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A review of the Revey Associates, Inc. REPORT OF INVESTIGATIONS "Impacts of Mechanical Equipment at Benson Brothers Proposed Red Shale Quarry on Rock Bluffs Delta County, Colorado" February, 2006. The following comments are based upon a review of the text of the report and photographs included in Attachment I. I did not have copies of the seismic records or any other attachments to this report. GENERAL COMMENTS The objective of the study by Revey Associates, Inc. was to assess concerns regarding the stability of highly jointed cliffs of Rollins sandstone that adjoin the proposed quarry site, and to assess the potential that vibrations generated by heavy equipment might trigger rock falls that could threaten outbuildings and homes below the cliff. The configuration of the proposed quarry site is shown in cross-section in Figure 1 of this review. The report refers to the site as "open rangeland", though in reality the proposed quarry has 21 homes within % mile of the perimeter. Several of the neazby homes, including one adjacent to the cliff, have been omitted from the site map in Figure 1 of the report. PreSeisTek, Inc. was retained to make measurements of ground vibrations generated by equipment similar to that to be used at the proposed quarry in Coalby Canyon. The experiments were carried out at the Benson Brothers quarry in Austin, Colorado, and results of the tests were reported in Figure 4 of the Revey report. There is no description of the experimental procedure used to obtain the data in Figure 4. From comments and photographs it appeazs that the experiment was conducted in unconsolidated sediments, the distance of the seismic sensor from the equipment ranged from 10 ft. to about 200 ft, the sensor or recording equipment had a low frequency cutoff of I S Hz, and the sensor measured ground velocity. The observed amplitude of ground motion and rate of attenuation of motion with distance from the equipment at this site is claimed to be equivalent to what will occur at the actual proposed quarry site in Coalby Canyon ten miles to the north. The report does not meet the stated objective since no assessment of risk is provided. SUMMARY OF CONCERNS The amplitude of ground motion generated by heavy equipment, and the manner in which it propagates is highly dependent upon the activity the equipment is engaged in, the elastic properties of the material, the stratigraphy of the geologic formations, and the topographic setting, and is highly site specific. Major technical concerns with the Revey report are summarized below, and a more detailed explanation of each is provided in the following section.