United States National Exposure

Environmental Protection Research Laboratory

Agency Las Vegas, NV 89193-3478

Research and Development EPA/600/SR-97/055 October 1997

Field Validation of a

Penetrometer-Based Fiber-Optic

Petroleum, Oil, and

Lubricant (POL) Sensor

William C. McGinnis and Stephen H. Lieberman

Project Summary

Comprehensive comparisons of in situ

measurements from a cone penetrometer-deployed laser induced fluorescence (LIF) petroleum, oil, and lubricant

(POL) sensor with traditional field

screening methods were performed. Operational procedures were developed

to facilitate comparison between methods and across multiple sites. Using a

field screening detect/non-detect criterion, agreement between sensor measurements corresponding to the

sampled interval and the laboratory analytical measurements on those samples

was better than 85 percent. Comparison between measurements from the

two accepted analytical techniques, on

splits of the same sample, was only

slightly better. We conclude that the

LIF-POL sensor, deployed from a cone

penetrometer, provides significant advantages for subsurface field screening of POL-contaminated sites. The LIF

technique offers the advantages of

rapid, in situ, real-time measurements,

coupled with increased data density,

not possible with traditional screening

methods.

This Project Summary was developed

by EPA’s Environmental Sciences Division, National Exposure Research Laboratory, Las Vegas, NV, to announce key

findings of the research project that is

fully documented in a separate report of

the same title (see Project Report ordering information at back).

Introduction

The U.S. Environmental Protection

Agency (EPA), Environmental Sciences

Division-Las Vegas (ESD-LV) evaluated

field screening techniques to expedite site

characterization and monitor corrective actions. In collaboration with the Naval Command, Control and Ocean Surveillance

Center, RDT&E Division (NRaD), the effort described here was undertaken to

evaluate the use of a cone penetrometer

system equipped with a fiber optic-based

laser-induced fluorescence (LIF) petroleum, oil, and lubricant (POL) sensor for

real-time field screening of subsurface

POL contamination.

The feasibility of using a truck-mounted

cone penetrometer system to push chemical sensors into the ground to delineate

subsurface contaminant plumes was first

demonstrated through the Department of

Defense (DOD) Tri-Service Site Characterization and Analysis Penetrometer System (SCAPS) program. The LIF cone

penetrometer test (CPT) technology was

developed through a collaborative effort

of the Army, Navy, and Air Force under

the Tri-Service SCAPS program. To satisfy the objective of this Inter-Agency

Agreement (IAG), a comprehensive intercomparison effort was established to directly compare sensor results with

conventional sampling and laboratory

analyses. This effort was proposed as a

jointly funded collaborative effort between

the U.S. EPA and the U.S. Navy and as

such leverages funding provided by Naval

Facilities Engineering Command. This IAG

enabled confirmatory sampling work to

be performed at two sites: Naval Air Station, Alameda, CA, and Guadalupe Oil

Field, Guadalupe, CA. To date, confirmatory sampling has been performed at 16

sites in addition to the two above listed
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sites, therefore summary results will be

presented.

System Description

The SCAPS system uses a truckmounted CPT platform to advance its

chemical and geotechnical sensing probe

into subsurface soils. CPT has been

widely used in the geotechnical industry

for determining soil strength and soil type

from measurements of tip resistance and

sleeve friction via an instrumented probe.

The CPT platform provides a 20-ton static

reaction force associated with the weight

of the truck. The forward portion of the

truck-mounted laboratory is the push

room. It contains the rods, hydraulic rams,

and associated system controllers. Underneath the SCAPS CPT push room is

the steam cleaning manifold for the rod

and probe decontamination system. The

rear portion of the truck-mounted laboratory is the isolatable data collection room

in which components of the LIF system

and onboard computers are located. The

combination of reaction mass and hydraulics can advance a 1-m long by 3.57-

cm diameter threaded-end rod into the

ground at a rate of 1 m/min in accordance with American Society of Testing

and Materials (ASTM) Standard D3441,

the standard for CPT. The rods, various

sensing probes, or sampling tools can be

advanced to depths in excess of 50 m in

naturally occurring soils. As the rods are

withdrawn, grout can be injected through

1⁄4-in.-diameter tubing within the interior of

the probe’s umbilical cable, hydraulically

sealing the push hole. The platform is

fitted with a self-contained decontamination system that allows the rods and probe

to be steam cleaned as they are withdrawn from the push hole, through the

steam cleaning manifold, and back into

the CPT push room. Subsurface investigation in this manner produces rinsate

but no soil cuttings as investigation derived waste.

LIF sensors rely on impinging ultraviolet (UV) light to excite molecular electrons to higher energy states. As the

electrons return to lower energy states,

the transition produces UV fluorescence

photons of longer wavelength than the

UV excitation. The LIF POL sensor probe

consists of a standard penetrometer probe

modified with a 1⁄4-in.-diameter flushmounted sapphire window which is 24 in.

behind the probe tip. Two 500-μm silica

clad silica optical fibers, one for laser

excitation and one for fluorescence emission, are included in the 300-ft umbilical

cable and are internally mounted in the

probe terminating at the sapphire window. Excitation light at 337 nm, generated from a pulsed nitrogen laser (0.8 ns

pulse width, 1.4 mJ pulse energy), travels

down the optical fiber and excites fluorescence from polycyclic aromatic hydrocarbons (PAHs) in the soil. The method

detects PAHs in the bulk soil matrix

throughout the vadose, capillary fringe,

and saturated zones. The emission fiber

collects the laser-induced fluorescence

and returns it to the surface.

At the surface, the fiber is coupled to a

spectrograph where the light is spectrally

dispersed. The dispersed light then impinges on an intensified linear photo diode array detector (1024 pixels) which is

gated on for 100 ns at the time of signal

return. An optical trigger from the pulsed

laser via a pulse delay generator is used

to gate the detector. The laser-induced

fluorescence signal is emitted over a broad

range of wavelengths longer than the excitation wavelength. Approximately 16

msec is required to read the fluorescent

signal from a single laser shot. The maximum spectral resolution is approximately

0.5 nm. The detector is set to measure

the wavelength range from 350 to 720

nm. In practice, the system usually integrates the emission from 20 laser shots

with detector pixels grouped by four. Since

the laser repetition rate is 10 Hz, the total

time to collect a fluorescence emission

spectrum is two seconds. This represents

approximately a 2.5- depth resolution. The

spectral resolution for pixels grouped by

four is approximately two nm. An optical

multichannel analyzer accumulates the

detector readings and reports the sum as

a single measurement to the data acquisition computer.

Data acquisition is automated under

software control using a 486 host computer. The computer sets and controls

the sensor system, stores fluorescent

emission spectra and strain gauge data,

and generates the real-time depth plots.

From the spectral curve at each depth,

the SCAPS software extracts the maximum intensity and associated peak wavelength for real-time depth display. SCAPS

standard electrical cone penetrometer instrumentation consists of strain gauges

measuring tip resistance and sleeve friction in accordance with ASTM Standard

D3441. An empirical relationship between

tip resistance and sleeve friction provides

a soil type classification. This data is contained in the real-time display strips as

cone pressure, sleeve friction, and soil

classification. As the probe is forced into

the ground, the real-time display presents

a 10-ft interval on a scrolling basis.

LIF is a nonspecific field screening technique which detects PAH compounds with

at least two aromatic rings but is most

effective for three and more aromatic rings.

To date, LIF measurements over optical

fibers have not been used extensively for

detection of the single ring aromatic compounds, BTEX (benzene, toluene,

ethylbenzene, and xylenes). The general

trend is the fewer the number of rings the

shorter the excitation wavelength required.

Greater attenuation of this shorter wavelength UV radiation in optical fibers is a

technological barrier for transmitting the

excitation pulse over long fiber lengths.

Table 1 presents detection limits for

common fuel products found as soil contaminants. Measurements were made in

the laboratory on spiked soils over a 50-

m fiber and are reported at the 95 percent

confidence level. Detection limits vary with

fuel type depending on constituent compound abundance. Detection limits also

vary with soil type due to particle size and

mineralogy. Most importantly, these limits

fall well within the range of utility considering regulatory action limits.

Table 1. Detection Limits for the LIF POL

Sensor

Fuel Type

Diesel

Diesel Fuel

Soil Unleaded Fuel Marine

Type Gasoline #2 (DFM)

Soil A 17 329 14

Sand ppm ppm ppm

Soil B 36 25 4

China Lake ppm ppm ppm

Soil C 121 83 5

Columbus ppm ppm ppm

Sampling Procedure

SCAPS site operations typically consist of two phases: site investigation and

validation. In the investigation phase,

pushes were performed to delineate the

plume boundaries. During the validation

phase, areas of interest were selected

from the first phase and then revisited. At

the selected locations, a validation push

was performed followed immediately by

collection of confirmatory soil samples.

During validation, the SCAPS CPT

pushed the LIF POL sensor probe into

the ground and acquired fluorescence and

geotechnical data. After the probe was

pushed to the total depth anticipated or

was blocked from further penetration, the

probe was retracted. The CPT rig moved

away from the location and a hollow stem

auger (HSA) drill rig was positioned approximately 20 cm (8 in.) from the push

hole. The HSA rig drilled a hole such that
3

the advancing auger flights destroyed the

push hole while allowing for the collection of split spoon soil samples within

approximately 7.5 cm (3 in.) (horizontally)

of the push cavity. This offset between

the push hole and the auger boring permitted sampling far enough apart so that

the soil samples were not affected by

possible cross contamination due to

sloughing down the penetrometer hole,

yet near enough to minimize variability

due to small scale spatial heterogeneities

of the soil and the contaminant distribution. This sampling strategy ensured that

samples were representative of the region sampled by the LIF POL sensor.

Each borehole was logged by a geologist. Soil samples were collected with a

split spoon sampler lined with 15-cm (6-

in.) long stainless steel tubes. The sampler was driven in advance of the lead

auger using a 63.5-kg (140-lb) slide hammer falling over a 75-cm (30-in.) distance,

in accordance with ASTM 1586, the Standard Penetration Test.

A California modified split spoon sampler was used for sample collection. The

split spoon sampler was a 75-cm (30-in.)

long, 7.5-cm (3-in.) diameter steel tool.

The sampler consisted of a 10-cm (4-in.)

long (reduced to 5 cm (2 in.) when fully

threaded) cutting head or shoe section,

followed by either a 45-cm (18-in.) or 60-

cm (24-in.) long sample barrel containing

three or four 15-cm (6-in.) long stainless

steel soil sampling tubes, and ending in a

waste soils catch barrel section.

Soil samples were collected at depth

intervals to confirm the LIF POL sensor

depth profile in both background and elevated fluorescence intervals. The sampler was overdrilled approximately 15 cm

(6 in.) prior to retrieval to reduce the

amount of sloughed soils typically found

in the bottom of the borehole. Only tubes

containing sample soils that appeared

relatively undisturbed were used. Samples

for confirmatory analysis were collected

from the lower and middle (deeper) 15-

cm (6-in.) soil tubes in the 45-cm (18-in.)

sampler. The sample was Teflon-sealed,

capped, taped, labeled, logged, and

placed into a chilled ice chest. Each confirmatory sample was analyzed by EPA

Method 418.1 Total Recoverable Petroleum Hydrocarbon (TRPH), a water analysis method modified for soil, and EPA

Method 8015-Modified Total Petroleum

Hydrocarbon (TPH). Samples for

geotechnical analysis (soil moisture, grain

size, and density) were sealed and

shipped in the stainless steel tubes retrieved from the split spoon sampler.

Those samples chosen for geotechnical

analysis were generally the uppermost

(shallowest) tube of the three from the

split spoon sampler, but only if the tube

appeared full as a result of complete

sample recovery by the split spoon sampler. In each boring, these sampling procedures were usually repeated four to

eight times to gather samples for traditional laboratory analytical measurements.

From three to eight validation borings were

performed at a site.

Analytical Methods

EPA method 418.1 (TRPH by infrared

absorption) and EPA method 8015- Modified (TPH by GC/FID) represent two of the

most frequently used methods employed

for delineating nonvolatile POL contamination. It is important to note that these

analytical methods do not measure exactly the same constituents that are targeted by the LIF POL sensor but were

selected because they represent the technology that is currently being used on a

day-to-day basis to make decisions about

the distribution of subsurface POL contamination. This data is then compared

with the in situ fluorescence data gathered with the sensor.

Data Analysis

LIF POL sensor data is evaluated on a

detect/non-detect basis to determine percentage agreement between sensor data

above or below a fluorescence threshold

and both TRPH and TPH results above or

below a sensor detection threshold.

SCAPS independently provides detect/

non-detect data relative to a specific detection limit derived for a specific fuel

product on a site-specific soil matrix. The

detection limit is determined for the site

by generating a concentration calibration

response curve for a set of calibration

standards (spiked site-specific soil

samples) prepared by standard addition.

Results and Discussion

For an in situ field screening measurement technique, such as LIF, determining

the accuracy of the technique presents a

particular challenge. This is because it is

not a simple matter to confidently assign

a “true” value to a subsurface contaminant distribution. With conventional laboratory-based measurements, the accuracy

of the method is a function of both the

sampling errors and errors associated with

the measurement method. To evaluate

the accuracy of a laboratory method, the

conventional approach is to compare the

results obtained from analysis of a spiked

sample of known concentration. It should

be recognized, however, that this approach does not address the issue of

whether the result is an accurate representation of the true value of the contaminant in the ground. In other words, errors

related to sampling are not addressed.

Because there is no independent measure of the subsurface value of contaminant concentration, it will be necessary to

evaluate the accuracy of the in situ measurement by comparing in situ results with

results from conventional methods that

may not provide a true value of the subsurface contaminant distribution because

of errors associated with the sampling

process.

It should be noted that the three methods for quantifying hydrocarbon contamination discussed in this document (namely

the analytic EPA Methods 418.1 and 8015-

Modified, and the LIF method) all measure and quantify the amount of

contaminant using a different physical

property of the contaminant. The EPA

Method 418.1 measures the infrared absorption of the extract from the soil

sample. The EPA Method 8015-Modified

passes the extract from the soil sample

through a gas chromatograph and uses a

flame ionization detector to measure the

contaminant according to the retention

time of the constituents. The LIF method

measures the fluorescence (under laser

excitation) from the PAHs present in the

contaminant.

The two EPA Method measurement

techniques require comparison to a similar measurement of a target fuel in order

to quantify the contaminant. Note that it is

not possible to ensure that the target fuel

is identical in composition to the contaminant extract. The EPA Method 418.1 uses

a single standard hydrocarbon mixture for

quantification, while EPA Method 8015-

Modified quantifies using a target fuel that

produces a similar chromatogram. The

LIF method does not use an extract from

the soil sample, but measures the contaminant in situ as it is presented to the

window of the probe. For this reason, the

LIF POL sensor is more sensitive to matrix effects. Because of this matrix sensitivity, the LIF POL sensor does not employ

a target fuel for quantification but only to

set a detection threshold for the site.

Another difference between in situ and

conventional laboratory-based measurements is that laboratory measurements

usually employ extraction or matrix simplification procedures, whereas in situ

measurements offer limited opportunities

for controlling matrix effects. For the LIF

POL sensors, studies have shown that

variability in sensor response results from

changes in the sample matrix and from

variations in fluorescence response re-
4

lated to fuel product type, age, and origin

of the hydrocarbon contaminant. Since it

is not possible to account for all sources

of variability that affect sensor response

at this time, the sensor is intended to

operate as a field screening method. It

will provide only qualitative data on the

distribution of petroleum hydrocarbon contamination.

The approach for evaluating accuracy

presented here depends on the direct

comparison of in situ sensor data with

the analysis of discrete samples collected

as close as possible to the soil sample

measured by the in situ sensor. Although

it is believed that this approach provides

the best opportunity for evaluating the accuracy of the in situ measurement, it

should be noted that it will not be possible to account for all variability associated with the uncertainty in depth from

which the discrete samples are collected.

It is possible that the depth of the discrete sample may be in error by up to 15

cm (6 in.) in the vadose zone. Due to

sloughing and flowing sand conditions in

the water saturated zone, depth measurement uncertainty during discrete sampling

may be greater. In stratified soils, sharp

vertical boundaries of the contamination

plume may exist. This sampling error could

therefore lead to poor comparisons between in situ data and laboratory data.

For example, due to an error of 15 cm (6

in.) in the sample depth, contaminant concentration can change from strongly impacted (greater than 10,000 ppm) to not

impacted (less than 100 ppm). For this

reason, the depth of the sample must be

known for the comparability of the

samples to be firmly demonstrated. In

addition, because there will be several

inches of horizontal offset between the

push location and the location of the splitspoon sampler, there may also be some

small-scale horizontal variability that will

not be accounted for. Both the vertical

uncertainty and the small-scale horizontal

variability will not be a factor when comparing the two laboratory methods because splits of a homogenized sample

will be measured.

Summary Results for Sixteen

Sites

To date, validation efforts at 16 sites

have been completed. These sites presented varied hydrogeological conditions

including: (1) arid with deep groundwater

and (2) coastal with tidally-influenced shallow groundwater. These sites also presented various contaminant source

products including old refinery waste, heating oil, diesel fuel marine, and JP-5 jet

fuel.

Based on the results calculated for the

sites to date, the LIF POL sensor detection threshold varies somewhat from site

to site, but it is approximately 100 to 300

mg/kg as TRPH by EPA Method 418.1.

Scatter plots of the LIF POL sensor data

versus TPH and TRPH show a trend of

increased fluorescence with increased

TPH or TRPH. Table 2 contains the cumulative contingency analysis results on

a percentage basis showing better than

85 percent agreement between sensor

and analytical measurements. As expected, comparison between analytical

methods is slightly better since these

measurements were made on splits of

the same sample.

Guadalupe Oil Field Results

The SCAPS was employed at the

Guadalupe Oil Field in San Luis Obispo

County, CA, for subsurface investigation

of diluent contaminated soils on the 23rd

of August through the 2nd of September

1994. Validation pushes with overborings

and sampling were performed on the 7th

through the 8th of September 1994. A

total of thirty-two SCAPS push holes were

advanced during phase one investigation.

After review of phase one data, an additional four validation holes were pushed,

subsequently overbored, and a total of 23

soil samples collected. Soil samples were

sent to an analytical laboratory for analysis by EPA Methods 418.1 (TRPH by IR)

and 8015-Modified (TPH by GC/FID).

The calculated fluorescence threshold

was 350 relative fluorescent counts, with

a corresponding detection threshold of 77

ppm. Contingency analysis was performed

on the data. There were no false negatives versus TRPH and 6 percent versus

TPH. The percentage comparability or percentage correct versus both TRPH and

versus TPH was 88 percent. These results are very favorable considering 88

percent comparability between the two

laboratory analytical methods. Table 4

summarizes these contingency results.

Table 2. Sixteen Site Cumulative Contingency

Analysis Results Summary (n=552)

% % False % False

Comparison Correct Positive Negative

LIF vs. TRPH 87 5 7

LIF vs. TPH 86 7 7

TPH vs. TRPH 95 2 3

Naval Air Station, Alameda

Results

SCAPS field operations were undertaken at Naval Air Station (NAS), Alameda,

CA, Site 13 - Former Oil Refinery, from

the 17th of March through the 6th of April

1994. Validation operations were performed from the 4th through the 6th of

April 1994. A total of 37 pushes were

performed during phase one SCAPS investigation. After review of phase one

data, eight validation pushes were performed each directly followed by a hollow

stem auger boring and sample collection.

Forty-five samples were collected from

the eight validation borings.

The calculated fluorescence threshold

was 10,620 relative fluorescent counts,

with a corresponding detection threshold

of 137 ppm. Contingency analysis was

performed on the data. The percentage of

false negatives was 7 percent versus

TRPH and 4 percent versus TPH. The

percentage comparability or percentage

correct versus TRPH was 91 percent and

versus TPH was 87 percent. These results are very favorable considering the

comparison between laboratory analytical

methods with 11 percent false negative

and 87 percent comparability. Table 3

summarizes these contingency results.

Table 3. NAS, Alameda Contingency Analysis

Results Summary (n=45)

% % False % False

Comparison Correct Positive Negative

LIF vs. TRPH 91 2 7

LIF vs. TPH 87 9 4

TPH vs. TRPH 87 2 11

Table 4. Guadalupe Oil Field Contingency

Analysis Results Summary

% % False % False

Comparison Correct Positive Negative

LIF vs. TRPH 88 12 0

LIF vs. TPH 88 6 6

TPH vs. TRPH 88 12 0

Conclusions and

Recommendations

The SCAPS technology was developed

to provide rapid, in situ, real-time field

screening of the physical and chemical

characteristics of subsurface soil at hazardous waste sites. The current configu-
5

ration is designed to quickly, and cost

effectively distinguish hydrocarbon-contaminated areas from unimpacted areas.

Although the LIF POL sensor induces only

the PAH portion of the petroleum hydrocarbons to fluoresce, petroleum hydrocarbons are the general target analytes.

This capability allows further investigation

and remediation decisions to be made

more efficiently, on site, and reduces the

number of samples that need to be submitted to the laboratory for costly confirmatory analyses. A site can then be further

characterized with reduced numbers of

borings or wells placed on a plume specific sampling pattern rather than a grid.

Remediation efforts can be directed on

an expedited basis as a result of the

immediate availability of the LIF POL sensor and soil matrix data. Further, the

SCAPS CPT platform: (1) allows for the

characterization of contaminated sites with

minimal exposure of site personnel and

the community to toxic contaminants, and

(2) minimizes the volume of investigation

derived waste (IDW) generated during typical site characterization activities.

As a result of field experience and efforts undertaken to validate the SCAPS

LIF POL sensor, the following items are

recommended.

• Further development should be pursued to refine the LIF measurement technique for expanded use

in additional applications such as

monitoring in situ remediation.

• Continue research efforts to develop better quantitative aspects in

defining the dominant chemical

source of the fluorescence. Improve

contaminant discrimination by

spectral signature using neural network pattern recognition techniques

and developing a database of fluorescent signatures.

• Develop methods to compensate

for matrix effects using additional

sensors and algorithms accounting for grain size distribution and

volumetric moisture content.

The U.S. Environmental Protection

Agency, through its Office of Research

and Development, partially funded and

collaborated in the research described

here under Interagency Agreement

#DW17936217 with the U.S. Navy. It has

been subjected to the Agency’s peer and

administrative review and has been approved for publication as an EPA document. Mention of trade names or

commercial products does not constitute

endorsement or recommendation for use.
6

United States

Environmental Protection Agency

Center for Environmental Research Information

Cincinnati, OH 45268

Official Business

Penalty for Private Use

$300

EPA/600/SR-97/055

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35

William C. McGinnis and Stephen H. Lieberman are with Control and Ocean

Surveillance Center, San Diego, CA 92151.

Charlita G. Rosal is the EPA Project Officer (see below).

The complete report, entitled “Field Validation of a Penetrometer-Based FiberOptic Petroleum, Oil, and Lubricant (POL) Sensor,” (Order No. PB98-100472;

Cost: $21.50, subject to change) will be available only from

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

Telephone: 703-487-4650

The EPA Project Officer can be contacted at

Environmental Sciences Division

National Exposure Research Laboratory

U.S. Environmental Protection Agency

Las Vegas, NV 89193-3478