ASC Tech Services
Environmental contamination is risky business, to access risk, high-tech and unique geophysical site characterization methods can be employed. By utilizing these high tech gadgets that describe the ground and detail exactly what can’t be seen. Just like the Silicon Valley, new methods have surfaced and now more than ever it is easy to characterize the subsurface using direct push tools.
Using direct push (DP) logging and sampling tools indicate the nature of the soils at the site; permeability's, depths, and flow paths, and where contaminants are present.
The DP tools applied include the Membrane Interface Probe (MIP), Hydraulic Profiling Tool (HPT), electrical conductivity (EC), direct push slug testing with groundwater sampling, and dual tube soil coring. Each of these tools can be used to describe a certain aspect of the subsurface related either to the nature of the soil materials at depth, or the location and concentration of contaminants.
The first tool employed at the site was the MIP probe. A known plume of groundwater contaminated with chlorinated VOCs is located beneath the site. The MIP probe is used to locate these contaminants at depth. This information allows us to compare relative concentrations across a site, identify source areas, and select future groundwater sampling intervals.
At this particular site, MIP logs were made to a depth of 20 m. VOC contaminants were found at depths of 10.8m to 18m.
Based on the MIP logging performed at the site, depths were selected for discrete interval groundwater sampling to determine concentrations of selected VOCs. The sampled intervals were also used for hydraulic conductivity measurements using pneumatic slug testing techniques through the direct push groundwater sampler.
A relatively newer technique known as HPT was also employed at this site. HPT uses fluid injection pressure to measure the relative permeability of a soil and . Using this technique it compared favorably to our EC logs at the site. HPT logs clearly show the position of permeable materials as well as fine silt and sand beneath the site.
The lithological profiling results using the various direct push logging tools are confirmed using core samples obtained using Geoprobe Systems' DT325 coring system. This is a dual tube soil coring system that allows rapid recovery of 50mm diameter soil cores over the 20m depth of study at the site. These cores allow us to make a rapid visual confirmation of the lithology, the position of permeable materials and potential flow paths as predicted by HPT and EC logging.
Eric Garcia, CEG, CHG
ASC Tech Services