Ozone Case Study
Historic activities at the site involved degreasing and industrial clean-ing service using solvents, primarily tetrachloroethene (PCE) and trichloroethene (TCE) to support the growing aerospace industry in Southern California. Site investigations indicated the presence of volatile organic compounds (VOCs), including. PCE, TCE, cis-1,2-dicloroethene (1,2-DCE), 1,1-dichloroethane (1,1-DCA), 1,1-dichloroethene (1,1-DCE), 1,4-Dioxane and methylene chloride. Be-ginning in 2002, source removal occurred using soil excavation, as well as single and multi-phase extraction. Groundwater remediation began in 2004 using liquid oxidant injections and later achieved final closure levels using ozone gas injection.
Previous Remediation Efforts
Initially 822 tons of contaminated soil were removed by excavator and bucket auger. Starting in 2004, a multi-phase extraction (MPE) system was installed as an interim remedial measure. Between April and December 2004, approximately 16,000 pounds (lbs) of VOC’s were removed from the vadose and shallow groundwater zones. In October 2004, a remedial action plan and WDR permit were approved to inject sodium and potas-sium permanganate. The liquid oxidant materials were injected at approximately twenty-six (26) Geoprobe locations between depths of 65 and 75 feet bgs. Dissolved-phase VOC concentrations were reduced by 1-to-2 order of magnitude, but still remained elevated (500 to 5,000 ug/L). Additional groundwater remediation was necessary on-site and immediately down gradient.
To build upon and exceed the successes of previous remediation technologies, Piper Environmental Group was contacted to supply an integrated rental ozone system large enough to achieve site closure. Piper’s 28 pound per day (PPD) ozone system was selected for in-situ chemical oxidation based on several factors: first, ozone gas has a high oxidation potential and the ability to penetrate finer-grained aquifer materials where residual contamination is often locked; sec-ond, Piper’s unit generated higher ozone delivery than other vendor equipment available for rent; lastly, based on ease of implementation and cost (as an expense item and not capitalized) and most importantly, the ability to reach site closure quickly. The system was pre-built at Piper’s manufacturing facility and tested before it was shipped to the site. The system was then re-assembled on-site which allowed for immediate use. Unique to this site was the need for angled injec-tion wells that reached underneath occupied resi-dences. Ozone was injected into the saturated and capillary fringe zones.