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locations within the concrete-lined portion of the FCO Spillway chute, which in turn required special coordination with the OER Incident Command personnel and dam safety regulators, and had to be timed to coincide with short-duration spillway outages. Resources required to perform this work included concrete coring units, rock-coring drill rigs, surface and borehole geophysical testing, engineering geologists, field and office management, instrumentation specialists, and construction support (to build access roads, create drill pads, dig mud pits, etc.). Other required support included environmental scientists, archaeologists, and cultural resource specialists to confirm that the proposed drilling sites, surface geophysical lines, and other work items (e.g., temporary roads and/or equipment staging areas) would not impact documented sensitive areas within the project site. Ultimately, up to 10 drill rigs, with drilling contractors from three private firms and two federal agencies, were utilized to perform the drilling work. Two geophysical firms were selected to perform the P-wave surface refraction lines. Two geophysical firms performed downhole acoustic and optical televiewer surveys, and P-S suspension logging on select boreholes. For every drill rig, there was at least one engineering geologist to log the rock core. Experienced engineering geologists logging the rock core were resourced from within DWR, two federal agencies, and several consulting firms. The qualifications of the engineering geologists had to be reviewed and approved by Federal dam safety regulators prior to working on the site. In order to maintain consistency with so many engineering geologists, an exploration work plan was prepared in the days leading up to the initiation of the exploration program. The work plan detailed the logging nomenclature and field procedures defined for the project. At any given time, there were at least two experienced, on-site engineering geologists coordinating the scheduling and movement of drill rigs, clearing sites with environmental and cultural specialists, scheduling the rotating geology staff, interfacing with the OER Incident Command, holding safety meetings, and all the other typical daily routines for an exploration program (but 10 times as big). There were typically 15 to 20 engineering geologists on site daily during the peak of exploration who were logging rock core, geologically mapping rock exposures, and coordinating drill rig and personnel movements. Many engineering geologists and engineers were in the office, performing real-time data analysis for the design efforts. 4.3. QUALITY ASSURANCE AND QUALITY CONTROL The drill rig engineering geologists logging the rock core were from several different agencies and consulting firms. To ensure a consistent approach to recording drill hole information, including handling and logging of recovered rock core and performance of borehole testing, a full-time QA/QC Engineering Geologist was assigned to review field logs and recovered rock core throughout 117