1. Risk Assessment Contaminated Land
Objectives
to know the characteristics of soil and chemical contaminants affecting risk assessments of contaminated land.
to know the practical steps involved in identifying and quantifying the pollutant hazards
to know the risk assessment tools and frameworks used to manage contaminated land
References
Nathanail, Paul.: Reclamation of contaminated land / Paul Nathanail, Colin Ferguson and Paul Bardos 2003
BURA Breaking old ground: BURA guide to contaminated land assessment and development
Petts, Judith. Risk-based contaminated land investigation and assessment 1999
Nathanail, C. P Introduction to contaminated land management 1999
Risk assessment for contaminated sites in Europe Nottingham : LQM Press, 1998
Vol. 1. Scientific basis -- Vol. 2. Policy frameworks RIS
Cairney, T. The re-use of contaminated land : 1995
Environment Agency and DEFRA Websites –

2. Risk Management of Contaminated Land
Course Structure
Introduction
Subsurface Characteristics - Soils and Contaminants
Site Investigation (Hazard Assessment)
Interpretation of data (Risk Assessment)
Regulatory Frameworks (Risk Management)
Remediation (Risk Management)

3. The Contaminated Land Legacy
Parliamentary Office of
Science and Technology
1993
Expert Estimates:-
50,000 to 100,000 potentially contaminated sites in UK
100,000 to 300,000 hectares
(significantly less which pose risk to human health)

5. Potentially Contaminating Industries
Landfill and other waste disposal sites.
Gas works, coal-carbonization plants and ancillary by-product works.
Sewage works and farms.
Scrapyards.
Railway land, especially large sidings, depots and breaking yards.
Roads, airports and abandoned wartime airfields.
Docks, canals and abandoned or infilled port ancillaries, shipbreaking yards.
Oil refineries, petroleum storage and distribution sites.
Metal mines,, foundries, steelworks, metal finishing works.
Mineral extraction sites not yet infilled (quarries, coal)
Glass works.
Chemical works.
Munitions production and testing sites, wartime installations.
Asbestos works and building incorporating asbestos.
Tanneries and fellmongeries.
Paper and printing works.
Industries making or using wood preservatives, herbicides and pesticides.
Cotton and other textile mills and bleach works.
Metal plating works and yards.
Brickworks, potteries and ceramic works.
Nuclear power stations, radioactive storage/disposal installations.

6. Law & Legislation Common Law (Civil Law) case law, not specific to CL
Statutory Law
new regulations specific to CL

7. Common Law (Civil liability )
Law of Tort (breach of legal duty) i.e. Case Law
Rylands v. Fletcher 1866
A person bringing a dangerous item or substance onto his own land does so at their own risk
strictly liable for the consequences of any escape onto another’s land
substance must be ‘unnatural’ or ‘unnaturally there’
damage must be reasonably foreseeable
conduct of the defendant is irrelevant
Trespass
direct, unauthorised interference with another’s property
could cover spillage or deposit of pollutants
not yet tested in the courts

8. Common Law (Civil liability )
Negligence
fault based - failure to take care in situations in which damage is reasonably foreseeable
“care” extends to ‘future users’
liability is variable depending on the amount of care taken
does not cover purely economic losses
Nuisance (interpretation of degree of harm)
activity that interferes with another’s enjoyment of land
On-going interference - can obtain an injunction
Concluded interference - can obtain damages
foreseeable “omission to do what a reasonable person would do”
Time Limit - 6 Years
(begins from time of discovery)

9. Cambridge Water (CW) v. Eastern Counties Leather (ECL) Ltd
Perchloroethylene solvent escaped from tannery
Contamination of groundwater
Water company failed new EC standards
1. CW failed in High Court
case of negligence, nuisance, Rylands v. Fletcher dismissed as tanning was not unnatural
2. Prosecution upheld in Court of Appeal
ECL deemed liable, £1m damages (focused on Nuisance)
3. House of Lords Decision (in favour of ECL)
reversed the Court of Appeal decision
no liability under Rylands v. Fletcher as “not foreseeable”

10. Contaminated land - Disasters
Love Canal, USA (1978)
Hooker Chemical Company
Building in 1950’s (despite caveat in deeds)
illness, genetic disorders, residents evacuated
Lekkerkerk, Netherlands (1978)
building on reclaimed site
1600 illegally dumped drums
drinking water polluted, residents evacuated
Eastern Counties Leather vs Cambridge Water Co (UK 1993)

11. Nature of the Pollution
Some important factors which determine the fate of chemicals in soil.
Organic or Inorganic
Charge (ions)
Volatility, Molecular weight
Solubility, Hydrophilic character
Functional Groups, affects solubility (polar character)
Hydrophobic character, interaction with soil colloids
Quantity or Concentration
Toxicity and Biodegradability
Density (Specific Gravity), Viscosity

12. Soil Structure and Hydrology
Soil Depth and Horizons
Organic Matter content
Plant Residues
Humic Acids, Fulvic Acids, Humin.
Particle size distribution
Sand, Silt and Clay Fractions
Soil Permeability
Groundwater, Water-table
Vadose (unsaturated) zone
saturated zone

13. Movement in the Soil Liquids Vapours Gravity Advection Diffusion
vertical movement until sorption by soil matrix dominates.
LNAPL - as far as Capillary Zone or Water Table
DNAPL - through water table, stops at Impermeable Layer
Advection
transported by the flow of the bulk liquid (water) if dissolved
Vapours
Diffusion
random molecular movement
transported by bulk flow of soil vapour

14. Movement of Contaminants within an Aquifer
Spill
Spill
Soil Surface
Spill
Vadose
Zone
LNAPL
Capillary
Zone
DNAPL
Saturated Zone
(Aquifer)
Plume of soluble
components

15. Potential Outcomes for Contamination in Soil
Hazard stays fixed in soil matrix = MINIMAL RISK
Hazard stays fixed in soil matrix but site has receptors = RISK
Hazard moves into groundwater and is transported towards receptor. = RISK
Dust and Volatilisation give rise to subsequent Air Contamination = RISK
Which Are relevant to the site?
REMEDIATION eliminates or minimises RISKS

16. Typical effects of Hazards
Toxicity to Human Health
Uptake of contaminants by crops
Ingestion
Inhalation
Skin Contact
Contamination of water resources (Groundwater)
Toxicity to Ecosystems / Wildlife
Fire and Explosion
Chemical attack on buildings, materials and property

17. Risk Management For a contamination to present a risk there must be:
a potentially harmful Source
a Pathway along which the contaminant can travel.
a Receptor
a plausible Pollution Linkage.
SOURCE RECEPTOR
PATHWAY

18. Technical Approach to Risk Management of Contaminated Land
What are the key stages in the process?
Identify and assess Hazards
Collection of Data
Conceptual model (source-pathway-receptor linkages)
Evaluate and Quantify Risks posed by Hazards
Professional judgement
Generic Guidelines or screening values
Models (site-specific characteristics)
Prioritize sites (Local Authority)
fair and transparent process
Consider consequences of a change in use
force remediation of sites with “Risk”

19. 2. Site Investigation
(Hazard Assessment)

20. Objectives and Purpose of Site Investigation
Determine Contamination
nature, source, distribution, extent
acute effects (structures, biota)
Geotechnical Information
subsurface structures, cables, pipes, drains
soil properties, site geology
Water Environment
groundwater level and composition, local abstraction use
site run-off to surface waters

21. 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

22. 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/ etc)
Produce Photographic Evidence
Planning of Subsequent Investigations
Best estimation of the extent of contamination on the site

23. Exploratory Investigation
Confirms presence of contamination where the Preliminary Investigation is inconclusive
neither investigation can prove the Absence of contamination
Informed sampling locations
Sampling locations can form Stage 1 of the Main Investigation
Composite samples
Soil profile samples (depth)
Restricted range of chemical analysis (targeted e.g. BTEX)
helps with Planning of the Main Investigation

24. Main Investigation Planning Site Access Safety Procedures
clothing, respiratory, hygiene, confined space.
sample labelling, transport
Accident Procedure, First Aid.
Environmental Protection
dust suppression, Wheel wash, decontamination
Data Requirements
specific requirements of Regulatory bodies
sampling and analysis strategy
Long Term monitoring Requirements

25. Main Investigation - Sampling Strategy
Requirements to be addressed:
Nature of sample
air, water, soil
Sample Type and Size
spot, or composite (mixed)
Collection and Storage
containers, temperatures
Method of sampling
surface
augering
Trial pits and trenches
Boreholes - soil, water, gas
Depth
Pattern and Frequency of sampling

26. Main Investigation - Sampling Strategy
Grid Size
Site Size Grid Size
(hectares) (m)
Number
Site Size Number
(hectares) of Samples

27. Main Investigation - Chemical Analysis
Quality Assurance
NAMAS
National Measurements Accreditation Service
Accuracy
Submit a prepared control sample (known value)
Scope
Specific Analysis
based on Exploratory Investigation or Desk Study
Standard Suites pH
Phenols
Toluene extractable Matter (TEM)
coal tars
mineral oils
PAH, PCB, BTEX
Cd B
Pb Hg As Cr Zn
Chloride
Sulphate
Sulphide
Cyanide
sulphur

28. Main Investigation - Gas Analysis
In-Ground Gases
methane, hydrogen sulphide
VOC
On-site Methods
Geophysical (conductivity/magnetic field)
Remote Imaging (IR for methane)
Spot Sampling
Portable Instruments (GC, IR)
Detection Tubes (Drager)
Laboratory Analysis
sample collection (Tedlar bags)
standard analytical equipment

29. 3. Interpretation of Contamination Data
(Risk Assessment)

30. Technical Approach to Risk Management of Contaminated Land
What are the key stages in the process?
Identify and assess Hazards
Collection of Data
Conceptual model (source-pathway-receptor linkages)
Evaluate and Quantify Risks posed by Hazards
Professional judgement
Generic Guidelines or screening values
Models (site-specific characteristics)
Prioritize sites (Local Authority)
fair and transparent process
Consider consequences of a change in use
force remediation of sites with “Risk”

31. Tiered “Risk Assessment Framework”
Risk screening or Preliminary Risk Assessment
Desk study information
Tier 2
Generic Quantitative Risk Assessment
Uses Generic Assessment Criteria (GAC)
i.e. SGV for “typical standard site”
Tier 3
Detailed Quantitative Risk Assessment
requires modelling tools (CLEA)

32. Guidelines and Standards
system of fixed, legally binding values
(not particularly relevant to the soil situation. Why?)
Soil Guideline Values
ICRCL (Interdepartmental Committee on the Redevelopment of Contaminated Land)
BRE (Building Research Establishment)
Dutch Intervention and Target Values
New UK CLEA derived SGVs

33. Soil Guideline Values (SGV)
Different “typical land uses” defined
Residential (with and without vegetable growing)
allotments
Commercial / industrial
Certain circumstances are not covered by SGVs and require Tier 3 risk assessment (i.e. CLEA modeling)
Playing fields
Schools
Complete cover by hardstanding

34. Guidelines ICRCL 58/93 Threshold 250 50 1000 Action 5000 no limit 500
10,000
Trigger Values (mg/kg air-dried soil)
Contaminant
Complex Cyanides
PAH
Proposed Uses
Domestic gardens, allotments
Landscaped Areas
Buildings, hard cover
Domestic gardens, allotments, play areas
Landscaped areas, buildings, hard cover

35. Guidelines Examples of SGV (CLEA)
Standard Land Use
Cadmium
(mg/kg)
Mercury
Arsenic
Residential (with plant uptake)
130 8 20
Residential (without plant uptake)
200 15
Allotments
Commercial
5000
480
500

36. Toxicological Data TOX Reports (use in CLEA model)
Arsenic, Benzo(a)pyrene, Cadmium, Chromium, Inorganic CN, Lead, Mercury, Nickel, Phenol, Selenium, Dioxins, PCB, Benzene, Toluene, Ethyl Benzene, Xylene, Vinyl chloride, tetrachloroethane, 1,1,1, trichloroethane, 1,2dichloroethane, tetrachloromethane, Naphthalene, PAH.
Soil Guideline Value Reports (set the SGV)
Arsenic, Cadmium, Chromium, Inorganic Mercury, Nickel, Selenium, Lead, Benzo(a)pyrene, Benzene, Ethylbenzene, Toluene, Xylene, Phenol, Naphthalene.

37. SGV (from CLEA) SGV assume a standard site defaults conditions for:
Receptor behaviour
Age, weight height, skin area
Exposure frequency, soil ingestion rate, vegetable consumption rate, time on site
Land Use
Residential, Allotment, Commercial/Industrial
Depth of Soil
0.5m for ingestion
0.5m for plant uptake
0 – 0.1 m for dust inhalation
1m for vapour inhalation

38. Quantitative Risk Assessment
Human Health
CLEA Model (Contaminated Land Exposure Assessment)
RISC-HUMAN (C-soil model Netherlands)
Groundwater (Dispersion)
ConSim Model (Environment Agency)
Ecosystems
currently excluded
wildlife, biodiversity, HC50
research needed

39. Human Health Contaminated Land Exposure Assessment (CLEA)
Site Specific Data
Chemicals
Climate - precipitation, wind
Soil Properties
physico-chemical, pH
particle size distribution
permeability
organic content
Site Use
user activity patterns (vegetable consumption)
building type
Monte Carlo probabilistic model
Probability Density Functions (PDF)
compare with Tolerable Daily Soil Intake (TDSI)

40. Risk to Groundwater ConSim 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
addresses element of uncertainty
decay and biodegradation are calculated
output data graphical, probabilities of exceeding WQS

41. Unsaturated Zone Retardation
CONTAMINATED
SOIL
VADOSE
ZONE
AQUIFER
Simulated
Leach
Data
Level 2
Unsaturated Zone Retardation
Level 3
Dilution
Dispersion
Biodegradation
Level 1
Theoretical
Leach
Properties If
Concentration
< WQS
STOP If
Concentration
< WQS
STOP
Multi-Tiered Approach of the ConSim Model

42. Multi-Tiered Approach of the ConSim Model
Contaminant
Level 1
Vadose
Zone
Level 2
Saturated
Zone
Level 3

43. Assumptions for Guidelines and Models
Validity of analytical data
sample errors, heterogeneity of contamination
Toxicological and Ecotoxicological Reference Dose
databases incomplete
Predicted No Effect Concentration (PNEC)
Maximum Permissible Risk Concentration (MPC)
Tolerable Daily Intake (TDI)
Negligible Risk Concentration (NC)
Lowest (& No) Observable Effect Concentration (LOEC, NOEC)
Reference Dose (USEPA for carcinogens)
Uncertainties
contaminant transfer, uptake, availability, synergistic effect, metabolic detoxification, receptor behavior, soil properties (adhesion), dermal resorption data, average values representing statistical distributions of the exposure factors.

44. 4. Regulatory Frameworks
(Risk Management)

45. Technical Approach to Risk Management of Contaminated Land
What are the key stages in the process?
Identify and assess Hazards
Collection of Data
Conceptual model (source-pathway-receptor linkages)
Evaluate and Quantify Risks posed by Hazards
Professional judgement
Generic Guidelines or screening values
Models (site-specific characteristics)
Prioritize sites (Local Authority)
fair and transparent process
Consider consequences of a change in use
force remediation of sites with “Risk”

46. History of Contaminated Land Policy
USA
CERCLA 1980 (SUPERFUND)
SARA 1986
Netherlands
Soil Clean-up Act 1982
policy reversal 1987 UK
ICRCL (guidance)
EPA (STATUTORY LAW)
1993 “consultation”
EA (STATUTORY LAW)
PPC Regulations (2000) (STATUTORY LAW)

47. Framework Policy Objectives
Prevent new contamination
Deal with unacceptable risks to human health and the environment (Environmental)
Bring contaminated land back into beneficial use
(Economic)
to limit cost burdens to proportionate, manageable and economically sustainable levels (Social)
(Sustainable Development)

48. Contaminated Land Regime
Environment Act 1995
Section 57 (EA 1995) inserts Part IIA into the Environmental Protection Act 1990
Local Authority responsible
LA to formulate Strategy by mid-2002
LA actively identify contaminated sites & cause them to be remediated

49. Definition of Contaminated land
“Contaminated land is any land which appears to the regulatory authority, by reason of substances in, on or under the land, that:
a) significant harm is being caused or there is a significant possibility of such harm being caused; or
b) pollution of controlled water is being, or is likely to be caused” (Environment Act 1995)
“harm to the health of living organisms or other interference with the ecological systems of which they form part, and in the case of man, includes {harm to} his property”.

50. EA 1995 Enforcement Responsibilities Duties Tasks
Cause their area to be inspected to identify Contaminated Land
To determine whether a particular site is “contaminated”
To Act as enforcing authority for contaminated sites (other than Special Sites)
Establish responsibility for remediation.
Determine what remediation is required and to ensure that it takes place.
Arbitrate on the who bears what proportion of consequent liability.
Record and maintain prescribed information in a Public Register.

51. Section 108 Environment Act 1995 :-
Powers of Inspectors
Section 108 Environment Act 1995 :-
enter at any reasonable time
make any examination or investigation necessary
take photographs or samples
require the giving of information
order that premises or parts be left undisturbed

52. EA 1995 Information and Inspection
L.A’s may derive information form a number of
sources to enable an assessment to be made
Other Statutory Bodies
Its own Land Use records
Public Complaint
Land Owners

53. Prioritisation/Categorisation
Part I Assessment
Preliminary prioritisation of sites
into groups for Part II Assessment
under the following headings.
Development
Surface Waters
Groundwater
(This will comprise a desk top study
and can be carried out by
non- specialist personnel)
Part II Assessment
Sites in each group will be
categorised using individual risk
assessment
Priority given first to “Development Group A”
Site information examined
Site Visit
Establish contaminants, pathway and risk
Detailed exploratory survey where indicated
(Expert help will be required)

54. Part I Assessment GROUP A GROUP B GROUP C
Residential development, school
playground or allotment within 50 m
YES
Not Known
GROUP A NO
YES
Not Known
Industrial, commercial development
within 50 m or residential within 250 m
GROUP B NO
YES
Not Known
Site in agricultural or amenity use
including Parks and playgrounds
GROUP C NO

55. CLASS “A” CLASS “B” Any person who causes or knowingly
Appropriate Person
CLASS “A”
Any person who
causes or knowingly
permitted contaminating
substances to be IN, ON
or UNDER the site
CLASS “B”
Where reasonable enquiry
has failed to identify a
person fitting the definition
of “Class A”, the owner or
occupier of the land
If no Class A or Class B then site is an Orphan Site (ownership passes to LA)

56. Appropriate Persons - Exclusions
Class A – for abandoned mines
Class B - where pollution is to controlled water
Class B – for contaminants escaping to adjacent land
Class B - when they act in official capacity e.g. ‘insolvency practitioners’, ‘official receiver’
Class A – where land was sold with ‘information’ regarding level of contamination

57. Apportionment of Liability Inherited Problems
Adjoining Land
Contaminated land X
migration Y
“Person A” causes contamination of “Contaminated Land X”
Innocent “Person B” becomes owner/occupier of “Contaminated Land X”
“Person B” not liable to remediate “Adjoining Land Y” unless they had knowledge of the contamination at purchase (Caveat emptor)
Contaminant

58. Special Sites
Environment Agency becomes the enforcing authority after LA designates a site as a Special Site on the basis of:
Water Pollution Cases
Controlled water used for Drinking Water abstraction
Ecologically important sites (SSSI, reserves)
Major Aquifers
Industrial Cases
Pollution from sites involving Acid tar, Oil, Explosives, and Nuclear (excludes coal processing)
Defence Cases
Army, Navy, Airforce, Weapons Testing sites
Extends to contaminated sites adjacent to above cases

59. EA 1995 Remediation Notices
Where Pollution Linkage is confirmed
Remediation Notice served on each “appropriate person”
Can cover assessing site condition (detailed intrusive Site Investigation), preventative works, remediation and monitoring
Must be “reasonable” having regard to cost and seriousness of harm/pollution
Must be preceded by consultation (an opportunity for voluntary action)

60. Attributing Costs for Remediation Actions
Single-Linkage Action
Shared-Action (when more than than one pollution-linkage)
Single Liability Group
Multiple Liability Groups
Complex Variable Attribution of Responsibility. The costs may be shared:
Equally
In proportion to capital assets in the land (multiple Group B)
In proportion to costs relating the contamination caused be each member (multiple Group A)
As the enforcing authority sees as just and fair

61. Non-Compliance with Remediation Notice
Enforcing Authority can carry out the remediation and recover costs.
Non-compliance is a criminal offence, punishable by imposition of a fine of up to £20,000 plus £2,000 a day.

62. Recovery of Costs
Local Authorities must take into account:
HARDSHIP
LA must consider any hardship that may be caused.
BUSINESS CLOSURE OR INSOLVENCY
Where remediation costs would make a business insolvent, the authority should consider a reduction in costs. The main aim is to recover as much cost as possible without causing insolvency.

63. EA 1995 Public Registers
Will be maintained to include:
Remediation notices and appeals.
Remediation work carried out following a remediation notice.
Conviction for offences.

64. EA 1995 Conclusion
CL Regime brought into force 2000.
Local Authorities published Strategy 2002
New regime extremely complex and bureaucratic
Lack of significant new resources
Responsibility for “orphan sites”

65. Pollution Prevention & Control (PPC) Regulations 2000
IPPC Directive (96/61/EC)
enacted in UK as “The Pollution Prevention and Control (England and Wales) Regulations 2000”
Contaminated land covered under requirements for ‘Site Reports’
Regulator is ‘Environment Agency’

66. Pollution Prevention & Control (PPC) Regulations 2000
Principle of PPC
Specific Industrial Sectors are regulated
Aim to preserve land quality rather than deal with Historic pollution (I.e. stop future pollution)
Linked to Permit Application
authorises the site (or installation) to conduct specified industrial activity
Process requires ‘Site Report’
a detailed investigation of current state of the land that acts as a ‘baseline’
Closure of Site (or Change of Use)
Cessation Site Report compared with Original Site Report
Site must be remediated to ORIGINAL CONDITION and not ‘Suitable for use’

67. Pollution Prevention & Control (PPC) Regulations 2000
Purpose of a Site Report
To document the condition of the site with particular reference to substances in, on or under the land that may constitute a pollution risk
All land of the installation is covered
Phased approach
1a Desk Study (Conceptual Model)
1b Further Desk Study and Exploratory Investigations
2 Main Intrusive Investigation
Complex activities may be zoned
Technical Content
presentation of lateral and vertical distribution of contaminants
Site Report sent to LA (as statutory consultee)
Data can be used by LA under Part IIA EA 1995 legislation

68. 5. Site Remediation
(Risk Management)

69. Risk Management 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

70. Remediation of Contaminant Source
Removal
excavation and landfill (dig and dump)
Degradation
Bioremediation, Chemical and Thermal destruction
Natural Attenuation
Extraction
Soil washing, Vapour Extraction

71. Remediation - Contaminant Pathway
Engineering Methods
In-ground Barriers
Surface Covers
hard cover
vegetation
Solidification and Stabilization
Groundwater pumping

72. Contaminated land Remediation
Multifunctionality Approach
always apply highest technical level of clean-up
Suitable For Use
clean-up level determined by land use
favoured approach based on the “risk-environmental benefit”
residential with gardens
residential without gardens
parks and recreational areas
agricultural
industrial and commercial

73. Risk Based Corrective Action (RBCA)
The "formal" definition of RBCA is as follows:
“A streamlined approach in which exposure and risk assessment practices are integrated with traditional components of the corrective action process to ensure that appropriate and cost-effective remedies are selected, and that limited resources are properly allocated.”
The goals of a RBCA process are:
Protection of human health and environment
Practical and cost-effective application of risk-based decision-making

74. Natural Attenuation Spontaneous process Long Term
mostly biological
BTEX half life (chemical =108 yr , biological = <1 yr)
Long Term
Risk Based Corrective Action (RBCA)
Environmental benefit v. Cost
may be better to address consequences than to treat the source (e.g. borehole contaminants)
Lines of Evidence
Primary
(concentration v. time, concentration v. distance)
Secondary (supportive)
(DO level, pH, electron acceptors, active microbes)

75. Monitored Natural Attenuation
Not a “Do-Nothing” Option
quantify the natural breakdown process
Monitor Plume
position of the 10 ppm threshold
Sentinel
well
Receptor
Monitoring
wells
flow