In Situ Groundwater Treatment of Arsenic via Iron Coprecipitation with Air Sparge: Opportunities and Challenges

Michael Hay, Arcadis US, Inc.
Britt McMillan, Arcadis US, Inc.
Whitney Sauve, Arcadis US, Inc.
Daniel Groher, U.S. Army Corps of Engineers

Description

Arsenic, an Appendix IV constituent under the Coal Ash Rule, is a common constituent of concern in groundwater at coal combustion residual (CCR) impoundments. Where corrective measures are required, groundwater extraction and treatment is common, but can be costly. In situ treatment methods may be preferred, and environments where dissolved iron co-occurs with arsenic present opportunities for effective treatment. Results of in-situ air sparging (IAS) tests at two case study sites (the Vineland Chemical site in New Jersey and the Shepley’s Hill Landfill in Massachusetts) will be presented. IAS was used to introduce dissolved oxygen into groundwater to facilitate iron oxidation and arsenic coprecipitation. Although IAS systems are robust and show great promise, site-specific factors must be considered, such as aquifer pH (which influences iron oxidation rates), the dissolved iron to arsenic ratio, and soil and aquifer characteristics which must be conducive to air distribution. For example, whereas the source of iron and arsenic at Vineland is within the effective sparging zone, the greatest iron and arsenic concentrations at Shepley’s Hill are just above bedrock and necessitate alternative oxygen delivery strategies yet to be determined. A summary of remedial performance and lessons learned at these sites will be presented.

 
May 14th, 2:30 PM May 14th, 3:00 PM

In Situ Groundwater Treatment of Arsenic via Iron Coprecipitation with Air Sparge: Opportunities and Challenges

Grand Rapids, Michigan

Arsenic, an Appendix IV constituent under the Coal Ash Rule, is a common constituent of concern in groundwater at coal combustion residual (CCR) impoundments. Where corrective measures are required, groundwater extraction and treatment is common, but can be costly. In situ treatment methods may be preferred, and environments where dissolved iron co-occurs with arsenic present opportunities for effective treatment. Results of in-situ air sparging (IAS) tests at two case study sites (the Vineland Chemical site in New Jersey and the Shepley’s Hill Landfill in Massachusetts) will be presented. IAS was used to introduce dissolved oxygen into groundwater to facilitate iron oxidation and arsenic coprecipitation. Although IAS systems are robust and show great promise, site-specific factors must be considered, such as aquifer pH (which influences iron oxidation rates), the dissolved iron to arsenic ratio, and soil and aquifer characteristics which must be conducive to air distribution. For example, whereas the source of iron and arsenic at Vineland is within the effective sparging zone, the greatest iron and arsenic concentrations at Shepley’s Hill are just above bedrock and necessitate alternative oxygen delivery strategies yet to be determined. A summary of remedial performance and lessons learned at these sites will be presented.