Case Studies - CA003 - Pneumatic Fracturing & Feroxsm

Hunter's Point Navy Yard, San Francisco, California

In December of 2002, ARS successfully completed the field application of Feroxsm at Hunters Point Navy Yard adjacent to San Francisco Bay. The technology demonstration was selected under the US Navy’s Alternative Restoration Technology Team program which evaluates innovative remediation technologies to expedite regulatory process and implementation at Navy and Marine Corps sites. The objective of the project was to evaluate the applicability of the technology to address source contamination at this and other sites across this military facility, which is to be turned over for civilian use within the near future.

 

TCE, the target compound, was detected at concentrations as high as 88 mg/liter in the groundwater. Other than the high levels of contamination, the site setting and geology also presented particular challenges to the implementation of the technology. The treatment zone resides beneath a warehouse building and extends vertically across a fill layer and the underlying weathered bedrock. The thickness of the fill material, depth to the bedrock and the degree of weathering vary greatly within the treatment area. The ARS field team had to adjust the injection parameters frequently in response to the characteristics of different injection zones. Approximately 16,000 pounds of ZVI powder was distributed across the treatment area via four injection points. Field observations and data showed significant coverage of the injected iron.

 


Pre Injection Contours


Post Injection Contours

Treatment Monitoring Well Data:


Note: 12/01/02 - Baseline sampling one week before injection

Inside Building 272:

Performance evaluation sampling showed significant TCE destruction within three weeks subsequent to the Feroxsm implementation. A 99%-or-higher reduction of TCE was observed in the three hottest monitoring wells within the treatment zone. Groundwater quality data in monitoring wells outside and
beneath the treatment zone show the injection process did not lead to the mobilization of TCE -laden groundwater outside the treatment zone. This was a common concern often voiced in considering injection of reactive materials in a aquifer with high concentrations or product-phase of contaminants. Through careful planning and placement of injection points and use of our proprietary gas-based injection process, ARS can prevent or minimize such occurrences.

The TCE concentrations remained depressed as indicated by long-term monitoring by the Navy's consultant. An expanded implementation of the technology at the site is scheduled for the summer of 2004 to address the larger plume area.

What the Navy has to say about this project:

Zero Valent Iron (ZVI) Injection Technology Demonstration

Southwestern Division and NFESC recently demonstrated the use of zero valent iron (ZVI) for removal of chlorinated hydrocarbons at Hunters Point Naval Shipyard. Objectives of the project were to determine technology treatment efficacy, cost effectiveness, injection well radius of influence, and the possibility of plume displacement.

The new technology consists of pneumatic fracturing followed by the injection of ZVI into contaminated aquifers. ZVI is a dark gray powder with an average particle size of 40 microns. Pneumatic fracturing creates pathways in the subsurface so the injected ZVI particles reach zones of contamination for treatment. Once in the contamination zone the iron particles react with chlorinated compounds creating simpler, less chlorinated compounds. The reactions continue until only safe chloride ions and water are present.

After site characterization and regulatory approval of the work plan, the project team began ZVI injection and monitoring of the demonstration. The topsoil layer is mostly artificial fill with variable hydraulic conductivity. Below the fill is weathered bedrock down to 15 feet below ground surface. Geology below 15 feet is water bearing, fractured bedrock. Depth of injection is limited only by the depth of the injection well. For this project, vertical injection ranged from 7 ft to 32 ft.

A total of 16,000 lbs of ZVI was injected into four wells. Contaminants of concern were PCE, TCE, cis-1,2 DCE, vinyl chloride, chloroform, and carbon tetrachloride. TCE concentrations in the source zone exceeded 50,000 ppm. Contaminant removal was significant and ranged from 92.5 percent for chloroform to 99.4 percent for PCE.

The technology proved to be cost-effective at only $75 /cy without the need for long-term monitoring (LTM). In comparison, permeable reactive barriers are about $175/cy plus LTM, and pump/treat costs $300/cy and LTM. Dig and haul was an unacceptable remedy for this site. Injection well radius of influence was 15 feet and plume displacement during treatment was not observed.

Regulatory approval of the work plan proved to be the most significant obstacle during the project and caused a three-month delay. However, since we demonstrated ZVI injection is a viable treatment alternative, regulatory approval of future projects should be straightforward. The fall 2003 edition of RPM News has a more detailed write-up of this technology: http://enviro.nfesc.navy.mil/erb/erb_a/outreach/newsltr/rpmnews/2003fa.pdf

For further information contact Southwest Division at (619) 532-0930 or Naval Facilities Engineering Service Center at (805) 982-1660

Additional References:

 

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