IEM, ARR and EQRS: differences and interplay in contaminated site management

Written by Eric Azulay — SSP Engineer (contaminated land), Managing Director of SARL G.M.E.P · Published on July 3, 2026

Three tools, three stages of managing a contaminated site

The national methodology for managing contaminated land (ministerial doctrine, carried successively by the MEDDE, the MTES and then the MTECT, supported by INERIS and BRGM) draws on several risk assessment tools at distinct stages of the process: the IEM for the initial diagnosis, the EQRS for detailed risk assessment, and the ARR for post-remediation verification. These three approaches share a common foundation, the conceptual site model, but answer different questions and occur at different points in the process.

The IEM — Interpretation of Environmental Media Status

The IEM is the initial diagnosis of the management process. It consists of comparing the pollutant concentrations measured in the various media (soil, groundwater, ambient air or indoor air) against management values or toxicological reference values, to determine the compatibility of the current state of the media with the observed or planned use of the site.

The IEM typically answers the question: "is the current state of the site compatible with its use, without the need for a detailed risk assessment?". When the measured concentrations are well below the management values, the IEM can conclude that there is no significant risk without a full EQRS being necessary. Otherwise, or in case of uncertainty, an EQRS is undertaken to refine the assessment.

The EQRS — Quantitative Human Health Risk Assessment

The EQRS is a detailed assessment, specific to the site under study, which calculates quantitative risk indicators — the Hazard Quotient (QD) and the Individual Excess Risk (ERI) — based on specific exposure scenarios (target populations, transfer pathways, exposure duration and frequency). Unlike the IEM, which compares concentrations to generic values, the EQRS reconstructs the entire source-transfer-receptor chain specific to the site, including, where relevant, modeling of vapor intrusion (Johnson & Ettinger model) or of soil-groundwater-well transfer (Domenico model).

For a detailed presentation of the QD and ERI calculation, see our dedicated article on QD and ERI calculation in EQRS.

The ARR — Residual Risk Analysis

The ARR takes place after remediation work or management measures have been implemented (excavation, containment, groundwater treatment, use restriction). It follows the same methodology as the EQRS — calculation of the QD and the ERI — but based on the residual concentrations measured after the work, to verify that the remaining risk level is compatible with the intended use of the site. The ARR is thus, from a methodological standpoint, an EQRS applied to the post-remediation state of the site.

Chronological interplay

The central role of the conceptual site model (CSM)

The conceptual site model (Conceptual Site Model, CSM) is the structured, usually graphical, representation of the identified pollution sources, the possible transfer pathways (volatilization to air, leaching to groundwater, transfer by direct contact) and the potentially exposed receptors (resident populations, employees, ecosystems, water resource uses). It is the common methodological foundation on which the IEM, the EQRS and the ARR are built, and it must be updated at each stage based on new data acquired (results of additional investigations, effects of completed remediation work).

A robust conceptual model determines the relevance of the entire process: a source, transfer pathway or receptor omitted at this stage will not be taken into account in subsequent calculations, regardless of how rigorous the EQRS or ARR carried out later may be.

Content of a management plan

The management plan translates the results of the risk assessment (IEM or EQRS) into concrete actions. It generally includes:

• A summary of the conceptual model and the risk assessment results (QD, ERI by target population)
• The prioritization of issues — substances, transfer pathways and media that contribute most to the risk
• The management options considered (source treatment, containment, use restriction, public utility easements) and their cost-benefit analysis
• The monitoring measures to be implemented (piezometry, periodic checks) to verify the effectiveness of the measures over time
• Where relevant, the work program selected, its schedule and site monitoring arrangements

French doctrine for contaminated land management

This IEM / EQRS / ARR / management plan interplay is part of the national methodology for managing contaminated land, driven by the ministry in charge of the environment with the technical support of INERIS and BRGM. This doctrine promotes a proportionate and iterative approach: investigations and assessments are deepened as the issues become clearer, avoiding assessments disproportionate to the site's actual risk, while ensuring the protection of populations and the environment.

Common mistakes in the IEM / EQRS / ARR interplay

Confusion between these three tools is common among project owners and can sometimes delay the review of files. A few pitfalls to avoid:

Undertaking a full EQRS when an IEM would suffice

When the measured concentrations are well below the management values and the site's use is stable, a well-conducted IEM may be enough to reach a conclusion, avoiding a detailed EQRS disproportionate to the actual issue at stake.

Confusing EQRS and ARR

The ARR is not a new methodology: it applies the same calculation principles as the EQRS (QD, ERI), but based on the residual post-remediation concentrations and an updated exposure scenario reflecting the uses adopted after the work (for example, residential use with green spaces, after partial excavation of the most contaminated soils).

Neglecting to update the conceptual model

Each new investigation or remediation phase should trigger an update of the conceptual site model. A conceptual model frozen since the initial diagnosis, not updated after partial remediation work, mechanically skews the conclusions of the ARR carried out afterward.

Role of the authorities: DDT, DREAL, ARS

Several government departments may be involved in monitoring a contaminated site file, depending on the nature of the issues:

• DREAL (Regional Directorate for the Environment, Planning and Housing) — oversight of regulated facilities (ICPE), review of activity-cessation and remediation files, opinions on management plans
• DDT (Departmental Directorate for Territories) — review of files falling under the Water Law (groundwater drawdown, discharges), urban planning and land-use planning
• ARS (Regional Health Agency) — expertise on health issues, particularly when drinking water intakes, sensitive facilities (schools, daycare centers) or vulnerable populations are involved

The consistency and traceability of the documents submitted (conceptual model, IEM, EQRS, ARR, management plan) are essential to facilitate the review of the file by these various departments and to avoid repeated requests for additional information.

FAQ — IEM, ARR and EQRS

Methodological references

• Ministry / INERIS — National methodology for managing contaminated land
• INERIS — Guide to contaminated land diagnosis (IEM)
• French Environmental Code — ICPE (regulated facilities)
• INERIS — Detailed risk assessment (EDR)

Written by Eric Azulay — SSP Engineer (contaminated land), Managing Director of SARL G.M.E.P