MEMORANDUM

TO: Lisa Biddle, EPA

FROM: Sarah Yates, Brent Ruminski, ERG

DATE: March 31, 2015

SUBJECT: Unconventional Oil and Gas (UOG) Drilling Wastewater Memorandum 

(DCN SGE00740)

This memorandum describes the data and methods that ERG used to compile oil and gas 

drilling wastewater volumes and characterization data for the Technical Development Document 

(TDD) for Proposed Effluent Limitations Guidelines and Standards for Oil and Gas Extraction

(DCN SGE00704). In addition to explanations of data compilation and analyses, this

memorandum provides discussions about types of oil and gas drilling fluids, unconventional oil 

and gas (UOG1) drilling wastewater volumes (per well), UOG drilling wastewater 

characteristics, and UOG drilling wastewater management practices. The focus of this 

memorandum is on drilling wastewater generated by UOG wells.

Table 1 lists the tables and figures in this memorandum along with the corresponding 

TDD table or figure number and underlying supporting memo from which the figure/table was 

generated. For those figures/tables ERG generated specifically for this memorandum, the 

underlying data and analysis are contained in the Microsoft Excel Attachment 1 (DCN 

SGE00740.A01). Other tables and figures in the TDD that were not derived in Attachment 1 did 

not require calculations and/or analyses by ERG or are described in separate, supporting 

memoranda. Appendix F of the TDD contains a crosswalk of all tables and figures in the TDD

and the name of the relevant supporting memorandum, where applicable.

This memorandum will refer to the following terms used throughout the TDD, the 

supporting memoranda, and memoranda attachments: 

 Unconventional oil and gas (UOG) resources2- crude oil and natural gas3produced by 

wells drilled4into low porosity, low permeability formations. Development of UOG 

resources often requires hydraulic fracturing of the reservoir rock by injecting large 

amounts of fracturing fluid at high pressures to create a network of fissures in the rock 

formations, giving the oil and/or natural gas a pathway to travel to the well for extraction. 

 

1

In the TDD, EPA defines UOG as crude oil and natural gas produced by wells drilled into low porosity, low 

permeability formations which includes shale and tight oil and gas resources. While coalbed methane (CBM) is 

sometimes referred to as an unconventional resource in literature, it is not included in EPA’s definition.

2 UOG resource types are categorized into shale and tight formations.

3 Natural gas can include “natural gas liquids,” components that are liquid at ambient temperature and pressure.

4 UOG wells may be drilled using horizontal, vertical, or directional well trajectories. Literature sometimes refers to 

well trajectory as “drill type”.
Memorandum

March 31, 2015

Page 2

 Drilling wastewater - the liquid waste stream separated from recovered drilling fluid 

(e.g., mud) and drill cuttings during the drilling process. Drilling fluid is the circulating 

fluid used in the rotary drilling of wells to clean and condition the hole and to 

counterbalance formation pressure.

 UOG extraction wastewater - sources of wastewater pollutants associated with 

production, field exploration, drilling, well completion, or well treatment.5 UOG 

extraction wastewater includes produced water, drilling wastewater, and produced sand6.

 Produced water – the water (brine) brought up from the hydrocarbon-bearing strata 

during the extraction of oil and gas. This can include formation water, injection water, 

and any chemicals added downhole or during the oil/water separation process. Based on 

the stage of completion and production the well is in, produced water can be further 

broken down into the following components:

o Flowback –the produced water generated in the initial period after hydraulic 

fracturing (i.e., fracturing fluid, injection water, any chemicals added downhole, 

and varying amounts of formation water). After the hydraulic fracturing 

procedure is completed and pressure is released, the direction of fluid flow 

reverses, and the fluid flows up through the wellbore to the surface. The water 

that returns to the surface is commonly referred to as “flowback.” Flowback is 

typically reported as a percentage of fracturing fluid volume in literature and by 

industry.7

o Long-term produced water (LTPW) –the produced water generated during the 

production phase of the well after the initial flowback process. Long-term 

produced water includes increasing percentages of formation water that make up 

the total volume of long-term produced water. Long-term produced water 

continues to be produced throughout the lifetime of the well and is usually 

reported in terms of flow rates in literature and by industry.8

 

5

Stormwater is not considered a source of UOG extraction wastewater. In general, no NPDES permit is required for 

discharges of stormwater from any field activities or operations associated with oil and gas production, except as 

specified in 40 C.F.R. 122.26(c)(1)(iii) for discharges of a reportable quantity or that contribute to a violation of a 

water quality standard. States may impose additional requirements for management of drilling site stormwater. 

6 Drilling wastewater and produced sand are not discussed in this memorandum. Additional information about 

drilling wastewater can be found in ERG’s Unconventional Oil and Gas Drilling Wastewater memorandum (DCN 

SGE00740).

7 ERG analyzed flowback in terms of percent of fracturing fluid volume as opposed to rate because the flow rate 

changes rapidly over time during flowback making it difficult to summarize. 

8 ERG analyzed LTPW in terms of flow rates because these rates do not vary significantly over time. In addition, 

LTPW is generated over the entire life of the well, a period of time that varies significantly by well. Because well 

life is highly variable, ERG did not convert LTPW flow rates to a total volume.
Memorandum

March 31, 2015

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Table 1. List of Tables and Figures Discussed in this Memorandum

TDD Table or Figure 

Number Memo Table or Figure Number and Title

Memo.

Section

Underlying 

Supporting 

Attachment

Figure C-1

Figure 2. UOG Extraction Wastewater Volumes 

Breakdown by Drill Type for UOG Wells in 

Pennsylvania (2004 – 2013)

2.1 SGE00739.A03

a

Table C-4

Table 2. Average Drilling Wastewater Volumes for 

Horizontal and Vertical Oil and Gas Wells in 

Pennsylvania

2.1 SGE00739.A03

a

Table C-5

Table 3. UOG Drilling Wastewater Volumes Generated 

per Well by Formation 2.1 SGE00740.A01

b

Table C-10, C-12, C-14, 

C-16, and C-18

Table 4. Concentrations of Constituents in UOG Drilling 

Wastewater from Marcellus Shale Wells 2.2 SGE00740.A01

b

Figure D-2

Figure 3. UOG Drilling Wastewater Management and 

Disposal Methods 3 --

a

Figure D-3

Figure 4. Management of UOG Drilling Wastewater 

Generated by UOG Wells in Pennsylvania (2008 – 2013) 3 SGE00739.A03

c

a—This figure was generated by ERG for the purpose of this memorandum and the TDD but does not appear in any 

attachment.

b—These figures/tables were generated in this memorandum. The underlying data and analyses are contained in 

Attachment 1 (DCN SGE00740.A01).

c—These figures/tables were generated in another supporting memorandum (DCN SGE00739).

1. OVERVIEW OF OIL AND GAS DRILLING FLUIDS

Drilling fluid is the circulating fluid used during the rotary drilling of oil and gas wells to 

clean and condition the hole and to counterbalance formation pressure. During drilling, well 

operators circulate drilling fluids down the wellbore to cool the drill bit and to remove fragments 

of rock (i.e., drill cuttings)9from the wellbore. Other purposes of drilling fluids include: reducing

friction between the drilling string and the sides of the hole, preventing inflow of fluids from the 

formation into the hole, cooling the rotor and drill bit, transmitting sensor readings from

navigational tools, and providing stability to the borehole while drilling (DCN SGE00090, DCN 

SGE00635; DCN SGE01009). 

Figure 1 provides an overview of how oil and gas operators use drilling fluid. During the 

drilling process, drilling fluid (i.e., mud) is injected down the well bore where it collects the drill 

cuttings. The drilling fluids are circulated back up the well bore to the surface where the cuttings 

are removed using shakers, desilters and centrifuges. The drilling fluid is then reinjected down 

the wellbore. The drilling fluids may be continuously recycled until the end of the drilling 

process with this closed-loop process while cuttings are managed and/or disposed of when they 

are removed at the surface (DCN SGE00090; DCN SGE00635; DCN SGE01009).

 

9 The particles generated by drilling into subsurface geologic formations and carried out from the wellbore with the 

drilling fluid.
Memorandum

March 31, 2015

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Source: DCN SGE00801

Figure 1. Drilling Fluid Circulation

1.1 Types of Drilling Fluids

There are four general types of drilling fluids:

 Compressed gases;

 Water-based drilling fluid;

 Oil-based drilling fluid; and

 Synthetic oil-based drilling fluid.

Operators may use a combination of these drilling fluids while drilling a single well. The 

drilling fluid used typically depends on the properties of the formation, well depth, associated 

regulations, and cost considerations (DCN SGE01009). While drilling, operators must ensure 

that the weight of the drilling fluid on the bottom of the well bore exceeds the pressure within the 

formation. Pressures increase as well depth increases along with the likelihood of encountering 

gas pockets. At shallow depths during well drilling, where pressure and temperature are typically 
Memorandum

March 31, 2015

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low, drillers use compressed gases because they are the least expensive. As the well is drilled 

deeper, pressures and temperatures increase, requiring heavier drilling fluids (e.g., fresh water, 

water-based, or oil-based fluids) (DCN SGE00635).

The following list provides an overview of a typical drilling process in terms of the well 

depth versus the type of drilling fluid that operators might use. 

1. Shallow Depths: (e.g., 0 – 1,000 feet) Pressurized air is often used to drill 

vertically through the drinking water aquifer (DCN SGE00635; DCN SGE00345; 

DCN SGE00280; DCN SGE00774; DCN SGE00090, DCN SGE01009).

2. Shallow to Medium Depths: (e.g., 1,000 – 3,500 feet) As the vertical section of 

the well is drilled deeper, operators switch over to water-based drilling fluids. The 

purpose of the drilling fluid (e.g., cooling, stability) becomes more critical to

account for increased pressure, temperature, and potential for pressurized gas 

pockets at these depths (DCN SGE00635).

3. Medium to Deep Depths: (e.g., 3,500 feet and deeper) At some depth, operators 

may switch to oil- or synthetic- based fluids as the vertical section of the well is 

drilled deeper and pressure, temperature, and potential for pressurized gas pockets 

continue to increase (DCN SGE00635). However, synthetic-based fluids are not 

always used depending on the final depth and/or operator preference.

4. Formation Depths (i.e., Horizontal Leg): For horizontally- or directionallydrilled UOG wells, operators will continue to use the same drilling fluid they used 

at “medium to deep” depths for the directional or horizontal leg. Operators may 

use water-, oil-, or synthetic oil- based drilling fluids for this portion of the well 

drilling (DCN SGE00635).

Operators add chemicals to water- and oil- based drilling fluids to give the fluid its 

desired characteristics for drilling deeper, where pressure and temperature are higher relative to 

shallow depths. The following subsections describe the primary types of drilling fluids in more 

detail, including specific additives that may be used.

1.1.1 Compressed Gases

Compressed or pressurized air is often used as drilling fluid for shallow wells, for drilling 

through the drinking water aquifer, or for rapid drilling through stable, hard rock formations

(DCN SGE00635). Dry air, nitrogen gas, mist, foam and aerated fluids are included in this 

category (DCN SGE01009). The relatively low pressure of the gases (compared to water-based 

drilling fluids) minimizes losses of drilling fluid into the ground and generates a rapid rate of 

penetration.

1.1.2 Water-based Drilling Fluid

Water-based drilling fluids are more stable than compressed gases and are used at 

medium depths. However, they are also more expensive to use than compressed gases. Water-
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March 31, 2015

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based fluids include water or a water miscible fluid as the suspending medium for solids. Waterbased fluids may contain the following additives (DCN SGE00635; DCN SGE01009):

 Gels to enhance cutting-carrying properties;

 Lime to control pH;

 Polymers to prevent excessive seepage into the formation;

 Salts to increase density and conductivity to allow the operator to analyze downhole 

conditions via electric currents; and/or

 Barite (barium sulfate), as needed, to add weight to the fluid.

1.1.3 Oil-based Drilling Fluid

Oil-based drilling fluids use oil as their continuous phase with water as the dispersed 

phase. The oil is often diesel or mineral oil. Oil-based fluids are more effective than water-based 

fluids at performing the primary functions of drilling fluids; however, they are also more

expensive. Oil-based fluids better protect the formation from swelling, provide better weight 

control, and degrade less rapidly than water-based fluid. Oil-based fluids may contain the 

following additives (DCN SGE00635; DCN SGE01009):

 Emulsifiers to keep water and fluid together;

 Gels to enhance cutting-carrying properties; and/or

 Barite, as needed, to add weight to the fluid.

1.1.4 Synthetic oil-based Drilling Fluid

Operators may also use synthetic oil-based drilling fluids which are technically 

equivalent to oil-based drilling fluids described in Section 1.1.3 in that they are designed for 

drilling at deep depths (e.g., horizontal laterals of wells) (DCN SGE01009). However, instead of 

using diesel oil and/or mineral oils, synthetic oil-based fluids use organic fluids (e.g., esters, 

polyeolefins, acetal, ether, and linear alkyl benzenes) that exhibit similar fluid properties as 

diesel and mineral oils. Synthetic-oil-based fluids have been referred as more environmentally 

friendly10 than oil-based fluids but are also more expensive (DCN SGE01009). Synthetic-based 

oil drilling fluids have lower toxicities, lower concentrations of certain priority pollutants11, 

lower bioaccumulation potential, and faster biodegradation rates than oil-based drilling fluid 

(DCN SGE01006; DCN SGE01009). The organic additives used in synthetic oil-based fluids are 

less toxic than the diesel and/or mineral oils used in oil-based drilling fluids (DCN SGE01009). 

Synthetic oil-based drilling fluids also result in a smaller volume of drilling wastewater that 

operators need to manage or dispose of.

 

10 Using synthetic-oil-based drilling fluids results in a lower volume of wastewater that must be disposed of. They 

also have lower toxicities, lower concentrations of certain priority pollutants, lower bioaccumulation potential, and 

faster biodegradation rates than oil-based drilling fluid.

11 These include polynuclear aromatic hydrocarbons (PAHs) that are priority pollutants in Appendix A to 40 CFR 

423. These pollutants are constituents in oil-based drilling fluids but not in synthetic oil-based drilling fluids.
Memorandum

March 31, 2015

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2. VOLUMES AND CHARACTERISTICS OF UOG DRILLING WASTEWATER

Drilling wastewater is the liquid waste stream separated from recovered drilling fluid12

(mud) and drill cuttings during the drilling process. As explained in Section 1, operators are able 

to circulate the same drilling fluid down the wellbore multiple times while drilling a single well. 

This is accomplished by removing the solids (i.e., drill cuttings)13 from the drilling fluid on the 

well pad. However, at some point the drilling fluid is no longer usable and must be managed or 

disposed of by the operator. 

This section summarizes UOG drilling wastewater volume and characterization data from 

available literature. Section 4 includes descriptions of the analyses that ERG performed to 

generate the data presented. 

2.1 Volumes of UOG Drilling Wastewater

On a per well basis, UOG drilling wastewater accounts for a small portion of the total 

UOG extraction wastewater compared to produced water. Figure 2 shows a breakdown of UOG 

extraction wastewater volumes generated from Marcellus shale wells in Pennsylvania based on 

data from Pennsylvania Department of Environmental Protection’s (PA DEP) statewide waste 

reports (DCN SGE00188) for all wells active between 2004 and 2013. An explanation of how 

ERG generated Figure 2 is described in a separate ERG memorandum: Analysis of PA DEP 

Waste Reports (DCN SGE00739). 14 On average, drilling wastewater contributes seven percent 

or less of total UOG extraction wastewater on a per well basis for UOG wells in Pennsylvania. In 

Figure 2, produced water is shown as its two primary components: flowback15 and long-term 

produced water16. The ratio of drilling wastewater to flowback and long-term produced water 

varies by formation and sometimes within the formation (DCN SGE00704).

 

12 As described in Section 1, drilling fluid is the circulating fluid used in the rotary drilling of wells to clean and 

condition the hole and to counterbalance formation pressure.

13 The particles generated by drilling into subsurface geologic formations and carried out from the wellbore with the 

drilling fluid.

14 ERG analyzed the quantity and type of wastewater (e.g., drilling wastewater, long-term produced water) as 

reported by operators in the PA DEP waste reports (DCN SGE00739).

15 Flowback is the produced water generated in the initial period after hydraulic fracturing (i.e., fracturing fluid, 

injection water, any chemicals added downhole, and varying amounts of formation water).

16 Long-term produced water is the produced water generated during the production phase of the well after the initial 

flowback process. Long-term produced water includes increasing percentages of formation water that make up the 

total volume of long-term produced water.
Memorandum

March 31, 2015

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Source: DCN SGE00739; DCN SGE00739.A03

Figure 2. UOG Extraction Wastewater Volumes Breakdown by Drill Type for UOG Wells 

in Pennsylvania (2004 – 2013) (TDD Figure C-1)

Nearly all of the drilling fluid used during drilling is recovered during the drilling process 

as drilling wastewater (DCN SGE00625).17 The volume of drilling fluid required in the drilling 

process varies with the length of the wellbore. The longer the wellbore, the more drilling fluid is 

required. For example, UOG wells that are drilled horizontally typically generate higher volumes 

of drilling wastewater than UOG wells that are drilled vertically. Table 2, based on PA DEP’s 

waste reports from 2004 to 2013 (DCN SGE00739), supports these generalizations.

Table 2. Average Drilling Wastewater Volumes for Horizontal and Vertical Oil and Gas 

Wells in Pennsylvania (TDD Table C-4)

Resource Type Drill Type

Average

Drilling Fluid 

Volume per 

Well (gallons)

Range of Drilling 

Fluid Volume 

per Well 

(gallons)a

Typical Total 

Measured Depthb

(feet)

Number of Data 

Points

UOG (shale) Horizontal 93,000 3,200 – 210,000 10,000 – 11,000 3,055

UOG (shale) Vertical 89,000 5,000 – 210,000 6,000 – 7,000 209

Source: DCN SGE00739.A03

a—These ranges are based on the 10th and 90th percentile of volumes reported for individual wells.

b—Total measured depth is the true length of wellbore drilled (i.e., sum of the vertical and horizontal).

Table 3 shows volumes of drilling wastewater generated per well by UOG formation

sorted from highest volume to lowest. Existing literature often reports total drilling fluid volume 

used per well rather than the drilling wastewater volume generated per well. As previously 

explained, operators confirmed that nearly all of the drilling fluid is recovered during the drilling 

 

17 Some of the drilling fluid volume may be lost in the cuttings, to evaporation, and/or to seepage into the formation 

but one operator reported these losses to be minimal.
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March 31, 2015

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process as wastewater (DCN SGE00625). Therefore, Table 3 presents all volumes as drilling 

wastewater volumes regardless of whether it was reported as drilling wastewater or drilling fluid

in the literature. Most data sources reported volumes without an indication of the well trajectory 

(i.e., horizontal, vertical, directional). As explained above, drilling fluid/wastewater volumes 

generally increase with the total measured depth. Therefore, Table 3 also presents the typical 

total measured depths for each formation that are reported in literature.

Table 3. UOG Drilling Wastewater Volumes Generated per Well by Formation (TDD 

Table C-5)

Resource 

Type Formation

Drilling Wastewater Volume 

(Gallons) Typical Total 

Measured Well 

Depthb(feet) 

Number of 

Data Points

Range

(Min – Max) Median

Shale

Haynesville & 

Bossier

420,000 -

1,100,000 600,000

13,000 – 19,000

5

Tight Anadarko Basin 200,000 - 420,000 310,000 --

c

2

Shale Niobrara --

a

300,000 7,500 – 13,000 1

Shale Barnett 170,000 - 500,000 250,000 8,500 – 14,000 6

Shale Permian 84,000 - 420,000 210,000 --

c

8

Tight Cleveland --

a

200,000 --

c

1

Tight Granite Wash --

a

200,000 --

c

1

Shale Eagle Ford 130,000 - 420,000 160,000 6,000 – 16,000 7

Shale Utica --

a

100,000 6,000 – 19,000 1

Tight Mississippi Lime --

a

100,000 --

c

1

Shale Marcellus 2,400 – 170,000 92,000 7,300 – 13,000 2,072

Source: See Attachment 1 (DCN SGE00740.A01).

a—ERG identified only one data point for these formations. Therefore, there is no range to display.

b—Total measured depth is the true length of wellbore drilled (i.e., sum of the vertical and horizontal).

c—Information is unknown.

2.2 Characteristics of UOG Drilling Wastewater

Several categories of constituents are present in most types of oil and gas drilling 

wastewater (DCN SGE00733):

Salt (typically measured as total dissolved solids or electrical conductivity);

Oil and grease;

Inorganic and organic compounds; and

Chemical additives used during drilling.

ERG has identified less information in the public literature on UOG drilling wastewater 

characteristics, as compared to information that has been found on UOG produced water 

characteristics. All of the data ERG located on UOG drilling wastewater was specific to the 

Marcellus Shale. Table 4 presents typical concentrations of select constituents that are frequently 

reported in UOG drilling wastewater from Marcellus shale wells. Where multiple data points

(i.e., samples) were available, Table 4 shows the range and median concentrations associated 

with each parameter and the associated number of data points. Constituents are grouped and 
Memorandum

March 31, 2015

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sorted by pollutant categories. Table 4 contains all of the drilling wastewater characterization 

data provided in Table C-10, Table C-12, Table C-14, Table C-16, and Table C-18 of the TDD.

As shown in Table 4, TSS concentrations can vary significantly in drilling wastewater. 

This is likely dependent on how efficiently the drill cuttings are removed by the operator during 

the drilling process (see Figure 1 in Section 1). Operators measured TSS concentrations as high 

as 60 percent by mass in drilling wastewater.
Memorandum

March 31, 2015

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Table 4. Concentrations of Constituents in UOG Drilling Wastewater from Marcellus 

Shale Wells

Constituent 

Category Parameter Units Range Median/Averagea

Number 

of 

Samples

Number 

of 

Detects

Classical and 

Conventional

Alkalinity (as 

CaCO) mg/L 110 - 42,000 1,600 11 11 

Ammonia mg/L 0.98 - 35 7 8 8 

BOD5 mg/L 80 - 1,100 390 8 8 

Chloride mg/L 160 - 23,000 12,000 12 12 

COD mg/L 150 - 9,300 1,800 8 8 

Hardness mg/L 1,400 - 46,000 4,400 12 12 

Oil and Grease mg/L ND - 150 2.5 8 4 

pH S.U. 6.8 - 12 9 12 12 

Phosphate mg/L 16 - 16 16 4 4 

Specific 

Conductance

uS/cm 1,100 - 60,000 19,000 10 10 

TDS mg/L 560 - 80,000 31,000 14 14 

TSS mg/L 120 - 600,000 28,000 16 16 

Ions

Contributing 

to TDS

Bromide mg/L 23 - 210 110 5 5 

Sulfate mg/L ND - 1,600 220 13 10 

Organics

Benzene μg/L ND - 40 ND 20 5 

Ethylbenzene μg/L --

b

9.6 4 4 

Ethylene glycol mg/L -- 500 1 1 

Toluene mg/L ND - 0.01 ND 8 1 

Xylene (m,p) μg/L ND - 80 ND 20 8 

Xylene (o) μg/L --

b

88 4 4 

Metals

Aluminum mg/L 1.7 - 6,900 38 12 12 

Arsenic mg/L ND - 4.2 ND 12 6 

Barium mg/L 2.6 - 2,000 13 14 14 

Beryllium mg/L ND - 0.018 ND 8 2 

Boron mg/L ND - 2.7 0.17 8 4 

Cadmium mg/L ND - 0.005 ND 8 1 

Calcium mg/L 150 - 15,000 1,300 13 13 

Chromium mg/L ND - 11 0.01 12 8 

Cobalt mg/L ND - 1.8 ND 8 3 

Copper mg/L ND - 17 0.83 8 6 

Iron mg/L 4.2 - 18,000 86 12 12 

Lead mg/L ND - 8 0.35 12 10 

Lithium mg/L ND - 1.2 ND 8 1 

Magnesium mg/L ND - 3,600 290 12 11 

Manganese mg/L ND - 350 4.3 12 11 
Memorandum

March 31, 2015

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Table 4. Concentrations of Constituents in UOG Drilling Wastewater from Marcellus 

Shale Wells

Constituent 

Category Parameter Units Range Median/Averagea

Number 

of 

Samples

Number 

of 

Detects

Mercury mg/L ND - 0.029 ND 8 2 

Molybdenum mg/L -- 0.1 1 1 

Nickel mg/L ND - 16 0.55 12 9 

Potassium mg/L --

b

8,800 4 4 

Selenium mg/L ND - 0.11 ND 8 3 

Silver mg/L ND - 0.01 ND 8 1 

Sodium mg/L 170 - 16,000 2,900 12 12 

Strontium mg/L 1.8 - 1,500 21 13 13 

Zinc mg/L ND - 38 2.1 12 10 

Radioactive 

Measurements

Gross alpha pCi/L 17 - 3,000 130 5 5 

Gross beta pCi/L 32 - 4,200 1,200 5 5 

Source: See Attachment 1 (DCN SGE00740.A01).

ND – non detect (not all sources report detection limits).

a—Median value in the “Reported Measured/Average Value” column in the “UOG DF WW Chara. Data” tab

b—Source only reported median value based on multiple samples.

3. MANAGEMENT OF UOG DRILLING WASTEWATER

As detailed in Section D.2 of the TDD, historically, the oil and gas industry has most 

commonly managed UOG extraction wastewater, which includes drilling wastewater, by

underground injection (DCN SGE00704). The UOG industry is increasingly turning to 

reuse/recycle, and, in some geographic areas, transfer to centralized waste treatment (CWT)

facilities to manage growing volumes of UOG extraction wastewater. The National Petroleum 

Council (NPC) describes oil and gas drilling wastewater management in three tiers (DCN 

SGE00733):

Tier 1: Waste Minimization – The generation of waste is minimized by using closed 

loop circulation systems during drilling, which reduces the total amount of waste that must be 

managed and/or disposed of in addition to minimizing costs.

Tier 2: Reuse/Recycle – Operators can reuse/recycle drilling wastewater in subsequent 

drilling and/or fracturing jobs18.

Tier 3: Disposal – When drilling wastewater cannot be managed via reuse/recycle, 

operators must use other management options, including disposal. 

Common methods for managing and/or disposing of drilling wastewater are listed below 

and shown in Figure 3 (DCN SGE00081).

 

18 One operator reported that treated drilling wastewater using induced gas flotation (IGF) may be used for hydraulic 

fracturing base fluid (DCN SGE00625)
Memorandum

March 31, 2015

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 Transfer to a CWT facility19;

 Disposal via injection into Class II disposal wells

20

;

 On-site burial – temporary fluid storage in on-site open earthen or lined pits with 

burial of residual solids after fluids are solidified, removed from the top, or 

evaporated;

 Disposal via landfill – fluids are solidified and then contained in constructed or 

natural excavations within the landfill; and

 Land application (not shown in Figure 3) – spreading over land surface where natural 

bioremediation is enhanced by tilling and nutrient applications.

Figure 3. UOG Drilling Wastewater Management and Disposal Methods (TDD Figure D-2)

Currently, the most detailed publicly available source of information on drilling 

wastewater management and disposal practices is specific to oil and gas extraction in 

Pennsylvania. PA DEP periodically releases a database that captures the management of drilling 

wastewater generated by all oil and gas wells in Pennsylvania (DCN SGE00739). Figure 4 shows 

a timeline of drilling wastewater management practices used by UOG operators in Pennsylvania

reported for 2008 through 2013. As can be seen in the figure, UOG drilling fluid volumes 

 

19 CWT facilities that accept UOG extraction wastewater are described in a separate ERG memorandum titled

Analysis of Centralized Waste Treatment (CWT) Facilities Accepting UOG Extraction Wastewater (DCN 

SGE00596).

20 Underground injection wells are described in a separate ERG memorandum titled Analysis of Active Underground 

Injection for Disposal Wells (DCN SGE00736).
Memorandum

March 31, 2015

Page 14

generated increased substantially in 2009 due to development of the Marcellus shale. UOG 

operators utilized POTWs from 2008 through 2011 to manage drilling wastewater (indicated by 

red in figure). However, the use of POTWs for the management of UOG drilling wastewater 

(and produced water) stopped after 2011. Over the same period of time, the use of reuse/recycle 

increased.

Note: As reported in the PA DEP Waste Reports, “Other” may include storage pending disposal or reuse and other 

(reported as “other”). 

Source: DCN SGE00739; DCN SGE00739.A03

Figure 4. Management of UOG Drilling Wastewater Generated by UOG Wells in 

Pennsylvania (2008 – 2013) (TDD Figure D-3)

4. METHODOLOGY FOR TDD FIGURES/TABLES GENERATED IN THIS MEMORANDUM

The following two subsections describe the methodology that ERG used to generate 

Table 3 (TDD Table C-5) and Table 4 (TDD Tables C-10, C-12, C-14, C-16, and C-18) in this 
Memorandum

March 31, 2015

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memorandum. As previously explained, all other figures and tables (e.g., Figure 4) in this 

memorandum are described in other supporting memoranda.

4.1 Table 3 – Drilling Wastewater Volumes Generated by UOG Wells by Formation

TDD Table C-5 “UOG Drilling Wastewater Volumes Generated per Well by Formation” 

(i.e., Table 3 in Section 2.1 of this memorandum) shows volumes of UOG drilling 

fluid/wastewater generated per well for various formations. The raw data and analysis are 

compiled in the “UOG DF WW Volume Data” and “UOG DF WW Volume Summary” tabs in 

Attachment 1 (DCN SGE00740.A01). The following two subsections explain how ERG 

generated this table.

4.1.1 UOG Drilling Wastewater Volume Data Entry

ERG entered raw UOG drilling wastewater volume data reported in literature into the 

“UOG DF WW Volume Data” tab in Attachment 1 (DCN SGE00740.A01). Where available, 

data fields entered included:21

 Resource type (i.e., shale, tight)

 Formation

 Well trajectory (i.e., horizontal, not reported)

 Volume (gallons) – This is the reported volume of drilling fluid used or drilling 

wastewater generated per well in gallons. Some references report volumes used for 

drilling UOG wells as opposed to wastewater generated. ERG presented the results as 

drilling wastewater volumes.22

 Number of data points – This is the number of wells the volume data is based on, if 

reported. If not reported, ERG assigned this value as 1. In some cases, this is 

equivalent to the number of wells the reported data is based on. However, as 

explained above, not all references reported the number of wells.

 Reference (i.e., DCN number)

4.1.2 UOG Drilling Wastewater Volume Summary Calculations 

After entering all data in the “UOG DF WW Volume Data” tab in Attachment 1 (DCN 

SGE00740.A01), ERG calculated the summary statistics that appear in the TDD Table C-5 (i.e., 

Table 3 in Section 2.1 of this memorandum) in the “UOG DF WW Volume Summary” tab. ERG 

calculated the following for each formation reported in the “UOG DF WW Volume Data” tab:

 Minimum value – Smallest value in the “Volume (gallons)” column in the “UOG DF

WW Volume Data” tab.

 

21 ERG marked data elements that were not included in the literature as “not reported” in Attachment 1.

22 Based on communication with industry, ERG assumed that the volume of drilling fluid used is equal to the 

volume of drilling wastewater generated on a per well basis (DCN SGE00625). ERG did not distinguish between 

reported volume of drilling fluid used and drilling wastewater generated in this analysis.
Memorandum

March 31, 2015

Page 16

 Maximum value – Largest value in the “Volume (gallons)” column in the “UOG DF

WW Volume Data” tab.

 Range – Combines the minimum and maximum values into a range.

 Median value – Median value in the “Volume (gallons)” column in the “UOG DF

WW Volume Data” tab.

 Number of data points – Sum of the “Number of Data Points” column in the data in 

the “UOG DF WW Volume Data” tab.

4.2 Tables 4 and 5 – Characteristics of Select Pollutants in UOG Drilling Wastewater

TDD Tables C-10, C-12, C-14, C-16, and C-18 (i.e., Table 4 in Section 2.2 of this 

memorandum) show concentrations of pollutants found in UOG drilling wastewater. The raw 

data and analysis are compiled in the “UOG DF WW Chara. Data” and “UOG DF WW Chara.

Summary” tabs in Attachment 1 (DCN SGE00740.A01). The following two subsections explain 

how ERG generated these tables.

4.2.1 UOG Drilling Wastewater Characteristics Data Entry and Standardization

ERG entered raw characterization data reported in literature into the “UOG DF WW 

Chara. Data” tab in Attachment 1 (DCN SGE00740.A01). Data fields entered included: 23

 Formation;

 Category [of pollutant] (e.g., classical, metal);

 Measured parameter;

 Reported measured/average value (i.e., value reported in literature);

 Uncertainty (applies to radioactive constituents);

 Number of samples;

 Units;

 Reference (i.e., DCN number); and

 Notes.

Because naming conventions, terminology, and measured units differed by data source, 

ERG standardized each data field to allow for comparison and summary of data across the entire 

dataset. The following list provides details on how ERG standardized data from literature in the 

“UOG DF WW Chara. Data” tab. 

 Parameter Standardization and Pollutant Category Assignments - ERG created a list 

of all parameters included in the various sources and consolidated parameter names to 

account for different spellings or abbreviations. For example, “Co” and “Cobalt” 

were standardized to “Cobalt.” Pollutant categories for each standard parameter name 

were also assigned to allow sorting of measured parameters. For example, aluminum 

was assigned to the “Metals” category.

 Reported Measured/Average Values - In some cases, data sources indicated that 

minimum, median, and/or maximum values did not exceed the limit of detection. To 

standardize the data for aggregation, ERG assigned all reported non detects as zero

 

23 ERG marked data elements that were not included in the literature as “not reported” in Attachment 1.
Memorandum

March 31, 2015

Page 17

values. After analyzing the data, any zero minimum, median, or maximum values 

were converted back to non detect in the TDD and memorandum tables.

 Wastewater Description – ERG only used literature that specifically reported the 

wastewater type associated with the characterization data as drilling wastewater. 

However, different sources may use different terms for drilling wastewater. ERG 

captured wastewater described as: “pit water”, “drilling”, and “mud”.

 Units of Measure Standardization – ERG converted reported pollutant concentrations 

to standardized units of measure appropriate for each parameter. For example, total 

suspended solids were sometimes reported as a percent. ERG converted these values 

to mg/L by multiplying the percent by 1,000,000 (e.g., 38% would be converted by 

multiplying 0.38 by 1,000,000 to get the value of 380,000 mg/L). 

4.2.2 UOG Drilling Wastewater Characteristics Summary Calculations 

After consolidating and standardizing all data in the “UOG DF WW Chara. Data” tab, 

ERG calculated summary statistics that appear in the “UOG DF WW Chara. Summary” tab in 

Attachment 1 (DCN SGE00740.A01). ERG calculated the following for each parameter reported 

in the “UOG DF WW Chara. Data” tab:

 Minimum value – Smallest value in the “Reported Measured/Average Value” column 

in the “UOG DF WW Chara. Data” tab.

 Maximum value – Largest value in the “Reported Measured/Average Value” column 

in the “UOG DF WW Chara. Data” tab.

 Range – Combines the minimum and maximum values into a range.

 Median value – Median value in the “Reported Measured/Average Value” column in 

the “UOG DF WW Chara. Data” tab.

24

 Number of data points – Sum of the number of data points represented by the data in 

the “UOG DF WW Chara. Data” tab.

 Number of detects – Sum of the number of data points that were not non-detects or 

zeros represented by the data in the “UOG DF WW Chara. Data” tab.

5. QUALITY CONTROL PROCEDURES

All of the analyses presented in this memorandum adhered to the Environmental 

Engineering Support for Clean Water Regulations Programmatic Quality Assurance Project 

Plan (PQAPP) (DCN SGE00957) and the Unconventional Oil and Gas (UOG) Supplemental 

Quality Assurance Project Plan (SQAPP) (DCN SGE00958), including collecting, evaluating, 

and analyzing existing data and information about drilling fluids and drilling wastewater.

Specifically, ERG used the procedures described in Section 4 of the PQAPP to gather and 

manage existing data in support of the UOG proposed rulemaking. ERG staff entered reference 

information for relevant sources into the UOG Literature Review database. The ERG index 

keeper reviewed all reference information, assigned each reference a Document Control Number 

 

24 One source (SGE00774) provided the average measured result for four samples but did not provide the individual 

sample results. ERG did not weight these values during the calculation of the median value.
Memorandum

March 31, 2015

Page 18

(DCN), imported the reference information into the UOG Project File Index database, and saved 

referenced files in the Electronic Project File folder.

ERG also used the procedures described in Section 3 of the SQAPP when collecting 

existing data for use in the UOG proposed rulemaking. ERG used a combination of sources, 

including reports, papers, and online databases from state regulatory agencies such as 

departments of environmental protection and oil and gas commissions. As shown in Table 5 in 

this memorandum, ERG assigned a source flag (A, B, C or D) to all references used in these 

analyses. ERG defines each source flag as follows: 

 Source Flag A - Journal articles and documents prepared by or for a government 

agency (e.g., site visit reports, industry meeting notes); 

 Source Flag B - Documents prepared by a verified source25 that include citation 

information (e.g., operator reports, vendor documents, university publications); 

 Source Flag C - Documents prepared by a verified source that do not include citation 

information (e.g., operator reports, vendor documents, conference presentations); and 

 Source Flag D - Documents prepared by a source that could not be verified and that 

do not include citation information.

EPA and ERG followed the procedures described in Section 7.0 of the PQAPP to 

generate, evaluate, and analyze data using a spreadsheet. ERG conducted the following QA 

checks during the analyses:

 ERG performed a 20 percent check of all data entry.

 ERG performed a 100 percent check of all analyses and calculations, and documented 

these in the internal version of the spreadsheet.

 ERG had a senior staff member familiar with ELGs and the UOG proposed 

rulemaking review the results from each analysis.

6. REFERENCES

Table 5 provides DCNs and citations for references used in these analyses and their 

assigned source flag. Definitions for source flags are located in Section 3.0 of the SQAPP (DCN 

SGE00958) and also in Section 5 of this memorandum.

 

25 ERG considered sources as “verified” if we were able to find information about the author outside of the reference 

document. ERG primarily verified information by looking for company/organization websites that confirmed the 

author’s affiliation with the UOG industry
Memorandum

March 31, 2015

Page 19

Table 5. References

DCN Reference Citation

Source 

Flaga

SGE00010 U.S. DOE. Office of Fossil Energy NETL. April 2009. A

SGE00081

American Petroleum Institute (API). 2009. Environmental Protection for Onshore 

Oil and Gas Production Operations and Leases. (July). Available online at: 

http://www.api.org/~/media/Files/Policy/Exploration/API_RP_51R.ashx. B

SGE00090

NYSDEC; Leff, Eugene. 2011. Supplemental Generic Environmental Impact 

Statement on the Oil, Gas, and Solution Mining Regulatory Program. New York 

State Department of Environmental Conservation (NYSDEC). A

SGE00188

O'Connell, James, ERG.2014. Pennsylvania Department of Environmental 

Protection’s (PA DEP) Statewide Oil and Gas Waste Reports. (December). A

SGE00276

U.S. EPA. 2012. Meeting with XTO Energy, Inc. about Unconventional Oil and 

Gas Sanitized. A

SGE00280

U.S. EPA. 2013. Site Visit Report Anadarko Petroleum Corporation Marcellus 

Shale Gas Operations. (January 9). A

SGE00298.A18

Don Warlick. 2012. Water Management for Shale Plays An Overview of the 

Niobrara Shale. Warlick Energy. C

SGE00345

Lewis, Aurana. 2012. Wastewater Generation And Disposal From Natural Gas 

Wells in Pennsylvania. Duke University. B

SGE00368

US EPA Region 3. 2012. Key Documents About Mid-Atlantic Oil and Gas 

Extraction. Available online at: http://www.epa.gov/region3/marcellus_shale/ A

SGE00368.A01

US EPA Region 3. 2013. Key Documents About Mid-Atlantic Oil and Gas 

Extraction. Available online at: 

http://www.epa.gov/region3/marcellus_shale/pdf/responses2info-req5-12-

11/swepi255-508.pdf A

SGE00428 ERG. 2013. Notes on Penn State Webinar: The Utica Reservoir. B

SGE00625

US EPA. 2015. Site Visit Report Southwestern Energy Fayetteville Shale 

Operations. Sanitized. A

SGE00635

US EPA. 2012. Site Visit Report Chesapeake Energy Corporation Marcellus Shale 

Gas Operations Sanitized. A

SGE00639

Nicot et al. 2012. Oil & Gas Water Use in Texas: Update to the 2011 Mining 

Water Use Report. Univ of TX at Austin. (September) B

SGE00641

Nicot, Jean-Philippe. 2013. Geographical, Geological, and Hydrogeological 

Attributes of Formations in the Footprint of the Eagle Ford Shale. A

SGE00691

U.S. Environmental Protection Agency (U.S. EPA). 2013. Summary of the 

Technical Workshop on Water Acquisition Modeling: Assessing Impacts Through 

Modeling and Other Means. (September). A

SGE00704

U.S. EPA. 2015. Technical Development Document for Proposed Effluent 

Limitations Guidelines and Standards for Oil and Gas Extraction. Office of Water 

Engineering and Analysis Division. A

SGE00732

Huffmyer, Russell and Gehucheten. 2013. Recovering Valuable Byproducts from 

Oil and Gas Wastes. HDR Engineering, Inc. IWC-13-37. (November 17). B

SGE00733

National Petroleum Council (NPC). 2011. Waste Management Paper #2-24. 

Technology Subgroup of the Operations & Environment Task Group. (September 

15). B

SGE00739

ERG. 2015. Analysis of Pennsylvania Department of Environmental Protection’s 

Oil and Gas Waste Reports. A
Memorandum

March 31, 2015

Page 20

Table 5. References

DCN Reference Citation

Source 

Flaga

SGE00739.A03

ERG. 2015. Analysis of Pennsylvania Department of Environmental Protection’s 

Oil and Gas Waste Reports - Attachment 3 - Data Calculations. A

SGE00774

Ziemkiewicz, Paul. 2013. Water Quality Literature Review and Field Monitoring 

of Active Shale Gas Wells. Phase I: Assessing Environmental Impacts of 

Horizontal Gas Well Drilling Operations. West Virginia Department of 

Environmental Protection. (Feb. 15). B

SGE00801

Argonne National Laboratory (ANL). 2011. Drilling Waste Management 

Information System. A

SGE00957

Eastern Research Group, Inc. 2013. Environmental Engineering Support for Clean 

Water Regulations Programmatic Quality Assurance Project Plan (PQAPP). A

SGE00958

Eastern Research Group, Inc. 2014. Unconventional Oil and Gas (UOG) 

Supplemental Quality Assurance Project Plan (SQAPP). A

SGE00986

Rost, J. (2010). Municipal Authority of the City of McKeesport Analysis of Gas 

Well Wastewaters as Required Under the PA DEP Administrative Order Dated 

October 23, 2008 (File 2). A

SGE00987

Rost, J. (2010). Municipal Authority of the City of McKeesport Analysis of Gas 

Well Wastewaters as Required Under the PA DEP Administrative Order Dated 

October 23, 2008 (File 1). A

SGE01006

U.S. EPA. 2000. Development Document for Final Effluent Limitations 

Guidelines and Standards for Synthetic-Based Drilling Fluids and Other NonAqueous Drilling Fluids in the Oil and Gas Extraction Point Source Category. 

EPA-821-B-00-013. (December). A

SGE01009

Caen, R., Darley, H.C.H., and G. R. Gray. 2011. Composition and Properties of 

Drilling and Completion Fluids. 6th edition. Gulf Professional Publishing: 

Waltham, MA. B

a—ERG defines each source flag as follows: 

 Source Flag A - Journal articles and documents prepared by or for a government agency (e.g., site visit reports, 

industry meeting notes); 

 Source Flag B - Documents prepared by a verified source that include citation information (e.g., operator 

reports, vendor documents, university publications); 

 Source Flag C - Documents prepared by a verified source that do not include citation information (e.g., operator 

reports, vendor documents, conference presentations); and 

 Source Flag D - Documents prepared by a source that could not be verified and that do not include citation 

information.
ATTACHMENT 1: UOG DRILLING WASTEWATER VOLUME AND CHARACTERIZATION

DATA EXCEL FILE (DCN SGE00740.A01)