EPA-R2-73 135
JANUARY 1973 Environmental Protection Technology Series
Investigation of Use
of Gel Material
for Mine Sealing
% PROl^
Office of Research and Monitoring
U.S. Environmental Protection Agency
Washington. DC 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
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EPA-R2-73-135
January 1973
INVESTIGATION OF USE OF GEL
MATERIAL FOR MINE SEALING
By
Neville K. Chung
Project 14010 EKW
Project Officer
Ronald D. Hill
Mine Drainage Pollution Control Activities
Environmental Protection Agency
National Environmental Research Center
Cincinnati, Ohio 45268
Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
For sale by the Superintendent ol Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price J1.25
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EPA Review Notice
This report has been reviewed by the Environ-
mental Protection Agency and approved for
publication. Approval does not signify that
the contents necessarily reflect the views
and policies of the Environmental Protection
Agency, nor does mention of trade names or
commercial products constitute endorsement
or recommendation for use.
11
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ABSTRACT
Laboratory testing of commercially available chemical
grouts was conducted to evaluate their potential use,
in conjunction with a cheap filler, for remote sealing
of mine voids. By close control of the setting time and
proper distribution of the grout slurry it was believed
that a mine seal could be placed through a borehole from
the surface without the benefit of retaining bulkheads.
A slurry mix consisting of an acrylamide grout with
flyash or mine refuse as a filler was found to produce a
strong controllable gel which resisted chemical attack
in the laboratory over an eleven week exposure period.
An attempt to demonstrate a novel technique for applica-
tion of the selected grout slurry in a mine entry with
high flow was not successful. The results suggest that
the technique may be applicable in dry or low flow
situations. However, the estimated cost of a mine seal
using the gel material is presently not competitive with
existing methods.
Groundwater monitor wells were drilled for the purpose
of determining the effect of mine sealing on groundwater
conditions. Data reflecting pre-seal conditions was
compiled, but because the sealing of the mine was not
completed the monitoring program has been postponed.
This report was submitted in fulfillment of Project
Number CR-100 Contract 14010 EKW, under the joint
sponsorship of the U. S. Environmental Protection Agency
and the Commonwealth of Pennsylvania, by Dravo Corporation,
Pittsburgh, Pennsylvania 15222.
111
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CONTENTS
Section Page
I CONCLUSIONS 1
II RECOMMENDATIONS 3
III INTRODUCTION 5
Previous Investigations 5
Purpose and Scope of Present Study 6
IV DEVELOPMENT OF SEAL MATERIAL 9
Chemical Grouts Tested 12
Fillers Tested 13
Testing Procedures 13
Evaluation of Grout Slurries 14
Selected Grout Mix 23
V LOCATION AND DESCRIPTION OF TEST SITE 25
Mine Location and Description 25
Acid Drainage Characteristics 28
VI GROUNDWATER MONITORING STATIONS 35
Location and Description of
Monitor Wells 35
Sampling Program 38
VII MINE SEALING OPERATIONS 51
Double Bulkhead Seals 51
Sealing of Air Vent 54
Construction of Safety Bulkhead 54
Injection Nozzle Tests 57
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CONTENTS (Continued)
Section Page
VII MINE SEALING OPERATIONS
Injection of Gel Material 57
VIII ACKNOWLEDGEMENTS 67
VI
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FIGURES
PAGE
1 Arrangement of Proposed Mine Seal 10
2 Injection Procedure for Grout Seal 11
3 Preparation of Test Cubes 15
4 Unconfined Compressive Strength Test 15
5 Test Cube Storage Controlled Humidity Vault 16
6 Elasticity of Flyash-AM9 Gel 19
7 Deformation and Failure of Test Cylinder 20
8 Compressive Strength and Volume Changes of
Flyash-AM9 Gel Immersed in Acid Solution 21
9 Compressive Strength and Volume Changes of
Mine Refuse-Flyash-AM9 Gel Immersed in
Acid Solution 22
10 General Location Map 26
11 Mine Portal Area 27
12 Acid Drainage Flow Variation 29
13 Statistical Variation of Mine Drainage Flow 30
14 Iron, Acid and Sulfate Concentrations in
Mine Acid Flow 31
15 Iron, Acidity and Sulfate Loading to Stream 32
16 Location of Wells and Surface Sampling
Stations 36
17 Typical Groundwater Monitor Well 37
18 Double Bulkhead Seals 53
19 Pressure Gauge-Relief Pipe Installed in
Place of Old Air Vent 55
Vll
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FIGURES (continued)
PAGE
20 Protection of Excavated Mine Entry 56
21 Concrete Bulkhead Details 58
22 View of Concrete Safety Bulkhead 59
23 Bench-Scale Test of Gel Material 60
24 Angle of Repose Achieved in Lab Test 60
25 Yard Tests of Injection Nozzle 61
26 Slurry Batcher and Weigh Bin 63
27 Slurry Injection Pipe and Pumping Equipment 64
28 View of Mine Entry through Observation
Window in Bulkhead 65
Vlll
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TABLES
No.
1 Precipitation in Vicinity of Keystone
State Park 33
2 Drilling Logs of Monitor Wells 39
3 Drilling Logs of Existing Park Wells 40
4 Results of Analyses - Sampling Station MD 41
5 Results of Analyses - Sampling Station CR 42
6 Results of Analyses - Sampling Station SP 43
7 Results of Analyses - Sampling Station C-l 44
8 Results of Analyses - Sampling Station C-2 45
9 Results of Analyses - Sampling Station B-l 46
10 Results of Analyses - Sampling Station B-2 47
11 Results of Analyses - Sampling Station B-3 48
IX
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SECTION I
CONCLUSIONS
1. A slurry consisting of an acrylamide grout with
flyash or neutralized mine refuse as a filler can produce
a stiff gel which may be useful in remote sealing of mine
voids. The setting time is controllable, and the gel
material is strong, resilient and resistant to attack
by mine acid.
2. The cost of the materials and placement are at
present higher than that for a concrete seal. Reductions
are possible through use of a modified mix, possibly with
cement as an admixture, and refinement of injection
procedures.
3. Dilution and erosion of the gel material prevents
successful formation of a gel seal in high flow mines.
Application of the material and technique to dry or low
flow situations has not been tested.
4. A concrete seal can be placed between ungrouted
stone bulkheads but settling of the concrete may occur
due to movement of the unconsolidated aggregate,
resulting in increased grout requirement in the subse-
quent pressure grouting operation.
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SECTION II
RECOMMENDATIONS
1. It is recommended that a groundwater monitoring
program be included in plans for completion of mine
drainage abatement work at the Salem No. 2 Mine at
Keystone State Park, since information is lacking at the
present time regarding the effect of mine sealing on
groundwater conditions, and monitor wells have already
been drilled at the Keystone site.
2. The location of the mine portal area on State property
which is not developed presently for recreational use,
and the existence of a reinforced concrete safety bulkhead
with view ports and sample valve, make the site ideal for
further test work. It is recommended that this asset be
explored prior to making a final decision on sealing.
If no testing is foreseen, closing of the drain valve
and sample valve in the bulkhead will make it a concrete
seal.
3. It is recommended that grout stabilization of the
stone bulkheads be retained as normal procedure in
construction of double bulkhead seals.
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SECTION III
INTRODUCTION
Acid mine drainage is formed by the oxidation of iron
disulfides, usually pyrites, found in association with
coal, when the pyrites are exposed to air and water.
The result is a dilute solution of sulfuric acid and iron
sulfate. Though there are available treatment techniques,
such as neutralization with lime to adjust pH and precip-
itate iron, it is generally agreed that measures aimed
at preventing the formation of acid drainage hold the
most promise for curbing this source of pollution, par-
ticularly from inactive mines.
There are presently over 3000 miles of streams in
Pennsylvania affected by mine drainage, most of it
originating from abandoned deep mines. Estimates for
abatement have been set at two billion dollars, and the
major portion of this cost is for source control. New
techniques are constantly being sought, largely through
research'and development programs sponsored by the U. S.
Environmental Protection Agency and various State
agencies.
Previous Investigations
Techniques which have been investigated for the prevention
of mine acid formation are based on excluding oxygen from
the pyritic surfaces. This is usually accomplished by
sealing the mine openings to prevent entry of air and to
cause the mine cavity to fill with water.
Seal construction methods tested have included:
a) placement of an aggregate mass followed by injection
of grout into the aggregate.
b) placement of a permeable limestone plug for in situ
neutralization and sealing by precipitates.
c) injection of quicksetting cement grout into expendable
cloth retainers.
d) formation of forward and rear retaining bulkheads
with a quick-setting slurry followed by injection of a
cement intermediate plug.
e) placement of forward and rear retaining bulkheads of
aggregate through vertical boreholes, followed by
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stabilization of the bulkheads by injection of grout and
injection of a concrete plug between the bulkheads.
The last method, using two bulkheads of stone with a
concrete plug between them, was recently employed in
sealing over 100 mine openings in Butler County,
Pennsylvania.
Purpose and Scope of Present Study
The work reported herein was undertaken to develop a new
mine sealing technique using a chemical grout with a
filler material as the sealant. A chemical grout is a
mixture of chemicals which will produce a stiff gel from
a dilute aqueous solution when properly catalyzed. The
setting time is predictable and controllable, and the
gel material is essentially impermeable. It was theorized
that a chemical grout with a cheap filler such as flyash
could produce a strong, chemically resistant, impermeable
material suitable for a mine seal, and that by proper
distribution of the grout slurry and control of the gel
time the seal could be built up without the benefit of
retaining bulkheads.
Three major phases of activity were proposed:
1) Laboratory testing of commercially available grouts
and filler materials to evaluate and select one or more
formulations suitable for the proposed remote mine seal
construction.
2) Demonstration of a technique for application of the
gel material by sealing three entries of an abandoned
deep mine located in Derry Township, Westmoreland County,
Pennsylvania.
3) Post-construction surveillance to study the effective-
ness of the seals, and to determine changes in ground-
water quantity or quality resulting from placement of the
seals.
As the work progressed, information developed in each
phase suggested or dictated changes to the original
scope of work in succeeding phases. Two major changes
were made:
1) Double bulkhead type concrete seals, with ungrouted
stone bulkheads, were placed in two of the three mine
entries, and only one chemical grout seal attempted.
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2) The post-construction groundwater monitoring program
was postponed.
Although the surveillance program was not performed, a
set of groundwater monitor wells were completed in order
that background information regarding groundwater level
and quality could be developed prior to placement of any
mine seal. . This information, plus data on the flow and
quality of acid drainage from the mine, and stratigraphic
information developed from drilling of the monitor wells,
are included in this report to provide a reference point
for future work if performed at this site. The need for
information regarding the effect of mine sealing on
groundwater still exists, and it is assumed that this
aspect will be investigated when the sealing of the mine
is completed by injection of grout curtains.
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SECTION IV
DEVELOPMENT OF SEAL MATERIAL
Test Objectives
As proposed, the experimental mine seal was to be built
by injection of a gel material with controllable setting
time into the mine cavity through a vertical borehole
from the surface. The material would be self-supporting,
eliminating the need for retaining bulkheads. Following
placement of the seal, flyash would be pumped into the
mine side of the seal. The purpose of this backstop was
twofold. It was felt that if any leakage occurred flyash
would be carried in suspension into the seal and plug the
leak. Secondly any leakage that escaped the seal would
be neutralized by the flyash. A sketch of the proposed
seal is shown on Figure 1. The safety bulkhead shown is
for protection during development and testing of the seal.
Test work to develop a material suitable for the proposed
mine seal included evaluation of five different chemical
grouts with various combinations of flyash, mine refuse,
sand and gravel as fillers. Characteristics of prime
importance were a short, controllable setting time,
resistance to chemical attack by mine acid, and sufficient
strength to withstand expected forces.
To avoid formation of a point seal at the injection hole
which would prevent completion of the seal across the
entire width of the mine roof, it was felt that it would
be necessary to direct the grout slurry stream outward
away from the injection hole, and slightly upwards, in
order to build the seal up from the outer extremities
in a concave shape, as shown on Figure 2. A short gel
time of less than one minute would be required while
building up the seal in order to give an economical angle
of repose and prevent excessive running of the material
along the mine floor. On the other hand during the final
stages a longer gel time would be required to ensure
dispersion and penetration of the grout into the remaining
crevices. For maximum flexibility it was decided that the
material should have a highly controllable gel time from
greater than five minutes to a few seconds.
The mine floor at the test site slopes upward from an
elevation of 1016 feet at the entry to a maximum elevation
of approximately 1100 feet. The maximum hydraulic head
that could develop on a seal therefore is approximately
84 feet, equivalent to 36 psi. The maximum pressure which
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PLAN
FLYASH INJECTION HOLE
o
I
SEAL INJECTION HOLE
ELEVATION
FIGURE 1, ARRANGEMENT OF PROPOSED MINE SEAL
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INJECTION NOZZLE
y/^f\
ELEVATION
'A1
SECTION
FIGURE 2, INJECTION PROCEDURE FOR GROUT SEAL
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could be exerted by the overburden of about 30 feet was
estimated at 35 psi, essentially equivalent to the
maximum hydraulic head. Using a design safety factor of
3, which includes allowances for differences in filler
materials and between laboratory techniques and field
procedures, a compressive strength of 110 psi was selected
as the desired strength of a seal material.
Chemical Grouts Tested
Five commercially available chemical grouts were tested:
Trade Name Type
Terranier-C Phenolic polymer
AM-9 Vinyl polymer
Cyanaloc-62 Methylol bridge polymer
Terra Firma Chrome lignin
Geoseal Phenolic polymer
Terranier-C is a three-component system consisting of a
principal reactant, a catalyst and a secondary reactant
or crosslinking agent. The principal reactant is a
phenolic powder which is dissolved in water to make one
solution. A second solution is prepared containing the
catalyst, sodium dichromate, and a formaldehyde cross-
linking agent. A polymerization-crosslinking reaction
occurs when the two solutions are mixed.
AM-9 Chemical Grout is a four-component system consisting
of a reactant, catalyst, inhibitor and initiator. The
reactant is a mixture of two organic monomers, acrylamide
and N,N*-methylenebisacrylamide. It is a granular material
which is mixed with water to make a solution of desired
strength. The catalyst is B-dimethylaminopropionitrile
(DMAPN) an alkaline liquid. The inhibitor potassium
ferricyanide, is added in very small quantities to control
the reaction.
The reaction is triggered by the initiator, ammonium
persulfate, which is a very strong oxidizing agent. Two
solutions are prepared, one containing AM-9, DMAPN and
potassium ferricyanide, and the other ammonium persulfate.
Gelation occurs by a polymerization-crosslinking reaction
when the two solutions are mixed.
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Cyanaloc-62 consists of two components, a reactant and a
catalyst. The reactant is a viscous liquid monomer which
is diluted to desired strength with water. Polymerization
occurs when a solution of sodium bisulfate, the catalyst
is mixed with the reactant.
Terra Firma consists of a lignosulfonate reactant which
is catalyzed by sodium dichromate to form a chrome lignin
gel. Both materials dissolve readily in water to make
solutions of desired consistency for application.
Geoseal is a two-component system consisting of a phenolic
reactant and sodium hydroxide catalyst. The reactant is
a powder which is not dissolved in water, but added
directly to a solution of the catalyst. Polymerization
occurs when the two are mixed in certain proportions
which give a pH of between 9.5 and 10.2.
Fillers Tested
Flyash was the first material considered for testing as
a filler. It is cheap and readily available, and was also
proposed as a backstop behind the seal because of its
particle size and alkalinity. For the laboratory testing
800 Ib of flyash was obtained from Duquesne Light
Company's Elrama, Pa. station. This sample of ash had a
particle density of 2.11 gm/cc and a bulk density of
1.05 gm/cc, indicating approximately 50% voids.
Mine refuse from the mine site was investigated as a
possible filler material since if successful this would
also solve, at least partially, the problem of disposal
of this unsightly acid producing waste material. The
loosely compacted, claylike material was found to have a
particle density of 2.35 gm/cc and a bulk density of
1.53 gm/cc, indicating 34% voids. The material is acidic
with a pH of approximately 3.0.
Shot gravel and Ohio River highway grade sand were tested
briefly and found to offer no advantages over flyash or
mine refuse as fillers for the proposed seal material.
Testing Procedures
Preliminary tests were run with each material to determine
its particular characteristics and suitability as a
potential mine sealant. Mix proportions, strength, gel
time control, and compatibility with the fillers were
evaluated. Once these tests were completed, practicable
grout formulations were selected for further testing of
physical properties and stability.
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Test cubes were prepared by mixing selected proportions
of grout, water, filler and whenever necessary inhibitor
or crosslinking agent, for thirty minutes to insure
homogeneity, adding the catalyst or activator, and
pouring the slurry into ASTM standard 2-inch cube molds
shown on Figure 3. After solidification the cubes were
placed in a storage vault with humidity, controlled at
100% to prevent dehydration. Two or three cubes were
tested for compressive strength daily for one week.
(Figure 4.) After the first week cubes were tested once
per week for ten weeks. Figure 5 shows the controlled-
humidity storage vault.
Resistance to chemical attack from acid mine drainage
was tested by submerging cubes in an acid solution
prepared in the laboratory to simulate the most severe
condition anticipated. This solution contained 200 ppm
iron, 400 ppm sulfate, and had a pH of 2.0. Size,
compressive strength, and weight of test cubes were
checked weekly for ten weeks. The test solution was
examined for discoloration and sediment, and changed
weekly or whenever the pH value reached 3.5.
Evaluation of Grout Slurries
The preliminary tests which were conducted with each
material eliminated some of the materials and certain
combinations of materials from further, long-term testing.
Shot gravel and highway grade sand were tested as fillers
for added mass in combination with flyash and mine refuse.
They were found to yield lower compressive strength than
either flyash or mine refuse alone, and were therefore
eliminated from further consideration as fillers.
Tests with Terra Firma indicated that the gel time could
be effectively controlled only by varying the water
content, which affected the strength of the resultant gel.
Catalyst concentration was dependent on monomer concentra-
tion, which resulted in shorter gel times with increasing
concentrations of the chemical grout. This system was
also found to be incompatible with flyash due to the
alkalinity which results in precipitation of trivalent
chromium from the dichromate catalyst.
Geoseal is catalyzed by sodium hydroxide at a pH between
9.5 and 10.2. The caustic not only initiates the reaction
but is also necessary to dissolve the reactant to a true
solution. Polymerization therefore begins as soon as the
reactant is dissolved in the catalyst solution. This
necessitates a batch, or one-shot, system of application
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FIGURE 3, PREPARATION OF TEST CUBES
FIGURE
M & IL
UNCONFINED COMPRESSIVE STRENGTH TEST
- 15
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FIGURE 5, TEST CUBE STORAGE IN CONTROLLED-
HUMIDITY VAUL1
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which severely limits control of gel time and precludes
use of a very short gel time. A two-shot system was
devised by preparing the grout solution with less sodium
hydroxide than is necessary for gelation, and feeding the
remainder of the required caustic in a separate stream.
In theory this seemed feasible, but it could not be made
to work. The material increased in viscosity but would
not gel. An increased amount of caustic caused a gel
which was attacked by moisture indicating only a partial
reaction.
The addition of either flyash or mine refuse to a solution
of Terranier-C was found to start gelation immediately,
apparently due to a catalytic effect of polyvalent cations
in the fillers. It was discovered that a more stable
mixture, usable for 30 to 40 minutes, could be prepared
by adding dry Terranier-C to a flyash slurry or neutral-
ized mine refuse slurry. Test cubes made in this manner
were found to be hard and brittle with compressive strength
of 70 to 115 psi. When the cubes were immersed in a
synthetic mine acid solution, the solution turned a dark
reddish-brown color characteristic of the polymer within
one day.
Leaching of color continued for about seven weeks, during
which time the cubes shrank approximately 51 in volume,
but no corresponding loss of strength was detected. This
loss of color and shrinkage may indicate a condition
which could eventually lead to failure; however the
immediate problem with use of Terranier-C slurry as a
mine sealant was the initiation of setting by the fillers.
Cyanaloc-62 is acid catalyzed and therefore will not form
a gel with alkaline flyash. With mine refuse as a filler
gelling is initiated but proceeds very slowly, over a
period of hours. Test cubes made with a grout mix
consisting of 25 pounds mine refuse to 1 gallon of one-to-
one by volume Cyanaloc-62 solution had compressive strength
of 560 psi. However, after five weeks immersion in an acid
solution the cubes began to show signs of deterioration.
The surface developed a slimy appearance, and an 8% weight
loss was measured. A sudden, severe loss of strength
occurred during the eighth week. At the end of the ten
week test period the strength loss was 421 due to attack
by the acid. Test cubes stored at 1001 humidity showed
no similar loss of strength.
Testing of AM-9 chemical grout was narrowed down to
and 15% solutions after preliminary tests. The exothermic
- 17 -
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polymerization reaction released enough heat to cause
cracking of cubes made with a 30% solution, and a 5%
solution produced a very weak gel. The 20% solution was
eliminated from further testing after three weeks because
indications were that satisfactory strength would be
obtained with a 15% solution.
Both flyash, and mine refuse neutralized with lime or
flyash, were found to be compatible with AM-9. Test cubes
were made using 10% and 15% AM-9 solutions with the follow-
ing amounts of filler per gallon:
a) 15 Ib flyash
b) 20 Ib mine refuse, 22 gm CaO
c) 7 Ib flyash, 14 Ib mine refuse
All the components of the AM-9 system were easily handled
and readily dissolved to true solutions with viscosities
similar to water. Mine refuse alone was found to be
unsuitable as a filler because of its acidity, but neutral-
ization to a pH greater than 7 with either lime or flyash
made it an acceptable filler.
Gel time of AM-9 grout mixes was found to be highly
controllable by varying the amounts of catalyst DMAPN,
ammonium persulfate and potassium ferricyanide which
together comprise the catalyst system.
Grout mixes made with AM-9 were found to produce a material
which had a certain degree of elasticity. Figure 6 is a
plot of observed deformations of cubes made with 10%, 15%
and 20% AM-9 solutions and flyash versus applied compres-
sive stress. Elasticity of a test cylinder is illustrated
on Figure 7 which shows extreme deformation at failure.
It is believed that this property would be advantageous
in formation of a tight seal, after leakage is stopped by
pressure grouting or by flyash carried in suspension from
the backstop.
Compressive strength and size of test cubes immersed in
an acid solution simulating mine drainage were measured
weekly over an eleven week period. Figures 8 and 9 show
the compressive strengths and volume changes observed for
test cubes made using AM-9 with flyash alone and a combina-
tion of mine refuse and flyash as fillers. From the graphs
it would appear that the chemical stability of the cubes
made with a combination of flyash and mine refuse as filler
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160
FAILURE
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1.7 1.6 1.5 1.4 1.3
CUBE HEIGHT (INCHES)
2.O 1.9
1.2
FIGURE 6, ELASTICITY OF FLYASH-AM9 GEL
- 19 -
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FIGURE 7. DEFORMATION AND FAILURE OF
TEST CYLINDER
- 20 -
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TIME (WEEKS)
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FIGURE 8,
4567
TIME (WEEKS)
8
IO II
COMPRESS IVE STRENGTH & VOLUME CHANGES OF
FLYASH-AM9 GEL IMMERSED IN ACID SOLUTION
12
- 21 -
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250
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IT
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AM9
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TIME (WEEKS)
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TIME (WEEKS)
FIGURE 9, OPPRESSIVE STRENGTH & VOLUME CHANGES FOR MINE
REFUSE-FLYASH-AM9 GEL IMMERSED IN ACID SOLUTION
- 22 -
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is better than that of the cubes made with flyash alone
as the filler. However it is believed that the observed
variations in the strength and size of the cubes made
with flyash alone were due to neutralization of flyash
particles by acid at the surface of the cubes rather than
to reaction with the chemical grout material itself, and
a stable condition would be reached. When gels were
formed at a lower pH by neutralizing the flyash with mine
refuse (or vice versa) the observed strength and size were
uniform.
It should be noted that strength determinations are made
by destructive testing and that therefore each determina-
tion is_made on a different cube prepared from the same
grout mix. As a result some variation of observed strength
can be expected from cube to cube, regardless of the
curing time or exposure conditions.
Selected Grout Mix
Of the five chemical grouts tested only AM-9 was found to
meet all the essential requirements of adequate strength,
good gel time control and resistance to mine acid. The
compressive strength tests indicated that a 15% AM-9
solution would be required, whether flyash or mine refuse
was used as the filler. On the basis of a seal 12 feet
wide by 28 feet long, the cost of grouting chemicals alone
was estimated at $9,000 per seal. This was considerably
higher than original estimates, which had been based on
use of a cheaper grout material, and it appeared that even
if the material could be cheaply applied the overall cost
would exceed that of alternate sealing techniques.
It was agreed in a joint meeting with the project sponsors
to proceed with only one experimental grout seal, and seal
the other two mine entries with double bulkhead type
concrete seals. Though the cost of the gel seal was
expected to be uneconomical, it was felt that testing of
the injection technique was still desirable since if
successful, further research could be directed to reducing
the cost of both the materials and the procedure.
A grout slurry of 15 Ib flyash to one gallon of 15% AM-9
solution was selected for the test. Flyash offered
certain inherent advantages over mine refuse as a filler
for the proposed seal. Screening and neutralization were
not required, as with mine refuse. Also, since one aspect
of the proposed sealing operation consisted of pumping
flyash into the mine side of the grout seal, the use of
flyash as the filler would further simplify materials
- 23 -
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handling. The main reason for considering mine refuse
lay in the disposal aspect. However, in view of the
variable nature and quantity of this material from mine
to mine, any success with use of the material at this
mine would not necessarily be repeatable at another site
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SECTION V
LOCATION AND DESCRIPTION
OF TEST SITE
Mine Location and Description
The site selected for demonstration of the experimental
sealing material and technique is an abandoned deep mine
located in Derry Township, Westmoreland County, Pennsyl-
vania. Most of the mine, including the portal area, is
located within the Commonwealth of Pennsylvania's
Keystone State Park, approximately 35 miles east of
Pittsburgh. The location is shown on Figure 10.
The mine, which was known as the Salem No. 2 Mine, covers
approximately 300 acres, sloping upward at an approximate
grade of 31 from an elevation of 1016 feet at the entrance
to approximately 1100 feet at the highest point. There
were three openings located a short distance below the
spillway of Keystone Lake. The west opening was the main
portal, while the middle opening served as a fanway. The
third opening to the east was made by blowing a hole
through the mine roof by an explosive charge set within
the mine. The mine portal area is shown on Figure 11.
The main entry extends approximately half a mile in a
southerly direction beneath a wooded hill. Side entries
run east and southwest from the main entry. Beneath the
crest of the hill the mine lies some 200 feet below the
ground surface. Other than the portal area the thinnest
cover occurs in the southernmost extremities where the
mine is 40 to 60 feet below the ground surface.
A 12" air vent, located approximately 200 feet up from
the main entrance as shown on Figure 11 was the only
other opening found into the mine. No instance of
subsidence was known to a former miner who worked in the
mine for 20 years, and no evidence of holes or slumps
were found during field inspections of the mined area.
All three entries were blocked with rubble, and acid
drainage appeared to be coming only from the middle entry
in front of which the water was pooled. The overflow
drained into the small creek below the Lake. This creek
enters the Loyalhanna Creek, a tributary of the Allegheny
River, approximately 1-1/2 miles downstream.
- 25 -
-------
NEW YORK
PENNSYLVANIA
KEYSTONE STATE PARK
GREENSBURG
-^MARYLAND
>
N
VIRGINIA
25 5O
FIGURE 10, GENERAL LOCATION MAP
- 26 -
-------
o
FAN WAY
OUTCROP
SECONDARY PORTAL
EXISTING
FOUNDATIONS
200
SCALE FEET
FIGURE 11, MINE PORTAL AREA
- 27 -
-------
Acid Drainage Characteristics^
The acid drainage from the mine was measured and sampled
over a two-year period prior to the start of remedial
activity, from October 1967 to August 1969. The flow
generally ranged from 20,000 gallons per day (13.9 gpm)
to 160,000 gallons per day (111 gpm), with the lowest
flows occurring in late summer and fall, and the highest
flows occurring usually during the first three months
of the year. Figure 12 shows the flow variation over
the two-year sampling period. Flow rates plotted are
single measurements or averages of two to four measure-
ments taken during a given month. Occasional peak flows
up to 850,000 gallons per day (590 gpm) were reported;
however ninety percent of the time the flow was less than
160,000 gallons per day, and half the time less than
60,000 gallons per day, as shown by the statistical
analysis of all recorded flow measurements, Figure 13.
Concentrations of iron, acidity and sulfate in the mine
drainage over the sampling period are shown on Figure 14,
and the corresponding loadings in pounds per day are
shown on Figure 15. Again the values plotted are either
single determinations or averages of two to four samples
taken during a given month. The total pollution load due
to the mine drainage is related primarily to the flow
quantity and only secondarily to contaminant concentra-
tions. Peak loads generally coincided with high flow
periods.
Inasmuch as the mine drainage flow, and consequently the
pollution load, may be a function of the wetness or dry-
ness of any given period, an evaluation of abatement
measures should take into consideration the amount of
precipitation in the area over the study period. The
terrain above the mine is conducive to fairly rapid
surface runoff on all sides of the rounded hilltop.
However infiltration that does occur will find its way
into the mine cavity which, by virtue of its areal
extent and the relatively unimpeded routes it provides,
should be the principal flow control for subsurface
water. Precipitation data for the Keystone State Park
area for the years 1967, 1968 and 1969 is given on Table 1.
- 28 -
-------
t-o
VQ
600,000
500,000
IOO.OOO
0 NDJFMAMJJASONDJFMAMJJA
1967
1968
1969
FIGURE 12, ACID DRAINAGE FLOW VARIATION
-------
w
o
500,000
400,000
300.00O
200,000
100,000
90,000
80,000
^ 70,000
& 60.0OO
* 50,000
" 40,000
30,000
20,000
10,000
1 I » 1I 1 1 *
10 2O 30 40 50 60 70 80
PERCENTAGF OF TIME EQUAL TO OR LESS THAN
90 95
98 99
FIGURE 13, STATISTICAL VARIATION OF MINE DRAINAGE FLOW
-------
3000
-2000
j IOOO
0 N
1967
D J
FMAMJJASONDlJFMAMJJA
1968 ^ "969
1000
Q_
CL
800-
600-
g
o 400
i 200
ONDIJFMAMJJASOND
1967 4
1968
JFMAMJJA
1969
4OO
Z
a 300
200
IOO
ONDIJ FMAMJ JASONO
1967 4.
1968
J FMAMJJA
1969
FIGURE W, IRON, ACID & SULFATE CONCENTRATIONS IN MINE ACID FLOW
-------
TO 3347
ts>
I
1600
1400
o
x.
c/>
CD
s
£ 800
fi
_/
600
H
Q
IAOO
200
\
\
ON D ' J F MA M J
A S 0 N D
(967 «L-
1968
F M A M J 0 A
1969
FIGURE 15, IRON, ACIDITY & SULFATE IN MINE ACID FLOW
-------
TABLE I
PRECIPITATION IN VICINITY OF
KEYSTONE STATE PARK
(Average of Measurements at Blairsville, Vandergrift & Derry)
Inches of Precipitation
1967
Jan.
Feb.
March
April
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
ANNUAL
1.28
2.82
6.59
4.55
4.21
1.69
5.02
3.88
3.50
3.02
2.82
2.46
41.84
1968
Jan.
Feb.
March
April
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
2.47
1.25
3.39
2.05
6.88
1.61
4.15
4.69
2.80
1.93
3.85
3.80
38.87
1969
Jan.
Feb.
March
April
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
2.70*
1.03*
1.45*
4.54*
2.57*
3.64*
6.01
2.16
2.15
2.81
3.12
4.93
37.11
* No data from Derry. Donegal data used.
- 33 -
-------
SECTION VI
GROUNDWATER MONITORING STATIONS
Location and Description of Monitor Wells
In order to provide the means of evaluating the impact
of the sealing of the mine on groundwater in the area, a
set of groundwater monitor wells were drilled in the
locations shown on Figure 16.
Well A-2, located on top of the hill above the mine, was
drilled to a depth of 200 feet, or to approximately 15
feet of the top of the mine, in order to evaluate the
dewatering effects on the strata comprising the hill
above the mine by the mined area. Two wells were origi-
nally proposed, one on each of the two rounded hilltops;
however Well A-l was later eliminated.
Wells B-l, B-2 and B-3 were drilled for the purpose of
monitoring the groundwater in the immediate surrounding
area in order to determine its response to the inundation
of the mined area. Drilling depths were 230 feet, 225
feet and 200 feet respectively.
Wells C-l and C-2 near to Keystone Lake and Creek, were
drilled to 100 feet below their bottom elevations in order
to give warning of possible deep flow lines and inputs of
mine drainage polluted groundwater through the bottom
of the lake or stream as a response to vertical pressure
buildup as the mine fills. Depth of C-l is 156 feet, and
the depth of C-2, 110 feet.
All of the monitor wells are 6 inches diameter with 6-1/4"
I.D. casing extending from 1 foot above grade to below
bedrock. A screwed cap is provided on each well to
prevent entry of foreign matter. Ten feet high markers,
consisting of 6 inch diameter plates mounted on 1-1/2"
diameter pipe, were erected at each monitor well to
facilitate location and identification. A typical monitor
well is shown on Figure 17.
Water was encountered during drilling of all the wells
except well A-2 located on the crest of the hill. In
general the wells at higher elevations such as B-l and
B-2 yielded small quantities of water. At wells C-l and
C-2 which are at a low elevation and lie close to the
lake and stream, water was encountered at two separate
elevations.
- 35 -
-------
< '
EXISTING WATER WELLS
// ' '/ ' ' x
V A ! M x
^f / o
/ ;-'
NEW MONITOR WELLS AND
SAMPLING STATIONS
/
FIGURE 16, LOCATION OF WELLS AND SURFACE SAMPLING STATIONS
-------
MARKER
c
+1
o
1
\ \ ^ <-\
V
>
-<:
y
I^^-G-DIA.
j ROUND ROD WELDED TO CAP
/-I>2"DIA.
^ J
i 1_, ^_ or.DPurpn PAD
-
<
*
<
;
^c tc u c
r^"
U-^H
--O
1 §
1
! _^J
«
(5 ^
^
S r
S
^ ;
'o
1
,
.,
1
' ^^ &/4 I.D. CASING
/^ ROCK
6_^- 6"DIA.HOLE
FIGURE 17, TYPICAL GROUNDWATER MONITOR WELL
37
-------
The drilling logs of the monitor wells are tabulated on
Table 2, and logs of water wells previously drilled in the
park on Table 3, as an aid to defining the stratigraphy of
the area for future interpretation of groundwater changes
resulting from water buildup in the mine. The locations
of the existing water wells are shown on Figure 16. Well
No. 4 was not completed.
Sampling Program
In addition to the groundwater monitoring wells, surface
sampling stations SP and CR were established upstream and
downstream of the point where the mine drainage entered
the creek and at the mine opening itself, designated
station MD. Location of these sampling points are shown
on Figure 16.
Since the surveillance program has been postponed, there
is of course no data reflecting a change in the hydro-
geological environment due to mine water impoundment.
However, samples were taken from the monitor wells and
surface sampling stations on a more-or-less weekly
schedule over a two-month period prior to the scheduled
sealing, in order to establish background data on water
quality and level. These samples were analyzed for pH,
total iron, sulfate, acidity and total solids. On each
sampling tour the water level in the monitor well was
measured.
The data from the "pre-sealing" sampling program is
presented on Tables 4 through 11. At stations C-l and C-2
samples were taken from two depths approximately coincident
with the levels at which water was encountered during
drilling. Monitor well A-2 was dry throughout the sampling
period.
Some observations concerning the analytical data can be
made. Iron concentrations were generally higher in the
samples taken at the higher level in wells C-l and C-2
indicating possible influence of mine drainage. Total
solids concentrations in the samples taken January 20
at Sta. C-2 showed a sudden three-fold increase, but
there was no corresponding increase in acidity, iron or
sulfate concentration. On the contrary there was a
reduction in acidity. It is believed that this sudden
change in groundwater quality was due to contamination
by a cement-flyash grout mixture that was pumped into the
west entry the preceding week. This reinforces the
evidence of contamination of well C-l by water from the
mined area.
- 38 -
-------
TABLE 2
DRILLING LOGS OF MONITOR WELLS
Well A- 2
Strata
D«pth
0-4
4-21
21-33
33-49
49-56
56-67
67-83
83-92
92-94
94-94)4
94K>107
107-123
123-145
145-146
146-148
148-151
151-200
Descrip-
tion
Clay
Sand Rock
Shale
Sand Rock
Shale
Sand Rock
Shale
Sand Rock
Shale
Coal
Fire Clay
Sandy Shale
Sand Rock
Shale
Coal
Sandy Shale
Solid Rock
Well B-l
Strata
Depth
0-10
10-14
14-35
35-37
37-55
55-81
81-124K2
124)4-125
125-127
127-134
134-141
141-156
156-168
168-169'/2
169H-206
206-215
215-217
217-222
222-230
Descrip-
tion
Sand
Clay
Shale
Sand Rock
Shale
Sand Rock
Shale
Coal
Fire Cloy
Shale
Sand Rock
Sandy Shole
Sand Rock
Coal
Sand Rock
Sandy Shale
Sand Rock
Sandy Shale
Sand Rock
Water at 125'
Well B-2
Strata
Depth
0-18
18-61
61-63
63-66
66-77
77-120
120-123
123-126
126-146
146-159
159-183
183-186
186-190
190-192
192-213
213-218
218-224
224-225
Descrip-
tion
Clay
Shale
Coal
Fire Clay
Sandy Shale
Sand Rock
Coal
Fire Clay
Sand Rock
Shale
Sand Rock
Shale
Coal
Fire Clay
Sand Rock
Shale
Coal
Fire Clay
Water at 176'
Well B-3
Strata
Depth
0-1
1-16
16-21
21-26
26-28
28-39
39-43
43-46
46-52
52-79
79-98
98-102
102-104
104-106
106-110
110-111
111-126
126-135
135-140
140-200
Descrip-
tion
Topsoil
Clay
Shale
Solid Rock
Shale
Solid Rock
Coal
Fire Clay
Solid Rock
Shale
Solid Rock
Shale
Coal
Clay
Solid Rock
Coal
Solid Rock
Shale
Coal
Shale
Water at 49 '
Well C-l
Strata
Depth
0-9
9-45
45-49
49-55
55-62
62-72
72-85
85-90
90-91
91-100
100-123
123-134
134-137
137-151
151-155
155-156
Descrip-
tion
Topsoil
&Clay
Sand Rock
Coal
Shale
Sand Rock
Shale
Sand Rock
Sandy Shale
Coal
Shale
Sand Rock
Shale
Sandy Shale
Shale
Coal
Shale
Water at 49', 140'
Well C-2
Strata
Depth
0-8
8-10
10-28
28-30)4
30)6-34
34-38
38-40
40-45
45-70
70-75
75-84
84-93
93-95
95-104
104-108
108-110
Descrip-
tion
Topsoil
&Clay
Shale
Solid Rock
Coal
Shale
Sand Rock
Shale
Limestone
Shale
Sand Rock
Shale
Sand Rock
Shale
Sandy Shale
Sand Rock
Shale
Water at 28 ', 65 '
-------
TABLE 3
DRILLING LOGS OF EXISTING PARK WELLS
Well No. 1
Strata Dt pth
0-18
18-30
30-32
32-70
70-75
75-80
80-85
85-110
110-165
165-170
170-210
210-245
245-270
270-300
Description
Clay
Gray Shale
Coal
Gray Shale
Gray Sand
Coal
Gray Shale
Gray Sand
Gray Shale
Coal
Gray Sand
Gray Shole
Gray Sand
Gray Shale
and Sand
Wafer at 50', 110', 245'
Well No. 2
Strata Depth
0-9
9-11
11-25
25-37
37-50
50-52
52-55
55-60
60-70
70-75
75-80
80-82
82-130
130-135
135-145
145-170
Description
Clay
Dark Shale
Gray Shale
Dark Shale
Gr. Sand Rock
Coal
Gray Shale
Sand Rock
Gray Shale
Sand Rock
Gray Shale
Black Shale
Gray Shale
Sand Rock
Sandstone
Gray Shale
Water at 37', 40', 55',
105', 135', 160'
Well No. 3
Strata Depth
0-10
10-50
50-60
60-65
65-115
115-120
120-125
125-130
130-150
150-155
155-175
175-205
205-210
Description
Cfay
Gray Shale
Gray Sand
Coal
Gray Send
Gray Shale
Gray Sand
Coal
Gray Shale
Coal
Gray Shale
Gray Sand
Gray Shale
Water ol 25', 150', 175'
Well No. 5
Strata Depth
0-20
20-65
65-80
80-85
85-87
87-90
90-100
100-110
110-140
140-150
150-160
160-185
185-190
190-200
200-220
220-295
295-300
Description
Clay
Gray Shale
Gray Sand
Gray Shale
Gray Sand
Coal
Gray Shale
Gray Sand
Gray Shale
Gray Sand
Coal
Gray Shale
Coal
Gray Shale
Gray Sand
Gray Shale
Gray Sand
Wafer af 35', 80', 200'
Well No. 6
Strata Depth
0-15
15-40
40-47
47-48
48-50
50-70
70-90
90-100
100-105
105-110
110-135
135-140
140-150
150-175
175-190
Description
Cloy
Gray Shale
Gray Sand
Coal
Gray Shale
Gray Sand
Gray Shale
Gray Sand
Brown Shale
Coal
Gray Shale
Coal
Gray Shale
Gray Sand
Gray Shale
Water at 30', 45', 65',
100', 115'
o
I
-------
PH
Iron
Sulfate
Acidity ("hot")
T. Solids
TABLE 4
RESULTS OF ANALYSES
11-19-71
2.81+
105
1930
535
8l?2
11-30-71
2.62
3^8
1000
603
2811
SAMPLING
12-8-71
2.73
67.0
650
Uo?
1281
STATION MD
12-13-71
2.72
75
650
U25
1561
12-21-71
2.71
57.2
666
teu
1371
1-6-72
2.82
62. U
5M*
369
2025
1-13-72
2.86
56
532
1*60
1179
1-20-72
2.88
56.5
600
U58
1360
1-28-72
2.91
146.2
620
1*85
8691*
All concentrations in parts per million
-------
TABLE 5
RESULTS OF ANALYSES
1
to
1
PH
Iron
Sulfate
Acidity
T. Solids
11-19-71
6,27
5.29
23.5
7.38
239
11 -30 -71
7.62
8.3
16
1.6
279
SAMPLING
12-3-71
7.20
5.08
3U.O
3.1
116
STATION CR
12-13-71
7.^7
6.6
51
1.6
189
12-21-71
7.56
3.8
U5
l.U
10U
1-6-72
5-85
2.2
26
11.7
156
1-13-72
6.73
2
3^
6.1
158
1-20-72
7.26
3.5
te
3.6
206
1-28-72
6.83
2.6
33
6.3
141
All concentrations in parts per million
-------
TABLE 6
RESULTS OF ANALYSES
pH
Iron
Sulfate
Acidity
T. Solids
11 19-71
7.50
O.Ul
26.5
2.0
98
11-30-71
7.2U
0.8
26
3.3
109
SAMPLING
12-8-71
7-29
2.U6
26.5
3-1
101
STATION SP
32-13-71
7.96
U.3
16
l.l
86
32-21-71
7-93
1.1*
15
1.2
78
1-6-72
7.85
ND
16
1.3
96
1-13-72
7.26
1
17
3.2
lUi
1.20-72
7.9^
ND
16
1.3
99
1.28.72
6.80
1.0
15
10.9
179
All concentrations in parts per million
-------
TABLE 7
RESULTS OF ANALYSES
SAMPLING STATION C-l
11-19-71 11-30-71 12-8-71 12-13-71 12-^1-7:
Water Level (ft)
PH
Iron
Sulfate
Acidity
T. Solias
(u)
(L)
(u)
(L)
(u)
(L)
(u)
(L)
(u)
(L)
101*
7.68
7.63
0.93
1.58
12.0
10.5
7.0
5.75
29U
387
10U3 10146
8.11 8.01
7.87
1.8 12. U
12.1*
15 15.7
12.8
0.6 1.2
U.2
283 385
U07
10U7
8.51
8,53
10.7
8.6
ND
5
U.2
3.8
556
358
10UU
8.U9
8,U2
12.5
8.1
2
U
2.6
2.U
525
373
I 1-6-72
10U3
7.67
7.95
9.0
5^
2
2
7.9
3.8
357
3^6
1-13-72
10U3
7.76
7.57
12
8
5
u
7.U
n.5
381
U35
1-20-72
10UU
8.5U
8.35
9-1
6.9
2
2
5.0
ND
356
328
1-28-72
10UU
7.87
8.31
8.0
5.8
u
U
U.6
5.5
313
312
All concentrations in parts per million
(U) Sample taken at upper elevation, approximately 1030*
(L) Sample taken at lower elevation, approximately
ND None Detected
-------
TABLE 8
RESULTS OF ANALYSES
SAMPLING STATION C-2
Water Level (ft)
pH (U)
(L)
Iron (U)
(L)
in Sulfate (U)
(L)
Acidity (U)
(L)
T. Solids (U)
(L)
11-19-71
1011
7.2'i
7.69
3.59
3.^9
29-7
18.5
9-25
3.75
251
U58
11-30-71
1011
7.02
8.26
10. U
6.7
33
11
10.8
O.U
209
193
12-8-71
1010
6.76
7.57
10.3
7-77
31.0
19.2
U.o
7.3
183
302
12 -13 -71
1012
8.50
8.89
12.7
8.8
16
5
1.2
8.0
238
U6U
12-21-71
1010
8.M4
8.80
10.8
7.0
16
5
0.9
7.1
173
269
1-6-72
1012
7.09
7.55
lU.O
8.6
16
6
11.2
10.8
308
369
1-13-72
1032
6-93
7.^7
15
9
lU
8
22.8
11.0
320
352
1-20-72
1013
8.60
8.73
15.8
12.5
5
5
6.2
6.0
983
911
1-28-72
1013
8.55
8.83
10.8
8.5
3
h
3.5
3.8
783
656
All concentrations in parts per million
(U) Sample taken at upper elevation, approximately 990'
(L) Sample taken at, lower elevation, approximately 955'
ND None Detected
-------
TABLEJ)
RE S ULTS OF ANAL YSE S
CTv
Water Level (ft)
pH
Iron
Sulfate
Acidity
T. Solids
SAMPLING STATION B-l
12-13-71
1219
8.6**
9-9
13
2.8
651
12-21-71
1217
8.5U
fl.7
16
2ji
6U9
1-6-72
1218
7.78
3.3
15
2.9
1*39
1-13-72
1219
7.53
6
13
l'.3
652
1-20-72
1218
8.55
5.8
11
2.1
J*U3
All concentrations in parts ner million
-------
TABLE 10
Water Level (ft)
pH
Iron
Sulfate
Acidity
T. Solids
RESULTS OF ANALYSES
SAMPLING STATION B-2
11-30-71
1177
7.19
U.2
2»*
5-1
533
12-8-71
1177
7.15
6.60
2U.2
17.6
U22
12-13-71
1171*
8.08
7.3
7
1.0
UU9
12-21-71
1179
8.05
7.8
7
1.1
i+17
1-6-72
1183
7.50
6.1
7
16.0
555
1-13-72
1188
7.21
5
8
28.9
393
1-20-72
1189
8.10
7.8
7
1.3
UoU
All concentrations in parts per million
-------
TABLE 11
CO
RESULTS OF ANALYSES
SAMPLING STATION B-3
Water Level (ft)
pH
Iron
Sulfate
Acidity
T. Solids
11-19-71
10U9
6.7^
2.79
11.0
10.75
260
11-30-71
1055
7.93
ND
15
0.8
350
12-8-71
1056
6.33
6.1*9
2U.7
lU.9
519
12-13-71
1055
8.27
11.3
6
0.6
503
12-21-71
1057
8.10
12.5
5
1.6
U99
1-6-72
1059
6.50
U.9
13
18.1
325
1-13-72
1060
6.6k
26
9
16.8
501
1-20-72
1060
8.2k
16.9
U
0.6
Ma
1-28-72
1060
7.67
13.U
7
2.3
23U
All concentrations in parts per million
-------
There was a noticeable decrease in iron, sulfate, acidity
and total solids concentrations in the mine drainage
after the first two sampling tours. This may have been
due to dilution from increased runoff resulting from
frequent rains during this period, or to changes in the
mine environment brought about by the construction
activity, or both. Excavation of the fanway released
impounded acid water and permitted this corridor to
drain freely.
- 49 -
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SECTION VII
MINE SEALING OPERATIONS
The decision to place two double-bulkhead concrete seals
and only one experimental chemical grout seal was prompted
by the higher-than-expected cost of the grouting materials
which were determined by laboratory testing to be suitable
for the proposed mine sealing method. However, there were
other areas in which it was felt benefits could be derived
by substitution of the concrete seals at this site.
1. The potential hydraulic head that could develop on the
seals if the mine filled to its highest level was 84 feet.
The maximum head on any existing seal of this type was
about 35 feet. Therefore, it was possible that the oppor-
tunity would be afforded to evaluate the double bulkhead
concrete seals under a higher pressure than that to which
they had previously been exposed.
2. Installation of previous double bulkhead seals
included grout stabilization of the retaining stone bulk-
heads prior to placement of the concrete seals. It was
believed that this step could be eliminated. Installation
of double bulkhead concrete seals at the Keystone State
Park test site permitted testing this modification of the
construction procedure.
Double Bulkhead Seals
The double bulkhead concrete seals were installed in the
east and west mine entries. The bulkheads are normally
constructed by injecting coarse aggregate through vertical
drill holes across the mine corridor and vibrating the
material so that an alignment of intersecting truncated
cones are formed with a minimum of four feet diameter
contact zone at the mine roof. Grout is injected into
the bulkheads and then a concrete plug is injected into
the space between the bulkheads.
Six-inch diameter injection holes were drilled across the
east and west entries for placement of the bulkheads and
concrete seal. The alignment of the holes was not exactly
perpendicular to the bearing of the entries because they
were drilled before the middle entry was opened to permit
a survey. This however would be the rule rather than the
exception since accurate mine maps are seldom available
and openings often have to be established by exploratory
drilling. From the drilling logs the east and west entries
were estimated to be 12 to 14 feet wide and from 4 to 8
feet high depending on exact location.
- 51 -
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One hundred tons of aggregate, Pennsylvania Department of
Highway 2-B size and grading (l/2"+0 , were placed and
vibrated in the west entry through the applicable drill-
holes, sixty tons for the forward bulkhead and forty tons
for the rear bulkhead. In the east entry the forward
bulkhead consisted of seventy-seven tons and the rear
bulkhead sixty-eight tons of aggregate.
Attempts at taking pictures in the mine through boreholes
to examine the bulkhead location and assess the integrity
of the stone bulkheads were unsuccessful due to water and
high humidity which resulted in condensation on lens
surfaces. A considerable amount of water was backed up
in the west entry, and attempts to dewater the area by
excavation in front of the entry, and by pumping were not
completely successful.
It was decided to inject the concrete seals without
dewatering. A laboratory test showed that the concrete
would set satisfactorily when poured into an acid solution
simulating the mine acid, and based on the dimensions
of the mine cavity and the quantities of stone placed it
was concluded that in all probability the bulkheads were
satisfactory. Eighteen cubic yards of concrete were
poured in the east entry and thirty-five cubic yards in
the west entry. The completed seals are illustrated in
Figure 18.
The center plug areas of the seals were pressure grouted
through drill holes extending entirely through the concrete
plug to below the mine floor. A total of 1472 cubic feet
of flyash-cement grout were injected in the east entry
seal. For grouting of the west seal calcium chloride was
added as an accelerator because some seepage was noted
below this entry indicating possible water movement through
the seal area. A total of 3584 cubic feet of grout were
injected at this location.
The total cost for both double bulkhead seals in place
is estimated at $30,000. This includes the grouting of
the center plugs, but no curtain grouting.
Test holes were drilled in the center plug areas of the
double bulkhead seals downstream of the injection holes
five months after the seals were placed. These holes were
cored all the way through the seals to the mine floor, and
revealed no discontinuity of material in either of the
two concrete seals, therefore it is apparent that the mine
entries are completely filled in the area of the seals.
Core recovery, from the mine roof to the mine floor, was
- 52 -
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GRADE
GRADE
.PORTAL
EAST ENTRY
l4'-0"t
- 6 DIA.DRILL
HOLE (TYP.)
14'-0"t
foSftMsA S,'//
V*35C.Y. CONCRETE ^a
WEST FNTRY
FIGURE 18, DOUBLE BULKHEAD SEALS
- 53 -
-------
for the east seal and 40% for the west seal. This
represents a relatively high loss but is not unusual for
this type of application and may indicate only that
portions of the cement matrix are weak enough to be shat-
tered by the core drilling. The effectiveness of the
total mass as a seal would not necessarily be impaired.
Pressure testing would be required in order to assess
the effectiveness of the material within the seal area as
a hydraulic seal.
The boring logs showed that settling of the concrete
took place after the seals were poured. This could have
been due in part to displacement of gob and migration of
material into or through the stone bulkheads as well as
movement of the bulkheads themselves. In the east seal
nine inches of flyash-cement grout were found above the
concrete, and in the west seal twenty-two inches of grout
were recovered from between the mine roof and the concrete
seal. This grout usage offset any saving that was realized
by elimination of the grouting of the bulkheads, therefore
there appears to be no advantage to elimination of this
step in the construction procedure.
Sealing of Air Vent
The existing 12" diameter vent pipe, located on the first
cross connection between the main entry and the fanway as
shown on Figure 3, was removed and replaced with a 4-inch
stainless steel pipe which was concreted in place. This
pipe was fitted with a pressure gauge for possible use in
monitoring the progress of water buildup in the mine after
it is sealed. The gauge is mounted on a flange which may
be removed entirely for sampling or measuring water level
when this is below the gauge elevation. A 4" valve is
also provided to serve as a possible relief device should
it become necessary to lower the water level in the mine
after it has exceeded the elevation of the valve. A
sketch of the gauge-relief pipe is shown on Figure 19.
Construction of Safety Bulkhead
Because of the experimental nature of the proposed chemical
grout-flyash seal, a reinforced concrete safety bulkhead
was constructed in the middle entry which was selected
for the test of the material. The entry, which served as
the fanway when the mine was worked, was reestablished by
excavation, and a diversion channel was cut to divert the
drainage directly to the creek. For protection and
security of the opening, a wooden entry way was built
twelve feet out from the face of the mine, with cyclone
fence double gate at the end. The entrance is shown on
Figure 20.
- 54 -
-------
4"S.S.PIPE
*.r
;.«.'
XI1.'
PRESSURE GAUGE
4" EMERGENCY RELIEF PLASTIC
BALL VALVE
CONCRETE
L
MINE ROOF
I2"± 0. D. RETAINER PLATE WELDED
TO 4" PIPE
FIGURE 19, PRESSURE GAUGE-RELIEF PIPE INSTALLED
IN PLACE OF OLD AIR VENT
-------
FIGURE 20, PROTECTION OF EXCAVATED MINE ENTRY
- 56 -
-------
The reinforced concrete bulkhead was located approximately
18 feet in from the face of the mine. A drainage channel
and 6" drain pipe was installed in the mine floor to permit
free drainage of the mine while the bulkhead was being
built. A 4-inch diameter stainless steel pipe with plastic
ball valve was located approximately two feet up from the
mine floor to permit sampling, and to aid in the sealing
operation special plexiglass windows were included for
observation and light insertion. Bulkhead details are
shown on Figure 21. A photograph of the completed
installation is shown on Figure 22.
Injection Nozzle Tests
Preliminary tests in the laboratory, Figures 23 and 24,
showed that an AM9-flyash slurry consisting of 15 pounds
of flyash per gallon of 15% grout solution could easily
form a self-supporting mass with 20 to 25 degrees angle
of repose, but that proper distribution of the slurry was
essential to establishment of complete closure at the mine
roof. It was felt that this distribution could be accom-
plished through a single injection hole by use of a
nozzle that would direct the slurry outward and slightly
upward so that the seal is built up from the outer
extremities as previously illustrated in Figure 2.
Tests were conducted with an injection nozzle consisting
of two 3/8" nozzles at 180 degrees, inclined upward at
30 degrees, from the horizontal. To avoid plugging of the
injection piping when using short gel times the initiator
was added just ahead of the nozzle. As a result of the
tests it was concluded that a satisfactory distribution
could be achieved with the nozzle, and that mixing of the
ammonium persulfate solution with the grout slurry just
ahead of the nozzle was adequate to produce a controllable
gel. The nozzle tests are illustrated on Figure 25.
Pumping of the grout slurry was not continued to build up
a plug in the test area in view of the high cost of the
grout materials. It was hoped that with the viewing
ports built into the reinforced concrete safety bulkhead
the progress of the actual seal placement could be
monitored closely enough so that precise step by step
procedures would not have to be previously determined by
large scale testing.
Injection of Gel Material
Due to cold weather injection of the AM9-flyash grout was
delayed several weeks. It was decided to wait until at
least two days of above freezing temperatures were
reasonable assured before attempting to place the seal.
- 57 -
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DEEP DRAINAGE TRENCH
6 DIA.SCH.IO S.S.PIPE
(TYPE 3O4) ENCASED IN
CONCRETE.
4"DIA.SCH.IO S.S.PIPE ft
4"FLGD. PLASTIC BALL
VALVE FOR SAMPLING FLOW
a EMERGENCY RELIEF.
I
4'-6
(MINE CLEARANCE)
PLAN
-6"DIA.INJECTION HOLE
TO GRADE
s
(0
1 I2"SQ.PLEXIGLASS WINDOW
6"DIA.PLEXIGLASS WINDOWS
ELEVATION
SLIP ON FLANGE WITH
BLIND FLANGE
FIGURE 21, CONCRETE BULKHEAD
- 58 -
-------
.
-
-' »"
**"
"»
FIGURE 22, VIEW OF CONCRETE SAFETY BULKHEAD
- 59 -
-------
FIGURE 23, BENCH SCALE TEST OF GEL MATERIAL
If
FIGURE 24, ANGLE OF REPOSE ACHIEVED IN LAB TEST
- 60 -
-------
. r
« -
\
,
.'«*-?
p
FIGURE 25, YARD TESTS OF INJECTION NOZZLE
-------
On February 28, 1972, with a warm trend predicted,
preparations were made for the grouting operation. The
next day, final tests were run to check out equipment
and determine approximate proportions and gel times, using
water from the site at prevailing temperature and flyash
from the batch to be used in the actual grout mix, and on
March 1 injection of the grout into the mine began. Flyash,
AM-9 and catalyst DMAPN were batch mixed in a 2500 gallon,
two-compartment slurry batcher, shown on Figure 26 with a
material weigh bin above it. From the batcher the slurry
was pumped to a small hopper feeding progressive cavity
type injection pump of 30 gpm capacity. Ammonium persul-
fate, the reaction initiator, was fed by a smaller pump
into the injection pipe just ahead of the nozzle. The
injection pipe and pumps are shown on Figure 27.
Lights were inserted in the 6" diameter ports in the
safety bulkhead for illumination of the mine cavity, but
visibility was poor due to condensation and obstructions
which blocked view of the injection point. Figure 28
shows the view through the bulkhead.
The injection nozzle was oriented to direct the slurry
stream toward the walls and the grout pumped at a rate of
30 gallons per minute with a gel time of approximately
15 seconds. The anticipated result of this procedure was
that a wedge shaped mass would be built up on each side
of the mine corridor, starting at the walls and sloping
downward toward the middle where the mine drainage was
observed to be flowing. With proper control of the gel
time it was hoped that the two wedge shaped formations
could be gradually extended into the drainage channel
eventually damming the flow and causing it to spread out
behind the grout dam. However, this was not successful.
Observation of the drainage from the mine indicated that
much of the grout material was being lost. The gel time
was decreased from fifteen seconds to as low as five
seconds with no success in stopping grout loss. A
satisfactory gel was apparently achieved on both sides
of the entry, as evidenced by inability to remove the
catalyst injection hose when the operation was terminated,
but the flow in the middle of the mine floor was too high
to permit a gel to form.
The flow from the. mine measured by a v-notch weir was
found to be approximately 150 gallons per minute. This
was considerably higher than the 40 to 50 gallons per
minute measured a week earlier and was due to runoff
brought about by the sudden onset of very warm weather.
The air temperature rose to above 70°F during this period.
- 62 -
-------
FIGURE 26, SLURRY BATCHER AND WEIGH BIN
- 63 -
-------
FIGURE 27, SLURRY INJECTION PIPE AND PUMPING
EQUIPMENT
- 64 -
-------
FIGURE 28, VIEW OF MINE ENTRY THROUGH
OBSERVATION WINDOW IN BULKHEAD
- 65 -
-------
Due to the high flow much of the grout was diluted to the
point where it failed to gel, and the material that did
gel at the edge of the flowing water was washed away.
Some gelled material was collected outside the mine
entrance indicating that some of the grout had indeed
formed weak gels which were transported away by the flow-
ing water.
In view of the previously established high cost of grout
materials and the difficulties experienced in applying
the injection technique with the high mine flow, the
decision was made after consultation with State and
Federal project sponsors, to terminate the test. It was
felt that the method may be successful in low flow
situations, and with higher injection rate to minimize
dilution and erosion of the grout, but the cost remained
prohibitive.
Acid drainage abatement activities and sampling at the
mine site have been interrupted to permit compilation and
review of all information relative to the project prior
to completion of the work. In order to retain the possi-
bility of using the mine entry for further experimental
work, the reinforced concrete safety bulkhead was left
free-draining to minimize accumulation of gob which may
block off the view ports.
Work remaining to complete normal abatement procedures
at the Salem No. 2 mine, if no further experimental work
is planned, consist of injection of a grout curtain in
the strata adjacent to the mine entries.
- 66 -
-------
SECTION VIII
ACKNOWLEDGEMENTS
Mr. Ronald D. Hill, Chief, Mine Drainage Pollution
Control Activities, National Environmental Research
Center, Cincinnati, Ohio, who was the EPA Project Officer,
and Dr. David R. Maneval who served as Project Director
for the Department of Environmental Resources, Common-
wealth of Pennsylvania, offered many helpful suggestions
and comments during the course of this investigation.
Their valuable assistance is gratefully acknowledged.
This report was prepared by Neville K. Chung, Dravo Corporation,
Pittsburgh, Pennsylvania 15222.
U. S. GOVERNMENT PRINTING OFFICE : L973 514-151/140
- 67 -
-------
Acc«*ulcn Number
w
Sabjoct Field & Group
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
OitfartlzaUon
Dravo Corporation
Title
Investigation of use of gel material for mine sealing
Chung, Neville K.
Project D*ml£p*ttoa
EPA, Grant No. 14010 EKW
Woto
Environmental Protection Agency report
number, EPA-R2-72-135, December 1972.
23 I Dt>*cHplon (Starred Pint)
*Acid mine water, *Mine drainage, *Mine sealing, Abatement
\ldentifior* (Starred Flrmt)
Chemical grout
Abstract
Laboratory testing of commercially available chemical grouts was conducted to
evaluate their potential use, in conjunction with a cheap filler, for remote sealing of
mine voids. By close control of the setting time and proper distribution of the grout
slurry it was believed that a mine seal could be placed through a borehole from the
surface without the benefit of retaining bulkheads.
A slurry mix consisting of an acrylamide grout with flyash or mine refuse as a
filler was found to produce a strong controllable gel which resisted chemical attack in
the laboratory over an eleven week exposure period.
An attempt to demonstrate a novel technique for application of the selected grout
slurry in a mine entry with high flow was not successful. The results suggest that
the technique may be applicable in dry or low flow situations. However, the estimated
cost of a mine seal using the gel material is presently not competitive with existing
methods.
Groundwater monitor wells were drilled for the purpose of determining the effect of
mine sealing on groundwater conditions. Data reflecting pre-seal conditions was compiled,
but because the sealing of the mine was not completed the monitoring program has been
postponed.
Abstractor,
Neville R. Chung
Dravo Corporation
WR:I02
WRSIC
(REV. JUt-Y IB41I
SEND. WITH COPY OF DOCUMENT. TO: HATER RESOURCE* SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 2O24O
CPO! 1S70 - 4O7 ->91
------- |