Jackson, California

ERRG was retained by the California Department of Toxic Substance Control (DTSC) to complete a mine remediation project at the 100-year-old former Argonaut Mine in Jackson, California.  This remediation project was designed to correct seismic and hydraulic deficiencies within the existing Argonaut Dam that had been identified during recent investigations.  These improvements seismically stabilized the existing dam and 65,000 cubic yards of mine tailings stored upstream. The improvements also provided an engineered flood management system to safely move storm water around the dam.  The silt soils downstream and the tailings upstream contain elevated levels of Arsenic and heavy metals (from early 1900s gold ore processing).

Initially, ERRG designed and constructed an emergency system in less than 90 days and placed the system into operation.  The system included an earthen embankment; a series of 12-inch-diameter gravity drains; two diesel-powered pumps, associated float controls, and discharge piping; and a new culvert downstream of the dam to increase stormwater capacity downstream and to direct it away from the base of the dam.  In addition to designing and constructing the system, ERRG successfully operated the stormwater diversion system for the two winter wet seasons while the dam retrofit was designed to provide future increased structural integrity of the landfill dam.

Following installation of the emergency system, ERRG worked with the project design engineer and the interagency design team (DTSC, EPA, USACE, and City of Jackson) to review and provide comments to the overall project design.  ERRG constructed the final design remedy, which included installation and maintenance of erosion controls; installation of vibration and seismic sensor devices that included remote monitoring and text message alerts if establish safety thresholds were met or exceeded; excavation, transport, and onsite stockpiling of over 9,000 cubic yards of contaminated materials from downstream of the dam; demolition and removal of a portion of the concrete dam structure; assembly of an onsite concrete mixing plant to mix and place 8,735 cubic yards of cellular concrete inside the remaining arches of the dam to stabilize the structure without using vibratory compaction equipment; import, placement, and compaction of 38,350 tons of engineered fill material to construct the downstream buttress to stabilize the dam structure; and construction of a cast-in-place concrete stormwater control structure (consisting of 124,000 pounds of rebar and 541 cubic yards of 4500-psi concrete).

ERRG completed final grading, seeding, and erosion control matting installation on the completed buttress.  ERRG provided final as-built land survey of the completed buttress, spillway, stormwater control system, and soil stockpile areas.

The project received the American Society of Civil Engineers (ASCE) Sacramento Division’s 2018 Mining Project of the Year Award.

“The California Department of Toxic Substances Control (DTSC) would like to express their appreciation for all the hard work, dedication, communication and coordination from Engineering/Remediation Resources Group (ERRG) observed during the design and construction of the Argonaut Dam Retrofit in Jackson, California. Starting in 2015, with the design and construction of the Interim Action at Argonaut Dam through the end of construction in 2018 of the Retrofit of the Dam, ERRG has showed professionalism, knowledge, and communication of the highest quality.  By attending the coordination meetings with the design team… helped to save DTSC time and money by clarifying conflicts that only an experienced Field Construction Manager would notice in the design.”

– DTSC Project Manager