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Natural Oil Seep Inventory
Santa Barbara County is situated adjacent to two offshore basins:
the Santa Maria Basin, which is offshore of the northern coast of
the County, and the Santa Barbara-Ventura Basin, which forms the
Santa Barbara Channel. Both basins contain natural oil and gas seeps,
and both are sites of offshore oil and gas development. The natural
seepage leaves deposits of oil residues along the County's coastline,
typically in the form of "tar balls." Seeps in the Santa
Barbara Channel have been studied more thoroughly than those in
the Santa Maria Basin, and rough estimates exist for Channel seep
volumes. .
Offshore oil development carries a significant risk of oil spills
that can also leave oil residues on the County's coastline. Oil
spills from offshore oil projects adversely impacted the coastal
and marine environment of the County in 1969 and 1997. A large number
of small spills also occur, most of which probably have little impact.
According to the Minerals Management Service (MMS)
database, a total of 841 spills were reported in the Pacific Outer
Continental Shelf (OCS)
Region between 1969 and 1999, of which 95% were less than 1 barrel
(42 gallons). An important distinction between natural
seeps and major oil spills is that seeps are distributed over
a large region and throughout the year, whereas spills are concentrated
in both space and time.
When an offshore oil spill fouls the
coastal environment, the operator has
responsibilities under state and federal
law, and under County permit conditions,
for spill cleanup, resource restoration,
and environmental damages. However, assessment
of shoreline impacts is complicated by
the ubiquitous presence on beaches of
oil residues originating in natural seeps.
Because the precise chemical composition
of oil varies among oil reservoirs,
oil originating in natural seeps can
be differentiated from spilled oil by
chemical fingerprinting of oil from both
seeps and wells. Similarly, a baseline
inventory of shoreline tar deposits can
be developed by sampling and chemical
fingerprinting of tar found along the
shore. Such an inventory would facilitate
determining the source of shoreline contamination.
The United States Geological Survey
(USGS)
has previously undertaken preliminary
reconnaissance of the coastal tar residues,
comparing collected samples with a small
set of reference crude oils. Most of
these samples appeared to originate in
natural offshore seeps.
In 2001 the USGS and MMS began a three-year,
$900,000 project to examine natural seepage
in the southern Santa Maria Basin. Work
during the first year focused on assessing
existing information and shoreline sampling
of tar deposits. Work in year two involved
surveys to locate offshore seeps in the
study area, chemical characterization
of onshore tar samples, and development
of statistical methods for differentiating
tar samples. Progress was made in building
the tar fingerprint library and construction
of a GIS that brings together in a spatial
database many sources of data on offshore
seep locations, together with other data
layers, such as bathymetry and geology.
In the third year, USGS will sample tar
at offshore seeps, using divers and remotely
operated vehicles (ROVs). Researchers
in the USGS laboratory will concentrate
on refining their strategy for discriminating
tar from different sources and will work
to develop a better picture of the beach
tar deposition data.
In spring, 2002, the County of Santa
Barbara received funding from the California
Coastal Resources Grant Program to participate
in the project. The Energy Division participation
consists of beach tar sampling and support
for USGS laboratory analysis of the additional
tar samples generated. With the state
funding, we have been able to increase
the number of beaches sampled from 4
to 10, increase the sampling frequency
from quarterly to monthly, and extend
sampling period for a full year. The
funding also covers laboratory costs
for analysis of the additional samples,
including support for a laboratory technician
in USGS’ Menlo Park laboratory,
employed full-time for 14 months to analyze
tar samples, perform statistical analyses,
and maintain the tar database. The enhanced
sampling program will allow USGS to learn
more about the sources of beach tar and
to develop a better estimate of how much
tar is present on the beaches throughout
the year.
The Energy Division has now completed
its beach tar sampling program, which
ran from June, 2002, to May, 2003. Beach
tar was sampled monthly at ten beaches
spaced out along Santa Barbara’s
coast, from Brown’s beach, near
the San Luis County line, to Loon Point,
near Carpinteria. The sampling was carried
out by two field teams of three students
from the Department of Geology at U.C.S.B.,
coordinated by John Day, a Planner in
the Energy Division. The sampling methodology
was developed in cooperation with the
USGS, following their established protocol.
Tar deposition was estimated by weighing
the tar found along transects positioned
at random locations along the beaches,
and tar samples were collected for chemical
analysis. During the year, the field
teams weighed tar at nearly 600 transects
and collected over 300 tar samples for
analysis. In excess of 182 samples have
now been analyzed in the USGS laboratory.
The USGS researcher team completed
analyses of the tar deposition data in
March, 2004. The findings are likely
to be augmented or revised in the future,
depending on additional data and new
information that may come to light during
the final year of the USGS study (or
possibly extensions to that study). The
USGS submitted a provisional final report
for the County-funded project on March
25, bringing our joint undertaking to
a close. Following completion of the
MMS-funded project later this year, the
USGS will complete a final report on
the overall project and submit papers
to professional journals for peer review
and publication.
The study provides a solid basis for
evaluating the potential value of follow-on
studies of beach tar. It also will
inform the design of future studies.
For additional information on this
project and results, please follow
the links to Natural Seep Project Summary
and the Natural Seep Inventory Final
Report.
Please contact Dr.
John Day, (805) 568-2045 for more information.
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