[comments and questions on epa proposed ...albuquerque, nm 87102 (505) 242-2228 phone (505) 242-1106...

f y ^ : .. Chevron Mining, Inc., Questa Mine Site Proposed Cleanup Plan; Comments \ ^"^70 and Questions from Village of Questa

Kristina Bainbridge to: Phyllis Hoey, Mark Purcell, joseph.fox 03/31/2010 02:15 PM ' . "Marcus Rael", millergeotech, mayorgarcia, lao, "Brent P. Jaramillo",

elcoggins, councilwomanlouise, mgallegosSOS

Dear Ms. Hoey, Mr. Purcell, and Mr. Fox:

On behalf of the Village of Questa, please see attached correspondence dated March 31, 2010 from Deborah J. Miller, P.E., Ph.D. of Miller Geotechnical Consultants regarding the Village of Questa's comments and questions on the Questa Mine Site Proposed Cleanup Plan.

Thank you for your attention to this matter.

Sincerely,

Kristina M. Bainbridge Legal Assistant Robles, Rael & Anaya, P.C. 500 Marquette Ave. NW, Suite 700 Albuquerque, NM 87102 (505) 242-2228 Phone (505) 242-1106 Fax kristina@,roblesrael.com

RjDBliEStMBLIAfsi^i^ ***************************************

The unauthorized disclosure or interception of e-mail is a federal crime. See 18 U.S.C. § 2517(4). This e-mail is intended only for the use of those to whom it is addressed and may contain information which is privileged, confidential and exempt from disclosures under the law. If you have received this e-mail in error, do not distribute or copy it. Return it immediately with attachments, if any, and notify me by telephone at (SOS) 242-2228. Thank you.

VOQ Comments on EPA Plan 03.31.10.pdf

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iVliaER: VJEOTECHNICAI. V-» ONSUITANTS

3801 Automation Way, Suite 100 Fort Collins, CO 80525 (970)581-8988 MillerGeotechfSicomcast.net

March 31, 2010

Ms. June Hoey Community Involvement Coordinator U.S. Environmental Protection Agency Superfund Division (6SF-V0) 1445 Ross Avenue, Suite 1200 Dallas, Texas 75202-2733

Mr. Mark D. Purcell Mr. Joseph C. Fox Remedial Project Manager New Mexico Environment Department U.S. Environmental Protection Agency Ground Water Quality Bureau Region VI, Mail Code (6SF-PC) Mining Environmental Compliance Section 1445 Ross Avenue, Suite 1200 1190 St. Francis Drive Dallas, Texas 75202-2733 Santa Fe, New Mexico 87502

Subject: Chevron Mining, Inc., Questa Mine Site Proposed Cleanup Plan; Comments and Questions from Village of Questa

Dear Ms. Hoey, Mr. Purcell, and Mr. Fox:

The Village of Questa appreciates this opportunity to review and provide our comments on the Proposed Cleanup Plan for the Questa Mine and Tailing Facility (Proposed Plan). The Village of Questa, through its principal technical consultant Dr. Debora Miller of Miller Geotechnical Consultants (MGC), and its legal counsel Mr. Marcus Rael of Robles, Rael & Anaya, P.C. (RRA), has participated in stakeholder technical meetings, attended site inspections, reviewed data and analyses, and provided written technical comments throughout the CERCLA process. We have reviewed and provided comments on both EPA and Chevron Mining, Inc. (CMI) work products associated with the Rl/FS and risk assessments for the Questa Mine and Tailing Facility. The Village has submitted detailed questions, comments, and recommendations on the following key documents to date:

• Draft Final Baseline Ecological Risk Assessment (BERA, April, 2007) • Draft Final Baseline Human Health Risk Assessment (HHRA, September, 2007) • Draft Final Alternatives Evaluation Report (AER, November, 2007) • Draft Final Remedial Investigation Report, Revision 1 (RI, November, 2008) • Draft Final Feasibility Study Report, Revision 1 (FS, May, 2009)

Village of Questa Comments on Proposed Plan page 1

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In addition, in August, 2009, MGC and RRA, on behalf of the Village, provided comments and recornmendations to the National Remedy Review Board (NRRB) highlighting specific technical issues and concems pertinent to the remedy selection.

The Village's technical consultant and legal counsel have reviewed the Proposed Plan and attended informational meetings that were convened by EPA in Questa on January 21 and March 23, 2010. The Proposed Plan adequately addresses many ofthe key concems that have been raised to date by the Village.

Specifically, the Village supports the proposed approaches for cleanup as outlined in the Proposed Plan for the Mill Area; in the Red River, Riparian and South of Tailing Facility Area; and for Eagle Rock Lake. '

We are also generally supportive of the proposed approach in the Mine Site Area for groundwater capture and containment at the mouths of colluvial drainages and along the Front Rock piles. We generally concur with the concept for capture of seepage at the toes of the Capulin and Goathill North rock piles, but believe the piping systems for conveyance of these flows to the treatment location may need some modifications to avoid the highly unstable subsidence zone in the Goathill drainage.

The Village also endorses the proposed flexible "tool box" approach for evaluating and developing long-term reclamation designs on a case-by-case basis for the various waste rock piles. This approach is appropriate because the risks and consequences of failure, either in terms of long-term mass instability or failure of the reclamation cover systems, are different for different waste rock piles. A rational, risk-based, pile-by-pile approach will allow for consideration of various site-specific conditions such as: the location of a rock pile which influences the consequences of failure on human health and the environment (e.g., back country piles versus roadside/riverside piles); underlying slopes and other topographic constraints on regrading; potential exposure of natural scars that could exacerbate acid rock drainage (ARD); varying rock pile geotechnical and geochemical characteristics; and other factors affecting design decisions for each individual rock pile.

Although we are supportive of many aspects of the Proposed Plan, the Village has concems about Proposed Plan elements that are intended to mitigate groundwater and surface water quality impacts at both the tailing facility and the mine site. Our independent analyses of groundwater data from monitoring wells at the tailing facility, as described in our comments below, reveals serious deficiencies in data interpretation, lack of understanding of the current nature and extent of contamination and trends in contamination, and outright omission of key data in the risk assessment. Specific comments are provided, as follows:

1. Village of Questa (VOQ) Comment 1: Village's position on Mine Area Waste Rock Piles. The Village's support for the Proposed Plan's approach for the Mine Site waste rock piles is contingent on our assumption that additional studies will be done using test plots to answer remaining questions about cover performance and reclamation vegetation success that will be essential to minimizing long-term net infiltration. CMI's proposed pilot studies on the Goathill North rock pile should be approved and required. We believe these full-scale


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field tests are needed to validate infiltration models, vegetation success and reclamation cover performance. Further, we assume that risk-based assessments will include expanded failure modes analyses that consider environmental as well as stability and safety consequences of failure. These risk-based procedures should be applied for all the rock piles to optimize re-grade and reclamation design decisions. The Village is supportive of this process being done in a collaborative manner with appropriate stakeholder technical input, as it was done previously for the Front Rock piles under the short-term (operational) time frame scenario.

VOQ Comment 2: Uranium is present in tailing seepage south of Dam No. 1, but was not adequately addressed and highlighted in the RI/FS and risk assessment process which was the basis for the Proposed Plan. Uranium levels consistently exceed the drinking water standard (MCL = 0.03 mg/L) in three monitoring wells (MW-26, MW-29, and MW-9A), three extraction wells (EW-5A, EW-5D, and EW-6), the East Seep, and Seep Barriers 001 and 003, as shown on the attached Figure 1. These wells and seeps are situated in the upper alluvial aquifer south of Dam No. 1. Figure 2 shows that background levels of uranium in the upper alluvial aquifer, as characterized by monitoring wells up-gradient and to the east of the tailing facility, generally have uranium concentrations less than or equal to 0.01 mg/L. Upper alluvial wells having "elevated" uranium concentrations, which we interpret as being generally higher than about 0.02 mg/L, coincide with the mapped tailing seepage contaminant plumes south of Dam No. 1, in the east drainage southeast of Dam No. 4, and in the Change House area. The locations of wells which exhibit elevated uranium concentrations clearly show that the source ofthe uranium is tailing seepage.

The RI data collection and risk evaluation process evidently overlooked this important finding because uranium was not one of the constituents that was routinely analyzed in the DP-933 monitoring program until after the latest permit revision, which began implementation in 3 '̂' quarter of 2008. Uranium was originally included on the list of contaminants of concem (COCs) for the risk assessment because elevated concentrations were found in two measurements reported for Outfall 002 Pipe - which was one of very few available data points available for uranium as presented in the RI data set. MGC and the Village questioned this finding and highlighted the lack of testing for uranium in groundwater as early as 2007. It is our impression that uranium was not considered to be worthy of much attention and was therefore not evaluated to any great extent in the HHRA. Uranium was excluded in the evaluation of cancer risks (only arsenic was evaluated for cancer risk). The fact that this important primary drinking water contaminant apparently was either missed or ignored by the agencies in this evaluation process is of serious concem to the citizens of Questa.

With regard to the Proposed Plan, the Village believes that the general approach of enhanced capture and containment of the contaminated groundwater plumes is appropriate for controlling all seepage constituents emerging from the tailing, including uranium. We concur with the proposed expansion of the extraction system to include extraction well installations south ofthe Change House area.


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Additional monitoring wells should be installed to confirm the limits, both laterally and vertically, of elevated uranium and other COC's, principally in the area south ofthe Change House, between Embargo Road and the Red River. Data monitoring is lacking in this area since the time of RI data collection (2004). The need for this additional monitoring is discussed in more detail under our Comment 3.


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VOQ Comment 3: The limited RI data collection time frame on which the Proposed Plan is based is not adequate to characterize the ever-changing conditions at this active mine. The Village requests that the Plan define a long-term, enforceable process of environmental monitoring that is tied to additional actions as needed, for the duration of active mining. The monitoring program should be targeted toward assessing the effectiveness of implemented remedies. The Plan should also define a process for implementing additional or enhanced remedial measures as needed to achieve remedial action objectives, if the Proposed Plan remedies fail to keep up with changing conditions.

The Questa Mine is an active facility. Large quantities of tailing and impacted water will continue to be delivered to the tailing impoundrnent for many years or decades to come. The Proposed Plan tends to evaluate effectiveness and ability of remedial measures to achieve the Remedial Action Objectives (RAOs) from the perspective of post-closure conditions - i.e., after mining is ceased and reclamation covers are in place. While this scenario may be appropriate for the Mine Site waste rock piles and groundwater remediation systems, it is not appropriate for the tailing facility.

The Village is concemed that the current EPA Proposed Plan may be our final opportunity to set up an enforcement program that requires gathering and evaluating environmental data as the basis for evaluating the effectiveness of protective measures that are implemented under the Record of Decision (ROD). If measures that are implemented are found to be ineffective due to changing conditions, mechanisms must be defined for implementation of different or enhanced mitigation measures in the future.

The RI site characterization, which provided the data base foundation for the Proposed Plan, was largely based on a very limited "snapshot" of environmental data acquired primarily over about a two year period (2002-2004), with some subsequently obtained groundwater quality data and other information incorporated through 2008. We note significant changes have occurred between the 2002-2004 RI data collection period and more recent (2008) data, primarily at the tailing facility. This is due to substantially increased production and milling that occurred after the main RI data collection time period.

Specific examples ofthe rapidly changing groundwater contaminant conditions at the Tailing Facility are described as follows:

a. Data show clearly increasing trends in contaminant concentrations in both the basal alluvial aquifer south of Dam No. 1 (Figure 3) and in the basal bedrock aquifer west ofthe impoundment near Dam 5 A (Figure 4). These areas were specifically excluded from further consideration through the RI/FS screening process because contaminant levels were low at the time of the RI data collection period. Although contaminant concentrations remain lower than the preliminary remediation goals (PRGs) as of the 4* quarter 2009, the steadily increasing concentrations are of concem. The Proposed Plan does not address potential long-term seepage effects on these deeper aquifers.


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Additional monitoring wells are needed in the basal alluvial aquifer below Dam 1 and in the westem portion of the basal bedrock aquifer to monitor the effects of long-term recharge by tailing seepage on these deeper aquifer systems.

The contaminant plume south ofthe Change House area in the vicinity of MW-17 is mischaracterized in the RI and does not accurately represent the current extent of contamination. A side-by-side comparison of isoconcentration contour maps for molybdenum between 2" quarter 2004 and 2"'' quarter 2008 (Figure 5) reveals increased concentrations of molybdenum within the mapped plumes south and southeast of the Dam No. I impoundment. While concentrations have clearly increased, the interpretive mapping (which was done by hand) indicates very little change in the either lateral extent or shape of the inferred contaminant plumes. Critical data are lacking in the more recent (2008) Mo map which is missing control points south ofthe MW-17/MW-4 plume. The more recent map no longer includes TPZ-6U or TPZ-7U, which provided the only control points in the low-lying area between the impoundment and the river. We understand that those were temporary well points monitored only during the Rl data collection period (2002-2004). However, without data between Embargo Road and the river south of MW-4, the statement in the Rl (Section 5.5.1.3) that "...the extent of off-site migration is not believed to be beyond Embargo Road..." cannot be substantiated. Further, reviewing the concentration-time graphs for MW-4 and MW-7 (e.g., Figure 6), it is clear that Mo and SO4 concentrations increased substantially in response to high production years (late 2005-2007) following a period of low concentrations between 2002 and 2005. The maximum concentrations of Mo in MW-17 and MW-4 in the more recent data record were about 1.4 and 0.36 mg/L, respectively (in 2007). The concentrations in MW-4 are higher than the 0.2 mg/L values shown on both the 2004 and 2008 isoconcentration maps (Figure 5). If the map were re-contoured with maximum 0.36 mg/L control point instead of 0.2 mg/L the lateral extent ofthe mapped plume would have to be enlarged and would extend south of Embargo Road.

The Plan should include additional monitoring wells to replace the temporary piezometers TPZ-6U and TPZ-7U in the low-lying area between the impoundment and the River to evaluate the currerit extent of the plume south of the Change House area, and to monitor the effectiveness of the proposed extraction well system in containing that plume.


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VOQ Comment 4: The Proposed Plan preferred alternative (Subalternative 3B) components involving enhanced groundwater withdrawal with upgraded seepage collection, is supported by the Village with the following provision: The expanded seepage capture systems in the alluvial aquifer south and southeast of the Tailing Facility must be demonstrated to be very efficient. Positive cutoffs are needed to ensure effective capture and containment of contaminants.

Considering the previous comments, it is clear that contaminated groundwater plumes containing uranium and other contaminants are migrating off CMI property to the south and southeast of the impoundment. Further, there is some limited data showing increasing contaminant trends in the deeper alluvial aquifer below Dam No. 1, although current concentrations remain well below the remediation goals (Figure 3). It is imperative that these seepage plumes be contained to ensure long-term protection of the alluvial aquifer. Contaminants persist in the upper alluvial aquifer beyond the existing groundwater capture and pumpback systems below Dam No. 1. Based on the description of the interception systems that is provided in Section 3.5.4.8 ofthe RI, the majority of seepage that is collected (approximately 80%) is captured by trench barriers and subsurface drains, and only about 20% is collected by extraction wells. From these observations, the seepage barriers and interception drains appear to be the most effective measures. However, the existing barriers only partially penetrate the shallow aquifer, and have limited lateral extents. A more effective cutoff system will need to penetrate additional aquifer thickness, preferably tying into bedrock or aquitard layers at depth, and must be more extensive in the lateral dimension (cross-gradient) in order to capture more of the seepage from Dam No. 4, Dam No. 1 and the southeast plume. Additional subsurface geotechnical data are needed along proposed barrier alignments to support design of improved interception measures.

VOQ Comment 5. Village's position on basal bedrock aquifer: The Village has determined that it will support the part of the Proposed Plan preferred alternative for the Tailing Facility (Subalternative 3B) which explicitly does not include measures to clean up or prevent further degradation ofthe basal bedrock aquifer, with the following provisions:

a. Additional monitoring wells must be installed in the aquifer starting in Year 0 to significantly expand the area of monitored coverage on the west side ofthe facility, directly under the westem impoundment, and southwest ofthe facility.

b. Comprehensive aquifer characterization studies and water balance studies must be performed (initiated at Year 0) to gain a better understanding of the water balance and potential fate and transport mechanisms of tailing seepage in the bedrock fracture fio\y system. Groundwater models should be developed and validated with well data, to assess the long term risk to the aquifer under varying future tailing discharge scenarios. Available data indicate that molybdenum and sulfate concentrations are increasing in wells completed south of Dam No. 4, and also in the monitoring well MW-23 on the west side of the impoundment, as shown on Figure 4.


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Data such as these are of concern. One ofthe tasks ofthe aquifer impact assessment is to understand if those trends will be sustained or accelerated with increased production, or if the aquifer will be able to "absorb" the anticipated discharges through dilution and dispersion mechanisms to the extent that concentrations will not exceed the New Mexico groundwater standards.

c. A stakeholder review board should be convened comprised of appropriate groundwater and other technical experts representing key stakeholders. The purpose of the review board is to evaluate the findings of the aquifer impact assessment. The review board will make recommendations on whether or not to allow continued tailing seepage discharge to the basal bedrock aquifer based on their assessment of the aquifer's ability to effectively "treaf the discharges through dispersion and dilution over a long term. The objective is to ensure that the Red River and Rio Grande will not be adversely impacted by recharges from the tailing-seepage impacted bedrock aquifer.

In our previous comments to the National Remedy Review Board, the Village had recommended the following: Consideration should be given to installing impervious liners and seepage collection drain layers over the current surface ofthe impoundments. The liners and drain layers would capture and convey the drain-down seepage from future operational tailing deposition. The captured seepage should be treated to remove contaminants before discharging the treated water into the environment.

The Village of Questa is conditionally accepting the Proposed Plan, which will allow continued discharge of tailing seepage into the basal bedrock aquifer. This decision is largely based on the following mitigating considerations: (a) the contaminants of concem impacting the basal bedrock aquifer (molybdenum and sulfate) are secondary constituents which currently are present at concentrations that do not exceed the New Mexico secondary (e.g., irrigation) standards, (b) there are currently no primary drinking water constituents (such as uranium) with elevated concentrations in the basal bedrock aquifer, and (3) currently no one is using the bedrock aquifer for drinking water and it is unlikely that anyone will be accessing that aquifer in the near future because the down-gradient lands are mostly on federal property and the area is very remote. There is some uncertainty about whether or not the families at the fish hatchery are using water from this aquifer, and that question needs to be resolved to ensure that those people have a safe drinking water supply.

VOQ Comment 6. Village position on treatment of groundwater: EPA needs to clarify the goals of water treatment at the mine site and at the tailing facility, as it is unclear how water treatment will enhance environmental protection under this plan. Further explanation is needed, and EPA needs to justify the possibly prohibitive burden on mine operating costs.

The parts ofthe proposed plan for collecting and treating groundwater at the. mine site and the tailing facility are not clearly justified or explained in the context ofthe overall water


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usage/water balance under current mine operations. The following examples of typical operational water use are used to help formulate our questions on this topic.

a. Non-milling water use. Currently the mine discharges about 1600 gpm down the tailing pipeline during non-milling periods (based on 4* qtr 2009 data, which is assumed to be typical). CMI claims that this quantity of flow is typically necessary during non-milling periods to maintain the pipeline and to provide for dust

' suppression at the tailing impoundment.

Approximately 45% ofthe maintenance flow (720 gpm) is comprised of poor quality groundwater from underground mine dewatering (Decline pumps), Spring 13 and 31 collector drains, and GWW-1, -2, -3 seepage collection wells. The remaining 55% of the maintenance discharge (885 gpm) is obtained from good quality water sources (Columbine Wells, Mill Wells, and River diversion).

If the Proposed Plan is imjjlemented, it is unclear what will happen to the groundwater component that is treated at the mine site. There would appear to be two options: (1) the treated water could be discharged directly to the river under an NPDES permit, or (2) the treated water would be put back into the pipeline and sent down to the tailing facility. If option (1) is used, it is assumed that CMI would then need to pump additional good-quality water from the river or from mill wells to make up the quantities needed to maintain the slurry pipeline and for dust suppression at the tailing facility. Either option would be sending additional good quality water to the tailing facility where it will become degraded as it infiltrates the tailing.

Sending better quality water down the pipe during non-milling periods might improve the water quality of seepage emerging from the tailing. This may justify water treatment costs, but that has not been demonstrated through any analysis.

b. Water use during milling. It is our understanding that the Proposed Plan does not require treatment of process water during milling. During a typical milling period approximately 3,400 gpm of water is put into the pipeline (based on December 2008 data, assumed typical of milling periods). That water currently is comprised of approximately 2,700 gpm (80% of the fluid volume) from the good quality Columbine and Mill wells and river diversion water that is used in the milling process. After milling, this water is mixed downstream at the mill with 700 gpm (20% of the total fluid volume) comprised of the captured poor quality groundwater from the previously described sources. It is assumed that under the Proposed Plan, the 700-1- gpm of impacted groundwater would go to the water treatment plant, and again would be either (1) discharged directly to the river under an NPDES permit or (2) put back into the pipeline to be discharged at the tailing facility. The bulk of the process water (2700 gpm) would not be treated and would be slurried down to the tailing impoundment to discharge by seepage into the aquifers. The process water quality is poor because it is impacted by contact with the ore and tailing during the milling process and as the tailing are slurried down the pipeline.


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Questions about Benefits of Water Treatment. Under both the milling and non-milling scenarios described in (a) and (b) above, treatment of impacted groundwater at the mine site does not change or improve the groundwater cleanup situation at the mine. The proposed plan will improve the capture and containment of impacted groundwater upgradient from the river, thus mitigating degradation to the Red River and its alluvial aquifer. That benefit is achieved regardless of what happens to the impacted groundwater after it is captured. The benefits of removal and treatment of impacted groundwater at the mine site may be realized at the tailing facility. However, because most of the water that is delivered to the tailing during milling periods is not treated, and all water (during milling and non-milling periods) that is delivered to the tailing will ultimately be degraded by infiltration through the tailing, the incremental benefit that is derived by removing only a fraction of poor quality from the pipeline delivery stream is unclear.

The benefits of water treatment also are unclear given the significant differences between surface water and groundwater cleanup standards. It is assumed that water treatment plant (treated water) effluent will be controlled under NPDES discharge permits. The limits that will be set on these effluents are not yet defined, but it is assumed that the NPDES effluent limits will be higher than the groundwater limits. These limits will be determined to be protective ofthe Red River water quality, not groundwater quality. It would be of interest to compare the anticipated treated water effluent concentrations to existing discharge concentrations. At the mine site, the comparison should be made between the NPDES limits and the water quality of the impacted waters after treatment by lime addition.

The primary benefit of water treatment at the mine site appears to be a reduction in the amount of contaminated water delivered to the tailing impoundment. Analysis should be completed to evaluate whether or not the costs for water treatment to remove some fraction of total water contamination at the mine site justifies the benefits of marginally reduced contaminates delivered to the tailing impoundment. The major source of contaminated water - the milling process water - still ends up at the tailing impoundment.

The Village also questions the rationale for requiring immediate (Year 0) water treatment at the tailing facility. The vast majority (approximately 92%) of the total uncontrolled seepage from the tailing is discharged into the bedrock aquifer. Under the Proposed Plan, those discharges would not be captured and treated. Whether or not this practice is to be continued should be based on additional studies and aquifer impact assessment; as discussed under Comment 5. Assuming the basal aquifer remains the primary tailing seepage receptor, only a smaU fraction of tailing seepage would be treated (8 to 10 percent assuming very efficient capture in the alluvial aquifer).


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d. Summary of Village comments and questions regarding water treatment at the mine site and tailing facility: '

(1) What are the anticipated environmental benefits associated with water treatment at the mine site? From our analyses, we conclude that the primary benefits would be realized at the tailing impoundment because the water being delivered to the tailing facility would have somewhat better quality, notably during non-milling periods.

(2) Analysis should be performed to estimate the likely impacts on tailing seepage water quality assuming: (a) reduction of concentrations coming from the mill under the Proposed Plan scenario, and (b) continuation of current practice of treatment through lime addition at the mill only, accounting for anticipated increased volumes of impacted water that will be generated from enhanced groundwater collection systems. We anticipate the relative impact on seepage water quality will largely depend on the assumed future production and milling rates, because process water associated with tailing delivery will remain the principal source of poor quality seepage water.

(3) Do the marginal benefits of improving water quality delivered to the tailing impoundment, primarily during non-milling periods, justify the costs for constructing and operating a water treatment plant at the mine site?

(4) Most of the tailing seepage (estimated 92%) is discharged to the bedrock aquifer where it is treated through natural dilution and dispersion processes. Are the costs for requiring treatment of the remaining 8 to 10 percent of seepage that is captured from the alluvial aquifer justified?

7. VOQ Comment 7: The Village questions need to treat storm water.

a. What data indicate that storm water quality would require treatment beyond sediment removal in conventional temporary unlined detention/infiltration basins prior to allowing storm water to infiltrate to groundwater or be discharged to surface water?

b. Given the steep topography at the mine site, fairly high dams may need to be constmcted to create lined impoundment areas of adequate size to store all the runoff The sizing of these storage facilities would also be dependent on the capacity of the water treatment plant and the potential need to store back-to-back storm events if the plant capacity cannot treat water fast enough to empty the reservoirs quickly in between storms. These storage facilities are likely to be considered as high hazard water storage dams, which present new risks to the public and the environment in the event of failure, compared to the rnore modest sized infiltration basins currently in place.


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Storage and treatment of storm water will impose costly operational costs on the mine with dubious potential improvement to environmental protectiveness beyond the status quo. It seems likely ^hat the fraction of storm water infiltrating directly downward through the waste rock and the rubblized overburden above the block-caving subsidence zones is of poorer quality than the storm water runoff infiltrating from unlined detention basins below disturbed areas. What are the relative volumes and qualities of waters which directly infiltrate disturbed areas that cannot be contained versus runoff that would be stored for treatment?

Further data and modeling need to be completed to address these questions. It seems premature and unreasonable to impose a storm water treatment requirement in the Proposed Plan.

Conclusion In conclusion, the Village of Questa appreciates the opportunity to submit our comments on the Proposed Plan. The Questa Mine is an important employer in the community. According to CMI, there are adequate high quality ore reserves at the mine to sustain mining for another 30 to 40 years. The mine employs between approximately 130 and 300 local citizens depending on the levels of production. Local small contractors and other small businesses also benefit from sustained operations at the mine. Mine .production rates and employment numbers are largely determined by the market price of molybdenum. The recent global economic recession saw a sharp drop in molybdenum prices which forced a major slowdown of operations and a large reduction in the workforce in 2008. However, recently molybdenum prices are rising and employment numbers have improved since the 2008 layoffs.

The residents of Questa are arguably the stakeholders most directly impacted by both the positive economic benefits that the mine represents for the community, and the negative short-term and long-term adverse environmental effects associated with mining.

It is important to the Village that the remedy be effective. Protecting our environment and water resources is paramount. In particular, the Village insists that the contaminant plumes in the upper alluvial aquifer south and southeast of the Tailing Facility be fully contained with a robust system of deep groundwater barriers and extraction wells. Groundwater monitoring must be enhanced in the low-lying area south of the Change House to ensure that contaminants are cleaned up in areas where village residents may be at risk to exposure.

However, the Village is concemed that certain elements of the proposed remedy such as requiring treatment of storm water are overly burdensome and unnecessary. We also believe there should be more justification provided for requiring the mine to construct separate water treatment plants and provide treatment of contaminated groundwater starting at year 0 at both the rnine site and the tailing facility. The environmental benefits ofthis water treatment are unclear, since the majority of impacted water is associated with tailing disposal, and most ofthis process water will continue to be discharged to the bedrock aquifer system.


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Although we have identified a number of concems regarding some elements ofthe plan, we are supportive of most of the concepts. Our main concems relate to the ever-changing conditions at this operating mine. The ultimate nature and extent of contamination in the aquifers under the tailing facility may not be fully understood for years. We believe that additional monitoring and aquifer studies are critically important to better understand the long-term risks posed to the bedrock aquifer and the deep alluvial aquifer. We are tentatively supportive of the EPA's Proposed Plan for the Tailing Impoundment, with the understanding that these additional studies will be performed and vigilant monitoring will be done to protect precious water resources.

We hope and trust that the agencies will consider our comments as you move forward to a remedy decision.

Sincerely, MILLER GEOTECHNICAL CONSULTANTS, INC.

Debora J. Miller, P.E., Ph.D. President


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[comments and questions on epa proposed ...albuquerque, nm 87102 (505) 242-2228 phone (505) 242-1106...

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