Prepared in cooperation with the Ohio Water Development Authority

Chemical and Isotopic Characteristics of Methane in 

Groundwater of Ohio, 2016

Scientific Investigations Report 2018–5097

U.S. Department of the Interior

U.S. Geological Survey

Chemical and Isotopic Characteristics of 

Methane in Groundwater of Ohio, 2016

By Mary Ann Thomas

Scientific Investigations Report 2018–5097

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

RYAN K. ZINKE, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2018

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must be secured from the copyright owner.

Suggested citation: 

Thomas, M.A., 2018, Chemical and isotopic characteristics of methane in groundwater of Ohio, 2016: U.S. Geological 

Survey Scientific Investigations Report 2018–5097, 42 p., https://doi.org/10.3133/sir20185097.

ISSN 2328–031X (print) 

ISSN 2328–0328 (online) 
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................2

Description of the Study Area ............................................................................................................4

Background and Previous Studies ....................................................................................................7

Methods Used to Evaluate Methane Origin ............................................................................7

Conventional Gas Deposits ........................................................................................................7

Unconventional Gas Deposits ...................................................................................................7

Methane in Water Wells.............................................................................................................8

Methods of Study...........................................................................................................................................8

Sample Collection and Analysis.........................................................................................................8

Quality Control.....................................................................................................................................10

Isotopic Nomenclature ......................................................................................................................10

Characteristics of the Well Network ........................................................................................................11

Groundwater Quality ...................................................................................................................................12

Dissolved Gases and Methane Concentrations ............................................................................12

Dissolved Inorganic Constituents ....................................................................................................13

Stable Isotopes of Water...................................................................................................................14

Chemical and Isotopic Characteristics of Methane and Related Constituents ................................15

Stable Isotopes of Methane..............................................................................................................15

Gas Dryness.........................................................................................................................................15

Isotopic Characteristics of Microbial Methane ............................................................................17

Fractionation of Hydrogen Isotopes .......................................................................................18

Carbon Isotope System.............................................................................................................19

Carbon-13 of Dissolved Inorganic Carbon....................................................................19

Fractionation of Carbon Isotopes...................................................................................19

Rayleigh-Type Fractionation ...........................................................................................21

Methane Oxidation by Sulfate Reduction.....................................................................21

Carbon-14 of Methane .......................................................................................................................22

Interpretation of Methane Origin ..............................................................................................................23

Samples with Chemical and Isotopic Characteristics Consistent 

with Microbial Methane.......................................................................................................24

Samples with Chemical and Isotopic Characteristics not Consistent 

with Microbial Methane.......................................................................................................25

Limitations of the Study .....................................................................................................................26

Summary and Conclusions.........................................................................................................................27

References Cited..........................................................................................................................................29
iv

Figures

1. Maps showing location of Ohio counties and wells included in a study of methane in

domestic wells, 2016 ....................................................................................................................3

2. Maps showing geology of the study area. A, Major structural features of Ohio and

surrounding States. B, Location of domestic wells sampled for methane (2016) in

relation to bedrock formations of Ohio .....................................................................................5

3. Map showing location of domestic wells sampled for methane (2016) in relation to the

extent and thickness of glacial deposits in Ohio.....................................................................6

4. Graph showing composition of headspace gases in water samples from domestic

wells in Ohio, 2016 ......................................................................................................................12

5. Graph showing methane concentrations in water samples from domestic wells

in Ohio, 2016.................................................................................................................................12

6. Graph showing stable isotopes of water from domestic wells in Ohio, 2016...................14

7. Graphs showing gas classification diagrams showing samples from domestic wells

in Ohio. A, Whiticar plot. B, Bernard plot................................................................................16

8. Graph showing relation between the stable hydrogen isotopic signature of water and

methane for samples from domestic wells in Ohio, 2016.....................................................18

9. Graphs showing stable carbon isotopic signature (δ13C) of methane in relation to A,

δ13C of dissolved inorganic carbon and B, δ13C of carbon dioxide and δ13C fractionation

factors for samples from Ohio domestic wells, 2016 ............................................................20

10. Graph showing carbon-14 of methane from domestic wells in Ohio, 2016.......................22

11. Graph showing stable carbon isotopic signature of methane in relation to well depth

and geologic formation for 12 samples interpreted as microbial methane formed by

carbon dioxide reduction in Ohio domestic wells, 2016.......................................................24

Tables

1. Methods used for collection and analysis of water-quality samples..................................9

2. Results of quality-control samples analyzed at U.S. Geological Survey National

Water Quality Laboratory ..........................................................................................................34

3. Results of quality-control samples analyzed at Isotech Laboratories and

U.S. Geological Survey Reston Groundwater Dating Laboratory.......................................36

4. Characteristics of Ohio domestic wells sampled for methane, 2016.................................11

5. Water-quality data from Ohio domestic wells, 2016 .............................................................37

6. Methane concentrations and selected water-quality constituents from

Ohio domestic wells, 2016 .........................................................................................................13

7. Chemical and isotopic characteristics of methane and related constituents from

domestic wells in Ohio, 2016.....................................................................................................23
v

Conversion Factors

U.S. customary units to International System of Units 

Multiply By To obtain

Length

foot (ft) .03048 meter (m)

mile (mi) 1.609 kilometer (km)

Volume

gallon (gal) 3.785 liter (L)

Mass

ounce, avoirdupois 28.35 gram (g)

Supplemental Information

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25  ̊C). 

Concentrations of chemical constituents in water are given in milligrams per liter (mg/L) or 

micrograms per liter (μg/L). 
vi

Abbreviations 

BLS below land surface

CaCO3 calcium carbonate

CH4 methane

Cl chloride

CO2 carbon dioxide

CO3 carbonate

δ delta (stable isotope notation)

DIC dissolved inorganic carbon

GMWL Global Meteoric Water Line

HCO3 bicarbonate

H2CO3 carbonic acid

H2O water

Mg magnesium

Na sodium

NO3 nitrate

per mil parts per thousand

pMC percent modern carbon

SO4 sulfate

USGS U.S. Geological Survey
Chemical and Isotopic Characteristics of Methane in 

Groundwater of Ohio, 2016

By Mary Ann Thomas

Abstract

In 2016, the U.S. Geological Survey, in cooperation 

with the Ohio Water Development Authority, investigated the 

hydrogeologic setting, chemical and isotopic characteristics, 

and origin of methane in groundwater of Ohio. Understanding 

the occurrence and distribution of methane in groundwater is 

important in terms of public safety because methane in water 

wells can pose a risk of explosion. In addition, documenting the chemical and isotopic characteristics of methane in 

groundwater can make an important contribution to future 

stray gas investigations.

Water samples were collected from 15 domestic water 

wells known to produce methane, which were in 12 counties 

in diverse parts of Ohio. The wells were 75–345 feet deep and 

tapped a range of aquifer types, including glacial deposits and 

bedrock of Upper Ordovician, Upper Devonian, Lower Mississippian, and Pennsylvanian ages. Although the hydrogeologic settings were varied, there was a broad similarity among 

the well sites in that the bedrock was predominantly shale and 

the glacial deposits were predominantly clay.

The wells were sampled for dissolved inorganic constituents; dissolved organic carbon; methane and other dissolved 

gases; stable isotopes (carbon, hydrogen, and oxygen) of 

methane, water, and dissolved inorganic carbon; and carbon-14 of methane. Gas composition and stable isotopes of 

methane were used to differentiate thermogenic and microbial 

methane. The degree of fractionation of hydrogen and carbon isotopes was used to evaluate the pathway of microbial 

methanogenesis (carbon dioxide [CO2

] reduction or acetate 

fermentation) and the effects of secondary processes such as 

oxidation, mixing, and migration. The concentration of carbon-14 of methane was used to evaluate the relative age of the 

carbon source.

The quality of water from the 15 wells differed greatly; 

water types ranged from CaMgHCO3 to NaCl, and total dissolved solids concentrations ranged from 318 to 2,940 milligrams per liter (mg/L). Methane concentrations ranged from 1.2 

to 120 mg/L. Of the 15 samples, 12 had methane concentrations 

greater than 28 mg/L, the level that can pose a risk of explosion.

Of the 15 samples, 12 had chemical and isotopic characteristics or “signatures” consistent with microbial methane formed by CO2

reduction. CO2reduction is commonly

associated with microbial degradation of organic matter

in anaerobic aquifers and with the formation of microbial

shale gas and coalbed methane along margins of sedimentary basins. Two of 15 samples were interpreted as having

a component of thermogenic methane based on the δ

13C of 

methane (−50.96 and −47.74 parts per thousand [per mil]) 

and gas dryness (28 and 5). One of 15 samples (from the

shallowest well) had chemical and isotopic characteristics

consistent with methane oxidation by sulfate reduction based

on light δ

13C of dissolved inorganic carbon (−31.6 per mil)

and evidence of sulfate reduction in terms of the odor and

appearance of the water.

For the 12 samples interpreted as microbial methane 

formed by CO2 reduction, the δ13C of methane varied from 

−75 to −56 per mil. Multiple samples from the same aquifer

demonstrated a general trend of increasing δ13C of methane

with depth. Samples with lighter δ13C of methane (−75 to

−62 per mil) were from shallower wells (or wells with shallow

open intervals), and the isotopic signature of the water was

consistent with modern or postglacial groundwater recharge.

Three samples with heavier δ13C of methane (−61 to −56 per

mil) were from deeper wells or more confined aquifers, where

the isotopic signature of water was consistent with older

(glacial) recharge. In addition, δ13C of dissolved inorganic

carbon was enriched (+12 to +18.9 per mil), and carbon-14 of

methane was consistent with carbon associated with Paleozoic

bedrock or older glacial deposits. These observations are generally consistent with increased Rayleigh-type fractionation

at greater depths; however, other interpretations are possible.

Isotopic signatures can be ambiguous, especially in areas with

complex geologic histories that include multiple episodes of

migration, mixing, and (or) oxidation.

Many of the wells were in proximity to multiple potential 

natural and anthropogenic pathways of methane migration; 

however, it is not possible to determine if the methane in any 

of the wells is related to human activities based on the chemical and isotopic data collected for this study.
2 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

Introduction

Methane (CH4) is a gas that forms from the breakdown 

of organic matter in a variety of environments. Thermogenic 

methane forms in the deep subsurface, where high temperatures transform sedimentary organic matter into conventional 

hydrocarbon deposits. Methane also forms by microbial processes (microbial methanogenesis) in shallower environments 

such as landfills, wetlands, marshes, and marine sediments. 

Conditions conducive to microbial methanogenesis also exist 

in parts of the groundwater system.

It is generally known that methane can exist naturally in 

groundwater; however, little is known about its occurrence and 

distribution in Ohio groundwater. When well water is pumped 

to the surface, decreasing pressure causes dissolved methane 

to come out of solution. If methane accumulates in a closed 

space, such as a well housing or basement, an explosive environment can form; immediate preventative action is recommended if methane concentrations greater than 28 milligrams 

per liter (mg/L) are detected in a water well (Eltschlager and 

others, 2001). An increased understanding of where methane 

is most likely to occur would allow public-safety education to 

be directed to areas of greatest need. 

When a rare explosion does occur, it can be important to 

determine whether the methane formed by natural processes 

in the aquifer or migrated from another location as stray gas. 

This can be difficult to discern because of the prevalence and 

variety of potential sources of methane and the general lack of 

information about naturally occurring methane in groundwater 

of Ohio. For example, are there chemical or isotopic 

characteristics that distinguish natural methane in groundwater 

from other sources, especially those linked to anthropogenic 

activities such as oil/gas production, coal mining, or landfills? 

Do the chemical isotopic characteristics of natural methane 

differ among aquifers? This type of information could 

contribute to future investigations of suspected contamination 

of groundwater by stray gas.

In 2016, the U.S. Geological Survey (USGS), in cooperation with the Ohio Water Development Authority, began an 

investigation to increase understanding of the occurrence and 

chemical/isotopic characteristics of methane in Ohio aquifers.

Purpose and Scope

This report presents results of an investigation of methane in groundwater of Ohio. The objectives were to (1) identify a network of domestic wells that produce methane, 

(2) describe the hydrogeologic settings in which methane is

detected, (3) document the chemical and isotopic characteristics of the methane and the coexisting water, and (4) evaluate

the origin of the methane, to the extent possible. The goal

was to select wells that produce methane that is unrelated to

human activities.

A total of 15 domestic water wells were selected from 

12 counties in diverse parts of Ohio (fig. 1). The wells were 

sampled once during 2016 and analyzed for field parameters; 

dissolved chemical constituents; dissolved gases; and carbon, hydrogen, and oxygen isotopes of methane, water, and 

dissolved inorganic carbon. Well logs and geologic spatial 

coverages were used to describe the hydrogeologic settings of 

the well sites. The nature and origin of methane was evaluated 

using methods attributed to Whiticar and others (1986), Whiticar (1999), Schoell (1980, 1988), Bernard and others (1978), 

and Coleman and others (1988, 1995).
Introduction 3

MAD18-EMNF00-1833_fig 01

Base from U.S. Geological Survey digital data, National Map 2015, StatePlane Ohio South, North American Datum of 1983

0 15 30 60 MILES

0 20 40 80 KILOMETERS Wells included in this study

EXPLANATION

Cincinnati

Columbus

Cleveland DEFIANCE HENRY 

CRAWFORD 

MONTGOMERY 

GREENE PERRY 

MUSKINGUM 

COLUMBIANA 

SUMMIT 

GEAUGA 

ASHTABULA

STARK 

42°

40°

38°

42°

40°

38°

84° 82°

84° 82°

Figure 1. Location of Ohio counties and wells included in a study of methane in domestic wells, 2016.
4 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

Description of the Study Area

Ohio is underlain by bedded sedimentary rocks that were 

deformed into broad arches and basins (fig. 2A). The Cincinnati and Findlay Arches underlie the Indiana-Ohio Platform 

in western Ohio, an area where bedrock is nearly flat lying. 

The northwestern corner of Ohio is along the southern margin 

of the Michigan Basin, where bedrock formations dip gently 

toward the north and northwest. Eastern Ohio is along the 

western margin of the Appalachian Basin, where bedrock 

formations dip gently toward the east and southeast. The 

sedimentary strata are about 2,500 feet (ft) thick in western 

Ohio, and increase to more than 13,000 ft thick in southeastern Ohio (Coogan, 1996). The strata are displaced by multiple fault systems, some of which extend to basement rocks 

(Baranoski, 2013).

The bedrock formations at land surface (or beneath glacial deposits) range in age from Ordovician to Upper Pennsylvanian/Lower Permian (fig. 2B) (Slucher and others, 2006). 

Upper Ordovician bedrock, which consists of interbedded 

shale and limestone, subcrops in southwestern Ohio near the 

Cincinnati Arch. Silurian bedrock, which consists of dolomite and lesser amounts of shale, subcrops in western Ohio. 

Devonian strata subcrop in the northwest corner of the State, 

along Lake Erie in Northern Ohio, and in a north-south trending band in central Ohio. Lower and Middle Devonian rocks 

are predominantly carbonates and shale, and Upper Devonian 

strata are organic-rich shales and sandstone. Mississippian 

bedrock, which consists of interbedded shales and sandstones, 

subcrops in eastern Ohio. Pennsylvanian and Lower Permian strata consist of alternating sequences of shale, sandstone, 

siltstone, limestone, and coal. These rocks subcrop in eastern 

and southeastern Ohio.

For about two-thirds of the State, bedrock is overlain 

by unconsolidated sediments, most of which were deposited during the most recent episode of Pleistocene glaciation 

(fig. 3). The deposits are predominantly fine grained and range 

in thickness from 0 to more than 700 ft (Ohio Department of 

Natural Resources, Division of Geological Survey, 2004b). 

The thickest glacial deposits are in deep buried valleys cut into 

bedrock by the ancient Teays River system. Groundwater used 

for drinking water is produced from glacial deposits and (or) 

bedrock. The largest groundwater supplies are from glacial 

outwash beneath principal streams and Silurian carbonate 

bedrock (Eberts and George, 2000). Shales provide sufficient 

water for domestic use in most areas. 

Ohio has a long history of coal mining and oil/gas 

(hydrocarbon) production. Coal is mined from Pennsylvanian 

and Permian bedrock in eastern and southeastern Ohio, and 

extensive fields of coal bed methane are in Harrison County 

(Ohio Department of Natural Resources, Division of Geological Survey, 2004a). Hydrocarbons are produced from a wide 

range of depths (50–9,100 ft) and geologic formations (Cambrian to Pennsylvanian), and commercial quantities of hydrocarbons have been identified in 67 of the 88 counties (Ohio 

Department of Natural Resources, Division of Geological 

Survey, 2004a). During the early 1900s, large volumes of oil 

were produced from Upper Ordovician Trenton Limestone in 

northwestern Ohio, but production has diminished. Since then, 

most of the hydrocarbon production has been from the eastern 

one-third of the State, where conventional wells have been 

used to produce hydrocarbons from sandstones of Cambrian–

Pennsylvanian-ages. Since about 2008, horizontal drilling and 

hydraulic fracturing have been used to extract unconventional 

shale gas, primarily from the Upper Ordovician age Utica 

Shale along the eastern and southeastern margins of the State.

A large percentage of hydrocarbons in Ohio are sourced 

from organic-rich Devonian shale in deep parts of the Appalachian, Michigan, and Illinois Basins, where the rocks are 

thermally mature (East and others, 2012). However, most of 

the Devonian shale in Ohio is thermally immature, indicating 

that hydrocarbons in Devonian or younger bedrock migrated 

from deeper in the basin or are of microbial origin (East and 

others, 2012).
Introduction 5

mad18-EMNF00-1833_fig 02

●!●!

●!

●!

●!

●!

●!

●!

●!

●!

●!

●! ●!

●!

●! CR-63

HY-53

DE-29 DE-28

PE-59

CO-31

SU-23

GR-755

MU-128

ST-141

ST-139

ST-140

AB-142 GE-368

MT-1286

82°

82°

84°

84°

40° 40°

Permian and/or Pennsylvanian

0 15 30 60 MILES

0 40 80 20 KILOMETERS

Bedrock formations

Devonian

Devonian and/or Mississippian

Mississippian

Ordovician

Pennsylvanian

Silurian

EXPLANATION

[Bedrock formations from Slucher and others, 2006]

0 35 70 140 MILES

0 110 220 55 KILOMETERS

80°

80°

82°

82°

84°

84°

86°

86°

88°

88°

42° 42°

40° 40°

Base from U.S. Geological Survey Small-scale Dataset—

State Boundaries of the United States 200506 

StatePlane Ohio South

North American Datum of 1983

EXPLANATION

Approximate boundaries of sedimentary 

 basins (after Coogan, 1996)

Base from U.S. Geological Survey digital data, 

National Map

2015 StatePlane Ohio South

North American Datum of 1983

LAKE MICHIGAN

Kankakee Arch

OHIO

ONTARIO

INDIANA

MICHIGAN

PENNSYLVANIA

WEST

VIRGINIA

KENTUCKY

Appalachian 

Basin

Michigan

Basin

Illinois basin ILLINOIS

NEW

YORK

Indiana-Ohio Platform

LAKE ERIE

Findlay Arch

Cincinnati Arch

A

B

Figure 2. Geology of the study area. A, Major structural features of Ohio and surrounding States. 

B, Location of domestic wells sampled for methane (2016) in relation to bedrock formations of Ohio. 
6 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

●!●

●

●

● ●

●

●

●

●

●!

●!

●!

●

●

CR-63

HY-53

DE-29 DE-28

PE-59

CO-31

SU-23

GR-755

MU-128

ST-141

ST-139

ST-140

GE-368 AB-142

MT-1286

80°

82°

82°

84°

84°

42° 42°

40° 40°

38° 38°

0 15 30 60 MILES

0 40 80 20 KILOMETERS Drift thickness, in feet

0−20

20.1−100

100.1−300

300.1−723

Base from U.S. Geological Survey digital data,

National Map, 2015

StatePlane Ohio South

North American Datum of 1983

EXPLANATION

[Drift thickness from Ohio Division of Geological Survey, 2004b]

Figure 3. Location of domestic wells sampled for methane (2016) in relation to the extent and thickness of glacial deposits in 

Ohio.
Introduction 7

Background and Previous Studies

Methane forms from the breakdown of organic matter by 

thermal or microbial processes. Thermogenic methane forms 

in the deep subsurface, where high temperatures and pressures 

crack complex organic compounds into successively simpler 

compounds, the simplest of which is methane. In contrast, 

microbial methane forms in shallower, lower-temperature 

environments as a byproduct of microbial reduction of organic 

matter. Acetate fermentation is the predominant microbial 

pathway in near-surface environments, and carbon dioxide 

(CO2) reduction is the predominant pathway in groundwater 

systems and marine sediments (Whiticar and others, 1986; 

Whiticar, 1999; Schoell, 1980, 1988).

Methods Used to Evaluate Methane Origin

The isotopic composition of methane is partly related to 

the environment of formation. Isotopes are atoms of the same 

element with different numbers of neutrons and, therefore, 

slightly different masses. Although the mass differences are 

minor, they can be sufficient to cause isotope fractionation, 

whereby isotopes preferentially partition into one phase or 

another. Isotope fractionation occurs during some microbial 

processes because microbes preferentially select lighter isotopes, which have weaker bonds that are easier to break. Partly 

as a result of isotope fractionation, methane formed by microbial processes is isotopically lighter than thermogenic methane, and this difference has been widely used as an indicator of 

methane origin (Schoell, 1980; Whiticar, 1999).

Another characteristic used to differentiate thermogenic 

and microbial methane is gas composition, specifically, the 

ratio of methane to higher-chain hydrocarbons. Because 

thermogenic gas forms by cracking apart complex organic 

compounds, it typically contains substantial concentrations 

of higher-chain hydrocarbons. In contrast, microbial processes produce gas that is predominantly methane, and has 

only minor amounts of ethane and propane (Bernard and 

others, 1978).

Gas classification diagrams based on gas composition and 

(or) stable isotopes of methane have been used to evaluate the 

origin of methane (Whiticar and others, 1986; Whiticar, 1999; 

Schoell, 1980, 1988; Bernard and others, 1978). The degree of 

2

H and 13C fractionation between methane and its precursors 

(water [H2O] and CO2) has been used to identify pathways of 

microbial methanogenesis. In addition, the concentration of 

carbon-14 (the radioactive isotope of carbon) in methane has 

been used to estimate the relative age of the carbon precursor 

(Coleman and others, 1988, 1995). A major complication is 

that chemical and isotopic characteristics or “signatures” of 

methane can be altered by secondary processes such as mixing, migration, and oxidation, so interpretations of methane 

origin can be ambiguous, especially in regions with complex 

geologic histories.

Conventional Gas Deposits

Thermogenic methane is typically associated with commercial production of conventional hydrocarbons, which form 

by thermal maturation of organic-rich source beds (shales) 

in deep parts of sedimentary basins. After formation, hydrocarbons migrate updip and accumulate in a porous reservoir 

bed with a low permeability seal. Conventional hydrocarbons 

are typically extracted using traditional vertical wells with or 

without enhanced secondary stimulation. Thermogenic methane is most productive in deeper sections of a basin where 

organic matter is more thermally mature and has experienced 

more thermal cracking.

Heavier carbon and hydrogen isotopic signatures and 

lower concentrations of higher-chain hydrocarbons are related 

to a greater degree of thermal maturity, which generally 

increases with depth/age of the formation. As a result, chemical and isotopic characteristics of methane and higher-chain 

hydrocarbons have been used to unravel the complex history of hydrocarbon formation, migration, and mixing in the 

Appalachian Basin (Jenden and others, 1993; Laughrey and 

Baldassare, 1998; Burruss and Laughrey, 2010; Baldassare 

and others, 2014). In addition, gas composition and isotopes 

of methane and higher-chain hydrocarbons have been used to 

distinguish thermogenic gas from different geologic formations; for example, in northern West Virginia, the chemical and 

isotopic characteristics of methane in Upper Devonian bedrock is distinctly different from methane in Middle Devonian 

Marcellus Shale (Sharma and others, 2015).

Unconventional Gas Deposits

Shale gas and coal bed methane are considered to be 

unconventional gas resources because they form in situ and 

are extracted using horizontal drilling and hydraulic fracturing. Although conventional hydrocarbons are predominantly 

of thermogenic origin, unconventional gas deposits can be 

thermogenic, microbial, or mixed (Golding and others, 2013). 

Chemical and isotopic data have been used to investigate the 

origin of methane in parts of the Michigan Basin (Martini 

and others, 1998; McIntosh and others, 2002) and Illinois 

Basin (Coleman and others, 1988; McIntosh and others, 2002; 

Strapoc and others, 2007; Schegel and others, 2011). Commercial reserves of shale gas in Upper Devonian shale in northern 

Michigan are largely of microbial origin where the influx of 

meteoric water during or since Pleistocene glaciation created 

a favorable environment for microbial methanogenesis. In 

contrast, methane in Upper Devonian shale is of thermogenic 

origin near the center of the basin, where burial depths are 

greater and temperatures are higher (Martini and others, 1998)

Strapoc and others (2007) investigated commercial 

deposits of coal bed methane in Pennsylvanian-age bedrock 

along the eastern margin of the Illinois Basin, in Indiana and 

Kentucky. Chemical and isotopic data showed that methane 
8 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

was microbial in Indiana, where thermally immature bedrock 

is relatively shallow, and open to invasion of meteoric water 

through fractures. In contrast, methane is of thermogenic origin in Kentucky, where the formation was deeply buried in an 

area that had been more tectonically active.

Osborn and McIntosh (2010) documented isotopic and 

chemical characteristics of methane from Upper Devonian 

shales in the northern Appalachian Basin. Microbial methane was detected in shallow water wells along the margin 

of Lake Erie in northeastern Ohio, Pennsylvania, and New 

York. At depths greater than about 500 ft, methane was determined to be largely thermogenic but had evidence of some 

microbial activity.

Methane in Water Wells

Prior to shale gas development in the Appalachian 

Basin, a 2005 sampling effort examined methane in northern 

Pennsylvania water wells (Breen and others, 2007; Révész 

and others, 2012). Since the start of shale gas development in the Appalachian Basin, the occurrence and isotopic 

characteristics of methane in water wells has been investigated in parts of eastern Ohio (Botner, 2015), northeastern 

Pennsylvania (Osborn and others, 2011; Warner and others, 

2012; Jackson and others, 2013; Molofsky and others, 2013; 

Darrah and others, 2015; Senior and others, 2016), New 

York (Heisig and Scott, 2013), and West Virginia (Chambers 

and others, 2015; Sharma and others, 2014; and Harkness 

and others, 2017). 

Methane was analyzed in samples from 27 water wells 

that tap Pennsylvanian-age bedrock in eastern Ohio, and the 

origin was interpreted to be microbial or coal bed methane 

(Botner, 2015). Multiple studies have investigated the origin 

of methane in groundwater of northeastern Pennsylvania and 

(or) New York. Some investigators linked the presence of 

thermogenic methane to proximity to active shale gas wells 

(Osborn and others, 2011). Other investigators concluded that 

the presence of thermogenic methane was related to proximity 

to valleys, which are underlain by fractures that serve as natural pathways for migration of methane and (or) brine (Molofsky and others, 2013; Heisig and Scott, 2013).

The chemical and isotopic characteristics of methane in 

water wells of northern West Virginia have been documented 

by Sharma and others (2014), Chambers and others (2015), 

and Harkness and others (2017). A detailed investigation 

that included noble gas tracers in addition to methane isotopes determined that methane in groundwater is primarily 

microbial, with a ubiquitous, low proportion of thermogenic 

methane that migrated (along with saline water) along natural 

pathways (Harkness and others, 2017).

Methods of Study

For this study, groundwater samples were collected 

from 15 domestic wells known to produce methane. The 

Ohio Department of Natural Resources well log database was 

queried to select well logs that included “methane” or “gas” 

as part of the drillers’ notes (Wayne Jones, Ohio Department 

of Natural Resources, written commun., 2016). The dataset 

included more than 1,000 wells, although a substantial number 

of wells were relatively old (pre-1970), could not be geographically located, or were abandoned after drilling because of 

an insufficient water supply. Some candidate wells also were 

identified through discussions with local health departments. 

Candidate sites were narrowed down by focusing on newer 

wells in a range of aquifers and geographic areas. An attempt 

was made to avoid sites near potential sources of methane 

related to human activities, but this proved to be impractical 

because potential sources of methane are ubiquitous.

Sample Collection and Analysis

Water samples were collected from domestic wells using 

existing submersible pumps. The wells were purged before 

sampling, and samples were collected from outside taps not 

connected to any form of water treatment. A summary of the 

methods used for collection and analysis of the samples is 

shown in table 1.

Unstable physical and chemical properties (pH, specific 

conductance, water temperature, turbidity, dissolved oxygen, alkalinity, and hydrogen sulfide) were measured in the 

field, and samples for analysis of major ions, nutrients, trace 

elements, arsenic speciation, and dissolved organic carbon 

were analyzed at the USGS National Water Quality Laboratory. Methods used for sample collection and preservation are 

described in U.S. Geological Survey (variously dated).

Samples of dissolved gases and isotopes of methane, 

water, and dissolved inorganic carbon (DIC) were analyzed 

at Isotech Laboratories, Champaign, Ill. Samples for analysis 

of dissolved gases and isotopes of carbon and hydrogen in 

methane (including carbon-14) were collected in collapsible, 

preevacuated containers in which a benzalkonium chloride 

preservative capsule had been inserted (Isotech Laboratories, 

Inc., 2014). Samples for analysis of isotopes of hydrogen 

and oxygen in water and carbon in DIC were filtered using 

a 45-micron capsule filter and preserved by chilling (Keith 

Hackley, Isotech Laboratories, written commun., 2016).

Dissolved gases analyzed at the USGS Reston Groundwater 

Dating Laboratory were collected in septum vials and analyzed 

for nitrogen, carbon dioxide, oxygen, argon, and methane using 

methods described in U.S. Geological Survey (2016a, 2016b).
Methods of Study 9

Table 1. Methods used for collection and analysis of water-quality samples.

[USGS, U.S. Geological Survey; mg/L, milligram per liter; μg/L, microgram per liter; δ, isotopic ratio delta notation] 

Laboratory Analytes Methods 

Measured before sample 

collection

Field parameters: pH, specific conductance, water temperature,

turbidity, dissolved oxygen, alkalinity, hydrogen sulfide

USGS (variously dated)

USGS National Water 

Quality Laboratory, 

Denver, Colorado

Major ions, in mg/L:

Calcium, magnesium, potassium, sodium, sulfate, chloride, 

bromide, fluoride, silica, dissolved solids

Sample collection:

USGS (variously dated);

Sample analysis:

Fishman (1993);

Garbarino and others (2012); 

Brenton and Arnette (1993)

Nutrients, in mg/L: 

Ammonia, nitrate plus nitrite, nitrite, orthophosphate, total 

nitrogen

Trace elements, in μg/L:

Aluminum, antimony, arsenic, barium, beryllium, cadmium, 

chromium, copper, iron, lead, lithium, manganese, molybdenum, 

nickel, silver, strontium, thallium, vanadium, zinc

Arsenic speciation, in μg/L:

Arsenite, arsenate, monomethlyarsonate, dimethylarsinate

Dissolved organic carbon, in mg/L

Isotech Laboratory, 

Champaign, Illinois

Dissolved gases:

Fixed gases, in mole percent:

Nitrogen, oxygen, carbon dioxide, argon, carbon monoxide,

 helium, hydrogen

Sample collection and analysis:

Isotech Laboratories, Inc. (2014)

Hydrocarbon gases, in mole percent:

 Methane (CH4), ethane (C2H6), ethene (C2H4), propane (C3H8), 

 propene (C3H6), n- and iso-butane (C4H10) n-and iso-pentane, (C5H12),

hexane and heavier hydrocarbons (C6H14

+

)

Hydrocarbon gases, in mg/L:

 Methane (CH4), ethane (C2H6), propane (C3H8)

Stable isotopes, in per mil:

Methane (δ13C; δ2H)

Water (δ2H; δ18O)

Dissolved inorganic carbon1 (δ13C)

Radiogenic isotopes, in percent modern carbon:

Methane, carbon-14 (14C)

USGS Groundwater 

Dating Laboratory, 

Reston, Virginia

Dissolved gases, in mole percent:

Nitrogen, oxygen, carbon dioxide, argon

Sample collection and analysis: 

USGS (2016a, 2016b)

1

Samples were unfiltered.
10 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

Quality Control

Quality-control samples were analyzed to assess variability and bias of the water-quality data collected during this 

study. Quality-control samples were analyzed at the USGS 

National Water Quality Laboratory for major ions, trace elements, nutrients, arsenic speciation, and dissolved organic 

carbon (table 2, p. 34). Before the start of sampling, an equipment blank was collected and analyzed for trace elements to 

identify if the sampling equipment could be a source of bias. 

During the 21⁄2 weeks of sample collection, two field blanks 

were collected to assess if field methods could be a source of 

bias. A total of three pairs of sequential replicates were collected to assess variability related to lab or field methods. The 

equipment and field blanks did not show detections of any of 

the constituents. For the replicate samples, the percent difference was calculated as the difference between concentrations 

for two samples divided by the mean concentration. Differences between replicate pairs were less than 15 percent for all 

constituents except for lithium (17 percent), dissolved organic 

carbon (38 percent) and zinc (57 percent). For lithium, the 

variability can be linked to small differences in low concentrations that were just above the reporting limits. For dissolved 

organic carbon and zinc, the cause of the variability is not 

known; however, it is not judged to be a substantial concern in 

relation to this investigation.

A total of two pairs of sequential replicates were analyzed 

for dissolved gases and isotopes of methane and water at 

Isotech Laboratories (table 3, p. 36). Differences between 

replicate pairs were less than 15 percent for all constituents, 

except for helium (17 percent), 13C of DIC (27 percent), and 

propane (29 percent). For helium and propane, the variability 

can be linked to small differences in low concentrations that 

were just above reporting limits. For the carbon isotopic 

composition of DIC, the calculated variability may overstate 

the actual variability because the carbon isotopic composition 

of DIC spans negative and positive values.

One of the replicate pairs analyzed at Isotech Laboratories also was submitted to the USGS Reston Groundwater Dating Laboratory to assess analytical differences 

between the two laboratories. The samples were analyzed 

for methane, oxygen, nitrogen, carbon dioxide, and argon. 

The results revealed substantial differences between the labs 

(from 29 percent to more than 190 percent), which are likely 

related to substantial differences in methods used for sample 

collection, preservation and holding times, and lab analysis 

(table 1). Another factor that likely affected the variability is 

that the replicate sample was from the well with the maximum 

methane concentration (120 mg/L as determined by Isotech 

Laboratories). The sample collection method recommended 

by Isotech Laboratories prevents methane loss from degassing 

better than the method recommended by the USGS Groundwater Dating Laboratory (Molofsky and others, 2013).

Isotopic Nomenclature

Isotopic ratios represent the relative difference in the ratio 

of the less abundant isotope to the more abundant isotope (R) 

with respect to a standard. Isotopic data are expressed in parts 

per thousand (per mil or ‰) using standard δ notation (Clark 

and Fritz, 1997): 

δsample = ([Rsample−Rstandard]/Rstandard)*1,000 (1)

A sample that is enriched in the heavy isotope relative 

to the standard has a positive δ value, and a sample that is 

depleted in the heavy isotope relative to the standard has a 

negative δ value. 

For stable carbon isotopes, R is 13C/12C, and the standard 

is Vienna Peedee belemnite (Clark and Fritz, 1997). For stable 

hydrogen isotopes, R is 2H/1H, and the standard is Vienna 

Standard Mean Ocean Water. For stable oxygen isotopes, R

is 18O/16O, and the standard is Vienna Standard Mean Ocean 

Water (Clark and Fritz, 1997).
Characteristics of the Well Network 11

Characteristics of the Well Network

The 15 wells sampled for this study produce water and 

methane from a range of aquifer types, including Pleistocene 

glacial deposits and four bedrock units: Pennsylvanian shale, 

sandstone, siltstone limestone, and coal; Lower Mississippian 

shale and sandstone; Upper Devonian organic-rich shale (also 

referred to as black shale); and Upper Ordovician shale and 

limestone (table 4). The unconsolidated deposits that overlie 

bedrock are predominantly glacial clay, and range in thickness 

from 4 to more than 171 ft. A similarity among the 15 wells is 

that the bedrock is predominantly shale and the glacial deposits are predominantly clay. 

The wells are 75–345 ft deep, with a median depth of 

about 171 ft. The water levels were 9.75 to 85.86 ft below land 

surface (BLS). The depth to the top of the open interval ranges 

from 31 to 190 ft BLS. In general, construction characteristics 

of the wells in eastern Ohio differed from those in western 

Ohio. The nine bedrock wells in eastern Ohio are constructed as 

open holes and produce water from relatively long open intervals (15 to 302 ft). Of the six wells in western Ohio, one bedrock well has an open interval of 254 ft, but the other five wells 

produce from well screens that are relatively short (3–13 ft).

Table 4. Characteristics of Ohio domestic wells sampled for methane, 2016. 

[ft, feet; BLS, below land surface; >, greater than]

Well

 identifier

Well 

depth 

(ft BLS)

Lithology and 

thickness (ft) 

of glacial deposits

Type of open 

interval; depths of 

open interval (ft)

Lithology; drillers notation of gas

Pennsylvanian shale, sandstone, siltstone, limestone, coal

ST-139 235 Clay/sand/gravel

160

Open hole

190–235

Shale overlain by 160-ft glacial deposits.

ST-140 295 Clay/sand

10

Open hole 

 149–295

Interbedded sandstone/sandy shale with thin coal and limestone.

ST-141 301 Clay

24

Open hole 

 69–301

Interbedded shale/sandstone with thin coal and limestone.

CO-31 345 Clay

15

Open hole 

 43–345

Interbedded shale/sandstone with black limestone and shale. 

Gas at 280 ft (black/gray shale).

MU-128 263 Clay 

50

Open hole 

 51–263

Interbedded shale/sandstone with thin coal. Gas at 131 ft 

(sandstone above thin coal).

Lower Mississippian shale and sandstone

AB-142 94 Clay/gravel

19

Open hole 

 31–94

Gray/black shale with sandstone. Gas at 94 ft (shale at base of well). 

GE-368 150 Clay and sand

32

Open hole 

 40–150

Shale and sandstone. Gas at 118 ft (shale).

SU-23 95 Clay; sand/gravel 

75

Open hole 

 80–95

Shale. Gas at 75 ft (interface of glacial deposits and shale).

PE-59 190 Loam

4

Open hole 

 169–190

Sandstone and shale. 

Upper Devonian black shale; glacial deposits 

DE-29 144 Clay/gravel/hardpan

>144

Well screen 

 141–144

144 ft of glacial deposits overlying Upper Devonian shale. Gas at 93 ft 

(thin sand within clay). 

HY-53 128 Clay/gravel/ hardpan

120

Well screen

 120–128

Black shale. Gas at 119 ft (thin sand/gravel directly above shale). 

DE-28 93 Clay

78

Well screen 

 80–93

Brown shale.

CR-63 75 Clay

35

Well screen 

 72–75

Black shale. Gas at 68 ft. Sulfur odor noted.

Upper Ordovician shale and limestone; glacial deposits

GR-755 171 Clay

>171

Well screen 

168–171

171 ft of clay valley fill overlying Ordovician limestone/shale bedrock. 

Gas at 165 ft (clay above open interval). 

MT-1286 300 Clay 36 Open hole 

46–300

Limestone with shale at base. Gas at 293 ft (shale).
12 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

Groundwater Quality

Water samples from the well network were analyzed 

for field parameters; major ions; trace elements; nutrients; 

dissolved organic carbon; dissolved gases; stable isotopes of 

water, methane, DIC; and the radioactive carbon isotope of 

methane (table 1). The water-quality dataset is presented in 

table 5 (p. 37) and is accessible on the National Water Information System web interface (U.S. Geological Survey, 2018).

Dissolved Gases and Methane Concentrations

Headspace gases of water samples were analyzed for 

nitrogen, carbon dioxide, oxygen, argon, carbon monoxide, 

hydrogen, helium, methane, and higher-chain hydrocarbons 

(ethane, ethene, propane, propene, n-butane, iso-butane, 

n-pentane, iso-pentane, and hexanes+

) (table 1). Dissolved

gas in groundwater exists under pressure, and as the water is 

pumped to the land surface, the pressure drops and dissolved 

gases come out of solution. Different gases come out of solution at different rates, so the composition of headspace gases 

does not necessarily represent equilibrium between the gas 

and water at subsurface formation pressures and temperatures 

(Coleman and others, 1988).

The composition of gas in each sample is shown in 

figure 4. (Only gases that make up more than 1 mole percent 

are shown on the plot.) The predominant gases were methane 

(5.46–93.31 mole percent) and nitrogen (3.87–70.77 mole 

percent). Concentrations of nitrogen and methane are nearly 

inversely related; methane was the dominant component in 

13 samples, and nitrogen was the dominant component in 2 

of 15 samples. At least one or more higher-chain hydrocarbons were detected in all samples. Ethane (C2

) was detected 

in all 15 samples (0.0029–12.42 mole percent), propane (C3) 

was detected in 5 samples (0.0001–2.49 mole percent), and 

hydrocarbons heavier than propane (C4+) were detected in 

3 samples (0.0006–0.2510 mole percent). One sample (SU23) had concentrations of higher-chain hydrocarbons that

totaled 15.47 mole percent. For the other 14 samples, the total

concentration of higher-chain hydrocarbons was 0.0029 to

0.3066 mole percent.

Concentrations of methane, in units of milligrams per 

liter, ranged from 1.2 to 120 mg/L (fig. 5). Twelve of the wells 

had methane concentrations greater than 28 mg/L, which is 

the approximate solubility of methane in water at atmospheric 

pressure. There is no regulatory level for methane in water; 

however, the U.S. Office of Surface Mining recommends 

that wells be vented if methane concentrations in well water 

exceed 28 mg/L (Eltschlager and others, 2001). 

EXPLANATION

Recommended action levels for 

methane in water (Eltschlager and 

others, 2001)

10−28 milligrams per liter: 

Provide warning related to venting 

of the well head and removal of 

ignition sources.

Greater than 28 milligrams per liter: 

Immediate venting of the well head to 

the atmosphere; further modification 

of the water system may be needed. 

Less than 10 milligrams per liter: 

Periodic monitoring 

is recommended. 

28 mg/L

10 mg/L

Methane concentration, 

in milligrams per liter

0

20

40

60

80

100

120

Sample identifier

MT-1286 CR-63 MU-128 AB-142 PE-59 SU-23 HY-53 DE-28 ST-139 GE-368 GR-755 DE-29 CO-31 ST-141 ST-140

MT-1286 CR-63 MU-128 AB-142 PE-59 SU-23 HY-53 DE-28 ST-139 GE-368 GR-755 DE-29 CO-31 ST-141 ST-140

EXPLANATION

Fixed

gases

Nitrogen

Carbon dioxide

Oxygen

Argon

Hydrocarbon 

gases 

Methane (C1

)

Ethane (C2)

Propane (C3)

Constituents that make up less than one 

mole volume percent are not shown. 

100

80

60

40

20

0

Mole percent

Figure 4. Composition of headspace gases in water samples from domestic wells in Ohio, 2016. 

Figure 5. Methane concentrations in water samples from domestic wells in Ohio, 2016. 
Groundwater Quality 13

Dissolved Inorganic Constituents

A wide range of water-quality conditions exist in the 

wells sampled for this study (table 6). The pH of water 

samples ranged from 7.0 to 9.0; alkalinity ranged from 225 

to 889 mg/L as CaCO3; dissolved solids ranged from 318 to 

2,940 mg/L; and chloride ranged from 7.04 to 1,350 mg/L. 

Water types ranged from CaMgHCO3 (generally characteristic of shallow, recently recharged water) to NaCl (generally 

characteristic of deeper, older waters). The most common 

water type, detected in five wells, was NaHCO3. This water 

type can be associated with intermediate to deeper parts of 

groundwater systems in which Na is derived from cation 

exchange with clay minerals and (or) mixing with NaCl 

waters, and HCO3

 is derived from dissolution of carbonate minerals and (or) microbial oxidation of organic matter 

(Hem, 1992; Back, 1966).

Methane is not expected to coexist with electron acceptors such as dissolved oxygen (DO), nitrate (NO3

), or sulfate 

(SO4); however, 1 or more of these constituents were detected 

in 6 samples (table 6). Detection of these electron acceptors in 

the presence of methane may indicate that the samples are a 

mix of water from multiple horizons with different redox conditions. Of the six samples with detections of DO, NO3

, and 

(or) SO4, five were from wells with relatively shallow open 

intervals (less than 50 ft BLS).

Table 6. Methane concentrations and selected water-quality constituents from Ohio domestic wells, 2016.

[mg/L, milligrams per liter; CaCO3, calcium carbonate; DO, dissolved oxygen; NO3, nitrate; SO4, sulfate; Na, sodium; Cl, chloride; <, less than; 

Ca, calcium; HCO3, bicarbonate; Mg, magnesium; H, hydrogen]

Well 

identifier

Methane 

(mg/L) Water type

Dissolved 

solids 

(mg/L)

pH 

(standard 

units)

Alkalinity 

(mg/L as

CaCO3)

Chloride

(mg/L)

Electron acceptors, in mg/L

DO NO3 SO4

Pennsylvanian shale, sandstone, siltstone, limestone, coal

ST-139 57 NaSO4Cl 1,120 8.2 454 727 0.2 <0.040 594

ST-140 8.7 CaNaHCO3 352 7.5 278 17.8 0.2 <0.040 0.03

ST-141 120 NaCl 2,940 7.7 442 1,350 0.2 <0.040 <0.36

CO-31 98 NaHCO3 1,240 8.1 889 117 0.3 0.655 5.54

MU-128 29 NaHCO3 754 8.1 452 140 0.2 <0.040 0.11

Lower Mississippian shale and sandstone

AB-142 36 NaHCO3 466 8.7 375 13.1 1.2 <0.040 0.24

GE-368 73 NaHCO3 645 9.0 320 60.8 0.2 <0.040 3.56

SU-23 39 CaMgHCO3 496 7.4 353 65.7 0.3 <0.040 0.18

PE-59 36 NaHCO3 514 8.0 359 66.0 0.2 <0.040 0.03

Upper Devonian black shale; glacial deposits

DE-29 91 CaNaHCO3 387 7.5 278 40.7 0.2 <0.040 0.07

HY-53 45 CaNaHCO3 421 7.9 252 80.8 0.2 <0.040 0.07

DE-28 47 CaNaHCO3 318 7.7 225 32.2 0.3 <0.040 0.06

CR-63 17 CaMgNaHCO3SO4 619 7.4 339 7.04 0.2 <0.040 233

Upper Ordovician shale and limestone; glacial deposits 

GR-755 80 CaMgNaHCO3 716 7.1 581 74.9 0.2 <0.040 0.25

MT-1286 1.2 CaMgHCO3 479 7 393 29.1 0.2 0.298 26
14 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

Stable Isotopes of Water

The isotopic composition of water (δ18OH2O, δ2HH2O) can 

provide information about its origin. Water undergoes isotopic 

fractionation when it falls as precipitation, and the isotopic 

characteristics are generally retained when precipitation 

recharges the groundwater system. Groundwater that originated as precipitation has characteristic ratios of δ2

HH2O and 

δ18OH2O that generally plot along the Global Meteoric Water 

Line (GMWL) (Craig, 1961). Isotopic fractionation is greater 

at cooler temperatures, so water recharged in cooler climates 

will have lighter isotopic ratios than water recharged in 

warmer climates. Deep-basin brines generally plot to the right 

of the GMWL as a result of evaporative concentration and (or) 

interaction with aquifer solids.

Samples from domestic wells had δ18OH2O of −16.05 to 

−7.15 per mil and δ2HH2O of −114.6 to −47.1 per mil (fig. 6).

The samples generally fall along the GMWL, consistent with

water that originated as precipitation. Also shown in figure 6 is

the range of isotopic ratios of water from Ohio rivers (Kendall

and Coplen, 2001). Of 15 samples, 12 have values within this

range, consistent with precipitation of the present-day climate.

On the other hand, 3 of 15 samples have lighter isotopic ratios, 

similar to average recharge during Pleistocene glaciation, when 

temperatures were cooler (Martini and others, 1998; McIntosh 

and others, 2002). None of the samples had isotopic signatures 

similar to brines of eastern Ohio (Breen and others, 1985).

The occurrence of isotopically light H2O in three samples indicates that bedrock formations in parts of Ohio have 

not been fully flushed by modern or postglacial recharge. Of 

the three samples with isotopically light H2O, two (DE-29 

and HY-53) are from the northwestern corner of Ohio, where 

a thick layer of glacial lakebed clay overlies Upper Devonian 

black (organic-rich) shales. Other investigators (Eberts and 

George, 2000; Churchill, 2000) also detected isotopically 

light groundwaters in the northwestern corner of Ohio and 

concluded that the lakebed clays inhibited the recharge of 

postglacial waters. The third sample with isotopically light 

H2O (CO-31) is from the deepest well sampled for the study 

(345 ft), in eastern Ohio. In later figures, the 3 samples with 

H2O isotopes indicative of glacial recharge are shown as dark 

blue diamonds, and the 12 samples with H2O isotopes indicative of modern or postglacial recharge are shown as light 

blue diamonds.

EXPLANATION

Samples from domestic water wells 1 Kendall and Coplen (2001)

2

 Martini and others (1999); McIntosh and 

others (2002)

3

 Craig (1961)

Brines from eastern Ohio (Breen 

and others, 1985)

ẟ18OH2O, in per mil

ẟ2

HH2O, in per mil

−160

−140

−120

−100

−80

−60

−40

−20

0

−20 −18 −16 −14 −12 −10 −8 −6 −4 −2 0

Average Pleistocene 

glacial meltwater2

HY-53

CO-31

DE-29

Global meteoric water line3

Ohio river 

water1

Figure 6. Stable isotopes of water from domestic wells in Ohio, 2016.
Chemical and Isotopic Characteristics of Methane and Related Constituents 15

Chemical and Isotopic Characteristics 

of Methane and Related Constituents

The origin of methane can be evaluated using selected 

chemical and isotopic characteristics of methane and related 

constituents. The following section describes information 

about methane origin based on stable isotopes of methane, gas 

dryness, and isotopic fractionation between methane and its 

microbial precursors—H2O and CO2. 

Stable Isotopes of Methane

Stable isotopes of methane (δ13CCH4, δ2HCH4) have been 

used to differentiate thermogenic and microbial methane 

(Schoell, 1980, 1988; Whiticar and others, 1986; Whiticar, 

1999). In part, microbial methane is isotopically lighter than 

thermogenic methane because microbes preferentially utilize 

lighter isotopes, which have lighter bonds that are easier 

to break. The isotopic signature of thermogenic methane is 

related to thermal maturity, which generally increases with 

age/depth of the source rock. In general, δ13CCH4 greater than 

−45 to −50 per mil is considered to be diagnostic of thermogenic methane, and δ13CCH4 less than about −60 or −55 per mil

is considered to be diagnostic of microbial methane (Schoell,

1980, 1988; Whiticar and others, 1986; Whiticar, 1999). However, δ13CCH4 ranges for thermogenic and microbial methane

can overlap; for example, microbial methane formed in a

closed system can have δ13CCH4 as high as −31 per mil (Martini

and others, 2003).

Samples from domestic wells had δ13CCH4 of −75.19 to 

−47.7 per mil and δ2HCH4 of −285.7 to −206 per mil. On a

Whiticar plot (Whiticar and others, 1986), 12 of 15 samples

plot in the fields for microbial methane, 1 sample plots in the

field for thermogenic methane, and 2 samples plot in between,

in areas of mixing or transition (fig. 7A). The field for microbial methane is subdivided into fields for acetate fermentation and CO2

 reduction; however, identifying pathways of

microbial methanogenesis based on Whiticar plot alone can be

misleading for study areas with isotopically light H2

O (Golding and others, 2013; Vinson and others, 2017). Therefore,

differentiating pathways of microbial methanogenesis will be

discussed in a later section of this report (“Isotopic Characteristics of Microbial Methane”).

For comparison, samples of methane from commercial 

hydrocarbon wells in eastern Ohio had δ13CCH4 of −53 to 

−37 per mil and δ2HCH4 of −315 to −150 per mil (Laughrey

and Baldassare 1998; Barton and others, 1998; Burruss and

Laughrey, 2010; and Osborn and McIntosh, 2010). On the

Whiticar plot (fig. 7A), these samples plot along a linear

trend; the lightest isotopic compositions are in the youngest

formations (Upper Devonian shales) at the shallowest depths

(550–1,200 ft), and the heaviest isotopic compositions are in

the oldest formations (Upper Cambrian/Ordovician bedrock)

at the greatest depths (7,000–8,500 ft).

Secondary processes such as mixing, migration, and 

oxidation can alter original isotopic signatures and lead to 

ambiguity in interpreting methane origin based on stable isotopes of methane. Mixing should create gas of an intermediate composition that lies along a mixing line between the 

endmembers. Increases in δ13CCH4 and δ2HCH4 can be caused 

by oxidation of microbial methane or mixing of microbial 

and thermogenic methane (Schoell, 1988).

Gas Dryness

The ratio of methane to the sum of ethane and propane (C1

/(C2+C3)) is referred to as gas dryness (Bernard 

and others, 1978; Golding and others, 2013). Thermogenic 

gas typically includes substantial concentrations of higherchain hydrocarbons because it forms by thermal cracking of 

complex organic compounds into successively simpler molecules, the simplest of which is methane. With increasing 

thermal maturity, gas dryness increases as additional higherchain hydrocarbons are cracked. On the other hand, microbial gas is predominantly methane, with minor amounts of 

ethane and propane (Bernard and others, 1978). In general, 

dryness values greater than about 1,000 are considered to 

be diagnostic for microbial origin, and values less than 100 

are considered to be diagnostic for thermogenic methane 

(Bernard and others, 1978; Golding and others, 2013).

A Bernard plot shows δ13CCH4 in relation to dryness 

(fig. 7B) (Bernard and others, 1978). Thermogenic methane 

plots in the lower right corner of the graph because it is 

isotopically heavier and includes a substantial proportion 

of higher-chain hydrocarbons (low dryness). Microbial 

methane plots in the upper left corner of the graph because it 

is isotopically lighter, with only minor amounts of higherchain hydrocarbons (increased dryness). Samples from 

domestic wells had dryness values of 5–29,772. Of the 

15 samples, 1 plots in the thermogenic field, 11 plot within 

the microbial field, and 3 plot in between (fig. 7B). For 

comparison, gas samples from commercial hydrocarbon 

wells in eastern Ohio had dryness values of 4–16, consistent 

with thermogenic methane (Laughrey and Baldassare, 1998; 

Barton and others, 1998; Burruss and Laughrey, 2010; and 

Osborn and McIntosh, 2010).

Secondary processes (mixing, migration, or oxidation) 

can shift δ13CCH4 and (or) C1

/(C2+C3), as shown by arrows 

on figure 7B. Mixing should create gas of an intermediate composition that lies along a mixing line between the 

endmembers. Microbial oxidation of methane should cause 

an increase in δ13CCH4 (because lighter isotopes are preferentially removed by microbes) and a decrease in dryness 

(because methane is oxidized more readily than higher-chain 

hydrocarbons) (Whiticar and others, 1986; Sharma and others, 2014). Migration (or diffusion) of thermogenic methane 

should cause an increase in dryness because lighter hydrocarbons should migrate more readily than heavier hydrocarbons (Schoell, 1980, 1988; Martini and others, 1998). 
16 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

Thermal maturation of thermogenic gas should also increase 

dryness, as complex organic molecules are progressively 

cracked to methane. Several processes can cause an increase 

in δ13CCH4, including mixing microbial methane with thermogenic methane, oxidation of methane by microbial processes, 

and Rayleigh-type fractionation in a partially closed system 

(oxidation of methane and Rayleigh-type fractionation will be 

discussed in later sections of this report).

A broad interpretation of the Whiticar plot (fig. 7A) and 

the Bernard plot (fig. 7B) is that 13 samples can be interpreted as predominantly microbial, and 2 samples (SU-23 

and MT-1286) can be interpreted as having a component of 

thermogenic methane. On figures 8 and 9, red dots are used 

to represent the two samples with a component of thermogenic methane.

Upper Cambrian (Laughrey and Baldassare, 1998) 

Ordovician (Burruss and Laughrey, 2010) 

Silurian (Burruss and Laughrey, 2010; Barton and others, 1998) 

Upper Devonian (Osborne and McIntosh, 2010)

Age of the producing formation

Samples from commercial oil/gas wells in Eastern Ohio

H2

O isotopes indicative of glacial recharge

H2O isotopes indicative of modern or postglacial recharge 

Samples from domestic wells sampled for this study

EXPLANATION

ẟ13CCH4, in per mil

−85 −80 −75 −70 −65 −60 −55 −50 −45 −40 −35 −30 −25

Gas dryness (C1 / C2 + C3

)

1

10

100

1,000

10,000

100,000

After Bernard and others (1978)

Mixing

Thermogenic

Migration

Thermal maturation

Microbial

Oxidation

B

ẟ2

HCH4, in per mil

−120

−140

−160

−180

−200

−220

−240

−260

−280

−300

−320

−85 −80 −75 −70 −65 −60 −55 −50 −45 −40 −35 −30

ẟ13CCH4, in per mil

Microbial — 

CO2

 reduction

Microbial — 

Acetate fermentation

Mix

Thermogenic

Oxidation

Thermal 

maturation

A

After Whticar and others (1986)

Figure 7. Gas classification diagrams showing samples from domestic wells in Ohio. A, Whiticar plot. B, Bernard plot. 
Chemical and Isotopic Characteristics of Methane and Related Constituents 17

Isotopic Characteristics of Microbial Methane

Microbial methane forms during the final stages of 

decomposition of organic matter in anaerobic environments. 

Conditions favorable for microbial methanogenesis include 

low temperatures and salinities; lack of other electron acceptors such as O2

, NO3, and SO4; and the presence of microbial 

communities capable of breaking down complex organic matter into compounds methanogens can utilize.

The isotopic composition of microbial methane is related 

to δ13C of the organic precursor, δ2H of coexisting water, and 

the predominant microbial process (pathway) that created 

the methane. There are two primary pathways of microbial 

methanogenesis—acetate fermentation and CO2 reduction. 

In general, acetate fermentation is associated with younger, 

fresher organic matter and warmer temperatures in near-surface environments, such as marshes, wetlands, landfills, and 

sewers (Schoell, 1988). Acetate fermentation is represented by 

the following simplified equation:

CH3COOH→CH4+CO2 (2)

where CH3COOH is acetate.

CO2

 reduction is associated with older organic matter and 

cooler temperatures in the subsurface and is the predominant 

pathway associated with groundwater systems, marine sediments, and relatively shallow deposits of microbial shale gas 

and coal bed methane (Schoell, 1988; Whiticar, 1999; Martini 

and others, 1998). CO2 reduction is represented by the following simplified equation:

CO2+4H2→CH4+2H2O (3)

The two pathways result in different degrees of carbon and hydrogen isotope fractionation; methane formed 

by CO2 reduction is typically depleted in δ13CCH4 and 

enriched in δ2HCH4, as compared to methane formed by 

acetate fermentation.
18 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

Fractionation of Hydrogen Isotopes

For microbial methane, δ2HCH4 is related to δ2HH2O of the 

coexisting water and the microbial pathway. If the isotopic 

characteristics of water are known, the difference between 

δ2HH2O and δ2HCH4 can provide evidence about the pathway of 

microbial methanogenesis.

For the CO2 reduction pathway, all the H in CH4 is 

derived from coexisting water and δ2HH2O and δ2HCH4 are 

expected to follow the equation below (Schoell, 1980; Whiticar and others, 1986):

δ2HCH4=δ2HH2O–160 (±10‰) (4)

For the acetate fermentation pathway, hydrogen is 

derived from water and acetate. H in acetate is isotopically lighter than H in water because acetate is an organic 

compound formed by microbial processes that favor lighter 

isotopes. As a result, methane formed by acetate fermentation shows a greater degree of H fractionation than methane 

formed by CO2

 reduction. The relation between methane and 

coexisting water is less well known for acetate fermentation 

than for CO2 reduction; the following equation was proposed 

for shallow freshwater systems where SO4 concentrations are 

low (Waldron and others, 1999; Golding and others, 2013):

δ2HCH4=0.675*δ2HH2O−284 (±6‰) (5)

In figure 8, δ2HH2O and δ2HCH4 are shown in relation to 

trends for acetate fermentation and CO2 reduction. Most of the 

samples plot near the trend for CO2 reduction, which is interpreted to be the predominant microbial pathway (for some of 

the samples that plot below the line, especially DE-29, acetate 

fermentation might also contribute to microbial methanogenesis). Of 15 samples, 12 have δ2

HH2O values within the range 

of modern or postglacial recharge, and 3 have δ2HH2O values 

consistent glacial recharge.

For thermogenic methane, δ2HCH4 is not expected to show 

a relation to δ2HH2O; however, the two samples interpreted as 

having a component of thermogenic methane (shown as red 

dots on fig. 8) plot in the same area as samples interpreted to 

have been formed by CO2 reduction using H2O with isotopic 

ratios similar to modern or postglacial groundwater recharge.

AAXXXX_fig 01

SU−23

MT−1286

H2O isotopes indicative of modern or post-glacial recharge

Samples with characteristics of thermogenic methane 

H2

O isotopes indicative of glacial recharge

EXPLANATION

Samples from domestic wells

CO2

 reduction (Schoell, 1980): ẟ2HCH4 = ẟ2HH2O - 160 (±10)

Acetate fermentation (Waldron and others, 1999): ẟ2

HCH4 = (.675) ẟ2HH2O - 284 (± -6)

CO2

 reduction

Acetate fermentation

Range of ẟ2HH2O for Ohio rivers 

(Kendall and Coplen, 2001)

−150

−200

−250

−300

−350

−400

ẟ2

HCH4, in per mil

−160 −140 −120 −100 −80 −60 −40 −20 0

ẟ2HH2O in per mil

Modern or postglacial recharge

Glacial recharge

Figure 8. Relation between the stable hydrogen isotopic 

signature of water and methane for samples from domestic 

wells in Ohio, 2016. 
Chemical and Isotopic Characteristics of Methane and Related Constituents 19

Carbon Isotope System

When CO2 enters the groundwater, it speciates into 

aqueous carbon dioxide (CO2 [aq]), carbonic acid (H2CO3), 

bicarbonate (HCO3

-

), and carbonate (CO3

2-). The concentration 

of each species depends on the pH, and at circumneutral pH, 

the predominant species is HCO3

-

. Dissolved inorganic carbon 

(DIC) refers to the total concentration of the four CO2 species.

Carbon-13 of Dissolved Inorganic Carbon

δ13CDIC of groundwater is derived from two primary 

sources (Clark and Fritz, 1997): (1) microbial degradation 

of soil or aquifer-derived organic carbon, which has δ13CDIC

of about −25 plus or minus (±) 2–3 per mil, and (2) dissolution of carbonate minerals, which are typically derived from 

seawater and have an average value of about 0 per mil. δ13CDIC

of groundwater reflects the relative contribution from these 

two sources, and values for groundwater are typically between 

about −20 and 0 per mil (Clark and Fritz, 1997).

Samples from 15 domestic wells had δ13CDIC of −31.6 to 

+18.9 per mil (fig. 9A). Seven samples had values between

−14.8 and −2.9 per mil, which is within the range of typical

groundwater. One sample had δ13CDIC of −31.6 per mil, which

is depleted relative to soil or aquifer-derived organic matter,

and is diagnostic of methane oxidation (see the “Methane

Oxidation by Sulfate Reduction” section of this report). Four

samples had δ13CDIC greater than +10 per mil, which is diagnostic of Rayleigh-type fractionation (see the “Rayleigh-Type

Fractionation” section of this report).

Fractionation of Carbon Isotopes

Microbial methanogenesis creates substantial 13C 

fractionation between CO2 and CH4, with a greater degree of 

fractionation for the CO2 reduction pathway than for acetate 

fermentation. The degree of 13C fractionation between CO2

and CH4 is represented by the fractionation factor (α13CCO2-CH4), 

computed as follows:

α13CCO2-CH4=(δ13CCO2+1,000)/(δ13CCH4+1,000) (6)

13C fractionation factors of 1.049–1.095 are consistent 

with CO2 reduction, and values of 1.039–1.058 are consistent 

with acetate fermentation (Whiticar and others, 1986). 13C 

fractionation factors of 1.0005–1.03 are indicative of methane 

oxidation or thermogenic methane.

For this study, samples were analyzed for δ13CDIC, and 

δ13CCO2 was estimated by subtracting 8 per mil, which is 

the approximate equilibrium isotopic fractionation between 

CO2 and HCO3

-

 at 25 degrees Celsius (°C) (Clark and Fritz, 

1997). Using this approximation, samples from 15 domestic 

wells had α13CCO2-CH4 of 1.021–1.077 (fig. 9B). A total of 

12 samples had α13CCO2-CH4 consistent with CO2 reduction. 

Four of the 12 samples had values that are also consistent 

with acetate fermentation. A total of three samples had values 

between 1.021 and 1.039, within the range for methane 

oxidation or thermogenic methane. Of these samples, two 

(SU-23, MT-1286) are interpreted as having a component of 

thermogenic methane based on δ13CCH4 and C1/(C2+C3). The 

third sample (CR-63) had δ13CDIC of −31.6 per mil, which is 

diagnostic for methane oxidation (see the “Methane Oxidation 

by Sulfate Reduction” section).
20 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

AAXXXX_fig 01

EXPLANATION

Samples with characteristics of thermogenic methane

α = 13C fractionation factor = α13CCO2 - CH4 = (ẟ13CCO2 + 1000) / (ẟ13CCH4 + 1000)

H2

O isotopes indicative of glacial recharge

H2O isotopes indicative of modern or post-glacial recharge

MT−1286

SU−23

α = 1.09

Extent of methanogenesis

Oxidation

Microbial 

CO2

 reduction

Microbial 

acetate 

fermentation

Oxidation or 

thermogenic 

methane

α = 1.07

α = 1.05

α = 1.03

B

ẟ13 CCO2, in per mil

ẟ13CCH4, in per mil

−50

−40

−30

−20

−10

0

10

20

30

−85 −80 −75 −70 −65 −60 −55 −50 −45 −40 −35

ẟ13CDIC, in per mil

δ13CCH4, in per mil

−85 −80 −75 −70 −65 −60 −55 −50 −45 −40 −35

−40

−30

−20

−10

0

10

20

30

A Enriched ẟ13CDIC: greater than +10 per mil

Range of ẟ13CDIC in typical groundwater: −20 to 0 per mil

Depleted ẟ13CDIC: less than −27 per mil

Oxidation

Figure 9. Stable carbon isotopic signature (δ13C) of methane in relation to A, δ13C of dissolved inorganic carbon and B, δ13C of 

carbon dioxide and δ13C fractionation factors for samples from Ohio domestic wells, 2016. 
Chemical and Isotopic Characteristics of Methane and Related Constituents 21

Rayleigh-Type Fractionation

In a partially closed groundwater system, the supply of 

CO2 from the soil zone is limited; therefore, as methanogenesis proceeds, the residual CO2

 becomes isotopically heavier 

and as a result, δ13CCH4 also becomes isotopically heavier. 

The progressive isotopic enrichment of the precursor (CO2) 

and product (CH4) in a partially closed system is attributed 

to Rayleigh-type fractionation (Coleman and others, 1988). 

δ13CDIC heavier than about +10 per mil is strong evidence for 

microbial methanogenesis in a partially closed groundwater 

system (Martini and others, 2003; Schoell, 1980, 1988).

A total of four samples from domestic wells had δ13CDIC

values of +10.8 to +18.9 per mil, consistent with CO2 reduction in a partially closed system (fig. 9A). Two of the samples 

are from wells in northwestern Ohio, where glacial lakebed 

clays inhibit recharge to the underlying black shale (Eberts 

and George, 2000). The other two samples are from the deepest wells sampled for this study (301 and 345 ft), which tap 

coal-bearing Pennsylvanian-age bedrock in eastern Ohio. Of 

the four samples with enriched δ13CDIC, three also had H2O 

isotopes indicative of glacial recharge. These observations are 

generally consistent with a partially closed system that has not 

been fully flushed with modern or postglacial recharge.

As CO2 reduction proceeds in a partially closed system, 

δ13CDIC and δ13CCH4 will progressively increase, but the 

magnitude of fractionation (α13CCO2-CH4) should remain about the 

same. This trend can be seen on figures 9A and 9B; eight samples 

fall along a trend of increasing δ13CDIC and δ13CCH4 (fig. 9A), but 

they all have α13CCO2-CH4 between 1.066 and 1.077 (fig. 9B).

Methane Oxidation by Sulfate Reduction

Methane can be oxidized in an anaerobic environment in 

the presence of sulfate (SO4), which acts as an electron acceptor. Methane oxidation by sulfate reduction is most likely to 

occur near the interface of sulfate-reducing and methanogenic 

zones (Martini and others, 2003). The net reaction is represented by the following equation:

CH4+SO4

2-→HCO3-

+HS-+H2O (7)

Methane oxidation is the opposite of CO2 reduction in 

that CH4 is the reactant and CO2 is the product. Oxidation of 

methane is a microbial process and therefore tends to favor 

lighter isotopes, and as the reaction proceeds, the δ13C of the 

product (δ13CCO2 or δ13CDIC) is depleted while the residual reactant (δ13CCH4) is enriched. δ13CDIC less than about −27 per mil 

is evidence of oxidation of methane (Martini and others, 2003; 

Whiticar and others, 1986; Whiticar, 1999).

One sample (CR-63) had a δ13CDIC of –31.6 per mil, 

which is in the range of values diagnostic for methane 

oxidation (fig. 9A). CR-63 was the shallowest well sampled 

for this study (75 ft). The water showed evidence of sulfate 

reduction in terms of high concentrations of SO4 (233 mg/L) 

and sulfide (0.4 mg/L), an extremely strong rotten egg odor, 

and an abundance of fine black particulates (presumably 

sulfide mineral precipitates.) On the Whiticar plot (fig. 7A) 

and Bernard plot (fig. 7B), CR-63 shows isotopic and 

compositional shifts that are expected as a result of methane 

oxidation, as indicated by the arrows on the diagrams.
22 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

Carbon-14 of Methane

Carbon-14 (14C) is a radioactive isotope of carbon that 

forms from cosmic radiation in the upper atmosphere. 14C 

has a half-life of 5,730 years and can be detected in organic 

materials that are less than about 50,000 years old (Coleman 

and others, 1995). 14C concentrations are expressed as percent 

modern carbon (pMC); 100 pMC represents the 14C concentration of CO2

 in the atmosphere before the start of atomic-bomb 

testing in about 1953. 14C concentrations can be greater than 

100 percent for organic matter younger than about 1953.

14C of methane (14CCH4) is not directly related to the 

time of methane formation but can provide information 

about the relative age of the carbon precursor. Coleman and 

others (1995) proposed that methane formed in landfills or 

sewers should have 14CCH4 similar to currently living materials (120–150 pMC), swamp and marsh gases should have 14CCH4 of about 30–120 pMC, methane formed from carbon in 

younger (less than 50,000 years) glacial deposits should have 14CCH4 less than about 30 pMC, and methane formed from carbon in Paleozoic bedrock or older glacial deposits (more than 

50,000 years) should have no detectable 14CCH4 (these may be 

broad generalizations because the concentration of 14C in the 

atmosphere has varied through geologic time [Plummer and 

others, 2004]).

Of the 15 samples, 14 had sufficient concentrations of 

methane to analyze for 14CCH4 (fig. 10). A total of eight samples 

had 14CCH4 less than the reporting limit of 0.4 pMC, consistent with methane formed from carbon in Paleozoic bedrock 

or older glacial deposits. A total of six samples had 14CCH4 of 

0.9–13.5 pMC, consistent with methane formed from organic 

matter in younger glacial deposits. None of the samples had 

14CCH4 expected to occur in methane from landfills, swamps, 

marshes, or other near-surface environments where acetate 

fermentation is expected to be the predominant pathway of 

microbial methanogenesis.

Of the two samples with components of thermogenic 

methane, one sample (SU-23) had a 14CCH4 value of 1.60, 

consistent with carbon from younger glacial deposits. The 

second sample with a component of thermogenic methane 

(MT-1286) did not have a sufficient CH4 concentration for 

determination of 14CCH4.

Swamp gas Landfill gas

Modified from Coleman and others (1995)

Lab detection limit = 0.4 pMC

Glacial

drift gas

“Ancient” 

carbon 

14CCH4, in percent modern carbon (pMC)

Number of samples1

1

Not measured for MT-1286 because the CH4 concentration was too low. 

Not detected

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

0

2

4

6

8

10

Figure 10. Carbon-14 of methane from domestic wells in Ohio, 2016. 
Interpretation of Methane Origin 23

Interpretation of Methane Origin

A well-by-well summary of chemical and isotopic 

characteristics used to evaluate methane origin is presented 

in table 7. Most of the samples have values consistent with 

microbial methanogenesis by CO2 reduction, based on the 

following criteria: (1) δ13CCH4 less than −60 or −55 per mil 

(Schoell, 1980; Whiticar and others, 1986) and (or) δ13CDIC

greater than +10 per mil (Martini and others, 1998); 

(2) C1/(C2+C3) greater than 1,000 (Bernard and others, 1978);

(3) α13CCO2-CH4 equal to 1.047 to 1.095 (Whiticar and others,

1986); and (4) α2HH2O-CH4 equal to about 1.2 (Schegel and 

others, 2011; Martini and others, 1998). Values that are outside of these ranges are highlighted in table 7. 

For 11 of 15 samples, all constituents are within the 

ranges of the above criteria for microbial CO2 reduction (ST139, ST-140, ST-141, CO-31, MU-128, AB-142, GE-368, 

GR-755, DE-28, DE-29, and HY-53). A 12th sample (PE-59) 

met three of the four criteria, except that C1/(C2+C3) was 

212, which is in between commonly used diagnostic values 

for microbial (greater than 1,000) and thermogenic (less than 

100) methane. For this discussion, PE-59 is included as one

of the 12 samples interpreted as microbial.

Table 7. Chemical and isotopic characteristics of methane and related constituents from domestic wells in Ohio, 2016.

[Shading indicates values outside of ranges diagnostic for carbon dioxide reduction; δ, isotopic ratio delta notation; α, isotopic fractionation factor; C, carbon; 

H, hydrogen; CH4, methane; C1, methane; C2, ethane; C3, propane; DIC, dissolved inorganic carbon; CO2, carbon dioxide; H2O, water; per mil, parts per thousand; <, less than; - -, not measured because methane concentration was too low] 

Well 

identifier

δ13CCH4, 

per mil

δ2HCH4,

per mil C1/(C2

+C3) δ13CDIC,

per mil α13CCO2-CH4 α2

HH2O-CH4

Water 

isotopic

signature

14CCH4

, 

percent 

modern carbon

Pennsylvanian shale, sandstone, siltstone, limestone, coal

ST-139 –69.11 –237.1 6,325 3 1.069 1.241 Postglacial <0.4

ST-140 –69.85 –243.5 1,824 –8.9 1.057 1.249 Postglacial 1.50

ST-141 –62.46 –241.9 1,620 10.8 1.070 1.244 Postglacial <0.4

CO-31 –61.19 –253.8 3,921 18.9 1.077 1.236 Glacial <0.4

MU-128 –67.48 –206.0 1,205 –13 1.050 1.196 Postglacial <0.4

Lower Mississippian shale and sandstone

AB-142 –75.19 –252.6 6,189 –6 1.066 1.260 Postglacial 13.50

GE-368 –64.31 –245.3 4,305 –8.8 1.051 1.246 Postglacial <0.4

SU-23 –47.74 –236.7 5 –2.9 1.039 1.233 Postglacial 1.60

PE-59 –69.55 –240.2 212 –9.4 1.056 1.251 Postglacial 0.90

Upper Devonian black shale; glacial deposits

DE-29 –59.45 –276.6 10,084 12 1.067 1.280 Glacial <0.4

HY-53 –56.8 –285.7 21,207 16.8 1.070 1.240 Glacial <0.4

DE-28 –70.17 –252.3 28,804 8.9 1.076 1.261 Postglacial 1.70

CR-63 –59.04 –220.7 527 –31.6 1.021 1.215 Postglacial 1.30

Upper Ordovician shale and limestone; glacial deposits

GR-755 –71.37 –232.1 29,772 2.6 1.071 1.240 Postglacial <0.4

MT-1286 –50.96 –230.7 28 –14.8 1.030 1.239 Postglacial --
24 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

Samples with Chemical and Isotopic 

Characteristics Consistent with Microbial 

Methane

A total of 12 samples had chemical and isotopic characteristics consistent with microbial methane formed predominantly by the CO2

 reduction pathway. Where three or 

more samples were analyzed from the same aquifer, δ13CCH4

showed a range of values. Samples from Upper Devonian 

black shale had values from −70.17 to −56.8 per mil, Lower 

Mississippian shale and sandstone had values from −75.19 to 

−64.31 per mil, and Pennsylvanian bedrock had values from

−69.85 to −61.19 per mil. For each of these aquifers, there

was a general trend of increasing δ13CCH4 with depth (fig. 11).

This observation is consistent with increased Rayleigh-type

fractionation at increased depths, where the groundwater is 

increasingly isolated, and residence time in the zone of methanogenesis increases. 

Although the data for 12 samples are generally consistent 

with a microbial origin, other interpretations are possible; 

for example, the increase in δ13CCH4 with depth could also 

be interpreted as increased mixing with thermogenic methane (and possibly brine) migrating from greater depths. This 

alternate interpretation could be especially applicable to wells 

in eastern Ohio, which generally have lower dryness and 

higher concentrations of chloride and bromide, as compared 

to wells in western Ohio. Harkness and others (2017) concluded that methane detected in groundwater of north-central 

West Virginia was predominantly microbial, but there was a 

pervasive signature of thermogenic methane, partly based on 

widespread detections of ethane.

DE-29

HY-53

AB-142 DE-28

GE-368

GR-775

PE-59

ST-139

MU-128

ST-141 ST-140

CO-31

Western Ohio

Eastern Ohio

EXPLANATION

Upper Devonian black shale, 

northwestern Ohio

Glacial deposits, Upper Ordovician shale 

and limestone, southwestern Ohio

Pennsylvanian shale, sandstone, 

siltstone, limestone, coal

Lower Mississippian shale and sandstone

0

50

100

150

200

250

300

350

400

−85 −80 −75 −70 −65 −60 −55 −50 −45

ẟ13CCH4, in per mil

Well depth, in feet

Figure 11. Stable carbon isotopic signature of methane in relation to well depth and 

geologic formation for 12 samples interpreted as microbial methane formed by carbon 

dioxide reduction in Ohio domestic wells, 2016. 
Interpretation of Methane Origin 25

Samples with Chemical and Isotopic 

Characteristics not Consistent with Microbial 

Methane

A total of three samples had multiple chemical and (or) 

isotopic characteristics outside of the ranges diagnostic for 

microbial methane formed predominantly by CO2 reduction 

(indicated as highlighted cells on table 7). A sample from the 

shallowest well (CR-63) had chemical and isotopic characteristics consistent with methane oxidation by sulfate reduction. The strongest evidence for methane oxidation is a light 

δ13CDIC of −31.6 per mil (fig. 9A). Additional observations in 

support of the interpretation include moderately heavy δ13CCH4

(−59.04 per mil) and δ2HCH4 (−220.7 per mil), relatively low 

dryness (527), and low α13CCO2-CH4 (1.021). In addition, the 

water showed strong evidence of SO4 reduction in the form of 

high concentrations of SO4 (233 mg/L) and hydrogen sulfide 

(0.401 mg/L), a strong rotten egg odor, and abundant black 

particles in the water (presumably sulfide mineral precipitate). 

The sample was from a 75-ft well that taps Upper Devonian 

black shale in an area of north-central Ohio, near the boundary 

of the Appalachian Basin and the Indiana-Ohio Platform.

Two samples (SU-23 and MT-1286) were interpreted as 

having a component of thermogenic methane based on (1) 

δ13CCH4 of −47.17 and −50.96 per mil, (2) dryness values of 5 

and 28 (figs. 7A, 7B), and (3) the presence of butane (C4) and 

pentane (C5) compounds. Both samples showed evidence for 

mixing with modern or postglacial recharge and (or) microbial 

methane based on (1) stable isotopes of H2O are indicative 

of modern or postglacial recharge; (2) the relation between 

δ2HH2O and δ2HCH4 is consistent with CO2 reduction (fig. 7); 

(3) δ13CDIC is within the range of typical groundwater (fig. 8A);

and (4) 14CCH4 is detected in SU-23 at 1.6 pMC, which is not

consistent with a solely thermogenic source (Coleman and

others, 1995).

One additional sample (PE-59) might also contain some 

thermogenic methane, based on gas composition; dryness 

was 212, which is in between diagnostic values for microbial 

(greater than 1,000) and thermogenic (less than 100) methane 

(fig. 7B). A decrease in dryness could be attributed to oxidation of microbial methane, but small concentrations of isobutane (0.0028 mole percent) and iso-pentane (0.0006 mole 

percent) were detected. It is uncertain if such low concentrations of these compounds can be the result of microbial processes. For this analysis, the methane in PE-59 is considered 

to be predominantly microbial.

The chemical and isotopic data collected for this study 

were not sufficient to distinguish whether thermogenic methane in SU-23 or MT-1286 (and possibly PE-59) is the result 

of (1) natural migration of a deep-seated source of methane or 

(2) contamination with stray gas related to human activities.

The sample with the strongest thermogenic signature (SU-23)

is from a well on the margin of a deep buried valley incised

into Upper Devonian black shale. In addition, the well is near

the Middleburg Fault, a major fault that extends to basement

rocks (Baranoski, 2013). One or both of these features could

serve as natural migration pathways for discharge of water

and (or) gas from the regional flow system. On the other hand,

there are multiple active and abandoned hydrocarbon wells

near SU-23, any of which could serve as a manmade pathway

of migration for thermogenic methane.
26 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

Limitations of the Study

The study has several limitations and uncertainties; some 

are related to the study design, and others are related to the 

methods of analysis. In terms of study design, the primary 

limitations are listed below.

1. The relatively small number of wells sampled is a limitation because hydrogeologic settings where methane

occurs in groundwater may not be represented in the

network of 15 wells sampled for this study.

2. Multiple potential natural and anthropogenic migration

pathways exist near most of the wells, especially those in

eastern Ohio. This creates some uncertainty as to whether

the methane samples are “naturally occurring” or not.

3. Most of the wells were constructed with long open

intervals that ranged from 15 to 302 ft. This adds uncertainty about which horizons are the source of the water

and methane; for example, it is possible that methane

was from one horizon and water was from another. In

addition, the water sampled could represent a mix from

multiple horizons, and this could obscure diagnostic

relations between water quality and gas characteristics.

4. A single sample was collected from each well, so it is

not possible to assess temporal variability of the data.

5. Additional types of chemical and isotopic analyses could

have been useful; for example, isotopes of higher-chain

hydrocarbons and (or) noble gases may have provided

additional information about migration pathways,

mixing, or oxidation (Harkness and others, 2017).

Additional limitations are related to uncertainties and

inconsistencies with established techniques for investigating 

methane origin using isotopic and chemical signatures (Bates 

and others, 2011; Golding and others, 2013; Vinson and others, 2017; and Harkness and others, 2017).

6. As discussed in earlier sections of this report, secondary

processes can obscure original isotopic and (or) chemical

signatures; for example, oxidation of microbial methane

can create isotopic shifts similar to mixing of microbial

and thermogenic methane. CO2 reduction in a partially

closed system can also cause isotopic shifts that could be

interpreted as mixing microbial methane with thermogenic methane.

7. There is some uncertainty about the amount and types

of higher-chain hydrocarbons that can be produced by

microbial processes (Hinrichs and others, 2006; Osborn

and McIntosh, 2010), and this adds uncertainty to differentiation of microbial and thermogenic methane.

8. Some of the data used to define isotopic signatures for

microbial methane were from recent sediments or lab

cultures, and there is uncertainty about how well the data

represent microbial methanogenesis using organic matter

in shale or coal (Vinson and others, 2017).

9. There is some uncertainty about 13C fractionation factors

diagnostic of microbial pathways of methanogenesis.

Bates and others (2011) noted that values of α13CCO2-CH4

were developed for methanogenesis in an open system,

whereas a partially closed system might be more

applicable. Vinson and others (2017) noted α13CCO2-CH4

values can be affected by nonmethanogenic processes

that produce or consume CH4 and (or) CO2.

10. There is some evidence that secondary microbial methanogenesis can alter the isotopic composition of methane

from thermogenic gas reservoirs. Isotopically enriched

δ13CDIC is considered to be unequivocal evidence of

microbial methanogenesis (Martini and others, 2003);

however, enriched δ13CDIC (+8 to +12 per mil) has been

detected in commercial wells that produce methane from

thermogenic gas reservoirs (Osborn and McIntosh, 2010;

Sharma and others, 2014).
Summary and Conclusions 27

Summary and Conclusions

In 2016, the U.S. Geological Survey, in cooperation 

with the Ohio Water Development Authority, investigated 

methane in Ohio groundwater, and the results are presented 

in this report. The objectives were to (1) identify a network of 

domestic wells that produce methane, (2) describe the hydrogeologic settings in which methane is detected, (3) document 

the chemical and isotopic characteristics of the methane and 

the coexisting water, and (4) evaluate the origin of the methane, to the extent possible.

A total of 15 domestic water wells were selected 

from 12 counties in diverse parts of Ohio. The wells were 

75–345 feet deep and tapped a range of aquifers, including 

Pleistocene glacial deposits and four bedrock units: 

Pennsylvanian shale, sandstone, siltstone, limestone, and coal; 

Lower Mississippian shale and sandstone; Upper Devonian 

organic-rich shale; and Upper Ordovician shale and limestone. 

The unconsolidated glacial deposits overlying bedrock were 

from 4 to more than 171 feet thick. A similarity among the 

15 wells is that the bedrock is predominantly shale, and the 

glacial deposits are predominantly clay.

The wells were sampled once during 2016. Samples 

were analyzed for major ions, nutrients, trace elements, 

arsenic speciation, and dissolved organic carbon at the 

U.S. Geological Survey National Water Quality Laboratory. 

Isotech Laboratories analyzed the samples for concentrations 

of methane and other dissolved gases; stable isotopes (carbon, 

hydrogen, and oxygen) of methane, water, and dissolved 

inorganic carbon; and 14-carbon of methane.

The isotopic composition of water (δ18OH2O, δ2HH2O) 

can provide information about its origin. Samples from the 

domestic wells had δ18OH2O of −16.05 to −7.15 parts per 

thousand (per mil), and δ2HH2O of −114.6 to −47.1 per mil. 

All samples had isotopic ratios consistent with water that 

originated as precipitation. Of the 15 samples, 12 had isotopic 

ratios consistent with modern or postglacial groundwater 

recharge, and 3 had lighter isotopic signatures, consistent 

with glacial recharge. The occurrence of isotopically light 

H2

O indicates that the aquifers have not been fully flushed by 

modern or postglacial recharge.

Concentrations of methane ranged from 1.2 to 120 milligrams per liter (mg/L). Of the 15 samples, 12 had methane 

concentrations greater than 28 mg/L, the level that poses a risk 

for explosion. The samples had a wide range of water quality: pH ranged from 7.0 to 9.0; alkalinity ranged from 225 

to 889 mg/L as CaCO3; dissolved solids ranged from 398 to 

2,940 mg/L; and chloride ranged from 7.04 to 1,350 mg/L. 

Water types ranged from CaMgHCO3 (generally characteristic 

of shallow, recently recharged water) to NaCl (generally characteristic of deeper, older waters). Methane is not expected 

to coexist with electron acceptors such as dissolved oxygen, 

nitrate, or sulfate; however, one or more of these constituents 

were detected in six samples, which indicates that some of the 

samples were a mix of water from multiple horizons with different redox conditions.

Stable isotopes of methane (δ13CCH4, δ2

HCH4) are used to 

differentiate thermogenic and microbial methane. In general, 

microbial methane is isotopically lighter than thermogenic 

methane because microbes preferentially utilize lighter 

isotopes, which have weaker bonds that are easier to break. 

δ13CCH4 greater than −45 to −50 per mil is diagnostic for 

thermogenic methane, and δ13CCH4 less than about −60 or 

−55 per mil is diagnostic for microbial methane. Samples from

this study had δ13CCH4 of −75.19 to −47.7 per mil and δ2HCH4

of −285.7 to −206 per mil. On a Whiticar plot, which shows

δ13CCH4 versus δ2HCH4, 12 of 15 samples plot in the fields for

microbial methane, 1 sample plots in the field for thermogenic

methane, and 2 samples plot in between.

Another characteristic used to differentiate microbial 

and thermogenic methane is gas dryness, the ratio of methane 

(C1) to the sum of ethane (C2) and propane (C3) (C1/[C2+C3]). 

Thermogenic gas typically includes substantial concentrations of higher-chain hydrocarbons whereas microbial gas is 

predominantly methane with minor amounts of ethane and 

propane. In general, gas dryness greater than about 1,000 is 

diagnostic for microbial methane, and dryness less than 100 is 

diagnostic for thermogenic methane. Samples from domestic 

wells had gas dryness of 5–29,772. On a Bernard plot, which 

shows δ13CCH4 in relation to gas dryness, 11 samples plot in 

the field for microbial methane, 1 sample plots in the field for 

thermogenic methane, and 3 samples plot in between. Interpretations of methane origin based on methane isotopes and 

gas dryness can be ambiguous because secondary processes 

(mixing, migration, and oxidation) can alter the original 

values. For example, several processes can cause an increase 

in δ13CCH4, including mixing microbial methane with thermogenic methane, oxidation of methane by microbial processes, 

and Rayleigh-type fractionation in a partially closed system.

A generalized interpretation of the Whiticar and Bernard 

plots is that 13 samples can be interpreted as predominantly 

microbial, and 2 samples (SU-23 and MT-1286) can be interpreted as having a component of thermogenic methane.

There are two primary pathways of microbial 

methanogenesis—acetate fermentation and CO2 reduction. 

In general, acetate fermentation is associated with younger, 

fresher organic matter and warmer temperatures in nearsurface environments, such as marshes, wetlands, landfills, 

and sewers. CO2

 reduction is associated with older organic 

matter and cooler temperatures in the subsurface and is the 

predominant pathway associated with groundwater systems, 

marine sediments, and relatively shallow deposits of microbial 

shale gas and coal bed methane.

The two microbial pathways result in different degrees 

of fractionation of hydrogen isotopes. For CO2 reduction, all 

the H in CH4 is derived from coexisting water, whereas for 

the acetate fermentation pathway, hydrogen is derived from 

water and acetate. As a result, methane formed by acetate 

fermentation shows a greater degree of H fractionation than 

methane formed by CO2 reduction. Based on relations between 

δ2HCH4 and δ2HH2O, CO2 reduction is the predominant pathway 

of microbial methanogenesis, although acetate fermentation 
28 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

may contribute to methanogenesis for some samples. The 

three samples with isotopically light H2O also have light δ2H 

of methane, and as a result, these samples plot in/near the 

field for acetate fermentation on a Whiticar plot; however, 

other evidence indicates that CO2 reduction was the primary 

microbial pathway of methane formation.

Microbial methanogenesis creates substantial 

fractionation of carbon isotopes between CO2 (or DIC) 

and CH4, with a greater degree of fractionation for the CO2

reduction than for acetate fermentation. The degree of 13C 

fractionation between CO2 and CH4 is indicated by the 

fractionation factor represented as α13CCO2-CH4. A total of 

12 samples had α13CCO2-CH4 of 1.050–1.077, within the range 

for microbial methanogenesis, and 3 samples had values 

between 1.021 and 1.039, within the range for methane 

oxidation or thermogenic methane.

The samples had a wide range of δ13CDIC (−31.6 to 

+18.9 per mil). Seven samples had values between −14.8 and

−2.9 per mil, within the range of typical groundwater. One

sample had δ13CDIC of −31.6 per mil, which is depleted relative

to soil or aquifer-derived organic matter, and is considered to

be diagnostic of methane oxidation. Four samples had δ13CDIC

greater than +10 per mil, which is considered to be diagnostic

of Rayleigh-type fractionation associated with CO2 reduction

in a partially closed groundwater system.

Carbon-14 (14C) is a radioactive isotope of carbon 

that can be detected in organic materials less than about 

50,000 years old. The concentration of 14C in methane can 

provide information about the relative age of the carbon 

source. Eight samples had 14CCH4 less than the reporting limit 

of 0.4 pMC, consistent with methane formed from carbon in 

Paleozoic bedrock or older glacial deposits. Six samples had 

14CCH4 of 0.9–13.5 pMC, consistent with methane formed from 

organic matter in younger glacial deposits. One sample did 

not have a sufficient CH4 concentration to analyze for 14CCH4. 

None of the samples had 14CCH4 concentrations consistent 

with methane from landfills, swamps, marshes, or other nearsurface environments where acetate fermentation is expected 

to be the predominant pathway of microbial methanogenesis.

Overall, 12 samples had chemical and isotopic 

characteristics consistent with microbial methane formed 

predominantly by the CO2 reduction pathway. Where multiple 

samples were analyzed from the same aquifer, δ13CCH4

generally increased with depth. The four samples with the 

heaviest δ13CCH4 also had the heaviest δ13CDIC (+10.8 to 

+18.9 per mil), and three of the four samples also had H2O

isotopes indicative of glacial recharge. These observations

are generally consistent with CO2 reduction in a partially

closed system that has not been fully flushed with modern

or postglacial recharge. Two of the samples are from the

northwestern corner of Ohio, where a thick layer of glacial

lakebed clay inhibits recharge to the underlying Upper

Devonian black shale. The other two samples are from the

deepest wells (301 and 345 feet), which tap Pennsylvanian

bedrock in eastern Ohio.

Other interpretations are also possible; for example, 

the increase in δ13CCH4 with depth could also be interpreted 

as increased mixing with thermogenic methane (and possibly brine) migrating from greater depths. This interpretation 

could be especially applicable to wells in eastern Ohio, which 

generally have lower C1/(C2+C3) and higher concentrations of 

chloride and bromide, as compared to wells in western Ohio.

A total of three samples had chemical and isotopic 

characteristics that are not consistent with microbial CO2

reduction. The sample from the shallowest well (CR-63) had 

characteristics consistent with methane oxidation by sulfate 

reduction (δ13CDIC of –31.6 per mil, slightly enriched δ13CCH4, 

high concentrations of SO4 and sulfide, a rotten egg odor, and 

an abundance of fine black particulates).

Two samples (SU-23 and MT-1286) were interpreted as 

having a component of thermogenic methane based on δ13CCH4

(−47.17 and −50.96 per mil), dryness (5 and 28), and the 

presence of butane (C4) and pentane (C5) hydrocarbons. For 

both samples, there also was evidence of mixing with modern/

postglacial recharge and (or) microbial methane. The chemical 

and isotopic data collected for this study were not sufficient 

to distinguish whether thermogenic methane in SU-23 or 

MT-1286 (or any of the other wells) is the result of (1) natural 

migration of deep methane/groundwater or (2) contamination 

with stray gas related to human activities.

The study has several limitations related to the study 

design. (1) The number of wells sampled was relatively 

small, and it is possible that methane occurs in hydrogeologic 

settings not represented by the well network. (2) Multiple 

potential natural and anthropogenic migration pathways exist 

near most of the wells, especially those in eastern Ohio; this 

creates some uncertainty as to whether the methane samples 

are naturally occurring or related to human activities. (3) Most 

of the wells were constructed with long open intervals, so 

water samples could be a mix from multiple horizons, and this 

could obscure diagnostic relations between water quality and 

gas characteristics. (4) A single sample was collected from 

each well, so it is not possible to assess temporal variability 

of the data. (5) Additional types of chemical and isotopic 

analyses may have been useful; for example, isotopes of 

higher-chain hydrocarbons and (or) noble gases may have 

provided additional information about migration pathways, 

mixing, or oxidation.

There also are several uncertainties and inconsistencies associated with the methods of analysis. (1) As discussed in earlier sections of this report, secondary processes 

can obscure original isotopic and (or) chemical signatures. 

(2) There is some uncertainty about the amount and types of

higher-chain hydrocarbons that can be produced by microbial processes, which can add uncertainty to differentiation

of microbial and thermogenic methane. (3) Some of the

data used to define isotopic signatures for microbial methane were from recent sediments or lab cultures, and there

is uncertainty about how well the data represent microbial

methanogenesis using organic matter in shale or coal. There is
References Cited 29

some uncertainty about 13C fractionation factors diagnostic of 

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processes that produce or consume CH4 and (or) CO2. (5) Isotopically enriched δ13CDIC is considered to be unequivocal 

evidence of microbial methanogenesis; however, enriched 

δ13CDIC has been detected in commercial wells that produce 

from thermogenic gas reservoirs.

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Strapoc, D., Mastalerz, M., Eble, C., and Schimmelmann, A., 

2007, Characterization of the origin of coalbed gases in 

southeastern Illinois Basin by compound-specific carbon 

and hydrogen stable isotope ratios: Organic Geochemistry, v. 38, no. 2, p. 267–287. [Also available at https://doi.

org/10.1016/j.orggeochem.2006.09.005.]

U.S. Geological Survey, variously dated, National field manual for the collection of water-quality data: U.S. Geological 

Survey Techniques of Water-Resources Investigations, book 

9, chaps. A1–A9, accessed January 23, 2016, at https://pubs.

er.usgs.gov/usgspubs/twri/twri09.
32 Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016

U.S. Geological Survey, 2016a, Dissolved gas analysis: U.S. 

Geological Survey web page, accessed March 23, 2018, at 

https://water.usgs.gov/lab/dissolved-gas/lab/analytical_procedures/.

U.S. Geological Survey, 2016b, Dissolved gas sampling 

instructions—Collection and analysis of ground-water 

samples for helium by gas chromatography: U.S. Geological Survey web page, accessed March 23, 2018, at https://

water.usgs.gov/lab/dissolved-gas/sampling/#hel.

U.S. Geological Survey, 2018, National Water Information 

System—Web interface, accessed June 12, 2018, at https://

doi.org/10.5066/F7P55KJN.

Vinson, D.S., Blair, N.E., and Martini, A.M., Larter, S., Orem, 

W.H., and McIntosh, J.C., 2017, Microbial methane from 

in situ biodegradation of coal and shale—A review and 

reevaluation of hydrogen and carbon isotope signatures: 

Chemical Geology, v. 453, no. 20, p. 128–145. [Also available at https://doi.org/10.1016/j.chemgeo.2017.01.027.]

Waldron, S., Lansdown, J.M., Scott, E.M., Fallick, A.E., and 

Hall, A.J., 1999, The global influence of the hydrogen isotope composition of water on that of bacteriogenic methane 

from shallow freshwater environments: Geochimica et Cosmochimica Acta, v. 63, no. 15, p. 2237–2245. [Also available at https://doi.org/10.1016/S0016-7037(99)00192-1.]

Warner, N.R., Jackson, R.B., Darrah, T.H., Osborn, S.G., 

Down, A., Zhao, K., White, A., and Vengosh, A., 2012, 

Geochemical evidence for possible natural migration of 

Marcellus Formation brine to shallow aquifers in Pennsylvania: Proceedings of the National Academy of Sciences, v. 

109, no. 30, p. 11961–11966. [Also available at https://doi.

org/10.1073/pnas.1121181109.]

Whiticar, M.J., 1999, Carbon and hydrogen isotope systematics of bacterial formation and oxidation of methane: Chemical Geology, v. 161, no. 1–3, p. 291–314. [Also available at 

https://doi.org/10.1016/S0009-2541(99)00092-3.]

Whiticar, M.J., Faber, E., and Schoell, M., 1986, Biogenic 

methane formation in marine and freshwater environments—CO2

 reduction vs. acetate fermentation—Isotopic 

evidence: Geochimica et Cosmochimica Acta, v. 50, no. 5, 

p. 693–709. [Also available at https://doi.org/10.1016/0016-

7037(86)90346-7.]
Tables 2, 3, and 5
Table 2. Results of quality-control samples analyzed at U.S. Geological Survey National Water Quality Laboratory. [mg/L, milligrams per liter; --, no data; <, less than; N, nitrogen; nd, no difference; P, phosphorus; μg/L, micrograms per liter; As, arsenic] Sample type Equipment blank Field blank Replicate Replicate 

Date 5/31/2016 6/15/2016 6/20/2016 6/2/2016 Percent difference 6/16/2016 Percent difference 6/

Time 1503, 1505 1106 1206 1100 1101 1100 1101 1000 

Constituent Dissolved solids (mg/L) -- <20 -- -- -- -- -- -- -- -- 

Calcium (mg/L) -- <0.022 -- -- -- -- -- -- -- -- 

Magnesium (mg/L) -- <0.011 -- -- -- -- -- -- -- -- 

Potassium (mg/L) -- <0.03 -- -- -- -- -- -- -- -- 

Sodium (mg/L) -- <0.06 -- -- -- -- -- -- -- -- 

Bromide (mg/L) -- <0.01 -- -- -- -- -- -- -- -- 

Chloride (mg/L) -- <0.02 -- -- -- -- -- -- -- -- 

Fluoride (mg/L) -- <0.01 -- -- -- -- -- -- -- -- 

Silica (mg/L) -- <0.018 -- -- -- -- -- -- -- -- 

Total nitrogen (mg/L) -- <0.05 -- -- -- -- -- -- -- 0.50 

Ammonia (mg/L as N) -- <0.01 -- -- -- -- -- -- -- 0.40 

Nitrite (mg/L as N) -- <0.001 -- -- -- -- -- -- -- <0.001 

Orthophosphate (mg/L as P) -- <0.004 -- -- -- -- -- -- -- 0.038 

Nitrate+Nitrile (mg/L as N) -- <0.04 -- -- -- -- -- -- -- <0.040 

Aluminum (μg/L) <3 -- -- <3 <3 nd -- -- -- -- Antimony (μg/L) <0.027 -- -- <0.027 <0.027 nd -- -- -- -- 

Barium (μg/L) <0.25 -- -- 523 511 -- -- -- -- 

Beryllium (μg/L) <0.020 -- -- <0.020 <0.020 nd -- -- -- -- 

Cadmium (μg/L) <0.030 -- -- <0.030 <0.030 nd -- -- -- -- 

Lead (μg/L) <0.040 -- -- <0.040 <0.040 nd -- -- -- -- 

Iron (μg/L) -- -- -- -- -- -- 

Manganese (μg/L) <0.4 -- -- 39.7 39.3 1.0 -- -- -- -- 

Molybdenum (μg/L) <0.05 -- -- 0.216 0.196 9.7 -- -- -- -- 

Silver (μg/L) <0.020 -- -- <0.020 <0.020 nd -- -- -- -- 

Uranium (μg/L) <0.0140 -- -- <0.0140 <0.0140 nd -- -- -- -- 

Boron (μg/L) <5 -- -- 112 109 2.7 -- -- -- -- 

Lithium (μg/L) <0.22 -- -- 0.981 0.824 17 -- -- -- -- 
Table 2. Results of quality-control samples analyzed at U.S. Geological Survey National Water Quality Laboratory.—Continued [mg/L, milligrams per liter; --, no data; <, less than; N, nitrogen; nd, no difference; P, phosphorus; μg/L, micrograms per liter; As, arsenic]

Sample type Equipment blank Field blank Replicate Replicate Date 5/31/2016 6/15/2016 6/20/2016 6/2/2016 Percent

difference

6/16/2016 Percent

difference

6

Time 1503, 1505 1106 1206 1100 1101 1100 1101 1000 

Constituent

Strontium (μg/L) <0.8 -- -- 1,270 1,260 0.8 -- -- -- -- 

Thallium (μg/L) <0.03 -- -- <0.030 <0.030 nd -- -- -- -- 

Arsenic (μg/L) <0.1 -- -- 39.5 39.7 0.5 -- -- -- -- 

Cobalt (μg/L) <0.05 -- -- 0.381 0.376 1.3 -- -- -- -- 

Chromium (μg/L) <0.3 -- -- 0.37 0.37 nd -- -- -- -- 

Copper (μg/L) <0.80 -- -- <0.80 <0.80 nd -- -- -- -- 

Nickel (μg/L) <0.2 -- -- 0.656 0.665 1.4 -- -- -- -- 

Selenium (μg/L) <0.05 -- -- 0.079 0.090 13 -- -- -- -- 

Vanadium (μg/L) <0.1 -- -- 0.75 0.75 nd -- -- -- -- 

Zinc (μg/L) <2 -- -- 20.8 37.4 57 -- -- -- -- 

Organic carbon (mg/L) <0.23 -- <0.23 -- -- -- 1.38 9.94 38 -- 

Arsenate (μg/L as As) -- -- <0.4 -- -- -- <0.4 <0.4 nd -- 

Arsenite (μg/L as As) -- -- <0.2 -- -- -- <0.2 <0.2 nd -- 

Dimethylarsinate a(μg/L as As)

-- -- <0.3 -- -- -- <0.3 <0.3 nd -- 

Monomethylarsonate 

(μg/L as As)

-- -- <0.8 -- -- -- <0.8 <0.8 nd -- 
Table 3. Results of quality-control samples analyzed at Isotech Laboratories and U.S. Geological Survey Reston Groundwater Dating Laboratory. [USGS, U.S. Geological Survey; <, less than; nd, no difference; --, no data; C, carbon; mg/L, milligram per liter; δ, isotopic ratio delta notation; per mil, parts per thousand; H, hDIC, dissolved inorganic carbon] Sample type Replicate—Isotech Laboratories Replicate—Isotech Laboratories Replicate—USGS Gro

Dating Laborat

Date 6/16/2016 Percent difference 6/21/2016 Percent difference 6/21/2016 

Time 1100 1101 1000 1011 1000 1011 Constituent Oxygen, mole percent 0.66 0.75 13 1.06 0.99 6.8 <0.02 <0.02 

Carbon dioxide, mole percent 1.07 1.06 0.9 0.98 0.97 1.0 12.85 12.25 

Carbon monoxide, mole percent <0.01 <0.01 nd <0.010 <0.010 nd -- -- 

Hydrogen, mole percent <0.01 <0.01 nd <0.010 <0.010 nd -- -- 

Dinitrogen, mole percent 5.39 5.40 0.2 7.03 7.23 2.8 5.20 5.23 

Argon, mole percent 0.131 0.131 nd 0.159 0.154 3.2 0.273 0.275 

Helium, mole percent 0.0092 0.0084 9.1 0.0059 0.0050 17 -- -- 

Methane, mole percent 92.68 92.59 0.1 90.76 90.64 0.1 -- -- 

Ethane, mole percent 0.0571 0.0570 0.2 0.0090 0.0091 1.1 -- -- 

Ethene, mole percent <0.0001 <0.0001 nd <0.0001 <0.0001 nd -- -- 

Propane, mole percent 0.0001 0.0001 nd <0.0001 <0.0001 nd -- -- 

n-Pentane, mole percent <0.0001 <0.0001 nd <0.0001 <0.0001 nd -- -- 

Propene, mole percent <0.0001 <0.0001 nd <0.0001 <0.0001 nd -- -- 

2-Methylpropane, mole percent <0.0001 <0.0001 nd <0.0001 <0.0001 nd -- -- 

Butane, mole percent <0.0001 <0.0001 nd <0.0001 <0.0001 nd -- -- 

n-Butane, mole percent <0.0001 <0.0001 nd <0.0001 <0.0001 nd -- -- 

2-Methylbutane, mole percent <0.0001 <0.0001 nd <0.0001 <0.0001 nd -- -- 

C6+ hydrocarbons, mole percent <0.0001 <0.0001 nd <0.0001 <0.0001 nd -- -- 

Methane, mg/L 120 120 nd 91 91 nd 68.18 67.08 

Ethane, mg/L 0.14 0.14 nd 0.0180 0.018 nd -- -- 

Propane, mg/L 0.0003 0.0004 29 <0.0002 <0.0002 nd -- -- 

δ13C in methane, per mil −62.46 −62.40 −0.1 -- -- -- -- -- 

δ2H in methane, per mil −241.9 −241.9 nd -- -- -- -- -- 

δ18O in water, per mil −8.69 −8.55 −1.6 -- -- -- -- -- 

δ2H in water, per mil −57.3 −56.4 −1.6 -- -- -- -- -- δ13C of DIC in water, per mil 10.8 8.2 27 -- -- -- -- -- 

14C of methane, percent modern carbon <0.4 <0.4 nd -- -- -- -- -- 

1 Percent difference was calculated using the average value of two replicates from each laboratory.
Table 5. Water-quality data from Ohio domestic wells, 2016. [mm Hg, millimeters mercury; --, no data; mg/L, milligrams per liter; μg/L, micrograms per liter; BLS, below land surface; μS/cm, microsiemens per centimeter; NTRU, nepheU, hydrogen sulfide odor not detected; M, hydrogen sulfide odor detected; CaCO3, calcium carbonate; N, nitrogen; <, less than; As, arsenic; DIC, dissolved inorganic carbon; CH

O, oxygen; δ, isotopic ratio delta notation; per mil, parts per thousand]

Well

identifier

Date 

(yyyymmdd)

Barometric 

pressure 

(mm Hg)

Air

temperature 

(degrees 

Celsius)

Water 

level 

(ft BLS)

Dissolved 

oxygen 

(mg/L)

pH 

(standard 

units)

Specific 

conductance 

(uS/cm)

Water

temperature 

(degrees 

Celsius)

Turbidity 

(NTRU)

Altitude 

of land 

surface 

(ft above 

NAVD88)

We

dept

(ft BL

AB-142 20160614 735 27 9.75 1.2 8.7 735 11.8 0.2 1,080 94 

GE-368 20160614 731 27 61.19 0.2 9 1120 11.9 0.1 1,137 150 

SU-23 20160615 729 24 -- 0.3 7.4 835 12.5 0.3 1,115 95 

ST-140 20160613 738 24 69.87 0.2 7.5 587 12.5 3 1,058 295 

ST-139 20160613 -- 27 21.65 0.2 8.2 1880 13.9 59 978 235 

ST-141 20160616 735 27 31.1 0.2 7.7 5030 12.7 1 1,104 30

CO-31 20160615 729 27 -- 0.3 8.1 1940 15.4 0.2 1,192 345 

PE-59 20160601 738 29 54.02 0.2 8 -- 12.5 5.3 873 190 

MU-128 20160601 -- 32 85.86 0.2 8.1 -- 14.2 8.9 866 263 

GR-755 20160602 742 26 -- 0.2 7.1 -- 13.5 2 857 171 

MT-1286 20160602 740 27 24.21 0.2 7 -- 13.7 25 899 300 

DE-28 20160620 744 32 24.33 0.3 7.7 543 15.3 3.6 716 93 

DE-29 20160621 748 27 47.75 0.2 7.5 641 13.4 0.2 736 144 

HY-53 20160620 746 32 51.83 0.2 7.9 743 14 5.4 738 128 

CR-63 20160621 732 27 26.64 0.2 7.4 985 14 2.1 1,011 75 
Table 5. Water-quality data from Ohio domestic wells, 2016.—Continued [yyyymmdd, date in year-month-day format; mm Hg, millimeters mercury; ft, feet; BLS, below land surface; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; Nratio unit; NAVD 88, North American Vertical Datum of 1988; CaCO3, calcium carbonate; U, hydrogen sulfide odor not detected; M, hydrogen sulfide odor detected; --, no data

<, less than; As, arsenic; δ, isotopic ratio delta notation; C, carbon; DIC, dissolved inorganic carbon; per mil, parts per thousand; CH4, methane; H, hydrogen; H2O, water; O, oxygen

Well identifier Bicarbonate (mg/L) Carbonate (mg/L) Hydroxide (mg/L) Sulfide (mg/L) Dissolved solids (mg/L) Calcium (mg/L) Magnesium (mg/L) Potassium (mg/L) Sodium (mg/L) Bromide (mg/L) Chloride (mg/L) Flu

(m

AB-142 438 9.4 0 0.082 466 0.416 0.153 0.96 192 0.153 13.1 1

GE-368 362 13.9 0.1 0.073 645 2.21 0.697 1.32 257 0.922 60.8 3

SU-23 429 0.5 0 0.09 496 104 41.4 3.83 13.9 0.216 65.7 0

ST-140 338 0.4 0 0.626 352 41.5 12.6 4.62 82.7 0.139 17.8 0

ST-139 544 4.8 0 0.262 1,120 3.59 1.34 4.6 431 2.5 727 0

ST-141 535 1.6 0 0 2,940 25.8 11.1 6.74 1,060 8.71 1,350 0

CO-31 1,070 8.4 0 0.645 1,240 3.78 1.51 3.36 500 1.03 117 1

PE-59 434 1.7 0 0.026 514 24.6 10.1 3 171 0.274 66 0

MU-128 543 4 0 0.097 754 1.87 0.325 1.13 296 0.684 140 2

GR-755 708 0.5 0 0.193 716 92.4 40.8 3.2 115 0.612 74.9 0MT-1286 479 0.3 0 0.015 479 107 44.1 4.98 24.1 0.127 29.1 0DE-28 274 0.6 0 0.001 318 28.4 11.8 2.33 72.3 0.264 32.2 1DE-29 338 0.6 0 0.005 387 34.6 13.9 2.3 88.1 0.422 40.7 1

HY-53 305 1.1 0 0.001 421 25.2 11.6 2.43 122 0.675 80.8 1

CR-63 412 0.6 0 0.401 619 78.8 44.3 5.7 77.4 0.146 7.04 1
Table 5. Water-quality data from Ohio domestic wells, 2016.—Continued [yyyymmdd, date in year-month-day format; mm Hg, millimeters mercury; ft, feet; BLS, below land surface; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; Nratio unit; NAVD 88, North American Vertical Datum of 1988; CaCO3, calcium carbonate; U, hydrogen sulfide odor not detected; M, hydrogen sulfide odor detected; --, no data

<, less than; As, arsenic; δ, isotopic ratio delta notation; C, carbon; DIC, dissolved inorganic carbon; per mil, parts per thousand; CH4, methane; H, hydrogen; H2O, water; O, oxygen

Well

identifier

Ammonia 

(mg/L as 

N)

Nitrate 

+ nitrite 

(mg/L 

as N)

Nitrite 

(mg/L 

as N)

Orthophosphate 

(mg/L as P)

Total

nitrogen

(mg/L)

Aluminum 

(μg/L)

Barium 

(μg/L)

Beryllium 

(μg/L)

Cadmium 

(μg/L)

Chromium 

(μg/L)

Cobalt 

(μg/L)

Copper 

(μg/L)

Iron 

(μg/L)

(

AB-142 0.33 <0.04 <0.001 0.093 0.38 <3 2.62 0.05 <0.03 <0.3 <0.05 <0.8 7.7 <GE-368 0.46 <0.04 <0.001 0.049 0.55 <3 6.35 <0.02 <0.03 <0.3 <0.05 <0.8 12.8 <

SU-23 0.21 <0.04 <0.001 0.009 0.25 <3 1,940 <0.02 <0.03 <0.3 <0.05 <0.8 898 <

ST-140 0.77 <0.04 <0.001 0.025 0.83 <3 101 0.028 <0.03 <0.3 <0.05 <0.8 208 ST-139 0.83 <0.04 <0.001 0.102 0.91 <3 307 0.032 <0.03 <0.3 <0.05 <0.8 97.4 

ST-141 1.7 <0.04 <0.001 0.033 1.77 <9 629 <0.06 <0.09 <0.9 <0.15 <2.4 296 <

CO-31 0.7 0.655 <0.001 0.032 0.78 <3 166 0.03 <0.03 <0.3 <0.05 <1.6 22.1 <

PE-59 3.05 <0.04 <0.001 0.087 3.35 <3 111 0.02 0.067 <0.3 0.051 <0.8 282 <

MU-128 0.25 <0.04 <0.001 0.08 0.34 <3 45.9 <0.02 <0.03 <0.3 0.053 <0.8 79.2 

GR-755 26.9 <0.04 0.001 0.806 27.9 <3 523 <0.02 <0.03 0.37 0.381 <0.8 3,730 <MT-1286 0.15 0.298 0.006 0.006 0.49 3.2 99.6 <0.02 <0.03 <0.3 0.109 2.4 <4 

DE-28 0.4 <0.04 <0.001 0.018 0.49 16.2 222 0.045 0.088 <0.3 <0.05 <0.8 176 <

DE-29 0.4 <0.04 <0.001 0.038 0.5 <3 307 0.047 0.108 <0.3 <0.05 <0.8 653 

HY-53 0.42 <0.04 <0.001 0.013 0.52 <3 178 0.037 0.255 <0.3 <0.05 <0.8 433 

CR-63 0.73 <0.04 <0.001 0.008 0.9 <3 99.4 0.064 <0.03 <0.3 <0.05 <0.8 11.7 <
Table 5. Water-quality data from Ohio domestic wells, 2016.—Continued [yyyymmdd, date in year-month-day format; mm Hg, millimeters mercury; ft, feet; BLS, below land surface; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; Nratio unit; NAVD 88, North American Vertical Datum of 1988; CaCO3, calcium carbonate; U, hydrogen sulfide odor not detected; M, hydrogen sulfide odor detected; --, no data

<, less than; As, arsenic; δ, isotopic ratio delta notation; C, carbon; DIC, dissolved inorganic carbon; per mil, parts per thousand; CH4, methane; H, hydrogen; H2O, water; O, oxygen

Well identifier Molybdenum (μg/L) Nickel (μg/L) Silver (μg/L) Strontium (μg/L) Thallium (μg/L) Vanadium (μg/L) Zinc (μg/L) Antimony (μg/L) Arsenate (μg/L as As) Arsenic (μg/L) Arsenite (μg/L as As) Dimethyl- arsinate (μg/L as As) Mon

meth

arson

(μg/L 

As

AB-142 0.076 <0.2 <0.02 12.4 <0.03 0.1 <2 <0.027 <0.4 <0.1 <0.2 <0.3 <0.GE-368 0.519 <0.2 <0.02 35.1 <0.03 0.84 <2 <0.027 <0.4 0.18 <0.2 <0.3 <0.

SU-23 0.172 0.22 <0.02 420 <0.03 <0.1 3.2 <0.027 0.4 0.38 <0.2 <0.3 <0.

ST-140 0.074 <0.2 <0.02 392 <0.03 <0.1 251 0.028 <0.4 <0.1 <0.2 <0.3 <0.ST-139 0.423 <0.2 <0.02 96.4 <0.03 1.5 12.3 <0.027 <0.4 0.33 <0.2 <0.3 <0.ST-141 0.702 <0.6 <0.06 724 <0.09 0.6 8.4 <0.081 <0.4 <0.3 <0.2 <0.3 <0.

CO-31 0.146 <0.4 <0.02 130 <0.06 <0.1 <2 <0.027 <0.4 <0.1 <0.2 <0.3 <0.

PE-59 15.9 <0.2 <0.02 447 <0.03 0.38 3.1 <0.027 0.8 34.1 31.5 <0.3 <0.

MU-128 0.163 <0.2 <0.02 64.8 <0.03 0.1 39.8 0.05 <0.4 0.14 <0.2 <0.3 <0.GR-755 0.216 0.66 <0.02 1,270 <0.03 0.75 20.8 <0.027 5.1 39.5 32.5 <0.3 <0.

MT-1286 1 0.71 <0.02 560 <0.03 <0.1 7.6 <0.027 <0.4 <0.1 <0.2 <0.3 <0.

DE-28 20.4 <0.2 0.028 4,420 <0.03 0.11 <2 <0.027 <0.4 <0.1 <0.2 <0.3 <0.

DE-29 26.4 <0.2 <0.02 4,210 <0.03 <0.1 270 <0.027 <0.4 0.16 <0.2 <0.3 <0.

HY-53 65.8 <0.2 <0.02 2,780 <0.03 <0.1 136 <0.027 <0.4 <0.1 <0.2 <0.3 <0.

CR-63 0.057 <0.2 <0.02 6,860 <0.03 <0.1 <2 <0.027 <0.4 0.111 <0.2 <0.3 <0.
Table 5. Water-quality data from Ohio domestic wells, 2016.—Continued [yyyymmdd, date in year-month-day format; mm Hg, millimeters mercury; ft, feet; BLS, below land surface; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; NTRUunit; NAVD 88, North American Vertical Datum of 1988; CaCO3, calcium carbonate; U, hydrogen sulfide odor not detected; M, hydrogen sulfide odor detected; --, no data; N, nitrog

<, less than; As, arsenic; δ, isotopic ratio delta notation; C, carbon; DIC, dissolved inorganic carbon; per mil, parts per thousand; CH4, methane; H, hydrogen; H2O, water; O, oxygen]

Well

identifier

Uranium 

(μg/L)

Dissolved 

organic 

carbon 

(mg/L)

Argon 

(mole 

percent 

of gases)

Oxygen 

(mole 

percent

 of gases)

Nitrogen 

(mole 

percent 

of gases)

Carbon 

dioxide 

(mole 

percent 

of gases)

Carbon 

monoxide 

(mole 

percent of 

gases)

Hydrogen 

(mole 

percent 

of gases)

Helium 

(mole 

percent 

of gases)

Methane 

(mole 

percent 

of gases)

Ethane 

(mole 

percent 

of gases)

Ethene 

(mole 

percent 

of gases)

Pro

(m

per

of g

AB-142 <0.014 0.48 0.568 1.01 26.41 0.21 <0.01 <0.01 -- 71.79 0.0116 <0.0001 <0.

GE-368 <0.014 0.42 0.319 0.61 12.9 0.051 <0.01 <0.01 0.013 86.09 0.02 <0.0001 <0.

SU-23 <0.014 0.94 0.1 2.26 5.66 3.3 <0.01 <0.01 -- 73.21 12.41 <0.0001 2.

ST-140 <0.014 0.45 1.25 2.06 61.19 3.2 <0.01 <0.01 -- 32.28 0.0177 <0.0001 <0.

ST-139 <0.014 0.36 0.409 0.67 19.47 0.37 <0.01 <0.01 0.012 79.06 0.0125 <0.0001 <0.

ST-141 <0.042 1.38 0.131 0.66 5.39 1.07 <0.01 <0.01 0.009 92.68 0.0571 <0.0001 0.

CO-31 <0.014 3.6 0.161 1.39 5.9 0.76 <0.01 <0.01 0.009 91.76 0.0234 <0.0001 <0.

PE-59 <0.014 2.67 0.588 2.66 31.1 0.94 <0.01 <0.01 -- 64.41 0.266 <0.0001 0.

MU-128 <0.014 1.57 0.307 2.35 15.97 1.41 <0.01 <0.01 -- 79.9 0.0663 <0.0001 <0.

GR-755 <0.014 16.2 0.221 0.28 7.82 5.33 <0.01 <0.01 0.01 86.34 0.0029 <0.0001 <0.

MT-1286 0.706 0.85 1.43 3.29 70.77 18.84 <0.01 <0.01 -- 5.46 0.154 <0.0001 0.

DE-28 <0.014 0.86 0.453 2.83 21.2 0.62 <0.01 <0.01 0.008 74.89 0.0026 <0.0001 <0.

DE-29 <0.014 2.58 0.159 1.06 7.03 0.98 <0.01 <0.01 0.006 90.76 0.009 <0.0001 <0.

HY-53 <0.014 1.03 0.091 1.87 3.87 0.85 <0.01 <0.01 -- 93.31 0.0042 <0.0001 0.

CR-63 0.0812 1.52 0.92 0.039 45.32 3.77 <0.01 <0.01 -- 49.86 0.0947 <0.0001 <0.
Table 5. Water-quality data from Ohio domestic wells, 2016.—Continued [yyyymmdd, date in year-month-day format; mm Hg, millimeters mercury; ft, feet; BLS, below land surface; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; Nratio unit; NAVD 88, North American Vertical Datum of 1988; CaCO3, calcium carbonate; U, hydrogen sulfide odor not detected; M, hydrogen sulfide odor detected; --, no data

<, less than; As, arsenic; δ, isotopic ratio delta notation; C, carbon; DIC, dissolved inorganic carbon; per mil, parts per thousand; CH4, methane; H, hydrogen; H2O, water; O, oxygen

Well identifier n-Butane (mole percent of gases) Iso- pentane (mole percent of gases) n-Pentane (mole percent of gases) Hexanes+ (mole percent of gases) Methane (mg/L) Ethane (mg/L) Propane (mg/L) δ13CDIC (per mil) δ13CCH4 (per mil) δ2HCH4 (per mil) 14CCH4 (percent modern carbon) 14CCH4 standa

deviati

(perce

moder

carbon

AB-142 <0.0001 <0.0001 <0.0001 <0.0001 36 0.012 <0.0002 –6 –75.19 –252.6 13.5 0.1 

GE-368 <0.0001 <0.0001 <0.0001 <0.0001 73 0.035 <0.0002 –8.8 –64.31 –245.3 <0.4 -- 

SU-23 0.251 0.0523 0.0362 0.0228 39 13 3.7 –2.9 –47.74 –236.7 1.6 0.1 

ST-140 <0.0001 <0.0001 <0.0001 <0.0001 8.7 0.0097 <0.0002 –8.9 –69.85 –243.5 1.5 0.1 

ST-139 <0.0001 <0.0001 <0.0001 <0.0001 57 0.019 <0.0002 3 –69.11 –237.1 <0.4 -- 

ST-141 <0.0001 <0.0001 <0.0001 <0.0001 120 0.14 0.0003 10.8 –62.46 –241.9 <0.4 -- 

CO-31 <0.0001 <0.0001 <0.0001 <0.0001 98 0.05 <0.0002 18.9 –61.19 –253.8 <0.4 -- 

PE-59 <0.0001 0.0006 <0.0001 <0.0001 36 0.3 0.059 –9.4 –69.55 –240.2 0.9 0.1 

MU-128 <0.0001 <0.0001 <0.0001 <0.0001 29 0.049 <0.0002 –13 –67.48 –206 <0.4 -- 

GR-755 <0.0001 <0.0001 <0.0001 <0.0001 80 0.0054 <0.0002 2.6 –71.37 –232.1 <0.4 -- 

MT-1286 0.0063 0.0009 <0.0001 <0.0001 1.2 0.068 0.025 –14.8 –50.96 –230.7 -- -- 

DE-28 <0.0001 <0.0001 <0.0001 <0.0001 47 0.0034 <0.0002 8.9 –70.17 –252.3 1.7 0.1 DE-29 <0.0001 <0.0001 <0.0001 <0.0001 91 0.018 <0.0002 12 –59.45 –276.6 <0.4 -- 

HY-53 <0.0001 <0.0001 <0.0001 <0.0001 45 0.0041 0.0003 16.8 –56.8 –285.7 <0.4 -- 

CR-63 <0.0001 <0.0001 <0.0001 <0.0001 17 0.066 <0.0002 –31.6 –59.04 –220.7 1.3 0.2 
For additional information, contact: 

Director, Ohio-Kentucky-Indiana Water Science Center

U.S. Geological Survey

6460 Busch Boulevard Ste. 100

Columbus, OH 43229-1737

Publishing support provided by the Madison and Rolla Publishing Service Centers
Thomas—Chemical and Isotopic Characteristics of Methane in Groundwater of Ohio, 2016—Scientific Investigations Report 2018–5097

ISSN 2328–03X (print)

ISSN 2328–0328 (online)

https://doi.org/10.3133/sir20185097