One site characterization method Envirologic utilizes at contaminated sites is the use of direct push logging tools. These tools are used to delineate the extent of a non-aqueous phase liquid (NAPL) body or dissolved contaminant plume, as well as to characterize hydrogeologic conditions. Defining the extent of a NAPL body or dissolved contaminant plume is critical in developing a conceptual site model (CSM) and evaluating various exposure pathways. Further, remediation techniques are more efficient and effective when the distribution of impact is adequately defined and the hydrogeologic conditions are understood. Using direct push logging tools to characterize a NAPL body or dissolved contaminant plume during the early stages of an environmental investigation can significantly reduce overall project costs and/or the investigative period.
There are various direct push logging tools that provide information regarding relative contaminant levels or aquifer properties, but they are all employed in a similar manner. A probe with different sensors (see Figure 1) is advanced into the ground via direct push technology, such as a Geoprobe®. The sensors on the probe relay data back to a computer (see Figure 2), which generates a continuous profile of the information (see Figure 3). The data is viewed in real time, which allows borings to be strategically placed while the investigation progresses.
Several options are available under the umbrella of direct push logging tools, including sensors that characterize chemical and hydrogeologic conditions. Options to define a NAPL body include laser induced fluorescence (LIF) and an optical image profiler (OIP), while a membrane interface probe (MIP) is geared toward characterizing dissolved phase contaminants (lower contaminant concentrations). As an example of how the chemical sensing tools work, LIF emits a laser signal that excites polycyclic aromatic hydrocarbons (PAHs), which are found in petroleum products and are very fluorescent. In reaction to the laser, the PAH molecules release excess energy and fluoresce. The LIF probe records the intensity of the PAH fluorescence in the NAPL body. The fluorescence response is generally strongest near the center of a NAPL body and decreases toward the fringe of the body. Different petroleum products (e.g., gasoline, diesel, machine oil, etc.) will generate different response signatures, which can help distinguish two separate NAPL bodies.
A hydraulic profiling tool (HPT) is commonly employed with a chemical sensing tool to generate a profile of aquifer conditions. This information helps evaluate the ease at which groundwater (and contaminants) migrates through different soil horizons. When employed together, the chemical sensing tool and HPT generate a powerful dataset that allows an environmental professional to evaluate the distribution of impact within the context of soil horizons that may act as a preferential pathway (sand or gravel layer).
Envirologic completed a LIF study to characterize the extent of NAPL at a former bulk petroleum storage facility (see Figure 4). A total of 30 LIF borings were advanced across the site. Two LIF borings identified a previously unknown NAPL arm along the northern portion of the site. Additional LIF borings confirmed that previous remedial efforts decreased the vertical extent of the NAPL body near the source area. Results from the LIF study indicated that the NAPL body migrated from the source area to beyond the western property boundary. Soil sampling was then conducted across the NAPL body to evaluate exposure risks; the LIF study helped reduce the number of soil borings and analytical samples that were necessary to complete the exposure assessment.
In addition to petroleum contaminated sites, Envirologic also has experience using direct push logging tools to characterize conditions at sites impacted with brine waste and chlorinated solvents.
By Derrick Lingle, Project Manager
Figure 1 - Integrated DNAPL Site Characterization and Tools Selection - Appendix G. (2015, April). Retrieved from https://www.itrcweb.org/DNAPL-ISC_tools-selection/Default.htm#Welcome.htm%3FTocPath%3D_____1
Figure 3 - MiHpt: A combined MIP-HPT probe! Retrieved from https://geoprobe.com/mihpt-combination
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site characterization • direct push logging tools • napl • contaminant plume • hydrogeologic conditions • exposure pathways • conceptual site model • csm • remediation techniques • environmental investigatin • aquifer • laser induced fluorescence • lif • optical image profiler • oip • soil borings • petroleum contamination • hydraulic profiling tool • hpt • brine waste • chlorinated solvents