1. (1) Open pits that will be left as a result of the mining operation shall be assessed prior to, and following, mining operations for the potential to contaminate water to the extent that it might not meet water-quality standards due to buildup of acid or toxic metals.

2. (2) If the Department finds that the potential for water accumulation in the pit(s) exists, the permit applicant shall submit a closure plan for the pit that will address contamination prevention and possible remedial treatment of the water. The closure plan shall, at a minimum, examine the following alternatives:

   1. (a) Avoidance, during mining, of acid-generating materials that can be left in place, rather than being exposed to oxidation and weathering;
   2. (b) Removal from the pit and disposal, during or after the mining operation, of residual acid-generating materials that would otherwise be left exposed to oxidation and weathering;
   3. (c) Protective capping in-situ of residual acid-generating materials;
   4. (d) Treatment methods for correcting acidity and toxicity of accumulated water;
   5. (e) Installation of an impermeable liner under ponded water to prevent groundwater contamination;
   6. (f) Backfilling of the pit(s) to the level necessary to, in conjunction with other appropriate control measures, prevent oxidation of residual acid-generating materials.

Statutory/Other Authority

ORS 468.020

Statutes/Other Implemented

ORS 468.020, 468B.030 & 468B.160

History

DEQ 23-1992, f. & cert. ef. 9-8-92