Response to DEQ Request for Additional Information for the Eagle Project Groundwater Discharge Permit Application

Transcription

1 Jonathan C. Cherry, P.E. Manager Environment and Governmental Affairs Kennecott Eagle Minerals Company 1004 Harbor Hill Drive Suite 103 Marquette, Michigan Phone: Kennecott Eagle Minerals Michigan Department of Environmental Quality Constitution Hall 525 West Allegan Street Lansing, MI Dear Ms. Bailey: RE: Response to DEQ Request for Additional Information for the Eagle Project Groundwater Discharge Permit Application On May 10, 2006 the Michigan Department of Environmental Quality (DEQ) forwarded to Kennecott Eagle Minerals Company (KEMC) a memorandum addressing DEQ s review of KEMC s responses to your March 22, 2006 request for additional information on KEMC s application for a groundwater discharge permit. Specifically, the May 10 memorandum requests information on seven additional items. Each of the seven comments is addressed in the attached response document. In responding to this latest set of comments, KEMC believes the application to be complete and looks forward to DEQ moving into the next phase of their review of the application. KEMC appreciates the DEQ s diligent review of this application. Should you have any questions please contact me at (906) Sincerely, Jonathan Cherry, P.E. Manager Environment and Governmental Affairs Encl cc: Mr. James R. Janiczek, MDEQ Lansing, w/ Encl Ms. Kristen Mariuzza, MDEQ - Gwinn, w/ Encl Mr. David Porter, MDEQ - Cadillac, w/ Encl Mr. Hal Fitch, MDEQ - Lansing, w/ Encl Mr. Joe Maki, MDEQ - Gwinn, w/ Encl Mr. Gene Smary, Warner Norcross and Judd, LLP, w/ Encl Mr. Stephen Donohue, Foth & Van Dyke, w/ Encl Mr. Stephen Thomas, Golder Associates, Inc., w/ Encl

2 Response to DEQ s May 10, 2006 Memorandum Comment 1: Please provide all input parameters for the GMS software. Table 1 should contain all parameters that were used as input to GMS and omit any parameter not directly used in the modeling effort. Response to Comment 1: All model physical input parameters are included in Table 1. The model layers use uniform properties for each layer, apart from the area northeast of where the confining unit (B and C zones, layer 2) pinches out beneath the slope. By excluding the storage coefficient values that were not used in the model, a revised Table 1 looks like this: Hydrologic Unit(s) (Zone) TABLE 1 Summary of Modeled Properties Horizontal Hydraulic Conductivity (Kh) (ft/day) Vertical Hydraulic Conductivity (Kv) (ft/day) Model Layer Effective Porosity (n e ) (-) 1 A * B/C D Note: * - Layers 1 and 2 to the northeast of where the B/C unit pinches out uses Zone D properties. Comment 2: It does not appear that recharge from precipitation was modeled. Please identify what value was used or explain the omission. Response to Comment 2: An explicit precipitation-derived recharge was not included as a source of water to the model. The use of a constant head boundary provides water inflow to the model domain and generates a groundwater flow pattern consistent with water level measurements in local wells. A sensitivity run indicates that, although baseline water levels would be slightly higher, the addition of 10 inches of recharge would not have a significant effect on the mounding response (see Figure 1 attached). Comment 3: Please provide an electronic copy of the model including all necessary files to recreate the model including the base map. Response to Comment 3: A CD that contains the MODFLOW model files is included as an Attachment 1 to this response. (Note: CD is included only in original copy to Ms. Bailey at MDEQ). Comment 4: Please explain the use of 0.15 for an effective porosity. This value appears low for aquifers at the site. Typical values for a sandy aquifer generally range between 0.25 and Response to Comment 4: Total porosity is the ratio of void space between soil particles and the total volume of soil. Total porosity is greater than effective porosity. Effective porosity is the volume of soil spaces through which water can travel divided by the total volume of soil. An effective porosity of 0.15 for the two aquifers at the site is not an unreasonable value for soils of this type. We agree that total porosity is likely to be higher (up to 0.35). Effective porosity is used in the advective transport calculations to estimate travel times, and the use of a higher effective porosity than 0.15 would yield lower groundwater velocities and longer travel times. Regardless, effective porosity does not influence the degree of mounding or the resulting flow field. Comment 5: A sensitivity analysis should be conducted to quantify the uncertainty associated with the hydraulic conductivity estimates. The model should be ran with high and low estimates and the corresponding mounding presented on a graph. Response to Comment 5: The hydraulic conductivities used in the model are representative of average values estimated based on aquifer testing during the site characterization (by Fletcher Driscoll and Associates). We have re-run the model with a series of revised hydraulic conductivity values to assess the mounding responses to possible variations. The changes from the original model (Table 1) are as follows:

3 Sensitivity Run 1: Layer 1 K h = 50 ft/day, Layer 3 K h = 40 ft/day (already discussed in the April 25 th report) Sensitivity Run 2: Layer 1 K h = 20 ft/day, Layer 3 K h = 20 ft/day (K h /K v for both layers remains 10:1) Sensitivity Run 3: Layer 2* K h = 0.1 ft/day, Layer 2 K v = 0.01 ft/day Sensitivity Run 4: Layer 1 K v = 1.2 ft/day, Layer 3 K v = 1 ft/day (K h /K v for both layers is 25:1) Sensitivity Run 5: Layer 1 K h = 50 ft/day, Layer 3 K h = 40 ft/day; Layer 2 K h = 0.5 ft/day, K v = 0.01 ft/day. Note: * - only applies to Layer 2 northeast of mergence of layers 1 and 3. Of the five sensitivity cases, Run 2 resulted in the greatest mounding at the infiltration site (25 feet). However, the mounding is no greater than for the original model beyond a radial distance of 2,000 feet from the site and is easily absorbed within the unsaturated glacial deposits which are about 80 feet thick at the infiltration site. Sensitivity results are shown on Figure 2. Comment 6: The comment in the conclusions section stating Although the proposed infiltration system will increase groundwater levels below the site area, the change will not significantly alter the local groundwater flow regime should be removed. The model is not able to determine this because it has not been calibrated, does not use realistic boundary conditions, has an excessively large cell size, and has not modeled relevant surface features such as rivers, seeps, or bedrock outcrops. The current model may be able to provide mounding estimates but cannot accurately predict changes to the local groundwater flow regime. Response to Comment 6: The acknowledged limitations of the boundary conditions and calibration do not limit the model s ability to predict changes in flow direction caused by changes in applied stresses. Also, we believe that the model cell size (100ft by 100ft in plan) is not a limitation for predicting changes in flow near the site. We stand by our original statement - Although the proposed infiltration system will increase groundwater levels below the site area, the change will not significantly alter the local groundwater flow regime. Comment 7: The comment in the conclusions section stating The particle tracking indicated that none of the water will migrate to the main branch of the Salmon Trout River, located more than 4,000 feet west of the infiltration site should be removed. This comment is illogical since the Salmon Trout River was not modeled. By design the model could not possibly allow water to flow anywhere but to the northeast regardless of the discharge quantity. Groundwater not flowing to the Salmon Trout River is a function of how the model was built and not a conclusion of the modeling effort. Response to Comment 7: Obviously no discharge can occur at a non-existent sink feature. We could have used qualifiers such as we can reasonably infer that or some other qualifier. However, this does not alter the primary conclusions that groundwater at the infiltration site will migrate to the northeast and not to the southwest. Although they do not allow water to exit the model to the NW or SE, the lateral no-flow boundaries do not prevent some change in local flow regime occurring within the model if a sufficiently large recharge volume is applied at the site. While the resulting flow pattern can be influenced by the lateral boundaries, by setting them as far from the site as possible, the model is able to adequately assess local flow changes at the infiltration site. Additional Response to Comments 6 and 7: In general, Comments 6 and 7 of the May 10 memorandum address what DEQ believes to be limitations of the groundwater model included in the Groundwater Discharge Permit Application. DEQ infers that the modeling cannot support KEMC s conclusions that: (1) infiltration of treated water into the infiltration system will not significantly alter the local groundwater flow regime, and (2) the discharge will not impact the main branch of the Salmon Trout River (which is 4000 feet away from the infiltration site). KEMC believes that DEQ s comments on the modeling are inconsistent with DEQ s past guidance on information that is needed in the application to address the mounding and groundwater flow issues. More importantly, however, DEQ s comments incorrectly conclude that the modeling approach used to predict the impact on local flow regimes does not support KEMC s conclusions. KEMC attended several meetings with the DEQ in the early part of 2005 to plan activities associated with completion of the permit application. KEMC developed and submitted a Work Plan that was accepted by the DEQ per the Part 22 Rules. KEMC also held extensive discussions with DEQ staff, in both the Groundwater Permit Unit and the Geologic Survey Division, on the appropriate method for modeling groundwater mounding and flow associated with the infiltration of treated water. At those meetings there was general agreement that the site was well suited for an infiltration system given the thick deposit of unsaturated outwash sand. Moreover, DEQ staff indicated that analytical methods and other numerical simulations would be more than adequate for the KEMC

4 Groundwater Discharge Permit Application. Based on these directions, KEMC included in the application an analytical method that assesses mounding and a numerical model that assesses groundwater flow. In assessing mounding and local groundwater flow issues, KEMC followed the parsimonious principles that are inherent in groundwater modeling. As described by Anderson and Woessner (1992, page 28): in practice it is important to strive for parsimony, by which it is implied that the conceptual model has been simplified as much as possible yet retains enough of the complexity that it adequately reproduces system behavior. The groundwater flow model that is included in the Groundwater Discharge Permit Application is consistent with this fundamental principal of groundwater modeling. The groundwater flow model represents the important hydrogeologic features that will control groundwater mounding and flow such as: (1) the regional hydraulic gradient, (2) hydraulic conductivity, and (3) the dimensions of the hydrostratigraphic units. The results from the groundwater flow model clearly demonstrate that the change in groundwater flow due to the infiltration of treated water is very localized. Had the groundwater flow model shown a more wide spread change in groundwater flow it would have been an indication that a reversal in flow is possible. This would have warranted consideration of a more complex 3-dimensional analysis. The results of the groundwater flow model show this is clearly not the case and thus additional modeling is not warranted to address the questions concerning changes in regional flow due to the infiltration of treated water. As such KEMC believes that the DEQ has enough information in the application to assess the regulatory issues that need to be considered in writing the permit. KEMC recognizes that there are other broader groundwater and surface water related issues associated with the project that fall under the review of KEMC s Mine Permit Application (MPA) and Environmental Impact Assessment (EIA). For this reason, a more complex 3-dimensional groundwater flow model was included the EIA. The model in the EIA, which is being reviewed by qualified personnel on DEQ s team reviewing the MPA/EIA, corroborates the results of the modeling documented in the Groundwater Discharge Permit Application. However, the broader regional issues addressed in the three dimensional modeling performed in accordance with Part 632 are of tangential relevance to the limited impacts and issues pertinent to the DEQ s review of the groundwater discharge application. The documentation on the hydrogeology, groundwater chemistry, groundwater flow, hydrostratigraphic units, hydraulic characterization, and groundwater modeling relevant to the Groundwater Discharge Permit Application is thorough and consistent. KEMC believes that the DEQ has more than enough information meeting the requirements of the Part 22 Rules. References Anderson, M.P. and W.W. Woessner Applied Groundwater Modeling: Simulation of Flow and Advective Transport

5 Attachment 1 CD of MODFLOW Data Sets (Note: The CD included in this Attachment is only included in the original document sent to Ms. Bailey at DEQ)

6 20 Long-term Rise in Water Level above Static (feet) Original Model - no explicit background rechage Revised Model - with 10 in/yr background recharge 2 Up-gradient (SW) Down-gradient (NE) 0-4,000-3,000-2,000-1, ,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 Distance from Infiltration Area (feet) TITLE Model-predicted Mounding Response with background recharge Eagle Project Groundwater Modeling of Proposed Treated Water Infiltration DRAWN CHECKED REVIEWED SDT DATE SCALE FILE No Kenn_sens.pdf PROJECT No. DWG No. FIGURE No

7 Long-term Rise in Water Level from Static (feet) Original Model Sensitivity Run 1 Sensitivity Run 2 Sensitivity Run 3 Sensitivity Run 4 Sensitivity Run 5 5 Up-gradient (SW) Down-gradient (NE) 0-4,000-3,000-2,000-1, ,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 Distance from Infiltration Area (feet) TITLE Model-predicted Mounding Responses Sensitivity Runs Eagle Project Groundwater Modeling of Proposed Treated Water Infiltration DRAWN CHECKED REVIEWED SDT DATE SCALE FILE No Kenn_sens.pdf PROJECT No. DWG No. FIGURE No