iii

CONTENTS

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

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

Purpose and scope .........................................................................................................................................................3

Description of study area...............................................................................................................................................3

Methods of investigation........................................................................................................................................................3

Drilling...........................................................................................................................................................................3

Ground-water sample collection....................................................................................................................................4

Analytical methods ........................................................................................................................................................5

Water-level measurements.............................................................................................................................................5

Analytical results of ground-water sampling .........................................................................................................................8

Vertical and horizontal distribution of methyl tert-butyl ether and selected water-quality constituents in the

 surficial aquifer ..............................................................................................................................................................8

Summary and conclusions....................................................................................................................................................12

References cited ...................................................................................................................................................................13

Related web links .................................................................................................................................................................13

Figures

1a–1c. Maps showing location of:

1a. Dover Air Force Base and the Delaware Coastal Plain, Delaware.............................................................2

1b. Dover National Test Site at Dover Air Force Base, Delaware...................................................................2

1c. The Ground-Water Remediation Field Laboratory at the Dover National Test Site, 

Dover Air Force Base.............................................................................................................................2

1d. Aerial photograph showing the Dover National Test Site, Dover Air Force Base..................................................2

2. Map showing locations of transects of direct-push sampling sites and generalized ground-water-flow

direction at the Dover National Test Site, Dover Air Force Base......................................................................4

3a–3b. Maps showing hydraulic-head distribution in the:

3a. Upper part of the surficial aquifer, Dover National Test Site, Dover Air Force Base, 

July 1, 2001 ............................................................................................................................................6

3b. Lower part of the surficial aquifer, Dover National Test Site, Dover Air Force Base, 

July 1, 2001 ............................................................................................................................................7

4. Map showing plan-view distribution of methyl tert-butyl ether plume in the surficial aquifer at the

Dover National Test Site, Dover Air Force Base, June–July 2001..................................................................10

5. Hydrogeologic section showing vertical distribution of methyl tert-butyl ether along 

cross section A–A′ , Dover National Test Site, Dover Air Force Base, June–July 2001. ................................11

6. Boxplot of concentrations of dissolved oxygen for samples that contained greater than 

0.50 micrograms per liter of methyl tert-butyl ether, Dover National Test Site,

Dover Air Force Base, June–July 2001............................................................................................................12

Tables

1. Method reporting limits and maximum contaminant levels for volatile organic compounds at

Dover National Test Site, Dover Air Force Base, Delaware, June–July 2001....................................................8

2. Concentrations of methyl tert-butyl ether in ground water from direct-push samples collected at the

Dover National Test Site, Dover Air Force Base, Delaware, June–July 2001....................................................9
iv

Conversion Factors and Vertical Datum

_____________________________________________________________________________________________________________________________________

Multiply By To obtain

_____________________________________________________________________________________________________________________________________

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

gallon 3.785 liter (L)

_____________________________________________________________________________________________________________________________________

Temperature in degrees Celsius ( °C) may be converted to degrees Fahrenheit ( °F) as follows:

°

F = (1.8 x °C) + 32

Vertical datum: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929—a geodetic datum 

derived from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum 

of 1929.

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 either in milligrams per liter (mg/L) or

micrograms per liter (μg/L).

Acronyms and Abbreviations

°

C degrees Celsius

cis-1,2-DCE cis-1,2-dichloroethene

DAFB Dover Air Force Base

DI de-ionized

DNAPL dense non-aqueous phase liquid

DNTS Dover National Test Site

DO dissolved oxygen

ft feet

ft bls feet below land surface

ft msl feet mean sea level

GRFL Ground-Water Remediation Field Laboratory

MCL maximum contaminant level

MDL method detection limit

MRL method reporting limit

mg/L milligram per liter

mL milliliter

MTBE methyl tert-butyl ether

ND not detected

NETTS National Environmental Technology Test Site Program

PCE tetrachloroethene

QC quality control

SERDP Strategic Environmental Research and Development Program

TCE trichloroethene

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VOC volatile organic compound

μg/L microgram per liter

μS/cm microsiemens per centimeter at 25 °Celsius
Abstract 1

Distribution of Methyl Tert-Butyl Ether (MTBE) and Selected

Water-Quality Constituents in the Surficial Aquifer at the

Dover National Test Site, Dover Air Force Base, Delaware, 2001

By Marie Stewart, William R. Guertal, Jeffrey R. Barbaro, and Timothy J. McHale 

Abstract

A joint study by the Dover National Test Site, 

Dover Air Force Base, Delaware, and the U.S. 

Geological Survey was conducted from June 27 

through July 18, 2001, to determine the spatial 

distribution of the gasoline oxygenate additive 

methyl tert-butyl ether and selected water-quality 

constituents in the surficial aquifer underlying the 

Dover National Test Site. This report provides a 

summary assessment of the distribution of methyl 

tert-butyl ether and a preliminary screening of 

selected constituents that may affect natural 

attenuation and remediation demonstrations at the 

Dover National Test Site. The information 

gathered during this study is designed to assist 

potential remedial investigators who are 

considering conducting a methyl tert-butyl ether 

remedial demonstration at the test site. In 

addition, the study supported a planned enhanced 

bioremediation demonstration and assisted the 

Dover National Test Site in identifying possible 

locations for future methyl tert-butyl ether 

remediation demonstrations.

A direct-push drill rig was used to collect a 

total of 147 ground-water samples (115 VOC 

samples and 32 quality-assurance samples) at 

varying depths. Volatile organic compounds were 

above the method reporting limits in 59 of the 115 

ground-water samples. The concentrations ranged 

from below detection limits to maximum values of 

12.4 micrograms per liter of cis-1,2-dichloroethene, 1.14 micrograms per liter of trichloroethene, 2.65 micrograms per liter of tetrachloroethene, 1,070 micrograms per liter of methyl tertbutyl ether, 4.36 micrograms per liter of benzene, 

and 1.8 micrograms per liter of toluene. Vinyl 

chloride, ethylbenzene, p,m-xylene, and o-xylene 

were not detected in any of the samples collected 

during this investigation. Methyl tert-butyl ether 

was detected in 47 of the 115 ground-water 

samples. The highest concentrations of methyl 

tert-butyl ether were detected in the surficial 

aquifer from –4.6 to 6.4 feet mean sea level; however, methyl tert-butyl ether was detected as deep 

as –9.5 feet mean sea level. Increased methane 

concentrations and decreased dissolved oxygen 

concentrations that were found in association with 

the ground-water samples that contained methyl 

tert-butyl ether are preliminary indicators that will 

assist in determining if natural attenuation of 

methyl tert-butyl ether is occurring in the surficial 

aquifer. A full assessment of natural attenuation of 

methyl tert-butyl ether at the site is beyond the 

scope of this study, but the data collected during 

the study will be useful in selecting appropriate 

remedial methyl tert-butyl ether demonstrations.

Introduction

The Strategic Environmental Research and Development 

Program (SERDP) is the Department of Defense’s corporate 

environmental research and development program, executed 

in partnership with the Department of Energy and the U.S. 

Environmental Protection Agency (USEPA). Numerous 

other Federal and non-Federal organizations participate in 

the program. Dover Air Force Base (DAFB) (fig. 1a) was 

selected as one of the sites for SERDP's National Environmental Technology Test Site (NETTS). The NETTS Program is a comprehensive technology demonstration, 

evaluation, and transfer program. The Dover National Test 

Site (DNTS) (fig. 1b) is one of the NETTS locations. 

Located within DNTS is the Ground-Water Remediation 

Field Laboratory (GRFL) (fig. 1c). An aerial photograph of 

the DNTS is shown in figure 1d. 
2 Methyl Tert-Butyl Ether and Selected Water-Quality Constituents at Dover National Test Site, 2001
Methods of Investigation 3

 DNTS is charged with demonstrating emerging concepts, processes, and technologies under controlled conditions. DNTS also is designed to support the needs of 

principal investigators in developing and field-testing remediation technologies for the cleanup of soil and ground water 

contaminated with fuels and chlorinated solvents. Many of 

the studies are performed in sealed, sheet-piling cells that are 

isolated hydraulically from the Columbia aquifer, which is a 

surficial aquifer. Routine compliance sampling showed that 

the gasoline oxygenate additive methyl tert-butyl ether 

(MTBE) was present in the surficial aquifer outside of the 

sheet-piling cells. MTBE was never released nor detected 

inside of the test cells.

The objectives of this study were to determine the distribution of organic contaminants in the surficial aquifer, and to 

use this information to improve existing conceptual models 

and plan additional site-characterization work. In addition to 

the plume-mapping study, the USGS is continuing to provide 

technical support on ground-water quality issues for DNTS. 

The USGS also assesses ground-water flow in the surficial 

aquifer. The USGS assists the DNTS in providing support to 

principal investigators who are developing and field-testing 

technologies for the characterization and cleanup of soil and 

ground water contaminated with solvents, fuels, and the fuel 

additive MTBE.

Purpose and Scope

The purpose of this report is to provide data showing the 

distribution of MTBE in the surficial aquifer at the DNTS 

from June 27 through July 18, 2001. In addition, the 

intended use of these data is to identify ground-water areas 

contaminated with MTBE for the DNTS to host potential 

demonstrations of MTBE remedial technologies. This report 

also provides a preliminary screening of the geochemical 

constituents that potentially affect the natural attenuation 

of MTBE at the DNTS. The ground-water samples and 

associated quality-control (QC) samples were analyzed for 

volatile organic compounds (VOCs), MTBE, and selected 

field constituents by the DNTS analytical laboratory.

Field-screening methodologies were used to map the 

MTBE plume. In addition, field-screening methodologies 

were utilized to provide an initial screening of total iron, 

ferrous iron, sulfate, and sulfite. The study methods were 

designed to rapidly collect large numbers of samples over a 

large area. Sample collection was accomplished with a 

direct-push drill rig and the samples were analyzed at the 

DNTS. The data were used for contaminant plume mapping. 

In addition, the data can be used to determine if preliminary 

indicators of natural attenuation of MTBE are present in the 

aquifer. Natural attenuation of MTBE is the breakdown or 

reduction of MTBE levels in an aquifer by natural processes. 

The analytical data obtained during this investigation are 

consistent with U.S. Environmental Protection Agency 

(USEPA) analytical level III (U.S. Environmental Protection 

Agency, 1989). This level refers to laboratory analyses performed in accordance with standard USEPA 

procedures, and is appropriate for site characterization.

Description of Study Area

The DNTS is located in the northwestern corner of 

DAFB (fig. 1b). DAFB is in the Coastal Plain Physiographic 

Province, and is underlain by unconsolidated clastic sedimentary deposits (Dames and Moore, Inc. 2000). The generalized direction of ground-water flow in the surficial aquifer 

at DNTS is east-northeast to west-southwest. A detailed 

description of the study area can be found in Guertal and 

others, 2004.

A previous ground-water study was conducted by the 

U.S. Air Force (USAF) in an area upgradient of DNTS to 

evaluate the natural attenuation of ground water contaminated by petroleum hydrocarbons for the Installation Restoration Program Site SS27/XYZ Parking Apron (Air Force 

Center for Environmental Excellence, 1999). During this 

study, MTBE was detected in ground-water samples collected upgradient of DNTS. Concentrations ranged from 

10.9 to 1,430 μg/L (micrograms per liter) of MTBE. In addition, routine compliance sampling at the DNTS indicated 

that MTBE is present near the DNTS at concentrations ranging from below the reporting limit of 0.05 μg/L to 250 μg/L.

Methods of Investigation

To determine geochemical conditions in the surficial 

aquifer, dissolved oxygen (DO), total and ferrous iron, sulfate, sulfide, and methane were measured in most groundwater samples. This method was used to determine if 

electron acceptors and electron donors that are required for 

oxidation-reduction (redox) reactions to occur were present 

in the aquifer. An electron acceptor is a chemical entity that 

accepts electrons transferred to it from another compound 

and an electron donor is a chemical entity that donates electrons to another compound. Redox is a chemical reaction 

consisting of an oxidation reaction in which a substance 

loses or donates electrons, and a substance gains or accepts 

electrons. DO, ferrous iron, and sulfate levels assist in determining if natural attenuation of MTBE is occurring. The 

presence of methane assists in determining if anaerobic 

(oxygen-free) natural attenuation is occurring. Methanogenic conditions result when anaerobic bacterial fermentation produces methane (U.S. Environmental Protection 

Agency, 1995).

Drilling

Ground-water samples were collected using a direct-push 

drill rig. Ground-water samples were collected along four 

transects of direct-push boreholes oriented perpendicular to 

the general ground-water-flow direction. Samples were collected from multiple depths. The direct-push drilling methods are listed in Guertal and others, 2004.
4 Methyl Tert-Butyl Ether and Selected Water-Quality Constituents at Dover National Test Site, 2001

Ground-Water Sample Collection

A total of 147 ground-water samples (115 VOC 

samples and 32 quality-assurance samples) were collected 

from various depths at 48 locations from June 27 through 

July 18, 2001 (fig. 2). Ground-water samples were collected 

along four transects of direct-push boreholes oriented perpendicular to the general direction of ground-water flow. 

Field constituents (DO, specific conductance, pH, and 

temperature) were measured with a Hydrolab multi-probe 

meter at 104 of the 115 sample intervals. The Hydrolab was 

connected to a flow-through cell on the discharge line of a 

peristaltic pump. Total iron, ferrous iron, sulfide, and sulfate 

were analyzed colorimetrically in unfiltered samples with 

spectrophotometers that contain pre-programmed calibration 

curves in the field. Sulfide was analyzed with a Chemetrics 

sulfide kit and sulfate was analyzed with a Hach sulfate kit. 

Spectrophotometers were zeroed with raw ground water 

before each sample was read in the instrument. The method 

detection limit (MDL) for total and ferrous iron was

0.02 mg/L, and the MDL for methane was 25.4 μg/L. The 

MDL for sulfide was 0.01 mg/L for the instrument, and the 

lowest calibration standard that was used for sulfate was

7 mg/L.

A peristaltic pump, equipped with a short piece of silicone pump tubing, was used for purging and sampling. 

Reusable 1/4-inch-diameter Teflon tubing in line with the 
Methods of Investigation 5

pump was placed down-hole to collect the ground-water 

samples. Because reusable sample tubing was used at each 

sampling location, it was decontaminated between samples 

to avoid cross-contamination. After samples were collected, 

the outside of the tubing was washed using soapy de-ionized 

(DI) water. In addition, soapy DI water was pumped through 

the tubing for approximately 2–3 minutes using a peristaltic 

pump. A new piece of flexible tubing was used with the 

peristaltic pump for each sample. Three drops of concentrated hydrochloric acid were used as a sample preservative 

for all field blanks and ground-water samples, which were 

collected in 40-mL (milliliter) VOC septum vials with no 

headspace.

The samples were analyzed for MTBE, benzene, toluene, 

ethylbenzene, xylenes, cis-1,2-dichloroethene, trichloroethene, tetrachloroethene, vinyl chloride and methane. 

Methane was run on only 39 samples.

The following QC samples were collected: 1 equipment 

blank (DI water samples collected from the equipment at 

the start of the study), 14 field blanks (DI water samples 

collected after the field sampling equipment is cleaned), 

10 sequential duplicates (sequential aquifer water samples) 

and 7 screen blanks (DI water samples collected after the 

drilling equipment is cleaned). The QC sample results for 

the direct-push ground-water sampling at the DNTS are 

listed in Guertal and others, 2004. In addition, seven 

sequential duplicate field analyses were run on ferrous and 

total iron, sulfate, and sulfide, and check standards were run 

on sulfate daily. Twenty-one field blank samples were run 

for ferrous and total iron, sulfate, and sulfide.

Analytical Methods

VOCs were analyzed at the DNTS at DAFB. Samples 

were analyzed using the USEPA Method 8021B procedure 

(U.S. Environmental Protection Agency, 1996), Headspace 

Method 5021 (U.S. Environmental Protection Agency, 

December 1996). Samples were analyzed on a Hewlett 

Packard 6890A gas chromatograph (GC) equipped with 

flame-ionization and electron-capture detectors, a Hewlett 

Packard 7694 automatic headspace sampler, and a Supelco 

SPB-624 capillary column. To prepare samples and standards for analyses, 5 mL of sample was transferred to

20-mL headspace vials and sealed. For QC, check standards 

(Supelco custom VOC mixture and MTBE standards) were 

analyzed approximately every 10 samples during each sample run, and laboratory blanks prepared with reagent grade 

DI water were run periodically, as needed. A five-point calibration curve was used to determine VOC concentrations 

(Barbaro and Neupane, 2002). Analytical method reporting 

limits (MRLs) are shown in table 1. The maximum contaminant levels (MCLs) or primary standards are legally 

enforceable standards that apply to public water systems. 

Primary standards protect public health by limiting the levels 

of contaminants in drinking water. The USEPA has a drinking-water advisory of 20–40 μg/L for MTBE that is based on 

taste and odor (U.S. Environmental Protection Agency, 

1997).

According to USEPA Method 8021B, Method 5021 for 

headspace GC, recoveries must be below 20-percent difference, meaning that standard must be monitored frequently 

and compared against the initial calibration curve. If the 

recoveries ever exceed 20-percent difference, the standards 

need to be replaced, the initial calibration should be recomputed, and then the samples are rerun. Standards are 

replaced routinely according to the manufacturers’ specifications. A detailed explanation of the standard preparation can 

be found in the USEPA Method 8021B document (U.S. 

Environmental Protection Agency, December 1996).

Samples were analyzed for methane at the USGS field 

laboratory at Aberdeen Proving Ground, Maryland. All 

methane samples were collected in duplicate. Methane samples were analyzed using a GC with a flame-ionization 

detector. The procedure is described in detail in Baedeker 

and Cozzarelli (1992). The field laboratory at Aberdeen 

Proving Ground uses internal standards and surrogates on 

every sample and blank that is analyzed. In addition, the 

field laboratory participates in a blind sampling program 

(Spencer and others, 2000).

 Water-Level Measurements

To determine the direction of ground-water flow in the 

surficial aquifer, water-level measurements were collected 

on July 1, 2001, from wells in and around the DNTS. The 

water levels in the lower surficial aquifer ranged from 9.77 

to 16.97 ft (feet) mean sea level (msl). In the upper surficial 

aquifer, the water levels ranged from 10.19 to 18.54 ft msl. 

Hydraulic-head (water-level) distribution in the upper and 

lower parts of the surficial aquifer is shown in figures 3a–b. 

Ground-water flow in the upper and lower parts of the surficial aquifer generally was from the east-northeast to the 

west-southwest toward the St. Jones River, which is approximately 1,800 ft downgradient of the study area. Clay lenses 

located intermittently throughout the Columbia Formation 

caused minor variations in localized flow patterns; however, 

it is assumed that these heterogeneities in the formation do 

not affect the general direction of flow in the surficial aquifer. 
6 Methyl Tert-Butyl Ether and Selected Water-Quality Constituents at Dover National Test Site, 2001
Methods of Investigation 7
8 Methyl Tert-Butyl Ether and Selected Water-Quality Constituents at Dover National Test Site, 2001

 

Analytical Results of Ground-Water Sampling

VOCs were detected above the MRLs in 59 groundwater samples. The concentrations ranged from below 

reporting limits to maximum values of 1,070 μg/L of MTBE 

(MTBE was detected in 47 of the 115 ground-water samples), 4.36 μg/L of benzene, 1.8 μg/L of toluene, 12.4 μg/Lof 

cis-1,2-dichloroethene, 1.14 μg/L of trichloroethene, and 

2.65 μg/L of tetrachloroethene. Vinyl chloride, ethylbenzene, p,m-xylene, and o-xylene were not detected in any of 

the samples collected during this investigation. The analytical data tables are shown in Guertal and others (2004). All 

VOC concentrations were below their respective MCLs. 

The MCLs for selected VOCs are given in table 1. There 

currently is no MCL for MTBE in drinking water. The 

USEPA has a drinking-water advisory of 20–40 μg/L for 

MTBE that is based on taste and odor (U.S. Environmental 

Protection Agency, 1997).

Vertical and Horizontal Distribution of Methyl 

Tert-Butyl Ether and Selected Water-Quality 

Constituents in the Surficial Aquifer

The MTBE plume identified during this study is approximately 900 ft long and 200 ft wide, based on the 50-μg/L 

line of equal MTBE concentration (fig. 4). The MTBE 

source area was not located during this study. The northern 

boundary of the plume is well defined, but the southern 

boundary is not as defined. On the southern boundary, levels 

of less than 20 μg/L of MTBE were present. The MTBE 

concentrations from samples collected at the DNTS are 

listed in table 2. The highest concentrations of MTBE were 

found in the surficial aquifer from –4.6 to 6.4 ft msl. This 

depth range constitutes the middle part of the surficial aquifer, as shown in section A–A′ (fig. 5). However, MTBE was 

found as deep as –9.5 ft msl and as shallow as 12.3 ft msl. 

The land-surface elevations ranged from 27.6 ft msl in the 

upgradient portion of the plume to 37.4 ft msl in the downgradient portion of the plume.

In most locations, the lower boundary of the plume was 

not determined. In the core of the plume, the deepest samples that were collected all contained MTBE (fig. 5). It is 

assumed that the top of the Calvert Formation forms the 

lower boundary of the contaminant plume, because the 

Calvert Formation is a dense clay that is just below the 

Columbia Formation forming the lower boundary of the 

surficial aquifer.

Oxidation-reduction trends are found in association with 

natural attenuation of contamination in most aquifers. In the 

presence of organic contaminants, the naturally occurring 

microorganisms consume electron acceptors such as DO and 

sulfate, and produce metabolic by-products such as ferrous 

iron, sulfide, and methane. The presence of ferrous iron, 

methane, and sulfide in samples containing MTBE indicates 

that ground water in the MTBE plume is anaerobic. All 

analyses for ferrous iron, total iron, sulfide, sulfate, and 

methane were performed on unfiltered samples to avoid 

aeration.

Reduced DO levels generally were present in samples 

that contained greater than or equal to 0.5 μg/L of MTBE 

(fig. 6). In addition, the DO concentrations varied with 

depth, and ranged from below the reporting limit (0.2 mg/L) 

to 7.0 mg/L. In samples that were collected at shallow 

depths ranging from 6.5 ft to 12.6 ft msl, which also contained less than 5 μg/L of MTBE, DO concentrations ranged 

from less than 0.20 mg/L to 7.0 mg/L, whereas the samples 

collected within the MTBE plume contained 0.26 mg/L to 

3.8 mg/L of DO. At medium depths ranging from –4.6 ft to 

6.4 ft msl, in samples that were not collected in the MTBE 

plume, DO concentrations ranged from less than 0.20 mg/L 

to 4.4 mg/L. The samples collected within the MTBE plume 

contained less than 0.20 mg/L to 1.72 mg/L of DO. At 

greater depths ranging from –9.5 ft to –4.7 ft msl, in samples 

that were not collected in the MTBE plume, DO concentrations ranged from 0.26 mg/L to 3.5 mg/L. In samples that 

Table 1. Method reporting limits and 

maximum contaminant levels

for volatile organic compounds

at Dover National Test Site, Dover Air 

Force Base, Delaware, June–July 2001

[MTBE, methyl tert-butyl ether; PCE, tetrachloroethene; 

TCE, trichloroethene; cis-1,2-DCE, cis-1,2-dichloroethene; 

μg/L, micrograms per liter; DNTS, Dover National Test 

Site; --, no data]

Target 

Analyte/Volatile 

Organic

Compound

DNTS Modified

8021B Method

Reporting Limit 1

 (μg/L)

Maximum

Contaminant

Level

 (μg/L)

MTBE 0.5 --

PCE 1.3 5

TCE 0.8 5

cis-1,2-DCE 0.6 70

Benzene 0.6 5

Toluene 1.4 1,000

Ethylbenzene 1.3 700

p,m-Xylene 2.6 10,000

o-Xylene 1.2 10,000

1 U.S. Environmental Protection Agency, 1996.
Vertical and Horizontal Distribution of MTBE and Selected Water-Quality Constituents in the Surficial Aquifer 9

Table 2. Concentrations of methyl tert-butyl ether in ground water from direct-push samples collected at the Dover National Test Site,

Dover Air Force Base, Delaware, June–July 2001

[MTBE, methyl tert-butyl ether; μg/L, micrograms per liter; ND, not detected; values above the method reporting limit are in bold]

Sampleidentificationnumber

MTBE( μg/L)

Sampleidentificationnumber

MTBE( μg/L)

Sampleidentificationnumber

MTBE( μg/L)

Sampleidentificationnumber

MTBE( μg/L)

Sampleidentificationnumber

MTBE( μg/L)

Sampleidentificationnumber

MTBE( μg/L)

DN1-000C ND DN1-650C ND DN2-350B ND DN2-750B ND DN3-250B ND DN3-750B NDDN1-000B ND DN1-650B ND DN2-350A 3.45 DN2-750A 4.49 DN3-250A ND DN3-750A 11.3DN1-000A ND DN1-650A 6.27

DN2-400B 7.75 DN2-800C ND DN3-350B ND DN3-800B ND

DN1-250C ND DN1-700C ND DN2-400A 25.6 DN2-800B ND DN3-350A ND DN3-800A 8.21DN1-250B ND DN1-700B 22.5 DN2-800A 14.7DN1-250A ND DN1-700A 4.64 DN2-450B 37.2 DN3-400B ND DN3-850B ND

DN2-450A 127 DN2-850C ND DN3-400A ND DN3-850A ND

DN1-350C ND DN1-750C ND DN2-850B NDDN1-350B ND DN1-750B ND DN2-500C 29.2 DN2-850A 16.5 DN3-450B 17.4 DN3-950B NDDN1-350A ND DN1-750A ND DN2-500B 200 DN3-450A 42.7 DN3-950A ND

DN2-500A 213 DN2-900C ND

DN1-450C ND DN1-800C 248 DN2-900B ND DN3-500B 104 DN4-000A 63.0DN1-450B ND DN1-800B 74.1 DN2-550C 2.87 DN2-900A 7.23 DN3-500A 139DN1-450A ND DN1-800A 87.3 DN2-550B 111 DN4-100C ND

DN2-550A 84.7 DN2-950C ND DN3-550B 26.1 DN4-100B ND

DN1-451B ND DN1-850C 551 DN2-950B 2.15 DN3-550A 230 DN4-100A NDDN1-451A ND DN1-850B 1,070 DN2-600B ND DN2-950A 6.88

DN1-850A 290 DN2-600A 4.19 DN3-600B 3.08 DN4-200B ND

DN1-550C ND DN2-1000C ND DN3-600A 17.2 DN4-200A 7.01DN1-550B ND DN2-050B ND DN2-650B ND DN2-1000B 19.1DN1-550A ND DN2-050A ND DN2-650A 5.69 DN2-1000A 20.4 DN3-650B ND DN4-300B ND

DN3-650A 11.3 DN4-300A 1.41

DN1-600C ND DN2-150B ND DN2-700C ND DN3-100B NDDN1-600B ND DN2-150A ND DN2-700B ND DN3-100A ND DN3-700B ND DN4-500B NDDN1-600A 1.54 DN2-700A 8.18 DN3-700A 7.91 DN4-500A ND

DN2-250B NDDN2-250A ND
10 Methyl Tert-Butyl Ether and Selected Water-Quality Constituents at Dover National Test Site, 2001

 
Vertical and Horizontal Distribution of MTBE and Selected Water-Quality Constituents in the Surficial Aquifer 11
12 Methyl Tert-Butyl Ether and Selected Water-Quality Constituents at Dover National Test Site, 2001

 

were collected from the area within the MTBE plume, DO 

concentrations ranged from 0.21 mg/L to 0.68 mg/L.

Microbial iron reduction typically occurs after DO reduction (Weidemeier and others, 1999; Chapelle and others, 

1995). Ferrous iron concentrations ranged from below the 

MDL to 6.0 mg/L. Total iron concentrations ranged from 

below the MDL to 25.2 mg/L. When analyses are performed 

on unfiltered samples using direct-push technologies and 

analyzing with a colorimetric method in the field, turbidity 

can interfere with the analyses of total and ferrous iron. As a 

result, for low-level detections, the ferrous iron exceeded the 

total iron on occasion.

Methane concentrations ranged from below the MDL to 

741.1 μg/L. Methane concentrations were elevated in some 

samples that contained MTBE. Methane ranged from below 

the MDL to 534.8 μg/L in samples that were not collected 

from areas in the MTBE plume, and from below the MDL to 

741.1 μg/L in samples containing MTBE. In samples containing higher levels of MTBE, higher concentrations of 

methane were found. These data indicate that methanogenic 

conditions are present in the surficial aquifer.

Sulfide concentrations were below the MDL for all samples with the exception of sites DN3-400A and DN3-450A. 

Sulfate concentrations ranged from below the MDL to

149 mg/L. Sulfate reduction does not appear to affect natural attenuation of MTBE in this aquifer.

Summary and Conclusions

The U.S. Geological Survey provides technical assistance on ground-water quality issues for Dover National Test 

Site. The U.S. Geological Survey assesses ground-water 

flow in the surficial aquifer, and assists the Dover National 

Test Site in providing support to principal investigators who 

are developing and field-testing technologies for the characterization and cleanup of soil and ground water contaminated 

with solvents, fuels, and the fuel additive methyl tert-butyl 

ether. As part of this support, the U.S. Geological Survey 

conducted a plume mapping study to better determine the 

distribution of methyl tert-butyl ether at the site. The objectives of this plume mapping study were to determine the distribution of organic contaminants in the surficial aquifer, and 

to use this information to improve existing conceptual models and plan additional site-characterization work.

This report presents the analytical results from groundwater samples collected during a direct-push ground-water 

sampling study from June 27 through July 18, 2001. A total 

of 147 ground-water samples were collected from various 

depths at 48 locations from June 27 through July 18, 2001. 

The 147 samples included 115 volatile organic compound 

samples and 32 quality-control samples. Ground-water 

samples and associated quality-control samples were 

analyzed for volatile organic compounds, ferrous iron, total 

iron, sulfate, sulfide, dissolved oxygen, pH, specific conductance, temperature, and methane.

Volatile organic compounds above the method reporting 

limit were detected in 59 ground-water samples. The concentrations ranged from below detection limits to maximum 

values of 12.4 micrograms per liter of cis-1,2-dichloroethene, 1.14 micrograms per liter of trichloroethene, 2.65 

micrograms per liter of tetrachloroethene, 1,070 micrograms 

per liter of methyl tert-butyl ether, 4.36 micrograms per liter 

of benzene, and 1.8 micrograms per liter of toluene. Vinyl 

chloride, ethylbenzene, p,m-xylene, and o-xylene were not 

detected in any of the samples collected during this investigation. Methyl tert-butyl ether was detected in 47 of the 

115 ground-water samples. The methyl tert-butyl ether 

plume identified in this study is approximately 900 ft long 

and 200 feet wide, based on the 50-microgram per liter line 

of equal methyl tert-butyl ether concentration. The methyl 

tert-butyl ether source area was not located during this investigation.

Increased methane concentrations and decreased dissolved oxygen concentrations found in association with 

elevated concentrations of methyl tert-butyl ether are preliminary indicators that will assist in determining if natural 
References Cited 13

attenuation is occurring at the Dover National Test Site. 

However, additional data are needed to determine whether 

natural attenuation is occurring at a rate that will cause the 

plume to shrink or stablize.

References Cited

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Related Web Links

Strategic Environmental Research and Development

Program (SERDP), http://www.serdp.org/ (Accessed on 

July 24, 2003)

National Environmental Technology Test Sites (NETTS) 

Program, http://www.serdp.org/NETTS/ (Accessed on 

July 24, 2003)

Dover National Test Site, (DNTS), http://www.dnts.org/ 

(Accessed on July 24, 2003)

Environmental Behavior and Fate of Methyl Tert-Butyl 

Ether (MTBE), U.S. Geological Survey Fact Sheet 

FS–203–96 (Revised 2/98), http://ca.water.usgs.gov/

mtbe/fs20396/ref.html (Accessed on July 24, 2003)