Dissolved Methane in Groundwater, Upper Delaware River 

Basin, Pennsylvania and New York, 2007–12

Introduction

 The prospect of natural gas development from the Marcellus and Utica Shales 

has raised concerns about freshwater aquifers being vulnerable to contamination. Well 

owners are asking questions about subsurface methane, such as, “Does my well water 

have methane and is it safe to drink the water?” and “Is my well system at risk of an 

explosion hazard associated with a combustible gas like methane in groundwater?” 

McCoy’s Knob, near Hancock, New York. Photograph by Peter Nye, New York State Department of Environmental Conservation.

This newfound awareness of methane contamination of water 

wells by stray gas migration is based upon studies such as 

Molofsky and others (2011) who document the widespread 

natural occurrence of methane in drinking-water wells in 

Susquehanna County, Pennsylvania. In the same county, Osborn 

and others (2011) identified elevated methane concentrations 

in selected drinking-water wells in the vicinity of Marcellus 

Shale gas-development activities, although pre-development 

groundwater samples were not available for comparison. 

A compilation of dissolved methane concentrations in 

groundwater for New York State was published by Kappel and 

Nystrom (2012). Recent work documenting the occurrence 

and distribution of methane in groundwater was completed 

in southern Sullivan County, Pennsylvania (Sloto, 2013). 

Additional work is ongoing with respect to monitoring for stray 

gases in groundwater (Jackson and others, 2013). These studies 

and their results indicate the importance of collecting baseline 

or pre-development data. While such data are being collected 

in some areas, published data on methane in groundwater are 

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2013–1167

August 2013
2

sparse in the Upper Delaware River Basin of Pennsylvania, 

New York, and New Jersey. To manage drinking-water 

resources in areas of gas-well drilling and hydraulic fracturing 

in the Upper Delaware River Basin, the natural occurrence of 

methane in the tri-state aquifers needs to be documented. 

The purpose of this report is to present data on dissolved 

methane concentrations in the groundwater in the Upper 

Delaware River Basin. The scope is restricted to data for 

Pennsylvania and New York, no U.S. Geological Survey 

(USGS) methane analyses are presently available for 

northwestern New Jersey. 

Origin and Occurrence of Methane

Methane originates from several different sources. 

“Microbial” methane is produced through microbial 

fermentation (decomposition of organic matter) or methane 

produced by carbon dioxide reduction at shallow depths 

and low temperatures. “Thermogenic” methane is produced 

from organic matter buried millions of years ago, which has 

undergone physical and chemical changes at great temperature 

and pressure. Like methane, other hydrocarbons such as 

ethane, propane, and butane, or oil also can be produced 

thermogenically and are typically referred to as “wet gas.” In 

the Upper Delaware River Basin, only methane gas, referred 

to as “dry gas” is thought to be present. (Marcellus Center for 

Outreach and Research, 2013) 

Methane is a colorless, odorless, tasteless gas that can be 

flammable or explosive. It can trigger an explosion in enclosed/

confined spaces containing oxygen when an ignition source (an 

open flame or an electrical spark) is present. Methane can act as 

an asphyxiate by displacing air in confined spaces and replacing 

oxygen in animal circulatory systems. Burning methane can 

produce other toxic gases such as carbon monoxide (Eltschlager 

and others, 2001). 

In groundwater, methane can be dissolved or in a gaseous 

state. When methane is dissolved, it acts like the carbon dioxide 

gas used in carbonated beverages, where the gas is held within 

the fluid under the confining pressure of the sealed container. 

When the container is opened, pressure is reduced, and some 

of the gas comes out of solution, which causes bubbling and 

fizzing in the beverage. In aquifers, methane may be confined 

by overlying fine-grained deposits or unfractured bedrock. 

Dissolved methane concentrations in confined aquifers can be 

much greater than the saturation concentration at atmospheric 

pressure. As groundwater enters a well at atmospheric pressure, 

the natural gas can be released from the water, which can cause 

a column of gas to form above the water surface in the well or 

be released within a pressure tank, at faucets inside a home, or 

in structures enclosing the well, where it can become flammable 

or explosive (Eltschlager and others, 2001). 

Dissolved methane reaches saturation in water at 

28 milligrams per liter (mg/L) at atmospheric pressure and 

becomes flammable in air at about 5 percent by volume 

(Eltschlager and others, 2001). The Office of Surface Mining 

recommends that methane concentrations greater than 

28 mg/L in well water be addressed immediately by removing 

any potential ignition source and venting the gas away from 

confined spaces (Eltschlager and others, 2001). The Office of 

Surface Mining also recommends that methane concentrations 

ranging from 10 to 28 mg/L in water (or 3 to 5 percent by 

volume in air) signify an action level where the situation should 

be closely monitored. Monitoring is recommended because 

methane concentrations vary as a result of natural fluctuations 

in atmospheric pressure and groundwater level. In certain 

cases, a change in methane concentration can be attributed to 

anthropogenic effects such as increased groundwater pumpage 

or drilling new water or gas wells that could introduce natural 

gas from other bedrock strata. If methane concentrations 

increase in any confined area, the area needs to be vented to 

prevent methane gas buildup. Concentrations of methane less 

than 10 mg/L in water (or 1 to 3 percent by volume in air) 

are not as great an issue, but the gas needs to be monitored to 

observe any concentration increases over time (Eltschlager and 

others, 2001). Homeowners are encouraged to contact their 

local or State Health Department for further information about 

measuring and mitigating “action level” methane concentrations 

(as previously defined) in their water wells or in their homes as 

these concentrations vary over time.

Sedimentary Bedrock of the Upper Delaware 

River Basin

In the Upper Delaware River Basin, most drinking-water 

wells are completed in sedimentary bedrock formations of 

Ordovician to Pennsylvanian age (fig. 1). Although most 

bedrock units are present in New York and Pennsylvania, their 

names vary between the States. Some of the bedrock units in 

figure 1 contain strata with high levels of total organic carbon 

that might be sources of thermogenic methane, but the extent of 

such strata are not well documented. 

Dissolved Methane in Groundwater 

The collection of data on dissolved methane concentration 

in groundwater by the USGS in Pennsylvania and New York 

initially began with several groundwater age-dating aquifer 

studies in the mid-2000s. As part of the age-dating method, 

dissolved gas samples (nitrogen, argon, carbon dioxide, oxygen, 

and methane) were collected and analyzed to determine when 

groundwater recharge occurred. When shale gas development 

began in Pennsylvania and elsewhere, dissolved gas 

assessments, using standard USGS methods, were collected in 

order to characterize dissolved methane concentrations. 

The USGS New York Water Science Center, in 

cooperation with New York State Department of Environmental 

Conservation, has conducted groundwater-quality monitoring 

assessments in major river basins in New York (http://ny.water.

usgs.gov/projects/305b/). Beginning in 2010, those assessments 

included sampling for dissolved gases, including methane 

(Nystrom, 2012). Also, a USGS study conducted in cooperation 

with the National Park Service, collected groundwater-quality 

data including concentrations of dissolved methane at six wells 

in the Upper Delaware River Basin (Eckhardt and Sloto, 2012) 

In 2007, dissolved methane data were collected by the 

USGS Pennsylvania Water Science Center in a groundwater 

study of Pike County, Pennsylvania (Senior, 2009). In 2012, as 

part of the Delaware Basin WaterSMART program (http://water.

usgs.gov/watercensus/delaware.html), five additional 
3

Kappel_fig 01

Ordovician Silurian Devonian Mississippian Pennsylvanian

(485)

(443)

(419)

(359)

(323)

(299) Period (Millions of years before present)

Martinsburg Formation 

(Shale, sandstone)

Beekmantown Group

(Dolostone, some limestone)

Reedsville Formation

(Shale, sandstone)

Black River and Trenton Groups

(Limestone, some shale)

Beekmantown Group

(Dolostone, limestone)

Shawangunk Formation

(Sandstone, conglomerate)

Poxono Island through 

Manlius Formations

(Limestone, dolostone, shale)

Shawangunk Formation

(Sandstone, conglomerate)

Bloomsburg Formation

(Shale, siltstone, sandstone)

Decker through Poxono Island

Formations (Thin limestones,

shales)

Hamilton Group

(Shale, sandstone)

Manorkill through 

Slide Mountain Formations 

(Sandstone, shale, some

conglomerate)

Buttermilk Falls Limestone

Schoharie and Esopus

Formations (Limestone, some

shale, sandstone)

Mahantango Formation

(Shale, limestone, sandstone)

Catskill Formation

(Shale, siltstone, sandstone)

Helderberg Group (Limestone)

Pottsville Formation

(Coal-bearing sandstone, 

siltstone, shale)

Llewellyn Formation

(Sandstone, siltstone, shale,

coal)

Pocono Formation

(Sandstone, conglomerate)

Mauch Chunk Formation

(Shale, siltstone, sandstone)

Onondaga Formation (Limestone)

Utica Shale

Spechty Kopf Formation

(Sandstone, siltstone, mudstone)

Lock Haven Formation

(Sandstone, siltstone, shale)

Oriskany and Helderberg Groups

(Sandstone, limestone, shale)

Trenton and Black River Groups

(Limestone)

Not present in Upper 

Delaware Basin

Not present in Upper 

Delaware Basin

Esopus and Schoharie Formations

(Sandstone, shale, limestone)

Glenerie Formation (Limestone)

PENNSYLVANIA NEW YORK

Bloomsburg Formation

(Shale, siltstone, sandstone)

Marcellus Shale

Utica Shale

Marcellus Shale

Figure 1. Comparative bedrock stratigraphic column of the Upper 

Delaware River Basin, Pennsylvania and New York. Units and 

lithologies represent surface to near-surface bedrock stratigraphy 

most likely intersected in bedrock drinking-water wells. Descriptions 

were supplied by C. Dodge, W. Kochanov, and G. Blackmer of the 

Pennsylvania Geological Survey, and C. Ver Straeten of the New York 

State Geological Survey, January, 2013. Geologic Period ages from 

International Commission on Stratigraphy, 2013

groundwater samples were collected in the Upper Delaware 

River Basin in New York and Pennsylvania for dissolved-gas 

analyses; these results are also included in this report. In total, 

all of these studies provided dissolved methane concentration 

data for just 25 locations in the Upper Delaware River Basin 

(fig. 2). The map symbols (fig. 2) show concentration categories 

for the dissolved methane data in the supplemental data 

table 1. [Table 1 at http://pubs.usgs.gov/of/2013/1167/table/ 

Supplemental_data_table1_NYPA_methane .xlsx] 

 Results of the analyses collected during 2007–12 in the 

Upper Delaware River Basin indicate that concentrations of 

methane in groundwater from all but one well (96 percent of 

the wells) were less than the Office of Surface Mining action 

level of 10 mg/L (Eltschlager and others, 2001), and a large 

number of wells (52 percent) had no detectable methane 

(fig. 3). No wells had a dissolved methane concentration 

between 10 and 28 mg/L, and only one well (of 25) had a 

measured concentration greater than 28 mg/L (4 percent). 

These results are similar to those found in southern Sullivan 

County, Pennsylvania, by Sloto (2013). Sullivan County is 

about 75 miles west of the Delaware River Basin and has 

similar bedrock units—upper Devonian through Pennsylvanianaged bedrock.

Methane was detected in unconsolidated and bedrock 

aquifers across the basin (fig. 4). About 36 percent of the 

groundwater samples were from unconsolidated aquifers, 

and all of those samples had non-detect to low-level methane 

concentrations (methane concentrations <1 mg/L). Of the 

samples from bedrock aquifers (64 percent of the groundwater 

samples tested), 81 percent (13 of 16 samples from bedrock) 

had dissolved methane concentrations less than 1 mg/L. About 

13 percent of the groundwater samples (2 of 16 bedrock 

samples) had concentrations between 1 and 10 mg/L, and 

about 6 percent (1 of 16 bedrock groundwater samples) had 

a concentration greater than 28 mg/L. In the Upper Delaware 

River Basin, all of the sampled wells completed in bedrock 

were in upper to middle Devonian-aged bedrock.

The analysis of dissolved methane in groundwater in the 

Upper Delaware River Basin (2007–12) is meant to document 

the natural occurrence of methane in this region but does not 

indicate whether the methane has a microbial or thermogenic 

origin. The data describing the occurrence of methane come 

from a limited dataset collected for general groundwater-quality 

determinations. Nearly all of the concentrations of dissolved 

methane are less than the Office of Surface Mining’s action 

levels, but the limited set of available dissolved methane data 

does not allow for a more precise analysis at this time. The 

results of this study indicate the need for collection of additional 

methane data and analysis of groundwater from domestic and 

public water-supply wells in the tri-state area of the Upper 

Delaware River Basin.

Acknowledgments

U. S. Geological Survey personnel from the Pennsylvania 

Water Science Center (Ronald Sloto and Lisa Senior) and 

New York Water Science Center (David Eckhardt, Elizabeth 

Nystrom, and Paul Heisig) collected the dissolved methane data 

utilized in this report. Also, James Reddy developed the map of 

the Upper Delaware River Basin. 
4

Delaware River

Neversink River

East Branch Delaware River

West

Branch

Delaware

River

Pepacton 

Reservoir

Cannonsville 

Reservoir

Neversink 

Reservoir

Lake 

Wallenpaupack

River

Lackawaxen

Dyberry Creek

Middle

Creek

Brodhead Creek

Bush Kill

Hudson River

ULSTER

DELAWARE

PIKE

WAYNE SULLIVAN

ORANGE

SUSSEX

MONROE

GREENE

BROOME

LUZERNE

CHENANGO

MORRIS

SUSQUEHANNA

CARBON

OTSEGO

LACKAWANNA

WARREN

BERGEN

PASSAIC

SCHOHARIE

WYOMING

ALBANY

ROCKLAND

NORTHAMPTON ESSEX

CORTLAND

Scranton

Middletown

Binghamton

Port Jervis

East Stroudsburg

EXPLANATION

Dissolved methane concentration,

in milligrams per liter

Non-detect (less than 0.001), Bedrock

Non-detect (less than 0.001), Unconsolidated

0.001 to 1, Bedrock

0.001 to 1, Unconsolidated

1.01 to 10, Bedrock

Greater than 28, Bedrock

Geologic age

Triassic

Pennsylvanian

Mississippian

Devonian

Silurian

Upper and Middle Ordovician

Lower Ordovician and Upper Cambrian

Precambrian

Mafic intrusives

0 10 20 MILES

0 10 20 KILOMETERS

Geologic ages modified from Schruben

and others, 1994: 1:2,500,00

Shale rock outcrops modified from Fisher

and others, 1970: 1:250,000

Base from U.S. Geological Survey digital data

NEW YORK

PENNSYLVANIA

NEW YORK

NEW JERSEY

NEW JERSEY

Geology Upper Delaware River Basin boundary

PENNSYLVANIA

76° 75°30' 75° 74°30' 74°

42°30'

42°

41°30'

41°

NEW

JERSEY 

NEW YORK 

PENNSYLVANIA 

SULLIVAN COUNTY

WYOMING COUNTY

Upper Delaware

River Basin

MARYLAND 

Figure 2. Location of groundwater wells with dissolved methane concentrations, Upper Delaware River Basin, Pennsylvania 

and New York, 2007–12.
5

0

5

10

15

20

25

30

35

1 6 11 16 21

Dissolved methane concentration,

in milligrams per liter

Number of samples

Non-detect - 

13 samples

(52 percent)

>0.0 but <1.0 mg/L 

9 samples

(36 percent)

10.1 to 28.0 mg/L - 0 samples (0 percent)

>28.0 mg/L - 1 sample (4 percent)

25

1.0 to 10.0 mg/L - 2 samples (8 percent) 

Figure 3. Histogram showing dissolved methane 

concentrations, by concentration range, in groundwater samples 

from the Upper Delaware River Basin, Pennsylvania, and New 

York, 2007–12.

0

2

4

6

8

10

12

14

16

Nondetect<1.0 1.0 to

10.0

10.1 to 

28.0

> 28.0

52%

36%

8%

4%

0%

Devonian Age bedrock

(Middle and Upper)

Unconsolidated deposits

of Pleistocene and

Upper Cretaceous ages

Number of samples 

Dissolved methane concentrations, in milligrams per liter

EXPLANATION

Figure 4. Histogram showing dissolved methane concentrations, 

by geologic age of aquifer, in groundwater samples from the Upper 

Delaware River Basin, Pennsylvania, and New York, 2007–12.

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Point Mountain near Washington, New Jersey. Photograph by David B. Soete, Upper Delalware Council, Inc.

By William M. Kappel

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