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Memo to Erica Crosby <br />Roadside North Portal Subsidence <br />page 3• <br />At this point in time, based upon Exhibit 5, "Mine Plan -Life of Operation", it <br />doesn't appear that any retreat mining has been accomplished in the North Portal <br />area modern underground workings. Activity seems to have been limited to the <br />development on advance of mains and submains, only. It is unlikely that any <br />detectable subsidence has occurred. Without any subsidence induced strain and <br />distortion it is also unlikely that any hydrologic consequences have occurred. If <br />the operator completes the subsidence survey and implements the appropriate <br />mechanical, visual and hydrologic monitoring they will not have missed the <br />undisturbed initial window. However, they should not commence any retreat <br />mining until we are assured that whatever monitoring facilities are deemed <br />appropriate have been installed. <br />cc: Larry Routten <br />Susan McCannon <br />Doc: M:\COAL\JAP\NORTHPOR.SUB <br />JP/1P <br />