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6.4.4 EXHIBIT D - Mining Plan <br />5.) Based on the profile of the soils that exist at the site, the top layer of the profile for the soils is reported to be <br />approximately 10711 inches thick. Please commit to salvaging as much topsoil material as possible and state the range <br />of depth topsoil will be stripped and saved for reclamation. <br />6.) Please specifically state what seed mixture and seeding rate will be planted on the topsoil stockpile.• <br />7.) Will any overburden (non-topsoil material above primary commodity) be stripped during the mining operation? If so, <br />what is the average depth of this material? Where will it be stockpiled and how will it be stabilized from wind and water <br />erosion? If this material will be stockpiled, please indicate the location of the stockpile on the Exhibit C, Mining Plan <br />Map. Based on the NRCS soil's information submitted, it appears there are several lower horizons ranging in depth <br />down to 34 inches in the Buena Vista soils to 60 inches for the remaining soil types at the site. Given the slopes will be <br />constructed out of blasted ryholite bedrock, additional overburden should be salvaged to be re-spread prior to <br />spreading topsoil on the reclaimed slopes to help hold the topsoil in place and provide a deep root zone for adequate <br />revegetation. <br />8.) Since explosives will be used at the site, the applicant must demonstrate that offsite areas will not be adversely <br />affected by blasting by submitting a Geotechnical Stability Exhibit in accordance to Rule 6.5 (4). The only reference to <br />the proposed blasting is mentioned in Exhibit D, mining plan. The operator stated, "Blast hole drilling will be performed <br />with hole sizes 2.5" - 4.0" diameter and bench height 20'-30'. Blasting will be performed by a licensed blaster utilizing <br />best non-electrical blasting techniques to minimize ground vibrations and air blast and each shot will be monitored via <br />seismic recorders placed between the blast and nearest residence, approximately 2000 feet southeast of the mining <br />area. Mining will progress to the north, west, and east from the existing mining face located in the north central portion <br />of the property. Typical shot volumes will be in the range of 2000-3000 tons per round". <br />The information provided is inadequate for the Division to properly analyze the potential impacts from the proposed <br />blasting operations at the Silver Cliff Pit. Rule 6.5(4) requires, "sites where blasting is part of the proposed, mining and <br />reclamation, the Applicant shall demonstrate through appropriate blasting, geotechnical and structural engineering <br />analyses, that-off site areas will not be adversely affected by blasting". Therefore the operator must address and answer <br />the following concerns prior to application approval. <br />a) Given the proximity of houses and structures to the proposed mining and blasting area, the operator should <br />conduct a per-blast survey of these houses or structures. The pre- blast monitoring could be in the form of a <br />video, or photograph of existing cracks and visible damages to these properties. The operator should send a <br />letter to the nearby structure owners, to see if they would allow the operator access to conduct the pre-blast <br />survey of their structures: <br />b) The parameter normally used to assess the ground vibration is Peak Particle Velocity (PPV) expressed in <br />millimeters per second or feet per second (mm/sec. or ft/sec.). Most probable adverse impacts to structures <br />from a blast occur, from the vibration energy that is released after each blast. Rule 6.5(4) requires the operator <br />to demonstrate using appropriate blasting, vibration, geotechnical and structural engineering analyses to 's5ow, `-- <br />adverse impacts to nearby structures will not occur from the proposed blasting events. Adverse impacts from air <br />blasts, unless the structures are very close to the blast location, are very rare. <br />In lieu of such a demonstration and in order to protect structures from adverse impacts from vibration energy, <br />the Division normally places, as a permit condition, the most protective (PPV) that must not be exceeded, from <br />a single blast event. The peak particle velocity from a single blast event for this operation must not exceed 0.5 <br />ft/sec. However, if the operator demonstrates in accordance with Rule 6.5(4); peak particle velocity in excess of <br />0.5ft/sec will not adversely affect these structures; the Division will review the report and act accordingly. The <br />0.5 ft/sec. peak particle velocity is selected from the Office of Surface Mining Blasting Manual. According to the <br />21 Page