Laserfiche WebLink
.~, <br />the ground acceleration that would occur as ground motions <br />propagate into the facilities under analysis. This methodology is <br />acceptable to the Division, and is in keeping with the Division's <br />view, expressed during meetings with the operator, that the seismic <br />coefficient be equivalent to the horizontal acceleration at the <br />failure plane. Dr. Bray was able to develop an estimate for the <br />MHEA, and recommends an initial value to be used for the seismic <br />coefficient in pseudostatic analysis. However, he cautions that <br />"Additional work is required to confirm these estimates and they <br />should not be used to evaluate the final design". Since it is the <br />Division's intention to evaluate the final design (while <br />recognizing the need for design flexibility with Division approval) <br />during the amendment review process, we could not accept Dr. Bray's <br />values without additional information regarding the fundamental <br />period of the ore heap, and the predominant period of the pertinent <br />ground motions. Also, there would have to be some analysis of <br />ground acceleration attenuation (or amplification) for the wedge <br />failure mode of the ore heap, which is a case where the failure <br />surface is in very near proximity to bedrock, and where it would <br />seem prudent to use peak bedrock acceleration as the MHEA. <br />The Division's conclusion from the foregoing discussion is that it <br />is inappropriate for the applicant to state that a seismic <br />coefficient of 0.14g is being utilized to "expedite the permitting <br />process". Rather, it must be stated that the seismic coefficient <br />of 0.14g is being utilized because it is the best value available <br />given the current understanding of the potential for facility <br />failure under earthquake loading at the project site. <br />Uniform Building Code (UBC1 Seismic Zone <br />The applicant has noted that the project area is within UBC Seismic <br />Zone 1, and has adopted Seismic Zone 1 criteria as a facility <br />design criteria. Given the acknowledged potential seismicity of <br />the site it would seem essential that the precious metals recovery <br />facility be designed for UBC Seismic Zone 2 (this would correlate <br />with about 0.14g bedrock acceleration. The more conservative <br />zonation is needed because of personnel and hazardous materials <br />safety considerations. <br />Potential for Acid Generation and/or Metals Mobilization from <br />underdrains <br />As I stated in a memorandum dated March 28, 1994, and as has been <br />emphasized throughout the amendment 5 and amendment 6 processes, <br />rock utilized as underdrain fill must be demonstrated to be <br />chemically inert (non-acid or toxin producing). In the most recent <br />version of Volume I - Amendment 6, the applicant proposes to use <br />waste rock from the early stages of mining in the Cresson Pit to <br />construct the underdrain beneath the Arequa Gulch overburden. The <br />applicant states that "All such material has been subjected to <br />extensive assessments as to the acid-generation potential and the <br />material appears suitable". The Division is awaiting the results <br />of on-going, long term humidity cell testing of Cresson Pit <br />