['Tl:] TETRA TECH

June 23, 2017

Mr. Kirby Biggs; Task Monitor U.S. Environmental Protection Agency Office of Superfund Remediation & Technology Innovation Technology Innovation and Field Services Division Ariel Rios Building 1200 Pennsylvania Avenue, N.W. (Mailcode 5203P) Washington, DC 20460

Subject: Technical Review of Regional Consultation Package

i 111111111111111111111111111 IIIII IIIII 11111111 . 1885298 - RS SDMS

Phase 2 Construction Not Completed in 2016 Regional Consultation Package Update for Mining Influenced Water Mitigation, Control and Treatment Facilities of Planned FY 2017 Construction Activities; Bonita Peak NPL Site, Gold King Mine Level 7; San Juan County, Colorado

EPA Contract No. EP-S5-13-01 EPA Technical Direction Document (TDD) No. 0011/S05-0011-1704-011 Document Tracking No.: 1839

Dear Mr. Biggs:

Attached please find Tetra Tech's Technical Review of Regional Consultation Package for Phase 2 Construction Not Completed in 2016, Regional Consultation Package Update for Mining Influenced Water Mitigation, Control and Treatment Facilities of Planned FY 2017 Construction Activities, Bonita Peak NPL Site, Gold King Mine Level 7; San Juan County, Colorado; June 23, 2017.

This review was performed as an independent study in support of, and in accordance with, EPA Headquarters' consultation process for hardrock mining and mineral processing sites with planned field activities to be conducted during the Fiscal Year (FY) 2017 construction season 1• The review was funded by the Office ofSuperfund Remediation & Technology Innovation (OSRTI) Technology Innovation and Field Services Division (TIFSD) on behalf ofEPA's OSRTI Assessment and Remediation Division (ARD).

The review focused on evaluating the completeness and adequacy of submitted CP elements; identifying any significant issues of concern which would warrant a recommendation not to proceed with the planned field construction activities in FY 2017; and identifying any opportunities for beneficial improvement of planned activities and related planning documents.

The report findings, conclusions, and recommendations were based on an independent evaluation of existing site information and Region 8 site team knowledge, including the Final Phase 2 Technical Review Report prepared by Tetra Tech for the review of FY 2016 field activities.

1 United States Environmental Protection Agency, 2017. Developing Consultation Packages for CERCLA Activities at Abandoned Hardrock Mining and Mineral Processing Sites for the Fiscal Year (FY 2017 Construction Season; Memorandum from James Woolford, Director, Office ofSuperfund Remediation and Technology Innovation, and Reggie Cheatham, Director, Office of Emergency :Management April 4.

21 Junlper Ridge Road, Essex Junction. VT 05452 Tel 802.258.9485

www.tetratech.com

If you have any questions on the report, please contact me via telephone (802-288-9485) or email (jody.edwards@tetratech.com).

Best regards,

Jody Edwards, PG

cc: Shahid Mahmud/ EPA OSRTI ARD Kevin Scott/ Tetra Tech START Program Manager TDD file

21 Juniper Ridge Road, Essex Jurc1ion. VT 05t,52 Tel 602.288.9485

ww,N. tetratech .com

Draft Attachment 1

Technical Review of Regional Consultation Package for Mining Influenced Water Mitigation Control and Treatment Elements

of Planned FY 2017 Phase 2 Construction Activities Not Completed in 2016 Bonita Peak NPL Site, Gold King Mine Level 7, San Juan County, Colorado

June 23, 2017

NOTICE AND DISCLAIMER

Work described herein was performed by Tetra Tech, Inc. (Tetra Tech) for the U.S. Environmental Protection Agency (EPA) under Technical Direction Document 001 l/S05-00I 1-1704-011 of EPA contract EP-SS-13-01 with Tetra Tech of Chicago, lllinois.

EPA funded this independent technical review to support planning for removal and remedial activities at hardrock mining and mineral processing sites with identified and/or suspected mining-influenced water (MIW) hazards. The review was perfonned in support of, and in accordance with, the consultation process established by EPA Headquarters for hardrock mining and mineral processing sites with planned field activities to be conducted during the Fiscal Year (FY) 2017 construction season'.

See Appendix A for.complete notice and disclaimer information.

SUMMARY FINDINGS, CONCLUSIONS AND RECOMMENDATIONS

Following are the summary findings, conclusions and recommendations of this technical review report. The report should be read in its entirety for the purposes of site decision-making.

Based on the review of the site-specific consultation documentation provided by Region 8 and email clarifications received from and teleconference discussions with EPA Region 8 to questions raised during this technical review, it is the opinion of the technical review team that the current and planned MIW mitigation, control, and treatment elements of the proposed construction activities for FY 2017 are reasonable and appropriate for their intended purposes.

Notwithstanding the recommended beneficial improvements provided in this technical review report, no significant issues of concern were identified which would warrant a recommendation not to proceed with the MIW mitigation, control, and treatment elements planned for FY 2017 field construction ·activities.

1 United States Environmental Protection Agency, 20 I 7. Developing Consultation Packages for CERCLA Activities at Abandoned Hardrock Mining and Mineral Processing Sites for the Fiscal Year (FY 2017 Construction Season; Memorandum from James Woolford, Director, Office ofSuperfund Remediation and Technology Innovation, and Reggie Cheatham, Director, Office of Emergency Management April 4.

1.0 INTRODUCTION

Tetra Tech performed this technical review of the Phase 2 field construction activities not completed in 2016 (2017 Phase 2 Construction) planned for implementation during the Fiscal Year (FY) 2017 work season at the Bonita Peak NPL Site, Gold King Mine (GKM) Level 7, located in San Juan County, Colorado. This review was performed at the direction of EPA 's Office of Superfund Remediation and Technology Innovation (OSRTI) Technology Innovation and Field Services Division (TIFSD) on behalf ofEPA's OSRTI Assessment and Remediation Division (ARD).

As part of the EPA Headquarters FY 2017 consultation process, EPA regions are asked to submit a Regional Consultation Package (CP) that addresses technical and administrative criteria outlined in the agency's April 4, 2017 memorandum'.

Region 8 has requested a CP review of the field construction tasks which will be completed in the FY 2017 field construction season. These tasks focus on completion of tasks originally planned to be completed during the FY 2016 construction season, specifically:

• Installation of a flow control structure (FCS) in the new Level 7 adit; • Installation of a horizontal drain from the new Level 7 adit to the old Level 7 adit (horizontal

drain); and • Installation of a stability berm in front of the old Level 7 adit.

This technical review of the documents and data submitted by Region 8 for this site (collectively, referred to as "CP documentation") was performed under the oversight of the OSRTI personnel and with the cooperation and support of key Region 8 personnel, listed in the following table:

C Name ,. Organization .

Title Kirby Biggs EPA OSRTI TIFSD Team Leader, National Optimization Program Shahid Mahmud EPA OSRTI ARD Team Leader, Abandoned Mine Lands Team Rebecca Thomas EPA Region 8 BPMD Remedial Project Manager James Hanley EPA Region 8 Mining Engineer

Notes. U.S. Environmental Protection Agency (EPA); OSRTI = Office of Superfund Remed1at1on Technical Innovation; TIFSD = Technical Innovation Field Services Division; ARD= Assessment and Remediation Division; BPMD = Bonita Peak Mining District

This technical review report documents the technical review team's findings, conclusions and recommendations for the planned MJW mitigation, control and treatment associated with these proposed 2017 Phase 2 field construction activities.

Any unresolved technical findings, conclusions and recommendations in this report may be addressed in the future.

2 United States Environmental Protection Agency, 2017. Developing Consultation Packages for CERCLA Activities at Abandoned Hardrock Mining and Mineral Processing Sites for the Fiscal Year (FY 2017 Construction Season; Memorandum from James Woolford, Director, Office of Superfund Remediation and Technology Innovation, and Reggie Cheatham, Director, Office of Emergency Management April 4.

2

1.1. SPECIAL CONSIDERATIONS OF CP TECHNICAL REVIEW

The EPA 2017 Headquarters consultation process identifies the following five lines of technical inquiry that Regions are requested to respond to in their CP submittals:

1. What Work Activities Are Proposed to Be Performed? 2. Are Site Fluid Hazards Sufficiently Understood? 3. Are Proposed Work Activities Sufficiently Planned? 4. Do the Risk Activities Pose Risk of Uncontrolled Release? 5 .. Do Systems/Plans Exist to Prevent or Mitigate an Uncontrolled Release?

Within these broad lines of inquiry, EPA regions are also asked to provide: (1) a conceptual site model (CSM); (2) work plans and schedule; (3) design criteria, designs and construction plans; (4) Failure Modes and Effects Analysis (FMEA); and (5) verification that a carefully designed, coordinated, and up­to-date contingency, notifications, and emergency action plan (CNEAP) is in place and adequate to address any potential incidents.

In addition, the FY 2017 _consultation process was revised to support incorporation of existing documentation and data by reference to enable Regions to more efficiently develop CP submittals. Based on this, in addition to new information provided, Region 8 referenced previously provided FY 2016 CP documentation as a primary component of its FY 2017 CP submittal for the Phase 2 construction field activities. Accordingly, having previously reviewed the Region's FY 2016 CP submittal for the Phase 2 construction field activities, Tetra Tech used its Final Phase 2 Technical Review Report (Tetra Tech 20166) as the basis for developing this technical review memorandum. Analyses, findings, recommendations, and recommendations for beneficial improvement have been:

• Sustained, or in limited instances, modified for planned FY 2016 activities that remain as proposed FY 201 7 activities; and

• Removed for proposed FY 2016 activities that were implemented

1.2. REVIEW GOALS AND ACTIVITIES

The goals of this technical review included:

• Evaluation of the completeness and technical adequacy of submitted CP documentation; • Identification of any significant issues of concern which would warrant a recommendation not to

proceed with the planned GKM Level 7 field construction activities in FY 2017; and · • Identification of opportunities for beneficial improvement of planned activities and related

planning documents.

The following activities were performed to complete this technical review:

• Kick-off call with EPA OSRTI; • Receipt and initial review of CP documentation related to MIW mitigation, control, and

treatment; • Identification of additional information needs and request to receive additional documents and

data; • Receipt and review of additional information; • Internal consultations within the technical review team to confirm initial findings, conclusions,

and recommendations; • Development of this technical review report for formal documentation and submittal of findings,

conclusions, and recommendations.

3

1.3. TECHNICAL REVIEW TEAM

Members of the technical review team are li~ted in the following table:

. Name Organization Title

Jody Edwards, P.G. Tetra Tech, Inc. Principal Hydrogeologist I Senior Project Manager Review Team Leader

William P. Balaz Jr., P.E., P. ENG. Tetra Tech, Inc. Senior Mining and Civil Engineer

Eric Perry, Ph.D. Tetra Tech, Inc. Senior Hydrogeologist/Geochemist

Michelle Nolte Tetra Tech, Inc. Environmental Engineer II

2.0 INFORMATION REVIEWED

Appendix C lists the information reviewed, as provided by EPA Region 8, directly and by reference, including relevant information from the FY2016 CP review effort.

Limitations of this technical review related to the focus of this report, include:

I. Technical review was primarily based on review of available documents including data, designs, and construction plans provided by EPA Region 8, and clarifications provided during teleconference discussions with EPA Region 8 personnel, to evaluate regional site team readiness to perform planned FY 2017 field construction activities only;

2. Specific elements of design sheets and technical specifications considered relevant to review goals were subjected to general technical and qualitative review to confirm completeness, reasonableness, constructability, and performance. Detail sheets and calculations were not reviewed unless identified as important and relevant to the primary sheets reviewed;

3. The information reviewed was limited to: 1) the relevant 2016 CP documentation and new documentation of construction work completed in 20 I 6; 2) new site data obtained during FY 2016; and 3) documents associated with other work proposed for FY 2017 at nearby mines provided as reference material only and not subject to this technical review.

4. The FY 2016 estimates of MIW volume potentially present within the mine workings were accepted based on a review of estimating assumptions and general quantitative analysis to confirm reasonableness. The FY 2017 estimates of MIW volume potentially present within the mine workings (EPA 2017c) are identical to the FY 2016 estimates (Weston 2016c) and, therefore, are accepted without additional analysis.

5. For FY 2016, the existing and planned site water management infrastructure were compared to estimates ofMIW volume and were accepted in terms of the capacity of the infrastructure to contain, store, and treat a hypothetical release of the maximum estimated volume ofMIW. Based on the FY 2017 estimates of MIW volume potentially present within the mine workings being identical to the FY 2016 estimates, the capacity of infrastructure to contain, store, and treat a hypothetical release of the maximum estimated volume ofMIW was accepted without additional analysis.

6. The technical review did not include:

a. Consideration of longer-term site uncertainties; for example, confirming the locations and volumes of pooled MIW which may potentially be present in the underground workings associated with one or more of the additional mine sites and the significant bedrock fractures of the Eureka Graben located throughout the Bonita Peak Mining District;

4

b. Confinnation of all potential downstream receptors included in the emergency actions notifications list, or identification of additional downstream receptors, that might warrant inclusion in the notifications list;

c. Detailed evaluation of the final risk rankings of the potential failure modes (PFMs) identified in the failure modes and effects analysis (FMEA) for fluid hazards developed for the site (Weston 2016c);

d. Consideration of the holding pond PFM in the FMEA (as no work was planned on the holding ponds during 20 I 6 FY construction activities);

e. Evaluation of costs for implementation of the planned construction activities; f. Evaluation of site environmental compliance with federal, state, or local regulations; and g. Review of the as-built drawings or design drawings of the conveyance pipeline from the new

adit to the industrial wastewater treatment plant (IWTP) in regards to design detail and specific potential for failure.

3.0 SUMMARY UNDERSTANDING OF PLANNED FIELD CONSTRUCTION ACTIVITIES FOR FY 2017

Based on the review of site documents and data, and discussions with EPA Region 8 personnel, Tetra Tech understands:

I. Planned and on-going field construction activities are being performed by EPA Region 8, with the support of the following contractors and subcontractors:

a. Deere & Ault Consultants. Inc. (D&A) - remedial planning and design; b. Environmental Restoration LLC (ER) - environmental services; c. Harrison Western Construction Corporation (HWCC) construction services subcontractor to

ER; d. Weston Solutions Inc. /Weston)- specialty services and independent oversight (EPA Region

8 Superfund Technical Assessment and Response Team contractor).

2. The primary goal of planned and on-going field construction activities is to construct an integrated set of temporary solutions for MIW management while a pennanent site solution is developed (D&A 2016d as referenced in Weston 2016c). Planned FY 2017 construction activities are in significant part a continuum of FY 2016 activities, and primarily comprised of:

a. Constructing a temporary flow control structure (FCS) and monitoring instrumentation in the Level 7 'new' adit; ·

b. Drilling through 170 feet of competent bedrock and constructing a horizontal drain from the Level 7 'new' adit to the Level 7 'old' adit;

c. Connecting the FCS and the horizontal drain to the existing MIW drainage system, which consists of the following infrastructure: i. A sump constructed in the new adit floor inby the adit portal entrance which will receive

MIW discharges from the FCS and horizontal drain; ii. A 12-inch high-density polyethylene (HOPE) pipe, which conveys MIW to an existing

manhole located approximately 100 feet south of the new adit portal, and n1. A 12-inch HOPE drainage pipe that conveys MIW from the manhole to the Gladstone

Ponds; two lined holding ponds located in series and upgradient of the IWTP.

d. Constructing a temporary, earthen stabilization benn in front of the backfilled portal of the Level 7 'old' adit (D&A 2016e), which consists of: 1. Laying an approximately 2 foot thick bed of 1.5-inch coarse, washed aggregate to

support: a) Installing a new 36-inch HOPE extension pipe and connecting it to the existing 36-

inch corrugated drain pipe;

5

b) Installing two new 8-inch perforated polyvinyl chloride (PVC) pipes located on either side of the new 36-inch HDPE extension pipe; and

11. Emplacing the earthen berm, graded into the hillside at the portal entrance at a height of approximately 15 feet above ground surface and with 3:1 (horizontal:vertical) side slopes, as is common industry practice.

It is the technical review team's understanding that the FY2017 remedial activities at GKM are planned to be performed before the performance of planned FY2017 field construction activities at the nearby Red and Bonita Mine and American Tunnel. In addition, it is the technical review team's understanding that these proposed activities are not subject to this technical review.

The following sections focus on the MIW mitigation, control, and treatment elements of the planned FY 2017 construction activities.

4.0 GENERAL REVIEW FINDINGS AND CONCLUSIONS

The technical review team provides the following general review findings and conclusions related to the 2017 Phase 2 construction activities to be performed to address MIW mitigation, control, and treatment based on the CP review effort:

I. The CP documentation, supported by discussions with the regional site team, was sufficient to understand site conditions and planned FY 2017 construction activities to be performed to address MIW mitigation, control, and treatment;

2. Based on the regional site team's knowledge of site physical conditions and fluid hazard, the MIW mitigation, control, and treatment design plans and specifications for the:

a. New adit appear reasonable and appropriate for their intended purposes of constructing a temporary FCS and associated infrastructure and instrumentation;

b. Horizontal drain appear reasonable and appropriate for their intended purposes of assessing and draining potential MIW present; and

c. Old adit appear reasonable and appropriate for their intended purposes of constructing an earthen stabilization berm.

3. Region 8 has reported that the regional site team includes professionals with reasonable and diverse capabilities and related experience, including:

a. Mining engineering, b. Civil engineering, c. Chemical engineering, d. Mechanical and electrical engineering, e. Hydrology, f. Geology, g. Mine site operations, and h. IWTP operation.

5.0 SPECIFIC REVIEW FINDINGS, CONCLUSIONS AND RECOMMENDATIONS

The following subsections provide specific technical review findings, conclusions, and recommendations based on reviewing site documents provided by EPA Region 8 (See Appendix C). Recommendations include those that the technical review team believe are warranted and/or those provided as suggestions for beneficial improvement.

6

5.1. REGIONAL CONSULTATION PACKAGE

The technical review team reviewed the primary CP documentation provided by Region 8 and the updated documents listed in Appendix C (EPA 2017b).

It is the opinion of the technical review team that the regional site team's FY 2017 CP documentation, based on review of the relevant updated FY 2016 CP documentation, is generally reasonable and sufficient to support the independent evaluation of the MIW mitigation, control, and treatment elements of the planned FY 2017 field construction activities at GKM Level 7.

As previously indicated in the Final Phase 2 Technical Review Report for FY 2016 (Tetra Tech 2016b), the technical review team recommends that the regional site team consider the following beneficial improvements to the CP documentation identified during this technical review:

1. Continued use of the master list of site documents (EPA 2017b) as a working document, which is updated to track revisions of current documents and to catalogue new documents developed for the site. In addition, it is recommended that the hierarchy of governing primacy across the documents be identified; and

2. While D&A have provided resumes for project personnel, consider having site contractors who are working on multiple mine sites for EPA Region 8 provide resumes for key project personnel and written commitments that those personnel will be available for the project.

5.1.1. ASSESSMENT OF THE FLUID HAZARD

The technical review team reviewed the fluid hazard assessment provided in the 2016 CP documentation, and the following new 2017 CP documentation; D&A 2016e, D&A 2017a, D&A 2017b, D&A 2017c and Weston 2016c. ·

Key aspects of the fluid hazard as previously (Tetra Tech 2016b) and/or currently (Weston 2016c) understood by the regional site team include:

I. The general morphology and interconnections of the new and old adits as shown on Figure I.

2. The new adit floor elevation at the portal is 11,436 feet mean sea level (MSL) and the ' approximate floor elevation of the old adit portal is 11,438 feet MSL (D&A 20!6e). These portal elevations are below the last known recorded groundwater elevation in the vicinity of the mine· (D&A 20 I 6a).

3. Two additional portals (Sampson and Number 1 portals) are located approximately 450 and 500 feet northeast, respectively; and approximately 710 to 720 feet topographically upgradient, respectively, of the old and new adits (CDRMS 2009). Each of the portals were backfilled in 2009 with on-site materials and their associated wooden and metal debris was buried on-site (CDRMS 2009). A 1,600 foot long drill road from the Number One portal to immediately below the Sampson waste pile was re-contoured, ripped, mulched, and seeded (CDRMS 2009).

4. Interconnection of the ·old and new ad its at "three locations at elevations 12, 17 and 19 feet higher than the portar' (Weston 2016c).

5. Interconnection of the old and new adits with the remainder of known upgradient mine workings within the Bonita Peak Mining District, including, but not limited to: "Flow rate correlation of the Red and Bonita to the Gold King Mine shows there is a hydrological link between the mines (D&A, 2016a; D&A, 2017b ), and these flows are related to the increased water table elevation from bulkhead installations in the Ameridan Tunnel" (Weston 2016c).

7

Figure 1. General Morphology and Interconnections of New and Old Adits

.\£!if~

:><8A.~2 1~1.15~SU..VEY"Oa•"'.'

ll438 ncvAf0"i\CJDS1(0TOClRRtNflJ(NC:.w.~

_,, 1!4!;6

UA,-1.1 11455

•

\ YJ,a:c,r:'°'

8

itue (l~t"'P«,,ta,i}

1/~7? I. 4//"tl,:,,p,,,"fed; -

Figure 1

~ I r,y.(;',ll.Jr,,;r.t:H){)F.\_ (V<SfOt·•lmM.~W('.Nll"K~.

O~RllER ~11hC"S <YA.O KING ribSl'r.CT ~EOI.O·~ !.!Af' /1.'JO li-'.~·MSLf<\/.!< hlC>lf~.

2. .O..l a;,v,.no•,s ~OJIJSTI:t> rr, iWFF ENl31Nt!-Jll"'G ,t,?l."2[-<S 8E~CH~O,/l's, l<S sr~1£r-_.;;..i;: '.'>ill, :::rACk .. ()0 »:1t• oso,, N-'ll ·;;,n, vu>m 1,:>,5(;,,l trno~Jl'<P Jl.00\.ITO?C':1. GROONO SC,.~H~TO"! 1 (.l(,:;,'JWs-1~6-

El,,.,.,,,.., 1,-, "''~''" j .,,...,.., ~.,, •• ., I ~,....,.., n,, .• ,.,, I r....,

,-;,.~ I '1U) .. ,-w ,i,ro

" ,-~a, '~~,, !!_ .-~, ... ~, II

.!t • I ' I "'' 1 • - ' ~

,_

Sold King Mine li..el lo.. 1 - fl!!Of Elnaticm

'°"'""'"""''"'

D f. F. R E &. ,\ U t. Tj'"'•11111. IIIDIMJ9S9 Mi Mfr a 11.1.lt, 4;?2.'15 iCAU: .U NUTH

6. The "North Fork Fracture Zone" groundwater monitoring well (piezometer) was installed in late 2016 along Cement Creek near the base of the onsite waste rock pile to monitor groundwater elevation associated with the American Tunnel. A second shallow or near surface groundwater zone is also present, but is not instrumented with a piezometer for separate monitoring (D&A 2017a; D&A 2017b; D&A 2017c).

7. The regional groundwater table elevation in vicinity ofGKM Level 7 was estimated at 11,315 feet based on measurements collected in October, 2016 at new piezometer NFPZ-1. The 2016 NFPZ-1 water level measurement is approximately 120 feet below the GKM new adit elevation, but approximately 300 feet higher (11,015 feet) than a 2002 reading taken at American Tunnel Bulkhead 2, located near NFPZ-1, was closed. The last recorded water level measured at the American Tunnel bulkhead #1 in 2001 was at an elevation of 11,671 feet (D&A, 2016a)" (Weston 2016c) and is thought to represent the main Sunnyside mine-pool.

8. D&A (D&A 2017a) produced Figure 2, a 2-dimensional cross-section of groundwater levels in 2002 and 2016; based on the available data, which shows hydraulic head (water levels) having increased from 2002 to 2016. Water levels are indicated to be highest in the main Sunnyside mine pool.

9. Existing MIW discharge from the new adit presently ranges seasonally from 12 to 500 gallons per minute (gpm), but could potentially increase to 1,000 gpm (D&A 2016c). Current work plans are based on addressing MIW discharges up to 1,200 gpm (D&A 20 l 6c ).

10. A present potential risk ofuncontroHed discharge ofMIW from upgradient mine workings exists within the new adit. This potential risk drove the need for, and time sensitivity of, constructing the MIW management infrastructure during the FY 2016 construction season. Using an existing AutoCAD-based model, D&A estimates that as much as approximately 7.4 million gallons of MIW with a hydrostatic head of 62 feet could potentially be impounded by the FCS when constructed (D&A 2107c).

11. Currently, there is no MIW discharge from the portal of the old adit due to portal collapse and blockage, possibly in multiple locations (CORMS 2009; Weston 2016c; EPA 2017d); however, MIW is believed to be present within the old adit and could range between 3 and 5 feet of hydrostatic head (D&A 2016c; Weston 2016c). Based on the AutoCAD-based model; corresponding MIW volumes would range between 251,000 gallons and 3.6 million gallons, respectively;

12. A high likelihood of sludge deposition exists for the old adit. This likelihood is based on the documented history of sludge deposition in the new adit and the sludge discharged in 2015.

13. There is a risk for MIW discharge during construction, specifically: "If flows surge during construction, they may overwhelm the construction dewatering system and spill from the mine." In addition, the potential exists for "damage to the temporary section of the piping system from a roof fall or a blockage within the pipe system due to debris, sludge build up, etc." (Weston 2 I 06c).

14. There is a future potential risk ofMIW discharge after construction, specifically: "If water levels rise in the Gold King Mine after completion of the 2017 work, they present a potential hazard due to the forces that would be exerted on the planned temporary flow control structure or more importantly, blockages in the historic level 7 adit, the surrounding rock, and/or geologic formation weaknesses" (Weston 2016c). In addition, "While the current piping system should be able to handle these flows, the fact that they are close to the design limit will make the system more susceptible to plugs and make overflows into Cement Creek more likely" (Weston 2016c ). To help reduce this risk, Weston (2016c) recommends (1) establishing access to the portal and pipes as soon as possible, and (2) performing maintenance on flow conveyance infrastructure.

9

SW ~WOO ,1t)>11i;:N t

Cil:ll!f.i<:

I

Figure 2. Cross~Section of Mine Workings Showing Estimated Hydrostatic Conditions

~O!'ITB FOll!t: w.,~MO .,,.

PXL ~lll".11 !J!t4, I

""' \ C!c!ii'Cc¼l CiHi;t

\'1Qi>i1H %>f,I.I(

/M-VRJOOE} <'!ANSON !>£A,;:

r'>t

™" - I i _,,..,,/'... \W-"i'.Af>A1'-'~

• . ·- 1 ·• -/~~ "" - -,. _ _,,"' ·- •••

J riiJ:-~· "" - \ / ~ t". ,,;,• -----------------

t'®j ~;

:l'«»-j

-

~-

f{)(j(j'.J,AA't,C£-l-81J\:t.}(f,.A0 ("-W')

JAA!}t =• ~·\- ~--__ "" ! ~ "' , ,,;~r""-"""'="'-····~. ..:, ·,. -,-=----

"""'""' __ :t,.=---=-1,Ir-#! ---..:::::::· - --~'- --_ - ---•,_ - - -- -__ - -_ =-, ~-e'=--- ' " '!lL -·-··'·'" = . . . _::::~-=-=~_;:-'.._rt·--="''----' ""'"""''"""' I >\ -- '-'"'' - \ ,~"""'-""""' UM<n --------~ -~, i ~ •

--·- .e - -=-- :r·· ct.W¾1 D!t~X VO,. /// ; '... REI) lL &O*lff._ - f UM'.U! 01>1:~ ~lk"H'f --;1/ >'.

"-,,_ T$1"1'fr Wl</'¢1. hVthi11AiOO ~t:11,1:! ¼le.l' St.WY! M

. . ,,~,~<- ""' . -· '-"P -

,o;:,·-' .... . ' -~- -----= = ::.~ " ;;;~ ~.· -.,_ "'""'"'" -· ."IC¼~

""" ,.~, f~_n:RMfii.!,

O!~nmi.r.~ (tffl..l$!!~

l1<H,L • ,-.t. -••. t •• t •. t . •··: t, • •, ••• •..•..•. , ............. ., .• ·-······•··•·· .. ··•··•·"······•···M·OO ~ " ~ ~ ~ ·*"'1J 1M -J}<.M !!--«I ~

tiOrES.-

t ICE1 ~ D ~ M(){;fl ~ Ctllo,i,ll: ,:',t, (WfA

~ ~u ,. s 1.1.en:i t1it M!t'1't!CR1 JtmNl!l ~O;>ll'!MNl.'f AA!W:U:L m tMt ;l.'ll!l: )(Ul Mt:l 0011 l'f-.::NS

~ 'W)f#f:w.rtn ~ 1*it "O:)Lfl'l'.lll( -,.;!i, tl'fl.

al fXlSlll«\ ~.il.iMAO\ P,:C,,11.!00StiM'.M.. CU::V,\W..J-,1 ~

-0~

10

- - f\(*00 - ,_.

;a.""_,,,,"' EONIH. PEAK HIXIMG DISTTI.J(T

Am11/IQ1! Tmt11d Prtiil! A

\PIUl WH

15. The temporruy FCS was designed to resist a static head of 100 feet and significant surges, with valves in the structure to allow flows to be controlled as needed at the IWTP. This would be supported by remote monitoring of flows and water levels using pressure transducers and ultrasonic sensors behind the FCS (Weston 2016c).

16. Estimates of the potential MIW volume that could be impounded in the future by the temporary FCS were estimated based on the difference in assumed MIW pool elevations at depth within the Level 7 workings and adit dimensions (Weston 2016c). The quantity of impounded MlW could increase if water levels in the Sunnyside Mine and American Tunnel continue to rise, as indicated for the period 2002 to 2016 (D&A 2017a).

17. The Gladstone IWTP uses two holding ponds (North and South) located in series and upgradient from the IWTP to receive untreated MIW, dissipate water pressure and convey it via two 8-inch HDPE pipes into the IWTP reactor vessel (Alexco 2016). The ponds are specifically designed to provide storage for 6 hours ofMIW inflow during planned or unplanned IWTP outages. lfthe IWTP outage exceeds the 6 hours provided by the available holding storage volume, then a discharge from the holding pond(s) may occur.

18. Table I presents the order of magnitude North and South holding pond storage volumes that were calculated based on the limited information provided on Sheet S Pipe and Pond Layout, Enlarged Pond Plan (Weston 2016a). Detailed calculations of the order of magnitude storage volumes for each holding pond, assuming no appreciable sedimentation, were presented in the FY 2016 technical review report (Tetra Tech 2016b).

Table 1 - Order of Magnitude Storage Volumes of North and South Holding Ponds

Order ofMaenitude Storal'e Volume (2allons) Storage

Definition North South Total

Volume Holding Pond Holding Pond

(North & South Holding Ponds)

Standing water below

Unavailable level -in South pond when

NIA 78,534 78,534 plant feed equal MIW cominl! into ponds Volume between bottom of spillway and

Available unavailable storage 48,157 220,590 268,747 (south) and bottom of pond (north)

Design Volume of between spillway and bottom of 48,157 299,124 347,281

Capacity nond

19. Based on the FY 2016 calculations, the ponds have the following order of magnitude available storage volumes for MIW containment and storage:

a. North Holding Pond= 48, I 57 gallons b. South Holding Pond = 220,590 gallons c. Total combined= 268,747 gallons

The calculated 268,747 gallons of storage volume is greater than 259,000 gallons of storage capacity identified in_ the Operation and Maintenance Manual for the IWTP (Alexco 2016).

11

20. The total available capacity of the holding ponds will vary over time based on balance between the plant feed rate and the MIW inflow rate to the ponds from the GKM. The technical review team understands that the Red and Bonita Mine, which is also supported by the Gladstone IWTP, is not currently contributing flow. The following scenarios illustrate this relationship. If the IWTP feed rate:

a. ls greater than the mine water inflow rate then the pond empties and the available storage capacity therefore increases;

b. Equals the mine water inflow rate then the pond levels stabilize around a 1.4 feet depth in the south pond creating approximately 259,000 gallons of storage; and

c. Is less than the MIW inflow rate, then the pond fills and the available storage capacity is decreased.

21. A settling basin for suspended solids removal was recently constructed as pretreatment to the IWTf> for discharges from the American Tunnel. As the pond is not constructed to capture MIW discharge from GKM, it was not evaluated as part of this technical review.

It is the opinion of the technical review team that the regional site team's fluid hazard assessment associated with the mine workings and existing discharge is reasonable and appropriate. Under existing conditions in the GKM Level 7, no further MlW control efforts beyond the horizontal drain and the temporary FCS installation are recommended to support the planned FY 2017 construction activities.

Given the continued increase in hydraulic head of the Sunnyside mine pool, as indicated in Figure 2, the technical review team recommends continuing with efforts to characterize the regional groundwater regime as related to interconnectivity of mine workings and related MIW flow, pooling, and discharge.

The technical review team recommends that the regional site team consider the following beneficial improvements identified during review of the fluid hazard assessment:

I. Monitor groundwater levels in the North Fork fracture zone piezometer during adit dewatering to see ifthere are any changes in groundwater levels that provide information of value relative to MIW management;

2. Install a shallow monitoring well (NFPZ-2) adjacent to the North Fork fracture well to monitor near surface groundwater conditions as recommended by D&A (D&A 2016e );

3. After completion of initial dewatering efforts from the old adit, monitor the MIW flow and pressure in the horizontal drain as a mechanism for remotely monitoring MIW levels in, and discharge from, the old adit. Use the data (1) to determine the status ofMIW pooling, (2) to provide a basis for issuing an early warning for excess MIW pooling (if applicable), and (3) to support overall MIW management decision-making.

12

5.1.2. FAILURE MODE AND EFFECTS ANALYSIS FOR THE FLUID HAZARD

The technical review team reviewed the FMEA for the fluid hazard developed as part of CP submittal requirements (Weston 2016c ).

The FMEA focused on the risks of MIW discharge related to the PFMs associated with current conditions, construction, and post-construction ofMIW management-related infrastructure.

It is the opinion of the technical review team that the regional site team's FMEA for the fluid hazard is reasonable and sufficient for current conditions to support the independent evaluation of the MlW mitigation, control, and treatment elements of the FY 2017 construction activities for the GKM Level 7.

It is the opinion of the technical review team that:

l. The construction of the:

a. Temporary FCS presents a low to moderate risk of an MIW release, however, it is understood by the technical review team that a previously recommended temporary coffer dam was constructed to mitigate and manage potential uncontrolled releases associated with water management during construction;

b. Horizontal drain is unlikely to trigger an uncontrollable release of MIW; and c. Temporary earthen stabilization berm and associated drainage piping in front of the old adit

portal is unlikely to trigger an uncontrollable release ofMIW, provided that the horizontal drain is first constructed and any pooled MIW encountered in the old adit is removed, and

2. Based on the previous installation ofpiezometer NFPZ-1, an FMEA for the adjacent installation of piezometer NFPZ-2 does not appear to be warranted.

As previously indicated in the Final Phase 2 Technical Review Report for FY 2016 (Tetra Tech 2016b), the technical review team recommends the regional site team consider the following beneficial improvements to the MIW mitigation, control, and treatment elements of the FY 2017 construction activities as related to the results of the FMEA for the fluid hazard (Weston 2016c):

I. Developing and implementing a contingency to mitigate direct MIW discharge into the North Fork of Cement Creek as a result of a blockage of the:

a. Sump inby the portal of the new adit, b. Manhole located approximately 100 feet south of the new adit portal, c. Valve near the manhole, and d. Piping from the manhole to the IWTP;

2. Developing a contingency for using the constructed FCS and the new adit void space to provide temporary MIW storage in the event of an IWTP shutdown in excess of 6 hours which could result MIW inflow exceeding the holding capacity of the ponds.

3. With the FCS flow-through pipe valve closed, the inby adit void space can store up to 7.4 million gallons, which is approximately IO days storage based on a 500 gpm MIW discharge rate from the new portal adit. The 7.4 million gallon capacity is based on the AutoCAD-based model calculation of 62 feet of hydrostatic head and is within the design criterion of I 00 ft. of hydrostatic head upon which the design of the FCS was based;

4. Relocating the temporary concrete block and plastic sheeting coffer dam from the new adit portal to a location inby the FCS to help mitigate the impacts of surges (such as flow overwhelming the sump, which could be triggered by material collapses deeper in mine); ·

13

5. Increasing the size (diameter) ofMIW drainage pipe in any locations where flow constriction in pipes close to the design limit is identified to be the cause or potential cause of overflows elsewhere in the system that could result in discharge of MI W to the environment; and

6. Including a failure mode to include leaks, breakage, or other forms of breach in the MIW conveyance piping between the manhole and IWTP.

The technical review team additionally recommends that the regional site team consider the following beneficial improvements:

I. Updating the Fluid Hazard Analysis and Mitigation Technical Memorandum (Weston 2016c) to identify FY 2016 Phase 2 construction tasks that have been completed and which sections of the memorandum sustain as relevant for work to be performed during the FY 20 I 7 construction season;

2. Updating the FMEA to include a PFM for the flow meter and water level transducer on the temporary FCS.

5.1.3. DESCRIPTION OF WORK TO BE PERFORMED

The technical review team reviewed the description of work to be performed, as provided in the relevant updated 2017 CP documentation by EPA Region 8. This documentation includes the description of work activities in the fluid hazard analysis and mitigation document (D&A 2016c), and various construction plans and specifications (D&A 2015a, 2016a, and 2016d; ER 2016a) and 2017 BPMD Master Project Schedule (ER 2017b).

It is the opinion of the technical review team that the regional site team's descriptions of work to be performed (as supported by specific clarifications provided by Region 8 during teleconference consultations or email), are reasonable and sufficient to support the independent evaluation of the MIW mitigation, control, and treatment elements of the planned FY 2017 construction activities.

The technical review team provides the following recommendation for beneficial improvement:

I. Update the description of work to clarify which tasks have been completed in FY 2016 and which tasks will be completed in FY 2017 as it relates to the MIW mitigation, control, and treatment elements of the planned FY 2017 construction activities.

5.2. CONSTRUCTION WORK PLANS

The technical review team reviewed construction work plans and other related documents (D&A 2016a and 2016e; and ER 2016b), as well as the 2017 BPMD Master Project Schedule (ER 2017b), as provided in the CP documentation by EPA Region 8.

Based on the review of the documents, it is the opinion of the technical review team that the construction work plans (as supported by specific clarifications for work completed in FY 2016 provided by email from Region 8) appear reasonable and adequate to support the construction of the MIW mitigation, control, and treatment elements of the planned FY 2017 construction activities.

Review of the project schedule for FY 2017 indicates that field investigation activities are planned to be performed at the Red and Bonita Mine in June and October. Based on the technical review team's understanding that these activities are to be performed after the proposed activities for the GKM Level 7, the technical review team recommends that the schedule be revised to indicate that the June field investigation activities at Red and Bonita Mine will be performed after the completion of the proposed activities at GKM Level 7.

14

As previously indicated in the Final Phase 2 Technical Review Report for FY 2016 (Tetra Tech 2016b), the technical review team recommends that the regional site team consider the following beneficial improvements identified during the CP review:

1. To provide efficient access to construction plans information, include the most current version of construction work plans in the master list of documents recommended above in Section 5.1; and

2. To ensure application of current technical requirements during construction, maintain a revision log of modifications to construction work plan documents, change orders, and other notable field changes.

5.3. CONSTRUCTION DESIGN PLANS AND TECHNICAL SPECIFICATIONS

The technical review team reviewed construction design plans and technical specifications (D&A 2015a; 2016a, and 2016d; ER 2016a) as provided in the CP documentation by EPA Region 8 that are relevant for the proposed work to be completed in FY 2017.

It is the opinion of the technical review team that the construction design plans and technical specifications) appear reasonable and adequate for the purposes of constructing the MlW mitigation, control, and treatment elements of the planned FY 2017 GKM Level 7 construction activities.

As previously indicated in the Final Phase 2 Technical Review Report for FY 2016 (Tetra Tech 2016b), the technical review team recommends that the regional site team consider the following beneficial improvements identified during the CP review:

I. To provide efficient access to construction plans information, include the most·current version of design plans and specifications documents in the master list of documents recommended above in Section 5. I;

2. To ensure application of current technical requirements during construction, maintain a revision log of modifications to construction design plans (in addition to those indicated on specific design sheets) and specifications documents, change orders, and other notable field changes; and

3. Develop accurate as-built drawings and make them available to the project team as work progresses.

5.4. CONTINGENCY, NOTIFICATIONS AND EMERGENCY ACTION PLANNING

The technical review team reviewed the Emergency Action Plan (EAP) for the GKM site (Weston 2016b). The technical review team's review findings, conclusions and recommendations for beneficial improvements to the EAP are presented in Appendix B and are based upon recommendations previously provided during the 2016 CP review (Tetra Tech 2016a).

6.0 SUMMARY FINDINGS, CONCLUSIONS AND RECOMMENDATIONS

It is the opinion of the technical review team that the current and planned MIW mitigation, control, and treatment elements of the Phase 2 construction activities for FY 2017 are reasonable and appropriate for their intended purposes (as described in documents provided for CP review, and per the clarifications provided during teleconference discussions with and emails from EPA Region 8).

Notwithstanding the recommended beneficial improvements provided in this technical review report, no significant issues of concern were identified which would warrant a recommendation not to proceed with the MIW mitigation, control, and treatment elements planned for FY 2017 Phase 2 field construction activities. Any unresolved technical findings, conclusions and recommendations in this report may be addressed in the future.

15

APPENDIX A

NOTICE AND DISCLAIMER

Work described herein was performed by Tetra Tech, Inc. (Tetra Tech) for the U.S. Environmental Protection Agency (EPA) under Technical Direction Document 0011/SOS-OO 11-1704-011 of EPA contract EP-SS-13-0 I with Tetra Tech of Chicago, Illinois.

EPA funded this independent technical review to support planning for removal and remedial activities at hardrock mining and mineral processing sites with identified and/or suspected mining-influenced water (MIW) hazards. The review was performed in support of, and in accordance with, the consultation process established by EPA Headquarters3 for hardrock mining and mineral processing sites with planned field activities to be conducted during the Fiscal Year (FY) 2016 construction season.

Detailed consideration of EPA policy was not part of the scope of work for this review. This technical memorandum does not impose legally binding requirements, confer legal rights, impose legal obligations, implement any statutory or regulatory provisions, or change or substitute for any statutory or regulatory provisions. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

This report is provided to support EPA headquarters consultation and decision-making with regard to approval/disapproval to commence field activities at the site of concern. The report findings, conclusions, and recommendations (where applicable), are based on an independent evaluation of existing site information and regional site team knowledge. The report presents the technical findings, conclusions, and recommendations of the technical review team.

While certain recommendations may provide specific details to consider during the approved implementation of FY 2017 field construction activities, these recommendations are not meant to supersede other, more comprehensive planning documents such as work plans, sampling plans, and quality assurance project plans; nor are they intended to override applicable or relevant and appropriate requirements. Further analysis of the recommendations, including review of EPA policy, may be needed before implementation.

Reviews of health and safety plans (HASP) were performed to identify conflicts and potential conflicts with site contingency, notifications, and emergency action planning (CNEAP) documents. The reviews and recommendations provided on CNEAP-related elements of the HASPs do not constitute critiques, endorsements, or approvals of the HASPs as related to general human health and safety policies, requirements, procedures and/or technical methods. (Note: review of HASPs was performed as part of the technical review of the planned FY 2016 field construction activities only.)

It is important to note that the remediation of abandoned mine works involves inherent risks due to uncertainties and unknowns associated with the conditions of subsurface environments. While a number ofrisks can be foreseen and mitigated during rehabilitation and remediation, uncertainties and unknown risks are always present. Therefore, the risk of a potential failure mode not being identified cannot be completely eliminated. Thus, no warranties are expressed or implied with regard to EPA's successful performance of EPA-approved field construction activities; either directly or via the assignment to EPA contractors; by other federal and state agencies and their contractors; by potentially responsible parties (PRP) and their contractors; and by any subcontractors to any of the aforementioned contractors.

3 United States Environmental Protection Agency, 2016. EPA Work Activities at Abandoned Hardrock Mining and Mineral Processing Sites in Preparationfor Fiscal Year 2016 Construction Season; Memorandum from Mathy Stanislaus, Assistant Administrator, Office of Land and Emergency Management. March 29.

A-1

APPENDIXB

RECOMMENDATIONS FOR BENEFICIAL IMPROVEMENTS TO THE EMERGENCY ACTION PLAN

The technical review team recommends the site team consider the following beneficial improvements to the EAP:

1. Rename the document "Site Management Plan"; to signify that it is the governing EAP document for the site.

2. Include three primary sections:(]) Contingency; (2) Notifications; (3) Emergency Action Plan;

3. In the contingency section, integrate information on existing infrastructure and processes for containment, storage, and treatment, for example, but not limited to: a. Advisement of existing storage pond and WTP capacity for containment, storage, and

treatment of uncontrolled MlW discharges up to the maximum volume of the limiting capacity of one, the other, or both systems;

4. Use the "Gold King Mine Stakeholders Alert and Notifications Plan" as the basis for a revised notifications plan section. Integrate and expand upon current notification procedures· for non-MIW discharge-related emergency actions.

5. In the Emergency Action Plan section, include information on actions to take in the even\ of an uncontrolled MIW discharge; for example, but not limited to: a. Locations and process for safe mustering and accounting for personnel;

6. Incorporate existing Emergency Action Plan document content with the following modifications: a. Table of Contents - update to reflect organizational changes in the document;

b. Introduction - revise to explain modified document organization;

c. Section 1.1 Purpose - update to indicate focus on CNEAP elements;

d. Section 1.2 Potential Impacted Areas - update to specify downstream extent and diversity of potential human, environmental, cultural, and infrastructure receptors;

e. Section 2.1 Step One: Event Detection - modify to speak more directly to MIW discharge­related events, site personnel (for example, contractors), and specific monitoring systems and data;

f. Section 2.2. Step Two: Emergency Level Determination replace with Alert levels in "Gold King Mine Stakeholders Alert and Notifications Plan" and/or modify emergency levels to include potential impacts to human, environmental, cultural, and infrastructure receptors (as well as public relations and media);

g. Table I Guidance on Assigning Emergency Levels - update as applicable to reflect modifications to emergency levels made in Section 2.2, as well as changes in the comparative numeric ranking of levels based on those modifications;

h. Table 2: Site Personnel and Notification Contact Information -reverse the order within the document of Table 2 and the Emergency Contact Chain figure and update as applicable based on use of "Gold King Mine Stakeholders Alert and Notifications Plan" as the basis for a revised notifications plan section. Modify to reflect or incorporate the Notification Procedures in the "Gold King Mine Stakeholders Alert and Notifications Plan;";

B-1

1. Notification Message, pages 5 and 6 of 8 - revise message to provide more actionable information for the recipients and indicate that use of the notification message is not optional;

J- Section 2.4 Step Four: Expected Actions for Example Events_: modify to include MIW discharge-related events and direct the reader to the appropriate section of the primary call plan for uniformity in notifications procedures. Consider separating notifications into physical and medical emergencies and MIW-related events. Evaluate inclusion of additional 'physical emergencies, such as mine fires. For medical emergencies, direct the reader to the appropriate sections of the EPA employee and contractor HASPs, as applicable;

k. Section 2.4.1 Emergency Level I and 2 - modify per recommendations 6.g and 6.k above. Modify to confirm actions that can be taken by onsite personnel versus those that require off- site assistance;

I. Section 2.4.2.3 - consider directing the reader to the appropriate sections of the EPA employee and contractor HASPs for information on self-contained breathing apparatus (SCBA) storage and use;

m. Pond Berm Breach - modify text to include MIW discharge-related events and direct the reader to the appropriate section of the primary call plan for uniformity in notifications procedures. Modify any retained content to resolve the alignment of situations with actions; for example, for situation # 3 "If no injury or immediate response is warranted," the associated action of contacting the San Juan County Emergency Medical Services (EMS) does not appear to provide any benefit; and

n. Contact Chain Chart for all Emergency Levels - modify to include MIW discharge­related events and to align with "Gold King Mine Stakeholders Alert and Notifications Plan." Modify to specify what person or persons and from which organization(s) "Site Manager/Personnef' refers to. Modify to confirm whether the three EPA on scene coordinator (OSC) personnel listed are equal participants or alternates to each other depending upon who is available.

B-2

•

APPENDJXC

DOCUMENTS AND DATA REVIEWED

I. Alexco Environmental US Inc., 2016, Operations and Maintenance Manual Interim Water Treatment Plant (IWTP), Gold King Mine, Gladstone Colorado.

2. Colorado Division of Reclamation, Mining & Safety. 2009. Project Summary-Gold King Bond, Forfeiture M-1986-013, Phase II-2009, Reclamation at the Sampson, Number One, and Level Seven Portals.

3. Deere & Ault Consultants, Inc. (D&A). 2015. Gold King Mine; Flow Control Structure Concept. September I.

4. D&A. 2016a. Technical Memorandum-Gold King Mine Elevations and Dimensions; D&A Job No. CG-0251.003.00. March 4.

5. D&A. 2016b. Construction Plans for Gold King Mine Portal Stabilization, San Juan County, Colorado. June 17.

6. D&A. 2016c. Technical Memorandum- Gold King Mine Draft Work Plan 2016; D&A Job No. CG-0251.003.00. March 24.

7. D&A. 2016d. Construction Plans for Gold King Mine Portal Stabilization, San Juan County, Colorado; Issued for Construction. Prepared for Environmental Restoration, LLC; Revision No. 9, July 8.

8. D&A. 20 I 6e. Red & Bonita Bulkhead Filling & Monitoring Plan: Piezometer Installation near the North Fork of Cement Creek, San Juan County, Colorado; D&A Job No. CG-0251.002.01. December 22

9. D&A. 2017a. Bonita Peak Mining District; American Tunnel Profile A; Figure 2. April.

I 0. D&A. 2017b. Red and Bonita Mine Bulkhead Closure Evaluation 2017 Update; D&A Job No. CG-0628.001.00. April 10.

11. D&A. 2017c. Revised DRAFT Filling and Monitoring Plan, Red & Bonita Bulkhead and Associated Workings, Silverton, Colorado; D&A Job No. CG-0251.002.01. May 26.

12. Deere, Don W. Professional Resume. Deere & Ault Consultants, Inc.

13. deWolfe IJJ, Victor G. Professional Resume. Deere & Ault Consultants, Inc.

14. Environmental Restoration (ER). 2016a. Work/Operations Plan. April.

15. ER. 2016b. Site Health and Safety Plan, Emergency and Rapid Response Services, Gold King Mine Release Site, Silverton, CO. Prepared for U.S. Environmental Protection Agency- Region 8; Revision 01: April 29.

16. ER. 2017a. 2017 Gold King Phase II Project Schedule.

17. ER. 2017b. 2017 BPMD Master Schedule.

18. United States Environmental Protection Agency (EPA). 2015. Gold King Mine Stakeholders Alert and Notification Plan, Incident Command Gold King (ICGK). September 7.

19. EPA. 2016a. EPA GKM HASP; EPA Employee.

C-1

20. EPA. 2017a. Request for Consultation Package Review of Phase 2 Construction not completed in 2016, Regional Consultation Package Update for Mining-Influenced Water Mitigation, Control, and Treatment Facilities of FY 2017 Construction Activities, Bonita Peak NPL Site, Gold King Mine Level 7, San Juan County, Colorado, June 2017. June.

21. EPA. 2017b. Bonita Peak Mining District, Master Reference Document List. June 21.

22. EPA. 2017c. Revised Estimates of MJW Volume Present Within the Mine Workings, Memorandum From: James Hanley To: GKM Phase II Consultation Package. June 22.

23. EPA. 2017d. Additional Responses to Requests for Clarification or Information, June 23.

24. Goss, Christoph. Professional Resume. Deere & Ault Consultants, Inc.

25. Spitzer, Roy H. Professional Resume. Deere & Ault Consultants, Inc.

26. Tetra Tech. 2016a Draft Phase I Report Technical Review of Regional Consultation Package for Adit Rehabilitation Elements of Planned FY 2016 Construction Activities, Gold King Mine, San Juan County, Colorado. June 30.

27. Tetra Tech. 2016b. Final Phase 2 Report Technical Review of Regional Consultation Package for Mining Jrifluenced Water Mitigation Control and Treatment Elements of Planned FY 2016 Construction Activities, Gold King Mine, San Juan County, Colorado. August 16.

28. Weston Solutions, Inc. (Weston). 2016a. Gold King Mine -Pipe and Pond Layout; Unsurveyed Township 42 North, Range 7 West, New Mexico Principal Meridian, San Juan County, Colorado; January 19.

29. Weston. 2016b. Emergency Action Plan for the Gold King Mine Site; GoldKing Mine Treatment and Stabilization 2016. August 3.

30. Weston. 2016c. Technical Memorandum-Gold King Mine, San Juan County, Colorado-Fluid · Hazard and Mitigation, Document Control Number W0274.IF.00938. September 27.

C-2

.•