Because ether- and alcohol-based oxygenates exhibit different properties (specifically, Henry's law constant) than other common fuel contaminants such as BTEX, their presence may affect the size and design of the air sparging system required to remediate the site and, as a result, the cost of remediation. Research has shown that the removal of MTBE (ether-based) requires 5-10 times more airflow than used for BTEX alone.38 The other common ether-based oxygenates have higher Henry's law constants than MTBE and are theoretically more amenable to treatment via air sparging (although still less amenable than BTEX components). The common alcohol-based oxygenates have Henry's law constants two to three orders of magnitude lower than those of the ether-based oxygenates, and may theoretically require 100-1000 times greater airflow. In practice, air sparging may not be feasible if high enough airflow rates cannot be achieved without causing unwanted subsurface fracturing or contaminant mobilization. However, the biodegradation potential of both ether- and alcohol-based oxygenates will also influence system design and may reduce the airflow and time required for remediation.
In addition to the oxygenate-specific factors described above, additional variables may also affect the performance and cost of an air sparging system. These factors include the concentration, mass, and distribution of contaminants in the groundwater; subsurface geology and hydrogeology; cleanup goals; and requirements for site cleanup. For example, heterogeneity within the subsurface may result in preferential pathways that prevent injected air from contacting contaminated areas. These factors affect the number and spacing of air sparging wells, flow rates, and the length of time required for treatment, which typically will be determined during pilot testing. Air sparging also has potential to cause a lateral spread of dissolved or separate phase contaminant plumes. For example, in formations with laterally oriented clays interbedded with sand, there is a possibility of spreading the contamination when using air sparging.
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