vapour pressure
  • Henry’s Law Constant
  • Biodegradation (e.g. half-life in aerobic and anaerobic soils)
  • Nature of metabolites
  • Vegetable uptake (soil to plant concentration factor)
  • Weathering potential
  • Diffusion coefficient in air
  • Diffusion coefficient in water
  • Viscosity (gases and vapours)
  • Viscosity (non-aqueous phase liquids)
Processes such as contaminant leaching depend on a variety of factors including the rain water
infiltration rate at the site, soil permeability and the solubility and volatility of the contaminant
in the soil. The infiltration rate is in turn dependent on the runoff rate and the rate of evapotranspiration.
The soil permeability would depend on the degree of fracturing in the soil. Volatilisation is also
a contaminant migration process that depends on a variety of joint soil and contaminant factors such
as contaminant vapour pressure, contaminant solubility and soil sorption properties. Once dissolved contaminants enter groundwater they are subject to various groundwater processes,
including advection, dispersion and diffusion, which will affect the speed and distance such contaminants
can migrate away from the original source. The sorption of a contaminant onto soil will further reduce
the mobility of contaminants within the subsurface. This complex process depends on the concentration
and speciation of the contaminant and on the integrated sorption capacities of the different minerals
etc. within the soil. In particular, the ion exchange capacities of clays and organic matter in a soil
can have large controlling influences on a soils sorption behaviour. Likewise the biodegradation of a hydrocarbon compound is dependent on a number of different factors
relating to the chemical structure of the contaminant itself and the nature of the aerobic or anaerobic
microbes present in the soil. The microbial populations are dependent on supplies of nutrients and
on the redox state of the soil. Knowledge of the relevant soil and groundwater processes will allow an effective Site Conceptual
Model for the site to be constructed from which the level of risk posed by contamianants can be evaluated.
Without an realistic conceptual model that considers the likely soil and groundwater processes
that may inhibit or promote the availability or mobility of contaminants at the site a valid risk assessment
cannot be completed. This may result in unacceptable risks being ignored at the site or significant
time and money being expended on unjustified remedial measures. Equally, during the selection and design of remediation options, particularly those that rely
heavily on soil and groundwater processes (such as monitored natural attenuation and permeable
reactive barriers), a detailed analysis and understanding of the soil and groundwater processes
will be required in order to identify the most cost-effective risk management solution for the site.
Failure to make adequate consideration of these processes could result in excessive costs being
incurred or a failure to achieve the remedial objectives. For example, within the Environment Agency's
'Guidance on the assessment and monitoring of natural attenuation of contaminants in groundwater'
it is clearly stated that robust evidence demonstrating the effectiveness of natural soil and groundwater
processes, such dilution, sorption and microbial degradation, in minimising risks asociated with
contaminated groundwater.
 
2. Policy and Regulation
2.1 Policy
 
       
In the UK, the consideration of soil and groundwater processes is particularly evident in guidance 
published by the Environment Agency regarding the risk assessment and protection of water resources,
such as R&D 20 'Methodology for the derivation of remedial targets for soil and groundwater to protect
water resources' (EA, 1999).
 
2.2 Regulation


 
       
3. Funding
Site Project Funding


 
        
R&D funding
Soil Protection
Research Type: Applied

Topics: Brownfields Contaminated land, Contaminated land overview Contaminated land, Remediation options, Remediation options overview Groundwater protection, Groundwater protection overview Soil, Soil Overview

Submitted by: Maike Hauschild  Who does what?

Full Details |


Soil Biodiversity Programme
Research Type: Basic

Topics: Brownfields Contaminated land, Contaminated land overview Contaminated land, funding Soil, Soil Overview

Submitted by: Maike Hauschild  Who does what?

Full Details |


URGENT (Urban Regeneration and the Environment)
Research Type: Basic

Topics: Brownfields Contaminated land, Contaminated land overview Contaminated land, funding Groundwater protection, Groundwater protection overview Soil, Soil Overview

Submitted by: Maike Hauschild  Who does what?

Full Details |


'Infrastructure and Environment' programme and 'Engineering' programme
Research Type: Basic

Topics: Engineering, Infrastructure and Environment, Brownfields, Contaminated land, Groundwater protection, Funding, Brownfields Contaminated land, Contaminated land overview Contaminated land, funding Groundwater protection, Groundwater protection overview

Submitted by: Maike Hauschild  Who does what?

Full Details |


Bioremediation LINK Programme
Research Type: Applied, Basic

Topics: (1) To understand and exploit natural attenuation in groundwater and soil (demonstration, modelling, prediction, definition of operating window). (2) To improve engineered in-situ bioremediation, interfacing microbiology with engineering and hydrogeology; dealing with heterogeneity, improved process control and optimisation. (3) To translate the results of laboratory studies into the field (scale-up). (4) To position bioremediation within a risk management framework - bioavailability, risk-based end points and residue behaviour. (5) To develop the ability to monitor in-situ microbial processes. (6) To understand the constraints on in-situ microbial processes. (7) To integrate bioremediation with other technologies. (8) To quantify human health impacts of bioremediation and develop surrogate testing. (9) To address socio-economic issues- perception of bioremediation technologies and decision-support mechanisms.

Submitted by: Professor Paul Bardos  Who does what?

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Land Contamination
Research Type: Applied

Topics: site assessment for land contamination, decision support tools for risk management, remediation of contaminated soils, sediments, and groundwater, Brownfields Contaminated land, Contaminated land overview Contaminated land, funding Groundwater protection, Groundwater protection overview

Submitted by: Maike Hauschild  Who does what?

Full Details |


Defra Web Page on: Contaminated Land - funding
Research Type: Demonstration

Topics: There are several measures which support the clean up of contaminated land, and these are described on this web page

Submitted by: Professor Paul Bardos  Who does what?

Full Details |



Market Information


 
    
4: Management tools / decision support and guidance

No further information available

5. Authors


 
    
6. Acknowledgements