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By Gene Rotter of Shields,
Harper & Co. |
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Designing an Earthquake-Proof
Storage System at the Airport in
the Bay |
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Eight competitors
in the car rental marketplace took a break from the battle
for customers at San Francisco International Airport long
enough to cooperate in a major project that is unprecedented
in scope and attention to the task of leak prevention.
The puzzle was to design and build side by side off-airport
operations for the eight car rental companies (Hertz,
Avis, Alamo, Budget,Thrifty/Enterprise, National and
Dollar Rent-A-Car) that will satisfy all of their current
needs but still allow expansion or contraction independently
as market share grows and diminishes for those companies.
Add to those wishes the requirements of five major regulatory
agencies: the United States EPA, California Water Resources
Control Board, California Air Resources Board, San Mateo
County Environmental Health Department and the San Francisco
International Airport Commission and you get 13 entities
all wanting their needs satisfied. Believe me, as we
proceeded with this project, I often thought about the
number and wondered if there was any such thing as "luck." |
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Water, water everywhere |
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For those of you who have had
the fortunate experience of visiting or "City by the
Bay," you may remember that the airport is actually in
the Bay....having been built partially on landfill. The Bay
itself forms the entire northern, eastern and southern boundaries
of the airport, and the Pacific Ocean is just six miles to
the west. As many people know from television coverage of
the earthquake we had nine years ago, much of the fill land
in the Bay area can be quite unstable. Additionally, the site
has a very high water table (approximately six feet from the
surface).
If all that doesn't satisfy your definition of a challenging
design and construction task, add the requirement that
this project had to be coordinated with the design,
building and completion of a monorail being built to
connect the new car rental facility to the airport terminals.
Not related to this project, the airport is also building
a new international terminal; a Bay Area Rapid Transit
(BART) station; several new elevated roadways that connect
to the Highway 101 freeway near the airport; and finally
a new airport rail transit system to connect the new
international terminal with the parking garages.
All of the construction activity at the same rime and in the
same place made this project seem even bigger than it already
was. Photo
1 will give you and idea of how this construction activity
looks from the air.
The consortium of car rental agencies chose RHL Design Group
of Petaluma, California as the architectural and engineering
firm for the project. The airport commission mandated that
the underground storage tanks be of triple wall fiberglass
construction because of the potential for earth movement,
both from the earthquakes (California has hundreds of them
each month...mostly tiny ones) and the vibrations that might
be caused by the monorail. RHL Group, in turn, chose our company,
Shields, Harper & Co. of Oakland, California to consult
and supply equipment for the project |
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Triple Wall Tanks |
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Because of the requirement
for triple wall fiberglass tanks as well as the length
of some of the piping runs, the selection of equipment
and monitoring methods posed still other considerable
challenges. Many leak detection devices do not have
third party approvals for either triple wall systems
or long pipe runs. As a result, several manufacturers
were consulted about their ability to customize their
product for the special requirements impose by the environmental
and regulatory requirements.
After consultation with development engineers from Containment
Solutions, Inc. (formerly Fluid Containment and Owens Corning
Tank Division), it was determined that triple wall tanks could
be built that would be monitored hydrostatically. Hydrostatic
monitoring is the method in which the cavity between the tanks
walls, sometimes call the interstitial space, is filled with
a liquid brine solution. The tank maker then builds a reservoir
on the top of the tanks where the level of the brine solution
can be monitored.
In the case of triple wall tanks, there are two reservoirs
to monitor the two interstices. As shown in Photo
2, each reservoir is on the outboard side of a manway
containing fittings. Able to hold up to five gallons of liquid,
the reservoir is normally only half filled and contains a
sensor that can determine if the monitoring liquid is rising
or falling.
There are 14 triple wall tanks serving the needs of the eight
companies. Eleven of the tanks are 12,000 gallon and three
are 15,000 gallon. Each tank has two manways in which all
of their four inch openings are located. The manways are contained
with 48 inch containment collars. The 48 inch diameter sumps
manufactured by Western Fiberglass are nearly seven feet deep,
and continuously wound for extra strength. One manway contains
the fittings for the fill and vapor recovery, while the other
contains fittings for the tank gauge, turbine pump, vent and
vapor opening. These features (except for the sumps) are shown
in Photo
2. |
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Tank installation |
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Since 14 tanks
needed to be installed in one big wet hole right next to the
monorail line, RHL Group decided that shoring would be critical
in the hole. RHL used heavy duty interlocking zee type steel
shoring that extends as deep as 50 feet below grade in several
locations around the hole.
Twelve inch I-beams were attached horizontally at five
levels around the hole. The shoring then had to be jacked
apart (width-wise) so that 12 inch diameter steel pipe
could be used as crossed braces between opposing I-beams.
The cross braces were welded to the I-beams, which had
been held in place by pressure when the jacks were released,
This formed a giant steel cage into which the tanks
were inserted. Photo
3 shows the excavation and shoring.
Four wire braid straps, as shown in Photo
4, anchored each tank to the lower cross braces so that
the tanks would stay in place until the 12 inch concrete slab
was poured above them. The straps hold the tanks in place
by attaching to the cross braces that were left in place along
with the shoring when the tanks were buried.
Once the slab was installed over the hole, the straps were
no longer needed to hold the tanks in place. Nonetheless,
abandoning the shoring and straps in place was determined
to be the most effective mettles of doing the installation.
From grade to the bottom of the tanks is approximately 17
feet. The tank hole itself was 165 feet long and about 3 feet
wide at the widest point (see center area of Photo
3). All the tanks are 10 feet in diameter. The 12,000
gallon tanks are 23 feet, 8 1/2 inches long and the 15,000
gallon tanks are 29 feet 2 inches long. |
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Piping installation |
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Once the tanks were set, the
contractor (Kvaerner Aronson of Sacramento, California) faced
the task of installing nearly 2 1/2 miles of double contained
piping, about half of which is shown in Photo
5.
Since union labor needed to be used, a call was sent to the
hiring hall every day--and every day a new (different) crew
was dispatched to the site. Each of the crews was trained
on site by the contractor's staff and Western Fiberglass representative,
Ron Trengove. It took more than two months to connect the
piping. Trengove said he had no trouble working with the members
of the plumbers union who learned their tasks quickly and
provided many helpful suggestions during the installation
process.
The rental car companies selected Co-Flex brand flexible Furon
piping because of its coaxial design. This piping was one
of the only products with that feature when the selection
was made in the summer of 1997. The double walled pipe was
installed inside a "RockGard" which is a protective,
corrugated PVC pipe that doubles (or should I say "triples")
as an additional level of containment. Photo
6 is a closer view of the piping run.
Although the longest pipe run is about 900 feet, the longest
continuous length is much shorter-"only" 210 feet.The
piping enters multiple four foot deep transition sumps along
the main raceway, which itself is more than 20 feet wide (see
Photo
7).
The transition piping sumps, custom designed by Western Fiberglass,
are four foot deep to allow the piping to maintain slope.
The sumps were designed to allow field installation of fiberglass
panels that divided the interior of the sumps into separate
sections so that each pipe that entered and exited the sump
could be monitored separately. Some sumps contain as many
as five lines entering near the bottom and exiting more than
three feet higher with a separate discriminating sensor for
each line. |
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Leak detection and monitoring |
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Twenty fueling islands with
60 dispensers are located perpendicular to the raceway. Most
of these are visible in Photo 7. Each time a section of piping
was completed (from sump to sump and sump to dispensers),
the local regulators came out and tested both the primary
and secondary pipe for tightness.
Each car rental agency has its "own" fuel tanks
and piping, so each is responsible for monitoring for any
leaks in its own system. Therefore, each company has its own
tank gauge system with leak monitoring sensors. The tanks
have sensors in the hydrostatic reservoirs of the annular
spaces. Every one of the 29 transition sumps has dividers
installed between the individual pipe runs; and each of those
sections is monitored by a discriminating sensor that can
detect the presence of either water or fuel. This allows each
car rental company to monitor its own tanks and piping even
though the car rental companies share a common tank hole,
pipe runs and sumps.
The tank and piping sensors are connected to Veeder Root TLS-350
consoles, as are both the sensors in the vapor recovery system
and the sensors below the dispensers. Each of the car rental
agencies has located these consoles in their on-site office
(see Photo
8). To monitor the piping, 230 discriminating sensors
were needed.
Hertz has the largest portion of the facility at the present
time and uses four of the 14 tanks. Since its location is
the farthest away from the tanks themselves, Hertz has longer
pipe runs and more sumps to monitor than any of the other
companies. This meant that Hertz needed two TLS-350 monitors
to monitor the eight interstitial spaces, four tank level
probes and more than 60 locations in the piping and vapor
recovery runs as well as the underpump dispenser sumps.
When any of the sensors show a fuel or high water alarm, the
stem provides for positive shut-down of the submerged pumps.
An alarm will sound only in the proper agency's office for
any one of the lines or tanks in any of the transition sumps
or dispenser sumps. Other tanks in the same tank hole and
other lines in the same raceway and even in the same transition
sump will continue to function while the source of the alarm
is checked. |
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Other major decisions |
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In addition to the slabs covering
the dispensers and piping raceway, a slab around the dispenser
islands of 300 x 700 feet will be poured in the coming months.
The slab around the dispensers will be 16 inches thick. RHL
Group expects 21/2 to three inches of settling during the
first two years. Most of this will occur during the first
year to 18 months.
Since the settling will be uneven and unpredictable, it wasn't
possible to use hard piping under this slab.That is why flexible
piping was selected for both product piping and vapor recovery
piping.
All of the Tokheim commercial dispensers are outfitted with
a "balance" vapor recovery system. Shields, Harper
has been advising customers in California to use balance systems
rather than vapor assist systems for the last several years;
one reason being that onboard vapor recovery systems (ORVR)
in new vehicles tend to be incompatible with existing vapor
assist systems.
In choosing a balance system for this project, vapor pots
needed to be installed and monitored. Vapor pots are required
since, with balance systems, the slope of the vapor recovery
pipe cannot be maintained all the way back to the tanks. Therefore,
condensation must be collected and monitored.
These vapor pots collect condensation and are connected to
Red jacket submerged pumps. The pumps siphon back any collected
liquid into the pumping system. RHL Group members consulted
with Red Jacket engineers on their ability to do this task.
The Red jacket engineers recommended the use of two HP CPT
(constant pressure turbine) submerged pumps, which were used
in this project. ,
Because of the distance from the tanks to the dispensers and
the number of nozzles served by those tanks, five of the 14
tanks have two turbines installed to service the same two
inch line. It is expected that under the most adverse circumstances,
flow rates of six to eight gallons per minute can be maintained. |
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Monitoring the progress |
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The size of this project alone
makes it unusual. The fact that the tanks are triple wall
and that the piping is double wall contained inside of a third
pipe made the monitoring an exceptional challenge. In California,
the local regulatory agency (city or, county) is responsible
for implementing both the state and federal regulations and
therefore was an integral part of the planning process. Environmental
health officials from the County of San Mateo were involved
each step of the way in the decision making process since
no other installations like this exist in the immediate area.
Regulatory and environmental agencies are expected to work
together-but not necessarily private sector competitors. The
most unusual aspect of this project revolved around the cooperation
of the car rental agencies to accommodate the airport commission,
which owns the land, and is responsible to the public.
A trustee account was established for funds to be deposited
by the car rental agencies in proportion to each of their
market share. When an expense was incurred, such as a bill
for tanks, other equipment, concrete, labor, etc., a check
was issued from the trustee account. This was done instead
of forcing the suppliers to attempt to bill each agency according
to their respective percentage. This allowed the eight companies
to share one design firm, one, equipment supplier and one
contractor.
As unique as the design and features of the fueling site itself
have turned out, the cooperation and method of accomplishing
the task among the car rental agencies are the two most unusual
aspects of this project.
For those of you planning to visit the Bay Area next year
or in the future, plan on renting a car so you can ride the
monorail to the facility. There you will get a sense of the
San Francisco Airport and its joint car rental project all
for yourself. |
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Gene
Rotter is a Shields, Harper District
Manager. He has extensive industry experience as a construction
manager. |
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Read
Bart Scowley's "CARB Goes Back to Drawing Board" |
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This article re-printed
by permission of Petroleum Equipment & Technology. |
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