Correlation of High Resolution Eri Results to Geochemical Zonation at a Degraded LNAPL Site in Grand Junction, Colorado.

Geochemical zonation in the subsurface has been imaged successfully at several environmental sites impacted by LNAPL using GeoTrax Survey™ technology (a high resolution form of electrical resistivity imaging). One of these sites is located in Grand Junction, Colorado, and shows a zone of decreased sulfate that is electrically distinct from zones containing oxygen and nitrate in the subsurface. <br>Overall, the site presents as electrically conductive (<8 ohm-m), with extremely conductive zones (< 1 ohm-m) in the eastern portion of the site, and very conductive zones (1 – 3 ohm-m) in the central and western portions of the site. RockWorks ™ visualization software was used to create a 3-D model of site, which integrated GeoTrax Survey™ images, groundwater analytical data, monitoring well locations, and groundwater elevation data. Bio-parameter data was also included in the 3-D model, and consisted of dissolved oxygen, sulfate, nitrate, and redox potential. the 3-D model demonstrates a strong correlation between the conductivity of the site and geochemical zones which are expected to indicate the type of bacteria present. Data in the 3-D model show oxygen and/or nitrogen zones near the eastern portion of the site that correlate well with extremely conductive zones (<1 ohm-m), and sulfate areas in the central and western portions of the site correlated well to the very conductive zones (1-3 ohm-m). Data obtained at this site indicate that it is possible to use GeoTrax Survey™ technology to identify geochemical zones that correlate to various nutrient reducing bacteria. these findings are significant to environmental professionals investigating and/or remediating LNAPL impacted sites. Specifically, this approach can be used to support natural attenuation arguments and/or identify areas where bioactivity is nutrient limited, thereby allowing efficient and focused deployment of bioamendment technologies to enhance existing levels of natural attenuation.