DT22 Soil Sampling System Overview
The DT22 soil sampling system is a dual tube system from Geoprobe® that utilizes a 2.25-inch outer diameter percussion driven casing that remains in place during sampling. This quick and efficient direct push system is used to collect continuous core samples of unconsolidated materials from within a sealed casing. The inch and an eighth diameter samples are collected and retrieved within a liner that is threaded onto the leading end of a string of Geoprobe® 1.25 inch Light-Weight Center Rods. These rods weigh 68% less than regular 1.25 inch probe rods. When using 60-inch liners, sample volumes up to approximately 1 liter may be collected.
In additional to soil sampling, groundwater sampling and monitoring can take place within this system. DT22 can be run with Geoprobe® 54, 66, 67 and 78 Series rigs.
Assembly begins on the outer casing by installing a DT22 cutting shoe on the leading end of a 2.25-inch by five foot probe rod. A standard cutting shoe is used when collecting soil and SP22 groundwater samples. When installing a monitoring well in conjunction with collecting soil samples, a DT22 Expendable Cutting Shoe Holder and Expendable Cutting Shoe are used. O-rings can be added at each rod joint if required by your project.
Next, we’ll assemble the inner string. If the first sampling interval begins below ground level, a discrete point is used on the leading end of a 1.25 inner rod string in place of a sample liner. The discrete point firmly seats within the cutting shoe and seals the tool string as it is driven into the subsurface. This is followed by a DT22 threadless drive cap. The inner string assembly is installed into the outer casing, and a 2.25-inch drive cap is placed on the outer casing.
To reach the top of the sampling interval, the dual tube system with the discrete point is driven to a depth of five feet. The drive cap is removed and the inner string is pulled to the surface with an extra rod and leaf puller, removing the discrete point and opening up the cutting shoe for sampling.
To prepare the inner rod string for sampling, a DT22 liner is attached to the bottom of a DT22 liner drive head.
With the liner firmly attached to the drive head and secured with a set screw, four foot light-weight center rod is threaded onto the top of the DT22 liner drive head. The center rod and liner assembly are inserted into the outer casing. Next, a five foot long 2.25-inch. outer casing is added to the tool string. This is followed by a DT22 drive cushion and a 2.25-in. drive cap. The drive cushion keeps the liner in constant contact with the seat in the Cutting Shoe, therefore reducing the amount of material that will accumulate between the liner and casing.
Finally, a drive cap is added to top of the outer casing. The whole string is driven to a depth of 10 feet. After removing the drive cap, a drive cushion assist handle is used to remove the drive cushion.
The inner rods and DT22 liner with sample are then pulled from the outer casing using an extra rod and a leaf puller. As the filled liner is retracted, the fingers of the core catcher move back inward, thereby closing off the end of the liner and limiting soil loss. After removing the liner drive head, a DT22 liner cutter is used to reveal the sample from five to ten feet. This process is repeated for each sampling interval.
When taking an SP22 Groundwater sample, a stainless steel or PVC screen is lowered to the bottom of the DT22 outer casing on the leading end of a string of 1.25-inch. light-weight center rods. Adding an additional 2.25-in outer rod allows the outer casing to be retracted while the SP22 screen is held in place with the inner rods. This exposes the screen to the formation for groundwater sampling or slug testing. When sampling or testing is complete, the SP22 screen is removed with the inner rods and DT22 sampling may continue.
An expendable cutting shoe enables the operator to install a Geoprobe® Prepacked Screen Monitoring Well through the outer casing of the DT22 Dual Tube System. Soil sampling with an expendable cutting shoe is completed in the same way as with a standard DT22 cutting shoe. After the collection of continuous soil cores to the desired depth, prepacked screens can be inserted to the bottom of the outer casing on the leading end of a PVC riser string. The well is grouted during retrieval of the outer casing.
The DT22 Soil Sampling System is ideal for collecting continuous core samples of unconsolidated materials from within a sealed casing. A Screen Point 22 Groundwater Sampler can be used in conjunction with the DT22 system to perform groundwater sampling in one probe push. When used with an expendable cutting shoe, the operator can install a prepacked screen monitoring well through the outer casing after sampling. This system can be run with Geoprobe® 54, 66, 67 and 78 Series rigs.
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