A regional flux-based risk assessment approach of contaminated sites on groundwater bodies

(1)

A REGIONAL FLUX-BASED RISK ASSESSMENT APPROACH

OF CONTAMINATED SITES ON GROUNDWATER BODIES

Regional-scale, flux-based risk assessment

S. Brouyère , P. Jamin , F. Dollé , Ph. Orban , C. Hérivaux , I.C. Popescu & A. Dassargues

1,3

2

4 1,3

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University of Liège, Fac. Applied Sciences, Dpt ArGEnCo, GEO³, Hydrogeology and Environmental Geology, Liège, Belgium.

BRGM (French Geological Survey), Water department, Montpellier, France

³ University of Liège, Aquapôle Research Centre, Liège, Belgium

Service Publique de Wallonie, DGARNE-DGO3, Division de l'Eau, Direction des Eaux Souterraines, Namur, Belgium

Serge.Brouyere@ulg.ac.be

Regional Risk Assessment methodology

T

he EU Water Framework Directive requires management plans

about quality of surface and groundwater bodies. These plans can

not be without considering the effect of contaminated industrial sites

potentially harmful for water resource. In order to propose adequate but still

economically reliable measures, risk assessment of such sites remains

primordial.

The FRAC-WECO project aims to develop a new integrated

methodology for risk assessment at the regional scale. This method should

be based on a so-called megasite approach using criteria reflecting the

water quality deterioration, in a cumulative way, at the scale of the whole

water body.

The first application of this new methodology focuses on the

groundwater body RMW073

identified at risk of not reaching a good

quality status by 2015 due to its heavily industrial situation.

A socio-economical study is also under development to perform, from a

typology of remediation measures, a cost-effectiveness analysis to help

decision makers improve the groundwater quality.

“Gravels and alluvial deposits of the Meuse

river between Engis and Herstal”

Ò Spatial distribution of pollutant sources and receptors

Considering a large scale area for risk assessment involves many contaminant sources of many types (point-type: leaking storage tank, diffuse-type: smokestacks), many receptors (point-type: groundwater abstraction well, diffuse type: zone of biological interest, aquifer, river) and lots of pathways linking them to each other. Efficient management all the spatially distributed data requires GIS databases

Ú N

EED FOR

GIS

DATABASE FOR

S-P-R

DATA MANAGEMENT

Ò Cumulative effect of several pollutant

sources

From the perspective of water resource management, each contaminated industrial site taken individually does not necessary constitute a threat for the whole aquifer or the groundwater body. However, in heavily industrialised and urbanised areas, the cumulative effect of multiple contaminant sources is likely to present a risk. The risk assessment has to be flux based to consider cumulative effects of the contaminants

Ú N

EED FOR FLUX

-

BASED RISK

ASSESSMENT

Risk threshold Time, Distance Individualy considered, No risk Cumulative effect, Risk alluvial plain Meuse One point Multiple point Diffuse Biological zone One point Multiple point SOURCES P A THW A YS RECEPTORS Resource

FRAC-WECO project :

lux-based

isk

ssessment of

ontaminants

on

ater resources and

systems

F

R

A

C

W

ECO

S

TEP

1 :

C

REATION

,

FEEDING AND HANDLING OF A GEODATABASE

S

TEP

2 :

M

ODELLING OF GROUNDATER FLOW AND TRANSPORT OF CONTAMINANT

S

TEP

3 :

C

ALCULATION OF THE GROUNDWATER QUALITY INDEX FOR THE GROUNDWATER BODY USING

SEQ-ESO

(a)

GIS geodatabase for storing, managing and using all the spatially distributed information required for

regional risk assessment.

Calculation of vertical pollutant fluxes through soil and vadose zone using leaching-dispersion model.

(d)

Calculation of contaminants dispersion through the aquifer using a numerical groundwater flow and

transport model developed for the groundwater body to provide a map of contaminants plumes.

(e)

At each time step, classification of the generated plumes using the threshold values defined in the

Walloon Region SEQ-ESO system for groundwater quality evaluation.

(f)

Compute a global picture of the water quality on the basis of the finite difference grid for each time step.

(g)

Calculation of the global quality index [0-100] for the groundwater body at each time step using an

especially developed routine based on weighting-average procedure.

(

C

)

(b)

Specific activity-pollutant matrix module integrated into the geodatabase to list potentially generated

contaminant for each type of industrial activity.

?

Developed under Microsoft Access with the ability to be used with GIS-based applications. Organised according to the SPR schema.

GMS with MODFLOW/MT3D in finite differences used for groundwater flow and contaminant transport in saturated zone. ?

?

Geodatabase includes a list of relevant contaminants (75) and associated physical and chemical properties (solubility, Koc,...) governing their behaviour in the environment.

Activity-pollutant matrix : Most of the time the only available information about contaminant source is a list of industrial activities. This tool gives a list of pollutants potentially released by a given industrial activity and inversely.

Contaminant source

Contaminant flux to groundwater Soil

Aquifer / groundwater body

(f)

(g)

(e)

(d)

(c)

(b)

(a)

Application on RWM073 groundwater body: first tests of the approach

The first application of the Regional Risk Assessment method consider

:

3 types of industrial activities generating benzene

Worst case scenario with all industrial plants polluting

Simulation time: 20 years

Groundwater use thresholds corresponds to general quality of groundwater (SEQW)

worst case scenario

Final SEQ-ESO global index: 35

bad quality status

Ò

g

I : global quality index for the whole groundwater body at time t [-]

V : volume of water into the cell i [V] I : quality index for the cell i[-]

global

i i

V : volume of groundwater comprised in the zone where the risk is assessed [V]GW

ARLON NAMUR LIEGE BRUXELLES 0 12,500 25,000 50,000 Meters MEUSE RWM073

Conclusions and perspectives

Ò

Compliant with EU Water Framework Directive and Walloon legislation.

Integration of multiple contaminations to a single quality index easily transposable for further analysis.

Ò

Investigation of groundwater quality including degradation/improvement trends.

Coupled socio-economical approach as a support to WFD management plans.

Next step:

Acknowledgements

BELSPO as financial support for FRAC-WECO project SD/TE/02A

SPW and SPAQuE for participating to follow-up committee and

providing essential data.

Members of FRAC-WECO project : ULg, VUB, VITO, BRGM.

The groundwater body RWM073 “Gravels and alluvial deposits of the Meuse

river between Engis and Herstal” has been chosen for is heavy industrial past and

current situation and its presumed bad chemical status.

(a) Data about all the part of the SPR schema were collected and organised into a geodatabase. Sources of contaminant come from an inventory of industrial activities from Year 2000 on a cadastral frame and sorted using the 3rd Annex of the Walloon Soil Decree.

(b) Only industrial plants lying within the category “mining”, “gas station” and “metallurgy”, and with a area of >100 m² were considered. Benzene was chosen among that given by the activity pollutant matrix as the most commonly found pollutant.

(c) Pollutant leaching not considered. Contaminant supposed to be present at concentrations equal to solubility at the top of water table.

(d) GMS Modflow and MT3D used to perform groundwater flow and transport simulations using finite differences for a 20 years period. Evolution of SEQ-ESO indicator for benzene (SEQW thresholds)

0 20 40 60 80 100 0 2 4 6 8 10 12 14 16 18 20 Time [years] Iglobalqualityindex VERY GOOD GOOD MEDIUM BAD VERY BAD