Simulation-based risk assessment of contaminated sites under remediation scenarios, planning periods, and land-use patterns—a Canadian case study

Abstract

Risk assessment of contaminated sites is crucial for quantifying adverse impacts on human health and the environment. It also provides effective decision support for remediation and management of such sites. This study presents an integrated approach for environmental and health risk assessment of subsurface contamination through the incorporation of a multiphase multicomponent modeling system within a general risk assessment framework. The method is applied to a petroleum-contaminated site in western Canada. Three remediation scenarios with different efficiencies (0, 60, and 90%) and planning periods (10, 20, 40, 60, and 80 years later) are examined for each of the five potential land-use plans of the study site. Then three risky zones with different temporal and spatial distributions are identified based on the local environmental guidelines and the excess lifetime cancer risk criteria. The obtained results are useful for assessing potential human health effects when the groundwater is used for drinking water supply. They are also critical for evaluating environmental impacts when the groundwater is used for irrigation, stockbreeding, fish culture, or when the site remains the status quo. Moreover, the results indicate that the proposed method can effectively identify risky zones with different risk levels under various remediation actions, planning periods, and land-use patterns.

Appendix

List of nomenclature

The following symbols are used in this paper

AT:

averaging time [T]

BW:

average body weight [M]

CDI:

chronic daily intake] [MM⁻¹ T⁻¹]

CW:

pollutant concentration in groundwater [ML⁻¹]

$\tilde C_k$ :

overall concentration of component k [L³ L⁻³]

C _kl :

concentration of component k in phase l [L³ L⁻¹]

C _t :

total compressibility [mL⁻¹ T⁻¹)⁻¹]

${\vec {\vec D}}_{kl}$ :

dispersion flux of component k in phase l [L²]

D _m,kl :

molecular diffusion coefficient of component k in phase l [L² T⁻¹]

ED:

average exposure duration [T]

EF:

exposure frequency [TT⁻¹]

g :

acceleration of gravity [LT⁻¹]

IR:

human ingestion rate [LT⁻¹]

k :

component index

k _rl :

relative permeability of porous medium to phase l [L² L⁻¹]

${\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {K} } }$ :

intrinsic permeability tensor [L²]

l :

phase index

n _p :

number of phases

P _clw :

capillary pressure difference between phase l and water phase [mL⁻¹ T⁻¹]

P _l :

pressure of phase l [mL⁻¹ T⁻¹]

P _w :

water phase pressure [mL⁻¹ T⁻²]

Q _k :

injection/production rate for component k per bulk volume [L³ T⁻¹]

R _k :

total source/sink term for component k [L³ L⁻³ T⁻¹]

RfD:

reference dose [MM⁻¹ T⁻¹]

S _l :

saturation of phase l (volume fraction) [L³ L⁻³]

SF:

carcinogen slope factor [MTM⁻¹]

$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {u} _l$ :

Darcy velocity of phase l [LT⁻¹]

u _li :

Darcy velocity of phase l in direction I [LT⁻¹]

u _lj :

Darcy velocity of phase l in direction j [LT⁻¹]

$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {u} _l$ :

magnitude of the vector flux for phase l [LT⁻¹]

z :

vertical distance which is defined as positive downward [L]

δ _ij :

Kronecker delta function

ϕ:

soil porosity (volume fraction) [L³ L⁻³]

λ _rlc :

relative mobility of phase l [(mL⁻¹ T⁻¹)⁻¹]

λ _rTc :

total relative mobility [(mL⁻¹ T⁻¹)⁻¹]

μ _l :

viscosity of phase l [ML⁻² T⁻¹]

ρ _k :

density of component k [ML⁻³]

ρ _l :

density of phase l [ML⁻³]

τ:

tortuosity (defined with a value greater than 1)

${\vec \nabla }$ :

differential operator or divergence