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Leona Heights

Posted June 30, 2014

Work has begun at the Leona Heights Sulfur Mine Remediation Project!


The tailings are too acidic to support plant life

Upper Tailings Pile

The Leona Heights Sulfur Mine operated at the site from about 1900 through the 1920s where pyrite (an iron sulfide ore) was mined from volcanic bedrock and used to manufacture sulfuric acid.  Water flowing over and through the mining wastes dissolves sulfur and other metals, producing acid mine drainage that discharges into Leona Creek.  In the dry season, the main source of water to the creek is a groundwater seep.  During rain events, runoff from the watershed upstream of the site reacts with the mining waste, which greatly increases the amount of acid mine drainage discharged to the creek.  Water samples from the site have had pH levels as low as 3.   The acidic water increases the solubility of metals present in the mining wastes, resulting in the leaching of heavy metals into the creek.  The creek within the site has the characteristic orange color associated with acid mine drainage and contains elevated levels of cadmium, copper, mercury, nickel, lead, zinc and arsenic.

Groundwater seep with characteristic orange color associated with acid mine drainage.

Groundwater seep with characteristic orange color associated with acid mine drainage.

The following actions have been proposed to remediate the site:

  • Remove mining waste from the creek channel and from surrounding areas;
  • Grade and compact mining wastes and install a subsurface drainage system beneath the compacted mining waste to increase the stability of the compacted mining wastes;
  • Cover the consolidated mining waste with a geomembrane liner and a vegetated soil layer to isolate the mining wastes from water;
  • Reroute the seep drainage from its current location inside the mining waste to a new discharge point within the creek channel;
  • Reinforce steep slopes adjacent to the creek channel to improve the stability of the consolidated mining waste; and
  • Construct a stable creek channel that can accommodate a 100-year design storm and support natural sediment transport, incorporating cascades and step-pools that mimic natural creek channels on steep slopes.

The proposed consolidation, capping, revegetation, and drainage improvements are designed to minimize contact between stormwater runoff and mining wastes, thereby reducing the metal and excess sediment load in Leona Creek.