FIGURE 6-9. CORING DRILL AT THE AOMON CRYPT. The center monumentarea as viewed toward the west during drilling operations. (January 1979) The second action involved acquisition and analysis of core samples. A truck-mounted, core-drilling rig (Figure 6-9) was brought to the site and operated by the Army Corps of Engineers, Mobile District. Core samples were obtained on a 5-meter grid for each 2-foot interval down to rock, metal, or 30 feet, whichever occurred first. The mode of operation for the drill rig was to pound the 2-inch diameter coring tool through a 2-foot interval, extract the sample, rotary drill the same interval with a 4-inch bit using drilling mud to stabilize the sidewall, then obtain the next core. By using the rotary drill while the sample was being retrieved from the coring bit, the entire process progressed at a rapid pace. Approximately 1,000 soil samples were obtained from 125 holes between 1 December 1978 and 22 January 1979. (Work was halted briefly by Typhoon Alice.) 176