Conceptual Site Models

Purpose, Development,Content and Application

CP Annual Training

October 27, 2015

Conceptual Site Model (CSM) Purpose

•Typical environmental remediation project

–Particular program and rules (Remedial, VAP,RCRA) that directs a set of tasks:

•Site assessment and investigation

•Evaluation of remedial alternatives

•Remedy selection and implementation

•Post-construction activities, monitoring, O&M

–Generate volumes of information about the site

CSM Purpose

•Typical environmental remediation project

–What’s missing?

–What’s the common understanding of the projectinformation with respect to site-specific projectobjectives?

–The CSM, which exists to provide commonunderstanding among project stakeholders

CSM Purpose

•Conceptual understanding (example):

Board game – 2 to 4 players. Each starts with$1,500. Players move around the game board byrolling dice, and land on properties or reward orpenalty squares. Properties may be purchased,traded, mortgaged, developed with houses orhotels, and rent is collected from opponents landingon the property. Players are eliminated by goingbankrupt; the last player left wins. The game takeshours to complete.

CSM Purpose

•Board game example (conceptual understanding):

–Don’t need to know every rule to understand theconcept (could grasp the concept by observation)

–The concept prepares you to play the game throughits various stages

•CSM

–Provides a conceptual understanding of theinformation associated with remediation projectunder a particular program at a specific site thatprepares you to work through the project stages

CSM Purpose

•Remediation project, three aspects:

1.Regulatory framework +

2.Information/data +

3.CSM

(The CSM Provides direction on how to best utilizeinformation within a regulatory framework toachieve project objectives, i.e., identify data gaps)

CSM Purpose

MODEL

Qualitative

Quantitative

Simple

CSM

Detailed

CSM Purpose

•A model is a description of a system with theobjective of making predictions

•A model is based on data, but is not data

•A good model is one that achieves itsobjectives

•What are the objectives of a CSM?

CSM Objectives

1.Provide an iterative representation of acontaminated site in a simple, concise manner(evolves with new data and project stages)

2.Describe the site environmental system:

•Contamination sources, pathways, receptors

•Processes controlling contaminant transport

3.Facilitate a basic and common understanding of sitecontamination and potential exposure scenariosamong all stakeholders

CSM Development

•CSM is essentially a hypothesis for making site-specific predictions about:

–The occurrence of contamination

–The potential for adverse impacts to receptors

•Initially developed during the determination ofproject objectives, DQOs, RAOs…

•Continuously tested and revised (as necessary)during subsequent project stages, e.g., siteinvestigation, remedial alternative development, etc.

CSM Development

•Every hypothesis (and every CSM) is speculative to somedegree

•Development and subsequent revision?

–“Bottom up” approach works best: base CSM onassumptions that provide the simplest explanation of theobserved data (Occam’s razor: maximize certainty,minimize speculation)

–Don’t try to eliminate data gaps by increasing thecomplexity of the assumptions underlying the CSM!(Instead collect the data needed to fill the gap indicated bythe CSM; complexity ≠ accuracy or certainty)

CSM Development

•Development and use of a formal (written) CSM is acritical step in the site remediation process

•Helps ensure that all project stakeholders areworking with a similar understanding of the site

•Without a formal CSM, each stakeholder will developtheir own “informal CSM”

•Multiple informal CSMs lead to misunderstandingand disagreement, delays and increased costs

CSM Development

•Criteria for CSM development, maintenance and use:

1.The CSM should be applied as a systematic planningtool through all stages of a remediation project

2.The CSM should be iteratively updated (as data gapsare progressively filled, the CSM becomes moreaccurate)

3.The CSM should be maintained as a stand-alonedocument accessible to all stakeholders during thecourse of the project

CSM Components & Presentation

•The CSM

–Consists of a concise combination ofgraphical and written information that

–Describes (and clearly distinguishes) knownand hypothesized site conditions in amanner that is

–Readily understandable to all projectstakeholders

CSM Components & Presentation

•DERR recommends that the CSM include thefollowing components

–A pictorial model of site conditions (2-d or 3-d)

–A pathway receptor network diagram

–A brief written description

–Additional information (maps, tables, figures) ifnecessary

CSM Components & Presentation

•Pictorial model of site conditions, includingbut not necessarily limited to

–Topography and surface hydrology

–Locations of contaminant sources

–Structures and utilities

–Geology and hydrogeology

CSM Components & Presentation

CSM Components & Presentation

•Pathway network receptor (PNR) diagram

–Support risk assessment, remedy development

–Often used as stand-alone CSMs; however, PNRs

•Do not provide sufficient information concerningthe site hydrogeologic system

•May not identify all CSM data gaps

CSM Components & Presentation

CSM Components & Presentation

•Brief narrative, including:

–Current site conditions and site history

–Contaminant source characterization

–Migration pathway descriptions

–Identification of data gaps

•No need to include supporting data – this isprovided by of the reports (e.g., RI/FS)

CSM Project Life Cycle Utilization

•The CSM should be used through all stages (lifecycle) of a remediation project

–Dynamic systematic planning tool

–Basic framework for evaluating new data

–Should evolve as project progresses (increase in detailand accuracy)

•CSM project life cycle includes six stages orsuccessive versions of the same CSM (U.S. EPA)

CSM Project Life Cycle Utilization

CSM Project Life Cycle Utilization

•CSM will need to be updated and revisedduring this process

–Changes in project scope or regulatoryrequirements

–Recognition of a previously unknowncontaminant, pathway or receptor

–Changes in the planned end use of the site

CSM Project Life Cycle Utilization

•Changes to the CSM should increase itsaccuracy, but not to the detriment of itssimplicity (complexity ≠ accuracy)

•All project stakeholders should be providedthe opportunity to review, understand andprovide input into CSM revisions

•Final revisions and supporting informationshould be documented for later reference

Common CSM Problems

•Treating the CSM as an administrative task ratherthan a planning tool

•Dispersing CSM components throughout multipleproject documents

•Using an overly generic CSM that is notsufficiently site-specific to be useful

•Using an overly detailed CSM that presents datarather than a concise synopsis of site conditions

CSM References(Available Upon Request)

•DERR Conceptual Site Model Guidance (Draft)

•U.S. EPA, July 2011, Environmental Cleanup BestManagement Practices: Effective Use of theProject Life Cycle Conceptual Model, EPA 542 F–11– 011

•ASTM E1689–95, Standard Guide for DevelopingConceptual Site Models for Contaminated Sites(Reapproved 2014)

Questions?

Thanks for your time and attention!