STRATIGRAPHICS provided CPTU-EC (Piezometric Cone Penetration Test with soil Electrical Conductivity measurements) exploration services for ERM at  a Superfund site in Northern Virginia. The work was performed to support ERM’s sludge basin capping design . STRATIGRAPHICS provided services using its rubber tracked ATV CPT rig on the pilot and then  full scale production programs. We completed 258 CPTU-EC soundings with a total of 4410 ft of test in about 16 production days during these two programs.

The CPTU data were used for the evaluation of the presence of voids within the sludge basins and for distribution of leachate characteristics within the basins. Identification of voids was important for optimally positioning  de-watering wells to remove leachate from the basins. The sludge itself was relatively impermeable, so leachates could only be easily extracted from voids within the sludge. STRATIGRAPHICS developed a statistical analysis program for mapping the distribution of voids in each basin using acquired CPT data.
The EC data were also used to develop distributions of different leachate types within each basin. The leachates had stratified in density driven layers. Identifying the presence and thickness of the various leachate layers was used to develop estimates of different leachate volumes within the basins.

Several techniques were originally evaluated for conducting basin characterization, including CPTU-EC, drilling and sampling, Geoprobe, and surface geophysics. CPTU-EC proved to be the most useful method during the pilot study, and so was used for full production testing.

STRATIGRAPHICS provided CPTU for very soft sediment characterization for Tetratech and Battelle on the Grand Calumet River in Hammond and Gary, Indiana, within the greater Chicago metropolitan area. The instrumentation was deployed by hand due to the poor access for equipment on the extremely soft sediments. One section of river was so shallow that plywood planks were used to access test locations. Another shallow section included use of a small flat bottomed boat. Finally, a deeper section of river was accessed with a larger pontoon boat. STRATIGRAPHICS developed and manufactured sensors, adapters and light weight aluminum rod strings to conduct the testing.  

In addition to the hand deployed CPT, STRATIGRAPHICS conducts shallow sediment testing using a 5 meter long “stinger” CPT system, lowered from barge, boat or alongside a shorebank or levee using a small crane, hoist or excavator. Deeper overwater testing can be  conducted using CPT hydraulic push systems and large diameter stiffness casing.

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