Within the New Almaden Mining District, located with the Guadalupe River Watershed, mercury laden cinnabar ore was excavated and heated to extract the mercury. The leftover heat-processed wastes are referred to as calcines (our overview). Due to an inefficient extraction process, these calcines contain environmentally hazardous levels of mercury, ranging from 22 mg/kg to 233 mg/kg as measured within the Park and reported in a 2011 prioritization report. This project seeks to remove all, approximately three miles, of the calcine paved roadways (now trails) within the Almaden Quicksilver County Park.
When this mining district was in operation, calcine material was piled high near rivers, dumped into headwaters and left to the elements. In an effort to reuse this brittle, somewhat tacky material, operators used these toxic calcines to pave sections of the district to facilitate the movement of ores and wastes. No one was aware of the full impacts these decisions would have on the Guadalupe Watershed. Over the years, these roads have begun unraveling, slumping, and eroding into the landscape. If left unchecked, these roads would continue to be a source of mercury in this watershed for decades to come.
The Santa Clara County Parks and Recreation Department has partnered with the San Francisco Estuary Partnership and the U.S. Environmental Protection Agency to remove these calcines and to bury them within a permitted disposal site within the park, preventing this mercury from eroding into aquatic environments where it is transformed into highly toxic methylmercury. This will put the region one step closer to addressing all of the mercury sources into the Almaden Reservoir, the water body with the second highest methylmercury levels in the Guadalupe.
In addition to completely removing the calcine pavement and replacing it with durable hiking trails, this project will develop preliminary design plans for the remediation of the final source of mercury mine waste into the Almaden Reservoir, Jacques Gulch. Once the Calcine Pavement and Jacques Gulch are addressed, regulators believe that the reservoir will see substantial decreases in methylmercury concentrations in fish tissue. This projection is due to the highly erosive Santa Cruz mountain range, the reservoir’s other source of inflow. The clean sediments delivered to the reservoir during large storm events will eventually cap the mercury laden sediments, dramatically reducing the rate of methylmercury production.