Page:NTSB - Railroad Accident Report - Derailment on May 25, 1989.djvu/37
In addition to the two excavations, the pipeline was potholed at several other locations. At one location where the pipeline was potholed, a truck assembly [rail car] was found to have penetrated the natural soil. Calnev’s maintenance superintendent marked this location and later advised Calnev’s manager of operations of the need to perform a more thorough inspection of the pipeline at that location. By 4:00 a.m., on May 16, the path through the trona had extended north 300 to 400 feet to a point where the breach in the levee had been made.
The deputy fire chief testified that when he terminated his role as incident commander around 10:00 p.m. on May 15, Calnev’s manager of operations assured him that the pipeline was safe to operate.
Calnev’s manager of operations, who relieved the maintenance superintendent about 4:00 a.m. on May 16, supervised the remainder of the trona removal from over the pipeline. A foreman for Arizona Pipe Line Company arrived on site about 6:00 a.m. and relieved the backhoe operator who had worked through the night. According to Calnev’s manager of operations, two additional excavations of the pipeline were performed; he estimated the first excavation to be near the middle of lot 76 (figure 4, excavation #5), where the maintenance superintendent earlier had found a truck assembly, and the second location to be near the northern edge of lot 75 (figure 4, excavation #6). At both locations, the excavation was performed on the west side of the pipeline, a 20- to 25-foot section of the pipe was exposed from the 6 o’clock position to the 2 o’clock position facing north, and no damage to either the coating or the pipe was observed by Calnev personnel. The depth of pipe was determined to have been about 4 feet at the first location and 5 feet at the second location.
According to the testimony of Calnev officials and the backhoe operator, all the excavations were immediately backfilled after the coating and pipe were inspected for damage. Further testimony indicated that about 6 inches of debris-free native soil would be used to fill the remainder of the excavations, and that compaction of the soil was accomplished by "wheel-rolling" rather than by use of the backhoe bucket.
Beginning about 10:30 a.m. on May 16, Calnev began performing soft dig excavations of the pipeline about every 50 feet throughout the derailment area. At each location, an 8-foot-tall stake marked at 1-foot intervals was placed on top of the pipe, the top of the stake was surveyed to determine its
- According to the Arizona Pipe Line Company employee operating the backhoe, all potholes were dug manually using shovels. According to Calnev’s maintenance superintendent, "The primary function of a pothole is to determine the depth and location of the pipeline. An excavation would be a larger hole, a more complete excavation where you are actually attempting to visually ascertain the condition of the pipeline."
- A process by which vacuum-type excavation equipment makes about a 1-foot-diameter hole from ground level to the top of the pipeline.