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ORION DEVELOPS PILOT TEST FOR MTBE REMEDIATION
USING IN SITU CHEMICAL
OXIDATION
October
2005
Orion designed and implemented an in situ chemical
oxidation (ISCO) pilot test to evaluate the potential
effectiveness of combined ozone and hydrogen peroxide
injection to treat impacted groundwater.
Orion was retained to study the potential benefit
of ISCO technology for multiple sites impacted by total
petroleum hydrocarbons including benzene, toluene,
ethylbenzene, and xylenes (BTEX); methyl tert-butyl ether
(MTBE); and tert-butyl alcohol (TBA). Orion's goals were to
test the technology effectiveness, collect design data for
full-scale implementation, and develop protocols for future
pilot tests.
Two nested injection wells were installed and
spaced 20 feet apart in anticipation of a 10-foot radius of
influence. Each
well included a deep screened interval for ozone sparging and
a shallow screened interval for hydrogen peroxide
injection. A
PulseOx 100 manufactured by Applied Process Technology, Inc.,
generated and injected ozone, hydrogen peroxide, and
compressed air into the two injection points in pre-programmed
combinations, dosages, and sequences.
The pilot test ran as initially planned for 8
weeks; it was continued for an additional 4 weeks because
TPHg, BTEX, and MTBE concentrations were reduced
significantly.
Groundwater samples were collected 2, 4, 8, and 12
weeks after the pilot test started and analyzed for TPHg,
BTEX, and oxygenates.
Dissolved oxygen (DO), oxidation reduction potential
(ORP), temperature, conductivity, pH, and water levels were
monitored frequently during the pilot test. DO and ORP data
served as field indicators for monitoring the injection system
radius of influence.
By the end of the pilot test, DO had exceeded 20
milligrams per liter (mg/L) within a 15-foot radius of the
injection points.
TPHg and benzene concentrations were reduced by 2 to 3
orders of magnitude.
MTBE concentrations were reduced by 1 to 2 orders of
magnitude.
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The pilot test results provided design criteria for
future tests of this technology. The ISCO pilot test
demonstrated the following
conclusions:
1. Injection of ozone and hydrogen peroxide can
rapidly reduce TPHg, BTEX, and MTBE concentrations within 12
weeks, even within a source area containing over 100,000 ug/L
of TPHg and over 1,000 ug/L of benzene and MTBE.
2. Depending on the site lithology, a pilot test can
generate the data necessary to design a full-scale ozone and
peroxide injection system within 2 to 4 weeks of
operation. Two to
three injection points should be installed to account for
site-specific subsurface variation.
3. Injection of ozone and peroxide may reduce TBA
concentrations, although the rate of reduction within a source
area is slower than for TPHg, BTEX, and
MTBE.
4. The lateral impact of ISCO can be easily monitored
using a downhole DO and ORP probe in nearby observation
wells.
5.
An increase in TPHg and BTEX concentrations may
occur soon after injection begins and after injection ends
(rebound).
This increase is likely caused by
desorption of petroleum constituents sorbed to soil
particles.
6. If a pronounced smear zone is present at a site,
the remediation effectiveness can be increased by (1)
injecting peroxide into the capillary fringe, (2) operating
the injection system to provide controlled fluctuations of
the water table, or
(3) operating the system during periods of seasonally high
water levels.
Presented at the 1st International Conference
on Challenges in Site Remediation, Chicago, Illinois, 23
- 27 October 2005.
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