Laserfiche WebLink
RESPONSE/COMMENT.• Mine inflows were monitored and recorded throughout the life of mining operations and the <br />post mining reclamation period (Annual Hydrology Reports). As documented throughout the Annual Hydrology Reports, <br />approximately 85% of inf ows were pumped and accurately metered and the minor balance was estimated by qualified mine <br />personnel. This recorded inflow data is quite sufficient to make a reasonable projection for the approximate time required for <br />refilling of the mine. <br />Bishop - Brogden and Associates (BBA) has prepared a detailed response to the Division's technical evaluation of the <br />Southfield mine refilling which can be found in APPENDIX "B" attached to this submittal. <br />In the 2013 Summary Report? BBA attempted to model the refilling of the mine using: (i) an <br />estimate of the volume of the mine cavity, and (ii) estimated volumetric rates of mine inflow; <br />with three different scenarios of hydrogeologic connectivity within the workings. The report <br />concluded that the time for the water level in the mine to reach 5860.5' would be 106 -200 years. <br />There is significant uncertainty associated with the values of all of the input parameters for this <br />calculation, for example: <br />• There is confusion about the lowest elevation that could be measured at MWNW. <br />• There is uncertainty about the extent to which the mine cavity has collapsed, which has <br />implications for the volume of the remaining cavity. The 5,700 Acre feet value quoted <br />from page 2.05.6 -32 is a maximum value for the volume of the cavity, taking no account <br />of subsidence or natural caving. <br />• The mine inflow volumes (summarized in table 1) are quoted to a level of precision that <br />gives a misleading impression of the accuracy of the value. Since it remains unclear how <br />the estimates were made there can be very little confidence in these values. <br />• As acknowledged by BBA, the integrity of the seals within the mine workings is <br />unknown. <br />RESPONSE.- <br />✓ The elevation of the f oor of the mine workings is 5855 feet. The mine workings were 5.5 feet in height <br />in the vicinity of MW -NW, the referenced elevation of 5860.5 feet is the elevation of the roof of the <br />workings where the steel casing was cut off during mining operations; <br />✓ Subsidence and caving varies with the varying strata types. By approved design, portions of the mine <br />were not pillared (pillars left in place). These areas are depicted on the Southfield Final Closure <br />Map on file with the DRMS. <br />✓ Mine inflows were monitored and recorded throughout the life of mining operations (Annual <br />Hydrology Reports). Approximately 85% of the inflows were pumped and metered and the data <br />recorded by the Southfield mine engineer and qualified mine personnel; <br />✓ Integrity of the mine seals is unknown, therefore, BBA offered three models of potential <br />conditions that could exist in the mine. <br />The ideal location for a well to monitor the rate at which the mine is refilling and the quality of <br />water in the cavity would be at a lower elevation of the mine cavity, perhaps in the West Submain or 2 <br />West Submain, (drill holes SRI and SR61 would be well located). However the North <br />Dewatering Well was converted to MWNW with TR35 in 2003 for this purpose. MWNW has been <br />described as a monitoring well throughout the PAP and other documents, which is <br />inaccurate; really it is simply a cased hole, open to the mine workings. Nevertheless, and as stated on <br />page 2.05.6 -53, the purpose of this monitoring point is to: <br />"...trackprogressive mine flooding, water levels and water quality." <br />11 <br />