Ongoing Monitoring

• Continuous (hourly) flow measurements are made at the St Louis Tunnel discharge downstream of the historic portal (station DR-3) and at the pond system outfall (DR-6) to the Dolores River using automated instrumentation.
• Water samples are collected monthly from the St. Louis Tunnel discharge, two points within the pond system (discharge from Ponds 8 and 15), the outfall from the pond system to the Dolores River, and five locations in the Dolores River upstream, adjacent to, and downstream of the St. Louis settling pond system. The samples are analyzed for total and dissolved metals, potentially dissolved metals, alkalinity, hardness, total dissolved solids, total suspended solids, cyanide, salinity, and sulfate. The EPA START contractor collected split samples with ARCO contractors in November 2013.  ARCO was informed in January 2014 that the frequency of the water sampling can be reduced to quarterly.
• Groundwater samples are collected and water levels measured monthly when conditions permit in 48 monitoring wells (including some paired shallow/deep wells) located throughout the Site. In an effort to more completely evaluate removal alternatives and the contaminated groundwater near Ponds 16/17 and its migration, 17 of these wells were installed during 2013 and sampling and monitoring started in November 2013. Wells are located upgradient of the Site, along the hillside, along the adit collapse area, within the Pond 16/17 area, within Pond 13, along pond berms, and at the downgradient, southern boundary of the active settling ponds.

o    Prior to 2011 - 8 wells currently sampled (GW-1, GW-3, GW-4, GW-5, GW-6, GW-7, EB-1, EB-2)

o    2011 Wells - 12 wells currently sampled, though MW-2S and MW-3S are typically dry (MW-1S, MW-1D, MW-2S, MW-2D, MW-3S, MW-3D, MW-4S, MW-4D, MW-5S, MW-5D, MW-6S, MW-6D)

o    2012 Wells - 9 wells currently sampled, though MW-202 is frequently dry (MW-101, MW-102, MW-103, MW-104, MW-202, MW-204, CHV101-S, P13-102, P13-103)  

o    2 angled borings into the St Louis Tunnel (AT-2 and BAH-01)

o    2013 Wells - 17 wells sampled beginning November 2013 (MW-105, MW-106, MW-107, MW-108D, MW-108S, MW-109S, MW-110, MW-201, MW-203, MG-205, MW-207, MW-208, CHV-101D, CHV-101M, CHV-101U, PZ-1, PZ-2)

Solids Management

• Solids from historic water treatment (lime addition) are being removed from the ponds to increase pond storage capacity and reduce the potential for releases to the Dolores River. A decision will be made regarding the remaining treatment waste solids in the ponds following the selection of the water treatment technology and system design.
  • Approximately 7500 cubic yards of lime precipitation solids were removed from Pond 18 during 2011 and placed in drying cells constructed in the Pond 16/17 area. The solids are being monitored for drying and handling characteristics.
  • Approximately 2200 cubic yards of solids were dredged from Pond 15 during 2012 and placed in Pond 13 for draining and temporary storage.
  • Approximately 1500 cubic yards of solids were dredged or excavated from Ponds 11 and 12 during 2013 and placed in Pond 13 for draining and temporary storage.
  • Two feet of solids were left in each pond to reduce infiltration from the ponds to the underlying aquifer and potentially to the Dolores River.
  • Pond 14 dredging/excavation has not started. The berm improvements needed for safe pond access were completed during 2013, and the solids removal work is scheduled to be completed in 2014.
• Geotechnical/geologic evaluations of potential solids drying and repository sites were performed in 2011, 2012 and 2013. The 2011 investigation identified landslide deposits in the steep slope of CHC Hill that ruled out the initially preferred repository site located north of the pond system.  In 2012 and 2013, investigations focused on other potential onsite repository locations located to the south of the St. Louis Tunnel and in Pond 13, a relatively empty pond that does not receive St. Louis Tunnel flows.  The evaluation included a range of potential storage volumes based on the solids currently on site and estimated solids generation for the two primary water treatment methods being considered for the St. Louis Tunnel. An alternatives evaluation report was completed in 2013 indicating the preferred location.
• Repository preliminary designs and operating plans were submitted by ARCO to EPA in December 2013.  In addition, these plans were submitted to the State and County to allow ARCO to receive a Certificate of Designation to construct a waste repository pursuant to State solid waste regulations. (While a CD/permit is not required as part of the CERCLA action, long-term regulatory control is anticipated to fall under the State solid waste program.)  The recommended alternative is a lined cell at the “South Stacked Repository A” location, located east of the Pond 16/17 interim drying facility. ARCO is working with the U.S. Department of Agriculture Forest Service (USFS) to secure part of the land needed for the permanent solids repository.  EPA and USFS have coordinated on this topic.
• The Phase 1 Cell is designed for approximately 30,000 cubic yards (cy) of waste.  The repository design allows for expansion into the Pond 16/17 area, if needed, for a full build-out storage capacity of 365,000 cy.
• Calcines, a solid waste from roasting pyrite ore to produce sulfuric acid, are present within the Pond 16/17 area and elsewhere on site, such as beneath Pond 13 and between Pond 19 and the VCUP soils repository. The calcines were sampled and underwent geochemical analysis to determine if drainage from the lime precipitation solids or groundwater flowing through the calcines causes leaching of hazardous substances and potential migration off-site. The results are being evaluated in combination with groundwater levels, contaminant concentrations in monitoring wells, and proposed Site uses. Approximately 6640 cubic yards of calcines excavated as part of the demonstration-scale wetland project (see below) were placed in drying cells 3 and 4 in the Pond 16/17 area during 2013 for temporary storage.
• The Flood Dike, forming the west bank of the settling ponds adjacent to the Dolores River, was upgraded and raised in June 2012 based on 100-year flood modeling (HEC-RAS). Upgrades included: dike embankment filter material was added near seeps, larger and more riprap was added near the upper ponds (18 and 15), and the elevation of the dike along Pond 9 was increased to provide more freeboard relative to flood stage water elevations.
• Pond berms were evaluated during 2011, 2012 and 2013, and the results will be used to design pond structures if needed for the selected water treatment system.  In 2013, Pond 18 repairs were performed where a buried pipe that posed stability concerns was identified, and Pond 18 was partially filled with mine discharge.

Hydraulic Controls at St. Louis Tunnel Collapsed Adit Area and Mine Water Source Control

• The collapsed portion of the exposed St. Louis Tunnel extends approximately 250 feet to the buried section of tunnel (“debris plug”) overlain by loosely consolidated (sand to boulder size) colluvium. The “terrain trap,” as this area is referred to, presents difficult and unsafe conditions in which to attempt opening the tunnel or to construct controls to capture the mine water flowing from the tunnel through the debris plug. Two borings were drilled into the bedrock and the open section of tunnel. The water levels and associated pressure on the blockage have been monitored through the bore holes.

• Hydraulic control alternatives and potential failure modes were analyzed by ARCO.  A model was developed in 2013 to assist in determining the anticipated flows from the St. Louis Tunnel before and after hydraulic controls are installed.  These analyses and recommendations for hydraulic controls were submitted to EPA in October 2013.
• A mine workings model/map was developed by ARCO contractors using historical mine maps and documents. This information was obtained from current and former owners of the mines in the area, and ARCO has digitized the records and maps. 
• Underground mine workings investigations were performed during 2011 and 2012 to assess in-mine water chemistry, flow pathways, and the structural reliability of workings and to develop recommendations for rehabilitation needed to ensure access and continued transport of water to the St. Louis Tunnel. EPA, Colorado Division of Reclamation and Mining Safety (DRMS), and ARCO supported these efforts.

• The Blaine and 517 adit portals were reconstructed in 2012 to provide structurally safe conditions to enter the adits.  The portals and the initial sections of the adits were replaced with steel supports and steel lagging. The DRMS contractor performed this work.
• A coffer dam at approximately 350 feet inside the Blaine Adit was replaced in 2013 to ensure that acid mine water continues to flow to the 517 Shaft and does not discharge from the adit to Silver Creek.  The previous dam showed evidence of corrosion when the mine pool was drained for work in the adit in 2012.
• Blockages from rock falls in the mine that were impeding flow to the Morris Cook Incline were removed to allow flow to continue towards the Morris Cook Incline and the 517 Shaft.

• A transducer was installed in the 517 Shaft in the fall of 2011 to measure water level changes at the water surface (approximately 455 feet below ground); however, winter icing conditions over the shaft caused the cable to break and the transducer was lost down the shaft. Water levels in the 517 Shaft were measured continuously during an injection test conducted in 2012 and 2013 (see below).
• A base flow measurement project was conducted by EPA and its contractors, DRMS, and ARCO to determine the amount of water that flows from the Blaine Tunnel to the 517 Shaft via the Humboldt Drift. The four day operation, conducted from July 9 through 12, 2012, involved pumping the pooled mine water from the Blaine Adit level to the 517 Shaft via 6 inch piping, then measuring flow into the tunnel behind the coffer dam. Estimated base flow in the Blaine Tunnel ranged from 10 to 20 gpm at the time of pumping, substantially lower than other historical accounts of flow (e.g., 200 gpm) within the Blaine system. It is unknown if the lower flow was due to possible diversion of Blaine Adit water to the Number 3 Shaft that also connects to workings moving water towards the 517 Shaft or other pathways or to the exceptionally low snow pack in the 2011/2012 winter.
• A flume was installed in the Blaine Adit to measure the flow of water from the workings entering into the 517 Shaft via the Humboldt Drift. A pressure transducer was installed to measure flow through the flume and readings began in October 2012. The most recent download of flow data occurred during November 2013.
• Mine water source controls beyond those described above appear to be an unlikely option at this time based on the conditions of the underground workings.

Water Treatment Studies

• At this time, potential water treatment methods being considered include an active lime treatment system, in-situ treatment, passive treatment (including rock drain, constructed wetlands, bioreactor), and ion exchange. Active lime treatment is the default system if the other components are not adequate to meet potential discharge criteria.

• A pilot-scale wetland/sulfate reducing water treatment test was initiated in November 2012. The passive treatment system included a rock drain for manganese removal and a constructed wetland for removal of other metals. The treatment substrate is contained in a lined cell within Pond 9; the system continues to be operated and monitored while treating a flow of approximately 5 to 10 gpm. Results indicate that the system was successful in removing the primary contaminants (95 percent removal of cadmium and 99 percent removal of zinc). The pilot-scale system leaked and had hydraulic problems due to consolidation of fine-grained substrate materials. The results of the pilot-scale passive system are summarized in a report submitted in November 2013. The pilot-scale passive water treatment system will remain active to support the bacteria/inoculum until it can be transferred to the demonstration-scale system.
• A demonstration-scale (10 to 50 gpm) passive water treatment test was designed and construction began in 2013. The overall demonstration-scale design includes both a horizontal flow treatment system and a vertical flow treatment system.  The horizontal flow system includes a settling basin to remove solids and iron, a surface flow wetland for additional iron removal, a horizontal flow subsurface flow wetland to remove metals, an aeration channel to oxygenate the wetland discharge, and a rock drain to remove manganese. The vertical flow system includes a settling basin, a vertical flow biotreatment cell, and an aeration cascade. The systems were designed to allow various flow configurations to assist in determining the components needed for optimum system design. The subgrade preparations and support structure construction was completed during 2013. The liner and substrate materials were not installed due to weather conditions and contractor performance. The construction schedule was extended to June 2014 to allow the system to be reconfigured to include a vertical flow bioreactor in parallel with the horizontal flow subsurface wetland that will allow comparison of the relative effectiveness of the horizontal versus vertical flow anaerobic treatment cells. Also, the system start-up will now be in June, which is a better time of year to begin treatment in the wetland/anaerobic based system than October/November as was originally scheduled.
• A pilot-scale in-situ (517 Shaft Injection) water treatment test was conducted from September to November 2012 and from June 21 to July 9, 2013. During 2012, potassium carbonate and sodium hydroxide were injected into the 517 Shaft to treat water. The Blaine/Argentine mine water drainage travels through the 517 Shaft, and treatment in the shaft resulted in improved discharge water quality at the St. Louis Tunnel. Cadmium and zinc concentrations at the St. Louis Tunnel discharge point were reduced by approximately 40 percent during the test. The 2013 test used sodium hydroxide for neutralization. The test was halted before consistent contaminant reductions were observed at the St. Louis Tunnel discharge point. While treatment in the shaft is feasible, the long-term operation poses technical challenges that have not been addressed. These studies did provide additional information as to the source of metals loads with the respective cross-cuts connecting to the St. Louis Tunnel.
• Bench-scale ion exchange water treatment tests were conducted on Blaine Tunnel and St. Louis Tunnel waters during 2012, and ion exchange resins effective for removing contaminants from each water source were identified.
• Estimated ranges of flows from the above described model and historic flow data are being used for water treatment system design.

2.1.3 Enforcement Activities, Identity of Potentially Responsible Parties (PRPs)

A Unilateral Administrative Order (UAO) was issued to the Atlantic Richfield Company in May 2011 to implement the Removal Action specified in the Work Plan. 

 AECOM is the lead technical contractor for AR.  AECOM personnel and contractors performed the geotechnical and hydrological investigations at the Site during 2011, 2012 and 2013.   

AMEC Environment & Infrastructure, Inc. personnel, ARCO consultants, were on Site from mid- 2012 through December 2013 to conduct the 517 Shaft injection pilot test and the pilot-scale passive water treatment test,
and to oversee initial installation of the demonstration-scale passive water treatment system.

Anderson Engineering Consultants, Inc. (AECI) is the lead construction contractor for AR.  They maintain office facilities in Rico, perform monthly sampling and inspections, perform or contract for construction services, and provide for safe operations for all Site personnel. AECI contracted with Flare Construction for general construction services and with various other contractors for drilling, dredging, and other specialty efforts.

ARCO/British Petroleum (BP) maintains one or two personnel in Rico to provide oversight during fall and summer investigation and construction operations.

Colorado DRMS provided support for the 2011 and 2012 mine investigations and tracer studies, the Blaine Tunnel and 517 Shaft portal construction, and the 2011, 2012 and 2013 Blaine Tunnel coffer dam improvements, blockage removal, and flume installation.  DRMS contractor Ken Bethers Construction performed the 517 Tunnel and Blaine Tunnel portal rehabilitation and blockage removal work.

The EPA OSC was on Site for oversight activities.