MEMORANDUM

TO: Lisa Biddle, EPA

Karen Milam, EPA

FROM: Sarah Yates, ERG

Brent Ruminski, ERG

DATE: June 7, 2016

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

(DCN SGE01181)

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 

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

SGE01188). 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 (UOG)

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 SGE01181.A01). Tables and figures that are presented in the TDD not listed in Table 1

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

supporting memoranda. The Crosswalk Memorandum between Proposed and Final Technical 

Development Document for Effluent Limitations Guidelines and Standards for Oil and Gas 

Extraction: Tables and Figures (DCN SGE01334) contains a crosswalk of all tables and figures 

in the TDD. Appendix F of the TDD contains the name of the relevant supporting memorandum

for each TDD table and figure, where applicable. This memorandum is organized into the 

following sections:

 Section 1.0 overview of oil and gas drilling fluids

 Section 2.0 volumes and characteristics of UOG drilling wastewater

 Section 3.0 management of UOG drilling wastewater

 Section 4.0 methodology 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

 Section 5.0 describes ERG’s quality assurance procedures

 Section 6.0 lists the references used for these analyses

 Section 7.0 provides the attachment to this memorandum

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

data and analysis are contained in: 
Memorandum

June 7, 2016

Page 2

 Attachment 1 – UOG Drilling Wastewater Volume and Characterization Data 

Excel File (DCN SGE01181.A01).

For the tables/figures explained in more detail in this memorandum, Table 1 provides the 

TDD chapter, memorandum section, and attachment information. 

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 – 2014)

2.1 SGE01182.A03

a

Table C-4

Table 2. Average Drilling Wastewater Volumes for 

Horizontal and Vertical Oil and Gas Wells in 

Pennsylvania

2.1 SGE01182.A03

a

Table C-5

Table 3. UOG Drilling Wastewater Volumes Generated 

per Well by Formation 2.1 SGE01181.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 SGE01181.A01

b

Figure D-2

Figure 3. UOG Drilling Wastewater Management and 

Disposal Methods 3.0 --

a

Figure D-3

Figure 4. Management of UOG Drilling Wastewater 

Generated by UOG Wells in Pennsylvania (2008 – 2014)

3.0 SGE01182.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 SGE01181.A01).

c—These figures/tables were generated in another supporting memorandum (DCN SGE01182).

For definitions of common terms used throughout the TDD, the supporting memoranda, 

and memoranda attachments, please refer to the Glossary in the introduction of the TDD.

1.0 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)1from 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 

 

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

drilling fluid.
Memorandum

June 7, 2016

Page 3

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).

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.
Memorandum

June 7, 2016

Page 4

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 

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.
Memorandum

June 7, 2016

Page 5

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. Waterbased 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 drilling 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 drilling fluids have been referred to as more 

environmentally friendly than oil-based drilling fluids but are also more expensive (DCN 

SGE01009). Synthetic oil -based drilling fluids have lower toxicities, lower concentrations of 

certain priority pollutants2, lower bioaccumulation potential, and faster biodegradation rates than 

oil-based drilling fluid (DCN SGE01006; DCN SGE01009). The organic additives used in 

synthetic oil-based drilling fluids are less toxic than the diesel and/or mineral oils used in oilbased drilling fluids (DCN SGE01009). Synthetic oil-based drilling fluids also result in a smaller

volume of drilling wastewater to manage or dispose.

 

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

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

June 7, 2016

Page 6

2.0 VOLUMES AND CHARACTERISTICS OF UOG DRILLING WASTEWATER

Drilling wastewater is the liquid waste stream separated from recovered drilling fluid3

(mud) and drill cuttings during the drilling process. As explained in Section 1.0, 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)4from 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 4.0 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 SGE01245) for all wells active between 2004 and 2014. An explanation of how 

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

Waste Reports (DCN SGE01182). 5 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: flowback6and long-term 

produced water7. The ratio of drilling wastewater to flowback and long-term produced water 

varies by formation and sometimes within the formation (DCN SGE01188).

 

3 As described in Section 1.0, drilling fluid is the circulating fluid used in the rotary drilling of wells to clean and 

condition the hole and to counterbalance formation pressure.

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

drilling fluid.

5 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 SGE01182).

6 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).

7 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

June 7, 2016

Page 7

Source: DCN SGE01182; DCN SGE01182.A03

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

in Pennsylvania (2004 – 2014) (TDD Figure C-1)

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

as drilling wastewater (DCN SGE00625).8 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 2014 (DCN SGE01182), 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 90,000 3,400 – 200,000 7,300 – 13,000 3,961

UOG (shale) Vertical 83,000 5,000 – 190,000 6,000 – 7,000 230

Source: DCN SGE01182.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).

 

8 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.
Memorandum

June 7, 2016

Page 8

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 

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 3,400 – 200,000d 50,000 7,300 – 13,000 3,962

Source: See Attachment 1 (DCN SGE01181.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.

d—ERG used maximum and minimum volume data for all formations except for the Marcellus formation because 

of the limited number of data points that were identified in existing literature. Due to the large number of volume 

data points for the Marcellus formation, ERG calculated the 10th and 90th percentile values to display as the range 

as opposed to presenting maximum and minimum values.

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.
Memorandum

June 7, 2016

Page 9

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 

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 1.0). Operators measured TSS concentrations as high 

as 60 percent by mass in drilling wastewater.
Memorandum

June 7, 2016

Page 10

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 
Memorandum

June 7, 2016

Page 11

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

Manganese mg/L ND - 350 4.3 12 11 

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 SGE01181.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.

3.0 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 SGE01188). 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 jobs9.

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

operators must use other management options, including disposal. 

 

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

fracturing base fluid (DCN SGE00625)
Memorandum

June 7, 2016

Page 12

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

and shown in Figure 3 (DCN SGE00081).

 Transfer to a CWT facility10;

 Disposal via injection into Class II disposal wells

11;

 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 

 

10 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 

SGE01178).

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

Injection for Disposal Wells (DCN SGE01187).
Memorandum

June 7, 2016

Page 13

wastewater generated by all oil and gas wells (DCN SGE01182) and Figure 4 shows a timeline 

of drilling wastewater management practices used by UOG operators in Pennsylvania for 2008 

through 2014. As can be seen in the figure, UOG drilling fluid volumes 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 the figure). 

However, the use of POTWs for the management of UOG drilling wastewater (and produced 

water) stopped after 2011 with the use of reuse/recycle increasing starting in 2011.

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

(reported as “other”). 

Source: DCN SGE01182; DCN SGE01182.A03

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

Pennsylvania (2008 – 2014) (TDD Figure D-3)

4.0 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

June 7, 2016

Page 14

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 SGE01181.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 SGE01181.A01). Where available, 

data fields entered included:12

 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.13

 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 

SGE01181.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.

 

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

13 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

June 7, 2016

Page 15

 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 SGE01181.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 SGE01181.A01). Data fields entered included: 14

 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

 

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

June 7, 2016

Page 16

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 SGE01181.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.

15

 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.

5.0 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 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 

 

15 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

June 7, 2016

Page 17

(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 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 source16 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 rulemaking review 

the results from each analysis.

6.0 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 5.0 of this memorandum.

 

16 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

June 7, 2016

Page 18

Table 5. References

DCN Reference Citation

Source 

Flaga

SGE00010 Ground Water Protection Council. 2009. Modern Shale Development in the 

United States: A Primer.

A

SGE00081 API. 2009. Environmental Protection for Onshore Oil and Gas Production 

Operations and Leases.

B

SGE00090 NYSDEC. 2011. Suppl. Generic Env. Imp. Statement on Oil, Gas, & Soln. Mining 

Reg. Prgm. Prelim. Rev. Draft.

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.A01 U.S. EPA. 2013. Key Documents About Mid-Atlantic Oil and Gas Extraction. 

(January 9)

A

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

SGE00625 U.S. EPA. 2015. Site Visit Report: Southwestern Energy Fayetteville Shale Gas 

Operations. Sanitized.

A

SGE00635 U.S. 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)

A

SGE00641 Nicot, Jean-Philippe. 2013. Geographical, Geological, and Hydrogeological 

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

A

SGE00691 U.S. EPA. 2013. Summary of the Technical Workshop on Water Acquisition 

Modeling: Assessing Impacts Through Modeling and Other Means. (September).

A

SGE00732 Huffmyer, Russell and Gehucheten, John. 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

SGE00774 Ziemkiewicz, P. 2013. Water Quality Literature Review and Field Monitoring of 

Active Shale Gas Wells. (February 15).

A

SGE00801 Argonne National Laboratory (ANL). 2011. Drilling Waste Management 

Information System

A

SGE00957 ERG. 2013. Environmental Engineering Support for Clean Water Regulations 

Programmatic Quality Assurance Project Plan (PQAPP).

A

SGE00958 ERG. 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 PADEP Admin Order Dated 10/23/08.

A

SGE00987 Rost, J. 2010. Municipal Authority of the City of McKeesport Analysis of Gas 

Well Wastewaters as Required Under the PA DEP AO Dated October 23, 2008.

A
Memorandum

June 7, 2016

Page 19

Table 5. References

DCN Reference Citation

Source 

Flaga

SGE01006 U.S. EPA. 2000. Development Document Final Effluent Limitations Guidelines &

Standards Synthetic-Based Drilling Fluids & Other Non-Aqueous Drilling Fluids 

in O&G Extraction Point Source Category. 

A

SGE01009 Caen, R., Darley, et al. 2011. Composition and Properties of Drilling and 

Completion Fluids. 6th edition. Gulf Professional Publishing: Waltham, MA.

B

SGE01028 PA DEP. 2015. Technologically Enhanced Naturally Occurring Radioactive 

Materials (TENORM) Study Report.

A

SGE01178 ERG. 2016. Analysis of Centralized Waste Treatment Facilities (CWTs) 

Accepting UOG Extraction Wastewater.

A

SGE01182 ERG. 2016. Analysis of Pennsylvania Department of Environmental Protection’s 

Oil and Gas Waste Reports.

A

SGE01182.A03 ERG. 2016. Analysis of Pennsylvania Department of Environmental Protection’s 

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

A

SGE01187 ERG. 2016. Analysis of Active Underground Injection for Disposal Wells. A

SGE01188 U.S. EPA. 2016. Technical Development Document for Effluent Limitations 

Guidelines and Standards for Oil and Gas Extraction.

A

SGE01245 ERG. 2015. Pennsylvania Department of Environmental Protection’s (PA DEP) 

Statewide Oil and Gas Waste Reports. (November)

A

SGE01334 ERG. 2016. Memorandum Providing a Crosswalk between Tables and Figures in 

the Proposed and Final Technical Development Document for Effluent 

Limitations Guidelines and Standards for Oil and Gas Extraction.

A

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.

7.0 ATTACHMENT
ATTACHMENT 1: UOG DRILLING WASTEWATER VOLUME AND CHARACTERIZATION

DATA EXCEL FILE (DCN SGE01181.A01)