| Features
of acid tar lagoons
Lagoon Top Water:
Because of acid tar's low permeability, an uncapped acid tar
lagoon usually accumulates rain water that forms a surface layer.
The lagoon top water is contaminated by sulfuric acid, soluble
organic compounds and soluble contaminants from co-disposed
materials, such as iron, aluminum or other heavy metals etc.
Oily phase organic contaminants:
Free oily phase contaminants (NAPLs) may be found floating
on the surface of
ponded lagoon water or bound to mud and humus matter at the
bottom of the
ponded water. In the latter case these can be released by physical
disturbance.
Black Coating of organics:
A proportion of the organic contaminants that have migrated
from the acid tar
into the surface water typically adbsorbs onto surface soil
and vegetation at
the lagoon edges forming a thin black coating around the main
lagoon.
Weathered Tar Surface:
Capped acid tar lagoons often feature relatively thin layers
of exposed weathered acid tar due to bulk acid tar The project
cover both socio-economic and technical issues, with the objectives
of:migration. Mobile viscous acid tar driven by the pressure
of heavier capping soil finds its way up to the surface through
weak points of the capping layer. This viscous acid tar then
loses moisture content and volatile organic components and becomes
less mobile. The mobility is strongly temperature dependent;
acid tar is more
mobile during summer seasons due to higher temperatures.
Weathering - Weathered Black Tar:
Weathered black tar is an intermediate weathered form of acid
tar. It is usually found along pathways of surface acid tar
migration. Weathered black tar is a rubbery, flexible material
that is relatively mobile.
Weathering - Weathered Friable Tar:
Weathered Friable tar appears as a final form in the
weathering process. It is weathered from weathered black tar
through loss of the water content and organic solvents that
bind the mixture together. It is usually found at the end of
migration pathways and is a light, friable material that potentially
can be transferred offsite by wind blow.
Migration - 'Pond' of Viscous Tar:
In certain circumstances, depending on the topography, viscous
acid tar can migrate in bulk from the main lagoon and upwell
to form a relatively deep pond of viscous tar which is covered
by thin layer of weathered particulate tar. Its resemblance
to thin surface layers of hard weathered tar can be hazardous
to unwary site visitors.
Migration - Tar migration through fissures in the
ground:
Viscous acid tar may migrate through fissures in the ground
to upwell some distance from the main lagoon. On relatively
flat areas this tar can slowly spread out over several years
to produce a relatively thin layer covering a large area. This
tar typically weathers into weathered black tar and eventually
weathered friable tar.
GO BACK
All information herein is provided in good
faith. It is not intended to be, and should not be relied on
as, a substitute for professional advice. See disclaimer.
|
