Presented at the American Chemical Society National Meeting in San Francisco August 2014 on the Environmental Chemistry Track. One of the most serious contamination problems in LA in the early 2000's was leaking from underground gasoline storage tanks. At high levels of VOC's (thousands of ppm), the pump and treat effluent can simply be flared. At about 1,000 ppm, it requires too much auxiliary fuel to burn the effluent. A new collection system such as a carbon bed is required. Continuous monitoring is required to determine when breakthrough of the VOC's occurs. Then, the carbon bed should be changed. The most popular technique for carbon bed monitoring is photoionization and the 112 instrument includes a programmable setpoint that shuts down the pump allowing the carbon bed to be changed. The application of continuous monitoring instrumentation to soil vapor extraction (SVE) is described as one of the few innovative technologies that has gained wide use for cleaning up contaminated sights.

1. Monitoring and control of pump and
treat systems in gasoline stations
J.N.Driscoll & J. Maclachlan
PID Analyzers, LLC
Sandwich, MA
ACS Fall Meeting San Francisco, CA
Aug. 13, 2014 6PM
Paper #589

2. Introduction
• In the late 1980’s and 1990’s, leaking underground gasoline storage
tanks from gas stations were linked to VOC’s in drinking water
• Starting in the late 1980’s states began requiring double wall tanks
in new gasoline stations. In the late 1990’s & early 2000’s, EPA and
states also began requiring Gas Station operators to clean up
gasoline in soil & groundwater that had leaked from their stations .
LA county was no exception and required the cleanup of hundreds
of stations. This is the story of a number of those stations that
required the cleanup and used our PID analyzers.
• It starts by pumping air (at a high pressure) into the soil &
groundwater and removing VOC’s with a soil vapor recovery system
via a carbon bed and monitoring VOC’s at the exhaust with our with
our photoionization (PID) analyzer

3. Tank Removal

4. Typical Vapor Well
This is a well proven but long & tedious process

5. Pump & Treat System
• Pump & Treat System
– Air pump for sparging VOC’s from
Soil/groundwater
– Vapor Extraction Well
– Vacuum Pump to remove VOC’s
– Carbon Bed for VOC removal
– PID Analyzer from monitoring VOC’s from C Bed

6. Carbon Bed Cleanup Systems
• VOC’s are typically absorbed on carbon beds. The
process can be considered as separating the flow of
VOC’s from the air flow of a pump & treat system. The
VOC’s are pumped from the groundwater or soil which
is contaminated.
• The pollutant is adsorbed on the surface (mostly the
internal surface) of a of the carbon adsorbent material.
It is not absorbed by a chemical reaction. The adsorbed
material is held physically (chemisorption), and can be
released (desorbed/regenerated) easily by either heat
or vacuum.

7. Typical Carbon Bed Regeneration System

8. 112 @ Gasoline Station P & T Remediation

9. Cleanup in LA County
• The cleanup at the gasoline started with pump and treat. In
the initial stages, when the concentration of the exhaust
was > 1,000 ppm, the exhaust was flared. Below 1,000
ppm, when it was not feasible (too costly) because of the
cost of the natural gas to keep the plume burning.
• At this stage, carbon beds were added to the pump & treat
system. A photoionization based monitor was added at the
exit of the carbon bed. This analyzer had data logging
capability and a programmable setpoint that could be used
to switch off the pump when the breakthrough point of 4
ppm gasoline was exceeded. The input from the pump was
then switched to the second carbon bed.
• This process ran for nearly 6 years before the hydrocarbons
level in the soil were reduced to an acceptable levels.

10. 1990’s C Beds Used to Reduce
emissions of VOC’s and HAP’s
C Bed Collection System Industries
• Automotive
• Aerospace
• Chemical manufacturing
• Degreasing
• Electronics (photoresist)
• Food products
• Gravure printing (publications, packaging &
product)
• Paper film & foil coating (magnetic media, adhesive
tape)
• Pharmaceuticals (tablet coating, fluid bed drying, )
• Rubber (offset printing blankets, gloves, gaskets)
• Waste water treatment (Solvent removal)
• Remediation-Remediation (soil vapor extraction;
air strippers)
• HAP emissions abatement
• SVC Carbon Canister
Current PID Products Model 201W and low cost
Model 112 NEMA 4

11. Early History of the PID
• 1973- Started HNU Systems with the concept of developing
photoioniztion based instrumentation for environmental
monitoring
• 1974- Introduced the first portable PID for industrial hygiene
at the AICHE in Miami- Model PI101. The target market was
vinyl chloride where the PEL had been reduced from 500 ppm
to 1 ppm over a period of < 1 year because VC had been
declared a carcinogen.
• 1976-We introduced the first commercial PID for gas
chromatography at Pittcon- PID was 50x more sensitive than
FID for aromatics
• 1976- We introduced the Model 201 continuous PID and one
of the first applications was for carbon bed monitoring

12. Photoionization Process
Compound Ionization Potential
(eV)
Response
Benzene 9.25 High
Carbon dioxide 13.79 None
Carbon monoxide 14.01 None
Methane 12.98 None
Nitrogen 14.54 None
Oxygen 13.61 None
Trichloroethylene 9.00 High
Water 12.35 None
Ionization Potentials of Major and Minor components in Air
R + hv R+ + e -
where:
R = an ionizable species
hv= a photon with sufficient energy to ionize
species R

13. Comparison of 112 & 201 Specs for C Bed Monitors
112
• Specifications
– Single Detector- PID or FID
(total VOC’s)
– Range 0.1 to 3,000 ppm
– Wall mount NEMA 4 enclosure
– 7.5” x 9” x 6”
– Weight 7.5 #
• Options
• 4-20 mA to PLC
• 1 Programmable setpoint
• Expanded logging
201
Specifications
• Multiple Detectors-PID, FID, others
(to 4)
• Range ppb to 5,000 ppm
• Wall Mount NEMA 4
• 17” x 21 x 10” D
• Weight 35 #
• Auto & Remote Cal
• 201 FID has auto restart after flame
out
Options
• 4-20 mA, RS485
• Multiple setpoints –can replace PLC
• Expanded logging
• Direct internet connection
• Multipoint (2-8 points)

14. VP and BP of typical solvents
Shepard, Env.Expo, Boston, MA (2001)

15. What Component Should the Analyzer be
set for?
• The first components to breakthrough are the
most volatile like VCM in the previous slide.
• In the case of gasoline, the component to look for
would be hexane so the Analyzer should be
calibrated for hexane The setpoint for switching
the bed can be determined and programmed into
the analyzer.
• When the setpoint is reached, the contact closure
can be used to turn off the pump and in a remote
location a cell phone can be dialed to notify an
engineer that the bed needs to be switched.

16. Conclusions
• Soil vapor extraction (SVE) is one of the few
innovative technologies that has gained wide
use worldwide.
• This process was used to successfully cleanup
many gasoline stations in the US. The main
drawback is the long time required for the
process.
• The PID has proven to be an effective tool for
monitoring VOC’s from carbon beds.