In the last inspection of the Hastings Mine in 1997, sediments in a drainage below the mine were found to contain ten parts per million of mercury; furthermore, spring water below the mine exhibited a water concentration of .31 micrograms per liter (a violation of the State of California standard for receiving waters of .05 micrograms per liter). Miles of underground shafts were driven in the course of working the quicksilver deposits in the area. In 1989, Earth Metrics reviewed old 1918 maps of workings of the Hastings and St. John's Mines and found that mine shafts were not driven into the site prior to the year 1918.
In the context of the Hastings Mine's environmental impact assessment, it was revealed that sediments beneath the mine contained high levels of mercury; this led to concerns about the water quality. The excavation of extensive underground tunnels took place during the mining of quicksilver deposits in the region. In 1989, Earth Metrics reviewed old maps from 1918 and discovered that mine shafts were not built before this date.