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Report - Technical

OPTIONS FOR SEA WALL CLEANING OF ALVENUS OIL  August 26, 1984  Summary Prepared by: Todd
Baxter  NOAA SSC  In cooperation with the Scientific Support Group  GENERAL ECOLOGY AND
IMPACT REVIEW The primary ecological impact of ALVENUS oil on the Galveston sea wall area
has been to the attached, intertidal invertibrates and plant communities found on the
rocks at the base of the sea wall. Simple mechanical smothering by the oil coating, rather
than chemical toxicity of the oil is thought to be the main impact mechanism. Limited
damage to the planktonic and larval organisms found in the nearshore zone has been
suggested. The major impacts to this group should be limited to the zone of greatest
mixing, quite close to the base of the sea wall. The free moving adult organisms
associated with the sea wall habitat are most resistant to oil impact, largely due to
their ability to leave the oiled portions of the habitat. The central topic in discussing
habitat recovery is the ability of the local marine organisms to re-occupy the impacted
portions of the sea wall environment. This environment is exposed to the constant actions
of wind and wave. Year-round resident populations are adapted to clinging to, or
sheltering around the rocks of the sea wall. Other organisms are transient in nature,
often being present in the near- shore zone during limited periods of the year. Therefore,
many of the organisms of the sea wall are well adapted to rapid and repeated colonization
within the habitat. This is a decided benifit for recovery from the ALVENUS oiling.
CLEANUP OPTIONS AVAILABLE  1. Natural Weathering and Recovery.  No attempt would be made
to remove the oil coating now present. Natural weathering processes would harden the oil
into a dry, asphalt like coating which may be expected to remain intact for 2 to 3 years
under normal weather conditions. Re-colonization by the attached organisms is expected by
the second year, and should become more successful as the tar coat ages. The planktonic
and mobile adult organisms will return rapidly on the next annual or semiannual
reproductive cycle.  2. Hydro-Mechanical Removal.  The effects of "hydro-blasting" on
habitat recovery are mixed. This process will return the rock substrate to a natural
condition, possibly speeding re-colonization by the attached organisms. However, since the
ALVENUS oil has a low inherent toxicity this cleaning effect may be minimal when compared
to re-colonization over the weathered tar. Hydro-blasting is also non-selective, in that
it will destroy stressed organisms along with the oil and dead organisms. The stressed
survivors of an oil impact are thought to be quite important in re-establishing a healthy
intertidal community.  The process also returns oil to the water in a chemically un-
altered form. Many of the small particles of oil stripped from the rocks will escape
collection, mixing in the water column or returning to shore as the currents dictate.
Depending upon the degree of weathering these oil particles may also adhere together to
form tar balls. 3. Chemically Assisted Removal.  The use of a chemical agent attempts to
strike a compromise between the inherant toxicity of the chemical-oil complex formed, and
the benifits to be gained by a more rapid removal of the oil from the environment. Used
properly, a dispersant will accelerate the natural weathering process, while changing the
chemical and physical state of the oil to produce a suspension of very small droplets.
These fine particles are then available to natural bacteria populations present in the
sea, allowing natural bio-degradation at a much faster rate. The dispersed oil will not
tend to cohere as tar balls due to the find particle size and loss of surface tension. The
toxic nature of the resultant product must be controlled by providing adequate mixing and
dilution in the surrounding water mass so that the toxic threshold for the local organisms
is not reached.  TIME CONSIDERATIONS The hydro-mechanical process is most efficient when
applied to a hard surface, such as paint, which will chip and flake away. The process is
less efficient in removing soft, pliable coatings that will deform under the impact of the
sand and water particles.  The ALVENUS oil found on the Galveston sea wall has not
weathered enough to become hard. This is why hydro-blasting has been a slow and time
consuming process to date. As time passes and the oil hardens into tar the process should
become more efficient, requiring less time and effort to clean a unit area of the wall.  A
chemical oil dispersant is most effective on fresh oil. As weathering drys the oil to tar
the dispersant has less ability to penetrate and dissolve the oil. A dispersant use test
has been scheduled to determine if the ALVENUS oil is still fresh enough to be affected by
the chemical, and to what extent. End.