- RAPID OPTICAL SCREENING
delineation of hydrocarbon through laser-induced fluorescence. Recently
a client invited C2REM to visit a steam injection
DNAPL remediation project in central California. (NOTE: The project
itself is quite remarkable and may be the subject of a future article).
During this visit we were introduced to a recent technology presently
receiving a lot of attention. The product is known as the Rapid
Optical Screening Tool (ROST®) and has been acquired by Fugro Geosciences,
Inc. ROST®is a laser-induced fluorescence sensor deployed along
with standard Cone Penetration Testing (CPT) equipment.
product is a limited intrusion device used to delineate hydrocarbon
sources (at the soil/CPT interface) from non-impacted media down
to residual concentrations in soils, both above and below the water
table. The ROST® system uses an ultraviolet laser source coupled
with an optical detector to measure fluorescence (a technique known
as Laser-Induced Fluorescence Spectroscopy). The laser emits a continuous
pulse through a CPT as it is being advanced. This laser pulse is
received at the optical detector (referred to as the sapphire window)
and is correlated with known fluorescent characteristics for petroleum
products. This system generates a fluorescence vs. depth curve,
which can be used to produce a 3-dimensional picture of the extent
of impacted soil and/or aquifer zone(s).
the steam injection project discussed above, ROST® technology was
utilized to delineate creosote. The client stated that the ROST®
technology was more accurate, efficient and safer than the previous
sampling done by conventional soils and groundwater borings. At
this particular site, the ROST® system had a good correlation with
soils and groundwater analytical results from grab samples (using
conventional boring and sampling methods at noncontinuous intervals).
ROST® technology has also been verified by the U.S. EPA through
their environmental technology verification ETV program and the
results were published in a verification statement dated February
1997. In this statement, U.S. EPA concluded that the ROST® system
is an emerging technology worthy of consideration for site investigations
where aromatic hydrocarbons (e.g., petroleum, oils, lubricants,
and coal tars) are suspected. The technology offers a number of
advantages over conventional drilling and sampling technologies
for the purpose of screening a site to determine the nature and
extent of contamination. U.S. EPA's ETV statement indicates that
the typical operation process cost is approximately $4,200 - $5,300/day
and can produce, under normal circumstances, approximately 300 feet
/day of data (approximately $14-$20/foot).
limitations and issues which should be considered prior to utilizing
this technology includes:
phased hydrocarbons will not typically be detected by this system
(i.e., as materials migrate to the groundwater many constituents
will dissolve and no longer be detectable, however nonaqueous phased
constituents can be observed).
limitations of the cone penetrometer equipment, primarily hydraulics
(dependent largely on the subsurface stratigraphy).
this system is not quantitative, agencies will require conventional
sampling and analysis techniques in addition to the ROST® system
for risk assessments and/or when specific clean up requirements
are established for remediation. However, far fewer monitoring wells
or sampling locations should be required.
with variation in stratigraphy and/or unidentified fluorescent interference
can cause problems with clearly delineating subsurface conditions.