United States
Environmental
Protection
Agency
Office of Water Office of Solid Waste EPA
Regulations and and Emergency 530-SW-87-O05 R
Standards (WH-552) R«»P?n««
Washington, D.C. Washington, D.C.
20460
20460
V>EPA
TECHNICAL REPORT: APPENDIX B
EXPLORATION, DEVELOPMENT, AND PRODUCTION
CRUDE OIL Arli NATURAL GAS
SAMPLI
ATEGY
tnvi.oim.enul Pn*>ction
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OIL AND GAS EXPLORATION, DEVELOPMENT, AND PRODUCTION
SAMPLING STRATEGY - DRAFT
JANUARY 31, 1987
PREPARED FOR
U. S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF WATER - INDUSTRIAL TECHNOLOGY DIVISION
401 M STREET, SW (WH-552)
WASHINGTON, D. C. 20460
PREPARED BY
CENTEC CORPORATION
11260 ROGER BACON DRIVE
RESTON, VIRGINIA 22090
U.S. Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevard, 12th Floor
Chicago, II 60604-3590
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LIST OF ABBREVIATIONS
DOE — Department of Energy
EPA — Environmental Protection Agency
ITD — Industrial Technology Division
OSW — Office of Solid Waste
OWRS — Office of Water Regulations and Standards
QA — Quality Assurance
QC — Quality Control
RCRA — Resource Conservation and Recovery Act
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TABLE OF CONTENTS
INTRODUCTION
BACKGROUND .
SAMPLING DESIGN 7
Objective 7
Target Populations 8
Selection of Analytes 16
Sample Size 17
Site Selection Process 20
Implementation of the Sampling Design 27
STATISTICAL ANALYSIS 31
Sampling Design 31
Precision and Accuracy 33
CONCLUSION 35
REFERENCES 37
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LIST OF FIGURES AND TABLES
Figure 1
Figure 2
Site Selection Zones
Example of Process Used for Selection
of States Within Zones
10
24
Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
1984 Oil and Gas Production and Drilling
Activity
Summary of Analytes
Distribution of Types of Sample Sites . .
Percentage (by Zone) of 1984 Oil and Gas
Production and Drilling Activity
Planned Distribution of Probability Sites
And Specifically-Selected Sites Among Zones
Distribution of Probability Sites and
Specifically-Selected Sites Among Zones
12
18
19
23
28
29
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INTRODUCTION
This document is a revision of the May, 1986, EPA Oil and Gas
Exploration, Development, and Production, Sampling Strategy -
Draft (EPA, 1986). It reflects actual implementation of the
sampling strategy and incorporates comments regarding the May
1986 draft document. The EPA strategy for sampling wastes from
oil and gas exploration, development, and production is presented
herein. This strategy is a part of the Office of Solid Waste
(OSW)/ Office of Water Regulations and Standards (OWRS)
Exploration, Development, and Production of Crude Oil and Natural
Gas Field Sampling and Analysis Project, which in turn is part of
the OSW Oil, Gas, and Geothermal Exempt Waste Study. This
document presents the sampling project objectives, the sampling
design, the development of a concept of geographical "zones" with
common characteristics, and the details of selection of sample
sites.
EPA sampled wastes from the oil and gas extraction industry {see
the "Regulatory Background" section of the "Technical Report on
the Exploration, Development, and Production of Crude Oil and
Natural Gas" (EPA-530-SW-87-005)). In the process of oil and gas
extraction, liquid and solid wastes are generated. These wastes
are disposed in pits, injected underground, and/or discharged to
the environment in other ways (discharge water, for example). It
is estimated that there are 885,077 oil or gas wells producing in
the United States (IPAA, 1986). Prior to 1986, approximately
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70,000 wells were drilled annually. For 1986, an additional
40,000 drill sites were created (Oil and Gas Journal, 1986).
Each of these sources generates waste.
The first priority of the sampling project was to develop data
nationwide for the range of constituents in wastes from drilling
and production operations. This was achieved in the design of
the project by creating clusters of states, termed "zones," that
reflect geological formation, geographical distribution, drilling
and production activity, climate, and drilling methods. Zone
characteristics are described in detail in the "Sampling Design"
section of this document.
The sampling design also included identification of a target
population, selection of analytes, sample size, and the process
used for site selection. For example, after development of the
concept of zones, EPA. addressed the characteristics of the sites
to be sampled in each zone. To select sites within a zone, EPA
chose a random approach. This approach used randomization
techniques to select 69.4 percent of the samples and a directed
approach to select the remaining sites. The directed approach
assured that sites with certain characteristics would be sampled.
The "Statistical Analysis" section of this document gives the
technical details that support the site selection.
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BACKGROUND
EPA. regulates or makes determinations as to whether to regulate
the oil and gas extraction industry under several major
environmental statutes. These statutes include the Clean Water
Act (i.e., appropriate effluent limitations guidelines), the Safe
Drinking Water Act (i.e., the Underground Injection Control
program) and the Resource Conservation and Recovery Act (i.e.,
the regulatory determination under RCRA Section 3001(b)(2)(B),
which uses information from the study under Section 8002(m))
(see the "Regulatory Background" section of the "Technical Report
on the Exploration, Development, and Production of Crude Oil and
Natural Gas" (EPA-530-SW-87-005)). Therefore, this project was
designed as a screening sampling project to obtain information
fulfilling some requirements mandated by RCRA and the Clean Water
Act.
EPA conducted a comprehensive literature search (of both
published and unpublished information) regarding the oil and gas
industry. No nationwide waste characterization projects had been
conducted to test for organic analyses and for RCRA character-
istics (i.e., ignitability, reactivity, corrosivity, and
extraction-procedure toxicity). Therefore, the Agency decided to
undertake a sampling project to develop information for the study
required under RCRA Section 8002(m), which would be used in
making the regulatory determination under RCRA Section
3001(b)(2)(B). The sampling project was also intended to gather
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more information for the Agency's review of the existing effluent
limitations guidelines for the oil and gas industry and, if
appropriate, to develop future effluent limitations guidelines.
The purpose of this document is to describe the design and
rationale of the field sampling project. It includes the
criteria for site selection for the Environmental Protection
Agency (EPA) oil and gas sampling project. The objectives are
also described.
The sampling project produced site specific data on the sources,
volumes, and constituents of wastes from exploration, develop-
ment, and production of crude oil or natural gas. The results
are included in "Technical Report on the Exploration,
Development, and Production of Crude Oil and Natural Gas" (EPA-
530-SW-87-005). The sampling project gathered information about
the wastes from this industry and the control and disposal
practices being utilized by the industry.
The project did not include sampling of wastes from geothermal,
tar sands, or sampling of surface water, groundwater, or air.
For this sampling project, the Agency decided to concentrate its
available resources on characterizing drilling wastes and
produced water.
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Potential sample sites were selected by working with state and
regional authorities to identify candidate sites. These sites
were then used in the randomized site selection process.
Oil and gas wastes were sampled, preserved, and shipped according
to the EPA Sampling Plan and Sampling Quality Assurance/Quality
Control Plan (Appendix G of the EPA Technical Report, (EPA-530-
SW-87-005)). This QA/QC plan was specifically designed for this
sampling project. Analytes are listed in the List of Analytes
(Appendix F of the EPA Technical Report (EPA-530-SW-87-005)).
In addition to the sampling and analysis, reports describing
operations at each site were prepared. These reports contain
detailed site-specific data, including descriptions, sampling
information, engineering data, waste volumes, disposal practices
utilized, and cost information (Appendix C of the EPA Technical
Report (EPA-530-SW-87-005)).
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SAMPLING DESIGN
OBJECTIVE
The objectives of the sampling project are:
o To provide data to be included in the report to Congress
on wastes associated with oil and gas exploration,
development, and production activities as required by
RCRA
o To provide nationwide data on sources and volumes of oil
and gas wastes
o To provide information on the complexity and diversity of
the wastes generated by the industry, current disposal
practices and ultimate treatment
o To identify characteristics and constituents of the
wastes streams and to estimate the variability of
these waste streams
o To provide data that can be used in the design of a
larger, more comprehensive sample survey of the industry
The first priority of the sampling project was to develop data
nationwide for the range of constituents in wastes from drilling
and production operations. This design priority addressed four
of the objectives listed above. It was achieved through
execution of the sampling design described in this section. The
sampling design included identification of a target population,
selection of analytes, sample size, and the process used for site
selection.
Another goal of this project was to increase EPA's knowledge of
industrial processes such as drilling and production by gathering
technical information at each of the sample sites. This
objective was achieved by collecting relevant state and federal
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permits issued for'sample sites, collecting geological maps of
the areas, and by preparing reports describing the operations at
each sample site.
Another goal was to gain information about centralized treatment
facilities and centralized disposal pits handling oil and gas
wastes. The sampling design limited sampling to those facilities
designed solely for treatment of oil and gas wastes.
TARGET POPULATIONS
Drill Sites and Production Sites
The sampling design was based on identification of the target
populations for. drill sites and production sites. In the oil and
gas industry, total annual drilling activity was normally about
70,000 new drill sites per year, but slumped to about 40,000 in
1986 (Oil and Gas Journal, 1986). Total annual U.S. production
was estimated at 2.8 billion barrels of oil from 646,735 oil
wells, and 12,586,200 MMCF of gas from 238,342 gas wells in 1985
(IPAA, 1986). Many difficulties were apparent in attempting to
sample a large and heterogeneous population with the limited
sample size available in this program.
For these reasons drill site and production site populations were
divided into eleven zones, which were composed of groups of
individual states (refer to Site Selection Process for more
information regarding the importance of this decision).
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Development of zones. Clusters of states were defined according
to geological formation, geographic diversity, drilling and
production activity, climate, topography, drilling methods used,
and groundwater aquifers in certain areas. The U.S. was
subdivided into 11 zones, each representing a geologic and
geographic region of influence (Figure 1). State borders were
used as zone boundaries to conform with state record keeping and
regulations. The design of the sampling project dictated that
only the most current drilling and production records be
utilized. The most current records are kept largely by state
agencies. State agencies generally have site information
available on a day-to-day basis.
Geological distribution was the primary criterion for development
of zones. Geological formations have characteristics which
require adaptation of drilling techniques and/or drilling media.
Thus, geologic distribution directly affects drilling waste
composition. For instance, in tight hard-rock formations air
drilling (using air, other gas, mist, foam, or aerated mud) can
be used; in porous sandy formations rotary drilling (using
water-base or oil-base muds) may be necessary. Combinations of
drilling methods/media may be used as different geologic zones
are encountered.
The second criterion for development of zones was geography.
This sampling project was designed for nation-wide coverage of
the oil and gas extraction industry.
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Finally, consideration was given to climate, topography, drilling
methods used, and groundwater aquifers in certain areas.
Description of zones. Two test areas, Zone 1 and Zone 3 on
Figure 1, have essentially no drilling or production. Other
states with little or no production are necessarily included in
zones that were linked by similar characteristics.
A summary of drilling and production figures for 1984 is shown in
Table 1. A description of the distinctive features of each zone
is presented below.
It should be noted that Ohio was placed in Zone 5 when the zones
were created and for site selection in this project. However,
Ohio will be considered a member of Zone 2 in the future. This
change is due to comments received by EPA at a meeting in July
1986 with industry representatives and state officials. This
change occurred after site selection was complete and sampling
was underway. Thus, Ohio is grouped with Zone 5 states in
following discussions of sampling activities.
Zone 1. On Figure 1, Zone 1 is a non-producing zone. No
sampling was planned for the states in Zone 1.
Zone 2. Zone 2 includes New York, Pennsylvania, West
Virginia,Virginia, Kentucky, and Tennessee. Zone 2 encompasses
the northern part of the Appalachian Basin, where mountainous
terrain, hard-rock geology, and net precipitation combine to
create a difficult environment for waste disposal. Air drilling
is a predominant exploratory and developmental practice.
Produced water injection is practiced primarily in large fields.
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Table 1. 1984 Oil and Gas Production and Drilling Activity
And Gas Liquids Natural Gas
Production1 Production2
(iribbl) (nibbl/COE)
Zone 2
Kentucky3
New York
Pennsylvania3
Tennessee
Virginia
West Virginia
TOTAL
Zone 4
Alabama
Arkansas3
Florida3
Louisiana
Mississippi3
TOTAL
Zone 5
Illinois3
Indiana3
Ohio
Michigan3
TOTAL
Zone 6
Kansas
Nebraska
North Dakota
South Dakota
TOTAL
Zone 7
Oklahoma
Texas
TOTAL
Zone 8
Montana3
Wyoming
TOTAL
Zone 9
Colorado
New Mexico
Utah
TOTAL
Zone 10
California
Zone 11
Alaska
J-IOCC, 1985
2DOE, 1985
3IOCC, 1984
4API, 1986
11,635
952
4,491
968
0
3,303
16,858
19,878
21,519
23,401
187,371
31,613
283,782
28,873
5,320
14,971
30,888
80,052
75,723
6,470
52.654
1,343
136,190
168,604
1,165,757
1,334,361
30,063
127,116
157,179
29,102
79,335
38,054
146,491
412,400
631,079
8.064
4.660
20.436
0.863
1.432
24.808
60.263
23.646
23.284
4.101
357.267
34.848
443.146
0.178
0.023
26.080
24.899
51.150
81.111
0.397
13.566
0.431
95.505
360.912
1,012.337
1,373.249
9.774
103.524
113.298
36.988
163.280
31.597
231.875
76.220
52.216
Tots! Production
(mbbl)
11,643
957
4,511
969
1
3,327
21,408
19,902
21,542
23,405
187,728
31,648
284, 225
28,873
5,320
14,997
30,913
80,103
75,804
6,470
52,668
1,343
136,285
168,965
1,166,769
1,335,734
30,073
127,220
157,293
29,139
79,498
38,086
146, 723
412,476
631,131
Total Wells4
Drilled
3,546
517
3,261
307
66
1,821
9,518
365
866
20
5,775
606
77612
2,577
918
4,677
1,077
9,249
6,169
361
692
43
77265"
9,241
26,103
35,344
804
1,680
27484
1,778
1,609
486
37873
3,261
155
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States in Zone 2 are permitting publicly-owned treatment works
(POTWs) and commercial facilities to treat wastes associated with
oil and gas production. As of June 1986, four or five
commercial centralized treatment facilities were dedicated to oil
and gas waste treatment in Zone 2. There are approximately six
additional centralized treatment facilities in the planning
stage.
Total zone production in 1984 was 21,408 thousand barrels
(including natural gas as crude oil equivalent) (IOCC, 1985).
Total 1984 drilling activity was 9,518 wells drilled (API, 1986).
Zone 3. On Figure 1, Zone 3 is considered a non-producing
zone.No sampling was planned for the states in Zone 3.
Zone 4. Zone 4 is formed by Arkansas, Louisiana,
Mississippi, and Alabama. It includes the southern tip of the
Appalachian Basin, the Black Warrior Basin, the Mississippi Salt
Dome Basin, the eastern portion of the Gulf Coast Salt Dome
Basin, and several smaller basins and uplifts. It is a net
precipitation area, with major oil and gas production from both
onshore and coastal regions. Drilling is predominately conducted
with mud systems. Mud recycling and mud injection are
practiced. Muds from coastal and offshore oil and gas operations
which are unacceptable for offshore disposal are brought to Zone
4 for treatment, recovery, or disposal. Zone 4 also includes
natural gas production from coal deposits found in the Black
Warrior Basin. Injection is a common practice for enhanced oil
recovery, for produced water disposal, and for drilling mud
disposal. Construction, reclamation, and permanent disposal of
drilling muds are handled differently from state to state in
Zone 4.
Total zone production in 1984 was 284,225 thousand barrels
(including natural gas as crude oil equivalent). Total 1984
drilling activity was 7,632 wells drilled.
Zone 5. Zone 5 includes Michigan, Indiana, Illinois,
Wisconsin,Minnesota, Iowa, and Missouri. Three major basins in
this zone are the Illinois Basin, Michigan Basin, and the
Appalachian Basin. Mud drilling and air drilling are both
practiced. One unique situation in Michigan is that there are
areas where drilling must pass through substantial salt
formations to reach oil and gas formations. Wastes from these
drilling operations are typically salt-saturated, and may contain
organics and several tons of salt.
Total zone production in 1984 was 80,052 thousand barrels
(including natural gas as crude oil equivalent) (IOCC, 1985).
Total 1984 drilling activity was 9,239 wells drilled (API, 1986).
Zone 6. Zone 6 includes North Dakota, South Dakota,
Nebraska, and Kansas. In the Dakotas, the Williston Basin is the
major producing formation. Nebraska production is from the
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Denver Basin. Kansas produces from the Forest City Basin in the
east, and several smaller reservoirs in the west. Water-base mud
drilling predominates. Drilling pit contents are land-spread
after the supernatant has evaporated. Most reserve pits must be
reclaimed after land-spreading. Much of the production in Zone 6
is from stripper wells. Hydrogen sulfide and produced water
salinity is extremely high in the Dakotas, discouraging wildlife
and agricultural use of the wastes. Salinity and hydrogen
sulfide are low in Nebraska and Kansas.
Total zone production in 1984 was 136,285 thousand barrels
(including natural gas as crude oil equivalent) (IOCC, 1986).
Total 1984 drilling activity was 7,265 wells drilled (API, 1986).
Zone 7. Texas and Oklahoma combine to form Zone 7.
Although water-base drilling operations predominate in Texas and
Oklahoma, this zones uses oil-base muds as well. Production is
from a dozen major basins, dominated by the Gulf Coast Salt Dome
Basin, Permian Basin, and Anadarko Basin.
In Texas, reserve pit wastes may be land-applied if the chloride
content is less than 500 mg/L (inland). Oklahoma allows disposal
of drilling wastes by annular injection, evaporation of reserve
pits, or in centralized offsite pits. Injection of produced
water is practiced in most areas of Texas, except in coastal
areas where discharges are allowed. Produced water disposal pits
are banned in Texas. In Oklahoma, centralized offsite pits are
commonly used for disposal of produced water and drilling muds.
Oklahoma is grouped with Texas because they share climate,
geology, and terrain.
Total zone production in 1984 was 1,335,734 thousand barrels
(including natural gas as crude oil equivalent) (IOCC, 1985).
Total 1984 drilling activity was 35,344 wells drilled (API,
1986).
Zone 8. Zone 8 contains Montana, Wyoming, and Idaho.
Montana and Wyoming share the Big Horn Basin and Powder River
Basin. Idaho, a non-producing state, is also included. Lined
and unlined reserve pits are permitted by regulatory authorities
in Zone 8. Drilling waste pit reclamation may include treatment
and land application of the supernatant. This land application
usually takes the form of trenching in a radius around the pit,
or land-spreading (sometimes by spraying). Produced water is
injected or discharged under the provisions of the Agricultural
and Wildlife Water Use Subcategory of the onshore segment of the
oil and gas extraction industry effluent limitations guidelines
(EPA, 1979).
Total zone production in 1984 was 157,293 thousand barrels
(including natural gas as crude oil equivalent) (IOCC, 1985).
Total 1984 drilling activity was 2,484 wells drilled (API, 1986).
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Zone 9. Zone 9, commonly known as the "four corners" area,
includes Colorado, Utah, Nevada, Arizona, and New Mexico.
Production is primarily from the San Juan Basin, Paradox Basin,
and Denver Basin. Drilling wastes are disposed onsite by
evaporation and tilling into the soil. Colorado and New Mexico
also permit centralized offsite pits for disposal of drilling
wastes and produced water. Produced water is almost entirely
injected. Surface methods are used in Utah for produced water
disposal. The Agricultural and Wildlife Water Use subcategory of
the onshore segment of the oil and gas extraction industry
effluent limitations guidelines is also applicable to this zone
(EPA, 1979).
Total zone production in 1984 was 146,723 thousand barrels
(including natural gas as crude oil equivalent) (IOCC, 1985).
Total 1984 drilling activity was 3,873 wells drilled (API, 1986).
Zone 10. Zone 10 includes California, Oregon, and
Washington. California's San Joaquin Basin, Santa Maria Basin,
and Ventura Basin are the major producing zones for oil and gas.
Secondary and tertiary recovery production technologies are
common in Zone 10. Oregon is a newcomer to oil and gas
production, producing from several basins. Washington is a
non-producing state. Drilling wastes may be evaporated or
land-farmed except in California. Produced water is injected for
enhanced recovery, or may be disposed in evaporation/percolation
ponds. Use of produced water for irrigation is also allowed.
All three states have some geothermal exploratory activity, and
some active utilization of geothermal energy.
Total zone production in 1984 was 412,476 thousand barrels
(including natural gas as crude oil equivalent) (IOCC, 1985).
Total 1984 drilling activity was 3,261 wells drilled (API, 1986).
Zone 11. Alaska and Hawaii form Zone 11. Hawaii is a
non-producing state. In Alaska, South Central and North Slope
reserves produce oil and gas from wetlands. The South Central
area includes the Kenai Peninsula and Cook Inlet. Cook Inlet
drilling wastes and produced water are disposed offshore. Kenai
reserve pits are generally unlined. On the North Slope, drillers
are required to hold reserve pit wastes for one freeze/thaw
cycle, but are then permitted to discharge the supernatant to the
tundra. Annular injection is sometimes used for drilling wastes
and stimulation fluids. Lined reserve pits are required on
federal land.
Total zone production in 1984 was 631,131 thousand barrels
(including natural gas as crude oil equivalent) (IOCC, 1985).
Total 1984 drilling activity was 155 wells drilled (API, 1986).
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Thus, target populations for drill sites and production sites
were compartmentalized into nine zones for consideration in the
selection of sample sites (refer to Site Selection Process).
Centralized Pits and Centralized Treatment Facilities. EPA
decided to sample specifically identified sites to develop
preliminary information regarding these types of sites. The
Agency is interested in gathering information about the types of
processes, characteristics of commingled wastes, and the
characteristics of treated commingled wastes.
SELECTION OF ANALYTES
The analytes selected for testing in this program were those on
various regulatory lists or those specific to characterization of
wastes from this industry. The regulatory lists from which the
pollutants were taken were the:
Priority Pollutant List [NRDC vs Train, 8 ERG 2120
(DDC1976)]
Priority Pollutant Appendix C List [ibid.]
RCRA Appendix VIII List [50 FR 1999]
Michigan List [49 FR 49793]
Superfund Hazardous Substances List
Analytes to be added to the RCRA Appendix VIII List
(EPA memo from Robert April to Marcia Williams, 20
Dec 85)
Paragraph 4(c) List (NRDC vs Train, op. cit.;
high priority compounds detected in wastewaters)
List of Analytes (Appendix C of the EPA Technical
Report (EPA-530-SW-87-005). These are analytes specific
to EPA - Industrial Technology Division programs)
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This list includes all classical analytes and metals but does not
list every individual organic compound.
A few specific organic compounds not on the list were tested for
in wastes from centralized treatment facilities, from centralized
disposal pits, and from certain other sources. These compounds
were all of the tetra- through octa-chlorodibenzo-p-dioxins and
furans (136 compounds in all). Pesticides and herbicides also
were tested for in wastes from centralized treatment facilities,
from centralized disposal pits, and from certain other sources.
The analytes are summarized in Table 2.
SAMPLE SIZE
The total number of sample sites was planned to be 48; 49 sites
were actually sampled in this project. The Agency distributed
the number of sample sites among the types of sites needed as
shown in Table 3.
Eighty-six percent of the sites sampled were active drill or
production sites. This allocation reflected the Agency's
interest in developing information regarding drill wastes and
produced water. Fourteen percent of the sites sampled were
centralized waste storage or treatment facilities. This
allocation addressed the need to develop information regarding
long term storage of wastes, commingling of wastes, and/or
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Table 2. Summary of Analytes
Number of Analytes
Organics
Volatiles by GCMS
Isotope dilution 32
Reverse search 23
Semi-volatiles by GCMS
Isotope dilution 82
Reverse search 94
Dioxins and furans by GCMS 136
Pesticides by GC
Electron capture detector (BCD) 39
Flame photometric detector (FPD) 35
Herbicides by GC/ECD 3
Total organics 444
Metals
Atomic absorption 6
Calibrated Inductively Coupled Plasma (ICP) 21
ICP screening 41
Total metals 68
Conventionals by wet chemistry 19
RCRA (Corrosivity, Ignitability, Reactivity) __3
Total number of analytes 534
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Table 3. Distribution of Types of Sample Sites
Number of
Type of Site Sites Sampled
Drill sites 19
Production sites
Produced water 21
Tank bottom sludges 2
Centralized pits 4
Centralized treatment 3_
Total 49
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treating wastes from multiple oil and/or gas exploration,
development, or production sources.
The sampling design, which specifies types of sites, numbers of
sites, and the numbers and types of samples to be collected, was
restricted by:
o Funding
o Sampling time span (June-September, 1986)
o Availability of qualified sites
o Logistics
SITE SELECTION PROCESS
The site selection process was designed to handle two types of
sites: (1) sites randomly selected, and (2) sites specifically
selected on the basis of judgement. Known populations were
available for use in the site selection process for drill sites
and for production sites. These populations were utilized for
development of a protocol that produced randomized site
selection. A description of that protocol follows in "Random
Site Selection Process." Sixteen of nineteen total drill sites
were selected randomly. Seventeen of twenty-one total production
sites were selected randomly. The remaining sites were reserved
for specific site selection.
Centralized pits and centralized treatment facilities were
selected on the basis of judgement. About 15 percent of all
drill sites and 19 percent of all production sites were also
specifically selected. These sites were used to supplement equal
distribution of sites, to examine particular practices of
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interest, or to replace randomly selected sites which could not
be sampled. The site selection rationale for specifically
selected sites is described in "Specific Site Selection Process."
Random Site Selection Process
Random site selection was conducted in three tiers. The first
tier was based on the zones described in the section entitled
"Target Populations" and in Figure 1. Randomly selected sites
were distributed uniformly across the zones to ensure coverage.
Eighteen potential drill sites were assigned evenly across the
U.S., two to each active zone (see Implementation of Site
Selection for final account of sites sampled). A similar process
was used to identify zones for production sample sites. The
first nine production sites were distributed equally through the
zones, one site to each active zone. The remaining samples were
randomly distributed through the zones (see Figure 2 for example
of random selection of states within zones; a similar process was
used to select which zones had two production sites.)
The second tier identified the state in which each site was to be
located. This was essential to the sampling design since state
agencies provided current population data. Populations were
weighted within each zone according to statewide drilling or
production activity at the time of site selection. Drill sites
were weighted on the basis of total wells drilled in each state.
Production sites were weighted on the basis of total annual
hydrocarbon production. The basis for drill site and production
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site weighting is presented in Table 4. It should be noted that
1984 data were the most recently published data at the time of
site selection.
As shown in Table 4, probabilities were assigned as a function of
percent of zone drilling activity for drill sites and as a
percent of zone hydrocarbon production for production sites.
Using these probabilities and a random number table (Sorcim/IUS,
1984), two states were selected for drill site sampling in each
zone. (In four cases the same state was randomly selected for
both drill sites.) A similar process was used to identify states
for production samples. An example of the selection process is
presented in Figure 2.
In the third tier, EPA requested assistance from state agencies
to develop lists containing potential sites for the scheduled
date of each sample. Each list needed at least five potential
sites unless fewer than five appropriate sites were available.
(The actual size of the lists ranged from one to several
thousand.) For drill sites, EPA requested a list of sites in a
specific basin, with the well at or near completion. For
production sites, EPA requested a list of active production sites
in a specific basin. EPA assigned sequential integers to the
members of each list. (In some cases, unique state permit
numbers were used for site selection.) Using a random number
table (Sorcim/IUS, 1984), each site was selected from a list of
potential sites. A second site was also randomly selected from
B-22
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Table 4. Percentage (by Zone) of 1984 Oil and Gas Production
And Drilling Activity
Percent of Zone Percent of Zone
Production Drilling
Zone 2
Kentucky
New York
Pennsylvania
Tennessee
Virginia
West Virginia
TOTAL
Zone 4
Alabama
Arkansas
Florida
Louisiana
Mississippi
TOTAL
Zone 5
Illinois
Indiana
Michigan
Ohio
TOTAL
Zone 6
Kansas
Nebraska
North Dakota
South Dakota
TOTAL
Zone 7
Oklahoma
Texas
TOTAL
Zone 8
Montana
Wyoming
TOTAL
Zone 9
Colorado
New Mexico
Utah
TOTAL
Zone 10
California
Zone 11
Alaska
54
4
21
5
0
16
100
7
8
8
66
11
100
36
7
38
19
100
55
5
39
1
100
13
87
100
19
81
100
20
54
26
100
100
100
B-23
37
6
34
3
1
19
100
5
11
0
76
8
100
28
10
12
50
100
35
5
9
1
100
26
74
100
32
68
100
46
41
13
100
100
100
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STEP 1: Choose a zone for selection of states within zones.
In this example, Zone 7 was chosen.^
STEP 2: Using the most recent published reports, assign
sequential integers to each state within Zone 7 (our
example), in proportion to the type of activity and
sample. In this example, 26 integers (sequentially 001
through 026) were assigned to Oklahoma. This
assignment corresponds to Oklahoma's 26 percent of the
drilling activity in Zone 7. The next 74 integers (02?
through 101) were assigned to Texas (corresponding to
Texas' 74 percent of the zone's drilling activity).
NOTE: For selection of production sites, integers were
assigned proportional to percent of zone
production.
STEP 3: Use a random number table to select the appropriate
number of sites (see below). In this example, two
drill sites were to be selected. As can be seen on
the random table below, the first two integers
encountered between 001 and 101 were 039 and 098.2
Both integers fell between 027 and 101; thus, both
sites were selected to be sampled in Texas.
.4562287 .0285848 .5731043 .6380392 .7548944 .3618006 .2250784 .1348046
.2155620 .9452450 .1556293 .4536573 .7071668 .3958532 .4816542 .2067786
.4938779 .7347435 .8429384 .3673052 .9131544 .1442967 .0370935 .6366895
.1168452 .6056545 .7068156 .3519544 .9943023 .2877842 .9730231 .6278825
.056@ .0754877 .4359653 .4956858 .9607196 .0899488 .2435953 .4494166
.7653243 .6655329 .1916084 .9510508 .8813455 .1681906 .0238223 .9777881
.3698315 .2289397 .6174680 .1835056 .9382041 .2755072 .4383974 .7996694
.3141360 .2669989 .3748569 .8571130 .1391276 .3909494 .8686801 .5850169
.1252473 .6559180 .9897554 .7194242 .9280202 .0025309 .3163665 .5458144
.8458867 .7358407 .9800887 .5110891 .8861431 .7678877 .9859674 .2459249
.1100185 .752309BJ .0387286 .8410738 .1342213 .7776624 .2078029 .9753584
.8162183 .0272849 .4106072 .3258962 .7370280 .1285043 .0630326 .8790774
.1424900 .8112515 .4064430 .8053689 .6711154 .8894297 .1787127 .3390880
.3318185 .4773176 .6647042 .0880304 .0038059 .4757344 .4668019 .3502432
.6895318 .1914800 .9350022 .8752769 .4096173 .2021570 .2696246 .7030698
.2841714 .5214285 .1785454 .3206702 .0837761 .4720133 .0016623 .2077818
.7635107 .4388415 .8551911 .8988911 .3613879 .1734906 .6863279 .7909816
•"-Zone 7 is chosen as an example. The process was followed for
selection of states within each zone.
2The random numbers presented here represent an excerpt from a
table generated using Supercalc®3 software from the Sorcim/IUS
Corporation (Sorcim/IUS, 1984).
Figure 2. Example of Process Used for Selection of States Within
Zones.1
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the same list. The second site served as a back-up site when the
primary site proved inaccessible or inappropriate. For example,
flooding prevented access to one site. At another site the
sampling team arrived to find a four month old producing well at
the "drill site" which was selected. In both cases, the back-up
site was sampled.
Details of the site selection process for each site is presented
in trip reports prepared for each site. These reports are
presented in "Technical Report on the Exploration, Development,
and Production of Crude Oil and Natural Gas" (31 January 1987).
Specific Site Selection Process
A total of 30.6 percent of all sites in the sampling project were
specifically selected on the basis of judgement. All centralized
pits and centralized treatment facilities were specifically
chosen in addition to several drilling, production, and tank
bottom sites.
Other specifically selected sites were used to supplement equal
distribution of sites, to examine particular practices of
interest, or to replace random selected sites which could not be
sampled. Specifically selected sites included three drilling
sites, four production sites, one tank bottom site, four
centralized pits, and three centralized treatment facilities.
B-25
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One drill site was specifically selected in each of Zones 7, 10,
and 11. In Zone 7, a drill site was specifically selected
because the random site selection process did not choose
Oklahoma, a state with considerable drilling activity (see Table
1). In Zones 10 and 11, circumstances of site availability,
scheduling, and accessibility compelled specific selection of one
drill site in each zone.
One production site was specifically selected in Zone 7 and three
sites were specifically selected in Zone 4. In Zone 7, a
production site was specifically chosen because the random site
selection process did not choose Oklahoma, a state with
considerable production (see Table 1). Three sites in Zone 4
were specifically selected to further characterize the Gulf Coast
Salt Dome Basin.
A specifically-selected tank bottom site was chosen in Zone 10.
The absence of a tank bottom sample at the random selected site
compelled selection of a specific site nearby.
All centralized pits and centralized treatment facilities were
specifically selected. One centralized pit was chosen in Zone 7
and one in Zone 8; two were selected in Zone 9. One centralized
treatment facility was chosen in each of Zones 2, 4, and 11.
Locations and numbers of centralized pits and treatment
facilities were identified through discussions with state
officials through the EPA Eastern Workshop (EPA, 1985a) and EPA
B-26
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Western Workshop (EPA, 1985b) and through discussions with state
officials at the time the state officials were generating lists
of possible drill sites and production sites. No particular
state or zone was chosen in advance of selecting a centralized
pit or centralized treatment facility.
Summary of Sampling Design
Table 5 shows the detailed sampling design for this sampling
project as of May 5, 1986. (Actual implementation of the plan is
discussed in the next section.) EPA targeted 70 percent of the
planned 48 samples to be randomly selected, to be distributed
among the zones as shown in Table 5. Zone distribution of the
specifically-selected sites was considered tentative in
recognition that these sites might have to be utilized on a
quick-response basis as replacements for randomly-selected sites.
IMPLEMENTATION OF THE SAMPLING DESIGN
Table 6 shows the actual implementation of the sampling design.
A. comparison between Table 5 and Table 6 shows the degree of
implementation of the original sampling plan. Overall
implementation of the sampling strategy was high. For example,
EPA had targeted 70 percent of the sites for random selection;
69.4 percent of the sites were actually randomly selected.
EPA considered comments on the May, 1986, EPA Sampling Strategy -
Draft (EPA, 1986) in making some revisions to the sampling design
prior to its initiation. For instance, EPA recognized that some
B-27
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Table 5. Planned Distribution of Probability Sites and Specifically-
Selected Sites Among Zones.
NO. PROBABILITY SITES
NO. SPECIFIC SITES
JJ
1
M
00
Zone
2
4
5
6
7
8
9
10
11
TOTAL
Drill
2
2
2
2
2
2
2
2
_2
18
Prod. T.B.
2
2
2
1
2
1
2
1
_JL _z
14
Drill Prod. T.B. Cent. Pit Cent. Trtmt.
- 1 - 1
_ _ _ _ i
_ _ _ _
_ _ i _ —
1-1 1
- - 1
1 2
- 1 1
_= _1 -J, _= -1
226 3 3
TOTAL
6
5
4
4
7
4
7
5
_6
46
Abbreviations: Drill - drill site
Prod. - production site
T.B. - tank bottom sludge site
Cent. Pit - centralized pit site
Cent. Trtmt. - centralized treatment site
-------
CO
to
vo
Table 6. Distribution of Probability Sites and Specifically-
Selected Sites Among Zones.
NO. PROBABILITY SITES
NO. SPECIFIC SITES
Zone
2
4
5
6
7
8
9
10
11
TOTAL
Drill
2
2
2
2
2
2
2
1
_1
16
Prod. T.B.
2 1
2
1
1
2
2
3
2
_2 _z
17 1
Drill Prod. T.B. Cent. Pit Cent. Trtmt. TOTAL
- - - - 1 6
3 - - 1 8
_ _ 3
- - - - 3
11-1 - 7
1 - 5
2 - 7
1 - 1 - - 5
_J= _r _z _z -1 _5
3414 3 49
Abbreviations: Drill - drill site
Prod. - production site
T.B. - tank bottom sludge site
Cent. Pit - centralized pit site
Cent. Trtmt. - centralized treatment site
-------
tank bottom sludge samples might be available at randomly-
selected production sites. As randomly-selected sites were
preferred, Table 6 shows the realization of that expectation.
Of eighteen planned random drill sites, sampling was actually
conducted at sixteen. EPA was unable to locate a drill site at
or near completion during the sampling time span in the Cook
Inlet Basin of Alaska (Zone 11), or in southwest Wyoming (Zone
8). The planned Cook Inlet Basin site was replaced by a northern
Alaska site (this one specifically selected). The Wyoming site
was not replaceable because of the absence of any available site
within the schedule.
EPA conducted sampling at seventeen randomly .selected production
sites. Only one of two planned production sites was sampled in
Zone 5 (planned for Michigan) due to scheduling difficulties. To
compensate for this loss, EPA added one randomly-selected
production site to Zone 10 (in California) and one to Zone 11 (in
Alaska) later in the program.
EPA conducted tank bottom sludge sampling at two random sites and
one specifically-selected site, one less than originally planned.
Four centralized pits were sampled, one more than originally
planned. Centralized treatment facilities were sampled as
planned.
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STATISTICAL, ANALYSIS
SAMPLING DESIGN
One objective of the sample collection was to form estimates of
the national average pollutant concentration in each waste unit.
Statistical sampling methods were used to construct a sampling
design which would allow construction of such estimates, while
still allowing for examination of particular sites of special
interest.
In order to gain the maximum amount of information from the
numbers of samples and analyses planned, and to improve the
precision of the estimates derivable from this study, a
multi-stage stratified sampling design was employed. The
effectiveness of stratification depends on the association of the
stratification attributes with the quantities of interest. The
11 zones or strata in this study were geographically defined to
group common geological formations and operating practices
together, as these were deemed to be likely to be related to the
waste characteristics. Optimal allocation of samples to strata
depends on the relative numbers of sampling units in the strata
and the relative sizes of the intrastratum variances of the
quantities of interest. In this case, optimal sample size
allocation across strata was not possible, both because of the
limited prior information on the strata sizes and variances, and
because of the limited number of samples to be taken. The
samples were distributed uniformly across the strata to ensure
B-31
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maximal coverage—about two samples for each of the none zones in
the study (two zones have been excluded because there is
essentially no known oil and gas production, exploration, or
drilling in these zones).
The second stage of sampling was to select sites within zones.
Because no complete frame of sites was available, the site
selection was performed by selecting a state according to
specified probability from the region, and then selecting a site
from a list of sites meeting the design attributes (type of site,
etc.) known to the state regulatory agencies. For each site
assigned to a region, the state was selected with probability
proportional to the total oil and gas production in the region.
The use of such size measures provides sample estimates that are
more efficient for the key quantities of interest. In
calculating the estimated national average concentrations of
pollutants, the measured pollutant concentrations will be
weighted by the actual waste volume at the site to produce
volume-weighted average concentrations, with appropriate
accounting for the probabilities of selection of each site. The
key factor to obtaining valid national estimates is to obtain
samples according to a protocol that will produce a national
random sample.
As described in the Site Selection Process section, the sampling
design consisted of two sample site types: those selected as a
random sample of sites and those selected on the basis of
B-32
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judgment. The analytical results from the samples collected at
these sites were combined to form national estimates as follows.
Each directed sample collected at a specifically selected site
represents that site alone in any national estimate. The random
samples represent the population from which they are drawn. The
known probability of selection is used to weight the results of
samples collected at randomly-selected sites, and are combined
with the results of the directed samples in the proportion of the
waste volume at the directed sites to the waste volume of the
sampling population in producing the zone estimates that go into
the national average.
PRECISION AND ACCURACY
Clearly, about 20 randomly selected samples for an industry
segment is a very small sample size for a national estimate. To
get a sense of the precision, suppose we were to base a national
estimate of a proportion of sites with a characteristic such as
significant level of a pollutant, a simple random sample would
provide an estimate p = x/20.
This value can at best estimate a value within +/- 5% just
because the denominator is 20. That is, the possible estimates
for 100p% would be 0%, 5%, 10%, 15%, 20%, etc." Furthermore, the
estimate p is subject to sampling error of 2*SQR(p*(1-p)/20),
this being two times the standard error of the estimate. For an
estimate of 100p% = 50%, the sampling error would be on the order
of 22%.
B-33
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These calculations demonstrate the difficulty of using this small
sample size to provide discriminating national estimates.
Furthermore, regional estimates would be based on an even smaller
sample size and subject to a larger sampling error.
Consequently, the study is truly a screening study designed to
detect on the most blatant or extreme results reliably. As in
any sampling effort, the unexpected or important special case
discovered by this process can be the basis for further study by
"EPA, the Region or State Agencies, if warranted.
Though precision calculations for the multi-stage sampling plan
for this study would be more difficult, calculations based in
simple probability sampling give a general idea of the expected
precision for a national survey of this size. A larger sample
size was not used because of the cost constraints. The actual
sample design uses techniques typically employed in large
national surveys to improve the efficiency of sampling that is
subject to major constraints such as travel time to reach a
sampling site. Accuracy depends on the survey design and our
ability to follow the protocol. With the small sample size,
adherence to the sample design and protocol is especially
important.
B-34
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CONCLUSION
Based on the above considerations, EPA believes that the strategy
described in this document meets its needs for screening for
pollutants in wastes from the oil and gas extraction industry.
The information gathered in this project may be used to develop
more detailed strategies for further definition of various parts
of this industry, for greater coverage of strata, site types, or
pollutants specific to a given process within the industry.
B-35
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tn
i
u>
a\
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REFERENCES
American Petroleum Institute. 1986. Quarterly Completion
Report, Fourth Quarter, Vol. 1, No. 4 (March).
"First Quarter Crude Price, Drilling Plunges Wrack U.S. Oil
Industry." Oil and Gas Journal. 1986. Vol. 84, No. 13
(March 31).
Independent Petroleum Associates of America. 1986. The Oil and
Gas Producing Industry in Your State, 1986-1987.
(September).
Interstate Oil Compact Commission. 1984. The Oil and Gas
Compact Bulletin, Vol. XLIII, No. 2 (December).
Interstate Oil Compact Commission. 1985. The Oil and Gas
Compact Bulletin. Vol. XLIV, No. 1 (June).
U.S. DOE. 1985. Monthly Energy Review, DOE/EIA-0035 (85/10).
U.S. EPA. 1979. Effluent Guidelines Division. Office of Water
and Hazardous Materials. Development Document for Interim
final Effluent Limitations Guidelines and Proposed New
Source Performance Standards for the Oil and Gas Extraction
Point Source Category.! Prepared by Russell E. Train, Andrew
W. Breidenbach, Eckardt C. Beck, Robert B. Schaffer, Martin
Halper (September).
U.S. EPA. 1985. Industrial Technology Division. Onshore
Oil and Gas Workshop Meeting Report (July).
U.S. EPA. 1985. Industrial Technology Division. Proceedings
Onshore Oil and Gas State/Federal Western Workshop
(December).
U.S. EPA. 1986. Industrial Technology Division. Oil and Gas
Exploration, Development, and Production - Sampling Strategy
- Draft (May).
Federal Register. 1979. Vol. 44, No. 73 (April 13). Effluent
Guidelines and Standards, Oil and Gas Extraction Point
Source Category, 40 CFR Part 435.
Sorcim/IUS Corporation. 1984. SuperCalc®3, Sorcim/IUS Micro
Software, Release 2 (August).
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