Superfund Innovative Technology Evaluation (SITE)
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This document summarizes and analyzes the results of a 4-wk evaluation of the Accutech Remedial Systems, Inc. (ARS) Pneumatic Fracturing Extractionc(™), (PFE)(™) process for increasing the removal of volatile organic contaminants from the vadose zone, particularly where the ground formation is relatively impermeable to air flow. Based on the Superfund Innovative Technology Evaluation (SITE) Program demonstration at an industrial park in Somerville, New Jersey and data from other Accutech investigations, conclusions are presented concerning the technological effectiveness and the economics of the process, and its potential utility for other sites.
During the SITE demonstration, operations were carefully monitored to establish a database against which the vendor's claims for the technology could be evaluated reliably. These claims were that PFE would increase extracted air flow rates from the formation by at least 100% and the mass removal rate for the key contaminant, trichloroethene (TCE), by at least 50%. In addition, although no claim was made, evaluation of hot gas injection was also an objective.
It was found that Pneumatic Fracturing Extraction (PFE) does increase extracted air flow rates by considerably more than 100% and TCE removal rate by much more than the claimed 50% at this site. Specifically, based on comparison of 4-hr test results before and after fracturing, air flow rates were increased >600%, and TCE mass removal rates increased 675%. The increase in TCE mass removal rate appears to be due primarily to the increased air flow since TCE concentrations in the extracted air remained in the 50 to 60 ppmv range. In addition, the extracted air contained significantly higher concentrations of other VOCs after fracturing. The radius of influence for vapor extraction also was greatly enlarged by fracturing. Average extracted air flow rates from peripheral monitoring wells increased by approximately 700% to l,000% in wells 10 ft away, and 200% to 900% in wells 20 ft away.
With surrounding wells open as passive air inlets, the extracted air flow rate increase after fracturing was even higher, -19,500%, and the TCE removal rate increased -2,300%.
These results suggest that PFE can make low-permeable formations, such as the bedrock at this site, suitable for vapor extraction. Fewer extraction wells would be required, or remediation could be completed more quickly with PFE, thereby reducing remediation cost.
With PFE, the cost for full-scale remediation of the site was estimated at $307/kg ($140/lb) of TCE removed based on the SITE demonstration experience and information provided by the developer. Major cost factors were labor (29%), capital equipment (22%), VOC emission control (19%), site preparation (11%), and residuals management (10%). The nature of the formation, the nature and concentration of the contaminants, and other factors, including site preparations, need for post-treatment, etc., may affect total cost and operating efficiency. The cost estimate should be used with caution.
Based on the results of two experiments, the effects of hot gas injection remain unclear. In one test (90-hr), temperatures in surrounding monitoring wells increased, but TCE mass removal decreased when compared with a pretest without hot gas injection. In a second test (24-hr), TCE mass removal rates increased, primarily due to increased air flow rates, but temperatures did not increase.