August 12, 2013
Baseline sampling and monitoring criteria, including duration will be unique to each mining site, and it would not be practical to develop specific instructions that would apply to all sites. However, resources to be evaluated would likely be relatively consistent. For general environmental review requirements refer to the document titled, “EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska”. The document can be accessed at: http://yosemite.epa.gov/R10/WATER.NSF/Sole+Source+Aquifers/hardrockmining
Pre-application interactions with state and federal agencies are highly recommended for general planning and scoping activities. The interactions do not have to be formal, and any requests can be facilitated through the lead agencies. Specific baseline data requirements will likely be prescribed by the respective state and federal agencies.
In general, the number of groundwater monitoring wells and spacing would be variable depending on known groundwater flowpaths and subsurface geologic features. Monitoring wells would need to be adequately dispersed around the site, and groundwater should be collected from the surficial and bedrock aquifers.
For groundwater modeling and analysis, EPA recommends using the equations provided in the letter dated October 20, 2011 (attached). The equation is useful for determining the number of groundwater samples to be collected and analyzed for prescribed constituents to be statistically valid. The equation was formulated by Dr. Arthur Luben with EPA, and his assistance could be enlisted. A discussion with EPA indicated that this will likely be the tool EPA uses for future mining projects.
At least one year of monthly environmental sampling and groundwater level data should be obtained from each aquifer (surficial and bedrock) in order to evaluate seasonal fluctuations; although the collection of data during winter months may prove challenging. A minimum of one year is recommended to determine seasonal variability. Two years is preferred depending on the variability of the data collected. The constituent with the most variability will determine the total number of samples. EPA will request at least 12 monthly samples. The QA/QC plan for modeling requirements is attached.
Surface water monitoring should be conducted close to the NPDES point of compliance and upstream and downstream of the point of discharge from the potential mining project. Sampling upstream and downstream of the projected point of impact from the mining project will help in determining existing pollutant loads to the water body. Stream flow can be obtained from USGS stream gages. There should be an array of historical data.
Crandon Mine was proposed as a nickel-copper mine that underwent significant environmental review before the project was terminated in 2003. The Crandon Mine may provide a reasonable example of what can be expected for a greenfield mining project in Wisconsin. The Wisconsin Department of Natural Resources (WDNR) may have retained historical information on the state’s requirements for Crandon Mine. It is recommended that the WDNR be contacted them for additional information on state requirements for baseline data needs. A discussion on the on baseline data evaluated for the NorthMet project follows the discussion on Crandon Mine.
Information for the former Crandon Mine project was obtained from the May 2003, Preliminary Draft, Groundwater Hydrology Resources Memorandum prepared by Dr. Mark Meyers (University of Wisconsin, Platteville), as well as the August 2003 Crandon Mine EIS Groundwater Modeling Report.
The Groundwater Hydrology Technical Memorandum (TM) describes groundwater hydrology within the Crandon Mine Project impact area of influence and provided an impact analysis of the potential effects of the project on groundwater hydrology in support of the Draft Environmental Impact Statement. The groundwater hydrology impact analysis focused on impact topics developed from scoping comments received by the US Army Corps of Engineers. The impact analysis was conducted using baseline data collected by Exxon Mining Company (EMC), Crandon Mining Company, and Nicolet Minerals Company for a period of over 20 years.
The groundwater modeling report provides information on the baseline data used for modeling steady-state and transient.
Groundwater quality is discussed in the Groundwater Quality TM; however, that document is not available to the USACE staff.
Groundwater wells were used to calibrate the USACE Crandon Groundwater Model. 212 wells are used in the 1984 calibration, and 100 wells are used in the 1996 calibration. 44 wells are used in both years. Water levels for each well are listed for 1984 and 1996.
A regional water table surface map was developed. This map was generated for October 1984 conditions using 67 water table measurements in the site area, 105 regional groundwater measurements from private wells, and best available lake elevations. Private well data were extracted from a database developed by the U.S. Geological Survey (1994). Data for the site wells are contemporaneous. Private well data are not contemporaneous, with measurements taken over the period of 1946 to 1984. Similarly, some lake stages were not contemporaneous.
Rice Lake and Mole Lake were incorporated into the model. Groundwater well elevation data and lake elevation data for the 1996-1998 time frame were provided by the Mole Lake Band.
Annual precipitation records from a station near the site (South Pelican Lake) for the period 1952 through 1996 were analyzed.
Lake Surface Evaporation
11 years of pan evaporation data collected as Rainbow Reservoir, Wisconsin
EMC (1985) used a hydrograph separation technique to estimate baseflow from data collected between 1977 and 1980.
The rating equations used were empirical, based primarily on data collected in 1977 and 1978.
Steady-State Groundwater Flow Model
The USACE steady-state model reasonably represented the regional groundwater conditions using the WDNR High-end model data sets and the additional model area. This summary statement was based on consideration of the modeled steady-state heads, the modeled groundwater table contours, model water balances, and the baseflow gain in streams, as compared to conditions observed in October 1984.
The USACE steady-state model reasonably represented the regional groundwater conditions using the WDNR Low-end model data sets and the additional model area. This summary statement was based on consideration of the modeled steady-state heads, the modeled groundwater table contours, model water balances, and the baseflow gain in streams, as compared to the observed conditions in October 1984.
Transient Groundwater Flow Models
The report provides the results of the transient groundwater flow models. Transient models were used to test the robustness of the model to changes in precipitation and other variables controlling groundwater flow over a long period of time. A 7-year period of record was tested, representing normal groundwater conditions changing to drought conditions and then changing to wet conditions over time. The transient models lake surface and groundwater elevations were compared with the long-term observed lake surface and groundwater well hydrographs.
Area specific data were used in the models wherever possible as input data. In the absence of site data, documented, literature-based values were used as input parameters. For input value types, conservative values were selected from the range of parameters to maintain a conservative scenario for baseline groundwater flow modeling. A series of sensitivity analyses were performed on selected input parameters. This was completed in order to assess the sensitivity of the models to a range of values that were believed to be representative of the conditions present in the area.
The following Crandon Mine files can be downloaded from the following:
Y:\\Regulatory\orm_douments\dwb\Mining Projects - General\Crandon Mine
Crandon Mine Pre-Final Groundwater Modeling Report, Earth Tech, August 2003
Crandon Mine, Preliminary Draft Groundwater Technical Memorandum, Dr. Mark Meyers, May 2003
USACE EIS Model, Draft Files, Earth Tech, Inc, January, 2003
Updated USACE Crandon Mine Groundwater Flow Model, GeoTrans, Inc., 2002
Draft Drawdown Plot, ArcView Version, February 13, 2002
Nicolet Minerals Company Preliminary Engineering Report for Wastewater Treatment Facilities for the Crandon Project, November 1998.
The PolyMet project is another example of potential data needs for mining projects. Although the plant site for the PolyMet project is considered a brownfield site, the mine site, six miles to the east of the plant site, has not been previously disturbed by mining activities.
Weather stations have between 25 and 66 years of records
Wild Rice Surveys
Annually with several years (3 years) of records collected by PolyMet
Stream Flow Data
Stream flow data is most valuable when there is a long term of record because the record is less affected by climate variability in atypical years. Information can be collected from USGS gaging stations or monitored by applicant where necessary (10 -20 years)
Several years of water level measurements
Several years (3 years) of PolyMet data compared to 30 years from monitoring stations
Wetland Well Data
Four full years of monitoring wetland well data
Fish Species/Macroinvertebrate Communities
Two years of baseline survey data (2004 and 2009)
Historic Property Identification
Multiple historic property identification efforts have occurred over a 13-year period
Environmental Classification of waste Rock based on sulfur concentration
Several years of weekly weathering cycles