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Site Report: Mexican Mine Mill Tailings

Site Name: Mexican Mine Mill Tailings
Address: Treadwell Trail on SE Shore of Douglas Island on Gastineau Channel, Douglas, AK 99824
File Number: 1538.38.001
Hazard ID: 405
Status: Cleanup Complete - Institutional Controls
Staff: IC Unit, 9074655229 dec.icunit@alaska.gov
Latitude: 58.263834
Longitude: -134.367193
Horizontal Datum:NAD83

We make every effort to ensure the data presented here is accurate based on the best available information currently on file with DEC. It is therefore subject to change as new information becomes available. We recommend contacting the assigned project staff prior to making decisions based on this information.

Problems/Comments

The site consists of waste rock mine tailings located on Douglas Island that was deposited in the early 1900s from a gold ore extraction process that included mercury and/or cyanide. Elevated concentrations of lead, zinc, arsenic and mercury are present in ore processing waste rock areas at the site. These areas stand out by their lack of plant growth in an otherwise heavily vegetated temperate rain forest. The 35-acre site has been developed into a recreation facility. Areas of concern include the upper and lower tailings storage sites. The upper site was capped in the 1990s. The lower tailings site was characterized in 2006 and the cap was completed in 2007. The lower tailings cap covers 40,000 square feet and is 15 inches thick. The top 6 inches is crushed rock and the bottom 9 inches is larger shot rock. The S-SE side along the beach is contained with a sloped armor rock wall four feet high. With the site remedy completed, the two AOCs have entered the long-term monitoring phase. Maintenance of the cap is the only site work remaining; no further characterization is required. The remedial option used at this site is capping with soil that will support a vegetated layer. The upper tailings pile cover was completed with public and private funds during the 1990's on abandoned mine properties that contained numerous public safety and environmental hazards such as open shafts and acid rock drainage. Abandoned Mine Lands (AML) projects represent partnership efforts by the Western Governors Association, the CERCLA, or Superfund Program, Forest Service, USGS, Interior, BLM, NPS, and other federal agencies, the State of Alaska and the National MIning Association. On 12/16/10 the site name for Hazard ID 405 (file no. 1538.38.001) was changed from Treadwell Mine Complex to Mexican Mine Mill Tailings. All work recorded under this Hazard ID through this date pertained to the Mexican Mine Mill Tailings portion of the complex. A separate database record under the former name Treadwell Mine Complex(Hazard ID 25594) will track information on the other portions of the complex. Data collected in May of 2014 indicated the following contaminant concentrations in sediment in mg/kg: Cn 32, As 20, Cr 51, Hg 2, Se 4.4. Water data indicates that the water is not being contaminated.

Action Information

Action Date Action Description DEC Staff
8/26/1993 Site Added to Database Elevated levels of lead, zinc, arsenic and mercury are present at the site. Former Staff
11/10/1994 Site Ranked Using the AHRM Initial ranking. Former Staff
11/1/1999 Site Ranked Using the AHRM Re-ranked. Changed Air Exposure index from 0.2 to 1.0; Release Information Value from 0.2 to 1.0; and Quantity Value to 2.1. The unknown quantity value is based on the elevated arsenic levels at the cyanide tailings area. Volume or areal extent unknown. Bill Janes
11/12/1999 Site Ranked Using the AHRM Re-ranked. Changed the Value for Environmental/Recreation Area from 0 to 3 based on the fact that the entire complex is probably about a mile long. At one end is the Sandy Beach recreation area, a City park. Sandy Beach is comprised of old Treadwell mine tailings. At the other end is the cyanide mill tailings area. Obvious stress to vegetation because no vegetation is growing there. Former Staff
1/18/2001 Update or Other Action CERCLIS ID # AKD981767387. History: state-lead Discovery 3/1/87, PA 6/23/89, SI 6/30/91. Site Reassessment federal lead 6/30/99 thru 9/18/00. Bruce Wanstall
2/15/2002 Update or Other Action Project tickler update - Reviewed SI data. Conferred with Stephanie regarding potential health risks. Sent email to Carnahan recommending that we move on further investigation and probable cleanup. Bill Janes
12/15/2003 Site Ranked Using the AHRM GW values changed to minimals. GW not used in the area. Bill Janes
6/6/2005 GIS Position Updated GIS data transferred from Garmin GPS 76 calibrated for NAD 27. Accuracy estimate is high. Glory Hole adit lat long coordinates projected on Topozone map 1:50K and saved to electronic file at \\Jn-svrfile\groups\SPAR\Spar-Contaminated Sites\38 Case Files (Contaminated Sites)\1538 Douglas\1538.38.001 Treadwell Mine Complex Bruce Wanstall
1/3/2006 Meeting or Teleconference Held Janes and Wanstall met with a permitee representative and CBJ Planning Commission to discuss interim control measures at the lower cyanide tailings area to allow a closely supervised increase in recreational activity in 2006 and design of Site Characterization Plan to support development of permanent remedial alternatives. Bruce Wanstall
4/20/2006 Meeting or Teleconference Held ADEC met with the landowner AJT Mining Properties representative David Stone and legal representation Steve Sorensen of Simpson Tillinghast & Sorensen to coordinate a Site Characterization and Corrective Action Plan for the lower cyanide waste rock site at the Mexican Mine in the Treadwell Mine Complex. The cost recovery process and site closure with property restrictions were explained by ADEC. Bruce Wanstall
6/20/2006 Update or Other Action Discussion was held by telephone with Smith Bayliss LeResche about the mine tailings pile site conditions, the sampling plan and the condition of a stream that passes near the upper tailings pile. Bruce Wanstall
6/28/2006 Update or Other Action Treadwell MIne Cyanide Tailings Site Investigation Plan recieved; site visit and plan review scheduled in July 2006. Bruce Wanstall
7/10/2006 Proposed Plan Site Investigation and Tailings Stabilization Workplan approved with comments and requests. Bruce Wanstall
10/5/2006 Site Characterization Report Approved Investigation and laboratory Report reviewed and approved. Bruce Wanstall
12/13/2006 Update or Other Action ADEC sent a letter reminding the responsible party of their agreement to install a cap and re-vegetate the Mexican MIne contaminated site portion of the Treadwell Mine Complex. Site characterization of the lower tailings pile in 2006 by the AJT Mining Properties’ environmental consultant established that mercury in the waste rock exceeded the 18 AAC 75.341 Soil Cleanup Level Table B1 soil screening level for the migration to groundwater pathway. Statute and regulatory authority to cost recover expenses incurred by the ADEC was also stated. Bruce Wanstall
1/5/2007 Update or Other Action AJT Mining Properties has declined to accept responsibility for $1171.40 in costs ADEC incurred preparing for and meeting with the City and Borough of Juneau Planning Commission to assist in the permitting process for development of the former Mexican Mine cyanide waste rock site on Douglas Island. The CBJ permit was approved contingent upon AJT Mining Properties coordinating with ADEC to conduct a site investigation and develop a plan for remediation of the contaminated property. AJT accepted responsibility for ADEC project management costs beginning with a meeting held at the ADEC on April 20, 2006 to discuss the project. On 1/5/2007, a check for $547.58 was received by DOL for ADEC costs to date. Bruce Wanstall
9/27/2007 Exposure Tracking Model Ranking Although a formal determination for site control has not been made concerning its use, surface water and ground water on the property are not used, are unlikely to become used, and do not contribute to a source of drinking water in the area. Surface water drainage has been diverted away from the upper tailings pile to control leaching from the iron sulfide mineral known as pyrite (FeS2). The lower tailings pile is near tidewater at Gastineau Channel. Neither water body presents an unacceptable exposure risk via the ingestion pathway. Bruce Wanstall
10/17/2007 Meeting or Teleconference Held DEC and Nortech held a meeting at the lower tailings cap site; that area was almost entirely vegetated. The upper tailings pile will need some repairs to the cap that was installed by the State (DNR) in the 1990s. In general, it appears the site controls are effective in controlling the dermal exposure route. Tentative approval of the vegetated cover site remedy was verbally given along with a request that a binding long term maintenance and inspection agreement be submitted by landowner AJT Mining Properties Inc. Bruce Wanstall
12/5/2007 Document, Report, or Work plan Review - other Review the Treadwell Mine Cyanide Tailings Stabilization Cap Report dated 11/15/07; the summary document is attached. DEC approval letter for the site remedy long term maintenance plan was sent to AJT Mining Properties; the document is attached to the database record. Bruce Wanstall
12/7/2007 Long Term Monitoring Established ADEC has determined that the soil cap and surface drainage long term maintenance plan on the upper and lower tailings sites provides an effective site control remedy. Site remedy control ensures that residual soil contamination does not pose an unacceptable risk to human health and the environment. Should any areas within the lower tailings stabilization cap or the upper tailings area show damage to the vegetation within the tailings area or damage to the stabilization caps, the date of inspection, date of damage and actions taken to repair and prevent further damage shall be logged and made available to the ADEC. ADEC requests notification of plans to repair, modify, or expand the cap areas. Stormwater drainage ditches and culverts shall be maintained in such a manner that does not cause erosion within the tailings areas. Bruce Wanstall
1/10/2008 Institutional Control Record Established Institutional controls limit, prohibit or protect against activities that interfere with improvements designed to encapsulate or control residual contamintion per 18 AAC 75.990(54). There is residual soil contamination remaining at depth beneath the soil cover at the upper and lower tailings piles on the Treadwell Mine Complex. ADEC determined it does not pose an unacceptable risk to human health or the environment, subject to the following conditions: Any proposal to excavate the residual contaminated material shall be reported to ADEC and a work plan describing how the soil will be managed and/or disposed must be submitted for review and approval prior to excavation. Any proposal to transport soil and/or groundwater off site requires ADEC approval in accordance with 18 AAC 75.325(i). Bruce Wanstall
1/11/2008 Conditional Closure Approved The Treadwell Mine Complex shall be managed in accordance with the approved inspection and maintenance plan (prepared by Nortech and dated November 2007). Site inspections of the soil cap areas shall be conducted two times per year to ensure that site conditions remain stable. In the event the tailings pile areas are damaged or disturbed, ADEC shall be notified and a corrective action plan submitted for review and approval. This determination is in accordance with 18 AAC 75.380(d)(2) and does not preclude ADEC from requiring additional assessment and/or cleanup action if future information indicates that this site may pose an unacceptable risk to human health or the environment. Site Closure (without conditions) can be achieved when soil sampling confirms that all soil meets the most stringent 18 AAC 75.341 Migration to Groundwater, Over 40 Inch cleanup levels and ground water meets 18 AAC 75.345 Table C levels. Bruce Wanstall
12/1/2008 Site Visit ADEC traveled to the site with Jason Ginter (Nortech) and inspected the upper and lower tailings sites. Observations determined that maintenance of the ADEC-approved site control remedy is necessary in 2009 before resumption of Alaska Canopy Adventures business activity on the property. While the lower tailings cap appears intact and requires only minor drainage maintenance along the southern edge and spot repair along the beach, the upper tailings pile requires more extensive water management and surface cap repairs. The main access road passes alongside the upper tailings area and the former vegetation on the cap has been severely damaged. Surface water flowing onto the bare material is washing out channels in the tailings. Controls must be installed to divert surface water from entering the tailings pile. Bruce Wanstall
1/5/2009 Update or Other Action ADEC requests that a lined roadside drainage be installed between the road and the upper tailings pile with abutments that will prohibit any vehicles from entering the stabilization cap clearing. Top soil will be placed over the upper tailings pile and seeded to restore vegetation. If a vehicle pullout is needed for traffic then another location will have to be cleared for that purpose. Bruce Wanstall
5/13/2009 Site Visit ADEC accompanied the landowner to inspect repairs to the cap and improved water management system installed in spring 2009 at the upper cyanide tailings pile. The 2008 annual inspection found damage to the cap from vehicular activity related to the popular zip line recreational business that operates seasonally at the site. The repairs are acceptable to ADEC standard and the zip line managers have made protection of the upper and lower tailings caps a priority in the operations plan. Bruce Wanstall
10/24/2011 Site Visit ADEC traveled to the site with Jason Ginter (Nortech) and the landowner to inspected both the upper and lower tailing site caps. The lower site appeared to be intact with intermittent vegetation growing over top of the one-foot cap. No odor was noticed and surface water draining off the southwest hillside was diverted into an open drainage channel flowing away from the tailing cap. The upper tailing cap appeared intact with intermittent vegetation. The main access road along side of the upper tailings area had a culvert installed to divert uphill surface water flow away from the tailing cap. In spring 2012 another inspection will be conducted by ADEC. Erik Norberg
5/16/2013 Long Term Monitoring Complete Administrative action added during a quality control check. Kristin Thompson
12/16/2013 Institutional Control Compliance Review IC review conducted. Set the reminder system to contact the RP in spring so that the gravel pads covering the tailings piles can be inspected. Evonne Reese
5/15/2014 Site Visit DEC staff traveled to this site with a Nortech representative and the landowner to inspected both the upper and lower tailing site caps. The lower site cap was intact with intermittent vegetation growing over the top of the one-foot cap. No odor was present at either location. The upper tailings cap was also intact with intermittent vegetation. The abutments that prohibit vehicle traffic remain in place and seem to be effective. A culvert that diverts uphill surface water flow away from the tailings caps also seems to be effective since there was no sign of erosion on the cap’s surface. During the fall of 2014, after the tourist season, another inspection will be conducted by ADEC. A letter was issued to the landowner that includes the details of this inspection. Evonne Reese
7/16/2014 Document, Report, or Work plan Review - other Reviewed the Sediment and Surface Water Sampling Report for Treadwell Tailings – Mexican Mine dated June 30, 2015 issued by NORTECH. This sampling event was voluntary and requested by AJT Mining Properties. Samples include sediment from the upper/lower tailings piles and surface water from the creek near the tailings piles. Samples were analyzed for metals (arsenic, barium, cadmium, total chromium, lead, mercury, selenium, and silver), cyanide, and pH. The water sample results indicated that surface water has not been impacted by contamination emanating from the tailings. The sediment sample results showed concentrations of arsenic, chromium, mercury, selenium, cyanide that exceeded cleanup levels and were consistent with historic mining and cyanide leach processing of heavy metal ore. The tailings piles will be inspected during the fall of 2014. Evonne Reese
9/23/2014 Institutional Control Update A site inspection was performed on this date by by Evonne Reese and Sally Schlichting. A letter regarding the findings will follow in the near future. Evonne Reese
11/12/2014 Institutional Control Update Fall site inspection letter issued and mailed to the responsible party. Evonne Reese
5/11/2015 Institutional Control Update A spring 2015 site inspection has been planned for late May 2015. Evonne Reese
5/20/2015 Update or Other Action Staff name changed from IC Unit to Danielle Duncan. Evonne Reese
5/26/2015 Site Visit ADEC staff traveled to the site with J. Ginter (Nortech) and C. Johnson (AJT Properties) to inspect the caps on the upper and lower cyanide process tailings areas. The upper tailings cap is intact with thicker vegetation than observed during the fall 2014 inspection. The alders have grown nearly a foot tall and have no signs of stress (yellowed leaves, stunting etc.) at this time. There is a shot-rock utility road running through the upper tailings pile and it appears to be in good condition. The log abutment that prohibits vehicle traffic remains in place and effective. The lower tailings cap remains intact with little vegetation growing on the surface which may be a result of having used larger sized shot rock as armoring for the shot-rock utility road used occasionally by Alaska Canopy Adventures. The channel side of the tailings pile is contained with a sloped armor rock wall 4’ high and 225’ long and is in good condition. Overall, the cap appears to be providing a protective barrier between the tailings and the surface. Suggestions for maintenance of the institutional controls currently in place- 1. Please add copper to the list of potential COCs 2. The culvert input at the upper tailings cap is partially crushed at its opening. Please provide some protection for it so that is does not close and require replacement. 3. Please consider lining the bottom of the streambed at the lower tailings cap where water may travel at high velocity down slope carrying contaminated sediments. Danielle Duncan
7/2/2015 Update or Other Action On June 23, 2015, NORTECH mobilized to the site to improve erosion and sediment control measures. Straw waddles were placed in areas to capture sediments and allow surface water drainage. A geotextile fabric was placed at the outfall of a drain pipe from further uphill. The fabric was weighted down with soils from nearby (crush and run used for the road/parking area). A section of straw wattle was placed in a U shape, surrounding the outflow. An additional two sections of straw wattles were placed further downstream of the drainage area as well. The wattles were secured in place with wooden stakes. Danielle Duncan
9/29/2015 Exposure Tracking Model Ranking A new updated ranking with ETM has been completed for source area 71384 cyanide waste rock tailings pile. Danielle Duncan
5/17/2016 Update or Other Action Sent a letter today requesting scheduling of the annual site inspection. Danielle Duncan
7/5/2016 Site Visit Site visit with the RP and Nortech to inspect the tailings caps. The upper tailings cap is intact and was similar in appearance to previous site visits. The log abutment that prohibits vehicle traffic remains in place and effective. The culvert input at the upper tailings cap is in place. The lower tailings cap remains intact and as observed in the past site inspections, there is sparse vegetation growing on the surface. Suggestions for maintenance of the institutional controls currently in place- 1. The streambed at the lower tailings cap is receiving high amounts of runoff. ADEC requests that you install replacement straw wattle or another storm water protection best management practice (BMP) to reduce sedimentation into the stream. 2. According to ADEC records, the lower tailings cap covers 40,000 square feet and is 15 inches thick. The top 6 inches is crushed rock and the bottom 9 inches is larger shot rock. Please measure the depth of the current cap on the lower tailings pile and add material as necessary to ensure that a 15 inch cap covers the entire area. This will ensure that the institutional control of capping is preventing people and wildlife from contacting the tailings. Additionally, fortifying the cap should limit sediment migration to the intertidal area. Danielle Duncan
9/26/2016 Update or Other Action Rec'd a letter in response to my follow-up letter on the state of the tailings caps and erosion control measures. Drafted and sent a letter generally concurring with Nortech and look forward to reviewing information regarding additional erosion controls and determination of the current depth of the tailings cap. I instructed that no additional capping material be added prior to the ADEC's review of available information. Danielle Duncan
6/4/2018 Update or Other Action Sent a request for an update letter. Danielle Duncan
6/21/2018 Update or Other Action The responsible party is working with Nortech on a response to my request for update letter. Danielle Duncan
7/23/2018 Meeting or Teleconference Held Met with J. Ginter of Nortech to discuss my request for update letter and upcoming site visit. There are currently 2 options due to the appearance of the cap as eroded: the options are add an additional 15 inches to re-cap it or sample the surface and analyze for metals to determine whether or not the cap remains effective. Danielle Duncan
7/26/2018 Site Visit Site visit to inspect the tailings caps with Avista and Nortech. Danielle Duncan
1/17/2019 Site Characterization Workplan Approved Approved the Tailings Cap Assessment plan this date. The plan outlines activities to investigate the thickness of the lower tailings cap, sample the fines on the surface of the cap, and install three concrete survey stands. Danielle Duncan
5/16/2019 Site Visit Site visit with J. Barsis and Nortech to inspect the upper and lower tailings cap. Survey work has begun on the lower tailings cap and the cap (15 in) is uneven - some spots have 15 in. and others don't. Permanent survey monuments will be installed and additional cap material will be added and in the future, the depth of the cap will be evident from the monuments. there is no longer vehicular traffic on top of the lower cap. The upper cap area is still vegetated - run-off controls are still in place. The intertidal zone below the lower cap has abundant red staining and fine, yellow material exists underneath the surface sediment. This may require investigation in the future. Danielle Duncan
8/14/2019 Update or Other Action Provided comments on the Tailings Cap Assessment report - expect to review a final version soon. Danielle Duncan
9/6/2019 Institutional Control Update According to the Lower Tailings Cap Assessment Report Mexican Mine – Treadwell Mine Complex, the cap was evaluated for thickness and the thickness ranged from 7 to 14 inches thick. As a result, more material will be added to ensure that at least a 15-inch cap is present. Danielle Duncan
1/17/2020 Update or Other Action The Alaska Department of Environmental Conservation (ADEC) Juneau Office has reviewed and approved the 2019 Mexican Mine Mill Tailings Cap Maintenance dated January 9, 2020 and prepared by NORTECH, Inc. on behalf of AJT Mining Properties Inc. (AJT). The report was received in our office on January 9, 2020 via electronic mail. All site activities conformed to the 2017 ADEC Field Sampling Guidance and the work plan approved by the ADEC, therefore, the report is approved in accordance with 18 AAC 75.335(d). The approved cleanup levels for this site remain as noted in the 2008 Conditional Closure letter. If more information becomes available in the future, and you would like to propose another cleanup level, ADEC will evaluate the request. Amy Rodman
2/11/2020 Institutional Control Compliance Review I paid a personal visit to this property and took photos of the cap improvements with the addition of gravel to bring the overall cap thickness to 15 inches. Photos of this site visit are included in the Documents section of this database record. Evonne Reese
8/12/2020 Institutional Control Update Review the need for the IC requirement site inspection frequency of twice yearly since the property is no longer being used for zipline operations. Evonne Reese

Contaminant Information

Name Level Description Media Comments
Mercury - Total Between Method 2 Migration to Groundwater and Human Health/Ingestion/Inhalation Soil
Cadmium - Total Between Method 2 Migration to Groundwater and Human Health/Ingestion/Inhalation Soil
Arsenic - Total Between Method 2 Migration to Groundwater and Human Health/Ingestion/Inhalation Soil

Control Type

Type Details
Institutional Control Management Plan Control surficial damage from drainage or vehicular traffic. Inspect and maintain the soil cap over the upper and lower tailings piles to ensure that the site conditions remain stable. In the event that the tailings pile areas are damaged or disturbed, ADEC shall be notified and a corrective action plan submitted for review and approval.

Requirements

Description Details
Excavation / Soil Movement Restrictions Any proposal to excavate the residual contaminated material shall be reported to ADEC and a work plan describing how the soil will be managed and/or disposed must be submitted for review and approval prior to excavation. Any proposal to transport soil and/or groundwater off site requires ADEC approval in accordance with 18 AAC 75.325(i).
Maintenance / Inspection Of Engineering Controls The upper and lower tailings piles shall be inspected twice yearly to verify that the pads are not damaged and that conditions remain protective. In the event the tailings pile areas are damaged or disturbed, ADEC shall be notified and a corrective action plan submitted for review and approval.
Advance approval required to transport soil or groundwater off-site. Standard condition.
Movement or use of contaminated material (including on site) in a manner that results in a violation of the water quality standards is prohibited (18 AAC 70) Standard condition.
Hazard ID Site Name File Number
25594 Treadwell Mine Complex 1538.38.007

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State of Alaska Department of Environmental Conservation

P.O. Box 111800
Juneau, AK 99811-1800
Phone: 907-465-5066
Fax: 907-465-5245
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