U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007–5212

Prepared in cooperation with the U.S. Environmental Protection Agency

Real-Time and Delayed Analysis of Tree and Shrub Cores 

as Indicators of Subsurface Volatile Organic Compound 

Contamination, Durham Meadows Superfund Site, 

Durham, Connecticut, August 29, 2006

Real-Time and Delayed Analysis of Tree and Shrub Cores 

as Indicators of Subsurface Volatile Organic Compound 

Contamination, Durham Meadows Superfund Site, 

Durham, Connecticut, August 29, 2006

By Don A. Vroblesky, Richard E. Willey, Scott Clifford, and James J. Murphy

Prepared in cooperation with the U.S. Environmental Protection Agency

Scientific Investigations Report 2007–5212

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Vroblesky, D.A., Willey, R.E., Clifford, Scott, and Murphy, J.J., 2008, Real-time and delayed analysis of tree and shrub 

cores as indicators of subsurface volatile organic compound contamination, Durham Meadows Superfund Site, 

Durham, Connecticut, August 29, 2006: U.S. Geological Survey Scientific Investigations Report 2007–5212, 12 p. 

(online only at http://pubs.water.usgs.gov/sir2007-5212)
iii

Contents

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

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................1

Site Description.....................................................................................................................................2

Methods...........................................................................................................................................................2

Results and Discussion.................................................................................................................................4

Merriam Manufacturing Company Property, Durham Meadows Superfund Site.....................5

Other Areas at the Durham Meadows Superfund Site ................................................................10

Summary........................................................................................................................................................10

References Cited..........................................................................................................................................11

Figures

1. Map showing locations of trees and shrubs outside of the Merriam Manufacturing 

Company property, selected wells near trees, estimated extent of volatile organic 

compound contamination, and approximate direction of ground-water flow, 

Durham Meadows Superfund Site, Durham, Connecticut ....................................................3

2. Photograph showing block heater used to field heat the vegetation cores prior 

to field analysis .............................................................................................................................4

3. Graph showing comparison of trichloroethene concentrations in field-heated 

and analyzed vegetation cores to unheated vegetation cores analyzed the 

following day, Merriam Manufacturing Company property, Durham Meadows 

Superfund Site, Durham, Connecticut, August 29–30, 2006...................................................4

4–6. Maps showing vegetation cores in 2006, and in the combined results of 2003 

and 2006 soil-gas investigations at the Merriam Manufacturing Company 

property, Durham Meadows Superfund Site, Durham, Connecticut, for:

 4. 1,1,1-Trichloroethane...................................................................................................6

 5. Trichloroethene ............................................................................................................7

 6. Tetrachloroethene........................................................................................................8
iv

Tables

1. Descriptions of trees and shrubs examined in this investigation.........................................2

2. Concentrations of volatile organic compounds detected in vegetation cores, 

Durham Meadows Superfund Site, Durham, Connecticut, 2006 ..........................................5

3. Concentrations of volatile organic compounds in soil-gas samples in 2003 and 2006 

near the vegetation analyzed in 2006 for this investigation, the Durham Meadows 

Superfund Site, Durham, Connecticut.......................................................................................9

4. Precipitation in New Haven County, Connecticut, from August 25 

through August 29, 2006...............................................................................................................9

Conversion Factors

Multiply By To obtain

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Abbreviations used in this report

111TCA 1,1,1-trichloroethane

°C degree Celsius

μg/L microgram per liter

mL milliliter

ppb/v parts per billion by volume

PCE tetrachloroethene

TCE trichloroethene

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VOC volatile organic compound
Abstract 

This study examined volatile organic compound concentrations in cores from trees and shrubs for use as indicators 

of vadose-zone contamination or potential vapor intrusion 

by volatile organic compounds into buildings at the Durham 

Meadows Superfund Site, Durham, Connecticut. The study 

used both (1) real-time tree- and shrub-core analysis, which 

involved field heating the core samples for 5 to 10 minutes 

prior to field analysis, and (2) delayed analysis, which 

involved allowing the gases in the cores to equilibrate with 

the headspace gas in the sample vials unheated for 1 to 2 days 

prior to analysis. General correspondence was found between 

the two approaches, indicating that preheating and field 

analysis of vegetation cores is a viable approach to real-time 

monitoring of subsurface volatile organic compounds. In 

most cases, volatile organic compounds in cores from trees 

and shrubs at the Merriam Manufacturing Company property 

showed a general correspondence to the distribution of volatile 

organic compounds detected in a soil-gas survey, despite the 

fact that most of the soil-gas survey data in close proximity to 

the relevant trees were collected about 3 years prior to the treecore collection. Most of the trees cored at the Durham Meadows Superfund Site, outside of the Merriam Manufacturing 

Company property, contained no volatile organic compounds 

and were in areas where indoor air sampling and soil-gas 

sampling showed little or no volatile organic compound 

concentrations. An exception was tree DM11, which contained 

barely detectable concentrations of trichloroethene near a 

house where previous investigations found low concentrations 

of trichloroethene (0.13 to 1.2 parts per billion by volume) 

in indoor air and 7.7 micrograms per liter of trichloroethene 

in the ground water. The barely detectable concentration of 

trichloroethene in tree DM11 and the lack of volatile organic 

compound detection in nearby tree DM10 (adjacent to the well 

having 7.7 micrograms of trichloroethene) may be attributable 

to the relatively large depth to water (17.6 feet), the relatively 

low soil-vapor trichloroethene concentration, and the large 

amount of rainfall during and preceding the tree-coring event. 

The data indicate that real-time and delayed analyses of tree 

cores are viable approaches to examining subsurface volatile 

organic compound soil-gas or vadose-zone contamination at 

the Durham Meadows Superfund Site and other similar sites. 

Thus, the methods may have application for determining the 

potential for vapor intrusion into buildings.

Introduction

Previous investigations have shown that analysis of 

tree cores may be used to detect subsurface volatile organic 

compounds (VOCs) (Vroblesky and others, 1999, 2004). 

Recent studies indicate that the method can also be used to 

detect VOCs in soil gas, even when the roots are not in contact 

with the contaminated ground water (Schumacher and others, 

2004; Struckhoff, 2005a, 2005b), providing a potentially 

useful tool for examining soil-vapor concentrations. Typical 

tree-core sampling involves sealing a core in a vial, allowing 

the VOCs in the vial to equilibrate with the vial headspace 

for about 24 hours, and analyzing the sample by headspace 

gas chromatography (Vroblesky and others, 1999, 2004). If 

the tree-core samples could be analyzed onsite within a few 

minutes of collection, then the data could be used to direct the 

tree-coring effort and optimize plume mapping.

Purpose and Scope

The purpose of this report is to describe the results of a 

study to examine the use of real-time and delayed analysis 

of tree cores as indicators of potential vapor intrusion by 

VOCs at the Durham Meadows Superfund Site, Durham, 

Connecticut. The study was a cooperative effort between the 

Real-Time and Delayed Analysis of Tree and Shrub Cores 

as Indicators of Subsurface Volatile Organic Compound 

Contamination, Durham Meadows Superfund Site, 

Durham, Connecticut, August 29, 2006

By Don A. Vroblesky1, Richard E. Willey2, Scott Clifford2, and James J. Murphy2

1

U.S. Geological Survey, 720 Gracern Road, Columbia, South Carolina.

2

U.S. Environmental Protection Agency, Region 1, 1 Congress Street, 

Boston, Massachusetts.
2 Analysis of Tree and Shrub Cores as Indicators of Subsurface VOC Contamination, Durham Meadows Superfund Site

U.S. Geological Survey (USGS) and the U.S. Environmental 

Protection Agency (USEPA). The study examined tree cores 

from 12 trees and 2 shrubs of various species and leaf samples 

from 1 shrub. Tree-core analyses were done both in the field, 

facilitated by using a block heater to speed the transfer of 

VOCs from the core to the headspace in the sample vial, and 

in the laboratory following the more widely used approach of 

allowing the cores to equilibrate 1 or 2 days prior to analysis. 

Laboratory analyses of the tree cores were done by the USGS 

both onsite and offsite, and by the USEPA at the USEPA 

laboratory in North Chelmsford, Massachusetts. 

Site Description

The Durham Meadows Superfund Site is in the town 

of Durham, Connecticut, and includes an area of groundwater contamination generally centered on Main Street that 

encompasses industrial and residential properties, all of 

which are supplied with drinking water by individual bedrock 

wells (fig. 1). The site includes the Durham Manufacturing 

Company, a currently operating manufacturing facility 

located at 201 Main Street, and the Merriam Manufacturing 

Company property, a facility no longer in operation located 

at 281 Main Street. Both companies manufactured metal 

cabinets, boxes, and other items, and the companies’ past 

disposal of wastewater in lagoons or sludge drying beds, spills 

at both facilities, and inadequate drum storage practices at 

the Merriam Manufacturing Company property, among other 

factors, contributed to the contamination at each facility and 

in the overall area of ground water surrounding both facilities 

(U.S. Environmental Protection Agency, 2005). Contamination 

from VOCs has been detected in soil and ground water on both 

industrial properties, as well as in residential drinking-water 

wells surrounding both facilities (Metcalf & Eddy, Inc., 2005). 

The contaminants included, but were not limited to, trichloroethene (TCE), tetrachloroethene (PCE), and 1,1,1-trichloroethane (111TCA). In the contaminated ground-water area, 

approximately 38 domestic-supply wells have been provided 

with drinking-water-treatment systems (U.S. Environmental 

Protection Agency, 2005). The subsurface consists primarily 

of overburden (till) overlying bedrock. 

Methods

Vegetation cores were collected and analyzed from five 

trees (DM1 to DM5) and two shrubs (DM6 and DM7) on the 

Merriam Manufacturing Company property and seven trees 

elsewhere at the Durham Meadows Superfund Site (trees DM8 

to DM14) (fig. 1). Leaves were collected from a shrub in front 

of a school (DM15). 

Because the presence of VOCs in soil vapor at the 

Merriam Manufacturing Company property was widespread 

and well documented (U.S. Environmental Protection Agency, 

2005), tree-core locations in that area were selected on the 

Table 1. Descriptions of trees and shrubs examined in this 

investigation.

Tree

Diameter 

of trunk, 

in inches

Species

DM1 40 Maple (Acer sp.)

DM2 4.75 Catalpa (Catalpa sp.)

DM3 not measured Poplar (Populus sp.)

DM4 not measured Mulberry (Morus sp.)

DM5 4 Mulberry (Morus sp.)

DM6 2.75 Staghorn sumac (Rhus typhina)

DM7 2.2 Unidentified shrub, possibly silverberry (Elaeagnus commutate)

DM8 not measured Hemlock (Tsuga canadensis)

DM9 not measured Hemlock (Tsuga canadensis)

DM10 9.9 Dogwood (Cornus florida)

DM11 18.6 Unidentified tree

DM12 42.2 Sycamore (Platanus occidentalis)

DM13 15.4 Maple (Acer sp.)

DM14 31.5 Oak (Quercus sp.)

DM15 0.3 Unidentified shrub

basis of the availability of suitable trees. Outside of the Merriam Manufacturing Company property, a limited number of 

trees were chosen for this investigation based on (1) properties 

where a shallow ground-water monitoring well had been 

recently installed for contamination investigation and where 

the property owner granted access for tree-coring purposes, 

and either (2) information that vapor-intrusion or soil-gas 

concentrations showed the presence of subsurface VOCs near 

that location, or (3) the trees were within an area where VOC 

concentrations above about 1 percent of the solubility limit 

of the respective VOC was thought to be present in bedrock 

(Metcalf & Eddy, Inc., 2005; fig. 1). In some cases (trees DM8 

and DM9), no ground-water data were available, and only 

trace detections of VOCs were found in soil gas and indoor 

air from the adjacent home (Kahn, 2005), but the trees were 

sampled because they were in an area suspected to contain 

VOCs, they were adjacent to a house with an active drinkingwater-treatment system, and the property owner granted access 

for tree-coring purposes.

Vegetation cores were obtained on August 29, 2006, by 

use of a 0.169-inch (in.) diameter increment borer. Cores were 

collected from 14 trees of various species, which included 

two maples, two mulberries, two hemlocks, and one each of 

catalpa, poplar, Staghorn sumac, dogwood, sycamore, oak, 

and an unidentified shrub (table 1). In addition, leaf samples 

were collected from an unidentified shrub (DM15) in front of 

Strong School. 

All cores were approximately 3 in. in length from trees 

with a diameter of 4 in. or greater. Cores from DM6 and 
Methods 3

Figure 1. Locations of trees and shrubs outside of the Merriam Manufacturing Company property, selected wells near trees, estimated 

extent of volatile organic compound contamination, and approximate direction of ground-water flow, Durham Meadows Superfund Site, 

Durham, Connecticut (modified from Metcalf & Eddy, Inc., 2006).

Figure 1

Main Street

Maiden Lane

DM9

DM8

DM10

DM12

DM11

DM14

DM15

DM13

DM1-7

DM14

ME-253

Main

ME-95

Maple

ME-168 Main

ME-STR-B

ME-STR-A

N

ME-STR-A

EXPLANATION

100 METERS

0 200 400 FEET

0 50

Estimated extent of bedrock volatile organic

 compound contamination above 1 percent

 of the solubility limit of the respective

 contaminants (Metcalf & Eddy, Inc., 2005)

Approximate extent of ground-water

 trichloroethene concentrations greater than

 10 micrograms per liter (U.S. Environmental

 Protection Agency, 2005)

Bedrock ground-water flow directions

 (Metcalf & Eddy, Inc., 2005)

Overburden ground-water flow directions

 (Metcalf & Eddy, Inc., 2005)

Tree or shrub and identifier

Selected well and identifier

Building

Merriam

Manufacturing

Company property

Area of inset

in figures 4-6

Durham 

Manufacturing

Company

Strong School

Tributaries to Ball Brook

DURHAM MEADOWS

SUPERFUND SITE

LOCATION OF STUDY AREA IN CONNECTICUT
4 Analysis of Tree and Shrub Cores as Indicators of Subsurface VOC Contamination, Durham Meadows Superfund Site

DM7 were approximately 2 in. long. The sample from DM15 

consisted of leaves and stems. All vegetation core holes 

were sealed by inserting a wooden dowel rod. Each core was 

transferred to a 20-milliliter (mL) serum vial and sealed with 

a crimp cap within 30 seconds of collection. At most trees, 

cores were collected in duplicate, less than 1 in. apart and 

labeled as cores “A” and “B.” The cores were either heated 

and analyzed soon after collection or were stored at approximately 25 degrees Celsius (°C) until analyzed. At DM1, three 

collocated cores were collected less than an inch apart and 

labeled “A,” “B,” and “C.” Air blanks collected and analyzed 

from near trees DM1 and DM4 did not contain VOCs. 

All of the cores labeled with the suffix “A” were analyzed 

after preheating the core using a block heater (fig. 2) to speed 

the transfer of VOCs from the cores to the headspace in the 

vial, except for the cores labeled DM7A and DM10A. The 

“A” cores from vegetation sites DM1 to DM6 were heated to 

60–70 °C for 5 to 10 minutes immediately prior to analysis 

and were analyzed hot, onsite within 1 hour of collection by 

the USGS. Core DM7A was stored overnight and analyzed 

the following day, first by analyzing the unheated core, then 

heating the core and reanalyzing the same sample. Core 

DM10A was analyzed the day after core collection without 

heating the core.

All of the cores labeled “B,” except cores DM7B and 

DM10B, were stored at room temperature and analyzed 

unheated the day after collection by the USGS. Cores DM7B 

and DM10B were analyzed 2 days after collection by the 

USEPA, Region 1. In addition, cores DM2A and DM5A were 

reanalyzed by the USEPA, on September 1, 2006, 2 days 

after the initial analysis by the USGS. Thus, three of the five 

tree-core vials analyzed by the USEPA had been previously 

analyzed by piercing the septum of the cap with a syringe. 

Tree cores DM7B and DM10B were analyzed by the USEPA 

and did not have punctured septa from a previous analysis.

Sample analysis was accomplished by use of two 

approaches. Core samples were analyzed either on the day 

of collection or the day following collection by the USGS 

using photoionization detection on a Photovac 10SPlus gas 

chromatograph. Selected cores were analyzed by the USEPA 

using electron-capture detection on a Shimadzu 14A gas 

chromatograph. Minor differences in concentrations between 

USGS and USEPA data sets were expected because the 

samples were (1) equilibrated using different methods (heating 

versus nonheating), (2) analyzed using different methods 

(photoionization versus electron-capture), and (3) analyzed on 

different dates. 

Results and Discussion

Once the tree cores are sealed in the sample vials, the 

VOCs associated with the tree core begin to volatilize into the 

vial headspace. The volatilization can be fast enough so that 

detectable quantities of TCE can accumulate within the vial 

within minutes, although the equilibration rate sometimes can 

be gradual enough that after about 26 hours, the headspace 

TCE concentrations can be more than double those in the vial 

after only a few hours (D.A. Vroblesky, unpub. data, 2007). 

Field heating the sealed cores increases the volatilization rate 

of VOCs from the tree cores into the headspace of the vial. 

During this investigation, VOC concentrations in vegetation 

cores analyzed in the field after 5 to 10 minutes of heating 

showed close agreement (r2

 = 0.913) with VOC concentrations 

in unheated cores allowed to equilibrate 24 to 30 hours prior to 

analysis (fig. 3; table 2). In some cases, heating the tree cores 

can increase the equilibrium headspace VOC concentrations 

relative to unheated cores. The head-space TCE concentration 

in tree-core vial DM7A was 30 parts per billion by volume 

(ppb/v) after heating and was only 7 ppb/v after the same vial 

Figure 2. Block heater used to field heat the vegetation cores 

prior to field analysis.

Figure 3. Comparison of trichloroethene concentrations 

in field-heated and analyzed vegetation cores to unheated 

vegetation cores analyzed the following day, Merriam 

Manufacturing Company property, Durham Meadows 

Superfund Site, Durham, Connecticut, August 29–30, 2006.

Figure 2

1 10 100 1,000 10,000

TRICHLOROETHENE CONCENTRATIONS IN VEGETATION-CORE

 SAMPLES HEATED AND ANALYZED IN THE FIELD, 

IN PARTS PER BILLION BY VOLUME

1

10

100

1,000

10,000

TRICHLOROETHENE CONCENTRATIONS IN VEGETATION-CORE

SAMPLES ALLOWED TO EQUILIBRATE AT ROOM TEMPERATURE

FOR APPROXIMATELY 24 TO 30 HOURS, IN PARTS PER BILLION BY VOLUME 

1:1 correspondence

reference line

r

2=0.913
Results and Discussion 5

was allowed to cool to room temperature. A duplicate core 

(DM7B) allowed to equilibrate at room temperature overnight 

and analyzed 2 days later contained 6.4 ppb/v of TCE, which 

was a similar value to the room-temperature TCE concentration in tree-core vial DM7A. Thus, field analysis of preheated 

vegetation cores represents a viable approach to examining 

subsurface VOC concentrations. Field analysis of tree cores 

after heating has an advantage over allowing the cores to 

equilibrate at lower temperatures or for longer periods because 

the real-time data allow field personnel to more efficiently 

select trees to sample while mapping subsurface contamination. In some cases delayed analysis may be suitable, however, 

such as when field analytical equipment are not available, or 

when there are only a few trees available to sample so there is 

no need to use real-time data to direct the sampling effort. 

Merriam Manufacturing Company Property, 

Durham Meadows Superfund Site

 VOCs were found in cores from all of the trees and 

shrubs (DM1 to DM7) collected at the Merriam Manufacturing Company property (table 2). Soil-gas investigations at 

the Merriam Manufacturing Company property showed the 

presence of subsurface VOCs in 2003 and 2006 (figs. 4–6) 

(Anni Loughlin, U.S. Environmental Protection Agency, written commun., February 2007). Most of the trees and shrubs 

available for coring at the Merriam Manufacturing Company 

property were near locations where the soil-gas data were 

collected approximately 3 years before the vegetation-core 

data (figs. 4–6). Therefore, a close correspondence between 

the 2006 tree- and shrub-core data and the 2003 soil-gas data 

would not be expected. In most cases, however, the tree- and 

shrub-core data showed an apparent correspondence to the 

soil-gas data.

Vegetation cores from the three trees or shrubs that were 

analyzed for 111TCA in 2006 showed a close correspondence 

to the soil-gas 111TCA concentration distribution from 2003 

(fig. 4). The 111TCA concentration in the core from shrub 

DM7 was higher than in the core from tree DM5, consistent 

with the 2003 soil-gas survey that showed higher 111TCA 

concentrations near shrub DM7 than near tree DM5 (fig. 4). 

Tree DM2 contained no 111TCA and was located in an area 

where the 2003 soil-gas survey did not detect 111TCA (fig. 4).

Table 2. Concentrations of volatile organic compounds detected in vegetation cores, Durham Meadows Superfund Site, Durham, 

Connecticut, 2006.

[TCE, trichloroethene; ppb/v, parts per billion by volume; PCE, tetrachloroethene; 111TCA, 1,1,1-trichloroethane; <, less than; —, analysis not done; *, core C; 

**, unheated reanalysis of core A; ***, analysis of both the original and a duplicate core showed the same results]

Analysis by U.S. Geological Survey Analysis by U.S. Environmental Protection Agency

Tree

Core A, unless otherwise noted (heated)Core B, unless otherwise noted 

(unheated)

Core ID Date of 

analysis

111TCA, 

in ppb/v

TCE, 

in ppb/v

PCE, 

in ppb/v

Date of 

analysis

TCE, 

in ppb/v

Date of 

analysis

TCE, 

in ppb/v

PCE, 

in ppb/v

DM1 8/29/2006 12 8/30/2006 4 <16 — — — — —

DM1 8/30/2006 7* 8/30/2006 5* <16* — — — — —

DM2 8/29/2006 4 8/30/2006 4 16 A 9/1/2006 <1.6 9.2 12

DM3 8/29/2006 1,472 8/30/2006 1,342 582 A 9/1/2006 97 1,730 255

DM4 8/29/2006 326 8/30/2006 687 308 — — — — —

DM5 8/29/2006 116 8/30/2006 170 41 A 9/1/2006 5.6 212 20

DM6 8/29/2006 87 8/30/2006 64 <16 — — — — —

DM7 8/30/2006 30 8/30/2006 7** <16** B 9/1/2006 24 6.4 <1.3

DM8*** — — 8/30/2006 <3 <16 — — — — —

DM9 — — 8/30/2006 <3 <16 — — — — —

DM10 8/29/2006 <3 8/30/2006 — — B 9/1/2006 <1.6 <1.8 <1.3

DM11 8/30/2006 <3 8/30/2006 3 <16 — — — — —

DM12 — — 8/30/2006 <3 <16 — — — — —

DM13 — — 8/30/2006 <3 <16 — — — — —

DM14 — — 8/30/2006 <3 <16 — — — — —

DM15 — — 8/30/2006 <3 <16 — — — — —
6 Analysis of Tree and Shrub Cores as Indicators of Subsurface VOC Contamination, Durham Meadows Superfund Site

Figure 4. 1,1,1-Trichloroethane concentrations in vegetation cores in 2006, and in the combined results of 

2003 and 2006 soil-gas investigations at the Merriam Manufacturing Company property, Durham Meadows 

Superfund Site, Durham, Connecticut.

100

100

10 1

1

10

1,000

100

10

1

1

Tree containing less than 1.6 parts per billion by volume of 1,1,1-trichloroethane

Former areas of liquid storage in tanks and former paint booths

1,1,1-Trichloroethane in soil vapor, in parts per billion by volume, combination of

 soil-gas surveys in 2003 and 2006 (Anni Loughlin, U.S. Environmental Protection

 Agency, written commun., February 2007)

Soil-gas sampling point. Black indicates 2003 and open indicates 2006 sampling

Tree containing 5.6 parts per billion by volume of 1,1,1-trichloroethane

Tree containing 24 parts per billion by volume of 1,1,1-trichloroethane

EXPLANATION

Base map modified from Metcalf & Eddy, Inc. (2006)

0 25 50 75 100 FEET

0 5 10 15 20 25 METERS

SG-C/3

SG-C2

SG-D/2

SG-E/2

SG-C/4

SG-D/1

I4

SG-D/3

I4

DM5

DM2

DM7

Former

building

Existing

building

Former drum storage

MERRIAM MANUFACTURING 

COMPANY PROPERTY

Paved

DM5

DM2

DM7

N

Figure 4
Results and Discussion 7

Figure 5. Trichloroethene concentrations in vegetation cores in 2006, and in the combined results of 

2003 and 2006 soil-gas investigations at the Merriam Manufacturing Company property, Durham Meadows 

Superfund Site, Durham, Connecticut.

1,000

10,000

10,000

10,000

100

100

1,000

100

1

10

Base map modified from Metcalf & Eddy, Inc. (2006)

SG-C/3 SG-C2

SG-D/2

SG-E/2

SG-C/4

SG-D/1

I4

SG-D/3

DM5

DM2

DM3

DM4

DM6

DM7

DM1

Former

building

Existing

building

Former drum storage

MERRIAM MANUFACTURING 

COMPANY PROPERTY

Paved

1

Tree or shrub containing 4 to 100 parts per billion by volume of trichloroethene

Former areas of liquid storage in tanks and former paint booths

Trichloroethene in soil vapor, in parts per billion by volume, combination of

 soil-gas surveys in 2003 and 2006 (Anni Loughlin, U.S. Environmental Protection

 Agency, written commun., February 2007)

Soil-gas sampling point. Black indicates 2003 and open indicates 2006 sampling

Tree or shrub containing 101 to 300 parts per billion by volume of trichloroethene

Tree or shrub containing greater than 300 parts per billion by volume of trichloroethene

EXPLANATION

I4

DM5

DM2

DM7

0 25 50 75 100 FEET

0 5 10 15 20 25 METERS

N

Figure 5
8 Analysis of Tree and Shrub Cores as Indicators of Subsurface VOC Contamination, Durham Meadows Superfund Site

Figure 6. Tetrachloroethene concentrations in vegetation cores in 2006, and in the combined results of 

2003 and 2006 soil-gas investigations at the Merriam Manufacturing Company property, Durham Meadows 

Superfund Site, Durham, Connecticut.

1,000

100

1 10

10,000

100

1

Base map modified from Metcalf & Eddy, Inc. (2006)

SG-C/3 SG-C2

SG-D/2

SG-E/2

SG-C/4

SG-D/1

I4

SG-D/3

DM5

DM2

DM3

DM4

DM6

DM7

DM1

MERRIAM MANUFACTURING 

COMPANY PROPERTY

Paved

1

Tree or shrub containing less than 20 parts per billion by volume of tetrachloroethene

Former areas of liquid storage in tanks and former paint booths

Tetrachloroethene in soil vapor, in parts per billion by volume, combination of

 soil-gas surveys in 2003 and 2006 (Anni Loughlin, U.S. Environmental Protection

 Agency, written commun., February 2007)

Soil-gas sampling point. Black indicates 2003 and open indicates 2006 sampling

Tree or shrub containing 20 to 170 parts per billion by volume of tetrachloroethene

Tree or shrub containing greater than 500 parts per billion by volume of tetrachloroethene

EXPLANATION

I4

DM5

DM2

DM7

0 25 50 75 100 FEET

0 5 10 15 20 25 METERS

Figure 6

Former

building

Existing

building

Former drum storage

N
Results and Discussion 9

TCE concentrations in tree and shrub cores from the 

Merriam Manufacturing Company property also showed a 

general relation to soil-gas TCE concentrations (fig. 5). Trees 

DM2, DM6, and DM7 contained less than 300 ppb/v of TCE 

(table 2). The closest corresponding soil-gas sampling points 

in 2003 to those trees also contained less than 300 ppb/v of 

TCE (table 3). The trees containing the highest TCE concentrations were trees DM3 (1,472 ppb/v) and DM4 (326 ppb/v; 

table 2). These trees are grouped together in the same part of 

the site, likely indicating that this is an area of relatively high 

The relation between PCE concentrations in vegetation 

cores and soil gas is less apparent than it is for 111TCA and 

TCE concentrations in vegetation cores and soil gas (fig. 6). 

Tree DM1 and shrub DM6 contained no detectable concentrations of PCE (table 2). Consistent with this lack of detection, 

PCE concentrations in soil gas near tree DM1 and shrub 

DM5 in 2003 and 2006 were low (12 ppb/v at SG-D/1) or not 

detected. Tree DM2 also did not contain detectable concentrations of PCE; however, the nearest soil-gas sample (SG-E/2) 

to tree DM2 contained 109 ppb/v of PCE in 2003 (table 3). 

Possible explanations for the PCE-concentration differences between tree DM2 and the nearest soil-gas sample 

(SG-E/2) may be that the comparison is inappropriate 

because (1) the heterogeneity of the soil-gas concentrations may be such that soil PCE concentrations differ 

between the tree and the soil-gas sample locations, 

(2) the 3 years that elapsed between the soil-gas survey 

and the tree coring may have allowed changes in the 

soil-gas PCE concentration, such as from dechlorination 

or volatilization, or (3) the substantial amount of rain 

preceding and during collection of the vegetation cores 

may have diluted the contaminated water and gas being 

taken up by the vegetation (Vroblesky and others, 

2004). The cores were collected on a day of heavy rain 

and after multiple days of rain (3.57 in.), as measured in 

Meriden, New Hanover County, Connecticut, approximately 10 miles from the Durham Meadows Superfund 

Site (National Climatic Data Center, 2007; table 4). 

The general correspondence between soil-gas data 

and vegetation-core data implies that the VOCs detected 

in the trees and shrubs at the Merriam Manufacturing 

Company property were related to soil-gas, vadose-zone 

water, or residual vadose-zone contamination. The 

depth to overburden ground water at the Merriam 

Manufacturing Company property was deeper than the 

rooting depth of at least one VOC-containing tree at the 

site. The depth to overburden ground water was 15 to 

20 feet (ft) in parts of the property and was deeper than 

the drilling-refusal depth of 20 to 24 ft in other parts 

of the property (Anni Loughlin, U.S. Environmental 

Protection Agency, written commun., February 2007). 

The maximum depth of root tolerance in 3-year-old 

Table 3. Concentrations of volatile organic compounds in soil-gas 

samples in 2003 and 2006 near the vegetation analyzed in 2006 for 

this investigation, the Durham Meadows Superfund Site, Durham, 

Connecticut.

[TCE, trichloroethene; PCE, tetrachloroethene; 111TCA, 1,1,1-trichloroethane, 

ND, not detected]

Tree

Nearby 

soil-gas 

locations

Concentrations of volatile organic 

compounds in soil gas, 

in parts per billion by volumea

Date of 

soil-gas 

survey

111TCA TCE PCE

DM1 I4 ND 18 ND 2006

DM2 SG-E/2 ND 253 109 2003

DM3 SG-D/2 4,334 9,119 771 2003

DM3 SG-D/1 ND 422 12 2003

DM4 SG-D/2 4,334 9,119 771 2003

DM4 SG-D/1 ND 422 12 2003

DM5 SG-D/1 ND 422 12 2003

DM5 SG-C/4 1,010 208 ND 2003

DM6 SG-C/3 ND ND ND 2003

DM7 SG-C/2 248 82 ND 2003

a

Anni Loughlin, U.S. Environmental Protection Agency, written commun., 

February 2007.

subsurface TCE concentrations. A soil-gas location (SG-D/2) 

near trees DM3 and DM4 had more than 9,000 ppb/v of TCE 

in 2003 (table 3). A mid-range concentration of TCE was 

found in tree DM5 (116 ppb/v, USGS analysis; table 2). The 

closest 2003 soil-gas sampling points to tree DM5 also had 

mid-range TCE concentrations (208 to 422 ppb/v; table 3). 

Although only one cored tree (DM1) was in the vicinity 

of data-collection points from the 2006 soil-gas data, the TCE 

concentration in the tree also was similar to the soil-gas data. 

Tree DM1 contained a relatively low concentration of TCE 

(4–12 ppb/v), and is in a location where the 2006 soil-gas 

survey found relatively low TCE (18 ppb/v at site I4, fig. 5, 

table 3). 

Table 4. Precipitation in New Haven 

County, Connecticut, from August 25 

through August 29, 2006. 

(National Climatic Data Center, 2007)

Date Precipitation, 

in inches

8/25/2006 1.27

8/26/2006 0.07

8/27/2006 1.15

8/28/2006 0.17

8/29/2006 0.91
10 Analysis of Tree and Shrub Cores as Indicators of Subsurface VOC Contamination, Durham Meadows Superfund Site

mulberry trees was reported to be between about 1 and 2 ft 

in well-drained soils (Peper, 1998). Although Bunger and 

Thomson (1938) found mulberry roots extending to about 

7.9 ft deep, approximately 70 percent of the large roots were 

in the top 2 ft of soil. In 12- to 14-year-old mulberry trees 

growing in contaminated soil (polyaromatic hydrocarbons), 

root systems were found to extend to a depth of only about 

3.6 to 3.9 ft, with 70 percent of the large roots in the top 2 ft of 

soil (Olson and Fletcher, 1999; Olson and others, 2001).

Potential sources of the apparently shallow VOCs 

detected by the mulberry trees include soil gas, residual VOCs 

sorbed onto shallow soil, or VOCs transferred from deeper 

horizons to shallower sediment by hydraulic lift through 

the roots of nearby deeper-rooted trees. Hydraulic lift is a 

process by which differences in water potential allow trees 

to derive water from deep, wet roots and lose water through 

shallow dry roots (Richards and Caldwell, 1987; Caldwell and 

others, 1998). Hydraulic lift is a less probable mechanism for 

providing the VOCs detected by the shallow rooted species 

at the Durham Meadows Superfund Site because the large 

amount of rain preceding and during tree-core collection 

probably wet the shallow soil, reducing the potential for 

hydraulic lift. Moreover, water extracted by plants during the 

wet season typically comes from shallow layers where the 

root system is densest (Canadell and others, 1996). Because 

the tree coring was done following and during heavy rainfall 

events, it is likely that most of the water and VOCs taken up 

by the mulberry trees were derived from horizons shallower 

than the water table. Thus, at this site, tree-core data showing 

the presence of VOCs are indicative of shallow subsurface 

contamination.

Other Areas at the Durham Meadows 

Superfund Site

In the trees cored from areas at the Durham Meadows 

Superfund Site outside of the Merriam Manufacturing 

Company property, only one tree was found to contain VOCs. 

Tree DM11, an unidentified species, contained 3 ppb/v of 

TCE in core DM11B (table 2). The detection appears to be 

valid because a syringe blank analyzed immediately prior to 

analyzing tree core DM11B showed no detections of TCE 

concentration at 0.3 ppb/v. 

In the house adjacent to tree DM11, the USEPA detected 

TCE at 0.29 ppb/v in the basement indoor air and 0.25 ppb/v 

in the first floor air (Kahn, 2005). PCE was detected at 

0.13 ppb/v in the basement indoor air and 0.23 ppb/v on the 

first floor. TCE and PCE were found at low levels in the basement soil gas (1.2 ppb/v and 0.94 ppb/v, respectively), but not 

in soil-gas samples collected around the outside of the home. 

Ground water from a monitoring well at the house 

upslope from tree DM11 showed the presence of 7.7 micrograms per liter (μg/L) of TCE from about 12.8 to 17.3 ft below 

land surface on August 11, 2006 (well ME-168 Main; Metcalf 

& Eddy, Inc., 2006), although a dogwood tree (DM10) directly 

adjacent to the well contained no VOCs. The depth to ground 

water at the well was approximately 17.6 ft (Metcalf & Eddy, 

Inc., 2006). Slightly farther away at well ME-95 Maple 

(fig. 1), ground-water VOC concentrations were less than 1 

μg/L at a depth of 15.89 to 17 ft (Metcalf & Eddy, Inc., 2006). 

Thus, although relatively high VOC concentrations were found 

in water from the bedrock (fig. 1; Metcalf & Eddy, 2005), 

substantially lower VOC concentrations were found in water 

from the overburden. The lack of VOC detection in tree DM10 

and barely detectable concentrations of TCE in tree DM11 

probably is a combination of the relatively low soil-vapor 

TCE concentration, the relatively large depth to water, and the 

heavy amount of rainfall during and preceding the tree coring. 

The trace TCE detection in tree DM11 (and not tree DM10) 

may be because tree DM11 is in more intimate contact with 

the ground water by virtue of its larger size and lower elevation. The lack of VOC detections in the tree cores and shrub 

cutting (DM8–DM15) at the remaining sites in the Durham 

Meadows Superfund Site is consistent with the fact that indoor 

air sampling and soil-gas sampling at locations near those 

trees showed only low or no VOC concentrations. 

In May 2005, the USEPA collected soil-gas and air-grab 

samples from a home adjacent to trees DM8 and DM9. Indoor 

air samples showed only trace concentrations (less than 

2 ppb/v) of VOCs, making it unlikely that VOCs associated 

with contaminated ground water were entering the home 

(Kahn, 2005). No ground-water data are available from that 

site because well ME-253 Main, drilled in July 2006, did not 

encounter water to the depth of refusal at 13.7 ft (Metcalf & 

Eddy, Inc., 2006). 

Additionally, no detections of VOCs (less than 3 ppb/v) 

were found in cores of trees (DM13 and DM14) and clippings 

from a shrub (DM15) at the Strong School (fig. 1). Although 

5.7 parts per million of VOCs were detected in July 2006 by 

photoionization screening of cuttings during well drilling at 

well ME-STR-B, no ground-water data are available because 

wells ME-STR-A and ME-STR-B (fig. 1) did not encounter 

water to the depth of refusal at 12.6 to 12 ft, respectively 

(Metcalf & Eddy, Inc., 2006). In 2005, only trace concentrations of TCE were found in soil vapor and indoor air at the 

site. The USEPA detected 0.92 ppb/v in the crawl space, 

0.3 ppb/v in soil gas along the east wall of the school, and 

0.4 ppb/v in soil gas along the west wall of the school (Kahn, 

2005). The absence of VOCs in the analyzed tree and shrub 

samples may be due to the low concentrations of VOCs in the 

shallow subsurface, the relatively large depth to water, or the 

suppression of soil-gas concentrations by rainfall infiltration.

Summary

The U.S. Geological Survey and the U.S. Environmental 

Protection Agency participated in a joint effort to examine 

VOC concentrations in vegetation cores and shrub cuttings 

for use as indicators of potential vapor intrusion by VOCs at 
References Cited 11

the Durham Meadows Superfund Site, Durham, Connecticut. 

Cores were collected and analyzed from five trees (DM1 to 

DM5) and two shrubs (DM6 and DM7) at the Merriam Manufacturing Company property, a part of the Durham Meadows 

Superfund Site, and from seven trees elsewhere at the Durham 

Meadows Superfund Site (trees DM8 to DM14). Leaves 

were collected from an unidentified species of shrub in front 

of a school (DM15). The vegetation samples were obtained 

on August 29, 2006. Tree species included two maples, two 

mulberries, two hemlocks, and one each of catalpa, poplar, 

dogwood, sycamore, oak, and an unidentified tree. Shrubs 

included a staghorn sumac and two unidentified species.

The study used both (1) real-time vegetation-core 

analysis, which involved field heating the core samples for 5 

to 10 minutes prior to field analysis, and (2) delayed analysis, 

which involved allowing the gases in the cores to equilibrate 

with the headspace gas in the sample vials for 1 to 2 days at 

room temperature prior to analysis. A general correspondence 

was found between the two approaches, indicating that field 

analysis of vegetation cores is a viable approach to real-time 

monitoring of subsurface volatile organic compounds. 

VOCs were found in cores from all of the trees and shrubs 

(DM1–DM7) collected at the Merriam Manufacturing 

Company property. In most cases, the vegetation-core data 

showed a general relation to the soil-gas data for 111TCA, 

TCE, and PCE, despite the fact that most of the soil-gas data 

collected in close proximity to the tree cores were collected 

about 3 years prior to the tree-core data. Cores from tree DM2 

did not contain detectable PCE in 2006, however, although 

the nearest soil-gas sample (SG-E/2) to tree DM2 contained 

109 parts per billion by volume of PCE in 2003. In the case 

of tree DM2, possible explanations for the difference between 

the tree-core and soil-gas PCE concentrations include (1) the 

heterogeneity of the soil-gas concentrations may be such that 

soil PCE concentrations differ between the tree and the soilgas sample locations, (2) the 3 years that elapsed between the 

soil-gas survey and the tree coring may have allowed changes 

in the soil-gas PCE concentration, such as from dechlorination 

or volatilization, or (3) the substantial amount of rain preceding and during collection of the tree cores may have diluted 

the contaminated water and gas being taken up by the tree.

It is more likely that the VOCs detected in the trees and 

shrubs at the Merriam Manufacturing Company property 

were related to soil-gas or vadose-zone contamination rather 

than to direct uptake of ground water because (1) there was a 

general correspondence between the VOCs from vegetation 

samples and the VOCs from a soil-gas survey, (2) the depth 

to the water table at the Merriam Manufacturing Company 

property was greater than the probable depth of mulberry 

tree roots, and (3) the large amount of rain preceding and 

during the sampling probably reduced the potential, if any, 

for hydraulic lift by nearby deeper rooted species. Thus, at 

this site, vegetation-core data showing the presence of VOCs 

are indicative of shallow subsurface contamination. Because 

source areas sometimes are characterized by residual shallow 

soil contamination, the data from this investigation indicate 

that tree coring may be a useful tool for locating contaminant 

source areas.

In the trees cored from three areas at the Durham 

Meadows Superfund Site outside of the Merriam Manufacturing Company property, VOCs were either not detected or 

barely detected. Although a previous investigation showed the 

presence of substantial VOC concentrations in ground water 

from bedrock in the areas where tree cores were collected, the 

VOC concentrations in ground water from the overburden in 

these areas appear to be substantially lower than those in the 

bedrock. 

The only detected VOC in tree cores outside the Merriam 

Manufacturing Company property was TCE in tree DM11, 

and the concentration was barely above detection limits. An 

investigation showed low concentrations of TCE (0.13 to 

1.2 ppb/v) in indoor air at the adjacent house, and 7.7 μg/L of 

TCE in the ground water. A dogwood tree (DM10) near the 

well containing 7.7 μg/L of TCE contained no detected VOCs. 

The lack of VOC detection in tree DM10 and barely detectable 

concentration of TCE in tree DM11 probably is a combination 

of the relatively large depth to water (17.6 ft), the relatively 

low soil-vapor TCE concentration, and the heavy amount of 

rainfall during and preceding the tree coring. The trace TCE 

detection in tree DM11 (and not tree DM10) may be because 

tree DM11 is in more intimate contact with the ground water 

by virtue of its larger size and lower elevation. The lack 

of VOC detections in the tree cores or bush cuttings at the 

remaining two sites in the Durham Meadows Superfund Site 

is consistent with the fact that indoor air sampling and soil-gas 

sampling at locations near those trees showed only low or no 

VOC concentrations. 

The data from this investigation indicate that real-time 

and delayed analysis of vegetation cores are viable approaches 

to examining subsurface VOC soil-gas or vadose-zone 

contamination at the Durham Meadows Superfund Site. 

Thus, the methods may have application for determining the 

potential for vapor intrusion into buildings. The presence 

of VOCs in tree cores indicates the presence of subsurface 

VOCs and can be used as reconnaissance-level data to direct 

decisions regarding areas where more focused investigations 

may be warranted. 

References Cited

Bunger, M.T., and Thomson, H.J., 1938, Root development 

as a factor in the success or failure of windbreak trees 

in the Southern High Plains: Journal of Forestry, v. 36, 

p. 790–803.

Caldwell, M.M., Dawson, T.E., and Richards, J.H., 1998, 

Hydraulic lift—Consequences of water efflux for the roots 

of plants: Oecologia, v. 113, p. 151–161.
12 Analysis of Tree and Shrub Cores as Indicators of Subsurface VOC Contamination, Durham Meadows Superfund Site

Canadell, J., Jackson, R.B., Ehleringer, J.B., Mooney, H.A., 

Sala, O.E., and Schulze, E.-D., 1996, Maximum rooting 

depth of vegetation types at the global scale: Oecologia, 

v. 108, no. 4, p. 583–595.

Kahn, P.R., 2005, Final report, indoor air study, Durham 

Meadows, Durham, Connecticut, May 2005: U.S. Environmental Protection Agency New England Regional Laboratory, North Chelmsford, Massachusetts, 44 p.

Metcalf & Eddy, Inc., 2005, Draft final remedial investigation 

report, volume 1, Durham Meadows Superfund Site, Durham, Connecticut: Consultant’s report to the U.S. Environmental Protection Agency, June 2005, [variously paged].

Metcalf & Eddy, Inc., 2006, Technical memorandum for 

site-wide shallow groundwater investigation, final report, 

Durham Meadows Superfund Site, Durham, Connecticut: 

Consultant’s report to the U.S. Environmental Protection 

Agency, November 2006, [variously paged].

National Climatic Data Center, 2007, August 2006 quality 

controlled local climatological data for Meriden Markham 

Municipal Airport, Meriden, Connecticut; accessed 

April 19, 2007, at http://cdo.ncdc.noaa.gov/ulcdsw/ULCD. 

Olson, P.E., and Fletcher, J.S., 1999, Field evaluation of 

mulberry root structure with regard to phytoremediation: 

Bioremediation Journal, v. 3, no. 1, p. 27–34.

Olson, P.E., Flechter, J.S., and Philp, P.R., 2001, Natural 

attenuation/phytoremediation in the vadose zone of a former 

industrial sludge basin: Environmental Science and Pollution Research International, v. 8, no. 4, p. 243–249.

Peper, P.J., 1998, Comparison of root barriers installed at two 

depths for reduction of white mulberry roots in the subsurface, in Watson, G., and Neely, D., eds., The landscape 

below ground II, Proceedings of an International Workshop 

on Tree Root Development in Urban Soils, March 5–6, 

1998, San Francisco, California, International Society of 

Arboriculture, p. 82–93.

Richards, J.H., and Caldwell, M.M., 1987, Hydraulic lift—

Substantial nocturnal water transport between soil layers by 

Artemesia tridentate roots: Oecologia, v. 73, p. 486–489.

Schumacher, J.G., Struckhoff, G.C., and Burken, J.G., 2004, 

Assessment of subsurface chlorinated solvent contamination using tree cores at the Front Street Site and a former 

dry cleaning facility at the Riverfront Superfund Site, New 

Haven, Missouri, 1999–2003: U.S. Geological Survey Scientific Investigations Report 2004–5049, 35 p.

Struckhoff, G.C., Burken, J., and Schumacher, J., 2005a, 

Vadose zone PCE—An important source and fate in planted 

systems, presented at the 3rd International Phytotechnologies Conference, April 20–22, 2005, sponsored by The U.S. 

Environmental Protection Agency and the Midwest Hazardous Substance Research Center, Atlanta, Georgia.

Struckhoff, G.C., Burken, J., and Schumacher, J., 2005b, 

Vapor-phase exchange of perchloroethene between soil and 

plants: Environmental Science and Technology, v. 39, no. 6, 

p. 1563–1568.

U.S. Environmental Protection Agency, 2005, EPA Superfund record of decision—Durham Meadows: EPA/ROD/

RO1–05/007, 378 p.

Vroblesky, D.A., Clinton, B.D., Vose, J.M., Casey, C.C., Harvey, G.J., and Bradley, P.M., 2004, Groundwater chlorinated 

ethenes in tree trunk—Case studies, influence of recharge, 

and potential degradation mechanism: Ground Water Monitoring and Remediation, v. 24, no. 3, p. 124–138.

Vroblesky, D.A., Nietch, C.T., and Morris, J.T., 1999, Chlorinated ethenes from groundwater in tree trunks: Environmental Science and Technology, v. 33, no. 3, p. 510–515.
Prepared by:

USGS Enterprise Publishing Network

Raleigh Publishing Service Center

3916 Sunset Ridge Road

Raleigh, NC 27607

For additional information regarding this publication, contact:

Don A. Vroblesky

USGS South Carolina Water Science Center

720 Gracern Road, Suite 129

Columbia, SC 29210

phone: 1-803-750-6100

email: vroblesk@usgs.gov
Vroblesky and others—Analysis of Tree and Shrub Cores as Indicators of Subsurface VOC Contamination, Durham Meadows Superfund Site—Scientific Investigations Report 2007–5212