Conceptual Site Models (CSM)Developing a CSM and Assessing Source Pathway Receptor (SPR) Linkages

Kevin TearneyTechnical Director

Scope

• What is a Conceptual Site Model (CSM)

• Building a CSM to establish source pathway receptor linkages

• Where CSM fits into the Risk Assessment process

• Wrap up discussions and exchange of ideas about improving the use the CSMs in New Zealand

Page 2

Acknowledgement

• This presentation has drawn from numerous sources of information both in-house AECOM and external

• The information is all in the public domain

• An important source is MfE Contaminated Land Management Guidelines (CLMG) No.5 Site Investigation and Analysis of Soils (2016 Consultation Draft)

• I thank my colleagues for allowing me, knowingly or unknowingly, to use this information in this presentation

Page 3

CSM Definition and Use

• (CLMG No.5) - A CSM is - a representation or overall picture of the site that shows the possible

relationships between contaminants, exposure pathways and receptors

- used to design an investigation and support a decision-making process in the context of the investigation objectives, for example, is the site suitable for the proposed use i.e., can form the basis for risk based decision making

• (ASTM E 1689-95) – A CSM is- a written or pictorial representation of an environmental system and the

biological, physical and chemical processes that determine the transport of contaminants from sources through environmental media to environmental receptors

- used to integrate all site information and to determine whether information including data are missing (data gaps) and whether additional information needs to be collected

Page 4

Source – Pathway Receptor Linkages

• The relationship between contaminants and receptors, is commonly referred to as one or all of the following

- pollutant linkage

- hazard–pathway–receptor linkage

- source-pathway-receptor linkage

- source pathway target linkage

Where CLMG No.5 defines these as:

• a pollutant, hazard or source is a contaminant or potential contaminant

• a pathway is a means by which a receptor or target can be exposed to, or affected by, a contaminant under current or known proposed future land use

• a receptor or target is something, such as people, a water body or an ecosystem, that could be adversely affected by the contaminant

Page 5

CSM as a RISK Assessment Tool

• (CLMG No.5)- presented in written, pictorial or graphical format (or a combination of

these), taking into account the site complexity

- complexity should correspond to the scale and complexity of the known, or potential, contamination impacts and the range of exposure pathways and receptors

- can be highly specific and concentrate on just one contaminant, pathway and receptor, or it can cover multiple sources and receptors over a wide physical area

- site investigations that do not require demonstration of the relationships between contaminants, exposure pathways, and receptors (e.g., benchmarking site conditions) may not find the development and/or refinement of a CSM necessary

Page 6

CSM as a Communication Tool

• The CSM is also a communication tool between:

• site assessment team members

• discipline experts

• consultant and client

• client and regulator

• stakeholder groups

• The form of the CSM should therefore take account of the audience

Page 7

Pictorial CSM

Page 8

Pictorial CSM

Page 9

Pictorial CSM

Page 10

Pictorial CSM

Page 11

Graphical CSM

Page 12

CSM Role in Site Assessment

• Used to direct initial investigation works

• Updated as works proceed to fill data gaps

• Establishes SPR linkages

• Identifies receptors potentially at risk

• Facilitates the risk assessment process

Page 13

CSM Role in Site Assessment (CLMG No.5)

Page 14

Building a CSM

(CLMG No.5)

• Once the objectives are established, preliminary information should be gathered to develop a conceptual site model that describes the environmental setting of the site, potential contaminant sources, pathways for contaminant migration, and receptors (human and/or environmental)

• It is this model that guides the subsequent decisions on whether further investigations and/or remedial actions are required

Page 15

Building a CSM

• Building a CSM is not a single event; it is a multi-layered process requiring the understanding and assimilation of data from numerous sources and phases and work

• It usually starts with a PSI

• It achieves an increasing level of complexity as investigations progress through DSI stages

• It is firmly grounded in science but also requires the use of intuition and experience

Page 16

PSI DSI

Amount of data

in a CSM

Building a CSM

.

• The information required to develop and refine the CSM needs to take into account: - previous uses of the site (and surrounding area) as these

determine potential contaminant sources

- the environmental setting (geology, hydrogeology and hydrology), because this influences the transport and exposure pathways

- present and proposed future land uses of the site and surrounding area, because these determine potential receptors and exposure pathways

Page 17

Building a CSM – PSI Desk Top Review

• Desk top review of available information- current site use, layout and operational information, generally

obtained from the owner, historical information including environmental reports that may be available from the owner, and recent on-line aerial photographs

- council HAIL use and contaminated land databases if available

- photographic records, including historical (note: also look at surrounding use)

- interviewing people familiar with the site (often undertaken during the preliminary site inspection), including present and past owners, workers, neighbours, elderly local identities

- available historical society records, newspaper archives, and on-line resources or relevant literature relating to the site

Page 18

Building a CSM-PSI Desk Top Review (cont)

- Information held by territorial local authorities on the property file. Information held by the regional authorities, such as consents to discharge to air, land or water, land-use consents for earthworks, environmental reports, and relevant land-use registers or databases

- Certificates of title

- Land information memoranda (LIMs)

- Fire Service records for information about recorded incidents or spills

- Topographic maps

- Geological maps

- Council bore records

- Text books

Page 19

Building a CSM-PSI Site Inspection

• Site Inspection- undertaken during the development of a preliminary CSM

- involves a walk-over, often in the company of a land owner or occupier

- The objective of the inspection is to augment or confirm the findings of the desk top review records, and to identify information that may assist with the design of any subsequent field investigations, should that be required

- Photographs should be taken to document any observations made

Page 20

Building a CSM-PSI Site Inspection (cont)

• Information gathered during a site inspection typically includes:- general site condition, current use and layout, surrounding land

use, local topography, and surrounding environmental setting

- location and condition of surface watercourses, drainage systems, and groundwater wells

- visible signs of contamination or potential contamination, such as spills or leaks, surface staining, absent or stressed vegetation, and odours

- visible signs of areas of fill, stockpiled material, waste, ground disturbance, burnt areas, and former building foundations

- the location of chemical storage, transfer and waste storage areas

Page 21

Building a CSM-PSI Sampling

• Generally, environmental samples are not collected and analysed during the PSI phase of works.

• However, some samples may be taken during the site inspection to provide initial quantitative information to inform the CSM, such as- likely nature of probable contaminants

- shallow soil types

- depth to shallow groundwater

Page 22

Building a CSM – Preliminary CSM

• Information is used to build a preliminary CSM to assist with scoping the DSI

Page 23

Building a CSM –Sampling Strategy

• Sampling pattern directed by the preliminary CSM

Page 24

Building a CSM - DSI

• Refinement of the CSM is an iterative and ongoing process as new information becomes available from DSI stages

• Once the field observations and interpretation of analytical results have been incorporated into the CSM, the CSM should be reviewed to determine if sufficient information has been collected to address the investigation objectives

• At this time the appropriateness of the investigation objectives should be reviewed, as these may change in the light of new information

Page 25

Building a CSM - DSI

• Information to consider includes- variations in strata surfaces which can be a key element in

contaminant distribution/behaviour

- depth to groundwater, confined/unconfined relationships, perched groundwater (if present)

- groundwater flow direction and potential interaction with surrounding watercourses and/or service conduits

- zones of the site with different contamination characteristics (e.g. whether contaminants in the soil are likely to be on the surface or at depth, distributed over an entire area or in localised ‘hotspots’)

- location and type of human and environmental receptors

- type and properties of contaminants in target media–concentrations, toxicity, mobility, persistence, degradation products

Page 26

Building a CSM - DSI

• The local and site-specific geological and hydrogeological settings influence the fate and transport of potential contaminants on and in the vicinity of a site, and the potential exposure pathways to human health and environmental receptors

• For example, soil and aquifer permeability influences both the potential viability of an aquifer for potable water supply and the extent of migration of a contaminant in groundwater to a point of use

• The depth to groundwater is also relevant where contaminants may leach from soils

Page 27

Building a CSM

Simple vs Complex

• Don’t over simplify what it a complex situation

• Don’t over complicate what can be portrayed simply

Understand your audience

Page 28

CSM Development – ASTM E 1689-951) Assemble Information - Assemble historical and current site-related information from

maps, aerial images, cross sections, environmental data, records, reports, studies, and other information sources.

2) Identify contaminants - in the groundwater, surface water, soils, sediments, biota, and air. If no contaminants are found, the conceptual site model should be used to help document this finding.

3) Establish background COPC concentrations - establish the natural range of concentrations of an analyte and establish the extent to which contamination exceeds background levels.

4) Characterise Sources – including source location(s), boundaries, and volume(s); located accurately on site maps. Time of initiation, duration, and rate of contaminant release from the source. Also include potentially hazardous constituents and their concentrations in media at the source.

5) Identify Migration Pathways - Potential migration pathways through groundwater, surface water, air, soils, sediments, and biota should be identified for each source. Complete exposure pathways should be identified and distinguished from incomplete pathways.

6) Identify Environmental Receptors – currently or potentially exposed to site contaminants. This includes humans and other organisms that are in direct contact with the source of contamination, potentially present along the migration pathways, or located in the vicinity of the site.

Page 29

CSM Information (ASTM)Site Inspection - Google Earth, site visit, Phase I

Historical Use - archives, historical databases, geological state offices, planning divisions of communities and cities, interviews

Climatic data: hydrologic budget, fauna, flora, and land use, precipitation rates, air temperature, and prevailing wind speed and direction

Geology: types of geologic materials, structural geologic features, depositional environments, and geomorphology, geological state offices,

Hydrogeology:

- Aquifer characteristics:

a. Type (examples: unconfined, confined, or semi-confined),

b. Characteristics (examples: hydraulic conductivity, transmissivity, storitivity)

c. Geology (materials and structure),

- Hydrologic budget:

a. Recharge rates (examples: precipitation, artificial recharge),

b. Discharge rates (examples: evaporation, transpiration, groundwater pumping),

- Groundwater flow:

a. Hydraulic gradient (examples: groundwater elevations, flow direction),

b. Flow velocity (travel time),

c. Boundary conditions (examples: Dirichlet, Neumann),

Geochemistry – Chemical properties, lab results, former report results, public data-base

Page 30

Page 31

Pictorial CSM – a picture is worth a thousand words

Page 32

Pictorial CSM – VI CSM

Pictorial CSM - Exposure to Hydrocarbon Fuels

Page 33

Exposure Pathway Assessment

Potential pathway Risk pathway

status

Reasoning

Dissolved-phase

hydrocarbon discharge

off-site

Incomplete Conducted groundwater monitoring over the past

five years indicates that the hydrocarbon plume is

stable and contained on-site; the nearest

groundwater wells are over one kilometre distant;

the nearest surface water body is over one

kilometre from site. If future groundwater

monitoring indicates a change in plume stability,

an updated risk assessment should be performed.

Dermal contact and soil

ingestion (on-site

commercial land

occupants)

Incomplete Depth of hydrocarbon impact and concrete cover

over site. If concrete cover was altered, an

updated risk assessment should be performed.

Dermal contact and soil

ingestion (off-site

receptors)

Incomplete Hydrocarbon impact contained within site

boundaries. If future groundwater monitoring

indicates a change in plume stability, an updated

risk assessment should be performed.

Volatilisation of

hydrocarbon vapour

from soil and

groundwater to indoor

and outdoor air (on-site

commercial land

occupants and off-site

receptors)

Incomplete Soil vapour monitoring indicates volatilisation of

hydrocarbon vapour from soil and groundwater to

indoor and outdoor air does not present a risk for

on-site commercial land occupants or off-site

receptors. If on-site land use changes to a more

sensitive use, or changes in hydrocarbon plume

status are reported, an updated risk assessment

should be performed.

Dermal contact, soil

ingestion and

volatilisation of

hydrocarbon vapour

from soil and

groundwater to indoor

and outdoor air

(maintenance/excavation

workers)

Not assessed If excavations in the vicinity of the plume are to be

conducted, a risk assessment should be carried

out before the works begin.

Page 34

Flow Diagram CSM

Page 35

Risk Assessment

• Risk assessment is the process of evaluating the SPR model generated by the CSM to:- determine the probability that a hazard exists on the site

- characterise the hazard through adequate delineation of contamination horizontally and vertically, and assessment of contaminant concentrations

- identify and characterise potential pathways and receptors through assessment of geology, hydrogeology, building construction, site use, and other relevant site properties

- determine the likelihood that the hazard poses a risk to identified receptors, including potential receptors

- determine the magnitude of that risk

- propose any requirement for management methods to mitigate identified risks (as necessary)

Page 36

SPR Linkage - Recipe for Complete Linkage

Complete Linkage = A + B + C + D

A = Source B = Probable/Known Release

C = Pathway D = Receptor

If any are missing, it is an incomplete linkage

• Primary or secondary source (data) + release + pathway + receptor = a complete linkage

• If you don’t have data, but suspect the linkage is complete, it is potentially complete and is identified as a data gap

• Note: You can have a complete linkage without any risk

Complete Linkage = (A & B) + C + D

A/B C

D

��

�

�

A = Source B = Probable/Known Release

D = Receptor

C = Pathway

Tier 1 Comparison

• A key component of data interpretation for Tier 1 risk assessment is consideration of the guideline values used and their appropriateness for the site-specific conditions

• The results should always be assessed in the context of the CSM, the basis for the derivation of any guideline value should be understood, and the appropriateness for use considered in the context of the site

• The process involves comparison of detected concentrations of each contaminant to the applicable Tier 1 guideline with a complete pathway

• It provides a conservative assessment of risk

• If Site concentrations < guideline value = no further action

• If Site concentrations >guideline value- move to Tier 1.5 or Tier 2, o

- implement additional data collection or

- design and implement remedial action to achieve objectives

Page 39

CSM & Tier 1 SPR - Summary

• A qualitative written and/or illustrated narrative of site conditions summarising what is known or suspected about site conditions

• The CSM is an evergreen tool which may be modified in light of new information i.e. additional data, stages of investigation

• Describes the sources and contaminants, site setting, exposure pathway, transport mechanism, and receptor type

• Identifies actual verses perceived risks

• Data gaps and their significance

Complete Linkage = A + B + C + D

A = Source

B = Probable/Known Release

C = Pathway

D = Receptor

A/B C

D

��

�

�

A = Source

B = Probable/Known Release

D = Receptor

C = Pathway

Thank You

Kevin Tearney is a Technical Director with AECOM, specialising in the assessment and remediation of contaminated land and groundwater. He has over 30 years of industry experience gained mainly within New Zealand , Australia and the UK, providing advice and expertise in respect of land bank management, brownfield redevelopment and environmental due diligence. kevin.tearney@aecom.com

16 February 2016

Questions