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APPENDIX D <br />• March 2000 -11- 993-2099.150 <br />underground mine workings that may or may not be evident currently as <br />surface disturbances, with the depth of approximately 50 feet below the <br />Soil Liner Fill subgrade elevation. <br />All of the isolated features that are directly evident on surface consist of (1) open shafts, <br />(2) old shafts now completely or partially filled with soil and rock fragments (and often <br />pieces of timber) forming cone-shaped depressions in the surficial soil material, (3) mines <br />excavated in the surficial soils generally down to bedrock forming similar cone-shaped <br />depressions on surface, and collapsed adit portals. These are referred to in this report as <br />isolated shafts and shallow surface mines. <br />The underground workings within the Phase IV area that will require remediation are <br />generally mine workings which have been: (1) mined up so that the resulting crown pillar <br />is sufficiently thin to be of concern; (2) mined up to surface and are now evident as <br />• "daylighting" open features; or (3) collapsed and caved, and are now evident as surface <br />subsidence features. <br />5.0 RECOMMENDED REMEDIATION MEASURES <br />The general remediation measures for the underground workings are summarized in <br />Table 3, and discussed below. These remediation measures were developed based on the <br />results of the Phase III underground remediation program conducted during the Summer of <br />1999. The completed Phase III remediation program (which included over 70 workings) <br />provided important insights on the stabilization of underground workings. This experience <br />was used in the development of the remediation measures presented herein. <br />48 <br />I:M209MNAL RMWr2099A"D.1XOC Golder Associates