Characterization & Remediation of Contaminated Sites

Aim

To illustrate the role of Site Investigations in :

Risk Assessment (Site Prioritisation) and Risk Management (Remediation process selection and validation).

•Risk Assessment–Site Investigation

•Risk Management–Remediation Objectives –Process Selection

Assessing the Risks from Contaminated Land

Tools are needed to determine whether:

• The soil is uncontaminated. (safe)

• The soil is contaminated but presents no unacceptable additional risks to the specified target. (safe)

• The soil is contaminated and may present additional risks to the specified target. (further investigation)

• The soil is contaminated and presents an unacceptable risk to the defined target. (remediation required)

Overview of Risk Assessment

Phased Approach

• Collection of Data

• Conceptual model (source-pathway-receptor linkages)

• Identify and assess Hazards (Site Characterization)

• Evaluate and Quantify Risks posed by Hazards

– Professional judgement

– Generic Guidelines or screening values

– Models (site-specific characteristics)

• Prioritise sites

– fair and transparent process

The Role of Site Investigations in the Remediation Process

• Identification of Site• Preliminary Investigation• Planning of Investigation

– possible Exploratory Investigation• Main Investigation (Detailed Investigation)• Hazard & Risk Assessment• Identification of Remedial Options• Selection of Preferred Remedial Strategy• Monitor Implementation• Validation• Long-Term Monitoring

Phases

Preliminary Investigation

• Desk Study– Current Layout - buildings, drains, process areas, plant,

services.– Materials - feedstocks, products, wastes– History of the site

• Industrial uses

• previous incidents

• Disposal records

– Geology and Hydrology

desk study information obtained from:– Maps, photographs, local history, directories, Technical

Literature, Local / Government Bodies, residents, workers

Preliminary Investigation

• Site Reconnaissance (Site Walkover)– External observation of acute hazards (ruptured tanks, etc)– Visual inspection for Contamination

• discoloured soil, deposits, odours, gas (detection tubes)• vegetation - chlorosis, stress• condition of fences, metal structures• seepage through river banks, land drains

– Activities on neighbouring land (on-going)– Confirms Desk Study details (e.g buildings / services/ plant location)– Produce Photographic Evidence

• Planning of Subsequent Investigations– Best estimation of the extent of contamination on the site

Exploratory Investigation

• Used to confirm presence of contamination where the Preliminary Investigation is inconclusive– Informed sampling locations

• Geophysical techniques

– Sampling locations • can form Stage 1 of the Main Investigation

– Composite samples (surface grab samples)– Soil depth profile samples (Window sampling)– Restricted range of chemical analysis (targeted e.g.

BTEX)– helps with Planning of the Main Investigation

Main Investigation

• Planning– Safety Procedures

• exploring the unknown

– Environmental Protection• dust suppression, Wheel wash, decontamination

• Sampling– Data Requirements

• specific requirements of Regulatory bodies• informed sampling strategy (preliminary investigation)

– Methods• augering, window, trial pits and trenches, boreholes

Main Investigation

• Chemical Analysis – Quality Assurance

• NAMAS (National Measurements Accreditation Service)

– Standard Suites (ICRCL)

– Site Specific Contaminants

• Interpretation of Data– quantitative risk analysis, prioritisation, remedial targets

CdPbAsCrZnHg

ChlorideSulphateSulphideCyanidesulphur

pHPhenolsToluene extractable Matter (TEM)coal tarsmineral oilsPAH, PCB, BTEX

Remediation target values are set by:

• Guideline Values (e.g. Background or Threshold)

• Site-Specific Risk Values

– CLEA Model

– ConSim Model

Practical Considerations include:• Cost• Time Required• Technical Feasibility• The opinions of the Regulator (LA or EA)

Remediation Targets

Guidelines and Standards

• Standards– system of fixed, legally binding values

(not particularly relevant to the soil situation. Why?)

• Guidelines

values to be applied with Professional interpretation and judgement.

– ICRCL (Interdepartmental Committee on the Remediation of Contaminated Land)

– BRE (Building Research Establishment)

– Dutch Intervention and Target Values

Guidelines and StandardsICRCL 58/93

Contaminant

Complex Cyanides

PAH

Proposed Uses

Domestic gardens, allotments

Landscaped Areas

Buildings, hard cover

Domestic gardens, allotments, play areas

Landscaped areas, buildings, hard cover

Threshold

250

250

250

50

1000

Action

1000

5000

no limit

500

10,000

Trigger Values (mg/kg air-dried soil)

Quantitative Risk Assessment

• Human Health– CLEA Model (Contaminated Land Exposure Assessment)– C-soil Model (Netherlands)

• Groundwater (Dispersion)

– ConSim Model (Environment Agency)

Human HealthContaminated Land Exposure Assessment (CLEA)

• Site Specific Data– Contaminant concentrations– Climate - precipitation, wind– Soil Properties

• physico-chemical, pH, redox• particle size distribution• permeability• organic content

– Site Use• user activity patterns (visit frequency/duration)

– Monte Carlo Exposure Estimate• Probability Density Functions (PDF)• compare with Tolerable Daily Intake (TDI)

Risk to GroundwaterConSim Model (Environment Agency)

• Determines whether contaminant is likely to exceed WQS value at several locations in the aquifer

• Multi-Tiered Approach– (i)Leaching - (ii) Migration - (iii) Dispersion/Diffusion– Tier (iv) for complex geology

• Monte Carlo model– input data as PDF (Skill !)– addresses element of uncertainty– decay and biodegradation are calculated– output data graphical

CONTAMINATEDSOIL

Level 1

Level 3Dilution

DispersionBiodegradation

Level 2Unsaturated

Zone Retardation

SimulatedLeach Data

TheoreticalLeach

Properties

If Concentration

< WQS STOP

If Concentration

< WQS STOP

AQUIFERVADOSEZONE

Multi-Tiered Approach of the ConSim Model

Level 1

Level 2

Level 3

VadoseZone

SaturatedZone

Multi-Tiered Approach of the ConSim Model

Contaminant

Remediation Strategy

• Source– permanent reduction of risks– numerous technical approaches

• Pathway– risks managed in short to medium term– several different engineering approaches

• Target– not usually applicable or practicable

Remediation Technologies

non-technical high technology

• Soil Disposal Off-Site– Excavation, Landfill

• Containment– Capping, Barriers

• Restructuring– Redistribution and Dilution of Material

• Contaminant Stabilisation, Removal

and Destruction– Numerous Biological, Physical,

Chemical, Thermal Methods

Relatively lowcost, and simple.

Considerableexperience.

Expensive, complex,EmergingTechnologies

Remediation Technologies

• In-Situ

Treatment without physically removing the soil– Advantage - less disturbance, emissions, buildings, buried services– Disadvantage - out of sight, monitoring, heterogeneity of

contamination, soil structure (occluded clay lenses), mass transfer limitations, toxic hot-spots.

• Ex-Situ

Treatment after physical removal of soil – Advantage - Mixing distributes contaminants, mass transfer,

process control, treat graded fractions, representative sampling, improved rate, protects groundwater.

– Disadvantage - more work, space requirement, emissions, avoid buried services, aesthetic appearance

Remediation Technologies

• Intensive Process– Aim to achieve a rapid rate of remediatiohn– uses complex equipment– consume considerable resources

• power, reactants, labour, monitoring

– Generally detrimental to soil structure– Examples - Soil Washing, Incineration

• Extensive Process– Slower to Work– Low capital and Maintenance Costs– Soil Structure retained (Improved)– Examples - Phytoremediation, Bioremediation