Guidelines for Suggested District Submittal and Evaluation of Ground Control Plans

OMB No.: 1219-0026, Expiration: 7/31/22
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Sixty Two highwall accidents have occurred in our nation’s mine since 2002. In
order to reduce these accidents, MSHA District 2 has compiled guidelines and
templates from across the nation to provide the Western Pennsylvania coal mines a
tool in developing a Ground Control Plan for safe working conditions within
current prudent engineering design.
The fundamentals to a safe Ground Control Plan is to recognize the hazards and
reduce the miner’s exposure to the hazards. To assist in this process, two
documents are attached, ground control guidelines and a working template. These documents
provide numerous safety precautions that may or may not be applicable
to your specific mine. Since each mine and associated pit is unique (i.e. mining
methods, geology, topography, hydrology, etc), each Ground Control Plan will be
evaluated independently for the health and safety of the miners.
Therefore, the submitted Ground Control Plan shall be site specific.

Guidelines
for
Submittal and Evaluation of Ground Control Plans
(Submitted for Compliance with 30 CFR 77.1000 and 77.1000-1)

GROUND CONTROL PLAN GUIDELINES
The ground control plan for the safe control of all highwalls, pits, and spoil banks at the
mine should contain information for each type of production equipment used at the mine.
This information should show the methods of mining employed to ensure highwall and
spoil bank stability so as to provide for safe working conditions. The methods used should
be consistent with prudent engineering design in that actual mining processes will provide
safety for workers exposed to highwall and spoil bank hazards. These hazards include the
ground failing to support persons or equipment in a work area or material falling or
sliding into a work area from above.

1.

GROUND SLOPE

If the original ground slope exceeds 27 degrees, it becomes more difficult to operate a dozer on
the ground to effectively strip loose, hazardous material a safe distance from the top of proposed
highwalls when benching for first cuts and to slope any loose, unconsolidated material to the
angle of repose. In these instances it is usually practical to establish a bench or diversion ditch
for first cuts to protect workers. Work to be performed during later development of the pit could
be curtailed if the width of these benches is not capable of keeping any loose, hazardous material
from falling into the work areas to be developed below.
If these types of benches are to be used, the plan will have to reflect this (show in the engineered
drawing).

2. HIGHWALLS
The highwall height is based on stability.
The height of a highwall should not exceed a safe reach of the type of equipment available at the
mine to clean (scale) the highwall unless special precautions are taken. These precautions could
include blasting practices that shoot the face of the highwall clean, using equipment that is
capable of working out a safe distance from the base of the highwall while removing material to
the toe (such as a shovel), using equipment to clean the wall from the top edge, breaking the wall
down into benches that are spaced so as to allow for cleaning of the wall immediately above the
work area, or providing a buffer (such as a berm of material) at the base of the highwall that
keeps workers out a safe distance from the wall.
The angle of a highwall (slope) is usually determined by the type of blasting used to develop the
wall. When drilling vertically, the wall typically shoots out between 5 and 10 degrees unless
presplit. Angle drilling at 10 to 20 degrees is being done in some instances where cast blasting
occurs. The angle at which the highwall is developed should be included in the consideration of
pit widths. If an unsafe condition should exist or develop after a wall is established, the area to
be barricaded will be determined by the extent of the unsafe area in the wall and the angle of the
wall. Typically, material falling out of a vertical wall will land on the pit floor within the drop
zone (see Item #3& #7) near the toe of the wall, whereas material falling out of an angled wall
will kick out from the wall and would require a barricade to be established a greater distance
from the base of the wall.
Historically in District 2, highwalls or lowwalls over 60 feet in height were benched. However,
highwall’s and lowwall’s should be judged on a pit to pit bases, based on past mining conditions
of seam or area and sound engineering practices.
3. BENCHES
Bench spacing
Benches perform two important functions. First, they provide stability to a highwall by
increasing the safety factor of the highwall. Where a highwall contains numerous discontinuities
(joint sets, bedding planes, etc.), providing benches at select spacings can increase the stability of
the wall. Second, where sloughing rock and dirt are a problem, benches can be used to keep
these materials from falling into the pit. One of the factors used to determine bench spacings
would be their ability to perform the above functions.
Where bench spacings have been decreased to a minimum at surface mines and sloughing
material is still not contained (smaller size material), it would be necessary to determine if a
hazard is created by the sloughing material. It is likely that the bench spacing is such that the
drop zone is minimal (the angle of the wall will affect the drop zone) and the material is simply
falling at the base of the wall. This material may not be a hazard because it does not fall into a

travel or work area. Assignment of work duties near the wall will be considered in determining
if a hazard is created.
Another factor used to determine bench spacings would be the ability to maintain the exposed
face of the highwall. If access is provided to both the top and base of a wall to make it possible
for equipment such as end loaders and excavators to clean the wall, bench spacings up to 50 feet
are practical. This is important to consider for the development of highwalls that will be exposed
indefinitely, such as deep mine face-ups.
Highwalls developed for surface mining operations are normally not exposed for long periods of
time, and the equipment used allows workers to minimize their exposure to these types of walls.
This allows for extended bench spacings. Blasting techniques are selected to shoot the wall
clean initially. Excavators are used to clean the lip of the wall and any developed bench before
the shot is brought down. Dozers then clean the wall as the shot is brought down. The
effectiveness of these cleaning operations, the shortened exposure of the wall to weathering, and
the stability of the wall determine the extent of the bench spacings used. As long as the strata in
the wall remains stable and workers in the pit are not subjected to material sloughing out of the
wall, these methods are acceptable.
If the configuration of the highwall or techniques being used do not keep material from
falling into the pit where workers are exposed, changes to the ground control methods are
necessary. Providing a bench or additional benches in the wall, widening bench widths,
modifying blasting techniques, changing the orientation of mining, and more effective cleaning
methods would be some of the changes to consider.
Developing benches at equal spacings in a wall and maintaining bench widths to equal those
bench spacings provide for the best protection against shear plane failure. It may not be practical
to break the wall down in this manner. Increased bench spacings may be necessary.
Establishing a bench at 50 feet above the pit floor and having the next spacing occur at 70 or
more feet increases the possibility that shear plane failure in the upper section of the wall would
result in rock vaulting the bench at the 50-foot elevation in the wall and landing on the pit floor.
For this reason it is important to maintain wider benches (sometimes exceeding the drop zone for
the immediate wall above the bench) in order to contain material that may fall out of the wall
above the bench.
When highwalls are not presplit, they usually shoot out at an angle (5-10 degrees). Because of
this, bench widths will need to be wider than the drop zone width for the particular height of the
wall in question. Bench widths less than 20 feet should not be used.
Whenever bedding planes exist running along in the wall parallel with the pit floor, consideration
should be given to the possibility that the plane strikes at an upward angle back into the wall.
This condition causes shear plane failure. Joint sets that intersect back in a wall in such a way
that the intersection dip at an upward angle are the cause of wedge failures. The direction that
these joint sets run back into a wall can usually be determined. The strike direction of the
intersection of these joint sets usually cannot be determined. When these discontinuities are
4

exposed to changes in weather (freeze-thaw) and/or vibration (the detonation of a shot), failure
of the material can occur with very little warning.
Protection against these hazards can be achieved by the strategic placement of benches in the
wall at the elevation where these discontinuities are exposed in the face of the wall. This
increases the safety factor of the strata where they exist. When a shot that was drilled deep is
brought down, these conditions may show up high on the wall. The opportunity to provide a
bench at the elevation of the discontinuities is no longer available. Either extending the width of
the next bench to be established below these discontinuities, or limiting exposure to these
hazards at the pit level by barricading (or a buffer), should be considered.
Joint sets that intersect back in the wall with the intersection extending vertical form what is
termed “chimneys.” If the toe supporting this strata is solid and failure occurs, the “chimney”
will usually tip out of the wall. If the toe is weak, a “chimney” can slide out into the pit bringing
the material in the toe with it. These conditions should be corrected as they are exposed bringing
the shot down. At no time should any person work below the top of a “chimney” in an attempt
to dislodge it from the wall.
Where discontinuities present shear plane, wedge, or “chimney” failure concerns, changing the
orientation of lifts (panels) can be a solution. Drilling on an angle or obtaining some angle with
production shots that are not presplit can be a solution to the “chimney” problem if a solid toe is
supporting the “chimney.” The weight of the rock causes it to lie back into the wall.
The width of benches should be determined by two factors:
First, the bench should be wide enough to contain any material that sloughs out of the wall from
above the bench. It should be at least as wide as the drop zone width if the wall above is presplit
or wider to contain material kicked out from the angle of any wall drilled on angle or developed
without presplitting. It is recommended that benches be at least 20 feet wide. The drop zone for
falling material is the area at the base of the highwall (on the bench or pit floor) within which
most of the material falling out of the wall lands. The distance that this area extends out from the
base of the wall is usually determined by measuring out from the base of the highwall a distance
of approximately 25 percent of the highwall height. The drop zone for a 100-foot highwall
would be approximately 25 feet. The width of the bench should accommodate this distance.
Second, the extended exposure of the wall can cause sloughing material to accumulate on the
bench and may require cleaning to maintain the bench’s effectiveness. If cleaning benches will
be a function of the ground control plan, the bench width will have to be able to accommodate
the width of any equipment used on the bench and safe access to the bench will have to be

.

provided Equipment with a track width of 12 feet should not be used on a bench less than 30
feet wide. This is determined by doubling the track width and allowing a margin for irregularity
of widths caused by blasting. The effects of weather increases the potential for bench failure or
changes in the wall located above and below the bench. An evaluation would be necessary to
5

determine the stability of any bench and the wall above the bench before putting any type of
equipment on the bench.
When developing a bench, its width is determined by the location of the drilled blast holes and
the type of blasting to be done. Back break from the detonation of the blast can extend back into
the bench as much as 10 feet. Presplitting can reduce back break if the holes are spaced close
enough and plugged as near the top of the hole as possible to reduce the amount of stemming in
the hole. Back break weakens the cap rock at the bench level. Explosive suppliers may offer
other techniques that could be used to handle back-break problems.
When a drill sets up to drill a 30-foot bench, the holes will need to be drilled at least 40 feet from
the base of the wall unless drilling presplit holes. As the shot is taken down, the back-break
material will pull, leaving an approximate 30-foot bench. If holes are drilled 30 feet from the
base of the wall, the result will likely be an approximate 20-foot bench, which does not give
enough width to use equipment on the bench later to clean the bench. It is likely that some
sloughing material will also vault the bench. If this occurs, the ground control plan must be
revised to provide for wider benches or other effective changes.
Because of hidden conditions and extended exposure of some highwalls, it would be prudent to
allow for bench widths that allow for continued maintenance of the bench if ground failure
occurred at the bench level. This would require more pit width and is not always an option. The
use of 40-foot bench widths is not uncommon where pit widths allow. Consideration should be
given to this when determining widths of benches that will be expected to function over a long
period of time to ensure that mining operations are not curtailed at some later time because of
highwall conditions.
4.

SPOIL BANKS

The Spoil shall be at the angle of repose or less.
Definition:
Angle of repose: The maximum slope at which a heap of any loose or fragmented solid material
will stand without sliding or come to rest when poured or dumped in a pile or on a slope. U.S.
Department of the Interior, Bureau of Mines 1968
Dragline, pushed, and end dump spoil piles should not have bank slopes that exceed the natural
angle of repose of the spoil existing in the pile. This angle of repose should be determined for
the spoil being handled at a specific mine because spoil consistency can change from one site to
another. If this angle varies for different work sites at a mine, the ground control plan will have
to identify spoil angles specific to the work sites.
Any movement or bulging of the pile would indicate that the margin of safety is not acceptable
and the slope would have to be cut down to a lesser angle.
6

5. PIT WIDTHS
To determine pit widths, consideration should be given to the type of equipment and the method
of mining that will exist in the pit. Standards require that persons not be allowed to work near or
under dangerous highwalls or banks and that unsafe ground conditions be corrected promptly, or
the area posted. If pit widths are too narrow to allow for the barricading of unsafe ground
conditions that may occur or for the safe staging of trucks while being loaded or the room for a
roadway located away from the highwall, then mining operations may be curtailed.
A safe means to design a pit width is to incorporate the distance from the highwall (W) TABLE
3 Item 6.
6.

WORKING NEAR HIGHWALLS

The plan should take into consideration the location of persons in relation to spoil banks and
highwalls when they perform their duties of drilling, blasting, working a shot, cleaning wall,
chopping coal, and loading out coal.
The plan should not allow persons to work directly against a highwall. Traveling or working
near a highwall should not be done. Then, the highwall should be thoroughly inspected for
hazards including loose rock and either loose rock should be scaled off of the highwall or the
area beneath the loose rock should be cordoned off. Benching and providing rock catching
berms both effectively reduce miners’ exposure to the highwall by moving travelways and work
areas farther out from the base of the highwall. In addition, equipment should be worked
perpendicular to the base of the highwall thereby moving the equipment operator further out
from the highwall and providing the operator with a better view of the highwall face.
When working near highwalls the following safety precautions must be followed.
h. A bench is located in the highwall directly above the work area. The bench should be spaced
so as to make it possible to clean the face of the immediate wall (the section of wall from the
pit floor up to the first bench) with equipment available at the mine (see Item 3-Benches)
i. The worker is not positioned between the highwall and any part of any equipment that would
hinder their escape from falls or slides
j. Safe access to the top of the highwall is provided to allow for examinations of ground
conditions
k. The top of the highwall is cleaned of loose, hazardous material. This should be done before
the shot material exposing the highwall is brought down. This work should be done with a
7

machine such as an excavator that can reach the edge of the wall from safe staging and use
the outward force of the bucket to remove loose material from the top edge of the wall.
l. A buffer is provided that locates the workers out a safe distance from the toe of the wall
m. All equipment shall work perpendicular to the face of the highwall and or toe while in the
impact zone.
Rock Fall Potential
Eliminating hazards from the individual rocks falling from a highwall is done through a
combination of four techniques: supporting or controlling the fall path of potentially loose rock,
scaling the loose rock, providing rock catching benches or berms or both, and limiting miners’
exposure to areas where loose rock is on the highwall.

8

9

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7. END DUMP VALLEY FILLS

These fills are spoil piles that are unique in that they are established on inclined, original ground
that typically has been altered by clearing operations that result in variable coefficients of friction
between the material being placed and the original ground. This can result in slips on the face of
the fill that do not usually occur in typical spoil piles. Because of the different friction
coefficients existing in the pile, movement on the face of the pile does not always show up at the
top of the fill as tension cracks. Until the material being placed keys into the valley floor or the
opposing slope of the valley, the fill is unstable and movement on the face of the pile is normal.
Ground control plans should establish what the angle of repose of the outer slope of the end
dump valley fills is for a specific mine or area of the mine. The method of mining used at these
dump areas would include dumping a safe distance (not less than one truck length) back from the
outer edge at the top of these fills where the slope of the outer bank becomes steepened beyond
the established angle of repose and pushing the material to the edge of the fill. Double load the
blade to push the material over the top edge of the fill. A track-mounted dozer should be used
because it distributes the weight of the machine over a greater area than a rubber-tired dozer.
The method of mining used at end dump valley fills should require dumping back from tension
cracks that exist in the top of the fill, leaving enough room for the dozer to cut a horizontal lift
off the top of the fill beginning a safe distance back from the crack. Push the material over the
outer slope to increase the safety factor for the slope. Then another lift consisting of the dumped
material can be placed where the material was removed. This procedure will be less likely to
top-load the edge of the fill and cause the edge to fail. After that material is placed, dumping
near the edge could continue as long as tension cracks do not exist.
The method of mining used at end dump valley fills should include examinations made by a
person experienced in ground control (this could be the dozer operator working the fill) often
enough to determine that hazards do not exist at the dump site. The examiner would determine
that the outer slopes of the fill are not steepened beyond the established angle of repose, that
tension cracks do not exist, that adequate berms are maintained, that trucks or end loaders
dumping over the edge do not roll against berms, and that water does not impound on the fill.
When any of these hazards exist, supervision should be informed immediately and corrective
action taken.

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8. DEEP MINE FACE UP
Highwalls
When developing a highwall for facing up a deep mine, consideration should be given to the
extended exposure of the highwall and the necessity for persons to work near the highwall. Even
though canopies are provided, they can fail if a massive collapse of the highwall occurs. During
initial development of the highwall, it is practically impossible to know with certainty what the
integrity of the strata overlying the entries will be after the wall is developed. Development
should be planned to compensate for hidden faults that may exist in the strata.
Benching will provide stability for a wall containing hidden discontinuities (bedding planes, joint
sets), as well as contain sloughing material that can fall out of the wall above the bench due to
exposure. A bench should be provided in the highwall immediately above the pit floor with a
spacing not to exceed 50 feet. Bench spacings greater than 50 feet increase the likelihood that
shear plane failure would result in material falling into the pit below. Establishing a bench at not
more than 50 feet above the pit floor also makes it easier to clean the face of the wall with
available equipment.
Developing benches at equal spacings in a wall provides for the best stability. A bench spacing
of 30 feet would provide for better protection against shear plane failure if the wall is broken
down into equal (30-foot) bench spacings. It may not be practical to break the wall down into
30-foot spacings. Increased bench spacings may be necessary. The benefits of this
configuration cannot be overstated and should be considered if the pit room is available.
Unequal bench spacings are not recommended for deep mine face-ups. Establishing a bench
at 30 feet above the pit floor and having the next spacing occur at 50 or more feet increases the
possibility that shear plane failure in the upper section of the wall would result in rock vaulting
the bench at the 30-foot elevation in the wall and landing on the pit floor.
Where total highwall heights exceed 100 feet and equal bench spacings are not an option, it
would be better to break the wall down into two benches with not more than 50-foot spacings
immediately above the pit floor and establish any greater bench spacings in the upper portions of
the wall. This will provide better containment for material falling out of the upper portions of
the wall. Highwalls that exceed 100 feet in height are more difficult to examine, and early
indicators of failure (dribbling, shifts in strata, loosened material) may fail to be recognized.
Changes in highwall integrity at the upper bench levels of underground mine face-ups involving
highwall heights exceeding 100 feet will likely be impractical to correct after development. If
the highwall is configured with equal bench spacings in the lower portion of the wall that don’t
exceed 50 feet, broken down into at least two bench levels, and provided with bench widths that
will allow for equipment access (30-foot minimum), it will be more likely that these upper level
changes will not affect mining operations. This is because most failures at the upper level should
be contained by the developed benches and not be a hazard to workers in the pit. (Bench width
is critical--see the guidelines on drilling blast holes for benches in Item 3.)
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Benches should be wide enough to contain sloughing material falling out of the face of the wall
above. The extended exposure of the wall can cause sloughing material to accumulate on the
bench and may require cleaning to maintain the bench’s effectiveness. Cleaning benches should
be considered a function of any ground control plan for underground face-ups. To facilitate this,
bench widths will have to be able to accommodate the width of any equipment used on the
bench, and safe access to the bench must be provided. Equipment with a track width of 12 feet
should not be used on a bench less than 30 feet wide. This is determined by doubling the track
width and allowing a margin for irregularity of bench widths caused by blasting.
The effects of weather increases the potential for bench failure or changes in the wall located
above and below the bench. An evaluation would be necessary to determine the stability of any
bench and the wall above the bench before putting any type of equipment on the bench.
Consideration should be given to this when determining widths of benches that will be expected
to function over a long period of time.
Because of these hidden conditions and extended exposure of the wall it would be prudent to
allow for bench widths that allow for continued maintenance of the bench if ground failure
occurred at the bench level. This would require more pit width and is not always a option. The
use of 40-foot bench widths is recommended where pit widths allow.
The use of angled drilling can help control highwalls containing mud seams (joint sets) or where
presplitting will not take effect because of intersecting discontinuities (bedding planes, joint
sets). (See Item 2–HIGHWALLS.) This method causes unconsolidated material to lie back into
the wall. This is not recommended for strata that weathers excessively (such as some shales)
because a highwall developed in this material will continually slough, and the angled wall tends
to kick the sloughing material farther out into the pit. In addition, the wall will not shed water as
well, which leads to more deterioration of the wall.
Presplitting highwalls at underground face-ups can be a good way to shoot a clean wall and
controls bench development better (see Item 3--BENCHES). Caution should be used where
vertical joint sets run parallel with the wall. If these occur near the face of the wall, a very
dangerous condition can be developed in that the material from the face to the joint set can tip
out into the pit or slide out into the pit. If tension cracks show up on top of the wall and are
running parallel with the wall, it is likely that they are the result of this type of joint set. They
can be the result of a shift in the cap rock. This can be determined by checking their depth. If
they exceed 15 feet in depth (normally below the stemming depth of the blast holes), or are too
deep to measure, it is likely they are indicating a joint set.
Failure to presplit highwalls at underground face-ups can result in problems with highwall
conditions after blasting that are hard to correct. Taking additional lifts may not be
practical. Barricading in the pit near the underground mine openings is not a solution for
conditions other than sloughing of loose material. Where excessive back break occurs,
overhangs can exist in the wall after the blast. These overhangs can cause highwall failure
13

that will not be contained by a canopy (the weight of the material will exceed the capacity
of the canopy).
The method used to presplit should be discussed with the explosives manufacturer. The strata
will dictate the method to use for effective presplit. The use of presplit explosives, closer drill
hole spacings, and smaller diameter holes usually provide for the best results. This is not to say
that using 8-foot spacings with a 6½-inch-diameter hole and air decking will not give good
results. It is one of the most common methods used. Using a 2½-inch-diameter bit on 4-foot
spacings and presplit explosives will usually provide for very effective presplit. At the other
extreme, drilling with a 10_-inch bit on 10-foot spacings and using air deck usually does not
shoot effective presplits.
Using breaker holes is not recommended. Shooting presplit holes with the production shot is not
recommended.
When deep mine entries are developed at the base of preexisting highwalls where loose material
(small sized material where wall stability is not in question) cannot be controlled, and it is
impractical to take additional lifts to establish benches in the wall, areas between the canopies
will need to be barricaded or the highwalls supported with draping or other equivalent means to
control the loose material.
The use of earthen barricading is recommended (piled high enough to limit the access of persons
or equipment). In addition to limiting access, the barricade (or buffer) will help control material
sloughing into the pit. It is the most practical solution.
If draping is done it should be heavy wire mesh (chain link is sometimes used). This will allow
for water to escape out of the wall and better observation of the wall for indications of failure. If
gunite is used, weep holes need to be provided for the escape of water. The location of these
weep holes does not always ensure that water escapes, and this can lead to deterioration of the
draping. An additive should be added to the gunite to prevent acid damage.
Another justification for the use of spraying (normally to a depth of 1-2 inches) gunite draping is
to keep surface weathering from occurring. A problem with the use of gunite is that water can
accumulate in the strata of the wall at a later time and cause the draping to deteriorate.
Substantially constructed canopies of steel, reinforced concrete, or the equivalent have to be
provided at all intended drift and slope openings prior to those openings being used by workers
to enter or exit the mine. A 10-foot cut may be taken with a remote-controlled continuous
mining machine for the purpose of installing the canopies under the edge of the highwall. The
canopy must be installed and secured against movement prior to installing roof supports. The
canopy has to extend from the highwall for a distance which will provide for adequate protection
from falling highwall material. It is recommended that the canopy extend at least 30 feet from
the highwall. This takes into consideration the drop zone for vertical walls and the effect angled
walls have in kicking falling material farther out into the pit.
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Auger Hole Penetration from Outside the Highwall or from Inside a Mine
a.

Where auger holes penetrate the coal seam from outside the highwall, they must be filled
with concrete grout or the equivalent for a distance of 25 feet along the highwall on each
side of all drifts and the entire area between the drifts for the entire length of the auger holes.
This has to be done before underground mining begins. Once coal is removed for the
development of the entries, the safety factor will be less (failure of the wall could occur)
unless additional support is provided by grouting the auger holes as described above.

b.

Once the auger holes have been grouted, normal mining will take place using the steel arch
system or equivalent for support to at least 25 feet inby the end of the auger holes in each
drift.

c.

If auger holes are encountered underground, then safety precautions must address support of
the roof and ribs in these auger holes. If an opening is to be taken outside through auger
holes, then a plan will be required to be submitted as part of the Roof Control Plan.

Note:

Items b and c above will be addressed in the roof control plan required by 30 CFR
75.220 and should not be part of any Ground Control plan required by 30 CFR,
77.1000.

15

Other Information Where Appropriate
SURFACE BLASTING
Describe the blasting procedures and type of explosives used:

Describe the drilling equipment:

Drill Hole diameter:
Hole Spacing:
Angle of hole:

Hole Depth:
ft. by

ft.

degrees

Is pre-splitting to be done? [ ] Yes

[ ] No

When remote firing devices are used, the manufacturer’s safety precautions shall be followed.
AUGER MINING OPERATIONS
1. Type of Mining Machine
2. Manufactured by
3. Serial Number
4. Model Number

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5. Is the Auger Mining in the Vicinity of Abandoned or Active Underground Mines?

6. Coal Seam(s) to be Auger Mined:

inches

7. Coalbed Height for Each Seam Mined:
8. Maximum Depth of Penetration:

feet

9. Distance Between Auger Miner Holes:
10. Diameter/Width of Holes:

inches

inches

inches

DIAGRAM OF HOLES AND WEBBING

17

inches

18