Reports & Background

Reports & Background

The Silverton Caldera is highly mineralized, and acid rock drainage and poor water quality were prevalent long before the advent of mining. The area has been the focus of significant research on its geology and mineralization to better understand how metals loading has adversely affected the Animas River and aquatic life.

The reports below provide substantial research on a variety of topics pertaining to the Silverton Caldera, SGC’s reclamation activities, and water quality in the Animas River.


SGC’s comments on the EPA’s Proposed Plan for the Bonita Peak Repository, outlining suggestions for improvements. Cost-effectiveness, long-term-effectiveness, feasibility and safety, preservation of an historic mill, respect for private property rights, and minimization of environmental impacts all weigh conclusively in favor of a repository at Impoundment No. 4, and all weigh conclusively against a repository anywhere else.
A Conceptual Site Model for Mayflower Impoundment No. 4, which reaffirms that Impoundment No. 4 has little, if any, impact on underlying groundwater and is not the source of elevated concentrations of metals in the Animas River.
A presentation made to the Bonita Peak Community Advisory Group in May 2020, outlining that after 5 years and over $10 million dollars of intensive studies, there is no evidence that the Mayflower Mill and Impoundments are the source of anything but de minimis metals loading to the Animas River. These findings were supported by an expert geochemist from Knight Piésold, who reviewed data obtained during 5 years of extensive Mayflower Investigations. See Knight Piésold Technical Memorandum.
Scientific analysis summarizing the results of investigations since 2015 by David Bird of Knight Piésold has concluded that there is no evidence indicating that the Mayflower Facilities are the source of anything but negligible metals loading to the Animas River, if any.
The Bonita Peak Mining District (BPMD) Local Planning Group and the BPMD Community Advisory Group have requested that efforts to further improve water quality be focused on Cement Creek and recognize the benefits of bulkheading. This is consistent with the Comments and Recommendations of Pioneer Technical Services, an engineering firm specializing in abandoned mine land projects.
EPA has affirmatively refused to answer an October 2019 Public Interest Questionnaire.
A brief summary of two recent reports by Steven Lange, Executive Project Manager at Knight Piésold, examining water quality in the Animas River.
Utilizing the Colorado Department of Public Health and Environment's methodology, this paper evaluates water quality at A-72 over more than two decades, and was presented at the 13th International Conference on Mine Closure, in Perth Australia.
Built in 1929, the Mayflower Mill was essential to the Silverton Caldera's mining operations for decades. Donated to the San Juan County Historical Society by SGC, the iconic Mayflower Mill is now on the National Register of Historic Sites and is being operated as a Historical Tour and Interpretive Center. The Mill has been fully restored, and its extensive history is well-preserved and maintained to show today's visitors the pivotal role it played in shaping the region.
To facilitate water quality improvements, in addition to those already achieved by SGC, SGC has voluntarily provided EPA with design plans for a long term storage facility for sludge generated by EPA’s Gladstone Water Treatment Plant.
A peer review of the report Quantification of the Positive Effects of SGC’s Mining and Reclamation, conducted by an international firm specializing in earth and water resources.
This report examines and quantifies the positive effects of SGC’s actions on water quality in the Animas River by analyzing the Standard Residual Zinc Level at A-72, a well known water sampling point. The report concludes that there has been dramatic improvement in Animas River water quality since SGC acquired the Sunnyside Mine in 1985 and SGC’s mining, remediation and reclamation each played an important role in this improvement.
Since SGC acquired the Sunnyside Mine in November of 1985, water quality has improved. This Figure depicts the improvements to comparative Zinc levels before and after SGC’s acquisition.
Letter from the Colorado State Historic Preservation Officer to EPA regarding the importance of adhering to the National Historic Preservation Act (NHPA) and requesting involvement in EPA’s activities.
At the May 2019 Mine Design Operations and Closure Conference in Anaconda, Montana, USA, an analysis of Animas River water quality was presented utilizing over 22 years of data from sampling point A-72.
A letter from the Mountain States Legal Foundation (MSLF), a non-profit public interest legal foundation, to the EPA Inspector General regarding EPA’s conflict of interest as Lead Agency for the Bonita Peak Mining District. Read more on the MSLF website.
A summary of water quality data compared to the Colorado Department of Public Health and Environment’s zinc target, which illustrates the success of SGC’s bulkheading and remediation (updated March 4, 2019). This incorporates new data from River Watch released in February 2019.
An analysis of Animas River water samples from A-72, applying the Colorado Department of Public Health and Environment methodology, and presented at the 2019 SME Annual Conference & CMA 121st National Western Mining Conference.
A peer review of the report SGC Mining and Reclamation – Evaluating Animas River Water Quality at A-72, conducted by an independent firm specializing in earth and water resources.
January 2019 update letter to Colorado Department of Public Health and Environment (CDPHE) regarding most recent analysis of 22 years of water data from sampling point A-72.
Letter to Colorado Department of Public Health and Environment (CDPHE) regarding analysis of 22 years of water data from sampling point A-72.
An analysis of additional Animas River water sampling, including data from September 2018 and data obtained from River Watch. The new data reconfirms the fact that SGC’s bulkheading and remediation was successful and improved water quality by substantially reducing acid rock drainage and metals loading in the Animas River.
Three years after the Gold King Mine spill, Sacrison Engineering has analyzed the work conducted and identified many avoidable errors centering on EPA’s Gladstone Interim Water Treatment Plant.
A link to public comments about EPA’s Proposed Plan for Interim Remedial Actions at the Bonita Peak Mining District.
A comprehensive analysis of 20 years of water samples, including recent sampling from 2018, conclusively demonstrates that SGC’s bulkheading and remediation was successful and improved water quality by substantially reducing acid rock drainage and metals loading in the Animas River.
An expert analysis of EPA’s response to the Gold King Mine blowout.
A summary of the report "SGC Mining and Reclamation Activities and Metals Loading in the Animas River."

Researched and written by an expert in geochemistry, this report provides significant detail into the geology and natural conditions of the Silverton Caldera, the area’s mining history, and SGC’s mining and reclamation activities. It concludes that SGC’s mining and reclamation activities each substantially reduced metals loading in the Animas River from what would have otherwise been the case.

As part of its reclamation and remediation plan, SGC installed concrete bulkheads in the Bonita Peak area, which are stable and performing as designed. This report provides significant detail on the engineered concrete bulkheads SGC installed to isolate the interior workings of the mine and cause the water table to return toward natural levels.

The Bonita Peak area, located in the Silverton Caldera, and its complex geology and mineralization, has been studied extensively, with sufficient research and knowledge in place to support intelligent decision-making to improve water quality and reduce metals loading in the Animas River. Based on evidence-based research, the remaining significant source of metals loading in the Animas River is due to point sources in the Cement Creek drainage, and these flows should be targeted for treatment to substantially reduce metals loading in the Animas. The report concludes that further study is not required to make a decision on next steps to improve water quality in the Animas River.

With the goal of treating water in Cement Creek to improve water quality in the Animas River, this report compares two options: passive treatment or active treatment. The strong conclusion is that an active treatment plant will provide the greatest certainty of immediate beneficial results and will give flexibility for the future. There are many reasons why passive treatment is not the solution, including geography, weather, and passive treatment’s unproven effectiveness in this specific setting.

The report provides a thorough analysis of the Environmental Protection Agency’s actions around the Gold King Mine spill in August 2015 and how in September 2016, the “Bonita Peak Mining District” – a huge and diverse geographical area covering more than 100,000 acres – was added to the Superfund listing. The report also suggests a path forward.

The Timeline lists the activities the Animas River Stakeholders Group believes would have further reduced metals loading in the Upper Animas River Basin. The Timeline was prepared and several activities executed prior to the 2015 Gold King blowout.
Water quality in Cement Creek is affected by four major adits/portals (American Tunnel, Gold King Mine, Mogul Mine, and Red & Bonita), in addition to naturally mineralized conditions. This Report evaluates selected conventional water treatment methodologies and determines that: 1) lime treatment is the “best apparent” treatment methodology; and 2) treating flow from the four adits and some flow from Cement Creek is the “best case alternative”.
This study evaluates the contributions of the three major sub-drainages reporting to the upper Animas at A-72 and the contributions from the four major adits (American Tunnel, Gold King, Mogul and Red & Bonita) to total metals loading and water quality at CC48 (monitoring Cement Creek) and A-72 (monitoring all of the upper Animas drainage above Silverton). The research determined that control of metals laden water being released from the four adits is key to significantly reducing metals loading at A-72 under flow conditions expected over most of the year. Subsequent load and flow data supports this conclusion.