Examining Erosion at Malakoff Diggins State Historic Park, a Sierra Nevada Gold Mine

Science Center Objects

Located in Nevada County, California, Malakoff Diggins State Historic Park was the Sierra Nevada’s largest hydraulic gold mine, operating from 1866 to 1884. Historically, part of the process of hydraulic mining included using mercury to extract gold from produced sediment through the process of amalgamation. This process left thousands of pounds of mercury and other heavy metals in the area. Carried by runoff, these contaminants drain from the Malakoff Diggins mine pit as suspended sediment through the Hiller Tunnel and into Humbug Creek. Malakoff Diggins is the dominant source of sediment and metal contamination to Humbug Creek, which drains into the South Yuba River, feeding Englebright Lake, and the lower Yuba River, which eventually flows to the Sacramento–San Joaquin Delta.

Malakoff Diggins State Historic Park

Malakoff Diggins State Historic Park

The State of California has identified Humbug Creek as an impaired water body, and sediment and metal contamination within the creek poses a risk to human and wildlife health. The contamination from Malakoff Diggins State Historic Park is cause for concern for numerous local and state organizations, who are seeking an integrated, science-based approach to mitigating these problems at the site.

Objective

Working in cooperation with the California Department of Parks and Recreation (State Parks), and the Nevada Irrigation District (NID), the U.S. Geological Survey is conducting a study of the sediment and metal contamination sources in the Malakoff Diggins State Historic Park. The study seeks to understand erosion rates in the mining pit, focusing on different stratigraphic layers exposed on the pit wall. The USGS will also examine the sediment coming from the site to characterize components including grain-size distribution, mineralogy, and chemical composition. To do this, USGS scientists will examine sediment from both within the Malakoff Diggins mine pit, and suspended sediment being transported from the mine pit through the Hiller Tunnel into Humbug Creek.

With a more comprehensive understanding of the rate and extent of erosion, and the makeup of sediment in the pit and Humbug Creek, State Parks and other stakeholders can make informed decisions regarding how best to mitigate sediment-related problems. Results from this study will help these organizations understand what could be done to meet waste-discharge requirements set by the State of California under the Clean Water Act.

Science Plan

To meet the objectives of this study, the USGS has conducted ultra-high-resolution terrestrial Light Detection and Ranging (T-LiDAR) surveys at four locations within the Malakoff Diggins pit. Four surveys were conducted at each location over a 32-month time span (December 2014 to August 2017) to determine the rate of erosion over an extended time period. With the data, USGS and its cooperators can estimate erosion volumes and rates, to support the development of an annual sediment budget for the entire Malakoff Diggins pit.

During 2014-16, the USGS collected surface-sediment samples within the pit and from the Hiller Tunnel to characterize physical and chemical attributes including grain-size distribution, mineralogy, and geochemistry of eroding sediment and their relation to water-quality. These data will help USGS and its cooperators determine the proportions of eroded and transported sediment from different locations within the mine pit and upstream areas.

All data collected during this study will be made publicly available either on ScienceBase or in the National Water Information System (NWIS).