In-well air stripping
- The system consisted of a single well casing installed into the contaminated saturated zone, with two screened intervals below the groundwater table, and an air injection line extending into the groundwater within the well. The stripped VOC vapors were removed by a vacuum applied to the upper well casing and treated using a flameless oxidation process.
- The recharge screen was located in the saturated zone, rather than the usual location in the vadose zone, because of the presence of a hydraulic barrier between the vadose zone and the intake screen, which could adversely affect the groundwater circulation through the system.
- Effluent air flow rate from the well ranged from 50 to 69 scfm.
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- 1,1 DCE - 3,530 µg/L, cis-1,2-DCE - 45,000 µg/L, TCE - 1,650 µg/L
Wastes from various operations at the base
Type/Quantity of Media Treated:
Purpose/Significance of Application:
Field demonstration of in-well air stripping to treat groundwater contaminated with high levels of VOCs
Regulatory Requirements/Cleanup Goals:
- Objectives of demonstration included assessing the technology's ability to treat groundwater contaminated with high levels of chlorinated VOCs
- Total estimated VOC removed during demonstration - 92.5 pounds; average total VOC mass removed ranged from 0.01 to 0.14 pounds per hour
- The mean concentrations of contaminants in the treated water discharged from the system: 1,1 DCE - 27 µg/L, cis-1,2-DCE - 1,400 µg/L, and TCE - 32 µg/L
- Measurable pressure changes occurred at crossgradient locations 30 feet from the well
Fouling from iron precipitation and biological growth occurred, reducing pumping rates significantly. Iron precipitation was reduced by adding citric acid, but biological fouling was not successfully controlled.
- Projected capital costs for a full-scale single system - $190,000; projected annual O&M costs - $160,000 the first year, and $150,000 per year thereafter
A demonstration of in-well air stripping was performed at the NAS North Island, Installation Restoration Site 9 to assess the technology's ability to treat groundwater contaminated with high levels of chlorinated VOCs. The project was conducted under EPA's Superfund Innovative Technology Evaluation (SITE) program in conjunction with EPA's Technology innovation office, Naval Facilities Engineering Command Southwest Division (SWDIV), Navy Environmental Leadership Program, and Clean Sites, Inc.
During the demonstration, in-well air stripping removed an estimated 92.5 pounds of VOCs. The remediation at this site was challenging because the groundwater contained total dissolved solids (TDS) concentrations ranging from 18,000 to 41,000 mg/L, which are higher than those typically found in drinking water aquifers. Operational difficulties associated with biofouling and the precipitation of iron resulted in an incomplete evaluation of the technology.