Site-specific risk assessment and management of point and diffuse sources - Environmental Deterioration and Contamination: Problems and their Management - page 337

Figure 10.5 A BTEX-containing hydrocarbon plume close to a creek.

6 Further assessment is necessary for the clarification of the fate of the plume from

the source to the creek.

Case study 2

Point source contamination by petroleum hydrocarbons (measured as TPH total

petroleum hydrocarbon), including a large proportion of BTEX (benzene, toluene,
ethylbenzene and xylene). The plume has not yet reached the creek. The aquatic ecosys-
tem of the nearby creek is the most sensitive potential receptor. The task is to calculate
whether or not the contaminated soil and groundwater pose unacceptable risk to the
aquatic ecosystem. The situation, the monitoring wells and the extent of the plume is
shown on the map in Figure 10.5.

=

Concept of case study 2

Risk assessment concept is based on a three-tiered, stepwise refined risk assessment:

- Tier 1

Transport modeling for PEC calculation in the creek is based on measured con-
taminant concentration of the groundwater in the source (using a conservative
approach by considering only dilution rates, no partition and biodegradation)
and comparing PEC to generic surface water quality criteria (WQC);