You are visiting the web site of the EPSCI Program at the U.S. Dept. of Energy's Ames Laboratory, Ames, IA
On-site demonstration by contractor
The first task of the Marshalltown program was to carry out CPT pushes adjacent to several monitoring wells to compare and calibrate the SCAPS stratigraphic profile with the boring log. Two monitoring wells were chosen for this purpose because all of the major stratigraphic units were present and the depth to bedrock was defined within them. Because the CPT pushes were located a short distance from the monitoring wells, it was expected that there would be some minor differences due to the natural spatial variation associated with alluvial and glacial deposits.
The basic strategy for CPT placement was to fill in data gaps to verify and/or enhance the geologic and contamination conceptual models. Generally, the Ames Laboratory personnel overseeing the ESC process had primary responsibility to integrate all of the data from the various activities on site, including locating all underground utilities, and decide where to direct the SCAPS unit for each new push location. Digital friction ratio logs and fluorescence intensity logs were acquired from the CPT computer system and integrated into the existing site model developed from previous work at the site. This information was used to guide the selection of sampling locations for on-site quantitative analysis in the mobile laboratory.
A total of 43 stratigraphic logs in 34 locations were generated by the CPT system over the course of 10 working days. The system averaged approximately 208 pushed feet per day. Encounters early on with coarse gravel sediments and a broken probe resulted in a decision to drive a "dummy" rod to a depth of 15 to 20 feet before advancing the instrumented probes. For this reason, stratigraphic information in the upper 15 to 20 feet of most probe holes was not generated.
Several factors limited the use of the SCAPS in some parts of the site. The unit is designed for use on level to gently sloping terrain with clayey to sandy soils with small gravel sizes. The air-space above the truck must be free of obstructions such as power lines, and the large size of the truck requires ample open space to maneuver. The CPT probes will not penetrate boulders, cobbles, rubble, well compacted sediment, or sound bedrock.
Analog printouts of each log were produced within an hour of completion of the hole. Digital data (as text files) were not made available until near the end of the field work as a result of formatting problems. The CPT instrumentation was unique in its efficient production of reproducible stratigraphic information which was of high vertical resolution and accuracy, coupled with minimum ground disturbance. A clear disadvantage was its high susceptibility to unfavorable subsurface conditions (coarse gravels, buried debris, etc.) and to above ground features (tight work spaces, surface pavements, etc.).
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Last Modified: 1 January 2002 by dave eckels
Expedited Site Characterization: etd/technologies/projects/esc/technologies/cptlifdemo.html