June 5th, 2001
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