United States Office of Ground Water EPA/816-R-99-014J
Environmental and Drinking Water (4601) September 1999
Protection Agency
The Class V Underground Injection
Control Study
Volume 10
Mining, Sand, or Other Backfill Wells
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Table of Contents
Page
1. Summary 1
2. Introduction 2
3. Prevalence of Wells 3
4. Backfill Characteristics And Injection Practices 3
4.1 Injectate Characteristics 3
4.1.1 Mil Tailings 6
4.1.2 Coal Combustion Ash 10
4.1.3 Flue Gas Desulfurization Sludge 19
4.1.4 Coal Cleaning Waste 19
4.1.5 Mine Drainage Precipitate Waste 24
4.2 Well Characteristics 24
4.3 Operational Practices 26
4.3.1 Placement Methods 26
4.3.2 Integrated Mining and Backfilling 31
4.3.3 Retroactive Backfilling 33
4.3.4 Well Maintenance and Closure 33
5. Potential And Documented Damage to USDWs 33
5.1 Injectate Constituent Properties 33
5.2 Observed Impacts 35
5.2.1 Metal Mines 35
5.2.2 Coal Mines 37
6. Alternative And Best Management Practices 41
6.1 Injectate Characteristics 41
6.2 System Design and Construction 41
6.3 Well Operation 42
6.4 Well Closure 43
7. Current Regulatory Requirements 45
7.1 Federal Programs 45
7.1.1 SDWA 45
7.1.2 SMCRA 46
7.2 State and Local Programs 48
Attachment A: State and Local Program Descriptions 50
References 68
September 30, 1999
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MINING, SAND, OR OTHER BACKFILL WELLS
The U.S. Environmental Protection Agency (USEPA) conducted a study of Class V
underground injection wells to develop background information the Agency can use to evaluate the risk
that these wells pose to underground sources of drinking water (USDWs) and to determine whether
additional federal regulation is warranted. The final report for this study, which is called the Class V
Underground Injection Control (UIC) Study, consists of 23 volumes and five supporting appendices.
Volume 1 provides an overview of the study methods, the USEPA UIC Program, and general findings.
Volumes 2 through 23 present information summaries for each of the 23 categories of wells that were
studied (Volume 21 covers 2 well categories). This volume, which is Volume 10, covers Class V
mining, sand, or other backfill wells.
1. SUMMARY
Mine backfill wells are used in many mining regions throughout the country to inject a mixture of
water and sand, mill tailings, or other materials (e.g., coal combustion ash, coal cleaning wastes, acid
mine drainage (AMD) treatment sludge, flue gas desulfurization sludge) into mined out portions of
underground mines. On occasion, injection (in low porosity grout form) also occurs into the rubble
disposal areas at surface mining sites. Mine shafts and pipelines in an underground mine, as well as
more "conventional" drilled wells, used to place slurries and solids in underground mines are considered
mine backfill. Such wells may be used to provide subsidence control (the most common purpose),
enhanced ventilation control, fire control, reduced surface disposal of mine waste, enhanced recovery
of minerals, mitigation of AMD, and improved safety.
The physical characteristics and chemical composition of the materials that are injected into
backfill wells vary widely depending on the source of the backfill material, the method of injection, and
any additives (e.g., cement) that may be included. Data from leaching tests (e.g., USEPA Method
1311 Toxicity Characteristic Leaching Procedure (TCLP)) of backfill materials indicate that
concentrations of antimony, arsenic, barium, beryllium, boron, cadmium, chromium, lead, mercury,
molybdenum, nickel, selenium, thallium, sulfate, and zinc frequently exceed primary maximum
contaminant levels (MCLs) or health advisory levels (HALs). Concentrations of aluminum, copper,
iron, manganese, total dissolved solids (TDS), and sulfate, as well as the pH, frequently exceed
secondary MCLs.
At sites where water is present in the injection zone (the previously mined ore body), the mine
water may already exceed MCLs or HALs prior to injection either as a result of mining activity or
natural conditions. At such sites, one objective of injection often is to improve the already poor quality
of the mine water by reducing the availability of oxygen in the mine workings and/or neutralizing AMD.
In other areas, water from coal beds may be used to supply domestic wells.
No incidents of contamination of a USDW have been identified that are directly attributable to
injection into mine backfill wells. Although ground water contamination is not uncommon at mining
September 30, 1999
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sites, it is generally difficult to identify the specific causes. The chance that backfill injection will
contribute to ground water contamination is highly dependent onsite conditions, including mine
mineralogy, site hydrogeology, backfill characteristics, and injection practices. Some studies of the
effects of backfill injection on mine water quality show that concentrations of some cations and anions
can increase in mine water following injection, whereas concentrations of trace metals generally are
relatively unaffected or decline over time. Other studies (at other sites) show an increase in selected
metal concentrations.
The vulnerability of mine backfill wells to receiving spills or illicit discharges also depends on
site-specific conditions and practices. For example, if coal ash is hauled to a mine site, slurried with
water, and then injected, the likelihood of contamination of the injected material resulting from a spill or
illicit discharge is relatively low On the other hand, if mill tailings are collected in a tailings pond along
with site runoff and other facility wastes prior to injection, then the likelihood of contamination of the
backfill material by spills would be higher.
According to the state and USEPA Regional survey conducted for this study there are
approximately 5,000 documented mine backfill wells and more than 7,800 wells estimated to exist in
the United States A total of 17 states report having mine backfill wells. More than 90 percent of the
documented wells reported are in four states: Ohio (3,570), Idaho (575); West Virginia (401), and
North Dakota (200). In truth, there may be more due to the broad scope of this well type and the fact
that some state inventories may count these wells as subsidence control wells while others did not.
Also, the number of active wells at any given time varies widely due to their generally short life span,
most often a few days or less. The number of mine backfill wells has the potential to grow in the future
due to the growing movement to decrease surface disposal and control ground subsidence.
State regulations pertaining to mine backfill wells vary significantly in their scope and stringency.
Some states impose few restrictions while others require permitting, or impose requirements by contract
rather than regulation. Some of these approaches include permit by rule (e.g., West Virginia, Idaho,
North Dakota), general or area permits (e.g., Wyoming), and individual permits (e.g., Ohio). In
addition, federal requirements for planning and approval of mining activities include mine backfill
activities. These requirements apply in states that have not obtained primacy under the Surface Mining
Control and Reclamation Act and to activities on federal and Native American tribal lands.
2. INTRODUCTION
Under the existing UIC regulations, Class V injection wells include "sand backfill and other
backfill wells used to inject a mixture of water and sand, mill tailings or other solids into mined out
portions of subsurface mines whether what is injected is a radioactive waste or not" (40 CFR
146.5(e)(8)). Piping systems within mine shafts and workings, as well as more "conventional" drilled
wells, used to place slurries/solids in underground mines are considered mine backfill wells under the
USEPA's UIC regulations. Similarly, mine shafts are considered backfill wells if backfill is injected into
the shaft.
September 30, 1999
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Backfill injection is extremely diverse. Although subsidence control is a common objective of
backfilling, injection can be performed for a wide range of reasons, as noted above. The types of
materials that are injected are similarly diverse, and include materials (and various mixtures of materials)
resulting from coal mining and combustion, primary and precious metal mining, uranium mining, and
non-metal mining. The environmental settings in which the mines are located and injection occurs are
similarly diverse. This volume only provides an overview and a general categorization of mine
backfilling activities.
3. PREVALENCE OF WELLS
For this study, data on the number of Class V mining, sand, or other backfill wells were
collected through a survey of state and USEPA Regional UIC Programs. The survey methods are
summarized in Section 4 of \blume 1 of the Class V Study. Table 1 lists the numbers of Class V
mining, sand, or other backfill wells in each state, as determined from this survey. The table includes
the documented number and estimated number of wells in each state, along with the source and basis
for any estimate, when noted by the survey respondents. If a state is not listed in Table 1, it means that
the UIC Program responsible for that state indicated in its survey response that it did not have any
Class V mining, sand, or other backfill wells.
In 1998, a total of approximately 5,000 mine backfill wells were reported nationwide, all of
which are reported to be in 17 states. As indicated in Table 1, several states estimated that the actual
number of mine backfill wells is greater than the number reflected in their documented inventory. In
addition, some states did not provide inventory information, although it is likely that wells exist in some
of these states. Thus, the actual number of operating mine backfill wells in 1998 is estimated to be at
least 7,800. The fact that they often exist for a relatively short operating time (in some cases, a few
days or less) complicates development of a precise count of mine backfill wells in use during a given
year, as exemplified by the information provided by Pennsylvania, Texas, Illinois, and West Virginia and
summarized in Table 1.
4. BACKFILL CHARACTERISTICS AND INJECTION
PRACTICES
4.1 Injectate Characteristics
A wide assortment of materials are used for backfilling of underground mines. These materials
may include waste rock, mining and ore beneficiation wastes (e.g., mill tailings, coal cleaning wastes),
coal combustion ash and flue gas desulfurization (FGD) sludge resulting from coal combustion, or
sludge from AMD treatment operations. Mill tailings have been reported to be the most commonly
used mine backfill materials, because they are inexpensive and abundant (Underground Injection
Council Research Foundation, 1988).
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Table 1. Inventory of Mine Backfill Wells in the U.S.*
State
Documented
Number of Wells
Estimated Number of Wells
Number
Source of Estimate and Methodology1
USEPA Region 1 - None
USEPA Region 2 - None
USEPA Region 3
MD
PA
VA
WV
6
NR
NR
401
6
NR
NR
<401
N/A
Injection for subsidence control is common, but no wells were
reported to be active at the time of the survey. A total of 1,123
wells are planned as part of four projects awaiting approval.
PA only includes wells used for subsidence control in the
"backfill injection" category.
USEPA Region reports that backfill wells exist in VA, but the
number of wells is not documented by the Region and was not
available from the state.
Best professional judgement. Most backfill wells are used for
fire control and are closed when the fire is extinguished, so state
staff believe that most of these wells have been closed. Backfill
wells used for subsidence control (73) are also included in the
inventory.
USEPA Region 4
AL
KY
TN
22
NR
2
22
NR
2
N/A
State staff report that backfill wells exist in KY, but none are
documented.
N/A
USEPA Region 5
IL
IN
OH
19
98 (UIC)
83 (Region)
2 (DNR)
3,570
17
NR
6,400
2 of the 19 wells may not have commenced operations. UIC
inventory shows 34 wells, but state personnel believe many
have been closed and abandoned.
Combination of state and regional information: state does not
routinely distinguish mine backfill wells from some other
categories of Class V wells. The 1997 UIC inventory is a
compilation from the region and an 1 988 EEI study. DNR
believes that at least 2 wells are not included in the region's
inventory.
Best professional judgement, based on knowledge of areas
containing mines and installation frequency of backfilling wells.
USEPA Region 6
TX
61
61
Although 61 wells are in the UIC inventory, all of these wells
may be closed.
September 30, 1999
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Table 1. Inventory of Mine Backfill Wells in the U.S.
(continued)
State
Documented
Number of Wells
Estimated Number of Wells
Number
Source of Estimate and Methodology1
USEPA Region 7
KS
MO
48
15
48
15
N/A
N/A
USEPA Region 8
CO
MT
ND
SD
UT
WY
2
NR
200
1
0
20
NR
NR
200
1
2
>20
N/A
USEPA Region 8 Montana Operations Office staff believe that
backfill wells may exist in MT However, neither the USEPA
Region nor the state has inventory data on such wells.
N/A
N/A
State database shows that 2 wells are under construction, but
have never been completed due to economic factors.
Best professional judgement. The documented 20 wells do not
include subsidence prevention wells. No information was
available for subsidence prevention wells.
USEPA Region 9
CA
17
17
State personnel did not provide estimate but indicated that they
suspect that more than the documented number of wells exist.
USEPA Region 10
AK
ID
1
575
>1
575
N/A
N/A
All USEPA Regions
All States
5,060
>7,890
Total estimated number counts the documented number when
the estimate is NR.
1 Unless otherwise noted, the best professional judgement is that of the state or USEPA Regional staff completing the survey
questionnaire.
N/A Not available.
NR Although regional, state and/or territorial personnel reported the presence of the well type, the number of wells was not
reported, or the questionnaire was not returned.
* Backfill wells regulated by states primarily under other UIC categories are not included. For example, Kansas applies Class III
requirements (in addition to Class V requirements) to wells used to backfill solution-mined salt caverns.
September 30, 1999
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Backfill materials may also contain cementing agents and other additives, such as cement.
These agents normally are added to increase the suitability of the material for providing structural
support. The use of a particular backfill material depends on its availability, cost, and properties after
placement (Karfakis, 1996). Backfill material needs to be physically, hydrologically, chemically, and
mineralogically stable, especially when subsidence control is one of the objectives of backfilling. To
provide long-term stability, fill material must resist infiltration and conductance of ground water, because
water migration can weaken backfills by promoting chemical reactions. Further, low permeability
reduces the potential for contaminants to leach into ground water (Jude, 1995).
The characteristics of the backfill materials most commonly injected into underground mines are
discussed below. The information presented is not an exhaustive compilation given the wide range of
materials and practices. Examples of site-specific operations are provided in Section 4.3.
4.1.1 Mil Tailings
Mill tailings typically consist of a finely ground mixture of processed ore, disaggregated host
rock, and traces of the solutions used (if any) in ore beneficiation operations.1 In some backfill
applications, mill tailings (with or without size classification) are slurried with water and injected into
underground mines in what is often referred to as a "hydraulic sandfill" or "sand backfill" operation (see
Section 4.3) (Levens, 1993; Sutler Gold Mining Company, 1998; Scheetz Mining Company, 1999).2
In other applications, mill tailings are mixed with cement or other pozzolanic material3 to form a
pumpable material with relative low (10 to 25 percent) moisture content this is often referred to as
paste backfill. When mixed with cement or a similar additive, the resulting backfill may also be referred
to as cemented sandfill. The fine solid particles may consist of naturally occurring metamorphic and
igneous clay-sized to sand-sized material and metamorphic rock fragments (Brackebusch, 1994).
Available data on the chemical composition of mill tailings sandfill slurry or backfill paste
injected into mines are limited. Leachate data for mill tailings, however, are available and are included.
Table 2 provides information on tailings used as backfill at several facilities. As shown, these materials
may contain significant quantities of iron and trace metals.
The chemical characteristics of tailings used for backfill are determined primarily by the
characteristics of the ore body and host rock and to a lesser extent the extraction processes used.
Thus, in many cases the chemical characteristics of the mill tailings injected into underground
1 The particle size of mill tailings depends primarily on the beneficiation and processing techniques
employed.
2 These terms may also be used to refer to materials other than mill tailings, such as materials used in
backfilling of underground coal mines.
3 Material that reacts at ambient temperature with moisture to form a slow-hardening cement.
September 30, 1999 6
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Table 2. Chemical Characteristics of Selected Metal Mine Tailings Backfill
Pb-Zn Mine Tailing
Constituent
Aluminum
Arsenic
Barium
Cadmium
Calcium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Magnesium
Mercury
Molybdenum
Nickel
Potassium
Silicon
Sodium
Zinc
(ii
19,000
<300
200
16
2,300
90
10
210
53,000
1,800
5,600
1,900
<50
200
5,500
334,000
400
4,300
(21
15,000
500
80
8
3,300
80
20
250
57,000
1,500
5,000
2,400
<50
330
5,800
348,000
600
2,500
;s (ppm)*
(31
14,000
1,500
44
13
3,700
100
30
620
54,000
1,500
1,600
1,400
<50
240
5,100
358,000
500
5,800
ZnMine (ppm)**
(41 (51
6.00 0.006
33.0 <0.05
9.96 O.04
<0.05 O.0002
1,100 0.654
(1) Cemented tailings backfill collected from a test slope.
(2) Uncemented tailings backfill collected from a slope about 10 years after placement
(3) Uncemenled tailings backfill collected from new tailings.
(4) Sample of solids from lailings impoundment
(5) Sample of water from lailings impoundment
* Source: Levens, 1996
** Source: ASARCO, 1998
mines are similar to the ore body before it was mined even though the physical characteristics (i.e.,
particle size) have changed. As shown in Table 3 a, a variety of leaching tests have been performed to
evaluate the potential effect of the change in physical characteristics on the release of metals from
backfilled mill tailings at a lead and zinc mine. For the constituents analyzed, concentrations frequently
exceeded the primary drinking water standards (MCLs) or HALs in both of the acidic leaching tests.
When leaching tests were performed using deionized water, only lead concentrations exceeded a
health-based standard. The type of leaching test used varies depending on the conditions anticipated in
the mine. Laboratory leaching data from gold mines that also backfill tailings as part of mining
operations are shown in Table 3b. (Information on mine water analyses from backfilled slopes and
other field monitoring of leachate quality is discussion in Section 5.) As shown, concentrations of
arsenic, barium, chromium, lead, and nickel exceed MCLs in USEPA
September 30, 1999
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Table 3a. Chemical Characteristics of Leachates from Selected Mill Tailings
Drinking Water Health Advisory
Standard Level Pb-Zn Mine Tailings Leachate Concentrations (mg/1)
Constituent
Aluminum
Arsenic
Barium
Boron
Cadmium
Calcium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Magnesium
Nickel
Potassium
Silicon
Silver
Sodium
Sulfur
Sulfate
Zinc
mg/1
0.05 to
0.2
0.05
2
0.005
0.1
1.3
0.3
0.015
0.05
0.1
0.1
250
2/5
Primary
or
Secondary mg/1
S
P 0.002
P 2
0.6
P 0.005
P 0.1
P
S
P
S
P 0.1
S 0.1
S
P/S 2
Cancer
or HC1/HNO3*
Noncance
r (1)
2.1
C 1.2
N 0.3
N
N 0.17
23.0
N
0.69
306
32.0
32.4
11.2
N
0.9
2.2
N 0.04
0.52
7.8
N 21.9
(2)
2.0
6.0
0.03
0.84
0.21
35.4
0.40
0.13
0.56
312
21.6
29.4
12.4
0.16
0.9
2.2
0.02
0.12
37
14.9
(3)
1.9
10.4
0.02
0.51
0.34
38.8
0.25
0.17
0.69
186
27.8
9.5
6.4
0.21
0.8
1.7
0.03
0.41
86
35.4
Deionized water**
(4)
0.2
0.17
54.2
0.04
0.2
0.06
ND
7.3
6.6
7.9
86.1
0.06
(5)
2 2
0.08
96.1
0.09
0.2
ND
0.1
15.5
6.7
14.7
130
ND
(6)
0.2
0.06
__
183
ND
0.1
0.02
ND
26.6
8.5
14.0
366
0.05
H2SO4***
(4)
54.0
0.01
0.01
640
0.10
6.6
0.90
52.8
95.2
3.9
14.6
8.0
1,807
0.97
(5)
0.44
0.003
0.32
716
0.07
6.8
1.6
65.3
125
1.4
34.7
8.7
2,050
33.7
(6)
80.1
ND
1.8
623
0.68
97.6
3.9
64.8
110
3.0
157
9.4
3,622
336
ND = Not detected.
* Overnight shaking of 1 g of backfill with mixture of HC1 (2 cm3), HNO3 (4 cm3), and 20 cm3 water with filtering prior to analysis.
** Washing with deionized water for 7 days.
*** Washing with H2SO4 for 227 days.
(1) Cemented tailings backfill collected from a test stope.
(2) Uncemented tailings backfill collected from a stope about 10 years after placement.
(3) Uncemented tailings backfill collected from new tailings.
(4) Same tailings material as (1) with cement added in the laboratory.
(5) Same tailings material as (2) with cement added in the laboratory.
(6) Same tailings material as (3) with cement added in the laboratory.
Source: Levens, 1993; 1996
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Table 3b. Chemical Characteristics of Laboratory Leachates from Tailings Backfill
in Underground Gold Mines (concentrations in mg/1)
Constituent
Aluminum
Antimony
Arsenic
Barium
Beryllium
Cadmium
Chromium
Cobalt
Copper
Gold
Iron
Lead
Mercury
Molybdenum
Nickel
Selenium
Silver
Thallium
Vanadium
Zinc
Units
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
Drinking Water
Standards
0.05-0.2
0.006
0.05
2
0.004
0.005
0.1
-
1.3
--
0.3
0.015
0.002
-
0.1
0.05
0.1
0.002
--
5
S
P
P
P
P
P
P
P
S
P
P
P
P
S
P
S
Health Advisory Levels ( 1 )
0.003
0.002
2
0.0008
0.005
0.1
-
--
--
--
--
0.002
0.04
0.1
--
0.1
0.0005
--
2
N
C
N
C
N
N
N
N
N
N
N
N
--
0.030
0.623
--
O.001
0.004
--
--
--
--
0.001
0.0009
--
--
0.005
0.001
--
--
(2)
--
0.025
1.15
--
0.0012
0.30
--
--
--
--
0.030
0.0003
--
0.25
0.002
0.0021
--
--
0.030
(3)
--
0.06
8.2
--
0.0011
0.25
--
--
--
--
0.007
0.0002
--
0.10
0.002
0.0022
--
--
0.33
(4)
0.00976
0.0244
0.0415
O.0021
O.00275
O.0033
0.0025
0.0030
O.00505
O.00004
O.0043
O.00415
0.0108
0.0030
0.0118
0.0052
O.00525
(1) TCLP extraction analysis of sand backfill from Homestake Mine
(2) EP extraction analysis of backfill tailings from Homestake Mine open cut and fill slope 20 years after backfill
(3) EP extraction analysis of backfill tailings from Homestake Mine slope 2 years after backfill
(4) Underground fill material from Sutler Gold Mine
Source: Scheetz, 1999;Righettini, 1999
Method 1310 Extraction Procedure (EP) leachate from sand backfill but not in TCLP leachate
(USEPA Method 1311).
Backfilling of tailings also occurs in association with non-metal mining activities. For example,
backfilling of tailings occurs at a soda ash and caustic production facility in Wyoming. Available data
on chemical characteristics of the injected tailings slurry indicate that pH and presumably the dissolved
solids content exceed secondary MCLs of 6.5 to 8.5 for pH and 500 mg/1 for total dissolved solids, as
shown below (Tg Soda Ash, 1997).
September 30, 1999
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Parameter
PH
% Solids
No. of
Samples
207
207
Minimum
9.84
0.00
Maximum
12.49
29.58
Average
10.51
14.66
Mean
10.48
15.16
4.1.2 Coal Combustion Ash
Coal combustion ash and cement (when needed) are mixed (mass ratio on the order of 9:1) and
slurried with water to produce a high-volume, low-strength fluid material that is used to fill mined-out
sections of underground mines. Gradual hardening of the slurry after injection will occur without
bleeding (Vlasak, 1993). In addition, this material can be used in related mine applications such as
construction of packwalls and filling of abandoned entries (Jude, 1995).
Coal combustion ash characteristics depend primarily on the characteristics of the coal burned
and the type of combustion technology utilized. For example, fly ash from conventional pulverized coal
combustion (PCFA) is a powder-like substance typically collected from flue gas exhaust ducts using
electrostatic precipitators or fabric filter units. PCFA derived from burning subbituminous coal and
lignite produced in the Western U.S. typically has a calcium oxide content greater than 10 percent (on a
weight basis), making it a self-hardening and pozzolanic material when in the presence of water. PCFA
derived from bituminous or anthracite coal produced in the Eastern U.S., on the other hand, generally
has a much lower calcium oxide content and, thus, requires the addition of either cement or lime and
water to achieve hardening properties (Jude, 1995).
Another type of fly ash results from fluidized bed combustion (FBC). This type of fly ash is
derived from crushed coal and limestone burned in a "bed" of ash particles suspended upward by
blowing air in the combustion chamber. FBC ash is made up of larger particles composed mainly of
coal mineral matter, calcium sulfate and unreacted lime that result from the sulfation and calcination of
the limestone (Jude, 1995).
Available data on the chemical composition of coal combustion ash slurries injected into mines
are limited. Data on coal ash (prior to slurrying and/or mixing with other materials) and leachate data
for coal ash are available and are included for reference, although the leachate characteristics of
mixtures of ash and cement or other materials may differ. Tables 4a through 4e summarize information
from selected studies that provide information on the chemical characteristics of coal combustion ash.
As shown, trace metal composition varies over a wide range for each type of material (e.g., bottom
ash) and among types of materials. Table 4d further illustrates the variability by type of material and
type of coal based on data from a power plant in Kentucky. Table 4e provides a comparison of the
metal content of ash from a Pennsylvania facility to soil.
September 30, 1999 10
-------
Table 4a. Coal Combustion Ash Characteristics from Selected Studies
Data Source
Mechanical
Hopper Ash (a)
Fine Fly Ash (b)
1993 Data(c)
Analyte
Arsenic
Barium
Boron
Cadmium
Chromium
Cobalt
Copper
Fluorine
Lead
Manganese
Mercury
Selenium
Silver
Strontium
Vanadium
Zinc
Arsenic
Barium
Boron
Cadmium
Chromium
Cobalt
Copper
Fluorine
Lead
Manganese
Mercury
Selenium
Silver
Strontium
Vanadium
Zinc
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Selenium
Silver
Thallium
Vanadium
Zinc
Number of
Number of
Sampl£S Values Mean
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
46
81
74
12
27
66
83
78
76
27
71
81
62
11
61
79
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
35
3
3
0
0
41
8
1
2
7
0
16
42
4
5
0
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
10.5
76.4
1589
201.8
469.5
6.1
129
123
67.0
4.3
117.5
8.7
3.7
19.2
397
286.5
Concentration (ppm)
Minimum
3.3
52
205
0.40
83.3
6.22
42.0
2.50
5.2
123
0.008
0.13
0.08
396
100
56 7
2.3
110
10.0
0.10
3.6
4.90
33.0
0.40
3.10
24.5
0.005
0.60
0.04
30.0
11.9
14.0
0.2
0.0003
0.02
0.200
2.98
0.0100
0.19
0.20
0.02
0.013
0.1
0.0003
0.01
0.15
43.5
0.28
Maximum
160
1152
714
14.3
305
76.9
326
83.3
101
430
3.00
11.8
4.0
2430
377
215
279
5400
1300
18.0
437
79.0
349
320
252
750
2.50
19.0
8.0
3855
570
2300
205
391.0
10850
2105
2050
76.0
651
655
273
49.5
1270
49.5
49.5
85.0
5015
2200
Median
25.2
872
258
4.27
172
48.3
130
41.8
13.0
191
0.073
5.52
0.70
931
251
155
56.7
991
371
1.60
136
35.9
116
29.0
66.5
250
0.10
9.97
0.501
775
248
210
4.6
43.4
806.5
5.0
311
3.4
90
112
56.8
0.1
77.6
7.7
3.2
9.0
252
148
Source: USEPA, 1993b
(a) Mechanical hopper fly ash data from Tetra Tech's 1983 Study and presented in the 1988 ETC.
(b) Fine fly ash data from Tetra Tech's 1983 Study and presented in the 1988 ETC.
(c) Statistics calculated assuming that values below the detection are equal to Vi the detection limit.
September 30, 1999
11
-------
Table 4b. Coal Combustion Ash Characteristics from Pennsylvania Facilities
Concentration (ppm)
Elements No.
Major Elements
Aluminum
Calcium
Iron
Magnesium
Manganese
Sulfate
Trace Elements
Antimony
Arsenic
Barium
Boron
Cadmium
Chromium
Cobalt
Copper
Lead
Mercury
Molybdenu
m
Nickel
Selenium
Silver
Zinc
of Values
199
23
200
25
191
189
80
195
109
144
91
201
21
194
179
134
103
190
138
73
199
Minimum
12
3
8
.5
.07
4
.01
.03
.16
.016
.02
.05
4.32
.04
.04
.0003
.23
.015
.0022
.015
.05
Maximum
156000
400000
130000
3840
2980
10500
142
22320
2960
3995
30
360
82.6
474
225
5.44
108
753
7540
22
841
Mean
24661
59114
20872
1501
153
770
35.6
271.24
303.5
160
3.3
46.4
21.96
48.09
37.1
.56
20.4
44.8
63
3.7
61.5
Media
n
19160
6200
13663
1140
70
447
28.5
17.05
194
40
1.42
34
15
32.5
27.3
.4
16
22
3.4
1.2
26
Total number of values in solids data set = 242.
Source: Kim, 1997
September 30, 1999
12
-------
Table 4c. Summary of Fluidized Bed Combustion Ash Composition
(concentrations in ppm)
Material
Type Constituent
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Thallium
Vanadium
Zinc
Fly Ash Aluminum
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium
Cobalt
Copper
I r on
Lead
Manganese
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Thallium
Vanadium
Zinc
Combined Ash Aluminum
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Thallium
Vanadium
Zinc
Num. ot
Values
58
62
68
38
52
61
68
47
65
33
67
33
54
52
63
41
56
55
29
37
65
42
66
73
73
39
60
72
76
47
71
46
75
42
73
67
75
44
69
64
34
39
73
48
45
60
57
12
45
50
58
30
56
48
57
47
57
50
59
26
59
48
8
11
57
Minimum
Value
0 .
0.
0.
0.
0 .
0.
3.
0.
0 .
6 .
0.
34.
0 .
0.
2 .
1.
0 .
0.
0.
12.
1.
20.
0 .
0.
0.
0.
0 .
0.
0.
0.
0 .
22 .
0.
0.
0 .
0.
12.
1.
0 .
0.
0.
36.
1.
1 .
0.
0.
0 .
0.
0.
0.
8.
1.
1.
850.
0 .
20.
0.
0.
0 .
2.
0.
0.
0 .
19 .
6.
100
250
050
500
050
003
700
125
500
200
050
500
000
050
000
300
001
005
250
000
000
000
100
100
100
500
050
003
500
125
500
170
500
100
000
050
500
125
001
005
500
333
000
090
003
140
100
295
904
000
000
200
900
000
714
000
000
050
500
820
003
005
180
570
100
2 ^th
Percentile
2
3
7
0
1
0
5
1
1
9570
1
62
0
3
22
100
0
0
2
1150
20
23495
2
3
17
0
1
0
6
2
2
18620
1
86
0
3
32
150
2
0
2
160
28
14 617
0
7
120
0
14
0
19
2
19
8042
13
49
0
2
11
2950
1
0
1
21
14
.50
.50
. 00
.50
.50
.50
. 00
.40
.70
.00
.50
.00
.01
. 90
.50
.00
. 52
.50
.50
.00
.00
. 60
.86
.50
. 00
.50
.50
.50
.05
.00
.00
. 00
.50
.00
.10
.10
.80
.00
.05
.50
.50
.00
.00
. 50
.50
.08
.00
. 9 9
.40
.25
.30
.84
.10
.50
.00
.00
.06
.50
.35
.00
.25
. 35
.88
.50
.40
5 Oth
Percentile
1U6H2 .
9
62.
1.
3 .
0.
16.
3.
8.
13010.
2.
110.
0.
13.
66.
150.
2.
0.
3 .
3820.
26.
32835.
3 .
17.
177.
1.
6.
0.
29.
5.
28.
26530 .
17.
126.
0.
9
51.
214.
3 .
0.
3 .
2880.
36.
24585 .
10.
13.
180.
1.
21.
0.
34.
4.
26.
12765.
23.
61 .
0.
9
15.
4140.
4.
0.
5 .
38.
19.
.50
9 3
.15
. 10
. 15
.50
.18
. 90
9 0
. 00
.50
. 00
.10
. 00
.70
. 00
.00
.50
.50
. 00
.00
. 65
.50
. 00
. 00
.20
. 98
. 60
.50
. 00
.10
. 00
.50
.40
.31
. 00
. 20
.50
.50
.50
.50
. 00
.00
. 00
. 00
. 05
.00
. 91
. 10
. 69
.50
. 60
. 10
. 00
.00
. 80
. 26
. 9 6
.40
. 00
. 00
. 75
1 9
. 00
.90
/5th
Percentile
28.
34 .
172.
8.
22.
1.
41.
14 .
18.
15640.
26.
379.
0.
19 .
735.
240.
3.
1.
5.
5700.
33.
53415.
36.
39 .
320.
6 .
50.
2.
56 .
19 .
47.
32722 .
44.
196.
0.
21.
529.
3132.
5 .
2.
5.
3840.
54.
32950 .
26.
32.
253.
2.
31.
1.
47.
8.
37.
18175.
33.
91.
0 .
16.
23.
5400.
9 .
1.
18.
838.
26.
.00
.70
.00
.00
.74
.50
.85
.00
.50
.00
.00
.00
.10
.60
.00
.00
.50
.00
.00
.00
.10
. 00
.00
. 22
. 33
.00
.00
.10
.45
.00
.00
. 00
.80
.70
.95
.10
.00
.00
.40
.00
.00
.00
.50
. 00
.00
.49
.00
.51
.95
.34
.30
.00
.45
.00
.80
.00
.61
.00
.00
.00
.80
.70
. 55
.00
.00
9 Oth
Percentile
62.
58.
274.
15.
41.
3 .
56.
37 .
26.
18534.
56.
610.
0.
27.
1000.
1340.
3.
5 .
20 .
7550.
52.
88900 .
63.
9 3 .
540.
11.
101.
4.
77.
33 .
73.
50900 .
65.
470.
1.
28.
825.
8332.
23.
3 .
20 .
4830.
7 9
44300 .
43.
68.
457.
5 .
45.
3 .
53.
9 .
71.
26600.
52 .
133.
0 .
24.
70.
6362.
16.
2.
25 .
1700.
48.
00
00
00
00
38
60
10
90
00
00
00
00
43
00
00
00
50
00
00
00
70
00
55
70
00
00
95
00
60
90
35
00
00
00
68
50
00
49
00
40
00
00
77
00
87
90
70
00
00
49
70
80
00
00
30
00
80
00
60
00
00
45
00
00
10
9 ^th
Percentile
111.
82.
316.
17.
118.
6 .
74.
51.
42.
21111.
66.
719.
1.
48.
1270.
4700.
13.
7.
25.
8700.
147.
105920.
151.
115.
940.
15.
606.
7.
104.
75.
73 .
55962
73.
661.
7 .
48.
900.
11478.
39.
5.
25.
5430.
114.
64000.
51.
106.
650.
9 ,
49.
5.
56.
12.
249.
28074.
67.
170.
2.
27.
530.
6600.
22.
5.
25.
5000.
257.
.40
. 00
.10
. 00
. 00
. 75
.10
.40
.70
. 10
.00
.40
. 10
. 00
.00
. 00
.40
. 00
.00
. 00
.50
. 00
.70
. 00
.00
. 00
. 00
. 00
.00
.30
.35
00
.00
. 60
.35
. 64
.00
. 80
. 00
. 00
.00
. 00
.40
. 00
.70
. 15
. 00
.50
.00
. 00
. 00
.54
.00
.70
. 00
.40
.78
. 00
. 00
. 00
9 7
. 00
. 00
. 00
.00
Maximum
Value
1775.
119.
453.
31.
304.
14.
259.
128.
50.
31500.
89.
892.
208.
190.
1440.
11950.
45.
338.
50.
10000.
399.
176300 .
1370.
176.
7700.
1 6 .
2473.
13.
211.
178.
99.
81318 .
129.
57700.
384.
143.
1270.
14680.
166.
38.
39.
10000.
167.
75850 .
142.
115.
690.
9
1610.
7.
1906.
18.
408.
51600.
89.
905.
29.
41.
985.
9163.
27.
21.
25.
5000.
90619.
. 00
.70
.00
. 00
. 00
. 00
.80
.40
. 00
. 00
9 0
. 90
.90
. 00
.00
. 00
. 00
. 00
.00
. 00
. 00
. 00
. 00
. 00
.00
. 00
. 00
. 00
.10
.50
. 00
. 00
.50
. 00
. 20
. 60
.00
. 00
. 00
.50
.01
. 00
.90
. 00
.00
.50
. 00
.50
.00
. 00
. 00
.70
.10
. 00
. 00
. 00
.00
. 00
. 00
. 00
.00
. 80
. 00
. 00
.00
Source: Council of Industrial Boiler Owners (CIBO), 1997
September 30, 1999
13
-------
Table 4d. Comparison of Coal and Ash Content for Selected Metals
at a Kentucky Power Plant
High-sulfur Unit
Element
As
Be
Cd
Co
Cr
Hg
Mn
Ni
Pb
Sb
Se
Th
U
Feed Coal
Mean*
(Whole
Coal)
12
1.5
0.4
4.6
15
0.07
25
18
11
0.9
2.5
2
1.6
Feed Coal
Mean*
(Ash Basis)
120
15
3.6
45
150
0.69
250
170
110
8.7
26
20
16
Fly Ash
Mean*
170
19
5.5
59
170
0.39
270
220
150
13
8.9
22
19
Botto
m
Ash
Mean*
11
14
0.8
49
150
0.02
330
210
46
3.5
0.59
21
14
Low-sulfur Unit
Feed Coal
Mean*
(Whole
Coal)
3.3
2.4
0
1
11
19
0.03
14
17
11
0
5
2
1
7
6
9
4
Feed Coal
Mean*
(Ash Basis)
37
27
0.8
120
210
0.31
150
190
120
7.9
52
32
16
Fly Ash
Mean*
(Fine)
91
27
1
150
230
0.02
230
220
170
15
1.1
31
21
Fly Ash
Mean*
(Coarse)
54
22
0.8
97
190
0.02
210
160
100
8.9
0.82
30
15
Botto
m
Ash
Mean*
54
16
-
61
200
0.24
480
140
380
10
1.7
29
10
* Notes:
All elements are in parts per million and are presented on the whole coal and as-determined basis for the feed coal, and on as-determined
basis for the fly ash and bottom ash.
Leaders (--) indicate statistics could not be calculated owing to an insufficient number of analyses above the lower detection limit.
Source: Affolter, 1997.
September 30, 1999
14
-------
Table 4e. Comparison of Ash and Soil Composition for Selected Elements
at a Pennsylvania Power Plant
Constituents
Comparison of Ash to U.S. Soils
Ash
(mg/kg)*
Soil Soil
Average Range
(ppmw)* (ppmw)*
Comparison of Ash to Local Soils
Ash
(mg/kg)*
Residential Residential
Soil Soil
(mg/kg)* (mg/kg)*
(North) (South)
Aluminum
Antimony
Arsenic
Barium
Boron
Cadmium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Zinc
24100
25
24
1142
<10.0
0.5
28
7
23
9590
25
38
0.02
14
5000
2.4
1
13.8
66000
0.67
7.2
580
34
0.06
54
10
25
25,000
19
660
0.089
19
23,000
0.39
60
700 - >100,000
<1 - 8.8
0.1-97
10 - 5,000
<20 - 300
0.01 - 0.7
1.0-2,000
<5-70
<1 - 700
100->100,000
<5-70
<1 - 7,000
0.01 - 4.6
<3-7
<5 - 700
50 - 70,000
O.I-4.3
<5 - 2,900
24100
25
24
1142
<10.0
0/5
28
7
23
9590
25
38
0.02
14
5000
2.4
1
13.8
12,000
54
1.9
32
<10.0
0.5
11
23
32
32,000
27
1,020
0.02
<10.0
39
670
0.5
80
15,500
^0.0
2.6
71
0.5
13
25
34
33,700
18
400
0.02
47
460
0.5
110
* Notes:
Ash analysis from Northampton Generating Plant (July 1996).
U.S. soil analysis data based on results from a survey performed by the USGS team on native soils across the United States.
Local soil analysis data from a local survey performed by Hawk Mtn. Labs in early August 1996. Samples were taken near the
housing development on the north side of the quarry and along Chestnut Street on the south side.
Source: Ramsey, 1999
Tables 5a, 5b, 5c and 5d provide similar data from laboratory leaching studies using EP,
TCLP, and Synthetic Precipitation Leaching Procedure (SPLP) methods (USEPA Methods 1310,
1311, and 1312, respectively). As shown, the leachate concentrations vary depending on the study
and leaching method used, but in general antimony, arsenic, beryllium, cadmium, lead, molybdenum,
selenium, and thallium typically (at least 50 percent of the time) exceed MCLs or HALs. Leachate
concentrations of barium, boron, chromium, copper, iron, mercury, nickel, silver, and zinc also exceed
MCLs or HALs in some cases. Because laboratory leaching data are not always predictive of leachate
chemistry in the field (Robl, 1999), data from field studies are discussed in Section 5.
September 30, 1999
15
-------
Table 5a. Coal Combustion Ash Leachate Characteristics from Selected Studies
Concentration (mg/1)*
Number of
Number Non-Detected
Data Source Analyte of Samples Values
Mean Minimum Maximum Median
Drinking Water
Standard
Primary
or
mg/1 Secondary
Health Advisory
Level
Cancer or
Noncance
mg/1 r
Tetra Tech Arsenic
(a)
Barium
Cadmium
Chromium
Lead
Mercury
Selenium
Silver
ADL (b) Arsenic
Barium
Cadmium
Chromium VI
Lead
Mercury
Selenium
Silver
1993 Data (c) Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium VI
Copper
Lead
Mercury
Nickel
Selenium
Silver
Thallium
Vanadium
Zinc
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
1
76
76
5
8
78
78
8
77
74
7
77
75
1
14
16
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
1
19
16
3
0
21
25
1
39
67
1
18
59
1
3
1
0.012
0.222
0.0047
0.036
0.005
0.00042
0.01
0.00064
0.08
0.34
0.03
0.16
0.01
<0.002
0.05
<0.001
...
0.393
1 22
0.0187
4.01
0.0342
0.249
0.888
0.0968
0.0023
4.54
0.0698
0.0161
...
4.47
10.82
<0.004
0.003
0.0001
0.001
O.OOOl
O.OOOl
O.OOOl
O.OOOl
0.002
0.1
0.002
0.008
0.003
O.002
0.002
O.001
0.0495
0.001
0.005
0.001
0.126
0.0003
0.001
0.0036
0.008
0.00004
0.0495
0.0005
0.0001
0.0495
0.005
0.009
1.46
7.6
1.4
0.68
0.25
0.007
0.17
0.20
0.410
0.7
0.193
0.930
0.036
...
0.340
0.0495
16.4
22.5
0.0495
17.1
0.548
8.37
6.3
1.83
0.0495
29.4
0.376
0.520
0.0495
26.9
111.0
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
...
0.038
0.28
0.002
0.955
0.01
0.0405
0.17
0.01
0.0007
0.45
0.027
0.005
...
0.665
0.372
0.05
2
0.005
0.1
0.015
0.002
0.05
0.10
0.05
2
0.005
0.1
0.015
0.002
0.05
0.10
0.006
0.05
2
0.004
...
0.005
0.1
1.3
0.015
0.002
0.1
0.05
0.10
0.002
...
5
P
P
P
P
P
P
P
S
P
P
P
P
P
P
P
S
P
P
P
P
P
P
P
P
P
P
P
S
P
S
0.002
2
0.005
0.1
--
0.002
--
0.1
0.002
2
0.005
--
--
0.002
0.1
0.003
0.002
2
0.0008
0.6
0.005
--
--
--
0.002
0.1
--
0.1
0.0005
--
2
C
N
N
N
N
N
C
N
N
N
N
N
C
N
C
N
N
N
N
N
N
N
* All data were obtained using the Extraction Procedure (EP) Toxicity leaching procedure.
(a) Data from Tetra Tech's 1983 Study and presented in the 1988 ETC. Tetra Tech's results are for coal ash in general.
(b) Data from Arthur D. Little's 1985 Study and presented in the 1988 ETC.
(c) Statistics calculated assuming that values below the detection are equal to 1A the detection limit
: data not available
Source: USEPA, 1993b
September 30, 1999
16
-------
Table 5b. Coal Combustion Ash Leachate Characteristics from Selected Studies
^ , Health Advisory Levels T.. ..^ t.
Water
Standard Cancer or
Constituent (ma/1) mp/1 Noncnncer
Antimony 0.006P 0.003 N
Arsenic 0.05 P 0.002 C
Barium 2P 2 N
Beryllium 0.004P 0.0008 C
Boron -- 0.6 N
Cadmium 0.005 P 0.005 N
Chloride 250 S
Chromium 0.1P 0.1 N
Cobalt
Copper 1.3P
Cyanide, total 0.2P 0.2 N
Fluoride 4 P
Iron 0.3 S
Lead 0.015 P
Manganese 0.05 S
Mercury 0.002P 0.002 N
Nickel 0.1P 0.1 N
Selenium 0.05 P
Silver 0.1S 0.1 N
Sulfate 500 P
Thallium 0.002P 0.0005 N
Zinc 5 S 2 N
Source: Crislip, 1999
Table 5c. Coal Combustion Ash
TCLP
10/18/94
(me/1)
-
0.40
2
--
--
0.30
1.4
-
--
-
--
0.4
--
O.0002
0.046
O.05
--
Leachate
Kmcaid (50%)/Coffen (50%)
~ cf ~ ^ Fly Ash Leachate (mg/1)
Cnffcn Station ' \ & J
TCLP Deionized
8/22/97 TCLP TCLP TCLP TCLP TCLP Water
(mg/1) 3/31/98 4/30/98 5/7/98 8/9.0/98 11/17/98 4/30/98
0.140 0.07 0.0332
0.075 0.049 0.0267
0.47 0.641 0.376
0.015 ND ND
34.2 51.68 92.1
0.163 0.168 ND
0.083 0.166 0.39
0.11 ND ND
0.43 ND ND
..
0.17 ND ND
0.04 ND ND
0.88 ND ND
ND ND ND
0.97 ND ND
0.011 0.451 0.869
ND ND ND
ND
0.021 ND ND
3.21 0.045 0.177
Characteristics from
0.03 0.06 0.09
0.20 0.10 0.28
<1 <1 <1
0.019 <0.0002 <0.0001
49 35 23
0.21 0.0005 0.0052
3.4
0.31 0.023 0.043
0.11 0.007 0.004
0.67 0.023 0.028
0.011
8.1
10 0.02 0.09
0.07 O.01 O.06
1.9 0.10 0.1
O.0002 O.0002 0.0022
0.80 0.090 0.094
0.05 0.29 0.3
O.005 O.005 0.012
1210
<0.4 0.006 0.008
3.1 <1 <1
Pennsylvania Facilities
Mean/Median Leachate Concentrations Drinking Water Health Advisory
(in mg/1, by method) Standard Level
Elements ASTM(4)* EPTOX(IO)*
Antimony BDL .15/.15
Arsenic 01/.008 .06/.02
Barium .40/.20 .20/.24
Boron BDL 1.09/1.02
Cadmium .009/.009 .012/.004
Chromium .22/.22 .11/.02
Cobalt BDL BDL
Copper .06/.05 .03/.01
Lead .02/.02 .02/.02
Mercury BDL .001/.001
Molybdenum .02/.02 .10/.08
Nickel .06/.04 .17/.15
Selenium .015/.015 .03/.05
Silver BDL .001/.001
Zinc 18/18 35/29
SPLP(20)*
.13/.06
.18/.09
29/ 22
2. 1/. 19
.003/.003
.05/.06
.01/.01
.06/.04
BDL
.001/.001
.39/.09
.09/.08
.13/.11
.003/.003
04/03
TCLP(200)* mg/1
.28/.11 0.006
.10/.03 0.05
.40/.30 2
1.30/.50
.04/.02 0.005
.14/.08 0.1
.22/.05
.09/.05 1.3
.17/.15 0.015
.01/.003 0.002
.23/.19
.15/.12 0.1
.12/.05 0.05
.03/.02 0.1
65/14 5
P/S* mg/1 C/N*
P 0.003 N
P 0.002 C
P 2 N
0.6 N
P 0.005 N
P 0.1 N
--
P
P
P 0.002 N
0.04 N
P 0.1 N
P
S 0.1 N
S 2 N
*( ) Indicates number of samples per method; P=primary; S=secondary; C=cancer; N=non-cancer.
BDL=Below Detection Limit
Source: Kim, 1997
September 30, 1999
17
-------
Table 5d. Summary of Fluidized Bed Combustion Ash Leachate Test Results*
(concentrations in ppm)
Material
Type Constituent
Bed Ash Aluminum
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Thallium
Vanadium
Zinc
Fly Ash Aluminum
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Thallium
Vanadium
Zinc
Combined Ash Aluminum
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Thallium
Vanadium
Zinc
Num. of
Values
26
26
69
67
11
23
63
68
15
30
29
69
28
61
23
54
13
64
63
7
32
34
35
37
81
90
14
33
76
83
18
3 9
38
80
37
76
35
65
20
81
74
9
35
42
44
42
62
60
6
43
51
60
24
52
46
54
47
51
46
48
23
63
51
5
6
54
Minimum
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
o
0
0
o
0
o
0
0
0
0
0
0
0
o
0
0
o
0
0
o
0
1
0
0
0
0
0
0
0
0
0
0
o
0
0
o
0
0
0
0
0
0
0
1
0
0
o
0
0
Value
.05000
.00250
. 00100
.02500
.00008
. 00300
.00100
.00500
.05000
.01000
.04000
.00500
.00400
. 00010
.05000
.00500
. 12500
.00050
.00150
.00500
.02500
.00250
.04000
.00250
. 00050
.02500
.00008
.03000
.00100
00500
.00500
.00500
01000
.00100
.00250
. 00010
.02320
.00500
.21000
.00050
00400
.00500
.00750
00500
.01000
. 00010
.00230
.00500
00200
.00500
. 00250
.00330
.00070
. 00250
. 00005
.00100
. 00250
. 00010
.02500
.00500
.55400
.00100
.00250
.00100
. 00500
.00250
25th
Percentile
0.13000
0.05000
0 . 01000
0.05000
0.00500
0 . 10000
0.01600
0.02500
0.12500
0.02000
0.09900
0.02500
0.03350
0 . 00030
0.12500
0.02500
2 . 00000
0.00250
0.02400
0.04500
0.10500
0.02000
0.22000
0.03070
0.01100
0.08000
0.00330
0.10000
0.02000
0 02500
0.04500
0.02000
0 09000
0.02500
0.03000
0 . 00025
0.07000
0.02500
4.63000
0.00700
0 02000
0.04500
0.09000
0 02000
0.53500
0 . 00500
0.01000
0.05600
0 00200
0.09000
0 . 00250
0 02500
0.00500
0 . 01000
0.01500
0.02500
0 . 00500
0 . 00010
0.05000
0.02000
7.50000
0.00800
0.00500
0.00100
0.08599
0.00500
50th
Percentile
0.3250
0.3350
0.0500
0.2000
0.0250
0.1200
0.0250
0.0250
0.1400
0.0495
0.1900
0.0500
0.0545
0.0010
0.1600
0.0500
5.6000
0.0500
0.0250
0.0500
0.3300
0 . 0650
0.5000
0.1000
0.0500
0.3000
0.0105
0.2800
0.0250
0.0500
0.0980
0.0580
0.1800
0.0500
0.0500
0.0010
0.2000
0.0500
17.7000
0.0500
0.0250
0.0500
0.1300
0.0568
1.8650
0.0950
0.0250
0.1700
0 . 0095
0.1600
0.0050
0.0500
0.0180
0 . 0225
0.0700
0.0500
0.0500
0.0002
0.0865
0.0250
14.5000
0.0200
0.0050
0.0500
0.1535
0.0215
75th
Percentile
1. 6000
0.5000
0.0500
0.4520
0. 0500
0.5500
0.0300
0. 0550
0.1750
0.0600
0. 5100
0.2500
0.1900
0.0010
0.2400
0.1600
8.4000
0.0500
0.0430
0.3250
0.4550
0.1110
8.4500
0. 5000
0.0500
0. 6250
0. 0500
0. 6000
0. 0400
0.1200
0.1370
0.0850
0.5000
0.2685
0.3300
0.0010
0.3200
0. 1600
39.3000
0. 1000
0.0400
0.0500
0.2040
0.1400
4 . 0550
0.2700
0.0500
0 . 5 95 0
0.0500
0.4600
0.0130
0.1150
0.0250
0.0855
0.1780
0.1290
0.3100
0.0010
0. 2000
0.0920
20.0000
0. 0500
0.0150
0.4600
1.0000
0.1340
90th
Perc
10
0
o
0
0
2
0
0
0
0
2
0
0
o
0
0
11
0
0
0
1
0
23
1
0
1
0
0
0
o
0
0
o
0
0
0
0
0
54
0
0
0
0
0
8
0
0
1
7
0
0
0
0
o
0
0
o
0
0
0
24
0
0
0
2
0
entile
.5000
.7100
.1250
.9000
.0500
.6000
.0500
.1770
.2500
.1340
.7900
.3600
.7800
.0014
. 6100
.2360
.0000
. 1000
.1000
.5000
. 6400
.5100
. 9000
.1700
.1190
.5500
. 0500
.9800
.0600
.2000
.2500
.1330
.7600
.4450
.7300
.0040
.5900
.2500
.2500
.2000
.0520
.5000
.7000
.3700
.8900
.5000
.2500
.1585
.8000
. 6000
.0500
.2450
.0315
.4400
.3100
.2500
.4700
.0020
.4100
.2640
. 0000
.2400
.0400
.5000
.2000
.3000
95th
Percentile
13.140
0 . 920
0.180
1.000
0.280
2.800
0.090
0.220
0.310
0.158
3.200
0.418
7 . 600
0.010
0. 940
0 . 250
18.600
0.134
0.125
0.500
3.400
1.040
111.000
1.290
0.250
6.500
0.050
1.400
0.100
0.260
0 . 270
0.160
0. 900
0.518
1.100
0.010
0 . 610
0.330
63.400
0 . 266
0.100
0.500
1. 640
1.040
10.700
0.590
0.350
3 . 925
7.800
0 . 650
0.050
0.280
0 . 250
1.860
0.360
0.430
0.619
0.100
0.540
0.420
27 . 200
0 . 256
0.130
0 . 500
2.200
0.480
Maximum
Value
20.
1.
0.
8 .
0.
3.
0.
0.
0.
0.
38.
0.
10.
0.
1.
2.
18.
2.
0.
0.
40.
4.
120.
1.
0.
42.
0.
23.
0.
0.
0.
0.
7 .
0.
1.
0.
0.
1.
66.
0.
0.
0.
3 .
4.
18.
1.
0.
37.
7 .
26.
0.
0.
0.
6.
2.
1.
0.
0.
1.
0.
45.
0.
0.
0.
2.
2.
600
250
300
400
280
950
500
320
310
184
800
710
900
100
200
500
600
500
310
500
000
460
800
520
600
000
050
317
500
910
270
183
790
700
130
290
720
200
800
420
240
500
200
460
670
200
890
000
800
700
130
600
400
100
045
540
660
100
200
900
300
350
250
500
200
400
* Leachate date obtained primarily using EP and TCLP procedures, with some SPLP and other methods also used.
Source: Council of Industrial Boiler Owners (CBO), 1997
September 30, 1999
18
-------
4.1.3 Flue Gas Desulfurization Sludge
Flue gas desulfurization (FGD) sludge is generated by flue gas scrubber units at electric power
plants. The material is primarily composed of anhydrite, sulfite, and small amounts of unreacted calcium
oxide and calcium carbonate (Jude, 1995). Exact constituent concentrations, including metals, vary with
the type of coal burned and the technologies used. When FGD is injected as backfill in underground mines,
it is usually mixed with fly ash and quicklime, slurried, and pumped down surface boreholes into abandoned
mine workings (Jude, 1995).
Available data on the chemical composition of FGD slurries that are injected into mines are limited.
Table 6 presents chemical characteristics information for FGD sludge. Table 7a provides similar data from
EP toxicity testing of FGD sludge. As shown, median concentrations in the EP leachate exceed the MCL
or HAL for four constituents antimony, arsenic, boron, and thallium. Mean values exceed the relevant
MCL or HAL for these constituents plus five others (beryllium, cadmium, lead, mercury, and selenium),
while maximum values also exceed the applicable reference level for barium, chromium, nickel, and silver.
The extent to which leachate from FGD sludge under field conditions (i.e., injected into an underground
mine) will be similar to these laboratory EP leaching test results will vary depending on a variety of factors,
such as pH.
Table 7b provides data on leachate from mixtures of FGD sludge and coal combustion ash
obtained with a modified version of the TCLP procedure (USEPA Method 1311) that used mine water
(also shown in Table 7b) for the leaching solution. As shown, concentrations of arsenic, boron, sulfate, and
total dissolved solids measured in leachate were above the levels in the mine water and above MCLs or
HALs. In contrast, concentrations of beryllium, iron, and manganese water in the mine water were above
the relevant benchmark but were reduced to levels below the relevant benchmark in the leachate.
4.1.4 Coal Cleaning Waste
Coal cleaning waste that results from the wet cleaning of raw coal is comprised of extremely fine
solids, including coal particles and coal associated minerals, suspended in water. At some mines, coal
cleaning wastes are injected into underground mine workings. The chemical composition of the injected
material depends primarily on the characteristics of the coal, the associated rock, and the quality of the
water used in the coal cleaning process. At the New Elk Mine in Colorado, for example, the injected slurry
is comprised of a slightly alkaline, sodium bicarbonate water and as much as 30 percent coal, shale, and
sandstone solids. Data shown in Table 8 indicate that coal cleaning wastes and injected slurry at this facility
do not exceed the relevant primary or secondary MCLs or HALs for the constituents tested, with the
exception of arsenic and TDS4 (USEPA, 1995a; Lopez, 1995). Table 8 also indicates, however, that coal
cleaning waste slurry and slurry leachate from the Kindall 3 mine in Indiana exceed the
4 Available data for the injectate are for dissolved rather than total concentrations, which may be
higher and, thus, in some cases could exceed MCLs or HALs. It seems unlikely that the total values
would be greater than MCLs in this case, however, because the total values measured for the injectate
were less than the relevant health-based benchmarks.
September 30, 1999 19
-------
Table 5e. Leachate Characterization Data for Fly Ash Grout Mixtures
Leachate Concentration l (mg/I)
Drinking Water
Standard
Health
Advisory
Level
5/45/50
Constituent (28)
5/55/40
(28)
5/65/30
(28)
Grout Mixture (% Cement/% Fly Ash/% Sand)
Curing Time (Days)
5/75/20 5/85/10 7/55/38 7/65/28 7/75/18 7/85/8
(28) (28) (28) (28) (28) (28)
5/95/0
(41)
7/93/0
(41)
9/91/0
(91)
ma/1
ms/1
C/N*
Arsenic
Barium
Cadmium <0.0005
Chromium
Lead
Mercury
0.017
0.832
0.033
<0.002
0.019
0.834
0.028
<0.002
<0.004
1.040
<0.0005
0.019
<0.002
<0.0002
0.002 C
2 N
0.005 N
0.1 N
Selenium
0.020
0.006
* P = primary; S = secondary; C = cancer; N = non-cancer
1 Analyzed by the modified TCLP Method using deionized water as the extractant.
Source: Pappas, 1994
Table 6. FGD Sludge Characteristics from 1993 Study
Number of
Non-
Number of
Analyte Samples
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium VI
Copper
Lead
Mercury
Nickel
Selenium
Silver
Thallium
Vanadium
Zinc
31
36
35
14
18
36
36
36
34
15
35
34
29
6
33
36
Detected
Values Mean
25
5
3
7
11
22
5
0
2
7
1
9
20
6
16
1
15.8
53.6
352.1
27.7
144.8
19.2
90.7
62.4
121.7
5.2
72.5
12.1
3.5
9.0
104.9
921.0
Concentration (ppm)
Minimum
3.65
0.0075
0.08
0.900
5.00
0.005
0.17
0.04
0.01
0.073
3.7
0.0150
0.01
9.00
0.01
0.01
Maximum
90.0
341.0
2280
49.5
633.0
81.9
312.0
251.0
527.0
39.0
191.0
162.0
10.3
9.0
302.0
5070
Median
6.0
32.5
162.5
29.3
60.0
3.9
73.0
46.1
25.3
4.8
68.1
4.5
3.3
9.0
65.0
90.9
Statistics calculated assuming that values below the reported detection limit equal V2 the
detection limit.
Source: USEPA, 1993b
September 30, 1999
20
-------
Table 7 a. FGD Sludge Leachate Characteristics from Selected Studies*
Data
Source
ADL (a)
1993
Data (b)
Analyte
Arsenic
Barium
Cadmium
Chromium VI
Lead
Mercury
Selenium
Silver
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chromium VI
Copper
Lead
Mercury
Nickel
Selenium
Silver
Thallium
Vanadium
Zinc
Number of
Samples
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
10
25
23
10
12
25
23
11
22
23
11
25
22
10
11
12
Number
of Non-
Concentration (mg/1)
Drinking Water
Standard
Detected
Values
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
6
9
5
6
1
17
8
1
19
18
3
9
10
8
0
2
Mean
0.20
0.18
0.01
0.02
0.01
<0.002
0.020
<0.001
0.129
0.11
0.448
0.0013
9.60
0.066
0.075
0.040
0.056
0.002
0.043
0.051
0.037
0.070
0.126
0.040
Minimum
0.002
0.15
0.002
0.011
0.005
<0.002
0.008
<0.001
0.010
0.001
0.075
0.0005
0.050
0.0003
0.0055
0.005
0.0005
0.00005
0.0015
0.0015
0.0005
0.045
0.030
0.0015
* Leachate data based on Extraction Procedure (EP) testing.
(a) Data from Arthur D. Little's 1985 Study and presented in the
(b) Statistics calculated assuming that values below the detection
: data not available.
Maximum
0.065
0.23
0.020
0.026
...
...
0.049
0.570
1.60
2.80
0.003
36.0
1.50
0.200
0.120
0.680
0.013
0.220
0.230
0.200
0.170
0.270
0.172
1988 ETC.
are equal to
Median
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
0.030
0.030
0.230
0.0005
5.95
0.0025
0.050
0.022
0.009
0.0003
0.006
0.040
0.0195
0.045
0.074
0.007
mg/1
0.05
2
0.005
0.1
0.015
0.002
0.05
0.10
0.006
0.05
2
0.004
...
0.005
0.1
1.3
0.015
0.002
0.1
0.05
0.10
0.002
...
5
Primary or
Secondary
P
P
P
P
P
P
P
S
P
P
P
P
P
P
P
P
P
P
P
S
P
S
Health Advisory Level
(mg/1)
0.002
2
0.005
0.1
-
0.002
-
0.1
0.003
0.002
2
0.0008
0.6
0.005
0.1
-
-
0.002
0.1
-
0.1
0.0005
-
2
Cancer or
Noncancer
C
N
N
N
N
N
N
C
N
C
N
N
N
N
N
N
N
N
'/2 the detection limit.
Source: USEPA, 1993b
September 30, 1999
21
-------
Table 7b. FGD Sludge and Ash Mixture Leachate Characteristics Data
Drinking Water Standard
Constituent
Acidity
Alkalinity
Aluminum
Arsenic
Barium
Beryllium
Boron
Cadmium
Calcium
Chloride
Chromium
Cobalt
Copper
Cyanide
Iron
Lead
Lithium
Magnesium
Manganese
Mercury
Molybdenum
Nickel
Nitrate-Nitrite
pH
Phosphorus
Potassium
Selenium
Silicon
Silver
Sodium
Sulfate
TDS
Turbidity
Zinc
mg/1
-
-
0.05 to 0.2
0.05
2
0.004
-
0.005
-
250
0.1
-
1.3
0.2
0.3
0.015
-
-
0.05
0.002
-
0.1
10
6.5 to 8.5
-
-
0.05
0.1
-
500
500
5 NTU
5
Primary or
Secondary
S
P
P
P
P
S
P
P
P
S
P
S
P
P
P
S
P
S
P
S
P
S
Health Advisory Level
Cancer or Mine Water ^
mg/1 Noncancer (mg/1)
158
<1
2.88
0.002 C <0.004
2 N 0.021
0.0008 N 0.001
0.6 N 0.16
0.005 N <0.0005
54.1
<1
0.1 N 0.002
0.015
0.004
0.2 N <0.02
45.3
0.003
<0.1
22.3
3.65
0.002 N <0.0002
0.04 N <0.003
0.1 N 0.039
<0.05
3.67
0.04
3.1
<0.005
24.6
0.1 N 0.002
23.0
429
626
14.0 NTU
2 N 0.073
Modified TCLP
Low Ash Grout *
<1
77
0.89
0.017
0.148
0.0003
1.16
<0.0005
210
65
0.005
<0.002
0.002
<0.02
<0.01
<0.002
0.4
3.0
<0.01
<0.0002
0.064
<0.003
<0.05
-
<0.01
33.6
0.008
5.75
<0.0002
35.4
557
977
-
0.012
Leachate (1) (mg/1)
High Ash Grout **
<1
79
1.12
0.018
0.196
0.0002
1.14
<0.0005
207
63
0.005
<0.002
0.003
<0.02
0.01
<0.002
0.4
1.7
<0.01
<0.0002
0.090
<0.003
<0.05
-
<0.01
34.1
0.011
5.98
<0.0002
35.8
541
959
-
0.015
* TCLP text on low ash group (1.0:1.0 - Fly Ash:
** TCLP test on high ash grout (1.25:1.0 - Fly Ash:
(1) Roberts-Dawson Mine
Source: Whitlatch, 1998
FGD sludge ratio by dry weight) using mine water as the leaching solution.
FGD sludge ratio by dry weight) using mine water as the leaching solution.
September 30, 1999
22
-------
Table 8. Coal Cleaning Waste and Injectate Characteristics
Drinking Water Health Advisory
Standards Levels
Constituent
Aluminum
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Chloride
Chromium
Copper
Cyanide, free
Fluoride
Hardness (CaCO3)
Iron
Lead
Lithium
Manganese
Magnesium
Mercury
Molybdenum
Nickel
Nitrate as N
Nitrite as N
Nitrogen,
ammonia
PH
Selenium
Silver
Sodium
Sulfate
Thallium
Thiocyanate
Total alkalinity
TDS
Vanadium
Zinc
mg/1
0.05 to 0.2
0.006
0.05
2
0.004
-
0.005
250
0.1
1.3
0.2
4
-
0.3
0.015
-
0.05
-
0.002
-
0.1
10
1
6.5 to 8.5
0.05
0.1
-
500
0.002
-
-
500
-
5
P/S* mg/1 C/N*
S
P 0.003 N
P 0.002 C
P 2 N
P 0.0008 C
0.6 N
P 0.005 N
S
P 0.1 N
P
P 0.2 N
P
-
S
P
-
S
-
P 0.002 N
0.04 N
P 0.1 N
P
P
S
P
S 0.1 N
-
P
P 0.0005 N
-
-
S
-
S 2 N
New Elk Mine(1)
Coal Cleaning Waste
( mg/1)
Total Dissolved
<0.05
0.002
0.006 0.004
0.6
<0.005
0.03
<0.005 <0.005
8
<0.01 <0.01
<0.01 <0.01
<0.1
2
27
0.35 0.08
<0.02 <0.02
0.04
<0.01 <0.01
3
<0.0002 <0.0002
0.02
<0.02 <0.02
0.02
0.02
1.32
8.1
<0.001 0.001
<0.01 <0.01
518
128
<0.002
<0.1
--
1280
<0.01
0.02 0.02
Injectate Slurry
(dissolved
cone, in mg/1)
0.04
--
0.001
0.02
--
0.02
0.0013
72
--
0.01
--
1.5
49
0.03
--
--
--
--
--
--
0.01
0.38
0.3
0.16
8.2
0.007
--
39
130
--
--
215
--
--
--
Kindall 3
Coal Cleaning
Waste (total
cone, in mg/1)
--
<5
0.4
--
0.14
0.01
11
<0.03
0.02
--
0.51
994
0.02 **
<0.05
--
0.46
--
<0.3
<0.7
0.09
--
--
7.83
<5
<0.01
230
1175
--
--
210
--
--
0.1
Mine(2)
Injectate
Slurry (mg/1)
-
<0.050
0.76
-
-
0.0062
-
<0.0050
-
-
-
-
-
0.058
-
-
-
<0.00020
-
-
-
7.5
<0.050
<0.0050
-
-
-
-
-
-
-
-
(1) Source: Lopez, 1995
(2) Source: Endress, 1996
* P=primary; S=secondary; N=non-cancer, C=cancer
** dissolved
September 30, 1999
23
-------
primary MCLs for arsenic, cadmium, and lead and the secondary MCLs for IDS, sulfate, and manganese.
4.1.5 Mine Drainage Precipitate Waste
Mine drainage precipitate waste, or sludge, resulting from treatment (generally neutralization) of
AMD is composed of ferric oxide, gypsum, hydrated aluminum oxide, variable amounts of sulfates, calcium
salts, carbonates, bicarbonates and trace amounts of silica, phosphate, manganese, copper, and zinc
compounds (Smith, 1987). Additional metals (e.g., lead, arsenic, selenium) may be present depending on
the mineralogy of the coal and associated rocks of the drainage area.
4.2 Well Characteristics
Mine backfill materials are typically injected into underground mines through one or more drilled
wells or through a pipeline installed in the mine shaft and appropriate portions of the underground workings.
In some situations, injection may be directly into a mineshaft without a pipeline for distributing the injected
material within the mine workings.5 The specific injection method(s) selected by a facility depends primarily
on the backfilling objectives and method (see Section 4.3) to be used.
If drilled wells are used, the details of well construction (e.g., diameter, casing, cementing) are
determined by site-specific factors such as depth to the mine workings to be backfilled and the geology of
the overlying strata, as well as backfilling practices. If the mine workings to be backfilled are mostly
horizontal and relatively shallow (e.g., a few hundred feet or less below ground surface), backfilling may be
accomplished by injecting backfill material down a well until the well will not accept any additional material,
plugging the well, and then drilling and "filling" additional wells located at appropriate locations throughout
the mine workings. For example, the underground workings at the abandoned Roberts-Dawson
underground coal mine in Ohio were backfilled with 23,000 cubic yards of fly ash and FGD sludge injected
through 318 injection points (DOE, 1998a). Similarly, 227 injection points were used to backfill a 23-acre
portion of the Omega underground coal mine in West Virginia (DOE, 1998b).
In this type of backfill operation, each injection well is used for a relatively short period of time
(e.g., days). Such wells may have a casing run from the surface to the top of the mine workings (see Figure
1). Conductor pipe may also be used depending on the stability of near-surface rock and soil (Crislip,
1998). Alternatively, material may be injected down the drill pipe and a casing does not need to be
installed.
5 This approach might be used when the goal is to fill the mineshaft to prevent access rather than to
fill substantial portions of the mine workings.
September 30, 1999 24
-------
Figure 1. Example of Shallow Mine Backfill Injection Well Construction
Stfckup
CoalV
-13ft1
Competent
Hock
Fractured
Rock
IV Old Works
Surface
-Steel Casing
Cement
-225'
Source: Endress, 1996
September 30, 1999
25
-------
When the mine workings to be backfilled are deeper, fewer injection points may be needed but
more piping and related distribution equipment in the mine workings may be required. When deeper wells
are used, well construction may more typically involve the use of multiple casings, as illustrated in Figure 2.
When pipelines are used, as illustrated in Figure 3, they are used to convey the backfill to the desired
location in the mine. Distribution of backfill material by piping within a mine is common when active mines
are backfilled, especially mines that use mining methods dependent on on-going backfilling of mined-out
slopes.
4.3 Operational Practices
The operational practices for mine backfill wells vary depending on how the backfill material is
placed in the mine and the relationship between mining and backfilling activities. In general, operational
practices do not appear to make mine backfill wells particularly vulnerable to accidental contamination of
the injectate or to misuse, although monitoring of the injectate and ground water help minimize the potential
for misuse. In addition, backfill injection often occurs into zones already affected by prior activities (e.g.,
AMD formation following mining), sometimes with the primary objective of reducing existing contamination
problems.
4.3.1 Placement Methods
Injection of backfill into underground mines may be accomplished using hand, gravity, mechanical,
pneumatic, and hydraulic placement methods. The most popular methods are pneumatic and hydraulic
(Underground Injection Council Research Foundation, 1988). Hand and mechanical methods, such as belt
or sling packing machines, are restricted to construction of selected supports from within a mine.
Pneumatic Backfilling
In pneumatic backfilling operations, backfill material is transported into a mine through a well or
pipeline in a stream of continually flowing air, either in a vacuum or under pressure (see Figure 4). When a
"dense phase" approach is used, the pipeline is nearly filled with material that is moved as a fluid with low
velocity air pressure in slugs. When the more common "dilute phase" approach is used, an air/backfill
mixture typically consisting of less than 5 percent fill material is moved through a pipeline at relatively high
velocity as a fluid. Both approaches tend to be used where water is scarce, the mine is dry, or where water
would interfere with mining or the backfill process (Walker, 1993; Sand, 1990).
Hydraulic backfilling
Hydraulic backfilling, which is more common than pneumatic backfilling, is the practice of filling
mine voids with backfill material by washing or pumping the backfill material as a slurry through a well or
pipeline into the mine (see Figure 5). Hydraulic backfilling is normally accomplished by one of three
methods: controlled flushing, blind flushing, and pumped slurry injection.
September 30, 1999 26
-------
I
Figure 2.L..\iiiii|jlc ul Deep JVliiic oatlvlill liijciliun V ell C unsli iiiliun
Is)
-------
Figure 3. Example of Sandfill Injection Using a Mine Shaft Pipeline
DEWATER1NG -,
OUTFLOW /
SHAFT
BARRQN
COUNTY
ROCK
DEWATERINQ
LINE
HAULAGE
LEVEL
SAND BACKFILL LINE
IN PLACE ORE
CROSSCUT
RAISE USED AS
ORE PASS
CEMENT CAPS
CROSSCUT
STOPE
BACKFILLING
OPERATION
SAND BACKFILL
SAND BACKFILL
LINE
STQP1NG
OPERATION
WATER TABLE
DEWATERING SUMP
Source: Rouse, 1979
September 30, 1999
28
-------
Figure 4. Pneumatic Backfilling Schematics
' b> '&'.'-o.
Diute-phase corveciig
Average 3D-m/a carryiig vslccilies
rdiio
Den Etphsse conveyrig
G.5- to 1 D-rn/s cary ng v«lnclit5
25:1 ar-to-materisl ralic
Diutc- and doise-pti^epneumatic transport.
Venthdes end
subsequent
backfil access
Power Supply-
B
Hopaer feeder >
Arlock feeder
Nondirected system for pneumatb Ulnd baekfllllng.
venthde and suteequert
backfill aci>e>3
Raver Supaly
Power Su pply-
Hopper feeder-v
Ailockfeeder-v^*
& to 1 G-in dam pfidinc ~^r ~
--,
\\
3Sta7C-ft
EJettor-ncezd system for pneumafe Uhdbackfllkig
Take-up mechanism for elbow-barrel
Airlock feeder system for pneumafc Ulid backfilling.
Source: Sands, 1990
September 30, 1999
29
-------
Figure 5. Example Schematic of Stope Backfilling Using Hydraulic Sandfilling
Source: Sutler Gold Mining, 1998
September 30, 1999
30
-------
Controlled flushing is used in mines where workers can safely enter and gain access to key areas
during the filling operations. When this approach is used, bulkheads may be built in mine passages around
the perimeter of the area to be filled. One or more wells are constructed and cased from the surface to the
upper portion of the mine workings to be filled. At the base of the vertical portion of the well, additional
piping may be used to aid in distributing the slurry into the mine workings. Horizontal dispersal from the
point of discharge ranges from 300 to 1,000 or more feet, depending on the vertical distance from the
ground surface to the mine opening and the solids concentration of the slurry. Because controlled flushing
provides relatively uniform distribution of backfill material, it generally provides better structural support
than the other methods and so is preferred where conditions permit (Whaite, 1975).
Blind flushing is used when the mine workings are inaccessible to workers. With this approach, a
slurry of backfill material is gravity fed through a well (either a drilled well or a mine shaft) into the mine until
the well will not accept any additional backfill material. The quantity that can be injected down a single well
depends on the conditions underground, such as the slope, height, and the proximity of pillars in the mine
workings. Usually, hundreds of injection points are required (Whaite, 1975).
Pumped slurry injection is similar to blind flushing except that the slurry is pumped down a well
rather than injected by gravity. With this approach, increased distribution of the fill material within the mine
can be achieved due to the increased velocity at which the slurry is injected. As shown in Figure 6, solid
particles settle out near the borehole when the slurry is first delivered and the velocity of the injected slurry
drops as it enters the mine workings. As more material is injected, the fluid velocity increases in the mine
workings and the solid materials are transported farther from the borehole (Whaite, 1975).
4.3.2 Integrated Mining and Backfilling
At some mines, backfill activities are closely integrated with mining activities. For example, in the
case of base metal and uranium mining, a common operational practice is to develop a mine using a cut-
and-fill method, illustrated in Figure 3. This method involves the following steps:
a cross cut is driven from the main access shaft to the ore vein;
a raise, later to be used as an ore pass for delivering the broken ore to the haulage level, is driven
upwards to intersect the vein;
the raise is used as a platform to excavate a "slice" of ore to create a stope or excavated room
above the level of the raise;
after each horizontal "slice" is cleaned of ore, the orepass is extended upward; and
September 30, 1999 31
-------
Figure 6: Schematic Depiction of Pumped Slurry Backfill Injection
EJECTION BOREHOLE
PUMreD SLURRY
COALBED
J.L
FLOODED LINE ROOM
>H«KK
STRATUM
ROCK STRATU
DEPOSITED SOLPS
Source: Whaite, 1975
the void is slurry backfilled and capped with cement which provides a floor from which the next
"slice" of ore, and process is repeated (Underground Injection Practices Council Research
Foundation, 1988).
Alternatively, an "underhand" cut-and-fill method involving a "top down" rather than "bottom up" sequence
of cut and fill, such that the ceiling rather than the floor of the stope is comprised of cemented backfill, is
used. An example is the Bulldog Mountain Mine in the Creede Mining District of Colorado. In both
"bottom up" and "underhand" operations, backfill material is normally delivered through a pipeline down the
mine shaft to the stope being filled.
September 30, 1999
32
-------
4.3.3 Retroactive Backfilling
When backfilling is performed after mining is complete or largely complete, blind gravity or pumped
slurry injection are common approaches. As discussed above in Section 4.2, such applications may
involved hundreds of injection wells, each of which may be operated for only a few days, in an effort to get
thorough distribution of the fill material within the mine workings.
4.3.4 Well Maintenance and Closure
As mentioned, most backfill wells are used for short periods of time (e.g., days or weeks) and,
thus, little maintenance is required. When a backfill injection well is used on an on-going basis, periodic
integrity testing may be performed, as discussed in more detail in Section 6. When injection is through a
pipeline down a mine shaft, as would be typical at a site where backfilling is an integral part of mining
activity, maintenance would normally be a part of mine operations and would include inspection and repair
or replacement of piping as needed.
Available information provides few descriptions of well closure and abandonment practices.
Where wells are used to backfill slurries that are similar in may respects to grouts (i.e., self-cementing), it
appears that the injection borehole is simply grouted to the surface. In some cases, cementing of the
borehole may occur either near the surface or from the injection zone to the surface.
5. POTENTIAL AND DOCUMENTED DAMAGE TO USDWs
5.1 Injectate Constituent Properties
The primary constituent properties of concern when assessing the potential for Class V mining,
sand, or other backfill wells to adversely affect USDWs are toxicity persistence, and mobility. The toxicity
of a constituent is the potential of that contaminant to cause adverse health effects if consumed by humans.
Appendix D to the Class V UIC Study provides information on the health effects associated with
contaminants found above MCLs or HALs in the injectate of mining, sand, or other backfill wells and other
Class V wells. Based on the information presented in Section 4, the following constituents that were found
to routinely or frequently exceed health-based standards in TCLP or other leachate from one or more types
of backfill material: antimony, arsenic, barium, beryllium, boron, cadmium, chromium, lead, mercury,
molybdenum, nickel, selenium, thallium, and zinc. Aluminum, copper, iron, manganese, TDS, sulfate, and
pH have been measured above secondary MCLs in TCLP or other leachate and are also discussed,
although these standards are designed to minimize aesthetic (taste) effects not adverse health effects (health-
based standards do not exist for these parameters).
Persistence is the ability of a chemical to remain unchanged in composition, chemical state, and
physical state over time. Appendix E to the Class V UIC Study presents published half-lives of common
constituents in fluids released in mining, sand, or other backfill wells and other Class V wells. All of the
values reported in Appendix E are for ground water. Caution is advised in interpreting these values
because ambient conditions have a significant impact on the persistence of both inorganic and organic
September 30, 1999 33
-------
compounds. Appendix E also provides a discussion of mobility of certain constituents found in the injectate
of mining, sand, or other backfill wells and other Class V wells.
The persistence of constituents that leach from mine backfill following injection will depend on
complex solution-mineral equilibria that will be determined by site-specific conditions such as leachate and
ground water characteristics, host rock characteristics, and oxygen availability in the mine workings and the
surrounding formation. Because the point of injection for most backfill wells is typically within a permeable
unit, or into a zone where prior mining activity has created a preferential (as compared to adjacent
undisturbed formations) flow pathway, physical conditions are relative conducive to mobility. It should be
noted, however, that in some situations backfilling occurs under dry conditions, while in others the primary
objective of backfilling is to reduce the mobility of metals and other constituents in mine water by altering
the physical and chemical conditions in the mine.
For injected backfill, mobility of metals in the mine environment is primarily dependent on their
tendency to dissolve rather than remain in a solid form, which generally increases as pH decreases for most
metals. For iron, for example, the solubility decreases abruptly when pH increases above 6.5 due to the
oxidation of ferrous iron (Fe+2) to the much less soluble ferric iron (Fe+3), which readily precipitates as iron
oxide or iron hydroxide. This oxidation to ferric iron can also occur, with the resulting marked decrease in
solubility, under acidic conditions created by oxidation and hydrolysis reactions that occur when mine water
from a strongly reducing environment is exposed to an oxygen supply. In either case, the resulting decrease
in dissolved iron concentrations also reduces the concentrations of many other metals, notably arsenic and
selenium, that co-precipitate with iron and/or adsorb onto the iron oxides and hydroxides. Mine water is
frequently acidic due to the oxidation of sulfide minerals, with the result that the mobility of most metals is
generally relatively high absent measures that limit oxygen availability, such as backfill injection (Levens,
1996; EPRI, 1998; Freeze and Cherry, 1979; Robl, 1999).
Unlike most metals, the solubility of chromium in the +6 form is not especially dependent on pH.
Chromium in the +3 form is much more common in coal mines, however, and shows decreasing solubility
with increasing pH.
Some other constituents present in injected backfill and backfill leachate, such as boron and sulfate,
do not have solubilities controlled by pH. Most sulfate is likely to remain in solution although some
precipitation of sulfate may occur when enough calcium or magnesium is present. In addition, adsorption
may occur at very low pH values. Similarly, boron is also likely to be present in backfill leachate (EPRI,
1998).
As discussed in more detail below in Section 5.2, injection of backfill material often occurs at sites
where low pH water is present or in contact with the backfill injection zone. At these sites, mobility of most
metals present in the backfill will be greater than if injection occurred under neutral or alkaline pH
conditions. Nevertheless, backfill injection under these conditions can result in a decrease in total (injectate
plus in-situ sources) metal mobility in the mine for several reasons. First, some backfills can reduce water
flow rates through the mine. Second, backfill can reduce the oxidation of sulfides by reducing or eliminating
September 30, 1999 34
-------
direct contact with air through sealing or flooding of the mine voids.6 Third, some backfill materials that are
alkaline in nature, such as coal ash and FGD sludge, can at least temporarily increase the pH of acidic mine
water present in the injection zone (Levens, 1996; Whitlatch, 1998; Kim, 1998).
5.2 Observed Impacts
None of the 23 states included in Table 1 indicated documented cases in which mine backfill wells
have caused contamination of a USDW.7 Studies have been conducted, however, by government,
industry, and universities that examine the effects of backfill injection on ground water quality, in part
because coal beds in some areas supply water to domestic wells (University of Kentucky, 1998).
This section summarizes studies of the effects of backfill injection on ground water quality. It is
organized in two parts. The first part discusses backfill in metal mines and the second discusses backfill in
coal mines.8
5.2.1 Metal Mines
The potential or observed impacts of underground mine backfilling on ground water quality have
been evaluated in several studies of metal mines. For the Lincoln Mine Project, a gold mine in California,
the teachability of backfill material was measured and evaluated in the context of the conditions that occur
naturally at the mine. Ground water at the site is limited, occurring in the weathered bedrock (generally not
deeper than 20 to 30 feet) and limited bedrock fractures.9 Because the gold deposit contains arsenopyrite
(FeAsS) (0.2 to 0.65 percent by weight of the ore), the focus of ground water quality investigations has
been on arsenic. Analysis of samples from bedrock ground water monitoring wells over a four year period
shows naturally occurring arsenic concentrations that range from 0.0014 to 0.185 mg/1, with well-specific
averages ranging from 0.008 to 0.063 mg/1 for the six wells examined (Sutler Gold Mining Company,
1998). Maximum concentrations in three wells and the average concentration in one well exceed the MCL
6 Because the diffusion of oxygen in water is about four orders of magnitude less than in air, flooding
of a mine to eliminate direct air contact with pyrite or other sulfide minerals greatly reduces acid
generation and, thus, metal solubility and mobility (Sutler Gold Mining Company, 1998).
7 Where ground water contamination has been identified at mining sites, it has not been clearly
attributable to backfilling.
8 It should be noted, however, that backfill of tailings occurs in other contexts as well. For example,
at Solvay Soda Ash Joint Venture in Green River, Wyoming, tailings are injected along with processing
plant wastewater and fly ash from coal fired boilers. The injected tailings consist of shale breaks from
within the ore itself, calcium carbonate from the caustic soda plant, and low grade oil shale (Wyoming,
1996). The available data do not include specific studies related to ground water impacts from this or
other similarly "unique" situations and, thus, they are not discussed in this section.
9 Total water production from 4,450 feet of mine workings ranges from 5 gallons per minute (gpm) in
summer to 20 gpm in winter, with most of this water entering the mine from the surface through
ventilation boreholes.
September 30, 1999 35
-------
of 0.05 mg/1. The minimum concentration in five of the six wells exceeds the HAL of 0.002 mg/1. In
addition, assessment of the acid formation potential of the backfill material indicates that it was quite low,
with an acid neutralization/acid generation potential ratio of 98:1, due to the presence of carbonate minerals
that yield a mine water pH of 8.3+. Deionized water leaching of the backfill (sandfill) material showed an
arsenic concentration of 0.13 mg/1 compared to a reported average concentration of 0.2 mg/1 for ground
water in the ore zone (Sutler Gold Mining Company, 1998). Thus, it appears that the potential for release
of arsenic from backfill material to degrade ground water is low. In addition, suitability of ground water for
use as drinking water is low due to limited availability and naturally occurring arsenic.
The U.S. Bureau of Mines (USBM) also examined the impact of mine backfill material on ground
water quality. At a moderately deep underground lead-zinc mine located in the Coeur d'Alene Mining
District of northern Idaho, samples of ground water both before and after contact with a sandfilled stope
showed an increase in electrical conductance. Increased concentrations of Ca, Mg, SO4"2, and HCO3"
account for most of the increase. Sulfate levels increased from levels slightly below the MCL of 500 mg/1
to levels that ranged from 797 to 1,171 mg/1. Changes in other metal concentrations were generally mixed,
with relatively small increases observed for some sampling events and decreases observed for others. Zinc
was an exception, showing consistently higher levels after contact with the sandfill (at levels consistently less
than the non-cancer lifetime HAL of 2 mg/1). Lead and arsenic levels were present at levels above the
MCL before and after contact with the sandfill. For all of the metals, the levels observed both before and
after contact with backfill material were well below the maximum teachability values measured in the
laboratory, as shown above in Tables 2 and 3 (Levens, 1993).
In a related investigation, USBM also examines the effect of cemented sandfill on ground water by
analyzing samples collected both before and after contact with the backfill. In this investigation, samples
from exploratory boreholes represent water quality within the native rock, whereas samples from a sump
and seeps that contact the backfill within the mine represent water quality affected by backfilling.
Comparison with the uncemented backfill examined above showed a much greater acid neutralization
capacity. This is consistent with the higher pH values observed after contact with the cemented backfill
(6.5 to 9.3) as compared to the pH measured in the native rock boreholes (6.29 to 7.98).
Concentrations of Ca, K, Mg, and SO4"2 are also higher after backfill contact, with SO4"2
concentrations increasing to levels that in most cases exceeded the primary MCL. Concentrations of zinc
and lead also increased. Zinc levels remained well below the non-cancer lifetime HAL of 2 mg/1. Lead
levels, in contrast, were typically several times the MCL action level of 0.015 mg/1 before contact with the
backfill. After backfill contact, levels were sometimes increased and sometimes decreased, but generally
were above the MCL. Secondary MCLs were also exceeded both before and after contact with backfill
for Iron and Mn. Iron concentrations were generally lower after backfill contact while Mn concentrations
showed both increases and decreases following backfill contact (Levens, 1996).
Notable increases in the concentrations of Ca, K, and SO4"2 were also observed in the laboratory
for three cemented backfill samples after washing with deionized water (see Table 3). Further laboratory
exposure (for 227 days) to a sulfuric acid wash showed additional increases in Ca, SO4"2, and metal
concentrations. Concentrations of most constituents measured in the laboratory were notably higher than
September 30, 1999 36
-------
those measured in the field following contact with backfill. Notable exceptions are Ba, K, and Na, which
showed lower concentrations in the laboratory than were observed in the field. Cadmium, lead, and SO4"2
concentrations exceeded primary MCLs while concentrations of iron, manganese, silver, and zinc exceeded
secondary MCLs in the laboratory leaching tests (Levens, 1996).
Observed differences in leachate concentrations appear to be due to differences in the particle-size
distribution of the backfill (tailings) material, with generally lower concentrations for backfill containing a
wide size distribution. In addition, the presence of sulfide minerals and Ca and Mg carbonates in the
backfill appeared to be important in determining the acid neutralizing capacity of the cemented material and,
thus, the release of some metals. The data also indicate that backfill cementing may help reduce metal
release and that ground water, to which releases occur, may contain metals at concentrations above MCLs
(Levens, 1996).
At the Homestake mine in South Dakota, samples were collected from drainage from the sand
backfill that was placed in slopes. Results indicate that the pH fluctuates around 8.0. As shown in Table 9,
concentrations of arsenic, iron, and nickel in exceed MCLs or HALs in some samples of drainage from a
backfilled stope. Arsenic and iron concentrations also exceed MCLs in mine water collected at a variety of
locations in the mine (Scheetz, 1999).
Backfill injection has also been widely used in uranium mines. Field sampling of tailings and backfill,
and studies of water discharging from where backfill was used suggest that short- and long-term effects on
ground water quality are negligible both during and following completion of mining (Levens, 1996).
5.2.2 Coal Mines
A study conducted in 1987 assessed the injection of coal slurry wastes from coal preparation and
sludge from treatment of AMD into underground coal mines in West Virginia. The study examined water
quality using samples from 9 mines that had received injection of slurry or AMD treatment sludge. Slurry
injection (at 6 mines) was found to improve the already degraded water quality by increasing alkalinity and
pH10, and decreasing concentration of iron and manganese. Sulfate concentrations also increased,
however. Only minor changes in trace
10 Mine water pH at the mines examined was 7 or greater, so the results indicated by these sites may
not apply to mines with acidic water (Smith, 1987).
September 30, 1999 37
-------
Table 9. Backfill Drainage At Homestake Mine, South Dakota
Constitue
nt
Aluminum
Arsenic
Cadmium
Chromium
Copper
Gold
Iron
Lead
Mercury
Nickel
Selenium
Zinc
CN Total
CNWAD
Drinking Water Health Advisory
Units Standards Levels (1)
mg/
mg/
mg/
mg/
mg/
mg/
mg/
mg/
mg/
mg/
mg/
mg/
mg/
0.05-0.2
0.05
0.005
0.1
1.3
--
0.3
0.015
0.002
0.1
0.05
5
--
mg/1
S
P 0.002 C
P 0.005 N
P 0.1 N
P
-
S
P
P 0.002 N
P 0.1 N
P
S 2 N
--
0.063
<0.001
<0.001
0.006
<0.001
0.59
<0.001
-
0.148
-
0.016
13.71
0.40
(2)
a
0.229
0.032
--
--
0.037
<0.001
--
--
--
0.010
<0.005
0.054
--
b
0.346
0.019
--
--
0.015
<0.001
--
--
--
0.005
<0.005
0.056
--
c
0.649
0.028
-
-
0.018
<0.001
-
-
-
0.005
<0.005
0.061
-
d
0.309
0.056
-
-
0.020
<0.001
-
-
-
0.005
<0.005
0.055
-
(3)
<0.005
<0.001
--
<0.005
<0.001
0.348
<0.001
<0.0002
0.008
<0.005
<0.050
--
a
0.001
0.001
<0.001
0.01
<0.001
0.06
0.005
0.0
NF
-
NF
-
(4)
b
0.001
0.001
NF
0.092
0.001
0.08
NF
0.0
NF
--
NF
--
c
0.003
0.001
<0.001
0.035
0.002
0.43
0.01
0.0
NF
--
0.016
--
NF = not found (not detected)
(1) Water issuing from sand backfill on the 7,100 foot level of the mine
(2) Water from selected underground sumps (labeled a-d) in the mine
(3) A combination of surface water and ground water from the upper underground levels of the mine
(4) Three samples (labeled a-c) of mine water (slope drainage) prior to treatment
Source: Scheetz, 1999
element concentrations were apparent following injection, and these changes do not appear to be threats to
drinking water (Smith, 1987).
Sludge injection (at 3 mines) appeared to increase alkalinity, pH, sulfate, and total suspended solids
(TSS). However, pH and alkalinity decreased when injected sludge had a much lower pH than the native
mine water. Sludge injection into mines with high (> 7) pH water resulted in lower iron and manganese
concentrations, except where the concentration of these elements were very low (<0.1 mg/1) prior to
injection. Injection into mines with low pH resulted in a great increase of iron concentrations, presumably
as a result of dissolution from the sludge. Most changes in trace element concentrations were negligible,
with the possible exception of arsenic, which showed a large apparent increase at one mine. However,
concern about potential analytical error complicate assessment of this result (Smith, 1987).
A recent study also examined the impact of injection of a grouting material composed of fly ash,
FBC, and FGD sludge into an abandoned underground mine near Friendsville, Maryland. At this site,
ground water (AMD) seeping from the mine was a known cause of surface water quality degradation, and
injection was initiated with the intention of improving both ground and surface water quality. Seepage water
quality measured before injection indicated Fe and Mn concentrations above secondary MCLs, SO4"2
concentrations generally above the primary MCLs, and Zn concentrations sometimes above the HAL.
September 30, 1999
38
-------
Immediately after injection11, acidity of the AMD
increased markedly along with dissolved iron and
aluminum concentrations, and then decreased to pre-
injection levels by the following summer. Ca and
SO4"2 concentrations also increased in the AMD
following injection and remain high (as of April 1998),
apparently due to dissolution of these materials from
the injected grout (see Figure 7) (Aljoe, 1999).
The initial increase in acidity of the AMD
following grouting most likely resulted from changes in
mine pool hydrology, including a drop in mine pool
elevation that occurred when water was pumped from
the mine to prepare the grout.12 This drop in
elevation would have exposed an estimated 10,500
cubic feet of highly-fractured, previously-submerged
material within the mine to atmospheric oxygen.
Another change could have been re-routing of flow
through new areas of the mine workings, thereby
mobilizing acidic products that had previously been
stored in stagnant zones within the mine. The
intention of the backfilling effort had been to entirely fill the mine voids with grout, thereby isolating the
pyritic surfaces from air and water and reducing the AMD production rate. This did not occur, however,
because limited information available on the size of the mine workings led to an underestimate of the
quantity of grout needed (Aljoe, 1999).
In a similar project initiated in 1997, grout comprised of a 1.25:1.00 (by dry weight) mixture of fly
ash and FGD filter cake with 5 percent added lime was injected through 318 drilled grout holes into an
abandoned underground coal mine near Conesville, OH. The objective of the injection project was to
inject grout that would seal old mine entries and coat the floor and walls of the abandoned mine chambers,
thereby reducing the amount of oxygen available and slowing the process of acid formation. Because
grouting was only completed in early 1998, it is too early to determine the net effect on water quality, which
will be monitored for three additional years.13 For all surface and ground water monitoring locations
7/25/95 2/10/96 8/28/96 3/16/97 10/2/97 4/20/98
Figure 7. Calcium and Sulfate Concentrations
and Loads at an Abandoned Maryland Coal
Mine (from Aljoe, 1999)
11 About 5,600 cubic yards of fly ash, FBC ash, and FGD sludge were injected as a slurry via 38
boreholes in October and November 1996.
12 Water to make the slurry was pumped from the main mine pool, which temporarily lowered the
level by about 2 feet.
13 Ground water is being monitored in the overlying Freeport Sandstone, the Middle Kitanning No. 6
coal seam, and the underlying Clarion Sandstone. Two perched aquifers exist: one in the Freeport
Sandstone, caused by the underlying claystone and siltstone which immediately overlies the No. 6 coal;
(continued...)
September 30, 1999
39
-------
(through September 1998), no measurable increase in arsenic, chromium, boron, or pH levels have been
observed since grout injection (Whitlatch, 1998).
Laboratory studies of the reaction between the grout and AMD showed a significant increase in
solution pH to approximately 8 and in the concentration of a number of ions, including arsenic and boron.
Only 1.32 percent of the arsenic present in the grout was released over the 168-day reaction time and the
resulting arsenic levels were below the primary MCL. Because further solubilization could result in higher
concentrations, both arsenic and boron will receive particular attention in the on-going monitoring program
(Whitlatch, 1998).
The reason for the apparent difference in the reaction between the grout and AMD in the
laboratory and the field is not yet clear, but it appears that conditions within the mine are unfavorable for the
development of acid neutralization reactions. This may be due to the fact that longer contact times are
required than are achieved in the mine. It should be noted, however, that the project is designed to achieve
AMD reduction through successful sealing of the mine and does not rely on acid neutralization by the grout.
Observations to date show that the water level has risen in the mine, indicating that the grout was of
sufficient strength to provide effective seals. In-situ core samples taken after about nine months indicate
that the grout is highly impermeable and has weathered very little (Whitlatch, 1998).
At sites in Greene and Clinton counties in Pennsylvania and Upshur county in West Virginia,
injection of mixtures of fly ash, FBC ash, lime, AMD treatment sludge, and/or cement with water has been
used in attempt to reduce AMD from reclaimed surface mined areas as well. At these sites, grout was
injected at relatively shallow (< 30 feet) depths in an attempt to fill voids in the spoil material, thereby
reducing contact between the buried pyrite and air and water (Kim, 1998).
At the Greene county site, the pH in wells in the injection area increased by 0.5 pH units and the
pH of the seep (discharge from the spoil area) increased slightly from 3.2 to 3.3 following grouting.
Acidity was unchanged in the injection area but decreased in the seep. In the injection area and the seep,
little difference in trace metal concentrations was observed before and after grouting (Kim, 1998).
At the Clinton county site, pH increased and acidity decreased in samples from the injection area
and discharges. The pH remained less than 3, however. Average trace metal data from about two years
after injection indicate higher concentrations of As, Co, Cu, Ni, and Zn in the injection area, but
concentrations in the discharge were closer to the discharge levels from areas without injection (Kim,
1998).
At the Upshur county site, the average pH of the water in the injection area decreased initially after
injection, but had increased when the water was sampled five years later. This increase, however, could
13 (...continued)
and one in the No. 6 coal caused by claystone, siltstone and limestone layers between it and the
underlying Clarion Sandstone. The lowest and most extensive aquifer is in the Clarion Sandstone and
intersects major hydrologic boundaries, such as Wills Creek.
September 30, 1999 40
-------
be due to the similar increases observed in the inflows and the ungrouted area. Acidity decreased in the
injection area, the inflows, and outflows immediately following injection. Five years after injection, acidity
had decreased further in the injection area and increased in the discharger, although it remained below the
pre-injection level. Also, concentrations of Ba, Be, Cd, Co, Cr, Cu, Ni, Pb, Sb, and Zn were generally
higher in the injection area and discharge than the inflow or control areas, but were still less than primary
and secondary MCLs (Kim, 1998).
6. ALTERNATIVE AND BEST MANAGEMENT PRACTICES
A number of best management practices (BMPs) can be implemented to provide increased benefits
and protection of USDWs with mine backfill wells. As discussed above, the effect of mine backfill
operations on ground water quality depends to a large extent on the characterisitics of the backfill and the
mine, and the interaction between the two. Thus, selecting the appropriate backfill materials for a mine and
selecting appropriate BMPs require characterization of the the backfill materials, including the potential to
cause AMD, and an understanding of where the backfill will be placed (especially with respect to the water
table) and how the backfill is expected to react over time in this environment.
BMPs are discussed below in relation to injectate characteristics, design and construction,
operation, and closure. The discussion is neither exhaustive nor represents an USEPA preference for the
stated BMPs. Each state, USEPA Region, and federal agency may require certain BMPs to be installed
and maintained based on that organization's priorities and site-specific considerations.
6.1 Injectate Characteristics
Some injected backfill materials have cement-like properties that cause them to harden following
injection. Although the importance of the cementing properties of the injected backfill will vary with site
conditions and the objectives, cement-like characteristics are generally, but not always, desirable.14
Cementing properties are intrinsic to some backfilled materials and can be created in all materials commonly
used for backfilling through the use of appropriate mixtures and additives. Cementing properties provide
both increased structural support (where backfill is provided to control subsidence) and reduced
permeability. Reduced permeability generally serves to reduce dissolution of constituents from the injected
material. In addition, flow rates through the backfilled zone are reduced, thereby reducing the availability of
oxygen and the release of constituents from the mine surfaces as well as the backfill material.
6.2 System Design and Construction
As discussed above, backfill injection is sometimes used with the intention of preventing or abating
AMD. Although injection is intended to increase pH and reduce acidity, the acidic conditions present in
14 Recent experimental work indicates injection of alkaline FBC ash in dilute slurry form may be
more effective in reducing AMD than ash injected in the form of low-permeability grout. In some
situations, the benefits from increased neutralization may outweigh the potential increase in the release of
trace metals from the ash (Canty, 1999).
September 30, 1999 41
-------
these applications will lead to the dissolution of some constituents from the injected backfill. This
dissolution can be reduced, however, by ensuring that the mine voids are filled as completely as possible
with the injected material, thereby reducing the availability of oxygen and the potential for additional acid
formation. To achieve this objective requires adequate distribution of the backfill within the mine workings,
which in turn requires appropriate quantities of injection material, appropriate well spacings, and injection
pressures that will distribute the material and effectively fill the mine voids. In addition, bonding agents
and/or materials to reduce the porosity of the injected backfill can help to reduce the residual void space
remaining after backfill injection. These considerations warrant special attention when injection occurs in
inactive mines where access and knowledge of the size and geometry of the mine workings are limited.
BMPs for well construction may vary significantly with site conditions and the type of backfill
injected. Backfill injection often occurs in abandoned mines or other settings where injection is performed
in an effort to improve existing poor ground water quality. In these situations, injection through uncased
boreholes may be appropriate if the wells are relatively shallow, the strata have sufficient integrity, the
injectate is grout-like in nature, and injection only occurs for a short period, such as a few days. At other
injection sites, however, casing is clearly needed to ensure that the injected material reaches the intended
formation. This is particularly true when the injection well is relatively deep, operates on an on-going basis,
passes through a USDW, and/or injects a low solids content fluid. In some cases, the site setting or the
nature of the injected material may make the use of tubing appropriate.
6.3 Well Operation
For backfill wells that operate on an on-going basis, which most often occurs in association with
backfilling that is integrated with mining operations, BMPs include mechanical integrity tests (MIT) before
the well is put into service and periodically during use. A variety of MITs may be run on backfill wells to
check casing integrity. For example, pressure tests may be run prior to initial well operation and
subsequently at periodic intervals, generally ranging from one to five years. Because mine backfill injection
is normally done without a tubing string, pressure testing requires that a temporary, retrievable bridge plug15
be set near the bottom of the casing. This retrievable plug approach is used at least at one site in Wyoming.
The appropriate pressure for a pressure test depends on anticipated well operating conditions. At the
Wyoming facility, testing at a pressure 10 percent greater than the maximum pressure reached during the
previous year (or maximum of 200 psi) is required (State of Wyoming 1988, 1996).
Due to the relatively high solids content of injected backfill as compared to other types of injected
fluids, abrasion can threaten casing integrity. Thus, caliper logs16 may be run periodically on the entire
length of the surface. A casing log run prior to well use provides a baseline against which subsequent logs
can be compared. In Wyoming, casing logs are repeated at nine month intervals unless the results show
15 An expandable plug used in a well's casing to isolate producing zones; also to isolate a section of
the borehole to be filled with cement when a well is plugged.
16 An instrument for measuring the inside diameter of a well.
September 30, 1999 42
-------
more than 20 percent reduction in the wall thickness of the casing, in which case the log is repeated every
six months (Wyoming 1988, 1996).
Other examples of MIT used in backfilling operations include Multifrequency Electromagnetic
Thickness (MET) logs and cement bond logs. MET has been used by Tg Soda Ash, Inc. during the
operation of an underground tailings disposal and mine backfilling system to evaluate corrosion and metal
loss (Tg Soda Ash, 1997). Cement bond logs (and caliper logs) have been used in the Big Island Trona
Mine to evaluate the integrity of cement to pipe and cement to formation bonding (Wickersham, 1995).
6.4 Well Closure
Appropriate well abandonment is important to ensure that the well does not provide a pathway
through which contamination of USDWs could occur. As with well construction and operation,
appropriate closure practices depend onsite conditions. In some situations, abandonment may be as simple
as allowing the injected material to fill the well bore after the mine stops accepting additional injected
material. This approach is most likely to be appropriate for shallow wells used for short periods to inject
self-cementing grouting materials into closed or abandoned mines.
In other situations, protection of USDWs may require plugging and abandonment using more
"conventional" cementing techniques. For example, in Wyoming abandonment includes setting a cast iron
bridge plug approximately 50 feet above the bottom of the casing. Cement is placed in the casing by
pumping through a tubing string in stages as the tubing is withdrawn. This is performed until the entire
casing is cemented to the surface. At the surface, the casing is cut off 5 feet below the ground surface and
the land surface reclaimed in accordance with mine abandonment permits (Wyoming 1988, 1996).
In another example, all injection wells, water withdrawal wells, and monitoring boreholes at the
Kindall 3 Mine in Indiana were required to be plugged and sealed with cement from the bottom to the
surface. Figure 8 provides example cross sections showing borehole plugging methods. In this example, a
cement basket is used instead of a bridge plug to establish the location in the casing at which cementing
begins.
September 30, 1999 43
-------
Figure 8. Cross Sections of Typical Borehole Plugging Methods
BOREHOLE INTO BOREHOLE WITH DEPTH BOREHOLE LESS
OLD WORKS OF 2W OR MORE THAN 2W DEEP
(NOOLD WORKS)
CEMENT
CEMENT
BASKET
OLD
is';**
§ifP
'ji-ip.-'i^1
Vii -
-------
7. CURRENT REGULATORY REQUIREMENTS
As discussed below, several federal, state, and local programs exist that either directly manage or
regulate Class V mining, sand, and other backfill wells. On the federal level, management and regulation of
these wells falls primarily under the UIC program authorized by the Safe Drinking Water Act (SDWA).
Some states and localities have used these authorities, as well as their own authorities, to extend the
controls in their areas to address concerns associated with mining, sand, and other backfill wells.
7.1 Federal Programs
7.1.1 SDWA
Class V wells are regulated under the authority of Part C of SDWA. Congress enacted the
SDWA to ensure protection of the quality of drinking water in the United States, and Part C specifically
mandates the regulation of underground injection of fluids through wells. USEPA has promulgated a series
of UIC regulations under this authority. USEPA directly implements these regulations for Class V wells in
19 states or territories (Alaska, American Samoa, Arizona, California, Colorado, Hawaii, Indiana, Iowa,
Kentucky, Michigan, Minnesota, Montana, New "fork, Pennsylvania, South Dakota, Tennessee, Virginia,
Virgin Islands, and Washington, DC). USEPA also directly implements all Class V UIC programs on
Tribal lands. In all other states, which are called Primacy States, state agencies implement the Class V UIC
program, with primary enforcement responsibility.
Mining, sand, and other backfill wells currently are not subject to any specific regulations tailored
just for them, but rather are subject to the UIC regulations that exist for all Class V wells. Under 40 CFR
144.12(a), owners or operators of all injection wells, including mining, sand, and other backfill wells, are
prohibited from engaging in any injection activity that allows the movement of fluids containing any
contaminant into USDWs, "if the presence of that contaminant may cause a violation of any primary
drinking water regulation ... or may otherwise adversely affect the health of persons."
Owners or operators of Class V wells are required to submit basic inventory information under 40
CFR 144.26. When the owner or operator submits inventory information and is operating the well such
that a USDW is not endangered, the operation of the Class V well is authorized by rule. Moreover, under
section 144.27, USEPA may require owners or operators of any Class V well, in USEPA-administered
programs, to submit additional information deemed necessary to protect USDWs. Owners or operators
who fail to submit the information required under sections 144.26 and 144.27 are prohibited from using
their wells.
Sections 144.12(c) and (d) prescribe mandatory and discretionary actions to be taken by the UIC
Program Director if a Class V well is not in compliance with section 144.12(a). Specifically, the Director
must choose between requiring the injector to apply for an individual permit, ordering such action as closure
of the well to prevent endangerment, or taking an enforcement action. Because mining, sand, and other
backfill wells (like other kinds of Class V wells) are authorized by rule, they do not have to obtain a permit
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unless required to do so by the UIC Program Director under 40 CFR 144.25. Authorization by rule
terminates upon the effective date of a permit issued or upon proper closure of the well.
Separate from the UIC program, the SDWA Amendments of 1996 establish a requirement for
source water assessments. USEPA published guidance describing how the states should carry out a source
water assessment program within the state's boundaries. The final guidance, entitled Source Water
Assessment and Programs Guidance (USEPA 816-R-97-009), was released in August 1997.
State staff must conduct source water assessments that are comprised of three steps. First, state
staff must delineate the boundaries of the assessment areas in the state from which one or more public
drinking water systems receive supplies of drinking water. In delineating these areas, state staff must use
"all reasonably available hydrogeologic information on the sources of the supply of drinking water in the
state and the water flow, recharge, and discharge and any other reliable information as the state deems
necessary to adequately determine such areas." Second, the state staff must identify contaminants of
concern, and for those contaminants, they must inventory significant potential sources of contamination in
delineated source water protection areas. Class V wells, including mining, sand, and other backfill wells,
should be considered as part of this source inventory, if present in a given area. Third, the state staff must
"determine the susceptibility of the public water systems in the delineated area to such contaminants." State
staff should complete all of these steps by May 2003 according to the final guidance.17
7.1.2 SMCRA
The Office of Surface Mining Reclamation and Enforcement (OSM) in the U. S. Department of the
Interior oversees state mining regulatory and reclamation activities under the Surface Mining Control and
Reclamation Act (SMCRA), or directly implements mining programs in states that have not obtained
primacy under SMCRA. The Office also directly regulates coal mining and reclamation activities on
federal and Indian lands. The Bureau of Land Management (BLM), also a part of the U. S. Department of
the Interior, is responsible for the management of public lands, including minerals leasing and oversight for
the development of energy and mineral leasing and compliance with regulations governing the extraction of
mineral resources. It is also responsible for subsurface resource management where mineral rights, but not
the land surface, are federally owned.
Regulations promulgated by the Office of Surface Mining in Title 30 Chapter 7 apply to mine
backfill wells if the well is located in a state that has not accepted primacy under SMCRA. In some
Primacy States, the federal requirements have also served as the model for the state regulations.
Part 784 of Chapter 7 addresses underground mining permit application requirements, and contains
minimum requirements for the reclamation and operation plan that must be submitted as part of the permit
application. Section 784.25 provides that each underground mining permit application must supply a plan
describing the design, operation, and maintenance of any proposed coal processing waste disposal facility
including flow diagrams and any other necessary drawings and maps, for the approval of the state
17 May 2003 is the deadline including an 18-month extension.
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regulatory authority and the Mine Safety and Health Administration under 30 CFR 817.81(f), the
permanent program performance standards for underground disposal of coal mining waste. The section
provides further that:
Each plan shall describe the sources and quality of waste to be stowed, area to be backfilled,
percent of the mine void to be filled, method of constructing underground retaining walls, influence
of the backfilling operation on active underground mine operations, surface area to be supported by
the backfill and the anticipated occurrence of surface effects following backfilling;
The applicant shall describe the source of the hydraulic transport mediums, method of dewatering
the backfill that is emplaced, retention of water underground, treatment of water if released to
surface streams, and the effect on the hydrology; and
The plan shall describe each permanent monitoring well to be located in the backfilled area, the
stratum underlying the mined coal, and gradient from the backfilled area except where pneumatic
backfilling operations are exempted from hydrologic monitoring (30 CFR 784.25).
Both §817.81(f), the permanent program requirements on underground disposal of coal mine waste
described above, and §817.71(j), the permanent program requirements on underground disposal of excess
spoil, provide that coal mine waste or excess spoil may be disposed of in underground mine workings "only
in accordance with a plan approved by the regulatory authority and MSHA under §784.25."
SMCRA also authorizes the promulgation of regulations addressing the surface effects of
underground coal mining operations. The statute provides in 30 U.S.C.A. §1266 that with respect to
surface disposal of mine wastes, tailings, coal processing wastes, and other wastes in areas other than the
mine workings or excavations, permitted mining operations are required to stabilize all waste piles and
ensure that the leachate from such piles will not fall below the water quality standards established under
federal or state law for surface or ground waters. The provision does not specify that leachate must result
from precipitation, and could be applied to leachate from injection into a surface rubble pile (which could
be defined as a Class V well).
BLM regulations establish performance standards for coal mining and for solid minerals other than
coal under federal leases and licenses. The rules pertaining to underground coal mining specify that
backfilling of exploratory drill holes, openings, and excavations must be in accordance with sound
engineering practices and an approved plan (43 CFR 3484.2). Non-coal mineral mining also must be
conducted according to an approved plan, which must address backfilling of drill holes (see e.g., 43 CFR
3522.3-3(c)(3)). In addition, BLM rules provide that the operator/lessee must dispose of all wastes
resulting from the mining, reduction, concentration, or separation of mineral substances in accordance with
the terms of the lease, approved mining plan, applicable federal, state, and local law and regulations and the
directions of the authorized officer (43 CFR 3596.2).
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7.2 State and Local Programs
Ninety-eight percent of the documented mine backfill wells and 99 percent of estimated wells in the
United States exist in 10 states: Idaho, Illinois, Indiana, Kansas, North Dakota, Ohio, Pennsylvania, Texas,
West Virginia, and Wyoming. Attachment A of this volume describes how each of these states current
regulate mining, sand, and other backfill wells.
In Indiana and Pennsylvania, USEPA Regions 5 and 3, respectively, directly implement the UIC
Class V program. The USEPA Regions apply inventory requirements and use permit by rule to ensure
non-endangerment of USDWs. Indiana, in addition, has enacted state regulations that apply to
underground mining operations, including backfilling of mines, that are implemented by the state's
Department of Natural Resources. Indiana's requirements for backfilling plans parallel requirements
established in 30 CFR 817.81(f) under SMCRA. Pennsylvania, in addition, regulates mine backfill well
projects through regulations implemented by the Bureau of Mining and Reclamation.
In the eight states that are Primacy States for Class V UIC wells, state regulations pertaining to
mine backfill wells vary significantly in their scope and stringency.
Mine tailing backfill wells are authorized by rule in Idaho, unless use of such a well results in
exceedance of water quality standards, when the well is required to obtain an individual permit or
close.
Illinois has enacted UIC Class V requirements that are identical to those of the USEPA. The state
applies inventory requirements and uses permit by rule to ensure non-endangerment of USDWs. In
addition, the state has enacted a Groundwater Protection Act and ground water quality regulations
that require responses to ground water contamination before it exceeds specified ground water
quality standards.
Kansas has incorporated the federal UIC Class V regulations by reference. (Mine backfill wells
that are designed to backfill salt caverns are covered by the state's Class HI UIC requirements, and
by water well requirements and are not discussed in this report.) Class V mine backfill wells are
permitted by rule.
North Dakota uses inventory requirements and permit by rule to ensure non-endangerment of
USDWs from mine backfill wells. In addition, the state places special requirements for siting,
construction, and operation of backfill wells into the contracts that the state enters into for
backfilling to address highway subsidence, the predominant backfilling activity that takes place in
the state.
Ohio authorizes by rule Class V UIC mine backfill wells and requires drilling and operating permits
for some types of wells, including backfill wells. In addition, Ohio's rules pertaining to underground
coal mines, administered by the Division of Mines and Reclamation, require the development of a
reclamation plan, including ground water monitoring, and specify that discharge of water into
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underground mines is prohibited unless approved by the Division of Mines. Ohio's requirements
for backfilling plans parallel the requirements in 30 CFR 817.81(f) under SMCRA.
In Texas, mine backfill wells are authorized by rule. The state's mining regulations exempt shafts
and boreholes authorized under the UIC program. The state requirements for Class V wells,
however, include siting, construction, and closure standards.
West Virginia issues individual permits or area permits to mine backfill wells.
Wyoming covers mine backfill wells under the general permit provisions of the state's Class V UIC
requirements. In addition to requiring the submission of information, the general permit
requirements also include a well operator to establish a monitoring program. In addition, the state's
regulations pertaining to underground coal mining require a permit to return coal-mining waste to
abandoned underground workings.
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ATTACHMENT A
STATE AND LOCAL PROGRAM DESCRIPTIONS
This attachment does not describe every state's control programs; instead it focuses on the ten
states where relatively large numbers of mine backfill wells are known to exist: Idaho, Illinois, Indiana,
Kansas, North Dakota, Ohio, Pennsylvania, Texas, West Virginia, and Wyoming. Altogether, these ten
states have a total of 4,992 documented mine backfill wells, which is almost 99 percent of the documented
well inventory for the nation.
Idaho
Idaho is a UIC Primacy State for Class V wells and has promulgated regulations for its UIC
program in the Idaho Administrative Code (IDAPA), Title 3, Chapter 3.
Permitting
Idaho's rules state that mine tailings backfill wells are authorized by rule as part of mining operations
"because federal studies show the threat of endangerment from use of these wells is low They are
therefore exempt from the MCLs and permitting requirements of the UIC rules, provided that their use is
limited to the injection of mine tailings only." For rule-authorized mine backfill wells inventory information
must be supplied (37.03.03.030.01 IDAPA).
The rules provide that the use of a well shall not result in water quality standards at points of
beneficial use being exceeded or otherwise affect a beneficial use. If water quality standards are exceeded
or beneficial uses affected, the rules state that the well may be put under the permit requirements of Title 3,
Chapter 3, or the well may be required to be remediated or closed (37.03.03.025.03.g IDAPA (Rule
25)).
If a mining backfill well is placed under the permitting requirements, detailed permit application
information is required. It includes information on location and construction of the proposed well; proposed
injectate; local features such as topography, wells producing water, surface waters, residences, and
geology; and maps and cross sections depicting all USDWs within a quarter mile radius of the injection
well, their location relative to the injection zone, and the direction of water movement. Corrective action
and contingency plans must be prepared and submitted, and proof of financial responsibility must be
supplied.
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Siting and Construction
Class V wells may be required to be located at a distance from a point of diversion for beneficial
use sufficient to minimize or prevent ground water18 contamination resulting from unauthorized or accidental
injection (37.03.03.050.03.a IDAPA)
Operating Requirements
Idaho's requirements for use of Class V wells are based on the premise that if the injected fluids
meet MCLs for drinking water at the wellhead, and if ground water produced from adjacent points of
diversion for beneficial use meets the water quality standards found in Idaho's "Water Quality Standards
and Wastewater Treatment Requirements," 16.01.02 IDAPA, administered by the Idaho Department of
Health and Welfare, the aquifer will be protected from unreasonable contamination. The state may, when
necessary "to protect the ground water resource from deterioration and preserve it for diversion to
beneficial use," require specific injection wells to be constructed and operated in compliance with
additional requirements (37.03.03.050.01 IDAPA (Rule 50)). Rule-authorized wells "shall conform to the
MCLs at the point of injection and not cause any water quality standards to be violated at the point of
beneficial use" (37.03.03.050.04.d. IDAPA).
Monitoring, recordkeeping, and reporting may be required if the state finds that the well may
adversely affect a drinking water source or is injecting a contaminant that could have an unacceptable effect
upon the quality of the ground waters of the state (37.03.03.055 IDAPA (Rule 55)). As a condition of use
of mine tailings backfill wells, the owner or operator may be required to monitor ground water
(37.03.030.025.03.g IDAPA (Rule 25)).
Financial Responsibility
No financial responsibility requirement exists for rule-authorized mine backfill wells. Operators of
permitted wells are required to demonstrate financial responsibility through a performance bond or other
appropriate means (the rule does not specify the amount(s) required) to abandon the injection well
according to the conditions of the permit (37.03.03.35.03.6 IDAPA).
Plugging and Abandonment
The Idaho Department of Water Resources (IDWR) has prepared "General Guidelines for
Abandonment of Injection Wells," which are not included in the regulatory requirements. IDWR expects to
approve the final abandonment procedure for each well. The General Guidelines recommend the following:
18 "Ground water" is defined as "any water that occurs beneath the surface of the earth in a
saturated geological formation of rock or soil." A "Drinking Water Source" is defined as "an aquifer
which contains water having less than ten thousand (10,000) mg/1 total dissolved solids" that has not been
exempted from that designation by the Director of the Department of Water Resources.
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The casing should be pulled, if possible, or cut a minimum of two feet below the land surface.
The total depth of the well should be measured.
If the casing is left in place, it should be perforated and neat cement with up to 5 percent bentonite
can be pressure-grouted to fill the hole. As an alternative, when the casing is not pulled, course
bentonite chips or pellets may be used. If the well extends into the aquifer, the chips or pellets must
be run over a screen to prevent any dust from entering the hole. Perforation of the casing is not
required under this alternative
If the well extends into the aquifer, a clean pit-run gravel or road mix may be used to fill the bore up
to ten feet below the top of the saturated zone or ten feet below the bottom of the casing,
whichever is deeper, and cement grout or bentonite clay used to the surface. Gravel may not be
used if the lilhology is undetermined or unsuitable.
A cement cap should be placed at the top of the casing if the casing is not pulled, with a minimum of
two feet of soil overlying the filled hole/cap.
Abandonment of the well must be witnessed by an IDWR representative.
Illinois
Illinois is a UIC Primacy State for Class V wells. The Illinois Environmental Protection Agency
(IEPA), Bureau of Land, has promulgated rules establishing a Class V UIC program in 35 Illinois
Administrative Code (IAC) 704. These rules are identical in substance to USEPA rules in 40 CFR 144
(704.101 IAC). In addition, Part 702, "RCRA and UIC Permit Programs," establishes requirements for
those UIC wells required to obtain a permit, while Part 705 describes the procedures for issuing UIC
permits. Finally, 35 IAC Part 730 sets out technical criteria and standards for the UIC program. Part 730
Subpart F currently does not specify technical criteria and standards for siting, construction, operating,
monitoring and reporting, mechanical integrity, or closure for Class V UIC wells, although other subparts of
Part 730 do so for other classes of UIC wells (730.151 IAC).
Permitting
Any underground injection, except into a well authorized by permit or rule, is prohibited. The
construction of any well required to have a permit is prohibited until the permit has been issued (704.12.
IAC). However, injection into Class V wells is authorized by rule (704.146 IAC). Owners or operators
of wells authorized by rule must submit inventory information (704.148 IAC). In addition, IEPA may
require submission of other information deemed necessary by IEPA (704.149 IAC). In addition to the
inventory information required from all Class V wells, certain categories of wells, including sand or other
backfill wells as defined by 35 IAC 730.105(e)(8), are required to submit additional information, including
the following:
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Location of each well by township, range, section, and quarter-section;
Date of completion of each well,
Identification and depth of the formation(s) into which each well is injecting,
Total depth of each well,
Casing and cementing record, tubing size, and depth of packer,
Nature of the inj ected fluids,
Average and maximum injection pressure at the wellhead,
Average and maximum injection rate, and
Date of the last MTTs, if any (704.148(b)(2) IAC).
Operating Requirements
No operating requirements are specified for Class V UIC wells permitted by rule. Such wells,
however, are subject to the state's ground water protection requirements. Under Illinois' Ground Water
Quality regulations, found in 35 HI. Adm.Code Part 620, a classification system is established for the
State's ground waters. The regulations also enact a nondegradation provision, establish standards for
quality of ground waters, and create procedures for the management and protection of ground waters. The
regulation defines "potential route" of ground water contamination to include, among others, abandoned and
improperly plugged wells of all kinds, drainage wells, and all injection wells. The regulation provides that no
person shall cause a violation of the state's Environmental Protection Act, the Groundwater Protection Act,
or regulations adopted under those Acts, including the Ground Water Quality regulations.
The fours classes of ground water established by the classification system are (I) potable resource
ground water;19 (II) general resource ground water, which cannot easily be tapped to supply drinking
water; (HI) special resource ground water, which is "demonstrably unique (e.g., irreplaceable"), vital for a
particularly sensitive ecological system (not further defined), or contributes to a dedicated nature preserve;
and (IV) other ground water, which is naturally saline, contaminated, or is limited in its resource potential
(e.g., within a zone of attenuation for a solid waste landfill, under a coal mine refuse disposal area, under a
potential contaminant source, within a previously mined area, or ground water that has been designated as
an exempt aquifer under the underground injection policy of 730.104 IAC (620.201 - 240 IAC). (Under
730.104 IAC an aquifer or portion of an aquifer that otherwise meets the criteria for a USDW may be
determined to be an exempted aquifer if it does not currently serve as a source of drinking water and it
cannot now and will not in the future serve as a source of drinking water.)
The Ground Water Quality regulations prohibit impairment of resource ground water and require
preventive notice and response procedures to detect and address contaminants before they exceed the
ground water quality standards for Class I and HI ground waters. The regulations also include ground
water quality standards for each class of ground water, as well as ground water quality restoration
standards. The latter include coal reclamation ground water quality standards, addressing inorganic
chemical constituents and pH in ground water, within an underground coal mine, or within the cumulative
19 "Potable" is defined as "generally fit for human consumption in accordance with accepted water
supply principles and practices."
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impact area of ground water for which the hydrologic balance has been disturbed from a permitted coal
mine (620.450(b). These requirements also address coal mine refuse disposal areas, but do not explicitly
address mine backfill activities.
Indiana
USEPA Region 5 directly implements the UIC program for Class V injection wells in Indiana. In
addition, however, state regulations found in Title 310 Indiana Administrative Code (IAC) administered by
the Indiana Department of Natural Resources (DNR), Division of Reclamation, apply to mine backfill wells.
Permitting
The DNR permitting rules require applications for underground mining operation permits to
describe proposed disposal methods and sites for placing underground development waste and excess spoil
generated at surface areas (310IAC 12-3-86). Each plan also must describe the design, operation, and
maintenance of any proposed coal processing waste disposal facility including the source and quality of
waste, the area to be backfilled, the method of constructing underground retaining walls, the source of the
hydraulic transport mediums, the method of dewatering the emplaced backfill, the retention of water
underground, the effect on the hydrology, each monitoring well to be located in the backfilled area, the
stratum underlying the mined coal, and the gradient from the backfilled area (310 IAC 12-3-91).
Regulations of the Water Pollution Control Board also specify that if an applicant for an National
Pollutant Discharge Elimination System (NPDES) permit proposes to dispose of pollutants by underground
injection as part of the overall effort to meet the requirements of the NPDES program, the application shall
be denied, unless conditions can be placed in the NPDES permit that will control the proposed discharge to
prevent pollution of ground water resources of such character and degree as would endanger or threaten to
endanger the public health and welfare (327IAC 5-4-2).
Siting and Construction
Approval must be obtained for return of coal processing waste to abandoned underground
workings (310 IAC 12-3-91). Plans submitted to the Division of Reclamation must identify the locations of
the wells.
Operating Requirements
Coal processing waste may be returned to underground mine workings only in accordance with the
waste disposal program approved under 310 IAC 12-3-91 (310 IAC 12-5-46 and 310 IAC 12-5-110).
The Division of Reclamation specifies operating requirements on a case-by-case basis. Quarterly ground
water analyses must be submitted, and must continue to be submitted following completion of injection
activities until a demonstration can be made that no adverse effects on the hydrologic balance have
occurred. Each drilled hole, well, or other exposed underground opening identified in the approved permit
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application for use to return coal processing waste or water to underground workings must be temporarily
sealed before use and protected during use (310IAC 12-5-9).
Mechanical Integrity Testing
Not specified by statute or regulation.
Financial Responsibility
Operators are required to post a performance bond with DNR's Division of Reclamation. The
bond is released upon a showing that following cessation of injection activities no adverse effects to the
hydrologic balance have occurred.
Plugging and Abandonment
If no longer in use, a drilled hole or well must be cased, sealed, or otherwise managed to prevent
acid or other toxic drainage from entering ground or surface waters and to minimize disturbance to the
prevailing hydrologic balance (310 IAC 12-5-74 and 310 IAC 12-5-76).
Kansas
Kansas is a UIC Primacy State for Class V wells. It has incorporated the federal UIC regulations
by reference in Kansas Administrative Regulations (KAR) Article 28-46.
Permitting
Mine backfill wells, except for wells backfilling salt caverns, are permitted by rule under KAR 28-
46. Mine backfill wells that are designed to backfill salt caverns are covered by regulations for Class m
salt solution mining wells (KAR 28-43) and also are covered by KAR 28-30.
Siting and construction
There are no siting or construction requirements for mine backfill wells, except for wells backfilling
salt caverns.
Operating requirements
There are no operating requirements for mine backfill wells, except for wells backfilling salt caverns.
The state requires salt cavern backfill well operators to prepare a closure plan and to fill wells with grout,
relying upon requirements for abandonment in 28-30 KAR.
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North Dakota
North Dakota is a UIC Primacy State for Class V wells. Regulations establishing the UIC program
are found in Article 33-25 of the North Dakota Administrative Code (NDAC).
Permitting
Underground injection is prohibited, unless authorized by permit or rule (33-25-01-03 NDAC).
Injection into a Class V well is authorized by rule indefinitely, subject to the requirements of subsections 4
(evidence of financial responsibility), 5 (maintenance of records until 3 years after plugging and
abandonment), and 6 (reporting within 24 hours of any endangerment of a USDW and any noncompliance
with a permit condition or malfunction of the injection system that could cause fluid migration into or
between USDWs) of § 33-25-01-10 and subsection 3 (notice to the Department of Health before
conversion or abandonment of the well) of §33-25-01-12 NDAC. The operator of a Class V well
authorized by rule may be required to apply for and obtain an individual or area permit under specific
circumstances, including cases in which protection of a USDW requires the injection operation to be
regulated by requirements not contained in the rules (33-25-01-16 NDAC).
Siting and Construction
Although not explicitly called for by the Class V requirements, siting and construction requirements
are imposed on mine backfill wells by the Abandoned Mine Lands Division of the Public Service
Commission on a case-by-case basis through the contract terms that the Division includes in its contracts
for backfilling services.. The wells are sited where abandoned underground mines that lie beneath towns or
highways have caused subsidence. The contracts call for the wells to be constructed as 5 inch diameter
holes cased with 3 inch ID. Schedule 40 PVC pipe., and to be 50-70 feet deep. None inject into
USDWs.
Operating Requirements
Operating requirements are established by contract. The contractors who construct and operate
the wells are required to inject grout in conformance with contract specifications, including specifications
concerning grout pressure at the well head, flow rates, pumping rates, and cumulative volume pumped;
grout constituents and consistency; records and recordkeeping; and permitting.
Subsection 5 of § 33-25-01-10 requires records to be maintained concerning the nature and
composition of injected fluids for three years after plugging and abandonment of the well. A single type of
injectate, which has been approved by the Department of Health, is utilized by the Abandoned Mines
Division of the Public Service Commission. Operations are generally concluded within 24 hours. A
qualified inspector is on-site whenever injection occurs.
Subsection 6 of § 33-25-01-10 requires a report within 24 hours of any monitoring or other
indication that any contaminant may cause an endangerment to a USDW, or any noncompliance with a
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permit condition or malfunction of the injection system that may cause fluid migration into or between
USDWs.
Mechanical Integrity Testing
Not specified by statute or regulation.
Financial Responsibility
Subsection 4 of § 33-25-01-10 requires operators to have sufficient financial responsibility and
resources to close, plug, and abandon the underground injection operation in a manner prescribed by the
Division of Water Supply and Pollution Control of the Department of Health. A surety bond, or other
evidence of adequate assurance, in an amount satisfactory to the Department, must be provided.
Plugging and Abandonment
Subsection 3 of § 33-25-01-12 requires notice before conversion or abandonment of the well.
Ohio
Ohio is a UIC Primacy State for Class V wells. Regulations establishing the UIC program are
found in Chapter 3745-34 of the Ohio Administrative Code (OAC). In addition, the Ohio Department of
Natural Resources, Division of Mines and Reclamation, regulates active and abandoned mines.
Permitting
Class V injection wells are defined to include sand backfill and other backfill wells used to inject a
mixture of water and sand, mill tailings or other solids into mined out portions of subsurface mines (3745-
34-04 OAC). Any underground injection, except as authorized by permit or rule, is prohibited. The
construction of any well required to have a permit is prohibited until the permit is issued (3745-34-06
OAC).
Injection into Class V injection wells is authorized by rule (3745-34-13 OAC).
However, a drilling and operating permit is required for injection into a Class V injection well of sewage,
industrial wastes, or other wastes (including backfill), as defined in § 6111.01 of the Ohio Revised Code,
into or above a USDW (3745-34-13 OAC and 3745-34-14 OAC).
Permit applications must include a description of the activities conducted by the applicant; facility
location, listing of other permits under specified programs, where the well is to be drilled, name of the
geological formation to be used and the proposed total depth of the well, type of drilling equipment to be
used, plan for disposal of water and other waste substances, composition of the substance to be injected,
topographic map indicating specified features, and description of the business (3745-34-16 OAC).
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Class V injection well permits may be issued on an area basis. The permit will specify requirements
for construction, monitoring, reporting, operation, and abandonment (3745-34-18 OAC).
Ohio's rules on underground coal mines, administered by the Division of Mines and Reclamation,
require the development of a reclamation plan that must be submitted as part of an application for a permit
to conduct coal mining (1501:13-4-14 OAC). The plan must include a description of the measures to be
used to seal or manage mine openings and to plug, case or manage exploration holes, other bore holes,
wells, and other openings within the proposed permit area (1501:13-4-14(D)(2)(g) OAC). It must include
a ground water monitoring plan, including identification of the monitoring parameters, sampling frequency,
and site locations, sufficient to monitor the suitability of the ground water for current and approved post-
mining land uses and the objectives for protection of the hydrologic balance established in the permit
(1501:13-4-14(F)(l)(a) OAC).
The rules require submission of a subsidence control plan, including a detailed description of the
subsidence control measures that will be taken to prevent or minimize subsidence, such as backfilling voids
(1501:13-4-14(M)((2)(e) OAC). The Ohio rules also adopt the MSHA requirements concerning return of
coal mine wastes to abandoned underground workings. They require the application to contain a plan that
describes the design, operation, and maintenance of any proposed coal processing waste disposal facility.
The plan must describe the source and quality of waste to be stowed, area to be backfilled, percent of the
mine void to be filled, method of constructing underground retaining walls, influence of the backfilling
operation on active underground mine operations, surface area to be supported by the backfill, and the
anticipated occurrence of surface effects following backfill. The application is required to
describe the source of the hydraulic transport mediums, method of dewatering the emplaced backfill,
retention of water underground, treatment of water if released to surface streams, and the effect on the
hydrology. The plan must describe each permanent monitoring well to be located in the backfilled area, the
stratum underlying the mined coal, and the gradient from the backfilled area. Pneumatic backfilling
operations are covered, except they may be exempted from requirements specifying hydrologic monitoring
(1501:13-4-14(N)(l)-(5) OAC).
Siting and Construction
The permit applicant must submit plans for testing, drilling, and construction, and no construction
may commence before permit issuance. Permits will contain conditions specifying construction
requirements (3745-34-27 OAC).
The mining rules specify that each exploration hole, other drill or borehole, shaft, well, or other
exposed mine opening must be cased, sealed, or otherwise managed as approved by the Division of Mines.
Each well or other opening identified in the approved permit application for use to return coal processing
waste or water to underground workings must be temporarily sealed before use and protected during use
by barricades, fences, or other protective devices. When no longer needed, they must be capped, sealed,
backfilled, or otherwise properly managed as required by the Division of Mines (1501:13-9-02 OAC).
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Operating Requirements
Permits contain conditions specifying operation requirements, including maximum injection volumes
and/or pressures and monitoring and reporting requirements (3745-34-27 OAC). Permittees are required
to maintain records of the nature and composition of all injected fluids for three years. Reports of any
noncompliance that may endanger health or the environment, including any monitoring or other information
that indicates that any contaminant may cause an endangerment to a USDW, or any noncompliance with a
permit condition or malfunction of the injection system that may cause fluid migration into or between
USDWs must be reported within 24 hours (3745-34-26 (J) and (K) OAC).
Wells must be inspected before commencing injection. The permittee must provide notice before
conversion or abandonment of the well (3745-34-26 (M) and (N) OAC).
The mining rules also establish a general requirement for protection of the hydrologic system from
mining activities. Backfilled materials are required to be placed so as to minimize contamination of ground
water systems with acid, toxic, or otherwise harmful mine drainage, and to minimize adverse effects of
mining on ground water systems outside the permit area (1501:13-9-04(K) OAC). Discharge of water
into underground mines is prohibited, unless specifically approved by the Division of Mines and by the
federal MSHA, and such discharges are limited to water, coal processing waste, fly ash from a coal-fired
facility, sludge from an acid-mine drainage treatment facility, flue-gas desulfurization sludge, inert material
used for stabilizing underground mines, and underground mine development wastes (1501:13-9-04(Q)
OAC).
Mechanical Integrity Testing
Permits may include a condition prohibiting injection operations until the permittee shows that the
well has mechanical integrity, as specified under § 3745-34-34 OAC ((3745-34-27 OAC). Detailed
specifications for mechanical integrity are included in § 3734-34-34.
Financial Responsibility
Permittees are required to maintain financial responsibility and resources sufficient to close, plug,
and abandon the underground injection operation (3734-34-27 OAC).
Plugging and Abandonment
Permits may include conditions to ensure that plugging and abandonment of the well will not allow
the movement of fluids either into or between USDWs (3745-34-27 OAC). There is no established
closure guidance or policy that lists specific materials or procedures to be employed. Site-specific closure
plans are reviewed by Ohio USEPA.
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Pennsylvania
USEPA Region 3 directly implements the UIC program for Class V injection wells in Pennsylvania.
However, the Bureau of Mining and Reclamation in the Department of Environmental Protection approves
mine backfill well projects. The Department has no specific regulations pertaining to mine backfill wells.
Technical specifications are provided to drilling contractors as part of the contract for mine backfill
projects. The technical specifications vary depending on the well location (i.e., anthracite coal regions or
bituminous coal regions).
Permitting
The drilling contractor is required to obtain all necessary permits, and to comply with all existing
laws, ordinances, rules and regulations relating to the contractor's operations.
Siting and Construction
The Department determines well siting. All work is required to be done under the direction of a
Resident Engineer or the Technical Specifications of the contract. Technical Specifications address
overburden drilling, drilling in material other than overburden, and casing with steel or PVC pipe.
Operating Requirements
Technical specifications address supply, delivery, and injection of grout material. A Department
inspector is onsite during operations.
Mechanical Integrity Testing
Not specified by statute or regulation.
Financial Responsibility
Not specified by statute or regulation.
Plugging and Abandonment
A technical specification addresses sealing of boreholes. The contractor is required to seal
boreholes according to the directions of the Department's representative. Sealing is required by means of a
minimum of 10 feet of cement backfill below the overburden/rock interface or below the bottom of the
smaller casing pipe, whichever is deeper. In the event that "significant" quantities of water are encountered,
the contractor may be required to set the plug below the aquifer and build the seal from that elevation.
September 30, 1999 60
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Texas
Texas is a UIC Primacy State for Class V wells. The Injection Well Act (Chapter 27 of the Texas
Water Code) and Title 3 of the Natural Resources Code provide statutory authority for the UIC program.
Regulations establishing the UIC program are found in Title 30, Chapter 331 of the Texas Administrative
Code (TAC).
Permitting
Underground injection is prohibited, unless authorized by permit or rule (331.7 TAC). Injection
into a Class V well is authorized by rule, although the Texas Natural Resources Control Commission
(TNRCC) may require the owner or operator of a well authorized by rule to apply for and obtain an
injection well permit (331.9 TAC). No permit or authorization by rule is allowed where an injection well
causes or allows the movement of fluid that would result in the pollution of a USDW. A permit or
authorization by rule must include terms and conditions reasonably necessary to protect fresh water from
pollution (331.5 TAC). Sand backfill wells used to inject a mixture of water and sand, mill tailings or other
solids into mined out portions of subsurface mines are specifically defined as Class V wells (331.11
(a)(4)(H) TAC). The state's mining regulations require permits for the construction, use, or operation of a
new shaft, but exempt penetrations or boreholes authorized by the TNRCC under the underground
injection control program and penetrations authorized by the TNRCC whose purpose is the transmission of
concrete slurries, muds, or bulk materials to underground mine workings (329.4 TAC). Therefore the
state's mining backfill wells are regulated under the UIC program and not the mining program.
Siting and Construction
All Class V wells are required to be completed in accordance with the following specifications in
the rules, unless otherwise authorized by the TNRCC:
A form provided either by the Water Well Drillers Board or the TNRCC must be completed.
The annular space between the borehole and the casing must be filled from ground level to a depth
of not less than 10 feet below the land surface or well head with cement slurry. Special
requirements are imposed in areas of shallow unconfmed ground water aquifers and in areas of
confined ground water aquifers with artesian head.
In all wells where plastic casing is used, a concrete slab or sealing block must be placed above the
cement slurry around the well at the ground surface (the rules include additional specifications
concerning the slab).
In wells where steel casing is used, a slab or block will be required above the cement slurry except
when a pitiess adaptor is used. The rules contain additional requirements concerning adaptors.
September 30, 1999 61
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All wells must be completed so that aquifers or zones containing waters that differ significantly in
chemical quality are not allowed to commingle through the borehole-casing annulus or the gravel
pack and cause degradation of any aquifer zone.
The well casing must be capped or completed in a manner that will prevent pollutants from entering
the well.
When "undesirable" water is encountered in a Class V well, the undesirable water must be sealed
off and confined to the zone(s) of origin (331.132 TAG).
Operating Requirements
Not specified by statute or regulation.
Mechanical Integrity Testing
Injection may be prohibited for Class V wells that lack mechanical integrity. The TNRCC may
require a demonstration of mechanical integrity at any time if there is reason to believe mechanical integrity
is lacking. The TNRCC may allow plugging of the well or require the permittee to perform additional
construction, operation, monitoring, reporting, and corrective actions which are necessary to prevent the
movement of fluid into or between USDWs caused by the lack of mechanical integrity. Inj ection may
resume on written notification from the TNRCC that mechanical integrity has been demonstrated (331.4
TAC).
Financial Responsibility
Chapter 27 of the Texas Water Code, "Injection Wells," enacts financial responsibility
requirements. However, the requirement, unless incorporated into a individual permit for a Class V well,
applies specifically only to Class I and Class HI wells (331.142 TAC).
Plugging and Abandonment
Plugging and abandonment of a well authorized by rule is required to be accomplished in
accordance with §331.46 TAC (331.9 TAC). In addition, closure standards specific to Class V wells
provide that closure is to be accomplished by removing all of the removable casing and filling the entire well
with cement to land surface. Alternatively, if the use of the well is to be permanently discontinued, and if the
well does not contain undesirable water, the well may be filled with fine sand, clay, or heavy mud followed
by a cement plug extending from the land surface to a depth of not less than 10 feet. If the use of a well
that contains undesirable water
is to be permanently discontinued, either the zone(s) containing undesirable water or the fresh water zone(s)
must be isolated with cement plugs and the remainder of the wellbore filled with sand, clay, or heavy mud to
form a base for a cement plug extending from the land surface to a depth of not less than 10 feet (331.133
TAC).
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West Virginia
West Virginia is a UIC Primacy State for Class V wells. Regulations establishing the UIC program
are found in Title 47-13 West Virginia Code of State Regulations (WVAC). The state regulates sand
backfill and other backfill wells used to inject a mixture of water and sand, mill tailings or other solids into
mined out portions of subsurface mines as Class V wells (47-13-3.4.5.b. WVAC).
Permitting
Class V injection wells are authorized by rule unless the Office of Water Resources of the Division
of Environmental Protection (DEP) requires an individual permit (47-13-12.4.a. and 47-13-13.2 WVAC).
All backfill wells in the state are required to have either individual permits or, if a group of wells in close
proximity injects into the same abandoned mine, an area permit (Parsons, 1999).
Siting and Construction
Individually permitted wells are subject to case-by-case construction requirements, based on plans
for testing, drilling, and construction submitted as part of the permit application. Wells subject to area
permits also are subject to construction requirements for all wells authorized by the permit (47-13-13.6, .7,
and .4.b.2 WVAC).
Operating Requirements
Owners or operators of Class V wells are required to submit inventory information describing the
well, including its construction features, the nature and volume of injected fluids, alternative means of
disposal, the environmental and economic consequences of well disposal and its alternatives, operation
status, location, and ownership information (47-13-12.2 WVAC).
Individual and area permits specify requirements for monitoring, reporting, and operation for all
wells authorized by the permit (47-13-13.4, .6, and .7 WVAC). Owners and operators must meet the
requirements for monitoring and records (requiring retention of records pursuant to 47-13-13.6.b. WVAC
concerning the nature and composition of injected fluids until 3 years after completion of plugging and
abandonment); immediate reporting of information indicating that any contaminant may cause an
endangerment to USDWs or any malfunction of the injection system that might cause fluid migration into or
between USDWs.
The rules enact a general prohibition against any underground injection activity that causes or allows
the movement of fluid containing any contaminant into USDWs, if the presence of that contaminant may
cause a violation of any primary drinking water regulations under 40 CFR Part 142 or promulgated under
the West Virginia Code or may adversely affect the health of persons. If at any time a Class V well may
cause a violation of the primary drinking water rules the well may be required to obtain a permit or take
other action, including closure, that will prevent the violation (47-13-13.1 WVAC). Inventory requirements
September 30, 1999 63
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for Class V wells include information regarding pollutant loads and schedules for attaining compliance with
water quality standards (47-13-13.2.d.l WVAC).
If protection of a USDW requires, the injection operation may be required to satisfy requirements
for corrective action, monitoring, and reporting, or operation, that are not contained in the UIC rules (47-
13-13.2.C.1.C. WVAC).
Mechanical Integrity
Backfill wells required to obtain an individual permit will be required to demonstrate that the well
has mechanical integrity (47-13-13. 7.h WVAC). Wells permitted by rule or subject to an area permit may
be required to demonstrate mechanical integrity.
Financial Responsibility
A Class V well required to obtain an individual permit will be required to demonstrate financial
responsibility and resources for plugging and abandonment. Evidence of financial responsibility includes
submission of a surety bond or other adequate assurance such as a financial statement of other material
acceptable to DEP.
Plugging and Abandonment
Backfill wells required to obtain an individual permit will be subject to permit conditions pertaining
to plugging and abandonment to ensure that the plugging and abandonment of the well will not allow the
movement of fluids into or between USDWs. A plan for plugging and abandonment will be required (47-
13-13. 7. f WVAC). Wells permitted by rule or subject to an area permit may be required to submit a plan
for plugging and abandonment.
Wyoming is a UIC Primacy State for Class V wells and the Wyoming Department of
Environmental Quality (DEQ) Water Quality Division, has promulgated regulations pertaining to its Class V
UIC program in Chapter 16, Water Quality Rules and Regulations (WQRR). Rules on ground water
pollution control permits are promulgated in Chapter 9, WQRR, but Class V wells are specifically
exempted from coverage by Chapter 9 (Chapter 9 Section 3(a) WQRR). The DEQ Land Quality Division
has promulgated requirements pertaining to coal and non-coal mining.
Permitting
Mining, sand, and backfill facilities (category 5B1) are covered by the General Permit provisions of
the state's Class V rules (Chapter 16 Section 7 WQRR). A general permit is a permit issued to a class of
operators, all of which inject similar types of fluids for similar purposes. General permits require less
information to be submitted by the applicant than individual permits, and do not require public notice for a
September 30, 1999 64
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facility to be included under the authorization of a general permit (Chapter 16 Section 2 (1) WQRR).
General permits specify the subclass of injection facility covered, the geographic area covered, the general
nature of the fluids discharged, and the location of the receiver where the discharge will be allowed.
The state's coal mining regulations (CRR) provide that a permit applicant who is proposing to
return coal-mining waste to abandoned underground workings must:
Describe the design, operation, and maintenance of any proposed coal-processing waste facility,
including flow diagrams and any other necessary drawings and maps, for the approval of the DEQ
and the Mine Safety and Health Administration;
Describe the sources and quality of waste to be stowed, area to be backfilled, percent of the mine
void to be filled, method of constructing underground retaining walls, influence of the backfilling
operation on active underground mine operations, surface area to be supported by the backfill and
the anticipated occurrence of surface effects following backfilling;
Describe the source of the hydraulic transport mediums, method of dewatering the placed backfill,
retainment of water underground, treatment of water if released to surface streams, and the effect
on the hydrologic regime;
Describe each permanent monitoring well to be located in the backfilled area, the stratum
underlying the mined coal, and gradient from the backfilled area except where pneumatic backfilling
operations are exempted from hydrologic monitoring; and
Be approved by MSHA as well as DEQ prior to implementation (Chapter 7 Section 2(b)(xv)
CRR).
Permit applicants for underground coal mines must describe in their permit application measures to
be taken in the mine to prevent or minimize subsidence, including backfilling of voids (Chapter 7 Section
l(a)(v)(C) CRR).
Siting and Construction
Class V facilities may not be located within 500 feet of any active public water supply well,
regardless of whether or not the well is completed in the same aquifer. This minimum distance may increase
or the existence of a Class V well may be prohibited within a wellhead protection area, source water
protection area, or water quality management area (Chapter 16 Section 10(n) WQRR).
A separate permit to construct is not required under Chapter 3 of the WQRR for any Class V
facility. Construction requirements are included in the UIC permit issued under Chapter 16 (Chapter 16,
Section 5 (v) WQRR). In order to be covered by a general permit, an operator must submit the
information required by Chapter 16 Section 6 (i), (ii) and (iii), which includes a brief description of the
nature of the business and activities to be conducted, information about the operator, and the location of the
September 30, 1999 65
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facility. Additional information also may be required as a condition of the general permit. The rules specify
that certain construction and operating requirements must be included (see operating requirements)
(Chapter 16 Section 10(d) WQRR).
A facility is covered by a general permit as soon as the DEQ has issued a general statement of
acceptance to allow the construction and operation of the facility (Chapter 16 Section 7 WQRR). The
facility must meet construction requirements in Chapter 16 Section 10 WQRR, submit notice of completion
of construction to the DEQ, and allow for inspection upon completion of construction prior to commencing
any injection activity (Chapter 16 Section 5(c)(I)(U) WQRR).
Operating Requirements
The general permit conditions include a requirement that the permittee properly operate and
maintain all facilities and systems, furnish information to the DEQ upon request, allow inspections,
establish a monitoring program pursuant to Chapter 16 Section 11 WQRR and report monitoring results,
give prior notice of physical alterations or additions, and orally report confirmed noncompliance resulting in
the migration of injected fluid into any zone outside of the permitted receiver within 24 hours and follow up
with a written report within 5 days. Detailed information requirements also are included in the general
permit, including a requirement to monitor the injectate at a specified frequency and report the information
to DEQ (Chapter 16 Section 7WQRR). A continuous monitoring program normally will not be required,
but monitoring frequency will depend on the ability of the facility to cause adverse environmental damage or
affect human health (Chapter 16 Section 7(e)(v) WQRR).
The rules (Chapter 16 Section 10(d) WQRR) also specify that the permittee must demonstrate:
Mechanical integrity of any well designed to remain in service for more than 60 days;
Provision for controlling the type of material injected and to insure that no hazardous waste is
injected;
Leak detection in all surface piping;
Provision for insuring that the backfill remains within the permitted area of injection; and
Provision to ensure that the injection does not cause a ground water standards violation for the
class of use of the receiver.
The mining regulations further provide that surface entries and accesses to underground workings
must be located, designed, constructed, and utilized to prevent or control gravity discharge of water from
the mine in excess of state or federal water quality standards (Chapter 7 Section 2(b)(ii) CRR).
Public notice must be given of any proposed measures to prevent or control adverse surface
effects, such as subsidence (Chapter 7 Section 3(a)(ii) CRR).
September 30, 1999 66
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Mechanical Integrity
Permittees are required to adopt measures to insure the mechanical integrity of any well designed to
remain in service for more than 60 days. No specific regulatory requirements on MIT have been enacted;
the specific tests to be used will depend on the specific well conditions.
Financial Responsibility
Not specified by statute or regulation.
Plugging and Abandonment
Wells may be abandoned in place if it is demonstrated to DEQ that no hazardous waste or
radioactive waste has ever been discharged through the facility, all piping allowed for the discharge has
either been removed or the ends of the piping have been plugged in such a way that the plug is permanent
and will not allow for a discharge, and all accumulated sludges are removed from holding tanks, lift stations,
or other waste handling structures prior to abandonment (Chapter 16 Section 12 (a) WQRR).
September 30, 1999 67
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