Union Mine Site

Project Profile
Location: El Dorado County
Owner: El Dorado County
Total Project Value: Unknown
Consultant/Engr. Cost: $90,000
Square Footage/Area: 150+/- acres
Completion Date: 1999-2007

The historic gold mine shafts, tunnels, and mill sites developed in the mid-1800s through early-1900s underlay the more current sanitary landfill waste disposal site causing surface water contamination.

Stratus personnel conducted studies regarding closure of the mine shafts and tunnels and monitored construction and installation of multiple landfill gas monitoring probes.

Project Challenges:
The site assessment determined that the tailings were Group B mining wastes under Title 27 of the California Code of Regulations, because the wastes were acid generating. Lead in the tailings was the chemical of concern at this site. The mine tailings were a threat to water quality because of the acid-generating characteristic and because some of the tailings were located within a flood plain.

Stratus Solutions:
The mine tailings were consolidated into a Waste Management Unit (WMU) on the site away from the flood plain. To ameliorate the acid-generating characteristic a neutralizing agent, in this case limestone from a local quarry was crushed and blended with the mine tailings. This material was capped with 1-foot of compacted soil overlain by a one-foot vegetative layer using material native to the site, and seeded with endemic grass species. Since its construction in 1998, the WMU has been monitored and reported by the client and Stratus personnel through Waste Discharge Requirements issued by the CRWQCB. No water quality impacts have been detected at the site since the WMU construction.

Stratus personnel conducted field mapping of mine tunnels and shafts to facilitate remedial design for landfill expansion.