You are here:
THE IMPACT OF PARTIAL DNAPL SOURCE ZONE REMEDIATION
Citation:
Bob, M. AND A L. Wood*. THE IMPACT OF PARTIAL DNAPL SOURCE ZONE REMEDIATION. Presented at 4th Int'l. Battelle Conf, Monterey, CA, May 24 - 27, 2004.
Impact/Purpose:
To inform the public.
Description:
Dense non-aqueous phase liquids (DNAPL) constitute a long-term source of groundwater contamination and a significant effort is usually required to treat these contaminated waters and bring them back to maximum contaminant level (MCL) required by the regulatory authorities.
Field-scale research and studies demonstrated that a high percentage of DNAPL mass can be removed by some in-situ treatment technologies such as alcohol or surfactant flushing, steam flooding, air sparging/venting, bioremediation and chemical oxidation. However, these studies have also shown that despite the high percentage of DNAPL mass removal, the efficiency of DNAPL extraction decays exponentially with increased mass removal. Removing all DNAPL mass is thus very difficult or impossible to achieve and may not be economical. With limited resources, assessing the impact of partial DNAPL source mass deletion should thus be an essential part of any remediation project.
In this research, the impact of partial remediation of DNAPL-contaminated sites is assessed. This assessment can be best carried out through examining the relationship between DNAPL mass depletion and contaminant mass flux from source zone. To this end, well-controlled laboratory experiments in 2-D physical models, prepared with a range of heterogeneity, are being conducted using PCE as a model DNAPL contaminant. In-situ treatment technologies include steam flooding, surfactant flooding, and air sparging. The 2-D flow chamber is constructed of two glass plates separated by 1.27 cm. The model length and height are 53 and 40 cm respectively. Naturally translucent silica sands of varying diameters are used as packing media. Detailed assessments of spatial distribution of water/air saturation as well as DNAPL concentration are obtained by light transmission technique. Images captured with very high dynamic range, low noise electronic charge coupled device (CCD) are analyzed pixel by pixel using image analysis software. Water/air saturation and DNAPL concentration across the 2-D chamber are measured as variations in the transmitted light intensity of these pixels. Changes of DNAPL concentration and spatial distribution as determined by pixel analyses of these images can thus be correlated with DNAPL source reduction.
The application of this innovative technique of light transmission provides a powerful tool for monitoring DNAPL within the whole system allowing thus for a detailed assessment of the impact of partial DNAPL source removal. This research also provides new insight into the correlation between media heterogeneity, DNAPL saturation distribution and partial source zone removal. In addition, data from this research allow for the comparison of the effectiveness of these in-situ remediation technologies, which permit optimization of remediation activities. Further, the results of this research will help in developing regulatory and policy guidelines for DNAPL source zone remediation.