Design Basis for Water Impounding Concrete Bulkhead, … · Bulkhead Design Basis 3 May 18, 2015...

1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http://mining.state.co.us

John W. Hickenlooper, Governor | Mike King, Executive Director | Virginia Brannon, Director

DATE: May 18, 2015 (Portions Updated September 17, 2015)

BY: Allen Sorenson and Kirstin Brown

RE: Design Basis for Water Impounding Concrete Bulkhead,

Red and Bonita Mine, San Juan County Colorado

Background

The Red and Bonita mine adit is located ten miles north of the Town of Silverton on the east side

of the valley of Cement Creek. The Red and Bonita adit drains the mine workings and

surrounding rock with a discharge at the portal measured at 336 gallons per minute (gpm) in May

2009. Subsequent flow measurements from the adit are 180 gpm in April 2010, 314 gpm in May

2012, 202 gpm in October 2012, and 197 gpm in May 2013. In July of 2015, the discharge was

consistently in excess of 500 gpm. On August 13, 2015 the discharge was measured at 400 gpm.

The source of the water draining from the Red and Bonita adit is likely from a relatively

permeable rock fracture zone or zones intersected by the adit more than 1000 feet east of the

portal. Red and Bonita drainage is one of the primary sources of heavy metal loading to Cement

Creek and the Animas River.

The Red and Bonita discharge pH measured in 2009-2011 is slightly acidic and the dissolved

metals carried by the discharge are derived by acid rock drainage (ARD) mechanisms through

the oxidation of sulfide minerals. After the collapsed portal was reopened by the U.S.

Environmental Protection Agency (EPA) in 2011, the pH of the adit discharge became more

acidic, exhibiting a pH of between four and five standard units during the summer of 2012. It

has also been observed that the pH of the adit discharge drops when metal oxy-hydroxide

sediments and precipitates are stirred-up by activities within the mine. Otherwise, the pH of the

mine water has ranged from a low of 5.31 to a high of 6.06 standard units over the course of nine

sampling event from September of 2010 to May of 2013.

Water impounding concrete bulkheads installed at strategic locations in draining and discharging

underground mine workings have the potential to flood the workings and create a mine pool that

will eventually establish a ground water system with water table and flow paths similar to the

pre-mining system. Saturation of sulfide minerals in the flooded workings and country rock will

create relatively anoxic conditions and limit the generation of ARD. Bulkhead installation will

1313 Sherman Street, Room 215

Denver, CO 80203

Bulkhead Design Basis 2 May 18, 2015

Red and Bonita Mine

eliminate rapid and continuous collection and discharge of ground water though open mine

workings and minimize direct discharge of ARD from mine portals. Bulkheads serve to smooth

mine discharge hydrographs by returning ground water flow paths to low velocity, low gradient

fracture flow or porous media pathways. Bulkheads further serve to prevent periodic surge

releases, or blowout type releases of ground water backed up behind collapses and ice dams that

are characteristic of abandoned and unmaintained draining mines. Bulkhead installation in

mines that are determined to be good candidates has the potential to significantly reduce metal

loading to receiving streams.

During 2013 and 2014, the EPA and the Colorado Inactive Mine Reclamation Program (CIRMP)

conducted investigations of the feasibility to install a water impounding concrete bulkhead in the

Red and Bonita adit. As a result of those investigations, EPA will be installing a bulkhead into

the adit in 2015, and has tasked CIMRP to assist in the design of the bulkhead. The objective of

the bulkhead is reduction in metal loading to Cement Creek and the Upper Animas River caused

by dissolved metals in the Red and Bonita mine drainage.

Mine Drainage into Cement Creek

Multiple bulkheads have previously been installed in mine workings in the vicinity of the Red

and Bonita mine. Notably, since bulkheads were installed in the American Tunnel in the 1990s

and early 2000s, the American Tunnel being located approximately one-half mile south and 330

feet lower in elevation than the Red and Bonita workings, the flow at the Red and Bonita portal

has increased from a negligible discharge to the present levels that are frequently in excess of

300 gpm. A review of mine drainage and previous mine drainage management activities is

contained in this section.

The American Tunnel portal is east of Cement Creek at the town site of Gladstone (Figures 1a, b,

and c). This tunnel started as the Gold King Tunnel in 1900, and was intended to undercut the

Gold King mine vein system, but raises from the tunnel up to the Gold King were never

constructed. In 1959, the tunnel was renamed the American Tunnel and driven to a total length

of two miles to undercut the Sunnyside Mine and serve as the mine’s primary haulage way. By

February of 1961, the American Tunnel was gravity draining the Sunnyside Mine, which had

flooded to an elevation of 11,500 feet, approximately fifty feet below the F-level of the mine,

during the preceding twenty-plus years of inactivity (Simon Hydro-Search, 1993).

Prior to August of 1996, the primary source of mine drainage to Cement Creek was from the

American Tunnel. The portal elevation of the American Tunnel is 10,617 feet. Measurement of


Red and Bonita Mine

flows in the American Tunnel were taken on October 2-3, 1991, see Figure 2. At that time,

discharge from the American Tunnel was 2160 gpm. American Tunnel discharge measurements

taken at the outlet of a settling pond at the tunnel portal from 1987 through 1991 were fairly

consistent between 1400-2000 gpm, with some outlying values measured (Simon Hydro-Search

1992). Based on the flow measurements taken in October 1991, American Tunnel bulkhead #1,

installed in 1996 impounds approximately 910 gpm inflows from the Washington, Brenneman,

and Sunnyside veins in the Sunnyside Mine, and from the fracture zone located at the American

Tunnel 0770 runaround located approximately 8000 feet inby the portal. American Tunnel

bulkhead #2 impounds 580 gpm of particularly acidic, metal laden water (compared to the other

inflows to the tunnel) from the fracture zone located between 2700 and 3100 feet inby the portal

(DRMS, 2001). This fracture zone is not associated with the prominent Bonita fault zone, which

is located more than 2500 feet to the east. Effectively, the American Tunnel drained mine

workings and fracture systems below the F-level of the mine, F-level elevation ranging from

approximately 11,550 to 11,600 feet.

The portal of the Terry Tunnel is in Eureka Gulch, a tributary to the South Fork of the Animas

River, below Lake Emma, and about two miles east of the Red and Bonita portal (Figures 1a, b,

and c). The portal elevation of the Terry Tunnel is 11,560 feet. The Terry Tunnel was one of the

primary access and haulage ways for the Sunnyside Mine prior to the completion of the

American Tunnel in 1961. Discharge from the Terry Tunnel was estimated at from 5 gpm base

flow to 100 gpm during spring runoff in 1978 and prior years. In June 1978, Lake Emma in

Sunnyside Basin collapsed into the upper workings of the Sunnyside Mine, and in the fourteen

years following the Lake Emma collapse, discharges from the Terry Tunnel were measured to

vary from 82 to greater than 1400 gpm due to surface water entering the mine via the Lake

Emma hole and infiltration through other near surface workings (Simon Hydro-Search 1992).

Effectively, the Terry Tunnel drained mine workings and fracture systems above the F-level of

the mine, and the drainage increased dramatically following the Lake Emma collapse.

The upper levels of the Sunnyside Mine, above F-level, are interconnected via vertical mine

workings to the American Tunnel (Figures 1b and 3), but the Terry Tunnel off of the F-level

provided the path of least resistance for drainage of the upper levels. In the 1990s, Sunnyside

Gold Corporation completed extensive reclamation in Sunnyside Basin, including backfilling

and sealing the Lake Emma hole. Water that continues to enter the upper mine workings feeds

the mine pool impounded behind American Tunnel bulkhead #1, and Terry Tunnel bulkhead #1,

the Terry Tunnel #1 bulkhead having been installed in September of 1994, and activated (bypass

valve closed) in July 1996. The reason for the nearly two year period between Terry Tunnel

bulkhead #1 construction and valve closure is that bulkhead activation would have diverted


Red and Bonita Mine

drainage from the Terry Tunnel to the American Tunnel, and the water treatment plant at the

American Tunnel portal did not have the capacity to treat that additional water during peak flow

periods. Therefore, Terry Tunnel bulkhead #1 bypass valve remained open until American

Tunnel #1 bulkhead was fully permitted and construction was completed, which occurred in July

of 1996. During the period between Terry Tunnel #1 construction and activation, outflows from

the Terry Tunnel were treated in accordance with requirements of the Colorado Discharge Permit

System at the Terry Tunnel water treatment plant. Terry Tunnel bulkhead #1 is located

approximately 3800 feet inby the tunnel portal.

The following table provides information on the nine bulkheads that were constructed by

Sunnyside Gold Corporation to impound the Sunnyside mine pool (Figure 4):

Bulkhead

Name

Construction

Date

Valve

Closed

Bulkhead

Elevation

Water

Pressure

Notes

F-Level

Secondary

1-28-1994

n/a

11,592 ft.

36 psi

(calculated)

Prevents direct discharge

to Mogul Mine

F-Level

Primary

3-8-1994

n/a

11,588 ft.

36 psi

(calculated)

Twinned with

F-level secondary

B-Level

Secondary

4-29-1994

n/a

12,148 ft.

Zero, Above

Mine Pool

Would prevent direct

discharge to Mogul

B-Level

Primary

5-24-1994

n/a

12,148 ft.

Zero, Above

Mine Pool

Twinned with

B-Level Secondary

Terry Tunnel

#1

9-1-1994

7-1996

11,555 ft.

40 psi

8-24-2000

3800 Feet Inby

the Tunnel Portal

American

Tunnel #1

7-7-1995

9-9-96

10,660 ft.

438 psi

5-14-2001

Initial Valve Closure 7-

29-96, Later Reopened

Terry Tunnel

#2

9-28-2000

10-5-00

11,521 ft.

Not

Measured

Stopped Discharge from

Near Surface Fractures

American

Tunnel #2

8-24-2001

8-31-01

10,612 ft.

175 psi

8-15-2002

Design Pressure, Ground

Surface in N. Fk. 277 psi

American

Tunnel #3

11-12-2002

12-3-02

10,595 ft.

Not

Measured

Reduced Discharge from

Near Surface Fractures

Table 1: Sunnyside Mine Bulkheads

American Tunnel bulkhead #1 is located 7950 feet inby the portal, at an elevation of 10,660 feet,

and is 2130 feet below the overlying ground surface (Figure 5). The following data relates to the

development of the mine pool behind American Tunnel bulkhead #1 (DRMS, 2002):

Date Pressure at Bulkhead (psi) Notes


Red and Bonita Mine

Date Pressure at Bulkhead (psi) Notes

9/9/1996 151 Valve Permanently Closed

Red and Bonita Mine Portal Elevation 10, 957 feet

9/3/1997 312 Top of Mine Pool 11,380 feet

Mogul Mine Portal Elevation 11,400 feet; Gold King Level #7 Portal Elevation 11,440 feet



10/10/2000 440


3/27/2001 438

5/14/2001 438 Final Pressure Reading

Table 2: Filling of Sunnyside Mine Pool Relative to Adit Elevations

These data indicate that the Sunnyside Mine pool equilibrated at elevation 11,671 feet, which is

116 feet above the elevation of Terry Tunnel bulkhead #1, and 714 feet above the elevation of

the proposed Red and Bonita bulkhead. The mine pool elevation is also 171 feet higher than the

observed water level in the mine in 1959, prior to completion of the American Tunnel, and

drainage of the mine through the completed tunnel (Simon Hydro-Search, 1992). The higher

equilibrium elevation of the mine pool in 2001, compared to 1959, is likely the influence of

increased inflows of surface water into the mine through the Lake Emma area in Sunnyside

Basin.

Other draining mines of significance along Cement Creek are the Mogul Mine and the Gold

King level #7 (Figures 1a, b, and c). The following table details discharge flow rates from the

mine portals before and after the closure of valves on Sunnyside Mine bulkheads (DRMS, 2003

and ARSG, 2013):

DATE

Mogul Mine

Discharge

(gpm)

DATE

Gold King Level

#7 Discharge

(gpm)

DATE

Red and Bonita

Discharge

(gpm)

7/30/1992 2.22

9/23/1992 2.36

8/2/1993 13.20 8/19/1993 2.50

9/17/1993 6.60 9/30/1993 2.56

11/3/1993 2.00

6/28/1994 11.70 7/25/1994 7.50

9/9/1994 5.54 9/29/1994 No flow

8/23/1995 18.00

9/20/1995 18.00 10/30/1995 0.40


Red and Bonita Mine

DATE

Mogul Mine

Discharge

(gpm)

DATE

Gold King Level

#7 Discharge

(gpm)

DATE

Red and Bonita

Discharge

(gpm)

7/16/1996 6.60 6/25/1996 26.00

7/29/1996

Valves on American Tunnel bulkhead #1 and Terry Tunnel Bulkhead #1 closed.

American Tunnel valve subsequently opened and closed several times, with

permanent valve closure on 9/9/1996.

9/23/1996 9.81 9/12/1996 0.50

7/7/1997 18.30 7/2/1997 41.00 6/26/1997 17.00

9/10/1997 16.60 9/19/1997 4.47 9/10/1997 DRY

7/7/1998 69.00 6/29/1998 31.20 6/29/1998 1.00

9/11/1998 16.61 9/11/1998 3.00 9/30/1998 DRY

7/9/1999 35.00 7/1/1999 37.00 7/1/1999 DRY

9/3/1999 141.00 9/10/1999 15.00 9/10/1999 DRY

10/1/1999 142.00

11/8/1999 100.00

8/4/2000 129.00 6/29/2000 59.00 7/18/2000 DRY

9/12/2000 139.00 9/13/2000 72.00 9/18/2000 DRY

10/5/2000 Terry Tunnel bulkhead #2 bypass pipe grouted

7/9/2001 249.00 7/9/2001 38.02 6/25/2001 DRY

8/30/2001 159.18 8/30/2001 29.23 9/17/2001 DRY

8/31/2001 American Tunnel bulkhead #2 valve closed

11/1/2001 211.00

5/15/2002 113.00

6/11/2002 147.47 6/7/2002 36.00 6/20/2002 3.00

7/19/2002 149.00

9/5/2002 157.00 9/12/2002 40.00 9/5/2002 10.00

12/3/2002 American Tunnel bulkhead #3 bypass pipe grouted

9/2004 9/2004 72

5/20/2009 116 5/20/2009 190

11/18/09 55 9/22/2009 252

6/30/2010 62 6/2/2010 250

11/4/2011 46 11/3/2010 212

6/15/2011 95 6/14/2011 147

10/19/11 43 10/18/2011 141

Table 3: Mine Discharge Flow Measurements Before and After Bulkheads in American and

Terry Tunnels

In contrast to the Mogul and Gold King discharge data in the foregoing table, with the exception

of a 17 gallon per minute discharge measured June 26, 1997, and a 1 gallon per minute discharge


Red and Bonita Mine

on June 29, 1998, the Red and Bonita mine portal was observed to be dry until 2002. Measured

discharges from the Red and Bonita in 2002 were 3 gpm on June 20th

, and 10 gpm on September

5th

. By September of 2004, discharge from the Red and Bonita mine portal was observed to have

significantly increased and was measured at 72 gpm (ARSG, 2010).

American Tunnel bulkhead #2 bypass pipe valve closure occurred on August 31, 2001. The

bulkhead was installed 2000 feet inby the portal at an elevation of 10,612 feet. On August 15,

2002, the final equilibrium pressure reading of 175 psi was collected at the bulkhead, equating to

a water table elevation of 11,015 feet (DRMS, 2002b). This elevation is 58 feet higher than the

elevation of the proposed Red and Bonita bulkhead, but several hundred feet below the Mogul

and Gold King level #7 portals. American Tunnel bulkhead #2 was designed and located in

order to impound the inflows to the tunnel from the fracture zone at 2700 to 3100 feet inby and

seepage from a fault at 2030 feet inby the portal. The fracture zone and associated water inflow

intersected the American Tunnel 640 feet directly below the North Fork of Cement Creek. The

design intent of the bulkhead was to force water into the fracture zone. Therefore, the bulkhead

was designed to resist a maximum water head of 640 feet (DRMS, 2001). As will be discussed

below, the timing of discharge from the Red and Bonita, the proximity of the Red and Bonita to

American Tunnel bulkhead #2, the geologic structure and topography between the mines, all

indicate that the Red and Bonita drainage is derived from water backed up behind American

Tunnel bulkhead #2, and not from the Sunnyside mine pool impounded by American Tunnel

bulkhead #1.

Following restoration of the collapsed Red and Bonita portal in 2011, EPA and their contractors

prepared the mine for mapping and hydrologic investigations. In August 2013, CIMRP mapped

the mine (Figure 6). Approximately 2000 linear feet of mine workings were mapped. Mapping

was terminated at the east end of each of the main headings where the adit was flooded to the

roof. The source of the water discharging from the Red and Bonita was not located, and must be

a water producing fracture zone or zones penetrated by the workings to the east of the extent of

the mapping that was completed. Based on the size of the mine waste dump, it is estimated that

as much as 1560 linear feet of adit (3560 linear feet total mine workings) was driven into the

flooded zone that is now inaccessible (DRMS, 2007). In contrast to the extent of workings

estimated from the size of the mine dumps, Ransome, 1901, states that about 3000 feet of work

had been done from the Red and Bonita adit. Figure 7 illustrates the spatial relation of the

American Tunnel bulkhead #2, the fractured rock zone that intersects the American Tunnel

where the tunnel passes under the North Fork of Cement Creek, and the farthest possible eastern

extent of the Red and Bonita mine workings. The actual eastern extent of Red and Bonita is

probably well west of the point shown on Figure 7 because: 1) there are likely multiple headings


Red and Bonita Mine

within the mine, not just a single thread as the point shown on Figure 7 assumes, and 2) the

actual footage of workings likely falls between 3000 (Ransome, 1901), and 3560 (DRMS, 2007),

but the maximum (3560 feet) was used in the preparation of Figure 7.

The Red and Bonita adit had been driven, relatively minor stoping had occurred, and the mine

had been abandoned by between 1897 and 1907 (Ransome, 1901; NPS, 2010). The portal has

been caved and the mine inaccessible since that period of operations until the EPA rehabilitated

the portal in 2011. There are diversions and other works within the Red and Bonita that

demonstrate that the early miners had to manage water inflows to the workings, and the

vegetation kill-zone in the valley below the Red and Bonita mine dump indicates that the mine

had discharged historically, although the vegetation also appears to have been smothered by

tailings from the Red and Bonita mill. However, CIMRP has found no information sources to

indicate drainage from Red and Bonita was occurring in the 1950s, prior to drainage of the

Sunnyside Mine via the extension of the American Tunnel discussed previously. It is likely that

the initial driving of the American Tunnel (then called the Gold King Tunnel) around 1900, had

cut the water bearing fracture zone 2700 to 3100 feet inby, which drained the Red and Bonita

curtailing its discharge. The initial driving of the tunnel around 1900 reportedly terminated

approximately one mile from the portal. Once American Tunnel #2 bulkhead was constructed

and the valve closed, the fracture zone re-saturated and drainage from the Red and Bonita

recommenced.

The following table presents mine discharge flow rates on Cement Creek from the most recently

published source (EPA, 2012).

Mine

Elevation

(feet

AMSL)

Bulkhead

Install

Flow Rate (gpm)

July

2005

September

2005

October

2006

Average

2010

Average

2011

July

2012

Mogul 11,376 2003 21 27 11 54 56 128

Gold King 7 Level 11,386 None 42 135 314 206 140 128

Red & Bonita 10,893 None 210 224 233 216 319 314

American Tunnel 10,540

1996

2001

2002

95 90 84 101 101 193

Table 4: Mine Drainage Data 2005-2012, note that elevations in this table are from the source

document, and differ from portal elevations cited elsewhere in this memo

The data and discussion provided in this section lead to the following conclusions:


Red and Bonita Mine

1. There were three basic sources of water feeding the drainage from the American Tunnel

prior to bulkhead installation. These sources are 1) the veins and fractures associated

with the Sunnyside Mine, which are inby the bulkhead #1 location, 2) water bearing

fractures and faults located between bulkheads #1 and #2, and 3) seepage, primarily

diffuse, outby bulkhead #2, and partially controlled by bulkhead #3.

2. Increased flows from the Mogul Mine and Gold King level #7 since the installation of

bulkheads in the American Tunnel is caused primarily by the elevation of the water table

related to the mine pool impounded by American Tunnel bulkhead #1. Although

discharge from Gold King level #7 continued to increase following installation of

American Tunnel #2, the increased discharge cannot be related to bulkhead #2, since the

pressure head on bulkhead #2 equilibrated below the elevation of Gold King level #7.

3. Increased flow from the Red and Bonita Mine since the installation of bulkheads in the

American Tunnel is caused primarily by the elevation of the water table related to

saturation of fractures behind American Tunnel bulkhead #2.

These conclusions bear on the determination of the probable hydraulic head that will develop

behind the proposed Red and Bonita bulkhead, as described in the next section.

Bulkhead Design Basis

Einarson and Abel (1990) present a step-by-step procedure for design of underground water

impounding bulkheads. Their procedure uses American Concrete Institute’s “Building Code

Requirements for Reinforced Concrete (ACI 318-89)” because the bulkheads are analogous to

reinforced deep-beam concrete structures and because of the inherent conservatism of the code.

Lang (1999) describes hydraulic jacking considerations and water hammer under seismic loading

for water impounding concrete bulkheads installed in mine tunnels. In April 2015, EPA issued a

Request for Proposals (RFP) to construct a water impounding concrete bulkhead in the Red and

Bonita adit. The RFP included construction requirements and specifications for the bulkhead

installation and appurtenances. The design of the Red and Bonita bulkhead generally follows the

Einarson and Abel template and the design considerations described by Lang. The design basis

for the proposed Red and Bonita bulkhead is described in this memorandum and detailed in the

design spreadsheets included in Appendix A. The bulkhead construction requirements and

specifications document is included as Appendix B.

As discussed previously, American Tunnel bulkhead #2 was designed and constructed to resist a

maximum water head of 640 feet, equating to a water table at 11, 252 feet elevation. Figures 10


Red and Bonita Mine

and 11 illustrate the physical setting from which this design criterion was derived. The water

table above bulkhead #2 actually equilibrated at 11,015 feet elevation when the water intersected

an outlet to surface via the Red and Bonita mine, elevation 10,957 feet. Blocking the outlet to

surface with a bulkhead in the Red and Bonita would potentially cause fractured rock to fill with

ground water to the 11,252 foot water table elevation that was the design basis for American

Tunnel bulkhead #2. This would create a pressure head of 295 feet (128 psi) at the Red and

Bonita bulkhead. If the water table were to climb to elevations greater than 11,252 feet behind

the Red and Bonita bulkhead, the next obvious pathway for ground water to surface would be at

the Gold King level #7, 11,440, which would create a pressure head of 483 feet (209 psi) at the

Red and Bonita bulkhead. The potential for the pressure head at the Red and Bonita bulkhead to

rise higher than the Gold King level #7 (11,440 feet) is possible should a bulkhead be installed

within the Gold King mine workings. No recommendation or decision has been made to place a

bulkhead in the Gold King mine at this time.

If the relief point for water pressure behind the Red and Bonita bulkhead is North Fork of

Cement Creek 640 vertical feet above the American Tunnel, as illustrated on Figure 11, then the

pressure at the bulkhead would be likely to climb to greater than 128 psi. This is because a

ground water gradient must establish to drive the release of ground water to the North Fork

Creek bottom. As discussed previously, the hydraulic head that is held by American Tunnel

Bulkhead #2 equilibrated at an elevation 58 feet higher than the Red and Bonita adit, providing a

driving gradient for the release of ground water into the adit. If the same gradient were to

develop to drive ground water release to the North Fork, the hydraulic head held by the Red and

Bonita bulkhead would be 295 feet plus 58 feet, or 353 feet (153 psi). Similarly, if the relief

point for water pressure behind the Red and Bonita bulkhead is the Gold King level #7 mine

workings 483 vertical feet above the Red and Bonita adit, then the pressure at the bulkhead

would be likely to climb to greater than 209 psi. The hydraulic head held by the Red and Bonita

bulkhead under this scenario would be 483 feet plus 58 feet, or 541 feet (235 psi).Therefore, the

probable pressure head for the Red and Bonita bulkhead is considered to be between 353 and 541

feet. The lower head (353 feet or 153 psi) is more likely given that the fracture zone that is

believed to be the source of the Red and Bonita discharge, and the North Fork of Cement Creek

intersect at an elevation that is below the lowest Gold King workings. The potential for ground

water backed up by the Red and Bonita bulkhead to emerge at other locations, particularly mine

workings to the north of the Red and Bonita, is discussed in a subsequent section of this memo.

It is notable that if the head held by the Red and Bonita bulkhead climbs above 295 feet (128

psi), the pressure that the American Tunnel bulkhead #2 was designed to carry (277 psi), may be

exceeded. The American Tunnel bulkhead #2 was designed and constructed in such a way that


Red and Bonita Mine

there are substantial factors of safety in place. The relatively modest over pressurization of the

American Tunnel bulkhead #2 that can be anticipated would not be problematic. A more

detailed evaluation of the pressure American Tunnel bulkhead #2 can carry is the topic of a

separate and forthcoming memo.

Hydraulic Fracturing and Hydraulic Jacking Considerations

The portal of the Red and Bonita adit is faced-up in ferricrete, and the adit is then driven through

Burns Member rhyodacite of Silverton Volcanics Formation. In order for the bulkhead in the

Red and Bonita adit to be effective, it must be installed at a location where water pressure behind

the bulkhead will not hydraulically fracture (hydrofrac) the surrounding rock. Resistance to

hydrofracing is provided by the weight of the rock above the bulkhead to the ground surface. In

1993, Sunnyside Gold Corporation conducted density testing on rock sampled from the same

Burns Member formation in the vicinity of the Red and Bonita Mine (DRMS, 1993). The test

results are included in Figure 12. From these results, a rock density of 165 pounds per cubic foot

was selected to evaluate hydrofracing potential for the Red and Bonita bulkhead.

The bulkhead will be installed from approximately 260 feet to 275 feet from the adit portal.

From topographic map elevations it is estimated that ground surface is 196 feet vertically above

the roof of the adit at the planned bulkhead location. The ground surface elevation above the

bulkhead has been accurately surveyed; the survey results are currently under evaluation. The

required thickness of rock above the bulkhead to prevent hydrofracing was calculated for three

hydrostatic pressure scenarios. 1) A column of water from the bulkhead elevation (10,957 feet)

to Lake Emma outlet ditch elevation (12,210 feet), or 1253 feet of head. 2) A column of water

from the bulkhead elevation to the equilibrium elevation of the Sunnyside Mine pool impounded

by American Tunnel bulkhead #1 (11,671 feet), or 714 feet of head. 3) A column of water from

the bulkhead elevation to an elevation above the Gold King level #7 mine workings, which is

conservatively within the range of probable hydraulic head that will develop with the

bulkheading the Red and Bonita described above, 11,457 feet, or 500 feet of head. The results

are presented in the following table.

Pressure Head Water Pressure Required Rock Thickness

1253 feet (Lake Emma) 543 psi 237 feet

714 feet (Sunnyside Mine Pool) 309 psi 135 feet

500 feet (Conservative Probable Head) 217 psi 95 feet

1037 feet (Hydrofracing Point) 449 psi 196 feet

Table 5: Hydrofracing Pressure Tabulation


Red and Bonita Mine

The results in the foregoing table demonstrate that there is ample overhead rock thickness at the

proposed Red and Bonita bulkhead location to prevent hydrofracing for the probable hydrostatic

head that will develop. The table includes the derived water pressure (449 psi) at which

hydrofracing would initiate for the 196 foot height of rock above the bulkhead location. This

initiating pressure calculation will be redone when the surveyed ground surface elevation above

the bulkhead location has been established.

Hydraulic jacking develops when hydraulic pressure within a rock joint exceeds the confining or

overlying rock pressure to the extent sufficient to dilate the joint and significantly increase

hydraulic conductivity through the dilated joints. The so-called Norwegian Tunnel Criterion

(Lang, 1999) was used to evaluate hydraulic jacking potential at the Red and Bonita bulkhead

location. The thickness and therefore the weight of overlying rock to resist jacking in the

Norwegian Tunnel Criterion is measured perpendicular to the slope above the tunnel, which is 37

degrees at the Red and Bonita location. The thickness of rock measured perpendicular to the

mountain slope down to the proposed Red and Bonita bulkhead location is 157 feet, based on

current best available information. The results of the hydraulic jacking evaluation are presented

in the following table.

Pressure Head Water Pressure Required Rock Thickness

1253 feet (Lake Emma) 543 psi 653 feet

714 feet (Sunnyside Mine Pool) 309 psi 372 feet

500 feet (Probable Head) 217 psi 260 feet

300 feet (Jacking Point) 130 psi 157 feet

Table 6: Hydraulic Jacking Pressure Tabulation

The foregoing analysis indicates that hydraulic jacking may initiate at the Red and Bonita

bulkhead if and when the water pressure behind the bulkhead reaches 130 psi. Since this is

within the probable range of pressures that may be anticipated, it is possible that some degree of

hydraulic jacking will occur. Hydraulic jacking will not compromise the integrity of the

proposed bulkhead, but would potentially increase the hydraulic conductivity of the jointed rock

fabric around the bulkhead. However, in a single level horizontally driven mine with drainage,

like the Red and Bonita, installation of a bulkhead will cause a pressure head at the bulkhead that

will correlate closely with the piezometric level prior to mining. Therefore, if pressures

sufficient to dilate joints and increase rock mass hydraulic conductivity develop, then the joint

will have been similarly dilated prior to mining. Once rock joints are hydraulically jacked, there

is a permanent increase in hydraulic conductivity, i.e., complete return to the pre-jacked


Red and Bonita Mine

conductivity does not occur if and once the hydraulic jacking pressure is removed. In 2014, EPA

and CIMRP conducted packer testing to evaluate the integrity and permeability of the rock at the

proposed Red and Bonita bulkhead location. A report describing the packer testing and results is

included as Appendix C. The packer testing results demonstrate very low permeability rock,

with a secondary permeability index of 1.54 x 10-14

or less at the proposed bulkhead location,

indicating that hydraulic jacking to a degree that would cause problematic leakage around the

bulkhead is unlikely.

Bulkhead Length and Reinforcing

There are two bulkhead design spreadsheets included in Appendix A to this memorandum. One

spreadsheet provides bulkhead design details for a structure that would perform adequately under

a pressure head of 500 feet (217 psi), with a bulkhead length of six feet, properly reinforced. As

described previously, 500 feet of head is at the upper end of the range anticipated for the

proposed Red and Bonita bulkhead. The other spreadsheet provides bulkhead design details for

a structure that would perform adequately under a pressure head of 1253 feet (543 psi), with a

bulkhead length of fifteen feet, properly reinforced. This is the pressure head that would occur if

the Sunnyside mine pool were to climb to the Lake Emma outlet elevation, and if the head

associated with that mine pool were to be imposed on the Red and Bonita bulkhead. While this

scenario is considered a highly unlikely, EPA and CIMRP have determined that it is prudent to

construct the Red and Bonita bulkhead to this conservative standard. This decision is supported

by the relatively modest cost difference between constructing a six foot long versus a fifteen foot

long bulkhead at a location that is less than 300 feet from the adit portal.

Reference to the spreadsheets in Appendix A provides the design criteria and calculations

yielding the design for the fifteen foot long reinforced concrete bulkhead to be installed in the

Red and Bonita adit. The derivation of the earthquake load factor input to the design is as

follows.

The water impounding reinforced concrete bulkhead installed in the Mogul Mine was designed

for the 0.094 g horizontal acceleration calculated to derive from the maximum credible 6.5

magnitude earthquake along the Ridgeway Fault, 24 miles to the north-northwest (Abel, 2003).

This ground acceleration is considered conservative for the Red and Bonita bulkhead since it is

located a mile farther from the Ridgeway Fault than the Mogul bulkhead, and because the Red

and Bonita adit axis is nearly perpendicular to the line-of-site toward the Ridgeway Fault, which

will reduce the earthquake caused ground acceleration that may act on the bulkhead. Even

though the acceleration from the maximum credible earthquake on the Ridgeway Fault has been


Red and Bonita Mine

used in the design of other bulkheads in the vicinity of the Red and Bonita, and is considered

fully adequate for design purposes, EPA and CIMRP have chosen to use the more conservative

ground acceleration of 0.185 g for design of the Red and Bonita bulkhead. This is the peak

ground acceleration for the Red and Bonita bulkhead location from USGS Seismic Hazard Maps

and Data for an earthquake with a two percent probability of occurrence in 50-years, information

available at http://earthquake.usgs.gov/hazards/products.

A summary of the design for the Red and Bonita bulkhead follows. This design uses the

methodologies detailed in Einarson and Abel (1990) and Lang (1999) for maximum hydrostatic

head at the bulkhead of 1253 feet and an earthquake acceleration of 0.185 g.

bulkhead dimensions are 6’ x 8’ x 15’ long

bulkhead volume is 27 cubic yards

low pressure grouting is necessary around the upper contact of the concrete with the roof

of the adit

flexural reinforcing at the bulkhead outby end is #9 bars on 9 inch centers, both ways

temperature shrinkage rebar at the bulkhead inby end is #6 bars on 12 inch centers, both ways

eight inch stainless steel bypass and three-fourth inch monitoring piping will be installed

Concrete will use sulfate resistant Type V cement, 559 lbs. per cubic yard of concrete and 240 lbs. fly ash, water/cement ratio of 0.52 by weight, and will include Xypex®

admixture for waterproofing

The bulkhead concrete forms (Appendix B) have been designed to carry the loads illustrated in

Figure 13, and in fact did carry the loads when the bulkhead concrete was poured in August

2015.

Pressure Tracking following closure of Red and Bonita Bulkhead Valve

When the bypass valve is closed on the Red and Bonita bulkhead, the open mine workings will

be flooded and pressure head will begin to build within one day, more-or-less, calculated as

follows.

Inputs and Assumptions:

1. 2000 linear feet of open underground workings mapped (Figure 6). Unmapped workings

to the east are fully flooded.

2. 1725 linear feet of open underground workings inby the bulkhead, with typical 5 ft. wide

by 7 ft. high dimension. Total volume of open underground workings 60,375 cubic feet.

http://earthquake.usgs.gov/hazards/products


Red and Bonita Mine

For calculation, assume 75,000 cubic feet of open workings to flood in order to account

for stopes.

Mine Discharge

(Gallons per Minute)

Mine Discharge

(Cubic Feet per Minute)

Time to Flood Open Workings

(Hours)

150 20 62.5

300 40 31

450 60 21

Table 7: Time to Flood Mine Following Bypass Valve Closure

Upon closure of the bypass valve, the bulkhead must be inspected daily. When freezing

temperatures may be anticipated, an air tight brattice must be secured at the portal following

daily inspections. The following observations are critical to evaluation of bulkhead performance.

1. Leakage at the rock/concrete contact. Observation of leakage will trigger opening of the

bypass valve and additional contact grouting.

2. Pressure behind bulkhead to be read on the pressure gauge and the vibrating wire

piezometer. Pressure readings will be used to guide the regional monitoring program

described below.

3. Daily inspections may be discontinued once pressure increases have leveled off to less

than 5 psi per day for a minimum of three days.

As described previously, pressure relief points and potential locations for ground water discharge

related to the impoundment of the Red and Bonita drainage include the North Fork of Cement

Creek around 11,250 feet elevation and the Gold King level #7 portal at 11,440 feet elevation. In

addition, the Red and Bonita bulkhead could result in increased discharge from the American

Tunnel and increases or renewed diffuse discharge through springs and into the bed of Cement

Creek. Also, increased or new flow from the Mogul Mine (11,400 feet), the Adams Mine

(11,160 feet), and Adit 268-21 (11,170 feet) may result. Of these, the Adams Mine and Adit

268-21 have yet to be discussed in this memo, and are described below.

The portal of Adit 268-21 is located 500 feet northeast of the Red and Bonita portal and is 213

feet higher in elevation than the Red and Bonita (Figure 14). CIMRP installed a masonry block

wall safety closure, with drain pipe into Adit 268-21 in the 1980s. The adit was designated

feature 21 under CIMRP project number 268, hence the name. At the time of the safety closure

project, the extent of the adit was estimated to be more than 100 feet, but the adit was not entered

or mapped. The northernmost extent of the Red and Bonita mine workings are on the 764 drift

(Figure 6). It is possible that Adit 268-21 was driven to test the same vein followed by the 764

drift, but at a higher elevation. Assuming that the vein is vertical and continues to trend north-


Red and Bonita Mine

south, as in the 764 drift, Adit 268-21 would intersect the vein approximately 375 feet from the

portal. Because there is some potential that Adit 268-21 and the Red and Bonita intersect the

same vein, Adit 268-21 must be monitored for incipient drainage when 213 feet of head (92 psi)

develops behind the Red and Bonita bulkhead.

The portal of the Adams Mine is located 1200 feet north/northeast of the Red and Bonita portal

and is 203 feet higher in elevation than the Red and Bonita (Figure 14). CIMRP mapped the

Adams Mine in 1995 (Figure 15). The northernmost extent of the Red and Bonita mine

workings are on the 764 drift (Figure 6). The north terminus of the 764 drift is a distance of 360

feet horizontally, and 203 feet vertically, from the southernmost workings of the Adams Mine

(Figure 14). It is possible that the Adams vein and the vein followed by the 764 drift are the

same structure, or related structures. Due to the potential that the Adams Mine and the Red and

Bonita intersect the same vein, the Adams portal must be monitored for incipient drainage when

203 feet of head (88 psi) develops behind the Red and Bonita bulkhead.

The following table relates pressure behind the Red and Bonita bulkhead to mine portals and the

North Fork of Cement Creek to be monitored following closure of the bulkhead bypass valve.

Mine Portal of Creek Name Red and Bonita Bulkhead Pressure

American Tunnel 0 (zero) psi

Adams Mine 88 psi

Adit 268-21 92 psi

North Fork of Cement Creek 127 psi

Mogul Mine 192 psi

Gold King Level #7 209 psi

Table 8: Critical Monitoring Locations Related to Red and Bonita Bulkhead Pressure Readings

References:

Abel Jr., J.F., 1998, “Bulkhead Design for Acid Mine Drainage,” in Proceedings Western U.S.

Mining-Impacted Watersheds, Joint Conference on Remediation and Ecological

Risk Assessment Technologies, 36 Pages, Denver, Colorado, U.S.A.

Abel Jr., J.F., 2003, “Bulkhead Design, Mogul Mine, No. 1 Level,” prepared for Silver Wing

Co., July 14, 2003.

American Concrete Institute, 1989, “Building Code Requirements for Reinforced Concrete (ACI

318-89).”


Red and Bonita Mine

Animas River Stakeholders Group (ARSG), 2010, “Gladstone Area Mine Event Timeline,” Draft

Document dated November 23, 2010

Animas River Stakeholders Group (ARSG), 2013, “Combined Water Quality Data Spreadsheet,”

May 7, 2013, downloaded May 17, 2015 from

http://www.animasriverstakeholdersgroup.org/

Bredehoeft, J.D., Wolff, R.G., Keys, W.S., and Shuter, E., 1976, “Hydraulic Fracturing to

Determine the Regional In Situ Stress Field, Piceance Basin, Colorado,”

Geological Society of America Bulletin Volume 87, Pages 250-258.

Burbank, W.S., and Luedke, R.G., 1969, “Geology and Ore Deposits of the Eureka and

Adjoining Districts, San Juan Mountains, Colorado,” United States Geological

Survey (USGS), Professional Paper 535.

Colorado Division of Reclamation, Mining & Safety (DRMS), 1993, “Technical Revision (TR-

14) Submittal,” by Sunnyside Gold Corp., in DRMS Permit File M-1977-378,

March 18, 1993.

Colorado Division of Reclamation, Mining & Safety (DRMS), 2001, “Design of American

Tunnel Bulkheads #2 and #3,” by John F. Abel, Jr. for Sunnyside Gold Corp., in

DRMS Permit File M-1977-378, January 15, 2001.

Colorado Division of Reclamation, Mining & Safety (DRMS), 2002, “MLR – Annual Report,”

by Sunnyside Gold Corp., in DRMS Permit File M-1977-378, June 4, 2002.

Colorado Division of Reclamation, Mining & Safety (DRMS), 2002b, “Construction

Certification Report, American Tunnel Bulkhead #2,” by Sunnyside Gold Corp.,

in DRMS Permit File M-1977-378, August 20, 2002.

Colorado Division of Reclamation, Mining & Safety (DRMS), 2003. “MLR – Annual Report,”

by Sunnyside Gold Corp., in DRMS Permit File M-1977-378, June 6, 2003.

Colorado Division of Reclamation, Mining & Safety (DRMS), 2007. “Report of Structural

Geologic Investigation – Red and Bonita Mine,” August, 2007.

Colorado Division of Reclamation, Mining & Safety (DRMS), 2009. “Project Summary, Gold

King Bond Forfeiture,” in DRMS Permit File M-1986-013.

Environmental Protection Agency (EPA), 2012. “Water Quality Report - Four Mines within

Cement Creek Watershed.”

http://www.animasriverstakeholdersgroup.org/


Red and Bonita Mine

Einarson, D.S., and Abel Jr., J.F., 1990, “Tunnel Bulkheads for Acid Mine Drainage,” in

Proceedings International Symposium on Unique Underground Structures, Vol. 2,

Pages 71-1 to 71-20, Denver, Colorado, U.S.A.

Garrett, W.S., and Campbell-Pitt, L.T., 1961, “Design and Construction of Underground

Bulkheads and Water Barriers,” Seventh Commonwealth Mining and Metallurgy

Congress, Vol. 3, Pages 1283 to 1301.

Lang, Brennan, 1999, “Permanent Sealing of Tunnels to Retain Tailings or Acid Rock

Drainage,” in Mine, Water, and Environment, 1999 IMWA Congress, Sevilla,

Spain.

National Park Service, 2010, “Historic Mining Resources of San Juan County, Colorado,”

National Registry of Historic Places, Multiple Property Documentation Form.

Ransome, 1901, “A Report on the Economic Geology of the Silverton Quadrangle, Colorado,”

United States Geological Survey (USGS), Bulletin 182, Series A, Economic

Geology 12.

Simon Hydro-Search, 1992, “Preliminary Characterization of the Hydrology and Water

Chemistry of the Sunnyside Mine and Vicinity,” Prepared for: San Juan County

Mining Venture, February 11, 1992.

Simon Hydro-Search, 1993, “Evaluation of Hydraulic and Hydrochemical Aspects of Proposed

Bulkheads Sunnyside Mine,” Prepared for: Sunnyside Gold Corporation, March

12, 1993

Wang, C-K, and Salmon, C.G., Reinforced Concrete Design, 4th

Edition, Harper and Row, Publ.,

Inc.

Figure 1a: Draining Mines in Cement Creek and Eureka Gulch

Figure 1b. From Burbank and Luedke, 1969.

Figure 1c. NOTE: This figure is a schematic visualization and does not depict the vertical workings between the American Tunnel

and the upper levels of the Sunnyside Mine

Figure 2: Flow, pH, and Metals Load in the American Tunnel on October 2-3, 1991 (from

DRMS, 2001)

Figure 3: Schematic Cross Section Illustrating the Completion of the American Tunnel to Serve as Main Access and Haulage Way for

the Sunnyside Mine (Modified from Simon Hydro-Search, 1992)

Figure 4: Schematic of Mine Levels with Bulkhead Locations (Vertical Workings not shown). The Gold Prince and Mogul Bulkheads

are not included in Table 1, and the Terry Tunnel #2 Bulkhead is not shown in this Figure 4.

Figure 5. Modified from Burbank and Luedke, 1969.

1 mile 0

= BULKHEAD (approximate locations)

Figure 6: Red and Bonita Underground Workings Map

Figure 7: Spatial Relation of American Tunnel Bulkhead #2 and Water Producing Fracture Zone with Red and Bonita Mine Workings

Figure 8: Geologic Map Illustrating Mineralized Fissures, Faults, and Veins in the vicinity where the North Fork of Cement Creek

passes over the American Tunnel some 630 feet below. Note North-South and Northeast Trending Structures with Surface Expression

Directly over the Mapped and Potential Projected Red and Bonita Mine Workings. From Burbank and Luedke, 1969.

Figure 9: Simplified Structural Geology Map showing Northeast/Southwest Structure of Eureka Graben, Arcuate Bonita Fault from

the Collapse of the Silverton Caldera, and North/South Fractures that cut the American Tunnel West of the Gold King Mine (from

Simon Hydro-Search, 1992)

Figure 10: Plan View of American Tunnel from Portal to Station 34+00, showing the Location where North Fork of Cement Creek

crosses over the Tunnel. From DRMS, 2001.

Figure 11: Cross Section of the American Tunnel from Portal to Station 31+00. From DRMS, 2001.

Figure 12: Compressive Strength and Density Values for Volcanic Rocks near Red and Bonita

Mine (from DRMS, 1993)

Figure 13: Pressure Load Diagram for Bulkhead Concrete Forms

Figure 14: Location of Red and Bonita Mapped Workings, Adams Mine Workings, and Adit 268-21 Portal

Figure 15: Adams Mine Map

Appendix A

Red and Bonita Bulkhead

Design Calculation Spreadsheets

Appendix B


Construction Requirements and Specification

Appendix C


2014 Packer Test Results

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