NATO/CCMS Pilot Study Evaluation of Demonstrated and ... - CLU-IN

NATO/CCMS Pilot Project on Contaminated Land and Groundwater (Phase III) January 2002
The development of risk with time was calculated after each section of the experiment (Figure1) using the
corresponding concentrations of the relevant compounds as well as their toxicological properties. The
non-carcinogenic risk (Figure3) as well as the carcinogenic risk (data not shown) is dominated by
benzene, which is depleted from the NAPL rapidly. Since benzene is not readily degraded under
anaerobic conditions the risk is not significantly reduced under these conditions. However, after the
introduction of oxygen as it occurs in the field due to groundwater mixing, the risk is instantly reduced to
acceptable levels.
Figure 2: Benzene and ethylbenzene concentration
curves in the effluent of the flow through reactor
(section A), the denitrifying column (section B) and
the aerobic column (section C) respectively of the
continuous flow-through experiment.
4.4 Correlation with Field Data
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Figure 3: Development of the toxicological risk
(hazard index) after the dissolution of single
compounds from diesel fuel into the aqueous phase
and after anaerobic and aerobic degradation
respectively. The hazard index was calculated as the
additive risk of the single BTEX and PAH
compounds.
Results from the laboratory studies including the mathematical models finally were applied at the field
sites in Studen and Menziken in order to perform a risk assessment [7-9]. Several assumptions to simplify
the complex field situation and to acquire unknown parameters had to be made. This lead to the following
findings:
Using the composition data of diesel fuel or heating oil, the maximal concentrations of toxicologically
relevant compounds expected in the groundwater can be predicted (worst case scenario).
The efficiency of in situ bioremediation techniques can be assessed. With a mass balance calculation of
the inorganic species (oxygen, nitrate, etc.) measured in the Studen groundwater it could be determined
that about 200 kg of PHC were biodegraded within the time frame of 5 years. Comparing this result with
a theoretical calculation based on the mathematical dissolution model it could be shown that the removal
of 200 kg PHC through the dissolution process alone would take about 50 years. This indicates that
biological processes enhance the depletion of PHC, and hence shorten the time for PHC removal from the
subsurface.