HEALTH BASED RISK ASSESSMENT:

Proposed residential re-development of part of a former mixed domestic/ industrial landfill site, Fremantle, Swan Coastal Plain, Western Australia.

The site had received mixed domestic & industrial waste between 1956 and 1985.  The proposed redevelopment included residential, tourist, commercial & retail use. A comprehensive site investigation was undertaken, including 24 soil
bores, 10 groundwater monitoring bores, 15 trial pits & a landfill gas investigation. In addition, in-situ geotechnical testing of fill was conducted to assess foundation/settlement properties.

The HBRA was conducted in accordance with ANZECC/NHMRC 1992 guidelines. A screening level assessment identified contaminants of concern from observed concentrations.  Exposure route scenarios were developed for construction workers & ultimate users, including commercial/ maintenance & residents using standard exposure parameters.
The following risks to human health were identified:

-Exposure to solid wastes via dermal contact, inhalation & ingestion

-Risk of asphyxiation (LFG)

-Explosive risk

Proposed mitigation measures to reduce risk to acceptable levels included:

-Provision of a 1-metre inert cap.
-Gas monitors
-Active landfill gas (LFG) extraction and flaring
-Suspended pile foundations

Potential settlement of the fill would be mitigated through construction of suspended foundations above piles driven to bedrock.

The risk to groundwater was identified due to the landfill disperse & attenuate design philosophy.  Existing contaminants included nutrients, heavy metals, hydrocarbons & organics.
Proposed mitigation measures for groundwater contaminants included:

-Restricting downgradient usage within the groundwater attenuation zone & ongoing monitoring consistent with WRP27.

An LFG generation model was developed to predict generation rates & the risk of accumulation within built structures at potentially explosive or asphyxiative concentrations based on indoor
ventilation rates. Proposed mitigation measures for LFG included:

-Provision of an active LFG extraction system
-Prevention of below ground structures
-Use of ventilated footings
-Ongoing gas monitoring.

Stuart Jeffries
Hydrosolutions Pty Ltd

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Risk4

ALCOA World Alumina Australia:
Groundwater Risk Assessment, development of a Groundwater Management Plan, Kwinana Residue Storage Areas, Swan Coastal Plain, Western Australia

A new groundwater management strategy was developed on behalf of Alcoa at their alumina residue storage areas in Kwinana, Swan Coastal Plain, Western Australia.  The multidisciplinary project included:

-Community consultation identifying sensitivities & conveying management solutions
-Development of a hydrogeological database
-Review of planning controls and future landuse issues
-Risk assessment of potential leachate seepage rates under different scenarios
-Numerical modelling and contaminant simulation to predict impact ‘footprints’
-Hydrochemical modelling relating bulk Electrical Conductivity (EC) to specific contaminant concentrations
-Cost benefit analysis of remedial options.

A technical paper by SR Jeffries, RW Colman and D Cooling, entitled ‘Development of a Groundwater Management Strategy, Alumina Residue Storage, Kwinana, Western Australia’ was presented at Hydro2000, 3rd International Hydrology and Water Resource Symposium, Perth, 20-23 November 2000.

Stuart Jeffries
Hydrosolutions Pty Ltd

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Risk3

WA (Southwest) BASED MINER

Investigation of former solvent extraction mineral processing plant

An initial appraisal of land contamination associated with a former solvent extraction mineral processing plant was undertaken at an operational minesite.

The extraction process used an hydrofluoric acid digest, with tantalum and niobium selectively stripped using an organic solvent, MIBK.  Acidic waste effluent was neutralised with lime prior to discharge to a natural wetland.
The plant was decommissioned in 1989.

The study identified potential migration pathways to site workers, surface water and groundwater.

Recommendations were made for further investigation of the site.

Stuart Jeffries
Hydrosolutions Pty Ltd

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Contam13

Conceptual Hydrogeological Model, of the Gascoyne River Floodplain Aquifer Model, GASFAMs
Department of Water, Carnarvon, Western Australia

DoW has commissioned Cymod Systems to undertake the development of an updated numerical model of the Gascoyne River Aquifer Floodplain (GASFAMs), which supplies potable water to the town of Carnarvon and irrigation water to commercial banana plantations. Hydrosolutions is working with Cymod to develop a conceptual hydrogeological model as the basis for the numerical model.

Fresh unconfined groundwater is present within the River Bed Sand (RBS) aquifer, which is the bedload of the current river course.  Semi-confined or leaky fresh groundwater is present within the underlying Older Alluvial Aquifer (OAA), representing a braided river floodplain depositional environment.

The aquifer system is recharged  by rainfall and riverflow/ flood events at approximately three yearly intervals.  A water balance model was developed describing inflows from river flow and direct recharge, outflows from evaporatranspiration, coastal discharge and abstraction, and variationis in storage.

Over abstraction has previously resulted in saline up-coning and intrusion near the coast and laterally along the river, locally restricting the sustainbale groundwater resource.
A numerical models has been developed based on the hydrogeological conceptual model.  The numerical model will be used to assess the sustainable groundwater resource, as a management tool for existing licensed abstractions, and to assess  the potential for new in-land groundwater resources.
Stuart Jeffries
Hydrosolutions Pty Ltd
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Hydro22

A PERIODIC NEWSLETTER COMPILED FOR HYDROGEOLOGICAL &

ENVIRONMENTAL PROFESSIONALS IN W.A. INDUSTRY, MINING & RESOURCE

COMPANIES

Issue June 2011
___________________________

HEALTH RISK ASSESSMENT

Types:
• Public: assess potential impact on a human population due to exposure to an ‘agent’ arising from specific conditions over a given timeframe
• Occupational HRA: Generally simplified procedural risk control/ minimisation (e.g. JSAs/ Risk Matrix/ Health & Safety Plans)
• Environmental RA: Assess potential impact on an ecosystem or sensitive receptor (complemented by Ecological RA).
• Incident/consequence: assessment of impact from low frequency events, generally acute (short-term) exposure & severe harm.

Definitions:

• Hazard- a source of danger
• Risk- ‘the probability in a certain timeframe that an adverse outcome will occur in a persons/group/plant/animal/ecology of a specified area exposed to a particular dose or concentration of a hazardous agent, i.e. it depends on both the level of toxicity…& the level of exposure’
• Risk Assessment- characterisation of the nature & magnitude of risks associated with environmental hazards.  It is a tool in the decision making process.
• Contaminated- ‘having a substance present in or on the land, water or site at above background concentrations that presents/ has the potential to present a risk of harm to human health, the environment or any environmental value.’

Methodology:

1. Issue identification: of the concerns that RA needs to address, how it was identified, its cause, the adverse health effects, their timeframe & public perception
2. Hazard identification: the adverse health effects & their timeframe
 
3. Dose-response assessment: evaluation of qualitative & quantitative toxicity data to estimate ‘the incidence of adverse effects occurring in humans at different exposure levels’.
4. Exposure assessment for a relevant population: determine frequency/ magnitude/ extent/ duration & character of exposures to a hazard, through monitoring and/or predictive modelling 
5. Risk characterisation: describing the nature & incidence of effects for the exposure conditions examined, including the assumptions & uncertainties in the RA.

 Key Principles:

1. Actions should be protective of human health (HH) & the environment.
2. RA should be transparent (e.g. default values & methods used, conclusions v policy)
3. Include a summary of key issues, conclusions from each RA component, the likelihood of adverse health risks, & the strengths & limitations of the RA.
4. (Be) Consistent in general format
5. HRA is complemented by ERA
6. An appropriate level of conservatism is included to protect HH & the environment
7. Ensure that comparisons against environmental health criteria are endorsed by local regulators, or where not, are referred to them
8. Ensure compliance with methods outlined in EnHealth 2004
9. Use toxicological data or exposure criteria relevant to the local jurisdiction
10. Use toxicological assessments relevant to the local jurisdiction
11. Ensure currency of knowledge of scientific literature
12. Variations in RA due to particular statutory requirements need to be explained

Objectives of RA:

To ensure that HH & the environment are protected, & to allocate management resources to reduce risk/s to acceptable levels; through assessment of potential for exposure to contamination & severity of effect of exposure, to inform decisions for the requirement to manage contamination. 

 
The process of RA ‘…should enable consistent application of methodology’…between assessors & for similar scenarios.  It requires considerable expertise, qualifications & experience across a multidisciplinary team, but coordinated by an individual with overall responsibility.  High level RA may not therefore be applicable to more simple or self-evident situations.

The level of risk can be qualitative (e.g. high/medium/low) or quantitative (e.g. probability of occurrence).  Quantitative RA is rarely feasible due to limitations in toxicological/ exposure data, while qualitative RA can provide a basis for effective management decisions.

Uncertainty is inherent due to limitations in investigation/ sampling & data gaps require assumptions to be made which may compound.  Variability reflects the range of values which may not be adequately represented by a single value.

Application of RA to Consites (staged approach):

Conceptual Site Model (CSM): qualitative description of possible pathways of how exposure may occur (e.g. source/pathway/receptor analysis), may require continued revision.
• Tier 1: Screening RA: comparison of site data with generic assessment levels may screen out or identify priority potential contaminants of concern (pCoC)
• Tier 2: intermediate RA: adjustment of exposure assumptions for site specific conditions
• Tier 3: detailed (site-specific) RA: development of site-specific investigation/response levels through fate & transport modelling

Risk Communication (RC):

RC should be included through the RA & RC as information exchange about risk and its management.  It should allow all Stakeholders to make informed decisions based on the understandable presentation of data, and allow the incorporation of feedback to the process.   

RA Framework- Human Health

Issue (hazard) identification: identify the concerns to be addressed including:
a) Identification of environmental health issues
b) Placement in context/ prioritise
c) Interactions
d) Define scope & objectives of RA
e) (Set) Data quality objectives (DQOs)
2) Hazard (toxicity) assessment:
a) Hazard Identification: Qualitative description of health effects of pCoCs
b) Dose-response assessment: based on available toxicological studies
3) Exposure assessment:
a) Magnitude/ frequency/ extent/ character & duration of exposures in the past/present/future
4) Risk characterisation:
a) Integrate  hazard & exposure assessments
b) Evaluate overall quality of the assessment/ degree of confidence in conclusions
c) Uncertainties
d) Describe the risk to individuals/ populations
e) Communicates RA to the ‘risk manager’
f) Provide information for risk communication
g) Outcomes:
i) Qualitative (e.g. high/medium/low risk)
ii) Quantitatively (e.g. probability/ return period) 

Risk Management (RM):

Evaluation of the results of RA, including social, economic & political considerations.  Decision making must be documented.  Public involvement should be inherent, due to ‘right to know’ & since anecdotal data may be available to enhance a generic RA.  DEC objective is for management of Consites according to the magnitude of risk, hence responsible & prioritised remediation within an appropriate timeframe. (E.g. immediate response to a current risk).  AS31000/2009 defines risk in terms of likelihood & consequence & hence provides a qualitative estimate of risk.  

Also evaluates merits of alternative actions that may be taken to mitigate risks; for a consite with unacceptable levels of contamination, EPA July 2000 states:

• Principle 1: contaminated material shall be treated on-site to acceptable levels, or treated off-site & returned to site
• Principle 2: Disposal to landfill or ‘cap & contain’ will only be considered if treatment is not practical/ can be done acceptably/ risk of disturbance exceeds risk of leaving on site.

 
References:

Australian HRA Guidelines
• EnHealth 2004, Environmental HRA
• NEPC 1999 (EnHealth) Health Investigation Levels (HILs)
• NEPC 2003, (Ambient Air Quality) Measure
• NHMRC 2004, Australian Drinking Water Guidelines (ADWG)
• NHMRC, 2006, Ambient Air Quality Standards Setting, an approach to Health Based Hazard Assessment
• DEC 2006, The Use of Risk Assessment in Contaminated Site Assessment: Guidance on the Overall Approach
• DoH 2006, HRA in Western Australia
• AS31000, 2009 (4360) Risk Management- Principles & Guidelines
• DoH 2010, HRA (Scoping) Guidelines
• DoH 2010, Guidance on Using the Threshold of Toxicological Concern to Screening Evaluation of Air Toxics
Occupational HRA:
• NOHSC:3017 (1994) Assessment of Hazardous Substances
• NOHSC: 1003/3008 (1995) Atmospheric Contaminants Exposure Standards & Interpretation

EPA July 2000, Guidance Statement No.17, Remediation Hierarchy for Contaminated Land

Stuart Jeffries
Hydrosolutions Pty Ltd

RESIDENTIAL RE-DEVELOPMENT,  Hocking, Private Developer

A Mandatory Audit Review (MAR) of a proposed residential subdivision was
undertaken on behalf of a private developer, in response to a Western Australian Planning Commission
(WAPC) condition.

The subdivided lot was part of a larger ‘mega lot’ which had been used for uncontrolled waste disposal, and machinery parking and maintenance impacts from which did not affect the
 subdivided (residential)  lot.

An ACM investigation was undertaken along the former fenceline, consistent with Department of Health guidelines, which confirmed that there was no residual ACM present.

Minor groundwater impacts were identified from nitrate from former market gardening , while heavy
metals were consistent with local background groundwater quality.

In one of the monitoring bore TPH concentrations were above the limits of reporting (LOR)but below comparative guideline level. For this reason, it is strongly recommended that TPH and
BTEX due to the presence of UST on the adjacent Lot, monitoring be continued in
this bore until the TPH shows a decline trend or is below LOR.

On the basis of the Audit review completed, the recommended site classification was:
“Not contaminated-unrestricted use”
Stuart Jeffries
Hydrosolutions Pty Ltd

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Audit 18

GROUNDWATER NUMERICAL MODELLING

The process of quantifying & predicting the groundwater flow within an aquifer system using a computer representation. A successful model may incorporate degrees of complexity of a natural system which may not be adequately represented by simple/ idealised analytical or water balance models.   It will allow predictions of response to stresses, such as abstraction, landuse & climate changes etc.

Conceptual Hydrogeological Models
A conceptual model is a description & idealised quantification of groundwater occurrence, flow mechanisms, controls on flow and interactions with other natural systems, such as:
• Time variant abstractions
• Discharges to/ from surface water
• Loss by evapotranspiration/ support phraeotophytic vegetation/ leakage
• Recharge from direct rainfall/ leakage/ artificial recharge/ aquifer storage & recovery (ASR) etc
A conceptual model demonstrates the hydrogeological understanding of the aquifer, forming the basis for the numerical model.
 

Hydraulic Models

Hydraulic models provide a description of the groundwater occurrence & flow.  They are the initial fundamental step in aquifer representations.  Types of hydraulic models were discussed in Issue 5.  Typical applications include:
• Sustainable resource assessments
• Abstraction Impact/ interference
• Borefield management
• Dewatering assessments
• Baseflow impact on discharges
• Wellfield protection zones. 

SOLUTE TRANSPORT

Solute transport models are built upon an initial calibrated hydraulic model.  They seek to describe the movement of natural or man-made chemicals within groundwater in response to migration down the flow path or imposed stresses such as abstractions.

Natural Systems
Examples where movement of background chemicals may be important:
• Seawater intrusion from abstraction at the coastline (e.g. Bunbury)
• Saline intrusion into a freshwater aquifer (e.g. Gascoyne River floodplain)
• Management of (light) fresh groundwater lenses above (dense) saline groundwater on small islands (e.g. Rottnest).
Models used for these assessments include e.g. MODFLOW/MT3DMS with SEAWAT variable density flow module, where density/ viscosity/ heat transfer effects need to be included.

Contaminants
Contaminants are chemicals, water of differing quality or energy introduced into an aquifer that impairs/ prevents the beneficial use of groundwater (e.g. drinking water/ support of aquatic ecosystems etc). Typical examples:
• Boiler blow-down (hot) water discharged into an unlined pond
• Point sources, e.g. Leaking underground storage tanks (USTs), typically hydrocarbons from service stations, chemicals etc
• Diffuse sources, e.g. excess fertiliser applications as run-off recharge.
• Waste injection (e.g. licensed deep WI operation in Kwinana)
• ASR systems, where water (e.g. treated sewage) is recharged to temporarily store additional water. (e.g. Water Corporation Groundwater Replenishment Trial to the Leederville Aquifer at Beenyup)
It is often necessary to predict solute movement impacting on natural groundwater quality/ abstractions or discharge to surface water bodies. 

Solute Transport Models
The movement of solutes within groundwater is affected by advection (movement within bulk groundwater flow, dispersion (spreading), density variations, heat transfer and chemical reactions (e.g. adsorption, hydrolysis, biochemical decomposition etc).  Numerical models need to represent the significant conceptual complexities of the system; models typically used for these assessments include:
• MODFLOW with:
o MT3DMS: 3D multi-species with reactive transport
o RT3D: reactive solute transport
• FEFLOW: finite element model
• MARS2D/3D (finite-element model for groundwater & LNAPL migration with:
o Biof&t: transient multi-solute L/DNAPL flow simulation

HydroSolutions Pty Ltd

We are a specialist         hydrogeological consultancy providing expert services including investigation, potable & process resource development & dewatering.  Our environmental capabilities include contaminated site investigation, auditing, remediation & risk assessment – qualitative/ quantitative, health, & ecological.

Next issue – Modeling LNAPL recovery

Slurp/ suck or vent?

Visit us at: www.HydroSolutions.com.au
Broadband NetMeeting conferencing available for remote sites.

HP BILLITON IRON ORE PTY LTD

Initial Source Protection Plans (SPZs) for four potable water sources, Pilbara region, Western Australia

Source protection plans consistent with Department of Water and Water Corporation guidelines, were developed for the potable water abstraction bores supplying the following mining rail camp sites:
-Quarry 8
-Turner River camp
-Cowra camp
-High Rise

Conceptual hydrogeological models have been developed for each site based on a review of geological, hydrogeological &, meteorological data.

SPZs have been developed, based on groundwater time-of-travel zones estimated using analytical expressions, represented as circular “recharge” zones.

Time of travel zones were defined including:
-50day-SPZ Source Protection Area
-365day-SPZ equivalent to a wellhead protection area priority 2 area
-Total catchment area TCZ

Initial source protection plans were developed to identify sanitary protection zones around the wellhead for bacterial die-off, and landuses which were incompatible with source protection (e.g. waste disposal, fuel storage etc.)

Recommendations were made to refine the analytical models by obtaining more specific aquifer’s data, to
enable numerical  modelling to optimise the SPZs.

Stuart Jeffries
Hydrosolutions Pty Ltd

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Hydro27

Conceptual Hydrogeological Model, of the Gascoyne River Floodplain Aquifer Model, GASFAMs
Department of Water, Carnarvon, Western Australia

DoW has commissioned Cymod Systems to undertake the development of an updated numerical model of the Gascoyne River Aquifer Floodplain (GASFAMs), which supplies potable water to the town of Carnarvon and irrigation water to commercial banana plantations. Hydrosolutions is working with Cymod to develop a conceptual hydrogeological model as the basis for the numerical model.

Fresh unconfined groundwater is present within the River Bed Sand (RBS) aquifer, which is the bedload of the current river course.  Semi-confined or leaky fresh groundwater is present within the underlying Older Alluvial Aquifer (OAA), representing a braided river floodplain depositional environment.

The aquifer system is recharged  by rainfall and riverflow/ flood events at approximately three yearly intervals.  A water balance model was developed describing inflows from river flow and direct recharge, outflows from evaporatranspiration, coastal discharge and abstraction, and variations in storage.  

Over abstraction has previously resulted in saline up-coning and intrusion near the coast and laterally along the river, locally restricting the sustainbale groundwater resource.

A numerical model has been developed using the MODFLOW software program based on the hydrogeological conceptual model.  The numerical model will be used to assess the sustainable groundwater resource, as a management tool for existing licensed abstractions, and to assess  the potential for new in-land groundwater resources.

Stuart Jeffries
Hydrosolutions Pty Ltd

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Hydro22

PRIVATE DEVELOPER: DESK APPRAISAL OF FORMER MIXED INDUSTRIAL SITE, Derbyshire, England

A desk study was undertaken of a mixed industrial site, including part of a gas works, a former lead-acid battery manufacturer, timber mill and former cotton mill.  Anecdotal data was researched via archives and interviews with former site workers.  The geology was described from published and limited site-specific data.

The site hydrogeology comprised a deep valley incised into outcropping limestone, overlain by thin alluvium.  Shallow unconfined groundwater was in hydraulic continuity with a nearby class 1A river.  The site was split into five areas with similar historical activities/contaminants.

An initial qualitative risk assessment characterised the risk to the proposed site re-development.

Recommendations were made for a detailed investigation program.

Stuart Jeffries
Hydrosolutions Pty Ltd

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Contam12