Construction Begins On Argonaut Mine Dam Project

From CEQA: A project to retrofit the dilapidated Argonaut Mine Dam is underway, the latest phase in the Department of Toxic Substances Control’s plan to protect the Jackson community from contamination resulting from past operation of the historical mining site.

“The project will ensure public safety as it significantly reduces the potential for release of arsenic-contaminated mine tailings and other harmful chemicals into the environment,” said DTSC Director Barbara A. Lee.

The six-month project will upgrade the aging, early-1900s dam by filling the existing arches with concrete and placing a berm in front of the structure. The project also calls for building an earthen embankment and spillway to drain surface water. The dilapidated dam holds back more than 165,000 cubic yards of contaminated mine tailings and soil left behind from years of mining.

DTSC has been proactive in taking effective measures to protect the community prior to the dam’s retrofitting, including the construction of an interim system to divert stormwater to reduce the risk of a dam failure that could come from excessive pressure building up in rain-soaked soil behind the dam.

“The diversion system was necessary to mitigate the potential for dam failure until the design and construction of the dam retrofit was possible,” said DTSC Director Lee. “It has worked as anticipated despite record rainfall totals, and, above all, it has kept the public safe.” The interim diversion system will remain in place throughout construction, until the permanent storm-water diversion system is implemented as part of the dam retrofit.

On May 29, DTSC provided an update on the project during a Jackson City Council meeting. DTSC staff and a representative with the U.S. Environmental Protection Agency were on hand to answer questions about construction, water diversion plans, traffic impacts during construction, and the overall importance of the project.

During the meeting, DTSC said the following safety measures will be taken during construction:

• Work areas will be fenced, and access will be controlled and limited.
• Construction and soil/material transport will be primarily on site.
• Any trucks leaving the site will be tarped before entering public roads.
• Truck tires will be sprayed off with water.
• Dust control measures will be put in place.
• Air monitoring will be conducted to ensure that dust levels remain at a minimum.
• Work will be conducted between 7 a.m. and 5 p.m.

Last December, state officials signed off on the California Environmental Quality Act (CEQA) review and approved a Remedial Action Plan (RAP), two key requirements that cleared the way for the start of construction on the project. The selected remedy in the RAP was one of four identified by DTSC. The chosen plan is low-impact on the existing structure and relatively simple in design.

On May 17, DTSC and the Attorney General’s Office secured a temporary restraining order (TRO) from Amador County Superior Court granting DTSC access to the site to begin construction. Because the property owner did not voluntarily grant DTSC access to the site, a court order was needed to keep the project on schedule. A follow-up hearing on the TRO has been set for June 22.

The dam is located west of downtown Jackson at the intersection of Argonaut Drive and Sutter Street. The Argonaut Mine recovered gold by processing ore. The processing method of the time created the mine tailings, consisting of more than 165,000 cubic yards of hazardous levels of arsenic, lead, and mercury that could potentially be released under a catastrophic dam failure.

Image Via CEQA