This study evaluated air sparging at ten ongoing air sparging sites. The main objective was to demonstrate the Air Sparging Design Paradigm for effectively evaluating air distribution. The goal was to validate the design guidelines and modify the Paradigm as necessary based on site results. Air sparging is a treatment process where air is injected directly into the saturated subsurface to either volatilize contaminants for treatment or biodegrade contaminants via oxygen stimulation. The use of air sparging has increased rapidly since the early 1990s; however, current approaches must consider process complexity and design and operating conditions. Also, further demonstration of air sparging monitoring techniques at different sites was needed to validate their application and promote their regulatory acceptance.
The level of effort varied for the ten sites. A full-scale air sparging system was installed at one site, extensive diagnostic tests were conducted at four sites, and minimal diagnostic tests were conducted at five sites. Diagnostic tests included pressure response testing, deep vadose zone helium tracer testing, and dissolved oxygen monitoring. Based on all diagnostic tests, the data indicated that the sparging systems were operating inefficiently at three sites because of their inability to reach the entire target treatment zone. It was determined that the 15-feet well spacing recommended in the Design Paradigm would have been adequate to achieve acceptable target zone treatment at all sites. Also, poor instrumentation and monitoring compromised the effectiveness of many of the sparging systems. Proper air flow monitoring of each injection well is important for measurement and verification of the system.
There are currently no effective in-situ remediation technologies that can completely remove or destroy groundwater contaminants. Air sparging has become a commonly used in-situ solution for the treatment of hydrocarbon-impacted aquifers, particularly for petroleum hydrocarbon source zone remediation. The cost benefits of air sparging were compared to the use of sheet piling and removal of contaminated soil and groundwater for remediation of a petroleum hydrocarbon source zone. The total cost for the sheet piling installation with removal of contaminated soil and groundwater is approximately $900,000, with a unit cost of $474 per cubic yard and a total estimated remediation time of approximately 10 weeks. The cost for air sparging using the same site specific assumptions is approximately $268,000, with a unit cost of $141 per cubic yard and a total estimated remediation time of approximately two years.
Air sparging has been widely used at Department of Defense installations for many years; however, design practices and performance have varied during this time. Air sparging has gained widespread acceptance as a remedial alternative, and a more standardized approach will assist environmental managers to evaluate the usefulness of air sparging at their particular site. Air sparging generally results in lower remediation costs, assuming the air sparging system is correctly designed and operated. Air sparging is also less intrusive than removal of soil and groundwater but takes longer to achieve the desired remediation goals. (Project Completed - 2002)