An adjustment nut was also added for exact calibration of tube extension. The danger of cross contamination, wall sloughing or collapse has been virtually eliminated. In the event formations too hard for drive sampling are encountered, the 94mm system provides a wireline inner tube for punch coring clays or shales and a standard wireline core barrel inner tube for soft to extremely hard formations. The jobs required drilling over 50 holes at hazardous waste sites. Cross Section shows inner and outer barrels of Christensen 94mm Wireline Core Barrel System.
Outer tube remains in hole while sample is brought to surface by means of a wireline.
By minimizing round trips of the outer tube, the danger of cross-contamination or hole sloughing is also minimized. The investigations involved drilling to depths of 750 feet to define the stratigraphy and to install groundwater monitoring wells to depths of 500 feet in order to define the contaminant plume. The stratigraphy at the sites are extremely complex and continuous sampling was necessary for an accurate interpretation of the subsurface. A coil spring provides tension necessary to penetrate soils. If obstruction is encountered, the spring retracts, allowing the bit to drill through or displace it.