MEMORANDUM

TO: Lisa Biddle, EPA

Karen Milam, EPA

FROM: James K. O’Connell, ERG

Jason Sese, ERG

Brent Ruminski, ERG 

Sarah Yates, ERG

DATE: June 6, 2016

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

SGE01177)

This memorandum describes 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, it includes discussions about data limitations related to the drilling 

fluids and drilling wastewater from COG extraction operations.

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

applies to both COG and UOG extraction (except coalbed methane)1, the rule would add 

pretreatment standards only for facilities engaged in oil and gas extraction from UOG sources 

that send their discharges to POTWs. EPA is reserving 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 and final rule. Because COG extraction

wastewater was not included in the scope of this 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 obtained 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 COG extraction wastewater characterization data

 Section 2.0 COG extraction wastewater management practices on a national and 

state-level

 Section 3.0 methodology used by ERG to complete data analyses not described in 

other supporting memoranda

 Section 4.0 ERG’s quality control procedures

 Section 5.0 lists the references used for these analyses

 

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 memorandum.
Memorandum

June 6, 2016

Page 2

 Section 6.0 provides the attachments to this memorandum

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

data and analysis are contained in: 

 Attachment 1 – COG Drilling Wastewater Characterization Data (DCN 

SGE01177.A01).

 Attachment 2 – COG Produced Water Characterization Data (DCN 

SGE01177.A02).

 Attachment 3 – COG Wastewater Characterization Database (DCN 

SGE01177.A03).

 Attachment 4 – USGS Produced Water Database – COG Data (DCN 

SGE01177.A04).

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. Several categories of constituents are present in most types 

of drilling wastewater (DCN SGE00733):

 Salt (total dissolved solids);

 Oil and grease;

 Inorganic and organic compounds; and

 Chemical additives used during drilling.

ERG identified minimal available COG drilling wastewater characteristics data

(specifically chloride 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)2issued to a number of POTWs by the Pennsylvania Department 

of Environmental Protection (PA DEP) (DCN SGE00986, DCN SGE00987). The PA DEP data 

for COG drilling wastewater included chloride data showing concentrations between 16,000 

mg/L and 40,000 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.

 

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

wastewater from UOG operations. 
Memorandum

June 6, 2016

Page 3

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

including naturally occurring ions.3 Salinity or salt concentrations, referred to throughout this 

memorandum as TDS, can vary from less than 4,100 to 220,000 mg/L in COG produced water

(see Table 1). 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: chloride, sodium, calcium, cadmium, magnesium, bicarbonate, and sulfate

(DCN SGE01025, DCN SGE01133). Many metals 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).

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 in COG produced water 

from ERG’s analysis of the following sources:

 United States Geological Survey’s (USGS) Produced Water Geochemical 

Database v. 2.1 (PROVISIONAL) (DCN SGE001260)

4

 Pennsylvania Department of Environmental Protection’s (PA DEP) 

Technologically Enhanced Naturally Occurring Radioactive Materials 

(TENORM) Study Report (DCN SGE01028)

 

3 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).

4 This is a comprehensive database covering 37 states from 1885 to 2013.
Memorandum

June 6, 2016

Page 4

 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

Lower and 

Upper Rangea Median

Number of 

Data Points

Number of 

Detects

Classical and 

Conventional

Alkalinity mg/L 13 - 32 18 53 53

Bicarbonate mg/L 59 - 1,700 330 78,441 77,800

Carbonate mg/L 24 - 420 96 10,577 9,182

Chloride mg/L 710 - 150,000 39,000 84,170 84,141

Nitrate mg/L 4.1 - 340 44 3,245 3,222

pH SU 5.6 - 8.3 7.1 63,016 62,926

Phosphate mg/L 0.18 - 6.3 2 39 28

Specific Conductivity mg/L 48,000 - 210,000 120,000 270 258

Sulfate mg/L 20 - 3,200 440 75,690 74,314

Sulfide mg/L 0.41 - 530 12 96 74

TDS mg/L 4,100 - 220,000 59,000 76,595 76,569

TOC mg/L 24 - 770 130 275 275

Metals

Aluminum mg/L 0.086 - 32 0.8 830 795

Arsenic mg/L 0.69 - 240 20 39 36

Barium mg/L 2.2 - 200 30 7,482 7,027

Beryllium mg/L 0.00003 - 0.83 0.00013 146 146

Boron mg/L 2.3 - 99 16 1,805 1,747

Cadmium mg/L 0.005 - 8.7 3.1 42 36

Calcium mg/L 40 - 15,000 2,000 84,629 84,549

Chromium mg/L 0.0052 - 5 1 1,773 1,764

Cobalt mg/L 0.001 - 3 0.007 103 103

Copper mg/L 0.024 - 1.2 0.15 904 812

Fluorine mg/L 0.77 - 14 3 205 162

Lead mg/L 1 - 62 3 221 163

Lithium mg/L 1 - 47 6 5,057 4,912

Magnesium mg/L 15 - 2,800 500 83,376 83,046

Manganese mg/L 0.03 - 50 1.1 2,224 2,014

Mercury mg/L 0.0023 - 89 60 24 24

Molybdenum mg/L 0.0013 - 0.056 0.0056 370 370

Nickel mg/L 0.002 - 1.1 0.012 494 493

Potassium mg/L 11 - 2,300 140 17,834 17,783

Selenium mg/L 0.0084 - 380 0.065 54 54

Silver mg/L 0.0035 - 28 1.7 22 22
Memorandum

June 6, 2016

Page 5

Table 1. Concentrations of Constituents in COG Produced Water

Constituent 

Category Parameter Units

Lower and 

Upper Rangea Median

Number of 

Data Points

Number of 

Detects

Sodium mg/L 1,200 - 69,000 20,000 77,992 77,976

Strontium mg/L 10 - 1,300 180 6,041 5,938

Thallium mg/L 45 - 45 45 1 1

Thorium mg/L 0.017 - 1.3 0.048 26 26

Tin mg/L 0.0006 - 0.04 0.003 296 295

Titanium mg/L 0.0011 - 0.06 0.0054 390 390

Vanadium mg/L 0.0004 - 0.021 0.0024 299 299

Zinc mg/L 0.4 - 78 3 723 663

Radioactive 

Constituents

Gross Alpha pCi/L 690 - 2,500 1,800 4 4

Gross Beta pCi/L 530 - 1,100 910 4 4

Radium 226 pCi/L 130 - 5,100 660 9 9

Radium 228 pCi/L 31 - 690 130 4 4

Source: COG Wastewater Characterization Analysis - see Attachment 2 (DCN SGE01177.A02).

a –ERG defined lower and upper ranges using the 10th and 90th percentiles of the median values (i.e., the lower 

range corresponds to the 10th percentile of the median value and the upper range corresponds to the 90th 

percentile of the median value).

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 as specified by Standard Method 2540C-1997.

5 As reported in Table 1, the median 

concentration of TDS in COG produced water is approximately 59,000 mg/L. Salts are the 

majority of TDS in COG produced water consisting predominately of sodium and chloride (DCN 

SGE01025). Figure 2 supports these generalizations, which is based on ERG’s analysis of the 

USGS Produced Water Geochemical Database v. 2.1 (PROVISIONAL) (DCN SGE001260). As 

seen in the figure, on average, 91 percent of the TDS is comprised of sodium and chloride.

 

5 40 CFR part 136 lists Standard Method 2540C as an approved test method for TDS.
Memorandum

June 6, 2016

Page 6

Source: COG Wastewater Characterization Analysis - see Attachment 2 (DCN SGE01177.A02)

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

Water

2.0 COG EXTRACTION WASTEWATER MANAGEMENT PRACTICES

The following sections discuss management practices for extraction water from COG

resources from national and state-level sources6. 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 three national studies:

 1995: Overview of Exploration and Production Waste Volumes and Waste 

Management Practices in the United States published by ICF Consulting (DCN 

SGE01029)

 2007: Data from a previous report from 2007 included in the U.S. Produced 

Water Volumes and Management Practices in 2012 report published by John Veil 

in 2015 (DCN SGE01128)

 

6 ERG identified state-level COG extraction wastewater management data for California and Pennsylvania.
Memorandum

June 6, 2016

Page 7

 2012: Current data included in the U.S. Produced Water Volumes and 

Management Practices in 2012 report published by John Veil in 2015 (DCN 

SGE01128)

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 that 

the numbers primarily represent COG.

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

Total Produced Water Generated)

Management Practice 1995 2007 2012

Underground Injection : Enhanced Recovery 71% 59% 46%

Underground Injection : Disposal 21% 40% 40%

Surface Discharge 3% 0.8% 3%

Reuse/recycle 2%

2% 11%

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

Sources: DCN SGE01029; DCN SGE01128

2.2 California

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

enhanced recovery wells (DCN SGE00966, DCN SGE01214, DCN SGE01128). Operators also 

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 had

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, with most (64 of the 66 dischargers) discharging to the Joint 

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

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

2.3 Pennsylvania

ERG’s analysis of Pennsylvania’s 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 SGE01182). The results of this analysis 

are shown in Figure 3 and Figure 4 below for COG drilling wastewater and COG produced 

water, respectively. In 2014, five POTWs were accepting COG extraction wastewater from 3,853

different wells in Pennsylvania. In Pennsylvania, from 2004 through 2014, CWT facilities were 

the most commonly used management practice for both COG drilling wastewater and produced 

water. Reuse of COG produced water has gradually increased from 2004 to 2014.
Memorandum

June 6, 2016

Page 8

Source: DCN SGE01182

Figure 3. COG Drilling Wastewater Management Practices in Pennsylvania7

 

7 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.
Memorandum

June 6, 2016

Page 9

Source: DCN SGE01182

Figure 4. COG Produced Water Management Practices in Pennsylvania8

3.0 SUPPORTING METHODOLOGY

The following two subsections discuss ERG’s methodologies for analyzing COG 

extraction wastewater characteristics.

3.1 COG Drilling Wastewater Characterization Analysis

The following explains how ERG analyzed COG drilling wastewater characterization

data.

 

8 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.
Memorandum

June 6, 2016

Page 10

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 SGE01177.A01). ERG entered the following data fields into 

the spreadsheet:

9

 Resource type (i.e., COG);

 Formation;

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

 Measured Parameter;

 Reported Measured/Average10 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 measurement 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 SGE01245) to determine 

the resource type11.

 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 SGE01177.A01). ERG calculated the following for each parameter reported in the “DF 

WW Chara. Data” tab:

 

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

10 The “reported measured/average” value in the COG drilling wastewater and characterization data can represent 

medians, averages, or other uncharacterized single values.

11 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 SGE01182).
Memorandum

June 6, 2016

Page 11

 Lower range – 10th percentile value of the “Reported Measured/Average Value” 

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

 Upper range – 90th percentile value of the “Reported Measured/Average Value” 

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

 Range – Combines the lower and upper values into a range.

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

column in the “DF WW Chara. Data” tab.12

 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.

ERG defined lower and upper ranges using the 10th and 90th percentiles of the reported 

measured/average values (i.e., the lower range corresponds to the 10th percentile of the median 

value and the upper range corresponds to the 90th percentile of the median value).

3.2 COG Produced Water Characterization Analysis

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 SGE01177.A03). ERG’s analysis 

and summary of the compiled data are included in Attachment 2 (DCN SGE01177.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 below.

3.2.1 Data Sources

ERG compiled produced water characterization data from three sources: 

 2014 USGS Produced Waters Geochemical Database (USGS database)

(SGE01260)

 2015 PA DEP TENORM study report (PA DEP TENORM report) (DCN 

SGE01028) 

 1976 EPA Development Document for Interim Final ELGs and Proposed NSPS 

for the Oil and Gas Extraction PSC (1976 EPA Development Document) (DCN 

SGE00621)

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 SGE01177.A04). After completing 

the USGS database analysis, ERG standardized the data from the USGS database, PA DEP 

 

12 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 6, 2016

Page 12

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

Characterization database, included in Attachment 3 (DCN SGE01177.A03).

3.2.2 USGS Database Analysis

The USGS database contains geochemical and other information for produced waters 

from both conventional and unconventional oil and gas 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 SGE01177.A03).

ERG obtained data from the USGS database v.2.1 (provisional) (DCN SGE01260) from 

the USGS website on December 8, 2015 and aggregated the data using the steps below for 

inclusion in the “Raw Data 2 - USGS Data” table in the “COG Wastewater Characterization” 

database in Attachment 3 (DCN SGE01177.A03). The USGS National Produced Waters 

Geochemical Database v. 2.1 (PROVISIONAL) – Documentation file (DCN SGE01260) 

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 SGE01177.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 values13. Non-detect values 

were considered null because no limits of detection were provided.

 

13 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.
Memorandum

June 6, 2016

Page 13

Step 4 – Compile Min, Max, and Sample Data 

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

values14 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. 2.1

(PROVISIONAL) – Documentation” file (DCN SGE01260) 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 

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 SGE01177.A03). 

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

SGE01177.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)

 

14 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

June 6, 2016

Page 14

Table 3. USGS Produced Water Database Methodology

Query(s) Query Description

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.

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 SGE01177.A03) combines 

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

Development Document and presents standardized wastewater characterization information on a 

well basis, 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 value15, maximum value).

 

15 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

June 6, 2016

Page 15

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 SGE01177.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 SGE01177.A03). 

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 

SGE01177.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. 
Memorandum

June 6, 2016

Page 16

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. 

Minimum, Median16, and Maximum Data

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

given source, ERG compared the minimum, median16, and maximum values, where available, to 

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

(i.e., the minimum value is less than the median value which is less than the maximum value), 

ERG reviewed the values to determine if there was 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 lower range, median, and upper range 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 

SGE01177.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. 2.1 (PROVISIONAL) (DCN SGE01260)

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

 

16 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

June 6, 2016

Page 17

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

SGE01177.A03)

Table/Query Name Table/Query Description

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

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 by well ID and sample date. Also 

included is the count of data points for each well ID. For example, a record that 

had a measured value for TDS and chloride but not sodium was reported as 2

data points.

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
Memorandum

June 6, 2016

Page 18

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

SGE01177.A03)

Table/Query Name Table/Query Description

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 all of the data was compiled into a single standardized table in the Attachment 3 

database, ERG exported the data to the Microsoft Excel spreadsheet contained in Attachment 2. 

In Attachment 2 (DCN SGE01177.A02), ERG generated 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.

The “Summary COG PW Char Data” tab in Attachment 2 contains the standardized data 

generated by the database queries in Attachment 3. Using the raw data in the “COG PW Char 

Data” tab, ERG generated Table 1 in Section 1.2 by tabulating the lower range, median, and 

upper range of concentration along with the number of data points and detects17 for each 

applicable constituent.

18 ERG defined lower and upper ranges using the 10th and 90th percentiles

of the median values for each well ID (i.e., the lower range corresponds to the 10th percentile of 

the median value and the upper range corresponds to the 90th percentile of the median value).

The “TDS Contrib Data” tab in Attachment 2 contains the standardized TDS, chloride, 

and sodium data generated by the database query 201 in Attachment 3. These concentrations for 

TDS, chloride, and sodium are aggregated for each well ID and sample date. Only well IDs with 

measured values for all three constituents are included. On the “Summary TDS Contrib Data” 

tab, ERG calculated the average concentration for TDS, chloride, and sodium. Next, to estimate 

the typical concentration of “Other Dissolved Constituents”, ERG subtracted the sum of average 

chloride and average sodium concentrations from the average TDS concentration. ERG 

generated Figure 2 in Section 1.2 using these results.

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 

 

17 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. 

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

June 6, 2016

Page 19

(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.

 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 verified19 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 

SGE01177.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 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. et. al. 2011. Marcellus Shale Wastewater Issues in PACurrent & Emerging Treatment & Disposal Technologies. Penn State 

Cooperative

B

 

19 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

June 6, 2016

Page 20

Table 5. References Used for This Memorandum

DCN Source Citation Source Flaga

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 Fayetteville Shale Gas 

Operations. Sanitized.

A

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

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 U.S. Energy Information Administration. 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 AO 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 AO 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 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

SGE01128 Veil, J. 2015. US Produced Water Volumes & Management Practices in 2012. 

Veil Environmental, LLC. Prepared for Ground Water Protection Council 

(GWPC).

B

SGE01133 Benko, K.L. and Drewes, J.E. 2008. Produced Water in the Western US: 

Geographical Distribution, Occurrence, and Composition. US Bureau of 

Reclamation.

A

SGE01182 ERG. 2016. Analysis of Pennsylvania Department of Environmental 

Protection’s Oil and Gas Waste Reports.

A

SGE01214 California Council on Science and Technology. 2015. An Independent 

Scientific Assessment of Well Stimulation in California.

B

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

Statewide Oil and Gas Waste Reports. (November)

A

SGE01260 U.S. Geological Survey (USGS). 2014. National Produced Waters Geochemical 

Database v2.1 (Provisional).

A
Memorandum

June 6, 2016

Page 21

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

SGE01177.A01)
ATTACHMENT 2 – COG PRODUCED WATER CHARACTERIZATION DATA (DCN

SGE01177.A02)
ATTACHMENT 3 – COG WASTEWATER CHARACTERIZATION DATABASE (DCN

SGE01177.A03)
ATTACHMENT 4 –USGS PRODUCED WATER DATABASE – COG DATA (DCN SGE01177.A04)