|
Keep
on truckin'
Decontaminating beneath a
truck stop - while the trucks keep running
|
|
An Indiana truck stop needed to clean up two major fuel leakage plumes
at its huge overnight parking, repair and refueling site. But its owners
didn't want to close down while the work was being done.
One problem was leakage from old gas tanks that had seeped into the ground
water. The other was oozing from another underground storage tank 300 feet
away. This second plume had settled in the vadose
zone, the subsoil area sandwiched between the concrete parking lot and the
water table.
The site was to be cleaned up under a State of Indiana environmental
management program. But it was imperative to the owners that the
eighteen-wheelers keep running while the remediation went ahead.
Lee and Ryan Environmental Inc. of Indianapolis and Muncie, Indiana, was
chosen to investigate the site, conduct a site assessment, install test
borings, and ultimately, recommend a remediation action plan and implement
it.
One site, two methods
"There were two areas on the same site that required two different
methods of extracting the pollutants," says Jeff Fiscus,
project manager for the site. "To deal with the ground water
contamination, dual phase vacuum extraction wells would be installed."
For this ground water problem four vertical wells were drilled 15 feet deep,
where the test borings had been located. Liquid from these wells would be
extracted and piped approximately 300 feet to a building housing pumps,
compressors and extraction tank. The effluent would be run through granulated
activated carbon that would soak up and collect the hydrocarbons. When the
liquid was clean, it would be discharged.
For the second, larger, spill, bioventing - or air
injection - would be used. With this process a powerful pump and compressor
system pumps high-pressure air through slotted horizontal wellscreens
placed in the plume. The polluted area was directly below the parking lot
leading to the truck fuel lanes, so neither numerous vertical wells nor raw
excavation would work if the truck stop was to keep running.
Lee and Ryan Environmental's test boring showed
that the problem in the vadose zone went no deeper
than six feet below the parking lot. At this shallow depth, injecting air
would re-oxygenate the subsoil, stimulating naturally occurring microbes to
feed on the hydrocarbons and biodegrading the pollutants. Other carbon
molecules that the forced air lifted from the soil would rise, seep through
the cracks in the asphalt and concrete, and evaporate.
To install and develop the wells, Lee and Ryan Environmental brought in
Directed Technologies Drilling Inc. (DTD) out of
Tacoma, Washington. Led by Jim Doesburg, DTD has installed horizontal remediation wells on more
than 250 projects in the United States, Japan, the Czech Republic and Poland.
DTDs horizontal directional drilling effort was
supported by Dave Wampler of Jackson Creek Enterprises based in Allerton,
Iowa. Since his crews were busy on another project, Wampler secured local
equipment, including a Vermeer D33x44 Navigator horizontal directional
drilling rig to install over 2000 feet of horizontal wellscreens.
The drill would also handle the tie-in lines from the pump house to both the
vertical and horizontal well sites on the property.
Getting air to the problem
Once all the buried utilities, old septic systems and abandoned
concrete-filled tanks had been located and marked, drilling could being.
Three horizontal wells were to be installed to handle the polluted vadose zone soil under the parking lot and fuel lanes.
Two of the wells would be 190 feet long, placed 80 feet apart, and there would
be a smaller third well 70 feet long. Each of the wells would be six feet
underground, and ultimately connected with a manifold system. The underground
area surrounding each well that would be reached by air injected under
pressure would be roughly 35 to 50 feet.
According to Doesburg, the design of the slotted HDPE wellscreens was crucial to
getting constant air flow into the earth. "Slots were pre-cut into
4-inch-diameter HDPE pipe. They were more numerous
the further away that part of the well was from the blower motor. This was so
the air flow into the soil would be the same as it was through pipe closer to
the blower."
The installation operation started by cutting small four-foot square entrance
and exit pits through the six-inch asphalt overlay and the cracked six-inch
concrete base below it. Those pits were cut and excavated 20 feet in back and
beyond the intended location of the slotted wellscreens
so that the drillers could have the wellscreens at
a constant 6-foot depth throughout their run. The HDPE
for these front and back 20-foot sections would not be slotted so that the
air would only be injected into its target area.
CETGO Clean Drill was mixed with water in two
Vermeer ST750A mixing systems and used as the drilling fluid. This fluid had
some essential properties. When installing horizontal remediation wellscreens, whether for bioventing,
air sparging, soil vapor extraction or groundwater
extraction, the drilling fluid has to create the bore wall and suspend
cuttings. But it also needs to break down and biodegrade so that the injected
air can get through the wellscreen into the
formation.
"The problem with using clay-based bentonite
for environmental wells is that the same mechanism that helps keep the
drilling fluid in the hole is that which would prevent the air from getting
to where it's supposed to work," said Doesburg.
"A biodegradable drilling fluid breaks down so that after the horizontal
well is in the ground there won't be any barriers to proper flow. With this
product all we had to add was a little non-caustic enzyme to our flushing
process to speed up the degradation of the drilling fluid."
'Environmental' difficulties
The main challenge with the pilot boring of the wellscreens
was not so much the ground conditions but the surrounding environment. There
were 150 semis a day coming through the fuel lanes and into the parking lot
where the crew was working. According to Wampler, the biggest problem was not
congestion but locator interference.
"We used a DCI locator with a 30-foot sonde,
and sometimes we would have only a 10-foot-wide lane to work in with semis
frequently on either side," explained Wampler. "There was an
incredible, never-ending amount of signal interference from all the metal on
those trucks that acted like an antenna. When the signal came up, it jumped
to steel on the semis and bounced around. Then, there was the interference
from the electronic ignition on the trucks, which registered the same
megahertz as the sonde."
During the drilling and subsequent pullback, all cuttings were vacuumed into
a 3000-gallon truck and taken to an environmental landfill. The drilling crew
successfully drilled the pilot bores, pre-reamed with a 6-inch Vermeer
super-helical reamer or fluted reamer and pulled in the wellscreens.
At the far end of each wellscreen, a shale trap
packer was placed around the pipe. Shaped like a large dunce cap, twice the
diameter of the pipe, the unit is a rubber funnel that hose-clamps to the
pipe and seals off the borehole so air won't leak out.
Once the wellscreens were in, there was still
roughly 1,400 feet of conveyance or tie-in drilling to do, with the
subsequent pulling in of non-slotted 4-inch-diameter HDPE
pipe. These lines would connect all three wellscreens
with the pump house as well as tie in the vertical wells. Each of the four
vertical wells had an individual line to the pump house between 350 and 380
feet in length.
Wampler said later that being able to constantly monitor the mud flow on the
Navigator helped avoid any frac-outs. That, he
said, eased his fears of a nightmare scenario. A frac-out
in an environmental area has to be cleaned it up, and it has to go to an
environmental landfill. And if that frac-out
happens during the installation of a wellscreen,
the odds are air will also frac-out, ruining the
integrity of the remediation. Then, of course, there's the original job to go
back to and finish.
The clean-up process is expected to be ongoing for two and a-half years.
Edited from a story written by Richard Yach for
Vermeer Manufacturing Company.
|