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RULE 4 PERFORMANCE STANDARDS <br />4.09 Disposal of Excess Spoil and Underground Development Fill Waste <br />Colowyo originally constructed the excess spoil fill known as Streeter Fill in accordance with <br />Section 2.06.2, Experimental Practices Mining. The details of this alternative spoil disposal <br />practices are set forth in Section 2.06.2. <br />On March 3, 1986 Colowyo submitted a request to the Division for a Technical Revision to change <br />the status of the Streeter Fill Experimental Practice. The request was to change the Streeter Fill to <br />an excess spoil fill designed and constructed under the alternative design standards set forth in <br />Rule 4.09. (3). All the monitoring requirements of the fill will remain as originally approved to <br />insure the stability requirements of Rule 4.09 are met. <br />The Division approved the revision on August 18, 1986. <br />For further details regarding this Technical Revision and the history of Streeter Fill, refer to Section <br />2.06, Special Categories. <br />In December, 1993, Colowyo proposed a Technical Revision to the Division to reduce the <br />monitoring requirements for Streeter Fill. During the 1993 — 2006 period, the following <br />monitoring plan was implemented: <br />Streeter Fill Monitoring and Inspection Plan for Streeter Fill (1993-2006) <br />1) Colowyo conducted monitoring of the 12 Streeter Fill survey monuments once a year, <br />during the second calendar quarter of each year. For a location of the twelve survey <br />monuments (6700 N and S through 7200 N and S) and the baseline reference <br />monuments (AH -21, RP -2 and SRP -3) refer to Drawing 30A — Revised Streeter Fill <br />As -built. The revised Drawing 30A is intended to update the Permit only with respect <br />to 1) the Streeter fill survey monuments, 2) baseline reference monuments and 3) the <br />wells (W6900N, W6900S and W6700). The original Drawing 30 — Streeter Fill Design <br />and As Built will remain in the Permit and serve to represent all other aspects of Streeter <br />Fill. <br />2) Colowyo monitored water level in the Streeter Fill piezometer well (W6700) and <br />conduct a spring and seep survey quarterly. <br />3) In the event that the water table in the piezometer well rises to a level greater than 10 <br />feet above bedrock, Colowyo agreed to notify the Division within 2 working days and <br />to complete a survey of the twelve subsidence monuments and report the results to the <br />Division within one month. <br />4) Colowyo completed an annual inspection of the Streeter Fill each year of this time <br />period during the second calendar quarter by a registered engineer. This inspection <br />included a specific examination of items 1 and 2 above and included a discussion of <br />the facial conditions of the fill in order to determine whether the development of <br />perched water tables within the fill was affecting its surficial slope stability. <br />Rule 4 Performance Standards 4-35 Revision Date: 5/25/18 <br />Revision No.: RN -07 <br />