MEMORANDUM

TO: Lisa Biddle, EPA

FROM: Brent Ruminski, ERG

James K. O’Connell, ERG

Jason Sese, ERG

DATE: March 31, 2015

SUBJECT: Conventional Oil and Gas (COG) Memorandum for the Record (DCN 

SGE01016)

This memorandum discusses conventional oil and gas (COG) extraction wastewater

characteristics, as well as management and disposal practices used for COG extraction 

wastewater. This memorandum also describes the data and methods that ERG used to compile

this information. In addition, this memorandum includes discussions about data limitations 

related to the drilling fluids and drilling wastewater from COG extraction operations.

As explained in the preamble to the proposed rule, while the existing oil and gas 

regulation applies to both COG and UOG extraction (except coalbed methane)1, the proposed 

rule would add pretreatment standards only for facilities engaged in oil and gas extraction from 

UOG sources that send their discharges to POTWs. EPA proposes to reserve standards for 

conventional oil and gas extraction for possible future rulemaking, if appropriate. This is 

consistent with EPA’s stated scope throughout the development of the proposed rule. Because 

COG extraction wastewater was not explicitly included in the scope of the rulemaking, EPA 

does not have comprehensive information on the characteristics of COG extraction wastewater 

and the wastewater management strategies used for COG extraction wastewater. However, 

through reviewing the literature on UOG, EPA did obtain some information on COG extraction 

wastewater and this memorandum is intended to summarize that information.

This memorandum is organized into the following sections:

 Section 1.0 discusses COG extraction wastewater characterization data. 

 Section 2.0 discusses COG produced water management practices on a national 

and state-level.

 Section 3.0 describes the methodology used by ERG to complete data analyses

not described in other supporting memoranda.

 Section 4.0 describes ERG’s quality control procedures.

 Section 5.0 lists the references used for these analyses.

 Section 6.0 provides the attachments to this memorandum.

 

1

In Pennsylvania, CBM well data is categorized as “conventional”. Therefore, data about CBM wells may be 

included in the PA DEP data cited throughout this memo.
Memorandum

March 31, 2015

Page 2

This memorandum will refer to the following terms: 

 Conventional oil and gas (COG) resources - Crude oil and natural gas that is 

produced by a well drilled into a geologic formation in which the reservoir and 

fluid characteristics permit the oil and natural gas to readily flow to the wellbore

(DCN SGE00984). 

 Unconventional oil and gas (UOG) resources2- crude oil and natural gas3

produced by a well drilled4into a low porosity, low permeability formation.

 COG extraction wastewater - sources of wastewater pollutants associated with 

production, field exploration, drilling, well completion, or well treatment for 

conventional oil and gas extraction.

5 COG extraction wastewater includes 

produced water, drilling wastewater, and produced sand6.

 Drilling wastewater – the liquid waste stream separated from recovered drilling 

fluid (mud) and drill cuttings during the drilling process. 7

 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. 

1.0 COG EXTRACTION WASTEWATER CHARACTERIZATION DATA

The following subsections describe COG drilling wastewater characteristics and COG 

produced water characteristics and, where available, present relevant data.

1.1 COG Drilling Wastewater Characterization Data

This section discusses drilling wastewater characteristics for COG resources. Drilling 

wastewater is the liquid waste stream separated from recovered drilling fluid (mud) and drill 

cuttings during the drilling process. Nearly all of the initial drilling fluid is recovered during the 

drilling process as drilling wastewater (DCN SGE00625).8

Several categories of constituents are present in most types of drilling wastewater (DCN 

SGE00733):

 Salt (total dissolved solids);

 

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 Oil and gas wells may be drilled using horizontal, vertical, or directional well trajectories. Literature sometimes 

refers to well trajectory as “drill type”.

5

Stormwater is not considered a source of COG 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

Produced sand is not discussed in this memorandum. 

7Drilling fluid (mud) is the circulating fluid used in the rotary drilling of wells to clean and condition the hole and to 

counterbalance formation pressure. Drill cuttings are the particles generated by drilling into subsurface geologic 

formations and carried out from the wellbore with the drilling fluid. 

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

March 31, 2015

Page 3

 Oil and grease;

 Inorganic and organic compounds; and

 Chemical additives used during drilling.

ERG identified minimal available COG drilling wastewater characteristics data, all of 

which was specific to COG extraction wells in the Appalachian Basin. ERG identified COG 

drilling wastewater characterization data in technical evaluations of the impact of oil and gas 

wastewater pollutants on POTW unit processes completed in response to Administrative Orders 

(AOs)9issued to a number of POTWs by PA DEP (DCN SGE00986, DCN SGE00987). ERG 

identified chloride concentration data reporting concentrations between 10,000 mg/L and 

150,000 mg/L with a median value of 35,000 mg/L. 

1.2 COG Produced Water Characterization Data

This section discusses produced water characteristics for COG resources.

COG produced water typically reflects the characteristics of the COG formation, 

including naturally occurring ions.10 Salinity or salt concentrations, referred to throughout this 

memorandum as TDS, can vary from <5 – 500,000 mg/L in COG produced water (see Table 3). 

Figure 1 shows the ranges of TDS concentrations in COG produced water from various basins

containing COG resources. The following ions may contribute to TDS in COG produced water: 

sodium, calcium, cadmium, magnesium, chloride, bicarbonate, and sulfate. Barium, potassium, 

and strontium may also be present in COG produced water. Radioactive decay products in COG 

produced water, when present, are primarily in the form of radium 226 and radium 228 (DCN 

SGE01025).

 

9

PA DEP issued AOs to many POTWs in Pennsylvania that were accepting or suspected to begin accepting 

wastewater from UOG operations. 

10 Some COG wells may be hydraulically fractured but ERG has not included a discussion of the different waste 

streams that make up produced water if a well is fractured (i.e., flowback and long-term produced water).
Memorandum

March 31, 2015

Page 4

Source: DCN SGE01025

Figure 1. TDS Concentrations in COG Produced Water from Various Basins Containing 

COG Resources

Table 1 presents typical concentrations of select constituents from ERG’s analysis of the 

United States Geological Survey’s (USGS) Produced Water Geochemical Database v. 2.0 

(PROVISIONAL) (DCN SGE00956)11, the Pennsylvania Department of Environmental 

Protection’s (PA DEP) Technologically Enhanced Naturally Occurring Radioactive Materials 

(TENORM) Study Report (DCN SGE01028), and EPA’s Development Document for Interim 

Final Effluent Limitations Guidelines (ELGs) and Proposed New Source Performance Standards

(NSPS) for the Oil and Gas Extraction Point Source Category (PSC) (DCN SGE00621). The

table shows the ranges and median concentrations associated with each parameter, the associated 

number of data points, and the associated number of detects. Constituents are grouped and sorted 

by pollutant categories (e.g., Classical and Conventional) and represent all basins containing 

COG resources in the United States. The methodology ERG used to analyze these data is 

described in Section 3.2.

Table 1. Concentrations of Constituents in COG Produced Water

Constituent 

Category Parameter Units Rangea Median

Number of 

Data Points

Number of 

Detects

Classical and 

Conventional

Alkalinity mg/L 1.4 – 46 18 53 53 

Bicarbonate mg/L 0.11 - 200,000 330 75,567 74,977 

Carbonate mg/L 1 - 170,000 96 10,218 8,823 

Chloride mg/L 0.65 - 1,100,000 39,000 80,808 80,779 

Nitrate mg/L 0.1 - 280,000 44 3,234 3,212 

 

11 This is a comprehensive database covering 36 states from 1885 to 2012.
Memorandum

March 31, 2015

Page 5

Table 1. Concentrations of Constituents in COG Produced Water

Constituent 

Category Parameter Units Rangea Median

Number of 

Data Points

Number of 

Detects

pH SU 0.051 – 14 7.1 60,319 60,234

Phosphate mg/L 0.1 – 20 2 39 28 

Specific Conductivity mg/L 11,000 - 220,000 130,000 462 450 

Sulfate mg/L 0.2 - 92,000 450 73,004 71,758 

Sulfide mg/L 0.15 - 72,000 12 97 75 

TDS mg/L 3.4 - 530,000 61,000 75,103 75,077

TOC mg/L 6 - 2,400 130 275 275 

Metals

Aluminum mg/L 0.00018 - 2,200 0.8 817 782 

Arsenic mg/L 0.002 - 23,000 10 29 26

Barium mg/L 0.002 - 3,900 30 7,346 6,891

Beryllium mg/L 0.00002 - 5 0.0001 133 133 

Boron mg/L 0.01 - 650 15 1,774 1,716 

Cadmium mg/L 0.005 - 34,000 4,700 84 78

Calcium mg/L 0.008 - 110,000 2,000 81,353 81,273 

Chromium mg/L 0.0003 - 370 1 1,759 1,750

Cobalt mg/L 0.0003 - 3 0.0055 92 92 

Copper mg/L 0.0001 – 150 0.15 891 799 

Fluorine mg/L 0.05 - 22,000 1.6 174 131 

Lead mg/L 0.001 - 8,200 3 210 152

Lithium mg/L 0.08 - 1,700 6 4,921 4,776 

Magnesium mg/L 0.06 - 47,000 510 80,146 79,818 

Manganese mg/L 0.0007 - 4,100 1.1 2,308 2,097 

Mercury mg/L 0.0005 – 100 60 24 24 

Molybdenum mg/L 0.00028 - 1,500 0.005 351 351 

Nickel mg/L 0.0003 – 70 0.012 482 481 

Potassium mg/L 0.2 - 54,000 140 17,167 17,116 

Selenium mg/L 0.0008 - 0.8 0.021 23 23 

Silver mg/L 0.002 – 3 1 12 12 

Sodium mg/L 0.23 - 150,000 20,000 74,785 74,769 

Strontium mg/L 0.03 - 13,000 180 5,920 5,817 

Thallium mg/L NA 45 1 1 

Thorium mg/L 0.008 - 20 0.02 16 16 

Tin mg/L 0.0001 - 1,600 0.003 286 285 

Titanium mg/L 0.0002 - 30 0.0054 390 390 

Vanadium mg/L 0.00001 - 300 0.0024 299 299 

Zinc mg/L 0.0002 - 580 3 711 651 

Radioactive 

Constituents

Gross Alpha pCi/L 470 - 2,600 1,800 4 4 

Gross Beta pCi/L 400 - 1,100 910 4 4 

Radium 226 pCi/L 81 - 5,300 660 9 9 

Radium 228 pCi/L 26 - 900 130 4 4 
Memorandum

March 31, 2015

Page 6

Table 1. Concentrations of Constituents in COG Produced Water

Constituent 

Category Parameter Units Rangea Median

Number of 

Data Points

Number of 

Detects

NA – range is not applicable because minimum = median = maximum.

Source: COG Wastewater Characterization Analysis - see Attachment 2 (DCN SGE01016.A02).

a – ERG did not use reported minimum and maximum values for the summary tables; instead, ranges were 

defined using the lowest and highest median values (i.e., the minimum value corresponds to the minimum 

median value and the maximum value corresponds to the highest median value). See Section 3.2.4 for more 

details about these calculations.

TDS provides a measure of dissolved matter including salts (e.g., sodium, chloride), 

metals, minerals, and organic material (DCN SGE00046). TDS is not a specific chemical, but is 

defined as the portion of solids that pass through a filter with a nominal pore size of 2.0 μm or 

less (Standard Method 2540C-1997, ASTM D5907-03, and USGS I-1750-85). As reported in 

Table 1, the median concentration of TDS in COG produced water is approximately 60,000 

mg/L. Salts are the majority of TDS in COG produced water and sodium chloride contributes to 

the majority of the TDS in COG produced water (DCN SGE01025). Figure 2 supports these 

generalizations. As seen in the figure, on average, 98 percent of the TDS is comprised of sodium 

and chloride.

Source: COG Wastewater Characterization Analysis - see Attachment 2 (DCN SGE01016.A02)

Figure 2. Anions and Cations Contributing to TDS Concentrations in COG Produced 

Water
Memorandum

March 31, 2015

Page 7

2.0 COG EXTRACTION WASTEWATER MANAGEMENT PRACTICES

The following sections discuss management practices for produced water from COG

resources from national and state-level sources12. For management of drilling wastewater, COG

operators primarily use underground injection, reuse/recycle in subsequent drilling, and transfer 

to a centralized waste treatment (CWT) facility and/or publicly owned treatment works (POTW).

2.1 National Level Data

Table 2 summarizes information from two national studies (DCN SGE01029; DCN 

SGE00182). The first study is from 1995, and the most recent report represents 2007 data. There 

is limited nationwide data available in the literature on COG produced water management 

practices. These studies may have included some UOG extraction wastewater, but based on the 

study time frames and descriptions of the studied waste streams, ERG assumes it was negligible 

and that the numbers can be assumed to primarily represent COG.

Table 2. Nationwide Management of Oil and Gas Produced Water (Percent of Total 

Produced Water Generated)

Management Practices 1995 2007

Underground Injection : Enhanced Recovery 71% 55%

Underground Injection : Disposal 21% 39%

Surface Discharge 3% 4%

Reuse/recycle 2%

2%

Other (e.g., CWT, POTW, evaporation ponds) 3%

Sources: DCN SGE00182; DCN SGE01029

2.2 California

COG produced water in California is primarily managed using Class II disposal and 

enhanced recovery wells (DCN SGE00966, DCN SGE00182). Operators may use other COG 

produced water management practices, including sending wastewater to POTWs. Since 1982, 

COG operators in California have discharged some COG extraction wastewater to POTWs

(DCN SGE01026). As of June 2013, the Sanitation Districts of Los Angeles County have

permitted 66 COG “oil production dischargers” to discharge to three different POTWs. These 66 

dischargers collectively discharge approximately 3.12 million gallons per day (MGD) of COG 

extraction wastewater to POTWs. Of the 66 dischargers, 64 discharge to the Joint Water 

Pollution Control Plant in Carson, California. ERG determined that these 66 dischargers

represent individual wells that are drilled into COG formations (DCN SGE01026).

2.3 Pennsylvania

ERG’s analysis of management practices for COG extraction wastewater is presented in 

the Analysis of Pennsylvania Department of Environmental Protection’s (PA DEP) Oil and Gas 

Waste Reports memorandum (DCN SGE00739). The results of this analysis are shown in Figure 

3 and Figure 4 below for COG drilling wastewater and COG produced water, respectively. As of 

 

12 ERG identified state-level COG produced water management data for California and Pennsylvania.
Memorandum

March 31, 2015

Page 8

2013, four POTWs were accepting COG extraction wastewater from 2,710 different wells in 

Pennsylvania. In Pennsylvania, for the time period shown in Figure 3 and Figure 4 (i.e., 2004 

through 2013), CWT facilities were the most commonly used management practice for both 

COG drilling wastewater and COG produced water. Reuse of COG produced water has gradually 

increased from 2004 to 2013. 
Memorandum

March 31, 2015

Page 9

Note: As reported in the PA DEP Waste Reports, “Other” may include the following management 

practices: land application, road spreading, storage (pending disposal), or treated onsite prior to NPDES 

discharge. As previously mentioned, PA DEP includes CBM well data within the “conventional” well data; 

therefore, the data in Figure 3 may include some CBM data.

Source: DCN SGE00739

Figure 3. COG Drilling Wastewater Management Practices in Pennsylvania
Memorandum

March 31, 2015

Page 10

Note: As reported in the PA DEP Waste Reports, “Other” may include the following management 

practices: land application, road spreading, storage (pending disposal), encapsulation, landfill, or treated 

onsite prior to NPDES discharge. As previously mentioned, PA DEP includes CBM well data within the 

“conventional” well data; therefore, the data in Figure 4 may include some CBM data.

Source: DCN SGE00739

Figure 4. COG Produced Water Management Practices in Pennsylvania 

3.0 SUPPORTING METHODOLOGY

The following two sections discuss ERG’s methodologies for analyzing drilling 

wastewater and produced water characteristics for COG resources.

3.1 COG Drilling Wastewater Characterization Analysis

The following two subsections explain how ERG analyzed COG drilling wastewater 

characterization data.
Memorandum

March 31, 2015

Page 11

3.1.1 COG Drilling Wastewater Characteristics Data Entry and Standardization

ERG entered raw drilling wastewater characterization data into the “DF WW Chara. 

Data” tab in Attachment 1 (DCN SGE01016.A01). ERG entered the following data fields into 

the spreadsheet:

13

 Resource type (i.e., COG);

 Formation;

 Category (e.g., Classical and Conventional); 

 Measured Parameter;

 Reported Measured/Average

14 Value (i.e., value reported in literature);

 Number of Samples;

 Number of Detects;

 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 

“DF WW Chara. Data” tab. 

 Resource Type – ERG identified the well API number and/or well names 

associated with the raw data found in literature and cross-referenced one or both 

fields against to the PA DEP Waste Reports data (DCN SGE00188) to determine 

the resource type15.

 Pollutant Category Assignments – ERG assigned a pollutant category to each 

standard parameter name to allow sorting of measured parameters. For example, 

chloride was assigned to the “Classical and Conventional” category.

 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 

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

wastewater.

3.1.2 COG Drilling Wastewater Characteristics Summary Calculations 

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

calculated summary statistics that appear in the “DF WW Chara. Summary” tab in Attachment 1 

(DCN SGE01016.A01). ERG calculated the following for each parameter reported in the “DF 

WW Chara. Data” tab:

 

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

14 The “average” value in the COG drilling wastewater and characterization data can represent medians, averages, or 

other uncharacterized single values.

15 For more information about how the PA DEP Waste Reports identify resource type, see ERG’s Analysis of PA 

DEP’s Oil and Gas Waste Reports memorandum (DCN SGE00739).
Memorandum

March 31, 2015

Page 12

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

column in the “DF WW Chara. Data” tab.

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

column in the “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 “DF WW Chara. Data” tab.16

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

in the “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 “DF WW Chara. Data” tab.

3.2 COG Produced Water Characterization Database

ERG developed the COG Wastewater Characterization database to collect information

about constituents present in COG produced water. The database compiles information about 

each well (e.g., location), the type of wastewater sampled (i.e., produced water), measured 

constituents, and the range of measured concentrations recorded. The COG Wastewater 

Characterization database is included in Attachment 3 (DCN SGE01016.A03). ERG’s analysis 

and summary of the compiled data are included in Attachment 2 (DCN SGE01016.A02). 

The sources of the data in the COG Wastewater Characterization database and 

descriptions of ERG’s analyses of the collected data are described in detail in the following 

sections of this memorandum.

3.2.1 Data Sources

ERG compiled produced water characterization data from three sources: the 2014 USGS 

Produced Waters Geochemical Database (USGS database), the 2015 PA DEP TENORM study 

report (PA DEP TENORM report), and the 1976 EPA Development Document for Interim Final 

ELGs and Proposed NSPS for the Oil and Gas Extraction PSC (1976 EPA Development 

Document). ERG performed a separate analysis to aggregate data from the USGS database by 

well, as described in Section 3.2.2 and shown in Attachment 4 (DCN SGE01016.A04). After 

completing the USGS database analysis, ERG standardized the data from the USGS database,

PA DEP TENORM report, and 1976 EPA Development Document in the COG Wastewater 

Characterization database, included in Attachment 3 (DCN SGE01016.A03).

3.2.2 USGS Database Analysis

The USGS database contains geochemical and other information for produced waters 

from both conventional and unconventional well types. The database is a compilation of 25 

individual databases, publications, or reports. ERG used the USGS database to obtain produced 

water characterization data to include in the COG Wastewater Characterization Database in 

Attachment 3 (DCN SGE01016.A03).

 

16 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 13

ERG obtained data from the USGS database v.2.0 (provisional) (DCN SGE00956) from 

the USGS website on August 8, 2014 and aggregated the data for inclusion in the “Raw Data 2 -

USGS Data” table in the “COG Wastewater Characterization” database in Attachment 3 (DCN 

SGE01016.A03). The USGS National Produced Waters Geochemical Database v. 2.0 

(PROVISIONAL) – Documentation file (DCN SGE00956) provides additional background about 

this database and defines all of the fields within the tables in the database. ERG used the 

following methodology to analyze the USGS data:

Step 1 – Extract Relevant Data

ERG imported the USGS data into the “USGS Raw Data” table in ERG’s USGS 

Produced Waters database in Attachment 4 (DCN SGE01016.A04) and extracted entries 

where the well type was “conventional hydrocarbon”. 

Step 2 – Compile Unique List of Wells and Assign Well IDs

ERG compiled a list of unique wells, based on the following USGS database fields: 

original database/reference, basin, formation, well name, and well type. ERG assigned 

each unique well in the extracted dataset from Step 1 a “Well ID” that was used to 

aggregate constituent data by well. 

Step 3 – “Un-Crosstab” Data

Because the data were in a crosstab-type format where the parameter names were stored 

in the column headings, ERG used a Visual Basic code to pull the results of each column 

into a single table with three columns containing the following data: Well ID, Parameter, 

and Median Value. ERG then removed any negative or null values17. Non-detect values 

were considered null because no limits of detection were provided. 

Step 4 – Compile Min, Max, and Sample Data 

From the “un-crosstabbed” data set, ERG queried the reported minimum and maximum 

values18 for each unique Well ID and Parameter and added them to a final table. ERG 

also extracted the number of total samples, number of detects, and number of coded 

values (see the “USGS National Produced Waters Geochemical Database v. 2.0 

(PROVISIONAL) – Documentation” file (DCN SGE00956) for information on coded 

values). Coded values were then removed from the “un-crosstabbed” data set.

Step 5 – Calculate Medians

On the “un-crosstabbed” data set, ERG then ran a Visual Basic routine to calculate 

median values for each unique combination of Well ID and Parameter. ERG added the 

 

17 ERG identified some negative values in the data that referred to numeric codes (e.g., “-3=NA, not analyzed, 

unknown”). ERG also identified non-coded negative values in the data that referred to actual data values. ERG was 

unable to find an explanation of these values. These non-coded negative values accounted for a small percentage of 

the full data set; therefore, ERG is comfortable removing them from the analysis since they should not have a 

significant impact on the results.

18 ERG does not use these minimum and maximum values in the subsequent calculations and these values do not 

appear in Table 1. See Section 3.2.4 for an explanation of the values included in Table 1.
Memorandum

March 31, 2015

Page 14

calculated median values to the final summary table based on the data in the “uncrosstabbed” median table. Lastly, the final table was formatted for export into the COG 

Wastewater Characterization database (DCN SGE01016.A03). 

Table 3 shows the methodology for the analyses performed in Attachment 4 (DCN 

SGE01016.A04).

Table 3. USGS Produced Water Database Methodology

Query(s) Query Description

000 Initialized [USGS_Extracted] table.

001 Appended the entries from the entire set of [USGS Raw Data] into [USGS_Extracted], where the well 

type was “conventional hydrocarbon”. 

100 Initialized [List of Wells] table.

101 Extracted all unique combinations of IDDB, REFERENCE, BASIN, FORMATION, DFORM, WELL, 

and WELLTYPE and appended to [List of Wells]. WellID was auto numbered to create a list of all 

unique wells. 

102 Linked [USGS_Extracted] table to [List of Wells] table by IDDB, REFERENCE, BASIN, 

FORMATION, DFORM, WELL, and WELLTYPE, and updated [USGS_Extracted].[WellID] to be 

equal to [List of Wells].[WellID]. This query assigned WellID values in the [USGS_Extracted] table.

103 Updated [List of Wells].[WellID] to text format to allow for linking.

200 Initialized [USGS_Extracted_Data_Only_Crosstab] table.

201 Appended parameter data from [USGS_Extracted] table to [USGS_Extracted_Data_Only_Crosstab] 

table.

300 Initialized [USGS_Extracted_Data_Only_Uncrosstab] table.

301 Ran “Un-crosstab” Function, which pulls data from [USGS_Extracted_Data_Only_Crosstab] and 

outputs to the [USGS_Extracted_Data_Only_Uncrosstab] table.

302 Removed null values from the [USGS_Extracted_Data_Only_Uncrosstab] table.

303 Removed all negative (non-coded) values from the [USGS_Extracted_Data_Only_Uncrosstab] table.

400 Initialized [USGS_Extracted_Data_Only_Uncrosstab_Total Sample Count] table.

401 Queried and appended total number of samples for each combination of [WellID] and [Parameter] to the 

[USGS_Extracted_Data_Only_Uncrosstab_Total Sample Count] table.

402 Make table to extract data by detects, and each coded value (-1 through -4)

403 Updated [USGS_Extracted_Data_Only_Uncrosstab_Total Sample Count] table with the results of query 

402.

500 Removed all negative values (all remaining coded values) from the 

[USGS_Extracted_Data_Only_Uncrosstab] table.

501 Initialized [USGS_Extracted_Data_Only_Uncrosstab_MoreThan2Values] table.

502a Queried all combinations of [WellID] and [Parameter] that had more than 2 detected values. (Note: 

these queries were used to only calculate medians for situations where more 2 values were reported, 

which greatly reduces total calculation time).

502b Appended results of query 502a to [USGS_Extracted_Data_Only_Uncrosstab_MoreThan2Values] table.

600 Initialized [USGS_Extracted_Data_Only_Median_Summary] table.

601 Ran Visual Basic code to calculate medians for values 

[USGS_Extracted_Data_Only_Uncrosstab_MoreThan2Values] and output to 

[USGS_Extracted_Data_Only_Median_Summary] table.

700 (x2) Initialize [USGS Data Summary] and [USGS_Extracted_Data_Min and Max Per Well] tables

701 Appended [USGS_Extracted_Data_Only_Uncrosstab_Total Sample Count] table to [USGS Data 

Summary] table

702 Appended min and max data from [USGS_Extracted_Data_Only_Uncrosstab] to 

[USGS_Extracted_Data_Min and Max Per Well] table.
Memorandum

March 31, 2015

Page 15

Table 3. USGS Produced Water Database Methodology

Query(s) Query Description

703-706 Updated the [USGS Data Summary] table with the min, max, median values, and well information.

707 Updated special case units in [USGS Data Summary] based on [lkpUnits] crosswalk.

708 Updated remaining units in [USGS Data Summary].

709 Updated Number of Detect count to zero in [USGS Data Summary] if is null.

710 Removed min and max values from [USGS Data Summary] if there was only single value present.

711 Standardized the format for easy import in to a separate database: Added reference to USGS, 2014; set 

all WW Descriptions to “Produced”, etc.

3.2.3 COG Wastewater Characterization Database Key Fields and Standardization 

Methodology

The COG Wastewater Characterization database (DCN SGE01016.A03) combines 

information from the USGS database, the PA DEP TENORM report, and the 1976 EPA 

Development Document and presents standardized wastewater characterization information, 

including: 

 Measured constituent;

 Constituent category (e.g., metal);

 Wastewater description (i.e., produced water); 

 Sample information (e.g., number of samples, units); and 

 Concentration values (e.g., minimum value, median value19, maximum value).

ERG extracted the information listed above from each data source, where available. Missing data 

elements were marked as “unknown.” 

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 

database. The following sections provide details on how ERG standardized the overall dataset to 

establish consistency. All of the data, crosswalks, and analyses described below are contained 

within the COG Wastewater Characterization database (DCN SGE01016.A03).

Data Preparation

ERG prepared the USGS data using the methodology described in Section 3.2.2. ERG did 

not need to prepare the data from the PA DEP TENORM report or the 1976 EPA Development 

Document because these data were in a format that allowed them to be directly entered into the 

COG Wastewater Characterization database (DCN SGE01016.A03). 

 

19 The “median” field in the COG Wastewater Characterization database can represent medians, averages, or other 

uncharacterized single values. For the data from the USGS dataset, values in this field represent medians, as 

calculated by ERG (see Section 3.2.2). ERG did not calculate these values for the PA DEP and EPA 1976 datasets, 

therefore values are as reported in the data sources (i.e., medians, averages, or other uncharacterized single values).
Memorandum

March 31, 2015

Page 16

ERG placed data related to the measured constituent and wastewater description into 

“raw” data fields, capturing the data as they were reported by the source. Before performing any 

analyses on the dataset, ERG removed all leading and trailing spaces from the raw data fields. 

The queries related to the data preparation are “000a_create Pollutant Concentrations 

table shell” through “000g_Update Source Quality Flags”, shown in Table 4. 

Constituent Standardization and Constituent Category Assignments

ERG created a list of all constituents included in the underlying data sources and created 

a crosswalk “Pollutant Parameter Crosswalk” to standardize constituent names. For example, 

“Co” and “Cobalt” were standardized to “Cobalt.” 

In a separate “Pollutant Categories Crosswalk,” ERG assigned primary and secondary 

(optional) categories for each standard constituent name to allow for grouping and analysis of 

certain constituents. For example, aluminum was placed in the “Metals” category. All crosswalks 

used in the data standardization and/or analyses are contained in the database. 

The query related to the constituent standardization and category assignments is 

“001_Update Parameter Names and Categories”, shown in Table 4. 

Wastewater Description Standardization

ERG standardized wastewater descriptions provided in each data source using the “WW 

Description Crosswalk” in the COG Wastewater Characterization database (DCN 

SGE01016.A03). ERG captured wastewater descriptions as reported in the existing data source 

and did not reclassify any wastewater descriptions. ERG only standardized names (e.g., 

“produced formation water” was standardized to “produced water”).

The query related to the wastewater description standardization is “002_Update WW 

Descriptions”, shown in Table 4. 

Units of Measure Standardization

ERG converted reported constituent concentrations to standardized units of measure 

appropriate for each constituent. ERG established a crosswalk, “Unit Definition Crosswalk,” in 

the database to list units and conversion factors.

The queries related to the units of measure standardization are “003a_Update 

Units_Uranium pCi/L” through “003d_Update Units_pH”, shown in Table 4. 
Memorandum

March 31, 2015

Page 17

Minimum, Median20, and Maximum Data

For each set of reported constituent concentrations for a particular constituent from a 

given source, ERG compared the minimum, median20, and maximum values, where available, to 

ensure regularity in the data. If the reported values did not reflect the correct relative sequence 

(minimum value < median value < maximum value), ERG reviewed the values to determine the 

source of error, and if appropriate, corrected the values so that the correct relative sequence was 

maintained. ERG only considered non-null values in the analysis. Note that values reported as 

zero were not considered null values.

In some cases, data sources indicated that certain values were not measured because they 

did not exceed the limit of detection. Where a source reported a non-detect value but listed the 

associated limit of detection, ERG used the limit of detection as the measured value. Where a 

source reported a non-detect value but did not report the associated limit of detection, ERG did 

not assign a value. 

The queries related to the minimum, median, and maximum values standardization are 

“101 - Make Table Pollutant Conc FINAL” through “104_Median FINAL”, shown in Table 4. 

Table 4. Descriptions of Queries in COG Wastewater Characterization Database (DCN 

SGE01016.A03)

Table/Query Name Table/Query Description

Raw Data 1 – PADEP Raw data from the Pennsylvania Department of Environmental Protection’s (PA 

DEP) Technologically Enhanced Naturally Occurring Radioactive Materials 

(TENORM) Study Report (DCN SGE01028)

Raw Data 2 – USGS Data Raw data from the United States Geological Survey’s (USGS) Produced Water 

Geochemical Database v. 2.0 (PROVISIONAL) (DCN SGE00956)

Raw Data 3 – EPA 1976 Raw data from the EPA’s 1976 Development Document for Interim Final Effluent 

Limitations Guidelines (ELGs) and Proposed New Source Performance Standards

(NSPS) for the Oil and Gas Extraction Point Source Category (PSC) (DCN 

SGE00621)

Pollutant Categories 

Crosswalk

Crosswalk generated by ERG that assigns a pollutant category and (optional) 

secondary pollutant category to each raw pollutant name from existing literature; 

also flags pollutants of interest for this analysis

Pollutant Parameter 

Crosswalk

Crosswalk generated by ERG that matches raw pollutant names reported in existing 

literature to standardized pollutant names

Unit Definition Crosswalk Crosswalk generated by ERG that matches raw units reported in existing literature 

to standardized units and includes a conversion factor for the associated 

concentration values, where relevant

WW Description Crosswalk Crosswalk generated by ERG that matches raw wastewater descriptions reported in 

existing literature to standardized wastewater descriptions

000a_create Pollutant 

Concentrations table shell

Creates a blank table shell with the fields of interest for this analysis

000b_Append Raw Data 1 -

PADEP

Appends the data from the “Raw Data 1 – PADEP” table

000c_Append Raw Data 2 -

USGS Data

Appends the data from the “Raw Data 2 – USGS Data” table

 

20 The “median” field in the COG Wastewater Characterization database can represent medians, averages, or other 

uncharacterized single values. For the data from the USGS dataset, values in this field represent medians, as 

calculated by ERG (see Section 3.2.2). ERG did not calculate these values for the PA DEP and EPA 1976 datasets, 

therefore values are as reported in the data sources (i.e., medians, averages, or other uncharacterized single values).
Memorandum

March 31, 2015

Page 18

Table 4. Descriptions of Queries in COG Wastewater Characterization Database (DCN 

SGE01016.A03)

Table/Query Name Table/Query Description

000d_Append Raw Data 3 -

EPA 1976

Appends the data from the “Raw Data 3 – EPA 1976” table

000e_Trim Raw Fields Removes all leading and trailing spaces from the Parameter_Raw, Basin, 

WellType_Raw, WWSampleDescription_Raw, and Units_Raw fields

000f_Delete placeholder row Deletes the placeholder row created in query 000a and any rows that were 

unintentionally imported and do not contain any characterization data

000g_Update Source Quality 

Flags

Updates the “SourceQualityFlag” field to “A” for all entries in the “Pollutant 

Concentrations” tablea

001_Update Parameter 

Names and Categories

Updates the pollutant categories in the “Pollutant Concentrations” table using the 

“Pollutant Categories Crosswalk” and the “Pollutant Parameter Crosswalk” tables

002_Update WW 

Descriptions

Updates the wastewater descriptions categories in the “Pollutant Concentrations” 

table using the “WW Description Crosswalk” table

003a_Update Units_Uranium 

pCi/L

Updates the minimum, median, and maximum values and the units for instances 

where the pollutant reported was “Uranium” and the units reported were “mg/L” in 

the raw data

003b_Update Units_All 

Parameters

Updates the minimum, median, and maximum values and the units in the “Pollutant 

Concentrations” table using the “Unit Definition Crosswalk” table

003c_Update 

Units_Unitless_Specific 

Gravity

Updates the units to “Unitless” in the “Pollutant Concentrations” table for instances 

where the pollutant reported was “Specific Gravity”

003d_Update Units_pH Updates the units to “SU” in the “Pollutant Concentrations” table for instances 

where the pollutant reported was “pH”

101 - Make Table Pollutant 

Conc FINAL

Creates the “Pollutant Concentration_FINAL” table by pulling the pollutants of 

interest for this analysis from the “Pollutant Concentrations” table and excluding 

records where the “NumberSamples” field is null

102_Min FINAL Updates the minimum concentration value if the reported values did not reflect the 

correct relative sequence (minimum value < median value < maximum value)

103_Max FINAL Updates the maximum concentration value if the reported values did not reflect the 

correct relative sequence (minimum value < median value < maximum value)

104_Median FINAL Updates the median concentration value if the reported values did not reflect the 

correct relative sequence (minimum value < median value < maximum value)

201_TDS Contributing Ions 

Data

Pulls data for TDS, chloride, and sodium where the median concentration value is 

not null

202_COG Produced Water 

Characterization Data

Pulls data from the “Pollutant Concentration_FINAL” table where the median 

concentration value is not null for use in calculating summary values for Table 1

Pollutant Concentrations Table generated in query “000a_create Pollutant Concentrations table shell” and 

updated using queries 000b through 003d

Pollutant 

Concentrations_FINAL

Table generated in query “101 - Make Table Pollutant Conc FINAL” and updated 

in queries 102 through 104

a – See Section 4.0 for definitions of source flags

3.2.4 Data Summary Analysis 

Once ERG standardized all of the data and compiled it into a single summary table in the

database, ERG exported data for the selected constituents from the database to Excel to generate 

summary tables and figures for this memorandum. Attachment 2 (DCN SGE01016.A02) 

includes the Excel file with the exported data and all of the analyses that ERG conducted to 

generate summary tables and figures for this memorandum. The Table of Contents (TOC) in 

Attachment 2 indicates the specific tabs with data and calculations for each COG figure and 

table.
Memorandum

March 31, 2015

Page 19

ERG did not use reported minimum and maximum values for the summary tables; 

instead, ranges were defined using the lowest and highest median values (i.e., the minimum 

value corresponds to the minimum median value and the maximum value corresponds to the 

highest median value).21

ERG generated Table 1 in Section 1.2 by tabulating the minimum of the median data 

field, median of the median data field, maximum of the median data field, number of data points, 

and number of detects22 for each applicable constituent23.

ERG generated Figure 2 in Section 1.2 by first tabulating the median concentration for 

the primary ionic contributors to TDS (i.e., chloride, sodium)

24 (see the “TDS Contrib Ions Data” 

tab in Attachment 2, DCN SGE01016.A02). ERG listed the primary ionic contributors as 

individual constituents, while minor contributors were combined into the “Other Dissolved 

Constituents” category for the purpose of Figure 2.

4.0 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 data and information related to COG resources.

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 

(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 which are defined below. Only documents prepared by a government agency or for a 

government agency were used in this analysis.

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

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

 

21 As discussed previously, the “median” values may represent medians, averages, or other uncharacterized single 

values.

22 Number of data points was based on the total number of samples taken; number of detects was based on the 

number of data points with valid measurements. 

23 ERG excluded five pH values that were greater than 14 SU because these were determined to be outliers. 

24 ERG determined that chloride and sodium made up 98% of the TDS and therefore, included these two 

constituents as the primary ionic contributors in Figure 2.
Memorandum

March 31, 2015

Page 20

 Source Flag B – Documents prepared by a verified25 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.

EPA and ERG followed PQAPP procedures for spreadsheets (Section 7.0) and databases 

(Section 8.0) to generate, evaluate, and analyze data using a spreadsheet and databases. ERG 

conducted the following QA checks during the analyses:

 ERG created the databases and spreadsheets provided in Attachments 1-4 (DCN 

SGE01016.A01-04) to track useful data and to document analyses.

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

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

documented these checks in internal versions of the spreadsheets and databases.

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

rulemaking reviewed the results from each analysis in the spreadsheets and 

databases.

5.0 REFERENCES

Table 5 lists the references that ERG used for the analyses discussed in this 

memorandum. ERG assigned source flags to each of the sources referenced in this memorandum 

(see Section 4.0 for definitions of source flags).

Table 5. References Used for This Memorandum

DCN Source Citation Source Flaga

SGE00046 Abdalla, Charles W.; Drohan, Joy R.; Blunk, Kristen S.; Edson, Jessie. 2011. 

Marcellus Shale Wastewater Issues in Pennsylvania - Current and Emerging 

Treatment and Disposal Technologies. Penn State Cooperative Extension, 

College of Agricultural Sciences.

B

SGE00182 Clark, C.E., et al. 2009. Produced Water Volumes and Management Practices in 

the United States.

A

SGE00188 O'Connell, James, ERG.2014. Pennsylvania Department of Environmental 

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

A

SGE00621 U.S. EPA. 1976. Development Document for Interim Final Effluent Limitations 

Guidelines and Proposed New Source Performance Standards for the Oil and 

Gas Extraction Point Source Category. (September).

A

SGE00625 U.S. EPA. 2015. Site Visit Report: Southwestern Energy (SWN) Fayetteville 

Shale Gas Operations Sanitized.

A

 

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 oil and gas industry. 
Memorandum

March 31, 2015

Page 21

Table 5. References Used for This Memorandum

DCN Source Citation Source Flaga

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

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).

A

SGE00956 Madalyn S. Blondes, Kathleen D. Gans, James J. Thordson, Mark E Reidy, Burt 

Thomas, Mark A Engle, Yousif K Kharaka, Elizabeth L Rowan. U.S. 

Geological Survey (USGS) National Produced Waters Geochemical Database 

v2.0 (PROVISIONAL).

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

SGE00966 CCST. 2014. Advanced Well Stimulation Technologies in California: An 

Independent Review of Scientific and Technical Information.

A

SGE00984 Energy Information Administration (EIA). 2014. Glossary. Retrieved from 

http://www.eia.gov/tools/glossary

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 1).

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 2).

A

SGE01025 U.S. Department of the Interior Bureau of Reclamation. 2011. Oil and Gas 

Produced Water Management and Beneficial Use in the Western United States.

A

SGE01026 Sanitation Districts of Los Angeles County. 2013. Memorandum: Districts' 

Pretreatment Program for Oil Production. (June 14).

A

SGE01028 Pennsylvania Department of Environmental Protection (PA DEP). 2015. 

Technologically Enhanced Naturally Occurring Radioactive Materials 

(TENORM) Study Report.

A

SGE01029 ICF Consulting. 2000. Overview of Exploration and Production Waste Volumes 

and Waste Management Practices in the United States.

B

a—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).

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

information.

6.0 ATTACHMENTS
ATTACHMENT 1 – COG DRILLING WASTEWATER CHARACTERIZATION DATA (DCN

SGE01016.A01)
ATTACHMENT 2 – COG PRODUCED WATER CHARACTERIZATION DATA (DCN

SGE01016.A02)
ATTACHMENT 3 – COG WASTEWATER CHARACTERIZATION DATABASE (DCN

SGE01016.A03)
ATTACHMENT 4 –USGS PRODUCED WATER DATABASE – COG DATA (DCN SGE01016.A04)