Plume Data Comes to the Surface

All MIP data were collected and used for a 3D visualization of the results using the software GeoScene3D from I-GIS. In this view, seen from approximately 10 m. above the terrain, a green sphere is seen underneath the terrain, illustrating the contamination. The range of the sphere represents calculated “iso-response” (e.g. a DELCD response of 1.000.000 uV). Along with the contamination-sphere, the MIP logging points (shown with a green mark at the terrain level) and the groundwater monitoring wells are shown. The terrain is represented by an aerial photo of the investigation site. Finally, the nearby building is illustrated by a red/brown block of which a part is seen in the upper right corner. The extent of the contamination, in this form, is easily presented and easily understood.

Previous subsurface investigations had failed to clarify the extent of a tetrachloroethylene contamination at a former military laundry and dry cleaning facility in Alingsäs, east of Goteborg, Sweden. The contamination had been known about for some time; however, neither the path of the plume nor the direct source of the contamination had been previously mapped or located.

The Department of Environmental Engineering at the Swedish Geotechnical Institute (SGI) in Linkoping contacted European MIP (membrane interface probe) contractor, Ejlskov A/S in Aarhus, Denmark, to meet and develop an investigation strategy for the site. The plan was to conduct an investigation at the dry cleaning facility with the scope of delimiting the contamination source, tracking the plume, and gathering data to make decisions for further activities. According to Lennart Larsson, Civil Engineer/Project Manager with SGI, he contacted Ejlskov A/S because of SGI’s prior work with the company and the successful results they had seen with the MIP system. “We wanted to use the MIP logging system to pinpoint the contamination, take a few relevant soil samples, and select the best places for establishing monitoring wells,” Lennart said. “We really hoped the MIP was the right tool to use ... and it was!”

When you’re on a busy road, where’s the best place to install a monitoring well? Behind the safety barrier! Sune Andersen, Field Technician for Ejlskov A/S, uses the 7730DT and 3.25 in. tooling to install a monitoring well making the impossible possible!

Ejlskov A/S used their 7730DT machine and MIP system with the MP6510 Membrane Interface Probe, the MP6500 Controller, and FC5000 Field Instrument. They also used an SRI gas chromatograph with FID, PID and DELCD detectors to perform the analyses. “We needed big, reliable machinery and tools to be sure to reach the bedrock in every push,” said Palle Ejlskov, Director of Ejlskov A/S. “And we were successful with all of the MIP pushes with no problems.”

Ejlskov A/S provided the staff at SGI with what they hoped for. Within a few days after the planning session, 27 MIP logs were completed from around the site. Using a laptop and mobile phone, data was transmitted to SGI within minutes of completing the MIP logging. As the data was collected, the MIP field team could determine where to set up for the next MIP log.

“Although we were many miles from the site,” explained Fredric Engelke, Geologist/Project Manager with SGI, “we were an active part of the investigation because the site team provided us with nearly instanteous subsurface information from the site.” As a result, the
contamination was easily delimited and several other possible sources were investigated.

Ejlskov A/S finished the job by taking three continuous core samples, using the DT32 Dual Tube Soil Sampling System, and installing ten groundwater monitoring wells on the site, one of which was 19 meters deep. “The 7730DT,” Palle Ejlskov added, “is an excellent machine for these types of jobs!”

Using a DELCD detector, MIP Log 10 shows the presence of chlorinated substances (shown in blue) at about 1 m, at a higher level (apprx. 3.5 m.), and decreasing to the button of the log. The contamination (at apprx. 1 m.) is probably due to a leaking sewer line. The top of the contamination plume is located at 3.5 m. The strength of the contamination falls with increasing depth which is expected because the MIP logging point is located near the contamination source. The fear of chlorinated solvents moving on top of the bedrock can be rejected as no increase in response can be seen at the end of the log. There is a slight response on the PID detector (shown in black) at approximately 3.5 m. This is expected as the PID has a low sensitivity to normal chlorinated solvents.

MIP Log 18 is extremely boring – and extremely useful! It’s a good example that “nothing” can give you what you hoped for. This MIP data was taken next to a sewer collecting well, and in a possible direction for the contamination plume. If the sewer or well was leaking, some response would be expected in a depth of approximately 2 m. If the contamination was in a plume, a response (mainly of the DELCD, shown in blue) would be expected to appear in the lower portion of the log. One hour of work and the answer is clear ... no leaking sewer and no plume at this point. No further investigation was made in this area.

The 3D visualization allows the user to move freely around and watch the results of the MIP data in various ways. This view is from approximately 2 m. below terrain. The building is at the left, and the top of the bedrock is falling down to the right. The DELCD response results are shown both by color and by size of the square representing the MIP logging points. The plume shifts from being approximately 3 m. below terrain to following the top of the bedrock.