Acid tar lagoons : assessment and environmental interaction.

Acid tars are waste residues of obsolete benzole refining, oil re-refining and
white oil production processes. They are black, acidic, viscous semi-liquids
comprising an extremely complex mixture of water, sulfuric acid and a large
range of organic compounds. Acid tars were often dumped into excavations
and existing holes in the ground together with various co-disposed materials
without any treatment or engineered lining system leaving a legacy of acid tar
lagoons. Acid tars may pose potential risks to human health and the
environment because of their acidity, volatiles and other hazardous
components. The major contamination pathways of acid tar lagoons are
considered to be direct contact, gas emission, bulk tar migration offsite, and
surface and ground water contamination.
The leaching, weathering and migration behaviours of acid tars were
investigated by carrying out a series of batch, cascade and flow cell tests. The
results demonstrated that acid tars are capable of leaching Significant levels of
contaminants if disturbed, while the leaching level is Significantly lower under
simulated groundwater flow in a model soil. The time scale to leaching
stabilization was of the order of months in the model soil and is expected to
significantly exceed that in the natural environment.
To support this work a nubmber of analytical methods for determining
physical and chemical properties of acid tars had to be adapted from standard
techniques. These modified techniques are described in detail together with
recommendations for data integration and correlation of all analyses to form a
better understanding of acid tars and their potential environmental impact. The
overall findings of the research were integrated to generate a conceptual
model of acid tar lagoon processes to assist in assessment. Monitored Natural
Attenuation was evaluated and is considered to be a potentially viable
approach to the environmental management of some acid tar lagoons.