SOIL BIOREMEDIATION: How Long Does It Take?
CUTTING THROUGH THE CONFUSION AND HYPE
The idea that one might be able to spray a simple liquid across contaminated
soil to make hydrocarbon pollution disappear is an alluring one--particularly
for building owners seeking to avoid otherwise massive cleanup costs. And, it
is an allure that has been widely abused. Over the years, numerous short-lived
bioremediation contracting companies have made all manner of ridiculous claims
as they've conducted bioremediation projects that have been complete disasters.
Bioremediation Scams
During the early 1980s the financial press was filled with hyper-excited reports
about the profit-making potential of the oil-eating "super bugs" that they predicted
would be perfected by the emerging new "biotechnology" business. Throughout
the rest of the decade legions of fly-by-night local entrepreneurs sought to
exploit this publicity by offering all manner of treatments they called "bioremediation."
However, these treatments--usually sold for tens of thousands of dollars by
individuals who demanded advance payment from owners of heavily-polluted industrial
and commercial properties--often involved little more than water and a cheap
surfactant sprayed across the surface of the ground. Many scam artists claimed
their "treatments" would eliminate all petroleum pollution in a few days. Some
even promised "overnight" results. This sort of unscrupulous hucksterism resulted
in a large number of failed bioremediation projects and a growing sense of general
skepticism about the process. Ironically, at the same time, the legitimate microbiological
scientific community was achieving the major breakthroughs that actually made
industrial-grade bioremediation a practical reality.
Science, Not Magic
Bioremediation is a scientific procedure, not a magical cure-all. No bioremediation
material or method can eliminate a petroleum pollution problem overnight or
in a few days. Bioremediation is a process with variables and limitations that
must be appreciated before it can be used successfully. One major reason for
failure in the past has been the use of ineffective materials. Another has been
unrealistic expectations.
What to Expect
How long does it really take to lower petroleum pollution levels? In a properly
executed soil bioremediation project, you should generally be able to document
dramatic reductions in Total Petroleum Hydrocarbon (TPH) levels in a period
of time ranging from 90 to 150 days. Bioremediation moves much quicker in a
water environment where significant reductions can often be documented in a
few weeks.
But the exact time it takes to lower a given parts-per-million (ppm) level
of hydrocarbon pollution to an acceptable level varies widely. It depends on
the type, concentration, viscosity and age of the hydrocarbon pollutant as well
as specific site conditions, including temperature, weather and soil or water
chemistry. It also depends on what "acceptable" means. For instance, for owners
trying to sell a downtown commercial site in some states, the only "acceptable"
level might be less than 10 parts-per-million of TPH. On the other hand, petroleum
refineries in heavy industrial areas may need to lower very high levels of soil
pollution, say 60,000 parts per million, to a moderate level, say 10,000 parts
per million, to meet minimal site closure requirements.
Actual Project Results
Here are four examples of real time results achieved in recent typical soil
projects with standard commercial materials and methods:
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Tank Pull Site
3,000 cubic yards of gasoline contaminated soil tested out at 2,000 ppm.
Standard bioremediation inoculation methods and materials were used on soil
staged four-feet deep. The 2,000 ppm was dropped to 50 ppm in 160 days.
-
Industrial Plant Property
4,000 cubic yards of soil contaminated with a mixture of diesel and waste
oil that tested out at 1,000 ppm. The soil was treated in an 18-inch-high,
land farmed layer with standard bioremediation materials. The final sampling
and analysis at 120 days documented a non-detectable level of TPH.
-
Commercial Store Property
5,000 cubic yards of soil contaminated with diesel and waste oils located
at a bank-owned property. Using standard bioremediation materials and surface
land farming technique, the contamination levels were lowered from 500+
ppm to 17 ppm in 65 days.
-
Refinery Facility
10,000 cubic yards of soil contaminated with multiple hydrocarbon products
at an Exxon production site. Project goal was to lower 75,000 ppm to closure
requirement of 10,000 ppm. That closure level was documented in tests 150
days after treatment began with a normal mix of microbes, nutrients and
biological catalysts. This level could have been lowered further with additional
treatment over a longer period of time, but there was no incentive for Exxon
to do so inasmuch as it met minimum legal requirements once 10,000 ppm was
reached.
Continuing Controversies: Augmented versus Non-Augmented Bioremediation
It's important to point out that the above results were achieved with bioremediation
mixes that included concentrated, broad spectrum hydrocarbon-oxidizing microbes
as well as nutrients and biological catalysts. Further confusion about bioremediation
has recently been introduced as a growing number of companies offer "bioremediation"
materials that contain no microbes. These materials consist of various sorts
of chemicals, like surfactants, solvents and industrial-grade fertilizers, that
are sprayed into the ground and are supposed to facilitate action by "indigenous"
microbes already present in the soil.
These non-microbial methods have several serious drawbacks. For one thing,
they assume that a broad-spectrum of specialized hydrocarbon-oxidizing microbes
are hibernating in soil everywhere. This is not the case. For another thing,
the actual chemical substances can be dangerous to humans. For instance, during
the clean up of the Exxon Valdez spill in Alaska, a major test of such materials
resulted in chemical burns and blisters on the arms and faces of the workers
who applied them to polluted beaches.
Some officials now speak of "augmented" and "non-augmented" bioremediation
systems. "Augmented" bioremediation is the same as that described in this Web
Site--it involves adding substantial quantities of concentrated, broad spectrum
hydrocarbon-oxidizing microbes to the soil, or biologically "augmenting" the
soil.
"Non-augmented" bioremediation involves various experimental chemical systems
that do not include microbes. Instead, they attempt to activate whatever colonies
of local microorganisms might be present in the soil in the hopes that some
of those may be able to degrade some portions of the hydrocarbon pollution.