The Aurora Mercury Mine was active from 1853 up to the 1950´s the entire mine consisted of surface benches, 5 adits, 4 shafts with a total of 1,600 feet of underground workings.
The mercury retort furnace was used to retort the ore at the site, but was dismantled and removed , so little evidence of this and other historic structures remain.
The retorted mercury calcine tailings and furnance soot waste ranges in mercury concentration from 20 to 1,120 parts per million. The mercury cleanup level or objective was developed based on the concentration of mercury in native bedrock (non-mercury ore) materials, which has a background concentration of only 0.2 parts per million.
In the summer of 2000, restoration activities began with the removal of 8,000 cubic yards of mercury retort waste rock (calcines) and placement into a repository located adjacent to the site. All unearthed mining debris was also placed into the repository. The disturbed areas were recontoured and capped with two to three feet of non-mercury native soil. Native plant seeds from the adjacent vegetated areas were collected and then spread out under several inches of weed-free rice straw. To control erosion and stormwater runoff, rice straw hay bales were staked in the ground along the slope contours to help slow down the water and allow for the germination of the native plants. Total cost for restoration was $324,000.
During the winter of 2000/2001, two severe storms dumped over 4" of rain in the watershed above the restored site. The ephemeral drainage, which was recontoured through the site, overflowed and cut into the cap material causing extreme erosion. Creek reconstruction/stabilization was undertaken during in the Summer 2002 - Fall 2003 time period.
Risks: Water quality, Hg contamination
Location: Section 5, T12E, T18S, MDBM, San Benito Co.,CA
Field Office : Hollister
Congressional District: 17