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DRMS Response: Response accepted. <br />38a. Sandstone cliffs outcrop upslope and adjacent to County Road 79 in or near the proposed <br />subsided area. It is not clear given the current permit application materials where these <br />cliffs fall within the underground panel layout and the proposed subsided area. Please <br />provide a map and/or orthophoto that depict the location of these cliffs relative to the <br />proposed underground workings. <br />Northfield Response: Aerial photos and other information were used to determine the <br />location of the cliffs. The cliff locations are annotated on Map 7. <br />DRMS Response: From the information provided, significant exposures of sandstones cliff <br />faces fall within the angle of draw and directly above undermined azeas of Panels 21, 22, <br />and 23. Given the proximity of County Road #79, more information is necessary to <br />determine the potential for any rockfall caused by subsidence to travel downslope to the <br />county road. The Division must require that Northfield submit an analysis completed by an <br />expert in the field of rockfall analysis and safety mitigation. However, given that the <br />proposed mining that may produce rockfall is planned for yeazs 11-15 of production mining, <br />Northfield may want to consider stipulation of this analysis to be completed during some <br />period within one yeaz prior to the mining that may affect the cliffs. The Division also <br />recommends that observations of impacts due to undermining of the cliffs in the west %z of <br />Section 13 be included in any analysis given the similaz nature of the outcrop and geology. <br />Please indicate if a stipulation to the permit is acceptable for this futuNe analysis. <br />Rule 2.10 Maps and Plans <br />39. Please ensure that all maps, plans, and cross-sections required by Rule 2.10 are to be <br />prepared by, or under the direction of, and certified by, a qualified registered professional <br />engineer or professional geologist. (Rule 2.10.3(2)) <br />Northfield Response: Maps have been prepared in accordance with Rule 2.10.3. <br />DRMS Response: Final maps will be reviewed prior to approval. <br />This concludes our adequacy review of the revised materials. Please submit responses to the issues <br />identified in bold text as soon as possible. If you have any questions, please contact me. <br />Sincer y, -r <br />~~' " <br />Kent A. Gorham <br />Environmental Protection Specialist II <br />