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iii iiiiiiiinium <br />• • <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Department of Natural Resources <br />1313 Sherman 51., Room 215 <br />Denver, Colorado 80203 <br />Phone:13031866-3567 <br />FA%:13031872-8105 <br />To: 8usaa Burqmaier <br />From: Barbara Pavlik <br />Date: March 29, 1995 <br />Re: Yoast Mine (C-94-082) <br />II~~~ <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />Roy Romer <br />Governor <br />lames S Luchhead <br />Exec ulrvr DueUOr <br />Michael B. Long <br />Div is~on Direcloi <br />I have reviewed SCC's responses to my concerns regarding the <br />hydrologic aspects of the Yoast permit application and have the <br />following comments: <br />Tab 7 - Hydrologic Description <br />17) SCC's explanation of why the annular or bottom seals of <br />the referenced wells are believed to have failed is <br />adequate. However, in reviewing the well completion <br />reports to verify SCC's explanation, the Division <br />discovered that many (14) of the monitoring wells appear <br />to have been improperly completed. That is, no bentonite <br />seal or packer was place between the cement grout and the <br />filter pack. The wells in question are: YSAL1, YSAL2, <br />YSAL3, YSAL4, YSAL5, YSAL6, YSAL7, YSAL10, YSAL11, <br />YSAL12, YSAL13, YOVl, YOV8 and YW7. <br />Of the above wells, only YOV1 and YW7 were mentioned by <br />SCC as having rendered questionable data. SCC should <br />explain how (or if) the integrity of the filter pack was <br />maintained in these wells without a bentonite seal or <br />packer to prevent cement grout from clogging the filter <br />pack. Interestingly, reference to Table 7-4 (page 11) <br />shows that the wells with improper completion indicate <br />significantly greater saturated aquifer thicknesses than <br />the wells with proper completion. How does SCC relate <br />its estimate of saturated thickness with monitoring well <br />completion? <br />18) SCC's explanation of how the potentiometric contours were <br />derived is adequate. With regard to Rule <br />2.04.7(1)(a)(i), SCC has minimally addressed this comment <br />by stating that the Trout Creek Sandstone is the only <br />unit in the permit area that can be considered an aquifer <br />and that it is regional in extent. SCC does not appear <br />to have addressed the Twentymile Sandstone and whether or <br />