environmental,soil,engineers,contamination,groundwater,hydrogeologistsTech Focus


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.









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.  Download PDF


Email us for more information at info@orionenv.com.


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Orion Environmental Inc., 2006