Crosshole Sonic Logging (CSL) is a method for assessing the integrity of deep foundations made of concrete and/or grout. It is typically used to assess the quality of newly placed shafts or piles. CSL testing requires at least two access tubes (filled with water) fully bonded to the concrete. A source is lowered into one of the tubes and the receiver is lowered to the bottom of the other tube. The source transmits an ultrasonic pulse which is measured by the receiver. The source and receiver are pulled back to the surface at the same time where measurements are taken at a specific interval. Signal recordings and their first arrivals are analyzed to assess the integrity of the piles.