N.J. CROMAR, J.S. HEYWORTH & J.P. RALPH

A variety of reasons underlie the growing awareness of public, industry and government sectors of the need to manage contaminated sites:
 contaminated sites are widespread and have the potential to affect many individuals.
They can be found in industrial, agricultural, urban and business environments.
 community awareness of the potential hazards of contaminated sites is increasing.
 government regulations which dictate the need to remediate contaminated sites and which limit the uses of contaminated land are becoming more stringent.

The hazardous nature of site contaminants is becoming more defined as a result of ongoing toxicological and epidemiological studies. More chemicals are being shown to pose health risks.
 site remediation is expensive. Risk assessment seeks to identify the minimum essential remediation options which must be performed to allow particular uses of contaminated sites to be implemented.
A formalised process of risk assessment and management (RAM) has emerged as an important methodology for identifying and remediating contaminated sites. There now exists a framework that reduces the RAM of a contaminated site to a step-by-step process in which information is collected and disseminated and remediation options are developed and implemented (Figure 1). Thus, RAM of contaminated land appears to be a well defined process of investigation and engineering in which a satisfactory result is ensured if each step is completed.
In practice, the theoretical ideals of RAM are not always achievable. Information may not be available, the exercise may be prohibitively expensive, available technology may be limiting, time constraints might be imposed and concerned parties may not be in agreement over the issues involved. For these reasons, RAM of contaminated sites is a contentious issue. A balance between the interests of public and occupational safety on the one hand and the interests of business and land owners on the other hand can be difficult to achieve.
This case study is intended to illustrate the process and difficulties of RAM of a contaminated site. The case study is divided into the following major components of risk assessment:
 identification of contaminated sites
 site history and description
 preliminary sampling
 second stage sampling
 exposure assessment
 consequence assessment
 risk characterisation
 risk management
 risk perception and communication

Risk assessment procedures are reasonably well defined (e.g. ANZECC/NHMRC, 1992;
Contaminated Sites Monograph Series, 1991-1996, published by the South Australian Health
Commission) but are under constant review. Risk assessment of contaminated sites is a function of the following parameters:
 the source, identity, levels and distribution of contaminants (ie release assessment);
 toxicity of the contaminants with regard for factors which influence their toxicity and availability eg characteristics of risk groups which influence their susceptibility to health effects of the contaminants (ie consequence assessment);
 exposure of risk groups to the contaminants (ie exposure assessment);
 assessing risk outcomes (i.e. risk characterisation).
Qualifying and quantifying these parameters involves:
 sample collection and analysis;
 independent toxicological evaluation of the contaminants;
 identification of exposure routes and the relative contribution of each route;
 identification of genetic, behavioural and other relevant traits within risk groups which might impact upon the health effects of the contaminants to which they are exposed.
The rigour and success with which each of these parameters is defined is dependant on available technology, funding, time, political will and the skill of the assessors.
This case study is based on soil contamination in a hypothetical railyard. However, much of the information about this fictitious site was taken from a RAM report of an existing railyard which was found to be contaminated with asbestos and other hazardous substances. For this reason, the case study is not as comprehensive as a completely fictitious scenario could be; it has much the same strengths and weaknesses as those exhibited in the report on which this study is based. Readers are encouraged to treat the information critically, identify omissions in the report, suggest improvements in methodologies and question the validity of conclusions which have been made.

Figure 1.
Recommended approach to the assessment and management of a potentially contaminated site. Source: ANZECC/NHMRC (1992).
Initial Evaluation to Determine if Detailed Investigation is Necessary

Site History

No Problem Apparent
No Action Required
Site Description
Preliminary Sampling

Australian Soil Investigation Guidelines

Potential Problem

Development of Work Plan for Second Stage
Investigation Programme
Detailed Sampling and Analysis Plan
Health and Safety Plan
Community Participation Plan

Assess Nature and Extent of Contamination
Assess Public Health Risk
Assess Occupational Health Risk
Assess Environmental Impact

No Unacceptable Impacts
Detected. No Further Action
Required (Monitoring may

Unacceptable Impacts Detected
 be necessary)

No Further Action
Required (Depending on Action Taken)
Development of Work Plan
Determine Criteria for Site Clean-up
Develop Options for Site Management
Determine Contamination Mitigation or Clean-up Method
Take Action
Validate Action

Future Monitoring

Some of the fundamental terms used in risk assessment and management of contaminated land are defined below. They are adapted from El Saadi and Langley (1991b).
Toxicity: the inherent capacity to produce adverse health effects at some dose or under specific exposure conditions.
Hazard: the capacity to produce a particular type of adverse health effect e.g. one hazard of asbestos is asbestosis and another hazard of asbestos is mesothelioma.
Hazardous substance: a chemical, biological or physical agent which has a high potential for causing adverse health and/or environmental effects.
Risk: the probability that an adverse outcome will occur in a person, a group, or an ecological system that is exposed to a particular dose or concentration of a hazardous agent i.e. it depends on both the level of toxicity of the hazardous agent and the level of exposure.
Health risk assessment: the process of estimating the potential impact of a chemical or physical agent on a specified human population system under a specific set of conditions.
Environmental risk assessment: the process of estimating the potential impact of a chemical or physical agent on a specified ecological system under a specific set of conditions.
Health risk management: the regulatory process of evaluating alternative actions and selecting options in response to health risk assessments. The decision making will incorporate scientific, social, economic and political information. The process requires value judgements e.g. on the tolerability of risk and the reasonableness of costs.
Contamination: the presence of a hazardous substance(s) above response level (s).
Contaminated site: a site where the level(s) of a hazardous substance(s) are above response level(s) ie where the site specific assessment deems that a response is required to protect health or the environment.
Background levels: a range of values for a substance defined by nationwide testing but excluding high values resulting from localised geological idiosyncrasies.
Investigation level: the concentration of a contaminant above which further appropriate investigation and evaluation will be required to ascertain:
 the typical and extreme concentrations of the contaminant on the site;
 the horizontal and vertical distributions of the contaminant on the site;
 the physico-chemical forms of the contaminant;
 the bioavailability of the contaminant.
Response levels: soil levels of a contaminant at which some form of response to protect public health or the environment with a wide safety margin is required. Response levels apply to a specific site and site assessment.

As
BTEX
Cd
Cu em
EPA f
Hg
HIL
IARC
NATA ng
Ni
PAH
Pb
SEPA
SHC
TPH
TWA
TWADI
 g
USEPA
Zn
arsenic benzene, toluene, ethyl benzene and xylenes cadmium copper electron microscopy
Environment Protection Agency fibre mercury health-based further investigation level
International Association for Research on Cancer
National Association of Testing Authorities, Australia nanogram = 10
-9
grams nickel polyaromatic hydrocarbons lead
State Environment Protection Agency
State Health Commission total petroleum hydrocarbons
Time Weighted Average
Time Weighted Average Daily Intake microgram = 10
-6
grams
United States Environment Protection Agency zinc

A waste dump in a railyard was first suspected of posing a health hazard in the mid 1980s when the site was unofficially inspected by an officer of the Waste Management Commission.
The officer observed asbestos waste on the surface of the fill areas. No further action was taken as a result of this inspection for reasons which are unknown. Subsequent media reports contained claims that the railyard operators were aware that a contamination problem might exist but had not pursued the matter.
In 1994 railway workers uncovered material believed to be asbestos while excavating the site.
An asbestos contractor was employed to hand-pick and remove visible asbestos. Six 200 litre drums of asbestos waste were removed. Air samples collected in Jones Avenue, a residential street adjacent to the site (Figure 2), contained no detectable asbestos fibres.
In late 1994 or early 1995 a vehicle driving over the site caused a gravel road to collapse, revealing bags of asbestos. Railway workers alerted their union of the problem. Subsequently, local residents and environmental action groups became aware of the existence of asbestos and possible existence of metal contaminants on the site. They began to campaign for the contamination status of the site to be assessed and remediatory measures to be taken.
The railyards are situated in the suburb of Railville, about 5 km from the central business district of a medium sized Australian city. Railville is comprised of residential dwellings and light industries. The railyards contain an area of undeveloped land located west of the rail workshops which appears to have been used as a dumping ground for workshop wastes. The fill material is concentrated in two areas termed the northern and southern dump sites (Figure
2). Railway buildings and a car park abut the eastern border of the waste ground and a public railway line is situated to the south. Further south of this railway line is a complex of rail lines used to store rail vehicles and load and unload goods trains. The rear fences of residential homes on Jones Avenue and Smith Street border the northern and western boundaries of the site; the western tip of the south dump site comes to within less than 10 meters of the fence line. The site is fenced on all sides except the eastern side by cyclone mesh topped with razor wire to a height of about 3 metres. The razor wire on the northern and western boundaries was supplied by the railway in 1995 and has been erected parallel to and within 15 cm of the back fence of each of the Jones Avenue and Smith Street homes.
The disposal site covers an area of about 9 hectares (90,000 m
2
). It is a flat open tract of land.
The fill on the northern and southern dump sites occupies about 75 % of the waste ground and rises to about 1.5 meters above ground level essentially uniformly over the two areas. It supports low vegetation (mostly annual grasses) in winter but very little vegetation in summer.
Several large trees and shrubs are located between the two dump sites and near the fence lines on the western and southern borders. Some hard rubbish is visible including machinery, 44gallon drums and masonry.
Shallow excavation of the fill reveals hard rubbish (glass, bricks, metal etc) and blue asbestos waste. The original uses of the 44 gallon drums which present on the site are not known.
Groundwater occurs at depths between 3.2m and 3.9m below ground level.

N
Smith Street
Residential homes
Car Park
Northern dump site
Workshop
Access Road
Workshop
Storage Shed
Southern dump site
100 metres

(A) Suspicion that a site is contaminated
GENERIC QUESTIONS:
(a) How are sites initially identified as areas of possible contamination?
OR
(b) Is a site likely to be associated with adverse health effects due to the presence of soil contaminants?
Q1.1
Contamination of the railyard with toxic substances was first recognised officially because (a) asbestos was visible on the surface of the soil, (b) individuals recognised this material as asbestos and (c) these individuals were aware of the toxicity of asbestos. Contamination of other sites may not be so readily identified, e.g. if toxic substances are present but not visible or not generally known to be toxic.
List the processes which result in the discovery and identification of contaminated sites.
Q1.2
Identify the problems associated with contaminated sites - health, social, environmental and economic. Consider the individuals and groups who might be affected and the types of effects that they may experience.
Q1.3
What evidence is there for health effects arising directly from contaminated sites? Are there differences in risk from regional contamination (e.g. produced by a lead smelter over many years) compared to living on or near an isolated contaminated site?

(B) Site History and Site Description
GENERIC QUESTION:
(a) What information can be obtained about a site prior to soil analyses which will indicate the identity, source, distribution, age and concentration of contaminants which might be present?
OR
(b) How can you estimate the likelihood that a site is contaminated without analysing the soil?
Q1.4
Are other soil contaminants in addition to asbestos likely to be present in the railyard and from what railway or other activities might they have been derived?
Q1.5
Over what time period might these contaminants have been produced (i.e. over what time period have railways been producing the wastes identified in 1.4)?
Q1.6
What information would you seek in order to clarify the magnitude of contamination of the site and the problems that it might generate?
Q1.7
What are the sources of information which could assist in characterising contamination at the railyard? What problems might be associated with acquiring this information?

The history of the disposal site is patchy and based upon railway, contractor and government records and the recollections of railway staff and local residents. The railyard was opened in
1882 but, due to lack of railway records, waste dumping on the site can only be said to have commenced with certainty sometime before 1959. Wastes were produced at the site when locomotives were scrapped, by foundry activities (eg heat-treating metals, electroplating, welding) and possibly when railway sleepers were treated with wood preservatives. Dumping ended in 1989. The wastes have since been reported to contain asbestos, cyanide, copper, cadmium, foundry and electroplating wastes, scrap metal and general refuse. Wastes on the disposal site are concentrated in the southern and northern dump sites.The disposal site received an estimated 116,000 m 3 (ie a cube with sides almost 50 m long) of waste equivalent to approximately 232,000 tonnes between 1970 and 1987, most of it as above ground fill.
Waste containing chrysotile (white asbestos), amosite (brown asbestos) and crocidolite (blue asbestos) was produced in the rail workshop during the scrapping of steam locomotives from
1958 until 1987. Asbestos is distributed over much of the site. The total volume of all asbestos waste on the disposal site is estimated to be as much as 300 m
3
and is estimated to represent 0.26 % by volume and 0.04 % by weight of all of the total waste on the site. These values are based on the following calculations:
Estimated total volume of fill: 116,000 m3
Estimated total volume of asbestos: 300 m
3
= 0.259 % of total
Estimated total weight of fill: 232,000 tonnes
Estimated total weight of asbestos: 90 tonnes = 0.039 % of total
The total volume of blue asbestos dumped at the disposal site, based on the number of locomotives scrapped and the content of blue asbestos in an individual locomotive, is estimated to be over 100 m
3
. Total amounts of heavy metals and hazardous organics dumped at the disposal site have not been estimated. The nature of the activities conducted in the workshop (eg electroplating, heat-treating metals, welding, wood-preserving) suggest that the site contains copper, lead, zinc, arsenic, nickel, cyanide and petroleum hydrocarbons. The contents of metal drums which are scattered on the site are unknown.
The site may be sold in the near future for redevelopment although the uses to which the land will be put have not been clarified. It has been suggested that it could be developed for residential or industrial use or left as open space for recreational purposes.

(C) Preliminary Sampling
GENERIC QUESTIONS:
(a) What factors need to be considered when designing an exploratory sampling program for a potentially contaminated site?
OR
(b) What is the intent of preliminary sampling and how can it be achieved?
Q1.8
Soil sampling and analysis is time consuming and expensive. Furthermore, hazardous substances known to contaminate soil number in the hundreds, many of which require individual analysis i.e. a single soil sample may be analysed by several techniques, each technique being able to determine one compound or a group of related compounds. With these considerations in mind, specify the analytes which you would request be quantified in soil from the disposal site and state why you selected them.
Q1.9
What are the aims of your preliminary sampling program?
Q1.10
Design a sampling plan which you believe is adequate to meet the needs of your preliminary assessment. Specify the number of samples you would need, the location from which they were obtained and the amount of sample material to be taken. What steps would you take to ensure that the analytical results represent as true and accurate a picture as possible of the contaminant status of the disposal site?
Q1.11
What factors would you consider when selecting a laboratory to perform soil analyses? How could you be confidant that the results of the analyses are accurate measures of the levels of the analytes specified in 1.8
.

Preliminary soil and groundwater studies were undertaken. A summary of the results is given here. The specific locations of sites which were sampled in the preliminary studies are not known.
Surface samples were taken to a depth of 10 cm from 15 locations in the fill areas. Soil samples were also taken from bore holes which were drilled (depth unknown) at 41 locations in the fill areas. Six bore holes were converted to groundwater monitoring stations. Samples were analysed for arsenic, cadmium, copper, lead, nickel, zinc, total petroleum hydrocarbons
(TPH), polynuclear aromatic hydrocarbons (PAH) and asbestos. The results and the relevant
Health Investigation Levels are listed in Table 1.
Table 1. Summary of results of soil analyses
Analyte Source of soil sample
No. of samples in which HIL was exceeded
Concentration
(ppm)
Health
Investigation Level
(ppm)
*
Copper
Lead
Zinc
Arsenic
Cadmium
Nickel
Asbestos surface 8 bore surface 7 bore surface bore surface 1 bore surface 1 bore surface 5 bore surface 9 bore
10
11
7
8
1
5
10
11 up to 4,000 1,000 up to 7,000 up to 1,000 300 up to 1,500 up to 15,000 up to 23,000
210
350
140 up to 550 up to 2,000 600 up to 3,500 detected none set detected
7,000
100
20
*For a standard residential exposure scenario. Source: Imray and Langley (1996).
Low levels of TPHs (< 1 ppm) and PAHs (< 0.1 ppm) were found. Levels of contaminants in groundwater taken from 11 wells were below levels of concern.

(D) Second Stage Investigatory Sampling
GENERIC QUESTIONS:
What factors need to be considered when designing an investigatory sampling program for a site which was shown during preliminary sampling to be contaminated?
What is the aim of second stage investigatory sampling and how can it be achieved?
Q1.12
What are the aims of an investigatory (second stage) sampling program? Give your reasons why you believe a second stage investigation is or is not required in the light of the results of the preliminary investigation?
Q1.13
Specify the analytes which you would request be quantified in soil from the disposal site during the second stage investigation and state why you selected them.
Q1.14
Design a sampling plan which you believe is adequate to meet the needs of your second stage assessment. Specify the number of samples you would need and the locations from which they are to be obtained.

Asbestos contamination
Surface soil to a depth of 200 mm at each of 88 grid points defined by a hypothetical 30 metre square grid over the southern and northern fill sites (Figure 3) were visually and microscopically screened for asbestos waste. It is not clear how the samples were obtained so assume that soil cores were extracted. Asbestos was visible to the unaided eye in 17 samples.
Microscopic “respirable” asbestos fibres were detected in almost all samples (Figure 4). Most fibre counts were less than or equal to 15 fibres per microscope field and therefore estimated to correspond to less than 0.001% asbestos. This is the level of asbestos deemed necessary for hazardous air emissions of asbestos to form when the soil is disturbed (see next section
“Determining the Level of Asbestos in Soil”). More than 15 fibres per microscope field
(estimated to be equivalent to > 0.001 % asbestos) were counted in 24 samples and more than
38 fibres per microscope field (estimated to be equivalent to > 0.01 % asbestos) were counted in 3 of these 24 samples (Figure 4). It was suggested that some counts might be inflated due to misidentification of soil particles as asbestos.
Bores of unknown diameter were sunk to between 0.2 and 1.5 metres deep at 39 locations.
Visible asbestos was present in 6 of the bore samples and fibre counts exceeded the 0.001 % level in 5 of the bore samples.
The edges of the northern and southern waste mounds were excavated by shovel at 24 sites.
15 of the sites showed visible asbestos contamination. It was concluded that large volumes of blue asbestos occur in the south mound. The north mound also appears to contain deposits of blue asbestos but located further below the soil surface.
Airborne asbestos was sampled 18 times during on-site activities using Worksafe’s paraoccupational procedure which has a detection limit of 0.01 f/ml. Each air sample consisted of
230-560 litres and was filtered through a 0.8
 m filter. Four of the air samples yielded a fibre count in excess of the maximum occupational exposure standard of 0.01 f/ml. These counts
(0.023 f/ml, 0.027 f/ml, 0.036 f/ml and 0.05 f/ml).
Asbestos concentrations in groundwater were measured in 5 water samples. No sample contained asbestos concentrations in excess of USEPA recommended levels.

An exercise in critical assessment of analytical procedures and reporting.
A standard or recommended procedure for microscopic determination of trace levels of asbestos in soil were not available to the investigators. A method was developed to obtain this data and is described below. It is suggested that this method be critically analysed.
Method
1.
5 ml of soil or fill was dispersed in 10 ml distilled water for several minutes.
2.
After a settling period of 30-60 seconds a drop of water from above the semi-settled solids was placed between a microscope slide and cover slip and covered an area of 10 cm
2
.
3.
Asbestiform fibres were counted using phase contrast microscopy at 600 X and the rules of the Worksafe Australia’s (1988) guidance note except that fibres attached to or crossing non-respirable particles were counted.
4.
20 full fields of view each 0.348 mm in diameter were scanned.
5.
The procedure was tested using known mixtures of amosite (brown asbestos) in a pre-dried sandy soil (results shown below).
Asbestos (wt %)
0.1
0.01
0.001
It was concluded that for amphibole asbestos-contaminated soil the following estimates were applicable:
“Respirable” fibre count
410, 290, 480 Ave = 390

100
56.5, 33.5, 67, 51.5
14, 22, 24
Ave = 52

14
Ave = 20

5 count >15 fibres corresponds to >0.001% asbestos count >38 fibres corresponds to >0.01% asbestos count >290 fibres corresponds to >0.1% asbestos and counts exceeding 15 respirable fibres were interpreted to indicate that soil disturbance can lead to hazardous air emissions of asbestos.
Comment on the veracity of this assay and answer the following questions:
1.
How was the sample dispersed in water e.g. vortex mixing, shaking, swirling?
2.
What effects would changing the dispersion time and settling time have on fibre counts?
3.
Would the same fibre counts have been obtained if crocidolite (blue asbestos) and chrysotile (white asbestos) were used in place of amosite and if other soil types had been used in place of a sandy soil?
4.
The data is unclear. Were 3 fields counted at each asbestos level and if so how is a fractional count obtained (e.g. 33.5) and why were 20 fields counted when samples from the disposal site were examined? Alternatively, is each count the mean of 20 field counts and 3 different samples were examined? If so, were the 3 samples taken from a single standard preparation or from 3 different preparations?
5.
What is the measure of variance e.g. standard error or standard deviation, and does the magnitude of variance of each sample fibre count indicate that the procedure is reliable?
6.
What is the rationale underlying the conclusion that counts exceeding 15 respirable fibres might lead to hazardous air emissions of asbestos?

N
Smith Street
Residential homes
Northern dump site
Access Road
Workshop
Workshop
Storage Shed
Southern dump site
100 metres
Figure 3. Sampling points determined by a 30 metre square grid

N
0
2
0
0
4
4
0
6
0
3
3
9
8
4
0
1
Smith Street
11
Residential homes
0 8 11
7 12 8 3
Access Road
10 13 7 25
Northern dump site
2 8 7 17
9
28 19 13
12 15
11 12 17 11 15
14
Workshop
14
2 23 26 18 14 30 42 65 17
12 12
9 8
5 10 17 23
Southern dump site
22 31 4 5
15 26 8
17 14 6
Workshop
Storage Shed
11 11 17
4
8
7 6
23
2
36 33 31 54 14
100 metres
13 14
Figure 4. Asbestos fibre counts in soils on the site surface

Other contaminants
Surface soil samples were analysed for arsenic, lead, copper, zinc, nickel, cadmium, mercury, cyanide, polycyclic aromatic hydrocarbons and, in some cases, TPH and BTEX. Soil from boreholes was analysed for metals and drum contents were analysed for metals, cyanide and
TPH. Each of these substances is a well characterised toxin and earlier investigations indicated that they are or might be present in high concentrations at the disposal site. Both the southern and northern dump sites were found to contain numerous areas where the concentration of copper, lead, zinc, nickel, mercury and/or PAHs in the fill exceeded the HIL.
The levels of copper, lead and zinc in up to 30% of the soil samples exceeded the maximum level which would enable the fill to be classified a low level contaminated soil as defined by the EPA. Cyanide levels in all samples were below the HIL. Three soil samples taken from below the fill contained metals at concentrations above the HIL. The results of the analyses of drum contents were not provided.
To determine the likelihood that metals at the disposal site would leach from the fill, through the soil and into groundwater, a modelling exercise was performed to assess the mobility of copper, arsenic and lead in the soil which underlies the fill. The model incorporated the metal retention capacity and hydraulic conductivity of the soil which had already been assessed.
Several assumptions had to be made concerning the behaviour of metals in soil and the physical and chemical conditions within the soil. The height of the soil layer between the fill and groundwater was assumed to be 1 metre. It was concluded from the results of this study that the rate of movement of metals from the soil beneath the fill into groundwater is so low that the risk of groundwater contamination by metals is negligible.

GENERIC QUESTION:
What is the level and pattern of occupational and non-occupational exposure to hazardous substances from the contaminated site?
Q2.1
Propose exposure routes which may reasonably be expected to result in occupational and non-occupational exposure to contaminants in the disposal site.
Q2.2
Which of the contaminants might individuals be exposed to in greatest amounts and why?
Q2.3
Describe differences in the levels of exposure which are likely to exist between onsite railway staff and residents of adjacent residential homes.
Q2.4
Which groups of individuals are likely to receive high levels of exposure to soil contaminants and are particularly susceptible to health effects from exposure to soil contaminants? Give your reasons for selecting these groups.
Q2.5
How do you think the levels of occupational and non-occupational exposure may have changed over the last 30 years?
Q2.6
How might current and cumulative exposure to soil contaminants be assessed?
Q2.7
Can you make any immediate recommendations which will limit exposure to soil contaminants? State why you believe these recommendations should or should not be implemented.
Q2.8
Why is groundwater contamination of concern?
Q2.9
A number of media reports stated or suggested that the railyard contains high levels of cyanide yet very little cyanide was found in the preliminary and second stage soil analyses. How can this inconsistency be explained?

GENERIC QUESTION:
What is the level of exposure to a hazardous substance above which the risk and/or severity of adverse health effects becomes unacceptable?
Q3.1
Investigate and summarise published toxicological data on one of the contaminants detected in the railyard. Your summary should include:
 The maximum “safe” intake of the contaminant or the reasoning for proposing that no safe exposure level can be advocated.

Relevant conclusions of controlled dose-response investigations of the contaminant.

A critique of the assumptions which must be made when applying the conclusions from human and animal studies to human populations inadvertently exposed to the contaminant.

The mechanisms of adverse health effects caused by the contaminant.

GENERIC QUESTIONS:
(a) What is the aggregate risk to public health within this population?
(b) How does this risk compare with other risks accepted by the community?
(c) How much anxiety is the exposure causing?
(d) How does the exposure level relate to existing standards?
Q4.1
The following health risks associated with exposure to airborne asbestos are taken from Imray and Neville (1993):

The USEPA estimates that lifetime (70 yrs) exposure to 0.0001 f/ml corresponds to an excess lung cancer risk of:
2 x 10
-5
for smokers and
2 x 10
-6
for non-smokers.

The concentrations corresponding to a lifetime lung cancer excess risk level of 10 -4 are:
0.0005 f/ml for smokers and
0.005 f/ml for non-smokers.

Continuous exposure to air containing 0.0001 f/ml is expected to cause 2 to 3 deaths per 100,000 persons by mesothelioma over a 70 year lifetime. The risk is the same for smokers and non-smokers.
Use these risk estimates to estimate the aggregate risk of adverse health effects in the following scenarios. If insufficient information is supplied, state the assumptions you have made to achieve a quantitative result.
Scenario A.
The average continuous airborne concentration of asbestos in the occupational environment of the railway staff who were employed for 20 years to remove asbestos from trains was 0.03 f/ml. What is the risk that a railway worker will develop lung cancer due to occupational exposure to asbestos?
Scenario B.
Seventy railway staff worked for 30 yrs in the workshop where asbestos was routinely handled. Two of these staff have since died of mesothelioma. Estimate the average continuous concentration of airborne asbestos in the occupational environment which is consistent with this level of mortality due to mesothelioma.
Q4.2
Quantitative risk assessment is difficult to implement in practice and is not endorsed by some risk assessment experts. What are the problems associated with quantitative risk assessment?

Q4.3
How might the (potential) problems be perceived by:
Railway authorities
On-site railway staff
Occupational health and saftety personnel
Local residents
Local community groups
Government
Public health professionals
Media
Q4.4
How high a priority should be assigned to this particular public health problem?

GENERIC QUESTIONS:
(a) What are the options for managing this problem?
(b) How will we implement, monitor and evaluate the management strategy?
(c) What are the costs of remediation? Do they represent good “cost-benefit” relative to the allocation of expenditure to other health problems?
NB From additional material remember:
Problem/Context – Risks – Options – Decisions – Actions – Evaluation – (cyclical process).
Engage stakeholders early and throughout the process.
Below are SOME questions to aid your thinking. Do not rely on these. Be creative, think of appropriate management solutions of your own to this hypothetical scenario.
Define the problem and put it in context

Do the soil contaminants interact? Are their effects cumulative?
Analyse the risk associated with the problem in context
Consider the results from the Risk Assessment carried out previously.
 What are various stakeholders’ perceptions of the risks posed by the contaminated railyard?
Examine the options for addressing the risks

Propose a long-term management scheme for this site. List the advantages and disadvantages of your proposal.

Is the risk management option preventing risks, or just controlling them?
Make decisions about which options to implement

What considerations should be given to railway staff, local residents and the remediators to minimise health risks while the site is undergoing redevelopment?

Who is responsible for managing this site? What can the public do to speed up the management of this site?

Do benefits of risk management option reasonably relate to costs?
Take actions to implement decisions

Describe a monitoring program that will provide satisfactory warning of unacceptable health risks.


Frequency of monitoring? Costs, who bears?
And other action directives…
Conduct an evaluation of the action’s results

How would you evaluate the success of a management scheme?

For example, are decreased soil contaminant levels observed at the site?

Does the risk need to be re-evaluated in the light of risk management changes made?

GENERIC QUESTIONS:
(a) Who are the interested parties that need to be informed of health risks and decontamination of the site.
(b) How is the nature of the risk and the issues of management best communicated to interested parties?
Q6.1
Which individuals and groups should be consulted about the contaminated site?
Q6.2
What information should be provided to the public and when should the information be made available? What specialist modes of communication might be used to disseminate information amongst local residents?
Q6.3
To what level should the media be relied upon for disseminating information? What problems might be encountered with media involvement?

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