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By Bettina Boxall
Los Angeles Times
December 22, 2006
Los Angeles
has a plan for getting rid of some of the city's sewage sludge
that nobody wants in their backyard — bury it a mile below
Terminal Island in a sandstone formation.
In what is believed to be the first project of its kind, the
city has won federal environmental approval for a five-year
experiment to inject as much as 400 tons of treated sewage
sludge a day into a depleted oil field deep in the Earth.
If successful, officials said, the program could become not
only a national model but would give Los Angeles more ways to
dispose of one of its least desirable products.
Virtually all of the city's treated sewage sludge now goes to
a city-owned farm in Kern County, where voters issued an
emphatic return-to-sender statement earlier this year when
they approved a ballot measure that banned the sludge dumping.
The move was put on hold by the courts, but the city wants to
develop other options.
"For many years, we've been putting too many eggs in one
basket and it's ultimately our intent to diversify our program
to the best we can," said Omar Moghaddam, regulatory
affairs manager for the city's public works department.
Oil companies have long disposed of oil field waste by
injection drilling. But, Moghaddam said, this will mark the
first time that treated human waste will be pumped so far
below ground.
The sludge, which will be mixed with treated wastewater to
produce a slurry, will seep into porous sandstone and
decompose, producing methane gas and carbon dioxide. The
methane would be extracted to produce energy for the sewage
treatment plant on Terminal Island and the carbon dioxide
would remain sequestered below ground, reducing emissions of a
greenhouse gas.
All in all, it could be an environmental trifecta.
"We are very excited about it. It is a project that has
been in the works for a number of years," said David
Albright, a regional manager with the U.S. Environmental
Protection Agency, which recently issued a permit to the city
to conduct the experiment. "It is a very sophisticated
project. We certainly feel like the time has come to test this
technology."
Albright said there was no significant opposition to the EPA
permit, which the city applied for in 2001.
Deep-well injections can pose a threat to groundwater, but
Albright said there would be no fresh water at that depth. The
injection would occur at least half a mile below the nearest
water table, Moghaddam said, and that is contaminated with
saltwater.
In addition to the injection well, which would be lined with a
metal casing, the city will operate two monitoring wells.
If successful, Moghaddam said, the process could be used in
depleted oil fields anywhere. "This very much can be a
showcase for the entire nation," he said.
The methane could produce enough energy to power 3,500 homes,
while the carbon sequestration would cut carbon emissions by
81,000 tons a year, he said.
Los Angeles sewage treatment plants produce about 730 tons a
day of sludge, which is trucked to the city's Green Acres farm
15 miles southwest of Bakersfield. There it is tilled into the
soil and used to grow forage crops for dairy cattle.
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