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October 27-29, 1998 <br />BULKHEAD DESIGN FOR ACID MINE DRAINAGE <br />John F. Abel, Jr. <br />in Proc western U.S. Mining-Impacted Watersheds, Joint Conf on <br />Remediation and Ecological Risk Assessment Technologies, Denver, CO <br />ABSTRACT <br />Impounding acid mine drainage behind a bulkhead in a mine <br />tunnel has never been, and probably will never be, successful in <br />reestablishing the pre-mining groundwater regime. However, even <br />partially filling old mine workings should be beneficial. Partial <br />filling should raise the mine depressed water table to the mine <br />pool elevation. Partial filling of mine workings should decrease <br />the quantity of groundwater entering mine workings, resulting in <br />less mine drainage requiring treatment. Partial filling should <br />deprive the submerged sulfide minerals of most of the oxygen <br />necessary for producing acid, decreasing the rate of acid <br />generation. Partial filling should improve the quality of acid <br />water discharges from the mine. In effect, bulkheads can help but <br />will never completely cure acid mine drainage. <br />Acid mine drainage bulkheads have several significant unknowns <br />that potentially limit their usefulness: <br />1) What is the acceptable leakage around a tunnel <br />bulkhead? <br />2) What are the natural flow paths for impounded acid <br />mine water that may bypass a bulkhead into the open <br />tunnel downstream from the bulkhead or to the ground <br />surface? <br />3) How long will the bulkhead last? <br />4) Will unknown geologic conditions and(or) mine <br />connections prevent the mine pool from reaching the <br />planned elevation? <br />Concrete tunnel bulkheads designed to contain acid mine <br />drainage water must be: <br />(1) long enough to prevent leakage along the contact <br />between the concrete and the rock, <br />- 1 - <br />