Assessment of Sampling Error

Associated with Collection and

Analysis of Soil Samples at

Explosives-Contaminated Sites

Thomas F. Jenkins, Clarence L. Grant, Gurdarshan S. Brar,

Philip G. Thorne, Thomas A. Ranney and

Patricia W. Schumacher September 1996

SPECIAL REPORT 96-15
Abstract: This study is an assessment of short-range

heterogeneity in contaminant concentrations within surface soils at explosives-contaminated sites. Intensive

sampling was conducted over short distances. Discrete and composite samples were analyzed by both

on-site colorimetric methods and standard laboratory

protocols. Three locations were sampled at each of

three installations and the results used to estimate the

relative contributions of analytical error and sampling

error to the total uncertainty. The major contaminant at

seven of the nine sampling locations was TNT; results

from the on-site colorimetric method were in excellent

agreement with laboratory results using SW846 Method

8330. DNT and ammonium picrate were the contaminants present at the highest concentration in the other

two locations. For four sampling locations, short-range

concentration variations were modest and analyte disHow to get copies of CRREL technical publications:

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tribution was sufficiently Gaussian to apply normal

distribution statistics to fractionate the total error variances. For these four locations, analysis standard deviations were always much lower than the sampling

standard deviations; total error was dominated by sampling error, whether characterization was done using

on-site or laboratory analysis. The other five sampling

locations had enormous short-range heterogeneity and

sampling error overwhelmed analytical error. To improve the quality of site characterization data, emphasis should be placed on reducing sampling error by

the use of composite sampling strategies. Characterization of explosives-contaminated sites using composite sampling, in-field sample homogenization, and

on-site analysis is an efficient method of producing

data that are accurate and precise, and also representative of the area.
Special Report 96-15

Assessment of Sampling Error

Associated with Collection and

Analysis of Soil Samples at

Explosives-Contaminated Sites

Thomas F. Jenkins, Clarence L. Grant, Gurdarshan S. Brar,

Philip G. Thorne, Thomas A. Ranney and

Patricia W. Schumacher September 1996

Prepared for

U.S. ARMY ENVIRONMENTAL CENTER

SFIM-AEC-ET-CR-96157

Approved for public release; distribution is unlimited.

US Army Corps


of Engineers

Cold Regions Research &


Engineering Laboratory
PREFACE

This report was prepared by Dr. Thomas F. Jenkins, Research Chemist, Dr.

Gurdarshan S. Brar, Research Physical Scientist, Philip G. Thorne, Research Physical

Scientist, and Patricia W. Schumacher, Physical Science Technician, Geological

Sciences Division, Research and Engineering Directorate, U.S. Army Cold Regions

Research and Engineering Laboratory, Dr. Clarence L. Grant, Professor Emeritus,

University of New Hampshire, and Thomas A. Ranney, Science and Technology

Corporation, Hanover, New Hampshire. Funding was provided by the U.S. Army

Environmental Center, Aberdeen Proving Ground, Maryland, Martin H. Stutz,

Project Monitor.

The authors gratefully acknowledge Alan D. Hewitt and Marianne E. Walsh,

CRREL, for their technical review of this manuscript. In addition the authors

acknowledge Clyde Murray, Bureau of Land Management, Carson City, Nevada;

Douglas Peery, Quanterra Corporation, Knoxville, Tennessee; Sophie Hong, U.S.

Army Engineer District, Sacramento, and Harry Craig, U.S. EPA Region 10, Portland, Oregon, for helping locate appropriate sites to conduct this field sampling

study. Jane Mason, CRREL, is acknowledged for assistance in preparation of this

report.

This publication reflects the personal views of the authors and does not suggest

or reflect the policy, practices, programs or doctrine of the U.S. Army or Government

of the United States. The contents of this report are not to be used for advertising or

promotional purposes. Citation of brand names does not constitute an official

endorsement or approval of the use of such commercial products.

ii
CONTENTS

Page

Preface .................................................................................................................. ii

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

Background ................................................................................................... 1

Objectives....................................................................................................... 2

Experimental ........................................................................................................ 2

Sampling sites ............................................................................................... 2

Soil sampling procedure.............................................................................. 3

On-site soil processing ................................................................................. 4

Colorimetric on-site analysis for TNT and 2,4-DNT ............................... 6

On-site analysis method for ammonium picrate ..................................... 6

Soil processing for laboratory analysis...................................................... 7

Laboratory analysis for TNT and other neutral nitroaromatics

and nitramines ....................................................................................... 7

Laboratory analysis for ammonium picrate ............................................. 7

Chemicals and reagents ............................................................................... 7

Statistical analyses ........................................................................................ 8

Results and discussion ........................................................................................ 8

Monite site ..................................................................................................... 8

Hawthorne AAP ........................................................................................... 17

Volunteer AAP.............................................................................................. 23

Summary of results ............................................................................................. 32

Application of results .......................................................................................... 36

Literature cited ..................................................................................................... 37

Abstract ................................................................................................................. 39

ILLUSTRATIONS

Figure

1. Sampling sites ................................................................................................. 3

2. Sampling scheme ........................................................................................... 4

3. Soil sample preparation for analysis ........................................................... 5

4. Log-transformed TNT concentrations from sampling location 1 ........... 11

5. Log-transformed DNT concentrations from sampling location 2 .......... 14

6. Untransformed TNT concentrations from sampling location 5 .............. 21

7. Untransformed TNT concentrations from sampling location 9 .............. 30

8. Untransformed TNT concentrations from sampling locations

1, 3, 4, 5, 8, 9 ................................................................................................. 32

9. Log-transformed TNT concentrations from sampling locations

1, 3, 4, 5, 8, 9 ................................................................................................. 33

iii
Page

10. Untransformed TNT concentrations for composites from sampling

locations 1, 3, 4, 5, 8, 9 ................................................................................... 33

TABLES

Table

1. Results from sampling location 1, Monite site ....................................... 9

2. Results from sampling location 2, Monite site ....................................... 12

3. Results from sampling location 3, Monite site ....................................... 15

4. Results from sampling location 4, Hawthorne AAP site ..................... 17

5. Results from sampling location 5, Hawthorne AAP site ..................... 19

6. Results from sampling location 6, Hawthorne AAP site ..................... 21

7. Results from sampling location 7, Volunteer AAP site ........................ 24

8. Results from sampling location 8, Volunteer AAP site ........................ 28

9. Results from sampling location 9, Volunteer AAP site ........................ 30

10. Fractionation of total error into analytical and sampling

components ................................................................................................. 34

11. Comparison of measures of analytical precision, accuracy and

discrete sample representativeness ......................................................... 35

12. Comparison of results for discrete and composite soil analysis ......... 35

13. Dependence of total percent relative standard deviation on

compositing and analysis schemes using various assumed

values for sampling and analysis standard deviations ................. 37

iv
INTRODUCTION

Background

Determining the distribution of contaminants

at hazardous waste sites is a fundamental problem facing site investigators. In general, distributions are very site-specific, depending on a number of variables, including how the site was

contaminated, the physical and chemical properties of the contaminants involved, soil type, and

the geology and hydrogeology of the site. Lacking distribution information, it is impossible to

devise an optimal sampling strategy.

Accurate chemical characterization of a hazardous waste site requires a well-designed sampling plan. After defining the area of interest (target populations), which might be an entire site or

several defined areas within a site, workers collect samples according to one of several possible

schemes. In the absence of reliable historical information, it is difficult to choose among judgmental, random, systematic, stratified, or some

combination of these sampling plans. Many references recommend a preliminary study before devising a sampling plan (Gilbert 1987, van Ee et al.

1990, Huesemann 1994, Keith et al. 1995, Williams 1996).

Until recently, most studies of hazardous waste

sites have relied on shipping samples to off-site

laboratories for analysis. Besides the high cost

and potential for sample contamination or degradation of labile analytes, this arrangement does

not lend itself to the timely decisions that are

necessary in a step-wise plan. Recently, this problem has been addressed with the development

and promotion of field analytical methods (Triegel

1988, Jenkins and Walsh 1992, EPA 1993, Triegel et

al. 1994, Keith et al. 1995, Williams 1996, Barnard,

in press). Inexpensive on-site analysis methods

for the most common explosives in munitionscontaminated soils have been developed and are

now in common use. These procedures appear to

be sufficiently accurate and precise to enable their

use in mapping locations of contamination and, if

a sufficient number of samples are analyzed, in

providing estimates of spatial contaminant heterogeneity. With these field methods, sequential

modifications in sampling plans are feasible because data become available while sampling is

in progress.

On-site analytical methods are sometimes criticized as having inadequate precision, accuracy

and specificity. With respect to specificity, we agree

that the QA/QC plan must include laboratorybased confirmatory measurements on selected

samples. Similarly, accuracy should be verified

against reference methods for an appropriate number of samples. The precision issue, however, is a

different matter. Historically, the precision of methods used in hazardous waste characterization has

received an inordinate amount of attention compared to sampling error. Contaminated soils are

often extremely heterogeneous, which causes the

major error source to be sampling and subsampling. No amount of improvement in analytical precision can significantly reduce total measurement error when the analytical error is a minor

contributor to the total. Williams (1996) noted that

the newly released U.S. EPA DQO guidelines focus on the uncertainty of a specific decision rather

than the individual parameters that contribute to

the overall uncertainty. This is an encouraging

change.

A sampling plan can only be optimized after

the process of obtaining representative samples

has been adequately addressed. Numerous variaAssessment of Sampling Error Associated

with Collection and Analysis of

Soil Samples at Explosives-Contaminated Sites

THOMAS F. JENKINS, CLARENCE L. GRANT, GURDARSHAN S. BRAR,

PHILIP G. THORNE, THOMAS A. RANNEY AND PATRICIA W. SCHUMACHER
tions have been offered to describe the qualifications of representative samples (Gilbert 1987,

Barcelona 1988, Smith et al. 1988, Barnard, in

press). We are partial to the Gilbert definition, “A

representative unit is one selected for measurement from the target population in such a way

that it, in combination with other representative

units, will give an accurate picture of the phenomenon being studied.” According to Barnard,

“Representativeness is a statistical concept that is

a measure of how well a data set of sample measurements yields information concerning the

population.”

Explosives are solids at ambient temperature,

dissolve slowly and sparingly in aqueous solution and have low vapor pressures. These properties limit modes of mobility compared to other

contaminants such as fuels or solvents. Thus, the

areas of high concentrations that serve as sources

for contamination of ground water remain at or

near the surface where deposited, unless the soils

themselves are moved. Thus, characterizing the

contamination distribution for explosives will often be possible using samples of near-surface soils.

In this study we focus on how to obtain representative samples from surface soils contaminated

by munitions residues. Too often, local spatial

heterogeneity is bypassed in favor of grab sampling on the theory that heterogeneity will be

“averaged out” if sufficient samples are taken.

While there is validity in this position, it hardly

qualifies as cost-effective, especially when analysis cost often outpaces sample collection cost by

orders of magnitude. In addition to our experience, several authors have reported large local

spatial heterogeneity, often of the same magnitude as present on a much larger scale (see, for

example, Parkin 1987, Sabbe and Marx 1987, van

Ee et al. 1990, Starr et al. 1995). To address this

problem, others have used or recommended composite sampling (Cameron et al. 1971, Schaeffer et

al. 1980, Gilbert 1987, Garner et al. 1988, Paasivirta

and Paukku 1989, Parrish et al. 1990, Huesemann

1994, Fabrizio et al. 1995). We decided to investigate the feasibility of this approach, coupled to

both on-site analysis and conventional laboratory

analysis.

Compositing is sometimes discouraged because

it eliminates information regarding the variability of the individual samples composited. When

applied to large areas, this limitation may represent a valid concern, especially when concentrations are near a regulatory limit. However, when

used on localized areas in lieu of grab sampling,

we believe it is an attractive option to improve

representativeness of samples.

Objectives

The major objective of this work was to characterize the short-range heterogeneity of contaminants at explosives-contaminated sites. This was

done by conducting field sampling and analysis

studies at a number of explosives-contaminated

sites that varied in explosives analytes present,

mode of contamination, soil type and geohydrology. Statistical analyses of the results were conducted to determine the following:

1. Analytical error, which was estimated from

the pooled variances from duplicate analyses of

seven grab samples collected within a localized

area. Short-range sampling error was estimated

from the variance computed from the differences

of mean values of the seven grab (soil) samples.

2. The degree to which some form of composite sampling could be used to reduce sampling

error.

3. Whether inexpensive, colorimetric on-site

analysis methods could be used to provide an

accurate description of contaminant distribution

and a reliable estimate of sampling error.

EXPERIMENTAL

Throughout this report the following terminology will be used: installation will refer to the

government facility where sampling was conducted; sampling location will refer to any one of

the nine areas (three at each installation) where

sampling was conducted; and sample position

(or sample number) will refer to the specific spatial position where a discrete sample was collected.

Sampling sites

Sampling studies were conducted at three installations. These are Monite, a BLM (Bureau of

Land Management) installation near Sparks, Nevada; Hawthorne Army Ammunition Plant (AAP),

Hawthorne, Nevada; and Volunteer AAP, Chattanooga, Tennessee (Fig. 1).

The Monite installation is a small former industrial area that has about 1.5 acres of land contaminated with TNT and DNT. The company that

owned the site reportedly reclaimed explosives

from out-of-date military munitions, but since that

company declared bankruptcy and abandoned the

site many years ago, the history of contamination

2
is largely unknown. Several years ago, children

playing in the area found a barrel of DNT and the

site subsequently has undergone preliminary site

characterization. Based on the results of this characterization, C. Murray of BLM pointed out several potential sampling locations that had detectable explosives in the soil. Based on his

suggestions, we conducted preliminary soil sampling and the samples were analyzed using the

EnSys colorimetic on-site analysis method (EPA

1995b). The results of this initial sampling and

analysis revealed three areas that had very different types of contamination. One had TNT concentrations in the thousands of μg/g (location 1),

one had similar levels of DNT (location 2), and a

third had low μg/g levels of TNT (location 3).

These three locations were selected for intensive

sampling and analysis.

The second installation we visited was

Hawthorne AAP, which is located in west-central

Nevada (Fig. 1). This facility was established in

1928 and was operated for many years as a load,

assemble and pack facility for the Navy. In 1977 it

was transferred to Army control. We visited a

number of candidate sampling locations and selected three based on results of preliminary sampling and field analysis. The first sampling location was under a conveyer belt that took “empty”

boxes and crates from the inside of a melt facility

out for disposal. Red stains were visible on the

soil surface apparently from residual TNT crystals released from these boxes. The major contaminant in this area was TNT with soil concentrations in the thousands of μg/g (location 4). The

second sampling location at Hawthorne was at

an open burning area. The area was free of vegetation and had concentrations of TNT in the hundreds of μg/g (location 5). The final

location sampled at Hawthorne was

a disposal lagoon where the surface

soils were visually contaminated

with intense yellow crystalline material that we believed to be ammonium picrate (location 6).

The third installation sampled was

Volunteer AAP near Chattanooga,

Tennessee (Fig. 1). This installation

is a TNT and DNT production facility, although it has not actively produced these munitions compounds

since 1977. Here again, we selected

three sampling locations based on

preliminary sampling and colorimetric on-site analysis. The first sampling

location was at a loading area located adjacent to

a TNT production building (location 7 and location 7R). This area was also contaminated from

wash water from the facility and concentrations

of TNT in the soil were in the thousands of μg/g.

The second sampling location was within a drainage ditch that received spills of TNT production

wastewater (location 8). Individual samples collected within the ditch had elevations that differed by only a maximum of 25 cm; however,

TNT concentrations varied from 500–30,000 μg/g.

The final sampling location at Volunteer was an

area initially thought to be free of contamination,

but upon sampling and on-site analysis, we found

it to have TNT concentrations in the 4–40 μg/g

range (location 9).

Soil sampling procedure

A common pattern was used for soil sampling

at all nine locations. A plastic template was placed

on the ground with the center at the selected sampling location and oriented as shown in Figure 2,

with sample numbers 2 and 5 oriented north–

south. Seven samples were collected in a wheel

pattern with sample number 1 in the center. The

radius of the wheel was 61 cm and samples arranged around the wheel were separated by 61 cm.

All seven soil samples were collected at the

surface from 0 to 15 cm using a manual 5.0-cm

stainless-steel hand auger. When vegetation was

present, it was removed. Cores were transferred

to plastic zip lock bags and taken to a processing

area. At the Monite site, processing was conducted

outdoors in the shade to minimize the possibility

of photodegradation. At Hawthorne and Volunteer, soil processing was conducted in air-conditioned buildings.

BLM Sparks

Reno, Nevada

(Monite)

Hawthorne AAP

Nevada Volunteer AAP

Tennessee

Figure 1. Sampling sites.

3
On-site soil processing

Discrete samples

Soil samples from the Monite site and Hawthorne AAP were dry and mostly consisted of a

mixture of sands and gravels. These samples were

processed as follows. Soils were emptied from the

zip lock bags into 23-cm-diameter aluminum pie

pans. We dispersed the material by breaking up

the large clumps with gloved hands and removing large rocks. The pans were covered with a

second pie pan and the soil was swirled and

shaken vigorously to disperse and homogenize

the material, which was then coned and quartered. Approximately 5-g subsamples were removed from each quarter and combined to produce a sample of about 20-g for colorimetric on-site

analysis. The bulk sample was remixed, coned

and quartered again and a duplicate 20-g sample

for field analysis was removed as described above.

The sample was remixed a third time and another

20-g sample removed and placed in an amber 40-

mL glass vial for subsequent laboratory analysis.

The remaining sample was returned to its original zip lock bag and saved for preparation of a

composite sample for that sampling location.

Soils from Volunteer had a higher moisture

content and were composed of a higher percentage of finer grained material than soils from either Monite or Hawthorne. This made field homogenization more difficult and time consuming.

At Volunteer, soil samples were placed in zip lock

bags and initially kneaded by hand to break up

large clumps. They were then deposited in aluminum pie pans and further disaggregated by hand

until approximately pea sized or smaller pieces

were produced. For soil from sampling location

7, rocks greater than 0.5 cm were removed and

weighed. Soils were then coned and quartered

and further processed as described above.

Composite samples

For composite samples at the Monite site and

Hawthorne AAP, the soil remaining after discrete

samples were removed for each of the seven grab

samples within a wheel was combined in a large

aluminum roasting pan. While the portions used

to make the composite were not individually

weighed for Monite and Hawthorne, they were

approximately equal in weight. The soil was homogenized by hand mixing. Clumps were reduced

by hand crushing and the material was coned

and quartered. Approximately 5-g samples were

removed from each quarter and combined to produce a 20-g sample for field analysis. The soil was

coned, quartered and sampled six more times to

produce a total of seven replicates for field analysis. The soil was dispersed, coned and quartered

one final time and a 50-g sample removed and

placed in an amber glass bottle for subsequent

laboratory analysis.

At Volunteer, a similar procedure was used

except that equal weights of each individual

sample (100 or 600 g each, depending on wheel

location) were used to prepare composites. Otherwise samples were processed as above. A summary of the entire sampling design is shown in

Figure 3.

7

6

5

1

2

3

4

122 cm dia.

Samplers

(stainless steel auger)

5 cm dia.

27,800 on-site

42,800 lab

164 on-site

136 lab

500 on-site

416 lab

39,800 on-site

41,400 lab

24,400 on-site

27,700 lab

1280 on-site

1220 lab

331 on-site

286 lab

Figure 2. Sampling scheme (TNT concentrations shown are from

sampling location 1).

4
Composite

C1

SAMPLE 1

Lab

(20g) On-site

1a(2g)1b(2g)

1c(20 g)1d(20 g)

Composite

C2

SAMPLE 2

Lab

(20g) On-site

2a(2g)2b(2g)

2c(20 g)2d(20 g)

Composite

C3

SAMPLE 3

Lab

(20g) On-site

3a(2g)

3b(2g)

3c(20 g)

3d(20 g)

Composite

C4

SAMPLE 4

Lab

(20g) On-site

4a(2g)

4b(2g)

4c(20 g)4d(20 g)

Composite

C5

SAMPLE 5

Lab

(20g) On-site

5a(2g)5b(2g)

5c(20 g)5d(20 g)

Composite

C6

SAMPLE 6

Lab

(20g) On-site

6a(2g)6b(2g)

6c(20 g)6d(20 g)

Composite

C7

SAMPLE 7

Lab

(20g) On-site

7a(2g)7b(2g)

7c(20 g)7d(20 g)

BULK COMPOSITE

LABORATORY (50g)

7 Subsamples

H I J K L M N

(2g each)

ON-SITE

7 Subsamples

A B C D E F G

(20g each)

1

2

3

4 5

6

7

Figure 3. Soil sample preparation for analysis.

5
Colorimetric on-site

analysis for TNT

and 2,4-DNT

The 20-g soil samples at all three installations

were extracted in 150-mL plastic extraction bottles

by adding 100 mL of acetone, and shaking vigorously (Jenkins and Walsh 1992). Soil extracts from

all locations were analyzed using the EnSys TNT

method (EPA 1995b). The acetone contained 3%

water to ensure that adequate water was present

for the chemical reaction that produces color development. An extraction rate study was conducted on the soil from each site to determine the

appropriate extraction time. For soils from the

Monite site and Hawthorne AAP, a 3-minute extraction time was adequate. For samples from

Volunteer AAP, the 3-minute extraction time was

not adequate, so soils were extracted using 3 minutes of shaking, a 30-minute rest time, and a final

3-minute shaking period. After allowing the soil

to settle for at least 15 minutes, we removed an

aliquot of each extract using a Plastipak syringe

and filtered it through a Millex SR membrane.

Extracts were diluted as appropriate, such that

absorbances after reaction with the EnSys reagent

were less than 1.0.

For samples containing mainly TNT, the intensity of color of the extract prior to reaction with

the EnSys reagent often indicated the TNT concentration and served as a rough guide for sample

dilution. For extracts containing DNT, this was

not true and the degree of dilution needed for

each sample was obtained by on-site experimentation. Because soil concentration varied by such

a large amount, with concentrations in excess of

100,000 μg/g, acetone extracts had to be diluted

by ratios as high as 1:5000 to provide analyte

concentrations in the linear range of the method

(0–4 mg/L). In the field these dilutions were made

using glass μL syringes and graduated cylinders.

When this dilution process was assessed, relative

standard deviations were always less than 3%

(Jenkins et al. 1996).

For seven of the nine sampling locations, extracts became reddish when reacted with the

EnSys reagent, meaning that TNT was likely

present. For sampling location 2 at the Monite

site, extracts became blue-purple when reacted

with the EnSys reagent, showing that DNT was

the likely contaminant rather than TNT. At sampling location 6, acetone extracts were fluorescent yellow, denoting the presence of ammonium

picrate as the primary contaminant. Addition of

the EnSys reagent to these yellowish solutions

resulted in variable and unstable color changes.

Calibration for quantitation was achieved by

reacting a known standard of TNT in acetone

(containing 3% water) with the EnSys reagent for

samples from locations 1, 3, 4, 5, 7, 7R, 8 and 9.

Absorbance was measured at 540 nm with a battery operated spectrophotometer (Hach Model

DR/2000). Likewise, a standard with a known

concentration of DNT was used to calibrate soil

extracts from sampling location 2 and absorbance

was measured at 570 nm. Correction for background color in the extracts was obtained by measuring the absorbance of each extract prior to

addition of the EnSys reagent, doubling the value,

and subtracting it from the final absorbance after

addition of the reagent. Doubling the initial absorbance prior to subtraction takes into account

the increased absorbance caused by reaction of

humic organics in the extract with base, as discussed elsewhere (Jenkins and Walsh 1992).

On-site analysis method

for ammonium picrate

The on-site analysis method used for ammonium picrate was reported by Thorne and Jenkins

(1995). We extracted 20-g subsamples of soil from

sampling location 6 with 100 mL of acetone containing 3% (V/V) deionized water by manually

shaking for 3 minutes. A 4-mL aliquot was removed and the absorbance measured at 400 nm.

If the absorbance was above 1.0, the extract was

diluted with deionized water until the absorbance

was below 1.0. This dilution factor was used to

calculate how much of the original acetone extract could be applied to a 3-mL SPE-ALUMINAA (Supelco) cartridge.

The volumes used for analysis of the duplicate

subsamples of the discrete samples and for composites were as follows: for discrete samples from

positions 2, 3 and 7—20 mL; from positions 1 and

4—10 mL; from position 6—2 mL; from composites—1 mL; from position 5—0.4 mL. These quantities were diluted one-to-one with deionized water and added to the cartridges.

Picrate ions were retained on the alumina. Most

interferences were removed by passage of a 5-mL

aliquot of methanol followed by a 3-mL aliquot of

acetone. Picric acid was eluted from the cartridges

with 10 mL of acetone, which had been acidified

with four drops of concentrated sulfuric acid. The

initial absorbance at 400 nm was recorded and

used as a background correction. After adding an

6
additional 5 mL of unacidified acetone, we diluted this solution with 5 mL of deionized water;

a change from colorless or brownish- yellow to

deeper yellow revealed the presence of picrate.

The final absorbance at 400 nm was recorded. The

corrected absorbance was converted to μg/g of

picric acid on the basis of the response from calibration standards.

Soil processing for

laboratory analysis

All soil samples were returned to the laboratory in coolers by overnight carrier. Upon receipt

they were maintained at 4°C until processed.

Samples were placed in plastic weigh boats, plant

and other debris were removed, and they were

air dried in the dark until a constant weight was

achieved, usually within 48 hours or less. Weight

loss upon drying was used to calculate percent

moisture, which was then used to correct fieldmeasured analyte concentrations to a dry weight

basis for comparison with laboratory results.

Stones were removed from dried samples, which

were ground with a mortar and pestle to a fine

powder. The weight of stones removed from each

sample was recorded. Except for wheels 7 and 7R,

the amount of stones removed prior to laboratory

analysis did not significantly modify the soil from

that analyzed in the field. For wheels 7 and 7R,

the amount removed was large and this had an

effect on the level of agreement of results from

on-site and laboratory analyses, as will be discussed later.

Duplicate 2.00-g subsamples from each discrete

soil sample and seven replicate 2.00-g subsamples

from composites were weighed into 22-mL glass

vials equipped with Teflon-lined caps. A 10.0-mL

aliquot of acetonitrile was added to each vial, the

contents were vortex mixed for 15 seconds, and

the vials were placed in an ultrasonic bath that

was maintained below 35°C with cooling water.

Extractions were conducted for 18-hours. After

extraction, the vials were cooled to room temperature and a 10.0-mL aliquot of aqueous CaCl2

(about 3 g/L) was added. The vials were vortex

mixed and allowed to stand for at least 15 minutes while the solids settled. A portion of the

supernatant was removed using a Pasteur pipette

and filtered through a Millex SR membrane (0.5

μm). The extracts were diluted, based on the results from on-site analysis, using 1:1 acetonitrile/

reagent grade water. Processed extracts were

maintained at 4°C in the dark until analyzed.

Laboratory analysis for TNT

and other neutral nitroaromatics

and nitramines

Reversed phase HPLC analysis was conducted

as described in EPA SW846 Method 8330 (EPA

1995a). Primary analysis was conducted on a

Supelco LC-18 column eluted with 1:1 methanol/

water at 1.5 mL/min. Absorbance was recorded

at 254 nm on a Spectra Physics Model 8490 variable wavelength detector and peaks were recorded

on a Hewlett Packard 3396 Digital Integrator operated in the peak height mode. Selected samples

were subjected to second column confirmation on

a Supelco LC-CN column using either 35:65

methanol/water or 23:12:65 acetonitrile/methanol/water, depending on the specific analytes detected in the primary analysis (Jenkins and Golden

1993).

Laboratory analysis

for ammonium picrate

Picrate was analyzed by RP-HPLC on a 25- ×

4.6-cm (5-μm) LC-18 (Supelco) column. The picrate was eluted using 1.5 mL/min. of 60:40 0.05

M KH2PO4 (pH 3.5)/methanol and detected at

365 nm. Aliquots of the acetone extracts prepared

for the field method were diluted in eluent before

analysis. A minimum dilution of 1 to 4, extract to

eluent, had to be used to obtain an acceptable

peak shape for picrate. The estimated detection

limit at this dilution was 0.1 μg/g.

Chemicals and reagents

All standards for TNT and DNT were prepared

from Standard Analytical Reference Materials

(SARMS) obtained from the U.S. Army Environmental Center, Aberdeen Proving Ground, Maryland. Standards of TNT and DNT in acetone were

prepared using OmniSolv grade acetone from EM

Science. Standards of ammonium picrate for field

and laboratory procedures were prepared from

military grade material obtained from Hawthorne

AAP.

All acetone used in the field for soil extraction

and glassware cleaning was hardware grade obtained locally at each site. Acetonitrile and methanol used in the laboratory for soil extraction and

preparation of HPLC eluents were Baker, EM or

Mallinckrodt HPLC grade. Water used in the field

for cleaning, and for addition to extracts to ensure that an adequate water content was present

for the color-forming reaction, was distilled water obtained from local food stores. Laboratory

7
reagent grade water used for preparation of HPLC

eluents was obtained from a Millipore Milli-Q

Type 1 reagent grade water system.

Statistical analyses

To see if there were significant concentration

differences among sample positions at each sampling location, analytical results from both methods of analysis were subjected to one variable of

classification, completely randomized Analysis of

Variance (ANOVA) using CoStat version 1.03 software (CoHost Software, Inc.). For sampling locations 1, 2, 3, 6 and 8, where concentration variations were extremely large, variances were not

homogeneous (standard deviations were proportional to concentrations, i.e., relative standard deviations [RSDs] were constant). In these instances,

the concentrations were log-transformed prior to

doing ANOVA. When the ANOVA demonstrated

that there were significant differences among

sample positions for a given sampling location,

least significant differences (LSDs) were computed

to identify specific differences.

For sampling locations 4, 5, 7, 7R and 9, concentration ranges were less extreme and variances

approached homogeneity. In these cases variances

were fractionated to yield estimates of the standard deviations for subsampling plus analysis (SA)

and for the field sampling (SS). Henceforth, all

references to analytical error should be understood to include contributions from mixing and

subsampling, extraction, dilution, measurement

and concentration computations, while sampling

error refers to spatial heterogeneity at the sampling location. CoStat software was also used to

compute means and standard deviations of duplicates, overall means of the seven duplicates,

plus means and standard deviations of composites. Analytical precision of the seven duplicates

for each sampling location and each analysis

method was expressed as the average of the seven

RSDs.

One-way ANOVA was also used to compare

on-site vs. laboratory analyses of composites. A

paired t-test and correlation analysis was used to

compare on-site vs. laboratory analysis for sets of

seven samples for a given sampling location. These

tests were done with Sigma Stat (Jandel Scientific). In addition to the linear least squares model

with intercept, correlations were also computed

for the linear zero-intercept model on untransformed data. When intercepts are close to zero,

the correlation coefficient for the zero-intercept

model approaches the value for the model with

intercept. As the intercept moves away from zero,

the correlation coefficient (r) for the zero-intercept model will decrease relative to the value for

the model with intercept, thereby giving an indication of the significance of the intercept.

For all on-site vs. laboratory comparisons, except location 6 (picrate), the sum of TNB, TNT

and 2,4-DNT laboratory concentration estimates

were compared to on-site measurements. The

Janowsky ions produced for TNT and TNB both

have wavelengths of maximum absorption around

540 nm and their molar absorptivities at that wavelength are nearly equal. (There is a peak with

higher absorptivity at lower wavelength but high

humic background makes measurement at this

peak wavelength prone to interference.) In any

case, the on-site TNT method will record the sum

of TNT and TNB (Jenkins and Walsh 1992). The

absorptivity of the Janowsky ion from 2,4-DNT is

not maximum at 540 nm but it is significant. However, DNT reacts slower with the EnSys reagent

than TNT and TNB, and the rate of color formation varies with water concentration in the extract. Since the contribution of DNT to the field

TNT estimates will depend on analysis conditions, corrections are impractical, so we decided

to use the total of these three analytes to represent

laboratory concentrations.

One further aspect of the statistical analysis

requires mention. It has already been noted that

total absolute variances for the seven sample positions in some sampling locations were nonGaussian. Furthermore, they were computed without regard to the presence of variable amounts of

spatial correlation between positions. We observed

that the spatial correlations were irregular in some

cases, in contrast to a regular gradient such as the

directional concentration change that one might

find on the edge of a plume of highly mobile

compounds. For example, see the pattern of TNT

concentrations observed for sampling location 1

(Fig. 2). This spatial correlation undoubtedly introduces some bias in the variance estimates, but

we believe that the magnitude of this effect is

insufficient to significantly affect the conclusions.

RESULTS AND DISCUSSION

Monite site

Sampling location 1

Results for the on-site analysis and laboratory

analyses for sampling location 1 are presented in

8
Table 1. Results from sampling location 1, Monite site.

a. Analytical results.

TNT on-site

analysis Laboratory analysis (μg/g)

Sample (μg/g) TNB TNT 2,4-DNT Total

Discrete samples

1a 42,700 107 37,500 70 37,700

1b 36,900 104 45,000 — 45,100

2a 492 30 390 — 420

2b 507 30 382 — 412

3a 174 12 113 20 145

3b 154 11 116 — 127

4a 28,000 97 44,400 — 44,500

4b 27,600 — 41,200 — 41,200

5a 24,400 — 33,000 — 33,000

5b 24,400 — 22,400 — 22,400

6a 1,240 42 1,170 — 1,210

6b 1,310 33 1,200 — 1,230

7a 327 23 305 — 328

7b 334 17 227 — 244

mean 13,500 16,300

Composites

C1 12,900 — 11,800 — 11,800

C2 12,900 — 13,400 — 13,400

C3 13,300 — 13,600 — 13,600

C4 14,200 — 15,200 — 15,200

C5 13,000 — 13,900 — 13,900

C6 13,200 — 15,000 — 15,000

C7 12,500 — 16,100 — 16,100

mean 13,100 14,100

std. dev. 532 1,420

Table 1a. TNT was the major analyte present, with

concentrations varying from sample to sample

over 2 

1 2 orders of magnitude. Acetone extracts

for field analysis were highly colored even before

reaction with the EnSys reagent. Extracts for

samples 2, 3 and 7 were yellow, extracts from

sample 6 and the composites were orange, and

extracts of samples 1, 4 and 5 were dark brick red.

These colors are caused by the presence of

phototransformation products of TNT in these

surface soils. The intensity of color before reaction with the EnSys reagent correlated very well

with the TNT concentrations obtained by the colorimetric on-site method. Reaction of the acetone

extracts with the EnSys reagent resulted in the

development of red solutions, indicative of the

presence of TNT. Substantial dilutions (as high as

1:2000) were required to obtain absorbances in

the linear range of 0.0–1.0 absorbance units at 540

nm after reaction with the EnSys reagent.

Duplicate field analyses for a given soil at sampling location 1 were in excellent agreement (mean

RSD was 3.9%), pointing out that field sample

homogenization was adequate. Duplicate laboratory analyses varied to a greater extent than field

analyses (mean RSD was 11.1%), probably because of the smaller sample size used for lab analysis (2 vs. 20 g).

Since TNT concentrations varied by such a large

amount from sample to sample, the data were not

normally distributed and absolute variances were

not homogeneous. Since relative standard deviations were similar, this indicates that standard

deviations were proportional to concentration.

9
Thus, to perform analysis of variance (ANOVA),

we transformed data by taking the logarithm of

individual values (Table 1b). This was done for

both the field and laboratory results and an

ANOVA was conducted on both sets of log-transformed data (Table 1b). For the on-site analyses,

the F ratio was 233, indicting that a significant

difference was detected among the seven discrete

samples at greater than the 99.9% confidence level.

Results of a least significant difference test (LSD)

showed that all seven discrete samples were significantly different from each other at the 95%

confidence level. Similar results were obtained

when ANOVA was done on the laboratory results

(Table 1b). An F ratio of 613 was found, which

was significant at greater than the 99.9% level,

and the least significant difference test indicated

that all samples were statistically different from

Table 1 (cont’d). Results from sampling location 1, Monite site.

b. Statistical analysis of TNT concentrations (μg/g)

for discrete and composite samples.

Discrete samples

On-site analysis Laboratory total

Sample Mean Mean of logs Mean Mean of logs

1 39,800 4.599a† 41,400 4.615a

2 500 2.699e 416 2.619e

3 164 2.214g 136 2.132g

4 27,800 4.444b 42,800 4.632a

5 24,400 4.387c 27,700 4.434c

6 1,280 3.105d 1,220 3.087d

7 331 2.519f 286 2.452f

† Numbers designated with the same letter are not significantly different at the

95% confidence level.

ANOVA for log on-site analyses ANOVA for log lab analyses

F ratio = 233*** F ratio = 613***

Error MS = 0.0005547 Error MS = 0.00396

Least sign. diff. = 0.056 Least sign. diff. = 0.149

Linear correlation analysis for on-site analysis vs. lab analysis

(r = correlation coefficient)

Slope Intercept r

untransformed, non-zero intercept 0.805 359.1 0.973

untransformed, zero intercept 0.815 0 0.973

log-transformed data 0.926 0.251 0.999

Results of paired t-tests for on-site vs. lab results

Means of seven discrete samples, t = 1.35 (NS)

Means of log values for seven discrete samples, t = 0.07 (NS)

Composite samples

On-site analysis Laboratory total

n 7 7

mean value 13,100 14,100

standard deviation 532 1,420

RSD 4.06% 10.1%

ANOVA comparing on-site and lab analyses

F ratio = 3.05 (NS at 95% level)

 * Significant at the 95% level *** Significant at the 99.9% level

** Significant at the 99% level NS Not significant at the 95% level

10
one another, except samples 1 and 4. Thus, for

sampling location 1, very similar conclusions were

reached regarding the nature of the analyte distribution using either the results of on-site analyses

or results of laboratory analyses.

Because the mean concentrations and absolute

analytical variances for various samples from site

1 differ so drastically, it is not possible to directly

compare the uncertainties introduced by sampling with those from analysis by partitioning

variances of untransformed data using normal

distribution statistics. ANOVA of the log-transformed data indicates that even the log concentrations from various samples differ significantly

from one another, using analytical error as the

yardstick.

A simple way to compare sampling and analytical uncertainties is to compare the ratios of

extreme mean concentrations obtained for the

seven samples with those for duplicate analyses

from the same location. For location 1, the ratio of

highest mean concentration to lowest mean concentration was 243 for the field analyses and 304

for the laboratory analyses. The highest ratios for

duplicates were 1.16 for the field analyses and

1.47 for the laboratory analyses. Thus, for this

location, sampling error contributes many times

more uncertainty than analytical error for either

field or laboratory analysis.

Results for the field and laboratory analyses of

these discrete samples were compared in two

ways. Linear correlation analysis was conducted

using the untransformed data with and without

intercept, and for the log-transformed values with

intercept (Table 1b). Correlation coefficients were

0.973, 0.973 and 0.999 for untransformed data with

and without intercept and the log-transformed

data respectively. The correlation coefficient for

the zero intercept model is identical to that for the

model with non-zero intercept, and we interpret

this to mean that the intercept is not significantly

different from zero and that the accuracy of the

field method vs. the lab method can be estimated

from the slope of the best fit linear least squares

line (81.5%). The excellent correlation for the logtransformed data, as shown in Figure 4, demonstrates the equivalency of the results for the two

methods over several orders of magnitude of concentration.

Paired t-tests were also conducted on the seven

mean values and the log-transformed mean data

for the two methods of analysis (Table 1b). The tvalue for the untransformed data was 1.35 and

that for the log-transformed data was 0.07, neither significant at the 95% confidence level. We

must acknowledge that comparison of the

untransformed results is not truly legitimate because the concentration distribution is nonGaussian. Results of the paired t-tests agree with

those from correlation analysis, i.e., the laboratory and on-site results compare very favorably.

Results of the analyses of the composite samples

at sampling location 1 were also quite interesting.

The mean and standard deviation of the seven

on-site analyses for the composite was 13,100

± 532 μg/g in comparison to the mean of the

4

3

2

1

0 2 34 5

Laboratory Results (log μg/g)

On-site Results (log μg/g)

r = 0.999

Slope = 0.926

y-intercept = 0.251

5

1

Figure 4. Log-transformed TNT concentrations from sampling location 1—

linear model with intercept.

y

11
seven discrete samples, which was 13,500 μg/g

(Table 1b). Clearly, analysis of the composite provides a good estimate of the mean concentration

for the area sampled. For the laboratory analyses,

the mean and standard deviation of the seven

composites was 14,100 ± 1420 μg/g, while the

mean of the results for the seven discrete samples

was 16,300 μg/g. These results do not agree as

well as those for the on-site analyses, but they

appear to be quite adequate when compared to

the wide range of concentrations found for the

discrete samples. ANOVA was conducted to compare the laboratory and on-site analysis results

for the composite samples (Table 1b). The F ratio

of 3.05 says that the results of the laboratory and

on-site analyses for this sampling location were

not significantly different at the 95% confidence

level. This is true even with the good precision

(RSDs of 4.1 and 10.1% for field and laboratory)

obtained for the analyses of these composite

samples. Thus, for this location, a good indication

of the degree of contamination could be obtained

using a combination of composite sampling and

colorimetric on-site analysis.

Sampling location 2

Results for laboratory and on-site analyses of

soils from sampling location 2 are presented in

Table 2a. Soil samples from location 2 had an

aroma of shoe polish, pointing to the presence of

mononitrotoluenes, often present in conjunction

with high concentrations of DNT. Acetone exTable 2. Results from sampling location 2, Monite site.

a. Analytical results.

DNT on-site

analysis Laboratory analysis (μg/g)

Sample (μg/g) TNB TNT 2,4-DNT Total

Discrete samples

1a 31,700 — 2,370 113,000 115,000

1b 42,100 — 2,800 131,000 134,000

2a 8,290 — 1,900 5,820 7,720

2b 6,130 — 2,330 7,670 10,000

3a 29,300 — 5,260 47,000 52,300

3b 17,700 — 3,750 32,000 35,800

4a 24,400 — 4,700 29,500 34,200

4b 16,500 — 5,000 31,100 36,100

5a 9,610 — 334 10,600 10,900

5b 6,640 — 386 10,500 10,900

6a 14,500 — 383 16,700 17,100

6b 11,800 — 421 15,900 16,300

7a 3,070 — 481 3,450 3,930

7b 3,910 — 432 3,120 3,550

mean 16,100 34,900

Composites

C1 27,100 — 1,840 28,900 30,700

C2 23,500 — 2,060 31,600 33,700

C3 28,500 — 2,210 35,100 37,300

C4 23,400 — 2,020 31,300 33,300

C5 19,300 — 2,140 32,000 34,100

C6 23,200 — 2,120 33,200 35,300

C7 21,500 — 1,650 28,900 30,600

mean 23,800 33,600

std. dev. 3,140 2,390

12
tracts for location 2 were yellowish and, unlike

location 1, the intensity of the color did not correlate with the results of colorimetric on-site analysis. Addition of the EnSys reagent to extracts of

soils from this sampling location caused the development of an intense blue-purple color, also

indicative of the presence of DNT as the major

contaminant. Concentrations of DNT were estimated using absorbance measurements at 570 nm

as recommended by Jenkins and Walsh (1991).

On-site analysis results showed that DNT concentrations in the soil varied by over an order of

magnitude, ranging from about 3000 to 30,000

μg/g. Laboratory analyses showed the presence

of TNT at concentrations ranging from approximately 300–5000 μg/g. These amounts were included in the totals for lab results.

Agreement of duplicates for field analyses at

location 2 was poorer than at location 1, with a

mean RSD of 23.0%. A mean RSD of 10.0% was

Table 2 (cont’d).

b. Statistical analysis of DNT concentrations (μg/g)

for discrete and composite samples.

Discrete samples

On-site analysis Laboratory total

Sample Mean Mean of logs Mean Mean of logs

1 36,950 4.563a† 125,000 5.094a

2 7,210 3.853c 8,860 3.944d

3 23,500 4.358ab 44,000 4.636b

4 20,450 4.302ab 35,200 4.546b

5 8,125 3.903c 10,900 4.038d

6 13,150 4.117bc 16,700 4.223c

7 3,490 3.540d 3,740 3.572e

† Numbers designated with the same letter are not significantly different at

the 95% confidence level.

ANOVA for log on-site analyses ANOVA for log lab analyses

F ratio = 22.3*** F ratio = 153***

Error MS = 0.01098 Error MS = 0.00333

Least sign. diff. = 0.248 Least sign. diff. = 0.136

Linear correlation analysis for on-site analysis vs. lab analysis

(r = correlation coefficient)

Slope Intercept r

untransformed, non-zero intercept 0.262 6983 0.949

untransformed, zero intercept 0.350 0 0.817

log-transformed data 0.684 1.155 0.988

Results of paired t-tests for on-site vs. lab results

Means of seven discrete samples, t = 1.58 (NS)

Means of log values for seven discrete samples, t = 3.12*

Composite samples

On-site analysis Laboratory total

n 77

mean value 23,800 33,600

standard deviation 3,140 2,390

RSD 13.2% 7.1%

ANOVA comparing on-site and lab analyses

F ratio = 43.0***

 * Significant at the 95% level *** Significant at the 99.9% level

** Significant at the 99% level NS Not significant at the 95% level

13
found for the duplicate laboratory analyses, a

value very similar to that obtained for location 1.

The poorer agreement for field duplicates may be

in part attributable to incomplete field homogenization, but may also be ascribable to the on-site

method for DNT not being as reproducible as it is

for TNT (Jenkins and Walsh 1991). In fact, EnSys

does not even market their reagent for on-site

analysis of DNT.

As discussed for location 1, mean concentrations and analytical variances differed significantly

for samples at location 2. Thus, data did not appear to be normally distributed and were logtransformed. ANOVA and LSD tests were conducted with the log-transformed data (Table 2b).

Even with the large analytical error for the field

results, a significant difference was found among

samples using ANOVA (F ratio = 22.3) at greater

than the 99.9% confidence level, and many discrete samples at location 2 were significantly different from one another according to LSD analysis. A significant difference among samples was

also detected for the laboratory analyses (F ratio

= 153) at greater than the 99.9% level, with more

differences detected among individuals using LSD

analysis. If we use the same simple approach for

comparing the uncertainties introduced by sampling error and analytical error that we used for

location 1, ratios of highest to lowest means for

individual samples were 10.6 for on-site analyses

and 33.4 for lab analyses. The maximum differences in duplicates ratios were 1.48 and 1.46 for

field and lab analyses respectively. Thus, here

again, sampling error dominates over analytical

error with both methods.

To compare the field and laboratory results, we

again used both correlation analysis and a paired

t-test (Table 2b). Correlation analysis of the logtransformed results revealed a strong relationship between the two methods (r = 0.988) but a

slope of 0.684 was found for these log values,

indicating a significant low bias for the field DNT

results (Fig. 5). The paired t-test confirmed this

bias with a value of 3.12, which is significant at

the 95% level. Part of this bias is accounted for by

the laboratory total including TNT that is not

fully accounted for in the on-site analysis when

using measurements at 570 nm.

The results from the analysis of the composite

samples further confirmed the analytical bias detected for the discrete samples. A ratio of the mean

concentration for the on-site results divided by

the lab results was 0.71. ANOVA was conducted

to compare the on-site and lab results and an F

ratio of 43.0 was found, which was significant at

the 99.9% level (Table 2b).

The mean and standard deviation of the seven

composites analyzed by the field method were

23,800 ± 3140 μg/g, which compared to a mean of

the seven discrete samples of 16,100. For the laboratory results, the mean and standard deviation

for the seven composites were 33,600 ± 2390 μg/g

vs. a mean of the seven discrete samples of 34,800

μg/g. Compositing again appears to provide a

reliable estimate of the mean analyte concentration for the laboratory results. We initially thought

4.8

4.4

4.0

3.6

3.2 3.6 4.0 4.4 4.8 5.2

Laboratory Results (log μg/g)

On-site Results (log μg/g)

r = 0.988

Slope = 0.684

y-intercept = 1.155

Figure 5. Log-transformed DNT concentrations from sampling location 2—

linear model with intercept.

y

14
Table 3. Results from sampling location 3, Monite site.

a. Analytical results.

TNT on-site

analysis Laboratory analysis (μg/g)

Sample (μg/g) TNB TNT 2,4-DNT Total

Discrete samples

1a 4.6 0.03 4.1 1.0 5.1

1b 3.6 0.02 3.3 1.0 4.3

2a 1.7 — 0.2 1.5 1.7

2b 2.9 — 0.3 1.5 1.8

3a 3.1 0.12 0.8 1.1 2.0

3b 3.6 0.14 0.7 1.0 1.8

4a 4.1 — 0.6 0.8 1.4

4b 4.4 0.03 0.6 0.8 1.4

5a 5.3 — 0.4 0.5 0.9

5b 5.1 — 0.3 0.5 0.8

6a 4.6 — 0.1 0.6 0.7

6b 4.4 — 0.3 0.5 0.8

7a 149 0.04 75.4 0.7 76.1

7b 81.8 0.04 80.2 0.6 80.8

mean 19.8 12.9

Composites

C1 10.9 — 3.6 1.1 4.7

C2 13.0 — 2.4 1.1 3.5

C3 11.2 0.04 2.5 1.0 3.5

C4 13.3 — 2.6 1.2 3.8

C5 14.2 — 3.0 1.1 4.1

C6 12.4 — 4.1 1.2 5.3

C7 13.5 — 3.1 1.1 4.2

mean 12.6 4.2

std. dev. 1.22 0.66

that the difference between means for the discrete

samples and composites observed for the field

results may be attributable to our using only

roughly equal weights of individual samples when

preparing the composites here. However, this

should also have affected the laboratory results

and clearly this was not the case.

Sampling location 3

On-site analytical results for sampling location

3 are presented in Table 3a. At this location six of

the seven samples had very low levels of TNT (2–

5 μg/g), but the seventh location had a much

higher TNT concentration (> 80 μg/g). Because

TNT concentrations were low, the acetone extracts

used for on-site analysis were run without dilution. Extracts had a straw-yellow color that resulted in a significant background absorbance at

540 nm. Reaction with the EnSys reagent for these

samples resulted in a pink or orangish solution,

denoting the presence of low levels of TNT. Only

the extract from sample 7 needed to be diluted to

maintain the absorbance in the linear range after

reaction with the EnSys reagent.

Duplicate analyses for samples at this location

appeared to be quite acceptable, with mean RSDs

of 16.7% for the on-site analyses, meaning that

field homogenization was adequate. Laboratory

analyses for samples from this location were consistently lower than corresponding field analyses. This was also true for the composite samples

and it shows a positive bias for the field TNT

method for these soils.

ANOVA and LSD tests were conducted for field

and lab data both with and without logarithmic

transformation (Table 3b). We obtained F ratios of

64.6 for on-site and 911 for the lab that were significant at greater than the 99.9% confidence level,

15
indicating differences among samples. LSD tests

confirmed the difference between sample 7 and

the other six. Analysis of the log-transformed lab

data showed some differences among other

samples as well.

Comparison of the on-site and lab results using both correlation analysis and a paired t-test

yielded somewhat contradictory results owing to

the very large effect of one extremely high concentration sample (Table 3b). The positive bias of

the field method for soils at this location was

unambiguously confirmed by the composite

analyses (mean 12.6 μg/g for field and 4.16 μg/g

for lab). This bias may be caused by the presence

of unspecified environmental transformation

products of TNT, which were not determined using the RP-HPLC conditions specified in Method

8330, but which react with the EnSys reagent to

form a colored Janowsky complex.

The results for this sampling location show the

value of both compositing and on-site analysis

for site characterization at explosives-contamiTable 3 (cont’d). Results from sampling location 3, Monite site.

b. Statistical analysis of TNT concentrations (μg/g)

for discrete and composite samples.

Discrete samples

On-site analysis Laboratory total

Sample Mean Mean of logs Mean Mean of logs

1 4.1b† 0.610b 4.7b 0.670b

2 2.3b 0.346b 1.8b 0.243c

3 3.4b 0.524b 1.9b 0.278c

4 4.3b 0.628b 1.4b 0.146d

5 5.2b 0.716b 0.9b –0.072e

6 4.5b 0.653b 0.8b –0.126e

7 115a 2.043a 78.5a 1.894a

† Numbers designated with the same letter are not significantly different at

the 95% confidence level.

ANOVA for log on-site analyses ANOVA for log lab analyses

F ratio = 64.6*** F ratio = 911***

Error MS = 0.00991 Error MS = 0.00106

Least sign. diff. = 0.235 Least sign. diff. = 0.077

Linear correlation analysis for on-site analysis vs. lab analysis

(r = correlation coefficient)

Slope Intercept r

untransformed, non-zero intercept 1.447 1.23 0.999

untransformed, zero intercept 1.464 0 0.998

log-transformed data 0.715 0.479 0.879

Results of paired t-tests for on-site vs. lab results

Means of seven discrete samples, t = 1.40 (NS)

Means of log values for seven discrete samples, t = 2.87*

Composite samples

On-site analysis Laboratory total

n 7 7

mean value 12.6 4.16

standard deviation 1.22 0.66

RSD 9.66% 15.9%

ANOVA comparing on-site and lab analyses

F ratio = 264***

 * Significant at the 95% level *** Significant at the 99.9% level

** Significant at the 99% level NS Not significant at the 95% level

16
nated areas. If this location was characterized with

a single grab sample, the hot spot at sample 7

would most likely be missed. The availability of

an inexpensive on-site test would increase the

likelihood that investigators would detect this hot

spot and delineate its dimensions, thereby allowing its cleanup with minimal inclusion of soils

with concentrations below action levels.

Hawthorne AAP

Sampling location 4

Analytical results for sampling location 4 at

Hawthorne AAP are presented in Table 4a. Acetone extracts at this location turned reddish upon

reaction with the EnSys reagent, indicating that

TNT was likely to be the major contaminant

present. Laboratory analysis confirmed TNT being present at concentrations ranging from less

than 100 to over 6000 μg/g.

Precision estimates from duplicate on-site

analyses for sampling location 4 were approximately equivalent to corresponding laboratory

analyses (mean RSD for field was 12.5 vs. 13.5%

for lab), suggesting that on-site methods of homogenization were adequate for this soil.

Mean concentrations for individual samples at

location 4 differed substantially, but much less so

than those obtained for locations 1–3. For this

reason, ANOVA was first conducted with

untransformed data. The F ratios obtained were

166 and 133 for field and lab data, respectively

(Table 4b), which were statistically significant at

greater than the 99.9% level. Although log-transformed data were also analyzed and ANOVA gave

similar results, the variances for untransformed

Table 4. Results from sampling location 4, Hawthorne AAP site.

a. Analytical results.

TNT on-site

analysis Laboratory analysis (μg/g)

Sample (μg/g) TNB TNT 2,4-DNT Total

Discrete samples

1a 6180 68.2 6580 13.8 6660

1b 5570 63.3 5810 8.2 5880

2a 2900 18.8 3490 — 3510

2b 3320 48.2 3980 — 4030

3a 1270 50.8 1340 — 1390

3b 1060 47.6 1050 — 1100

4a 578 92.2 492 21.6 606

4b 549 79.1 472 15.7 567

5a 63.1 18.3 126 — 144

5b 107 — 72.5 — 72.5

6a 1740 44.0 2010 — 2050

6b 1920 50.3 1910 11.9 1970

7a 1090 50.3 1140 — 1190

7b 1270 36.4 1070 — 1110

mean 1970 2160

Composites

C1 1680 35.7 1510 7.1 1550

C2 1810 42.8 1660 6.9 1710

C3 1480 40.8 2170 — 2210

C4 1930 52.1 2300 — 2350

C5 2010 62.1 2180 25.9 2270

C6 1690 44.6 1890 — 1930

C7 1680 — 1930 21.6 1950

mean 1760 2000

std. dev. 178 298

17
results were sufficiently homogeneous to make

transformation unnecessary. LSD tests for both

on-site and lab results showed that six of the seven

samples were significantly different from one another. Partitioning the variances into analytical

error and sampling error gave analysis

standard deviations of 217 and 265 for

the field and lab methods, respectively

(Table 4b), and estimates for the sampling standard deviation of 1971 and

2154 from the field and lab data. Thus,

even for this sampling location, where

the analyte distribution was the least

heterogeneous of the four locations discussed thus far, sampling error was eight

to nine times greater than analytical error, regardless of whether analysis was

conducted on-site or in the lab.

The results from on-site and lab analysis were linearly correlated, and a slope

of the best fit regression line of 0.912

was obtained with an r of 0.997 (Table

4b). The relationship with zero intercept was slope = 0.911 and r = 0.997,

indicating that the accuracy of the field

test vs. the lab test was 91.1%. A paired

t-test of the on-site and lab results said

that they were not significantly different (Table 4b). ANOVA comparing onsite and lab methods for the composite

analyses produced an F ratio of 3.44,

which is not significant at the 95% level.

Overall, the on-site TNT method provided very reliable results for sampling

location 4.

Analysis of composite samples provided mean and standard deviation concentrations of 1760±178 and 2000±298

μg/g for on-site and lab methods respectively. Mean values from the seven

discrete samples were 1970 and 2160

μg/g respectively. Here, again, analysis

of composites provides acceptably reliable results with both methods. Overall, the results for sampling location 4

confirm the value of the on-site test in

providing rapid, reliable results for areas with concentrations varying over

orders of magnitude.

Sampling location 5

Analytical results for sampling location 5 are presented in Table 5a. Reaction of acetone extracts with the EnSys

reagent produced pink to reddish solutions, again

pointing to TNT as the likely major contaminant.

Laboratory analysis confirmed that TNT was the

contaminant present at the highest concentration

for all except sample 5. In sample 5, the TNT conTable 4 (cont’d). Results from sampling location 4, Hawthorne

AAP site.

b. Statistical analysis of TNT concentrations (μg/g) for discrete and composite samples.

Discrete samples

On-site analysis Laboratory total

Sample Mean Mean of logs Mean Mean of logs

1 5880a† 3.769a 6270a 3.797a

2 3110b 3.492b 3770b 3.575b

3 1170d 3.065c 1240d 3.092c

4 563e 2.727d 587de 2.768d

5 85.1e 1.915e 108e 2.009e

6 1830c 3.262c 2010c 3.304c

7 1180d 3.071c 1150d 3.060c

† Numbers designated with the same letter are not significantly different at

the 95% confidence level.

ANOVA for on-site and lab analyses

Untransformed

 On-site Lab

F ratios 166*** 133***

Error MS 47,163 70,287

Least sign. diff. 514 627

Analysis s 217 265

Sampling s 1,971 2,154

(s = standard deviation)

Linear correlation analysis for on-site analysis vs. lab analysis

(r = correlation coefficient)

 Slope Intercept r

untransformed, non-zero intercept 0.912 –1.846 0.997

untransformed, zero intercept 0.911 0 0.997

log-transformed data 1.020 –0.110 0.999

Results of paired t-tests for on-site vs. lab results

Means of seven discrete samples, t = 2.07 (NS)

Composite samples

On-site analysis Laboratory total

n 7 7

mean value 1760 2000

standard deviation 178 298

RSD 10.1% 14.9%

ANOVA comparing on-site and lab analyses

F ratio = 3.44 (NS)

* Significant at the 95% level *** Significant at the 99.9% level

** Significant at the 99% level NS Not significant at the 95% level

18
centration was very low (less than 2 μg/g) and

TNB was the compound present at the highest

concentration (about 10 μg/g). TNB reacts to the

EnSys reagent identically as does TNT with similar absorptivity and is not distinguishable from

TNT using on-site colorimetric analysis. In addition to TNB, 2,4-DNT was also present in these

samples at significant concentrations, but considerably lower than TNT, and it also reacts with the

EnSys reagent and contributes to the absorbance

at 540 nm. The TNT concentrations estimated from

the screening test for this location (about 12 to

almost 400 μg/g) agree reasonably well with the

concentrations of total nitroaromatics (sum of

TNT, TNB and 2,4-DNT) obtained from laboratory analysis.

Duplicate on-site and laboratory analyses for

soils from location 5 agree very well with mean

RSDs of 3.3 and 4.9%, respectively, indicating that

field homogenization was excellent and the precision of the on-site test is equivalent to that of the

lab method under these circumstances.

ANOVA was conducted on the data from discrete sample analysis, both with and without logtransformation, but as with location 4, transformation was unnecessary (Table 5b). The F ratios

for field and lab results were 1061 and 282, respectively, meaning that discrete samples from

location 5 were significantly different from one

another at greater than the 99.9% confidence level.

LSD tests showed that all seven samples were

significantly different from one another. Partitioning the variances into analytical and sampling

components gave estimates for analytical standard deviation of 5.3 and 11.0 μg/g for the on-site

and lab methods, respectively, while estimates

Table 5. Results from sampling location 5, Hawthorne AAP site.

a. Analytical results.

TNT on-site

analysis Laboratory analysis (μg/g)

Sample (μg/g) TNB TNT 2,4-DNT Total

Discrete samples

1a 127 33.5 63.8 27.7 125

1b 125 32.8 48.2 27.3 108

2a 116 52.8 214 2.6 269

2b 103 52.8 210 10.6 273

3a 379 57.0 286 14.7 358

3b 366 61.7 312 17.7 391

4a 59.1 14.6 37.6 1.9 54.1

4b 56.0 15.5 34.0 1.8 51.3

5a 12.4 10.0 1.9 1.0 12.9

5b 13.3 10.7 1.7 — 12.4

6a 170 17.2 222 12.2 251

6b 173 16.8 207 11.7 236

7a 240 40.4 53.4 15.4 109

7b 245 37.6 48.4 14.4 100

mean 156 168

Composites

C1 129 32.1 145 11.4 189

C2 137 32.1 144 9.2 185

C3 116 32.4 150 11.2 194

C4 138 34.1 163 10.8 208

C5 139 34.5 149 10.9 194

C6 147 33.7 142 11.5 187

C7 170 33.5 152 11.8 197

mean 139 193

std. dev. 16.6 7.72

19
for sampling standard deviations were 121 and

131 μg/g. Thus, here again, sampling error overwhelms analytical error by over an order of magnitude.

Linear correlation analyses for the field and

lab results were conducted in the same manner as

described for samples from other sampling locations (Table 5b). The best fit

linear regression is shown in Figure 6.

The slope for the best fit line with

intercept was 0.688, which was considerably lower than the slope for the

best fit line with zero intercept (slope

= 0.847). Nevertheless, a paired t-test

of field vs. lab results indicated that

results for the two methods were not

significantly different at the 95% confidence level. As can be seen in Figure

6, the two highly divergent samples

from the fitted model are on opposite

sides, which is to say that the large

random error tends to mask the systematic difference. However, ANOVA

comparing field and lab data for the

composite samples yielded an F ratio

of 60.8, which was significant at the

99.9% confidence level. The ratio of

field (139 μg/g) to laboratory (193

μg/g) results is 0.72, which is in excellent agreement with the slope (0.688)

of the linear least squares model (Fig.

6) and confirms the presence of bias.

Overall, the relationship between the

field and lab methods for location 5 is

poorer than those found for other sampling locations. Thus, while the accuracy of the field method for soils at

location 5 is not optimal compared

with what we have described previously, it is still acceptable in light of

the large degree of concentration heterogeneity.

Sampling location 6

Acetone extracts for soils at sampling location 6 were bright fluorescent-yellow, an indication that the

major contaminant was probably ammonium picrate. Laboratory results

confirmed that ammonium picrate

was the contaminant present at highest concentration, with TNT and other

nitroaromatics present at lower concentrations (Table 6a). Reaction of

these acetone extracts with the EnSys TNT reagent produced very erratic results; the test was

probably not functioning properly in the presence of ammonium picrate. Subsequent laboratory experiments confirmed that ammonium picrate interferes with the on-site TNT analysis test.

Table 5 (cont’d). Results from sampling location 5, Hawthorne

AAP site.

b. Statistical analysis of TNT concentrations (μg/g) for discrete

and composite.

Discrete samples

On-site analysis Laboratory total

Sample Mean Mean of logs Mean Mean of logs

1 126d† 2.101d 117d 2.065d

2 110e 2.039e 271b 2.433b

3 373a 2.571a 375a 2.573a

4 57.6f 1.760f 52.7e 1.722e

5 12.9g 1.109g 12.7f 1.102f

6 172c 2.234c 244c 2.387c

7 243b 2.385b 105d 2.019d

† Numbers designated with the same letter are not significantly different at the

95% confidence level.

ANOVA for on-site and lab analyses

Untransformed

On-site Lab

F ratios 1061*** 282***

Error MS 27.601 122.00

Least sign. diff. 12.4 26.1

Analysis s 5.3 11.0

Sampling s 121 131

(s = standard deviation)

Linear correlation analysis for on-site analysis vs. lab analysis

(r = correlation coefficient)

 Slope Intercept r

untransformed, non-zero intercept 0.688 40.63 0.745

untransformed, zero intercept 0.847 0 0.714

log-transformed data 0.848 0.296 0.894

Results of paired t-tests for on-site vs. lab results

Means of seven discrete samples, t = 0.35 (NS)

Composite samples

On-site analysis Laboratory total

n 7 7

mean value 139 193

standard deviation 16.6 7.72

RSD 12.0% 4.0%

ANOVA comparing on-site and lab analyses

F ratio = 60.8***

 * Significant at the 95% level *** Significant at the 99.9% level

** Significant at the 99% level NS Not significant at the 95% level

20
400

300

200

100

0 200 300 400

Laboratory Results (μg/g)

On-site Results (μg/g)

r = 0.745

Slope = 0.688

y-intercept = 40.6

100

Figure 6. Untransformed TNT concentrations from sampling location 5—

linear model with intercept.

Table 6. Results from sampling location 6, Hawthorne AAP site.

a. Analytical results.

Picrate

on-site analysis Laboratory analysis (μg/g)

Sample (μg/g) DNB TNT 2,4-DNT Picrate

Discrete samples

1a 23 0.44 0.67 2.28 7.5

1b 33 0.48 0.66 1.73 4.0

2a 5.6 0.22 0.39 0.29 <0.1

2b 8.4 0.20 0.42 0.17 <0.1

3a 6.2 1.07 0.38 1.54 0.7

3b 5.9 1.05 0.37 1.52 0.7

4a 82 2.09 0.16 0.24 80.7

4b 79 1.66 0.14 0.39 93.4

5a 4000 8.92 0.47 1.49 4260

5b 4400 9.46 0.48 1.49 4340

6a 1700 3.05 0.49 1.49 1700

6b 1800 2.90 0.11 0.28 2110

7a 12 0.56 0.41 1.40 1.4

7b 14 0.61 0.41 1.45 1.7

mean 869 899

Composites

C1 930 2.10 0.38 0.36 925

C2 940 2.15 0.48 0.48 981

C3 1000 2.37 0.38 0.41 1050

C4 1000 2.32 0.42 0.42 1100

C5 1000 2.52 0.38 0.43 1140

C6 980 2.13 0.38 0.41 980

C7 940 2.11 0.41 0.43 888

mean 970 1010

std. dev. 32.1 91.7

y

21
We were not equipped to conduct ammonium

picrate screening in the field. However, an on-site

method has been developed for ammonium picrate (Thorne and Jenkins 1995) and samples were

extracted in the laboratory with acetone and the

extracts subjected to the screening procedure as

described in the Experimental section. Results of

the field analysis procedure and the lab (HPLC)

method, also conducted with these same acetone

extracts, were consistent and demonstrated that

the ammonium picrate concentrations varied from

below detection limits to over 4000 μg/g for soils

at sampling location 6 (Table 6a).

We found, using the on-site method, that duplicate analyses on samples homogenized in the

field had a mean RSD of 11.6%, and, using the

HPLC method, a mean RSD of 11.9%. Unlike all

other comparisons, aliquots of the same extract

were used in these tests. Therefore, the two procedures appear to have approximately equal precision. Field homogenization was clearly adequate

for site characterization. ANOVA, using log-transTable 6 (cont’d). Results from sampling location 6, Hawthorne AAP

site.

b. Statistical analysis of ammonium picrate concentrations

(μg/g) for discrete and composite samples.

Discrete samples

On-site analysis Laboratory total

Sample Mean Mean of logs Mean Mean of logs

1 28 1.447d† 5.8 0.763d

2 7.0 0.845f <0.1 < –0.1f

3 6.1 0.785f 0.7 –0.155f

4 81 1.909c 87.1 1.940c

5 4200 3.623a 4300 3.634a

6 1750 3.243b 1900 3.279b

7 13 1.114e 1.6 0.204e

† Numbers designated with the same letter are not significantly different at the

95% confidence level.

ANOVA for log on-site analyses ANOVA for log lab analyses

F ratio = 589*** F ratio = 923***

Error MS = 0.00451 Error MS = 0.00675

Least sign. diff. = 0.159 Least sign. diff. = 0.194

Linear correlation analysis for on-site analysis vs. lab analysis (r = correlation coefficient)

Slope Intercept r

untransformed, non-zero intercept 0.968 –1.74 0.999

untransformed, zero intercept 0.967 0 0.999

log-transformed data 0.634 1.07 0.971

Results of paired t-tests for on-site vs. lab results

Means of seven discrete samples, t = 1.19(NS)

Means of log values for seven discrete samples, t = 2.34(NS)

Composite samples

On-site analysis Laboratory total

n 7 7

mean value 970 1010

standard deviation 32.1 91.7

RSD 3.31% 9.10%

ANOVA comparing on-site and lab analyses

F ratio = 1.14(NS)

 * Significant at the 95% level *** Significant at the 99.9% level

** Significant at the 99% level NS Not significant at the 95% level

22
formed data from both the screening and HPLC

determinations for the discrete samples, indicated

that samples were significantly different at greater

than the 99.9% confidence level. LSD tests showed

that the discrete samples were nearly all significantly different from one another (Table 6b).

Means and standard deviations from composite analyses were 970± 32 and 1010 ± 91 μg/g

for the screening and HPLC methods, respectively, which were not significantly different at

the 95% level. The mean values from the seven

discrete analyses were 869 and 901 μg/g for the

screening and HPLC methods respectively.

Correlation of screening results with those from

HPLC resulted in an r of 0.999 and a slope of

0.968 using a model with an intercept and the

untransformed data (Table 6b). The model with

zero intercept likewise gave a slope of 0.967 and

an r value of 0.999, indicating that the intercept in

the above model is not significantly different from

zero. Nevertheless, at very low levels (<10 μg/g),

there does appear to be a small positive bias for

the screening method and this is reflected by the

lower slope and correlation coefficient for the logtransformed model. At present we have not been

able to identify the source of this bias. This bias

was not detected using a paired t-test for the results from the seven discrete samples, which

meant that results from the two methods were

not significantly different at the 95% confidence

level. Similarly, there was no significant bias in

the means of the two methods applied to the

composite samples where the concentrations were

about 1000 μg/g.

Clearly, composite sampling and screening

analysis provides an inexpensive, precise approach for estimating site contamination levels

for ammonium picrate at this sampling location.

Volunteer AAP

Sampling locations 7 and 7R

Analytical results for sampling location 7, and

a duplicate set of samples from location 7, labeled

7R, are presented in Tables 7a and 7c respectively.

Location 7R was offset from location 7 by 15 cm,

so like-numbered samples from location 7 and 7R

are all located 15 cm apart. Acetone extracts for

these soils were dark brick-red, implying that

analyte concentrations were probably quite high.

When extracts were diluted (4.0 μL to 20 mL) and

reacted with EnSys reagent, a reddish color resulted, indicating that TNT was probably the major analyte present; this was later confirmed by

laboratory analysis. Concentrations of TNT ranged

from about 55,000 to 112,000 μg/g for location 7

and from about 40,000 to 119,000 μg/g for location 7R.

Samples from both locations 7 and 7R contained

a high percentage of stones compared with

samples from any other location. In the field, 15–

59% of the soil weight was removed during homogenization for location 7 and 20–40% was excluded for location 7R. RSDs for field analyses

were 13.3 and 4.9% for 7 and 7R, respectively,

indicating that the resulting material was fairly

homogeneous.

When these samples were further processed in

the laboratory, a large percentage of the remaining material proved to be smaller stones, which

we removed before laboratory analysis. The material excluded in the laboratory ranged from 51–

64% for location 7 and 47–67% for location 7R.

This was in addition to the material already excluded during field homogenization. Samples of

the segregated stones were extracted and analyzed in the same manner as the soil and the results for the stones segregated from sample 4 for

both locations 7 and 7R are presented in Table 7e.

TNT concentrations obtained for the stones ranged

from 6025 to 8150 μg/g, while the corresponding

soil for these samples had TNT concentrations

over 100,000 μg/g. Because the small stones had

much lower concentrations of TNT than the soil,

their exclusion from the material originally analyzed in the field using the colorimetric method,

prior to laboratory analysis, is the major factor

accounting for the higher concentrations observed

in the laboratory analyses.

A problem was encountered in the field that

affects the screening results presented for sample

location 7 (but not 7R). The automatic pipette used

to dispense the proper volume of extracting solvent malfunctioned at location 7 and the problem

was not discovered until the on-site analyses had

been completed. This problem resulted in varying amounts of acetone being used for extraction

from sample to sample rather than the 100 mL

specified. Probably the differences were not large,

but there is additional uncertainty in the results

because of this problem. The mean RSD for the

field analyses for location 7R was 4.9%, compared

to 13.3% for location 7. Laboratory results were

unaffected by this problem and nearly identical

mean RSDs were found for locations 7 and 7R (6.0

and 5.1% respectively).

ANOVA was conducted on the mean concentrations from the seven samples for both loca23
tions 7 and 7R (Tables 7b and 7d). Since concentrations differed by only a factor of 5 for individual samples, ANOVA was conducted on untransformed data. F ratios for field analyses were

7.8 and 47.8 for locations 7 and 7R, which were

significant at the 99% level and greater than the

99.9% level respectively. Corresponding F ratios

from the lab results were 14.3 and 39.0, significant

at 99% and greater than the 99.9% levels. These

ratios show that significant differences existed

among individual samples for both 7 and 7R. Samples 1, 4, 5 and 6 were not significantly different

from each other using the lab results for both 7

and 7R according to LSD tests. Likewise, samples

3 and 7 were not significantly different from each

other, while sample 2 was significantly different

from the other six samples for both 7 and 7R. The

fact that these two sets of independent results

give an identical picture of the analyte distribution on the site gives us added confidence that the

results are not random, but are depicting an accurate representation of concentration distributions.

Linear correlation analysis was conducted on

the results from lab and field analyses for 7 and

7R (Tables 7b and 7d); however, the introduction

of bias by excluding stones prior to lab analysis

makes these results only of marginal interest. In

fact, paired t-tests for field vs. lab data from the

two locations give contradictory conclusions, but

the composite samples from both locations clearly

demonstrate the expected bias. Thus, the results

for this location do not offer a valid comparison

of the accuracy of the field method and the lab

method. Nevertheless, the field method and the

lab analyses provide very similar pictures of

analyte distributions.

Table 7. Results from sampling location 7, Volunteer AAP site.

a. Analytical results.

TNT on-site

analysis Laboratory analysis (μg/g)

Sample (μg/g) TNB TNT 2,4-DNT Total

Discrete samples

1a 101,000 — 114,000 — 114,000

1b 129,000 — 109,000 — 109,000

2a 28,600 — 55,700 — 55,700

2b 27,300 — 54,700 — 54,700

3a 53,600 — 74,300 — 74,300

3b 49,700 — 71,000 — 71,000

4a 90,100 — 106,000 — 106,000

4b 130,000 — 102,000 — 102,000

5a 90,100 — 101,000 — 101,000

5b 95,700 — 101,000 — 101,000

6a 104,000 — 101,000 — 101,000

6b 65,300 — 101,000 — 101,000

7a 116,000 — 65,200 — 65,200

7b 108,000 — 93,000 — 93,000

mean 84,900 89,300

Composites

C1 56,400 — 105,000 — 105,000

C2 58,600 — 95,700 — 95,700

C3 54,300 — 126,000 — 126,000

C4 60,600 — 105,000 — 105,000

C5 54,600 — 104,000 — 104,000

C6 59,700 — 105,000 — 105,000

C7 54,900 — 108,000 — 108,000

mean 57,000 107,000

std. dev. 2,600 9,230

24
The results from analysis of composite samples

from locations 7 and 7R are particularly interesting (Tables 7b and 7d). Since the two sampling

locations were only 15 cm apart, either set of

samples could be used to characterize the site. If

composite sampling is a useful approach, results

from analysis of the two composites should produce similar results. In fact, nearly identical estimates of concentration were obtained by both the

laboratory and on-site analyses: 57,000 μg/g vs.

55,200 μg/g for the field and 107,000 μg/g for

both from the lab.

Table 7 (cont’d). Results from sampling location 7, Volunteer

AAP site.

b. Statistical analysis of TNT concentrations (μg/g) for discrete

and composite samples.

Discrete samples

On-site analysis Laboratory total

Sample Mean Mean of logs Mean Mean of logs

1 115,000a† 5.058a 112,000a 5.047a

2 28,000b 4.447c 55,200d 4.742d

3 51,700ab 4.713b 72,700cd 4.861c

4 110,000a 5.034a 104,000ab 5.017ab

5 92,900a 4.968a 101,000ab 5.004ab

6 84,800a 4.917a 101,000ab 5.004ab

7 112,000a 5.048a 79,100bc 4.891bc

† Numbers designated with the same letter are not significantly different at

the 95% confidence level.

ANOVA for on-site and lab analyses

Untransformed

On-site Lab

F ratios 7.80** 14.3**

Error MS 285,585,544 58,980,714

Least sign. diff. 39,960 18,160

Analysis s 16,900 7,680

Sampling s 31,200 19,800

(s = standard deviation)

Linear correlation analysis for on-site analysis vs. lab analysis

(r = correlation coefficient)

Slope Intercept r

untransformed, non-zero intercept 1.319 –32,833 0.815

untransformed, zero intercept 0.967 0 0.784

Results of paired t-tests for on-site vs. lab results

Means of seven discrete samples, t = 0.56 (NS)

Composite samples

On-site analysis Laboratory total

n 7 7

mean value 57,000 107000

standard deviation 2600 9230

RSD 4.56% 8.63%

ANOVA comparing on-site and lab analyses

F ratio = 190***

 * Significant at the 95% level *** Significant at the 99.9% level

** Significant at the 99% level NS Not significant at the 95% level

25
Sampling location 8

The analytical data for sampling location 8 are

presented in Table 8a. Acetone extracts of these

soils varied in color intensity, indicating that the

concentrations of contaminants were quite variable from sample to sample. After appropriate

dilution (ranging from 1:50 to 1:5000), reaction

with EnSys reagent produced reddish solutions,

showing that TNT was the probable contaminant.

Laboratory analysis confirmed the presence of

TNT with concentrations ranging from about 500

to almost 30,000 μg/g.

The mean RSD for duplicate field analyses of

the discrete samples from location 8 was 19.7%,

which was higher than for any of the other TNT

sites. In contrast, the mean RSD for the lab data

was 4.5%. Very similar RSDs were obtained from

the replicate analyses of the composite samples

(17.9% for field analyses and 4.3% for lab analyses). No specific explanation can be offered for

the unusually poor precision of the field measurements.

Because concentrations for the seven samples

at location 8 were clearly not normally distributed, log-transformed data were subjected to

ANOVA (Table 8b). F ratios were 71.2 for the field

results and 1553 for the lab results, denoting significant differences among samples at greater than

the 99.9% confidence level. LSD calculations for

both the field and lab data indicated that most

individual samples were significantly different

from one another.

Correlation analysis was conducted on the field

and lab data for both the untransformed and logtransformed data. The best fit linear regression

line for the untransformed data had a slope of

Table 7 (cont’d). Results from sampling location 7, Volunteer AAP site.

c. Analytical results for sampling location 7R.

TNT on-site

analysis Laboratory analysis (μg/g)

Sample (μg/g) TNB TNT 2,4-DNT Total

Discrete samples

1a 81,200 — 98,000 — 98,000

1b 82,800 — 119,000 — 119,000

2a 21,600 — 42,600 — 42,600

2b 21,900 — 37,900 — 37,900

3a 36,600 — 76,000 — 76,000

3b 40,700 — 67,200 — 67,200

4a 77,600 — 120,000 — 120,000

4b 74,800 — 119,000 — 119,000

5a 72,200 — 100,000 — 100,000

5b 70,400 — 103,000 — 103,000

6a 69,100 — 99,500 — 99,500

6b 87,400 — 100,000 — 100,000

7a 35,000 — 66,400 — 66,400

7b 33,200 — 68,600 — 68,600

mean 57,500 86,900

Composites

C1 63,200 — 117,000 — 117,000

C2 58,200 — 94,300 — 94,300

C3 58,100 — 111,000 — 111,000

C4 49,800 — 107,000 — 107,000

C5 51,500 — 101,000 — 101,000

C6 46,400 — 112,000 — 112,000

C7 56,600 — 105,000 — 105,000

mean 55,200 107,000

std. dev. 5,800 7,520

26
Table 7 (cont’d).

d. Statistical analysis of TNT concentrations (μg/g) for discrete and composite samples from sampling location 7R.

Discrete samples

On-site analysis Laboratory total

Sample Mean Mean of logs Mean Mean of logs

1 82,000a† 4.914a 109,000a 5.034a

2 21,700c 4.337c 40,300c 4.604c

3 38,700b 4.587b 71,600b 4.854b

4 76,200a 4.882a 119,000a 5.076a

5 71,300a 4.853a 101,000a 5.006a

6 78,200a 4.890a 100,000a 5.000a

7 34,100b 4.533b 67,500b 4.829b

† Numbers designated with the same letter are not significantly different at

the 95% confidence level.

ANOVA for on-site and lab analyses

Untransformed

On-site Lab

F ratios 47.8*** 39.0***

Error MS 26,175,779 39,933,637

Least sign. diff. 12,097 14,943

 Analysis s 5,120 6,320

Sampling s 24,700 27,560

(s = standard deviation)

Linear correlation analysis for on-site analysis vs. lab analysis

(r = correlation coefficient)

Slope Intercept r

untransformed, non-zero intercept 0.860 –17,291 0.960

untransformed, zero intercept 0.677 0 0.936

Results of paired t-tests for on-site vs. lab results

Means of seven discrete samples, t = 9.55***

Composite samples

On-site analysis Laboratory total

n 7 7

mean value 55,200 107,000

standard deviation 5,840 7,520

RSD 10.6% 7.05%

ANOVA comparing on-site and lab analyses

F ratio = 209***

* Significant at the 95% level *** Significant at the 99.9% level

** Significant at the 99% level NS Not significant at the 95% level

e. Analytical results for stones separated from soils from sampling locations 7 and 7R during laboratory homogenization.

Stones Soil

TNT TNT

Sample Discrete Weight concentration Weight concentration

location sample no. (g) (μg/g) (g) (μg/g)

7 4 9.44 6,025 8.93 106,000

8,150 102,000

7R 4 10.70 7,125 10.10 120,000

6,500 119,000

27
Table 8. Results from sampling location 8, Volunteer AAP site.

a. Analytical results.

TNT on-site

analysis Laboratory analysis (μg/g)

Sample (μg/g) TNB TNT 2,4-DNT Total

Discrete samples

1a 4,760 24.6 3,180 30.5 3,240

1b 3,160 53.1 3,250 21.7 3,320

2a 24,300 53.7 30,300 46.4 30,400

2b 37,300 53.1 28,200 36.4 28,300

3a 22,100 33.7 21,000 94.0 21,100

3b 24,300 48.8 21,400 123.0 21,600

4a 1,340 11.9 844 13.1 869

4b 2,320 12.5 801 17.7 831

5a 578 5.9 534 — 540

5b 582 6.1 506 2.9 515

6a 6,100 22.8 6,170 12.3 6,210

6b 7,460 18.1 5,210 11.4 5,240

7a 1,980 8.8 1,340 — 1,350

7b 2,650 10.5 1,230 18.7 1,260

mean 9,920 8,900

Composites

C1 9,690 26.6 9,970 30.8 10,000

C2 11,300 25.7 8,930 31.7 8,990

C3 12,700 31.4 9,880 38.7 9,950

C4 9,100 28.6 10,000 31.4 10,100

C5 15,000 26.2 9,440 — 9,470

C6 10,200 27.6 9,500 19.4 9,550

C7 11,000 26.9 9,260 26.0 9,310

mean 11,300 9,620

std. dev. 2,020 409

1.038 and an r of 0.999, indicating a very strong

relationship for the data (Table 8b). Similarly, a

slope of 1.070 and an r of 0.998 were found for the

best fit linear relationship with zero intercept. A

paired t-test for the untransformed data showed

a statistically significant t value of 4.71. A significant t value of 2.60 was also found for the paired

t-test with the log-transformed data. For all seven

samples, the field result was somewhat higher

than the lab result and this consistent pattern

caused the paired t-test to show a significant difference. Despite this small bias, the lab and field

data for the discrete samples at location 8 both

did quite well in portraying the levels of contamination for individual samples.

Results from replicate analyses of the composites failed to show that field results were significantly larger than lab results at the 95% level

(Table 8b), because of the unusually large variance for the field results. The means and standard deviations of the seven composites were

11,300±2020 and 9620±409 μg/g for the field and

lab data, respectively, compared with the means

of the discrete samples of 9940 μg/g from the field

results and 8900 μg/g from the lab results. Thus,

results from the composite analysis provide an

acceptably accurate estimate of the average concentrations on site.

Sampling location 9

The field and laboratory analyses for sampling

location 9 are presented in Table 9a. Acetone extracts from these soils were light yellow, implying

that, if analytes were present, they were in low

concentration. When undiluted extracts were reacted with EnSys reagent, pink to reddish solu28
tions were produced, indicative of the probable

presence of TNT. This site was located in an area

that was thought to be free of contamination by

personnel at Volunteer AAP. Laboratory analyses

confirmed the presence of TNT in these soils at

concentrations ranging from 7 to 40 μg/g.

Analytical precision for both the field and lab

analyses for samples from location 9 was excellent. The mean RSD for the field analyses was

4.1% for the discrete samples and the RSD from

replicate analysis of the composite was 9.0%. Likewise, the mean RSD for lab analysis of the discrete samples was 5.0% and the RSD from replicate analysis of the composite was 2.8%.

Like sampling locations 4, 5 and 7, results from

location 9 appeared to be sufficiently normally

distributed to conduct ANOVA without log-transformation. When this was done, F ratios of 217

and 321 were obtained for field and lab results,

respectively, indicating highly significant differences among discrete samples (Table 9b). LSD

tests showed that nearly all of the discrete samples

Table 8 (cont’d).

b. Statistical analysis of TNT concentrations (μg/g) for discrete

and composite samples.

Discrete samples

On-site analysis Laboratory total

Sample Mean Mean of logs Mean Mean of logs

1 3,960 3.589bc† 3,280 3.516d

2 30,800 4.479a 29,300 4.467a

3 23,200 4.365a 21,300 4.329b

4 1,830 3.246d 850 2.929f

5 580 2.763e 527 2.722g

6 6,780 3.829b 5,720 3.756c

7 2,320 3.365cd 1,300 3.115e

† Numbers designated with the same letter are not significantly different at

the 95% confidence level.

ANOVA for log on-site analyses ANOVA for log lab analyses

F ratio = 71.2*** F ratio = 1553***

Error MS = 0.01060 Error MS = 0.00059

Least sign. diff. = 0.244 Least sign. diff. = 0. 057

Linear correlation analysis for on-site analysis vs. lab analysis

(r = correlation coefficient)

Slope Intercept r

untransformed, non-zero intercept 1.038 686 0.999

untransformed, zero intercept 1.070 0 0.999

log-transformed data 0.991 0.062 0.960

Results of paired t-tests for on-site vs. lab results

Means of seven discrete samples, t = 4.71**

Means of log values for seven discrete samples, t = 2.60*

Composite samples

On-site analysis Laboratory total

n 7 7

mean value 11,300 9,620

standard deviation 2,020 409

RSD 17.9% 4.3%

ANOVA comparing on-site and lab analyses

F ratio = 4.54 (NS)

 * Significant at the 95% level *** Significant at the 99.9% level

** Significant at the 99% level NS Not significant at the 95% level

29
Table 9. Results from sampling location 9, Volunteer AAP site.

a. Analytical results.

TNT on-site

analysis Laboratory analysis (μg/g)

Sample (μg/g) TNB TNT 2,4-DNT Total

Discrete samples

1a 4.3 — 5.7 0.6 6.3

1b 4.1 — 4.9 0.5 5.4

2a 6.1 — 5.3 1.7 7.0

2b 5.9 — 5.5 0.9 6.4

3a 17.6 — 17.5 2.5 20.0

3b 19.9 — 16.1 2.0 18.1

4a 10.5 — 5.5 1.5 7.0

4b 10.7 — 5.2 1.4 6.6

5a 33.0 — 30.8 3.7 34.5

5b 35.8 — 29.6 3.5 33.1

6a 13.9 — 10.7 1.5 12.2

6b 14.4 — 10.4 1.3 11.7

7a 7.8 — 5.5 0.9 6.4

7b 7.3 — 5.4 0.9 6.3

mean 13.7 16.0

Composites

C1 15.1 — 10.4 1.4 11.8

C2 15.9 — 10.1 1.4 11.5

C3 16.5 — 10.7 1.4 12.1

C4 17.6 — 10.1 1.3 11.4

C5 19.4 — 10.3 1.4 11.7

C6 15.1 — 10.7 1.4 12.1

C7 16.6 — 10.9 1.4 12.3

mean 16.6 14.9

std. dev. 1.52 0.33

30

25

20

15

0

35

20 25 30 35

Laboratory Results (μg/g)

On-site Results (μg/g)

r = 0.984

Slope = 0.990

y-intercept = 0.856

15

10

5

5 10

Figure 7. Untransformed TNT concentrations from sampling location 9—

linear model with intercept.

y

30
were significantly different from one another.

When variances were fractionated into analytical

and sampling error, a standard deviation for analysis of 1.0 μg/g was obtained for both the field and

laboratory methods. Sampling error estimated

from the field analysis data was 10.4 μg/g and

from the lab data it was 12.4 μg/g, showing that

sampling error again dominated the total error at

this sampling location (Table 9b).

Correlation analysis with the field and lab data

from location 9 gave a best fit linear relationship

with a slope 0.990, a y-intercept of 0.856, and an r

of 0.984 (Table 9b, Fig. 7). The best fit zero intercept model had a slope of 1.032 and an r of 0.982,

suggesting that the intercept was probably not

significant. Results of a paired t-test indicated

that the results of the two methods were not significantly different at the 95% confidence level.

Table 9 (cont’d).

b. Statistical analysis of TNT concentrations (μg/g) for discrete

and composite samples.

Discrete samples

On-site analysis Laboratory total

Sample Mean Mean of logs Mean Mean of logs

1 4.2f† 0.625g 7.2d 0.854d

2 6.0ef 0.779f 7.6d 0.879d

3 18.7b 1.271b 24.3b 1.385b

4 10.6d 1.024d 8.8d 0.945d

5 34.4a 1.536a 40.5a 1.607a

6 14.1c 1.151c 14.7c 1.167c

7 7.6e 0.879e 8.7d 0.940d

† Numbers designated with the same letter are not significantly different at the

95% confidence level.

ANOVA for on-site and lab analyses

Untransformed

On-site Lab

F ratios 217*** 321***

Error MS 0.9974 95,854

Least sign. diff. 2.36 2.32

Analysis s 1.0 1.0

Sampling s 10.4 12.4

(s = standard deviation)

Linear correlation analysis for on-site analysis vs. lab analysis

(r = correlation coefficient)

Slope Intercept r

untransformed, non-zero intercept 0.990 0.856 0.984

untransformed, zero intercept 1.032 0 0.982

log-transformed data 1.000 0.019 0.939

Results of paired t-tests for on-site vs. lab results

Means of seven discrete samples, t = 2.17 (NS)

Composite samples

On-site analysis Laboratory total

n 7 7

mean value 16.6 14.9

standard deviation 1.52 0.33

RSD 9.0% 2.8%

ANOVA comparing on-site and lab analyses

F ratio = 8.43*

 * Significant at the 95% level *** Significant at the 99.9% level

** Significant at the 99% level NS Not significant at the 95% level

31
However, the analytical precision was so good

that a significant difference was detected in the

replicate analyses of the composite, even though

the mean concentrations of the field and lab results were 16.6 and 14.9 μg/g respectively. The

excellent agreement of on-site and lab results for

sampling location 9 is particularly encouraging

because the range of concentration encountered

is quite low (4–40 μg/g) and yet the two methods

provided very comparable results.

SUMMARY OF RESULTS

The results of this study provide information

on several topics critical to efficient and appropriate characterization of explosives-contaminated

sites. The first compares the capabilities of colorimetric on-site analysis for TNT, DNT and ammonium picrate in soil to laboratory analysis by

HPLC. Secondly, this study directly compares analytical and sampling error, thereby allowing development of strategies for improving data quality. Third, the results provide some guidance on

sampling strategies for collecting representative

samples, despite the enormous heterogeneity

present at these sites.

To assess the overall performance of the TNT

colorimetric on-site analysis method across the

soils from the three installations, the numerical

on-site analysis results for sampling locations 1,

3, 4, 5, 8 and 9 were correlated with the corresponding laboratory results. Data for sampling

locations 2, 6 and 7 were not used in this correlation. Results from sampling location 2 were eliminated because the major analyte present was DNT

rather than TNT and the relationship between the

two methods is different. Similarly, contamination at location 6 was largely ammonium picrate.

Results from location 7 were not used because the

major portion of the soils at this location were

stones, and about 50% by weight of each sample

processed in the field was eliminated prior to

laboratory analysis, thereby introducing a large

bias between methods.

Correlations of the results from the six locations are presented in Figures 8 and 9. The results

for the means of duplicates for the seven discrete

samples at each of the six sampling locations show

a very strong correlation between the on-site and

laboratory results (r = 0.979), with a slope of the

best fit linear regression line of 0.867 (Fig. 8). Because this plot includes concentration data, in

which the numerical values cover about five orders of magnitude, it is difficult to see the correlation for low-concentration data in Figure 8. Thus,

we plotted the on-site vs. lab data on a log-log

basis as well so that the characteristics of the relationship can be seen equivalently at different absolute concentrations (Fig. 9). Clearly, the log-log

plot shows that the linear relationship between

on-site and lab results is very strong for lab values above a log value of about 0.6 (concentration

about 4 μg/g). Data below this value are all from

sampling location 3, and it is not clear whether

the poor correlation for these low-concentration

30

20

10

0 20 30

Laboratory Results (μg/g)

On-site Results (μg/g)

r = 0.979

Slope = 0.867

y-intercept = 282

10 40 x 103

40 x 103

Figure 8. Untransformed TNT concentrations from sampling locations 1, 3, 4,

5, 8, 9—linear model with intercept.

y

32
samples is specific to location 3 or is simply due

to inaccuracy of the method at very low concentrations.

Figure 10 presents the results of a correlation

of on-site vs. lab results for the composites for

these same six sampling locations. For the composites, each point represents a mean of seven onsite and seven lab determinations. The on-site

and lab data were even more strongly correlated

for the composites (r = 0.989) and the slope of the

best fit linear relationship was 0.999. In both cases

the correlation coefficients for the best fit linear

relationships with zero intercept were equal to

those with non-zero intercept, which we interpret

to mean that the y-intercepts were not significantly different from zero and that the slope (of

the zero intercept line) can be considered an overall measure of the accuracy of the field method

relative to the lab method. Using this interpretation and the computed slopes from the zero intercept models, we found the accuracy across these

six sampling locations at three different installations, with concentrations varying from near the

detection limit of 1 μg/g to over 40,000 μg/g, to be

4

3

2

1

0

5

2 3 45

Laboratory Results (log μg/g)

On-site Results (log μg/g)

r = 0.988

Slope = 0.919

y-intercept = 0.241

0 1

Figure 9. Log-transformed TNT concentrations from sampling locations 1,

3, 4, 5, 8, 9—linear model with intercept.

Laboratory Results (μg/g)

On-site Results (μg/g)

r = 0.989

Slope = 0.999

y-intercept = 69.3

4,000 8,000 12,000 16,000

12

8

4

0

16 x 103

Figure 10. Untransformed TNT concentrations for composites from sampling

locations 1, 3, 4, 5, 8, 9—linear model with intercept.

y

y

33
either 87.6% for the discrete samples or 100.5%

for the composites. Clearly, use of the TNT colorimetric method, with this degree of accuracy, is

justified with nearly any conceivable data quality

objective, but particularly where we have direct

evidence of the short range heterogeneity present

in soils concentrations at these locations.

On-site results for 2,4-DNT were only available for sampling location 2 at the Monite site.

These results correlate well with laboratory analyses (Fig. 5) but the accuracy is not nearly as good

as that for TNT. Results are adequate for mapping analyte distributions, selecting samples for

more quantitative laboratory analysis and locating areas of high concentration. On-site results

may not be adequate for making decisions in the

field about concentrations necessary for action

levels.

The data obtained for the ammonium picrate

on-site method for sampling location 6 at

Hawthorne AAP are the first validation results

for the method developed by Thorne and Jenkins

(1995). These results were very encouraging and

it appears that this method may be as accurate,

relative to the lab method, as the on-site TNT

method.

The data from this study can also be used to

put in perspective the uncertainty introduced in

results by analysis vs. that from sampling. In doing so we must keep in mind that the goal of site

characterization is to provide data that can be

used to make decisions on whether the degree of

contamination for a given area warrants a cleanup

action. Although random grab sampling is appealing cost-wise, it may be totally inadequate

for decisions about remedial procedures. To provide data that can satisfy this need with a high

level of confidence, total error associated with

site characterization must be understood and reduced to acceptable levels. Little or no information has been available where the components of

error have been quantified for soil characterization at explosives-contaminated sites.

For some of the nine sampling locations studied here, analyte distribution exhibited such extremes that use of classical normal distribution

statistics to fractionate the error was not possible.

For locations 4, 5, 7, 7R and 9, however, we were

able to fractionate the total error variances because concentration variations were modest (Table

10). For these four locations, standard deviations

attributable to analysis were always much lower

than the corresponding standard deviations from

sampling and, hence, total error was dominated

by sampling error. This was true whether characterization was done using field analysis or laboratory analysis. For the other sampling locations,

sampling error was even greater and so overwhelmed analytical error that this type of fractionation would only be possible using asymmetric (logarithmic) limits. Clearly, if we want to

significantly improve the quality of site characterization data, the major effort should be placed

on reducing sampling error. Single grab samples

are totally inadequate.

To reduce sampling error, samples analyzed

must be more representative of average concentrations within the area that the sample is supposed to represent than is possible using discrete

grab samples. For the data here, if we assume that

the mean analyte concentration of the seven

samples taken from this circle with 122 cm diameter is the “true” concentration, we can assess the

difficulty in achieving representativeness by looking at the ratio of highest to lowest values in the

group of seven mean determinations. These ratios are presented in Table 11 under the heading

of local heterogeneity. These values range from

3.8 to 243 for the on-site TNT method and 3.0 to

315 for the lab method. Much larger grids than

Table 10. Fractionation of total error into analytical and sampling components.

Standard deviation Ratio

Analytical Sampling Sampling/analytical

Sampling location On-site Lab On-site Lab On-site Lab

Hawthorne location 4 217 265 1,970 2,150 9.1 8.1

Hawthorne location 5 5.3 11.0 121 131 22.8 11.9

Volunteer location 7 —* 7,680 —* 19,800 —* 2.6

Volunteer location 7R 5,120 6,320 24,700 27,600 6.1 4.4

Volunteer location 9 1.0 1.0 10.4 12.4 10.4 12.4

* Data unavailable.

34
the areas we sampled are typically used for site

characterization and this would only serve to further increase uncertainties from sampling.

Analysis of composite samples, however, gave

results that were good estimates of the mean of

the seven discrete samples, with a low standard

deviation (Table 12). It is also useful to note that

standard deviations for the on-site analysis of all

of the composite samples are low relative to mean

concentration (low RSDs), indicating that in-field

homogenization procedures used were adequate.

Thus, the number of analyses of the composite

Table 11. Comparison of measures of analytical precision, accuracy and discrete sample

representativeness.

Precision Accuracy Local heterogeneity

Largest Slope of Ratio of highest mean

concentration ratio 0-intercept concentration vs. lowest

Sample RSD of duplicates of duplicates model for discrete samples

location On-site Lab On-site Lab On-site vs. lab On-site Lab

1 3.9 11.1 1.157 1.473 0.815 243 315

2 (DNT) 23.0 10.0 1.655 1.461 0.350 10.6 33.4

3 16.7 6.5 1.822 1.186 1.464 50.0 98.1

4 12.5 13.5 1.696 1.986 0.911 69.0 58.1

5 3.3 4.9 1.126 1.157 0.847 28.9 29.5

6 (Picrate) 11.6 11.9 1.500 1.875 0.967 688 43,000

7R 4.9 5.1 1.265 1.214 0.677 3.8 3.0

8 19.7 4.5 1.731 1.185 1.070 53.1 55.6

9 4.1 5.1 1.131 1.167 1.032 8.2 5.7

Mean

(TNT only) 9.3 7.2 1.418 1.338 0.974 65.1 80.7

Table 12. Comparison of results for discrete and composite soil analysis.

Discrete Composite

Sampling Major On-site samples samples

Installation location analyte or lab mean ± SD* mean ± SD

Monite 1 TNT O 13,500 ± 16,800 13,100 ± 532

L 16,300 ± 20,200 14,100 ± 1,420

Monite 2 DNT O 16,100 ± 11,700 23,800 ± 3,140

L 34,800 ± 42,200 33,600 ± 2,390

Monite 3 TNT O 19.8 ± 42.0 12.6 ± 1.2

L 12.9 ± 29.0 4.16 ± 0.7

Hawthorne 4 TNT O 1,970 ± 1,980 1,750 ± 178

L 2,160 ± 2,160 2,000 ± 298

Hawthorne 5 TNT O 156 ± 121 139 ± 16.6

L 168 ± 131 193 ± 7.7

Hawthorne 6 Ammonium O 869 ± 1,600 970 ± 32

Picrate L 901 ± 1,660 1,010 ± 92

Volunteer 7 TNT O 84,900 ± 33,400 57,000 ± 2,600

L 89,100 ± 20,500 107,000 ± 9,230

Volunteer 7R TNT O 57,500 ± 25,000 54,800 ± 5,840

L 86,900 ± 27,900 107,000 ± 7,520

Volunteer 8 TNT O 9,920 ± 12,000 11,300 ± 2,020

L 8,910 ± 11,600 9,620 ± 409

Volunteer 9 TNT O 13.7 ± 10.4 16.6 ± 1.5

L 13.0 ± 10.3 11.8 ± 0.3

* The discrete sample standard deviations for locations 1, 2, 3, 6 and 8 are all larger than their corresponding

means because the results from these locations are not normally distributed. These results may be lognormally distributed, in which case the data should be transformed.

35
required to produce data with a high degree of

confidence is low. Characterization using a combination of composite sampling, adequate in-field

sample homogenization and on-site colorimetric

analysis, is an efficient method of producing data

that are not only accurate and precise, but are also

representative of the area.

APPLICATION OF RESULTS

The results presented here have several unifying themes that can be applied in designing future investigations of munitions-contaminated

sites. First, it is clear that there was extreme heterogeneity at all sampling locations. A single

sample from any of the 122-cm-diameter circles

could differ by orders of magnitude from the mean

concentration of the small area sampled. Relative

standard deviations (RSDs) for the seven discrete

samples were often greater than 100%.

A second consistent finding was that composite samples of the seven discrete samples could be

reliably homogenized and subsampled in the field.

This also opens the possibility of compositing discrete samples representing a larger area if concentration variations suggest that this approach

would be desirable. Most important, it permits

field processing without elaborate apparatus.

Another major finding was that the specificity

and accuracy of the TNT on-site method was quite

adequate. The two locations where TNT was not

the major contaminant were readily identified and

the seven locations where TNT appeared to be

the primary contaminant were confirmed by the

reference HPLC method. The on-site concentration estimates agreed very well with laboratory

estimates, except for location 7, where major bias

was introduced by removing small stones during

the grinding operation. For the other six TNT

locations, the agreement shown in Figures 9 and

10 was excellent. Admittedly, there were small

but statistically significant differences in concentration estimates at some locations, but their magnitude was insufficient to impart meaningful differences in conclusions. Of course, each site should

include some reference laboratory analyses to validate the on-site analyses.

For location 2, where DNT was the major contaminant, there was a rather large bias between

on-site and laboratory results. This was not unexpected since the on-site DNT method is not as

reliable as the TNT method. On-site and laboratory results for ammonium picrate at location 6

were generally in good agreement but more results from other sites are needed.

Perhaps the most surprising finding was the

consistency of the overall precision of results for

TNT. For the seven locations where TNT was the

primary contaminant, average RSDs for duplicate subsamples using the on-site method with

the discrete samples ranged from 3.9 to 19.7%,

with a mean value of 9.3%. Comparable laboratory results yielded RSDs from 4.6 to 13.5% with

a mean value of 7.2%. Replicate analyses of composites produced RSDs ranging from 4.1 to 17.9%

(pooled = 10.6%) for on-site results and 2.8 to

15.9% (pooled = 9.6%) for laboratory analyses.

The estimates are approximately equal for composites despite the extra mixing step, probably

because the wide concentration variations of discrete samples required large differences in dilutions and the ten-times larger sample size used in

the on-site analysis. Nonetheless, the consistency

of the pooled estimates is both surprising and

reassuring. We believe that it is fair to claim that

subsampling and analysis (SA) typically yields

RSDs of about 10% for both field and laboratory

methods and that extremes of 5 to 20% are to be

expected. Compared to the RSDs for sampling,

these precision estimates represent very acceptable levels.

Compositing is an effective way to reduce intersample variance caused by the heterogeneous

distribution of contaminants. The total variance

for the formation and analysis of composites can

be expressed as

 

C

C

n

C

k T

2 S A

2 2

= +

where CT = total percent relative standard deviation

CS = percent relative standard deviations

of sampling

CA = percent relative standard deviations

of analysis

n = number of discrete samples formed

into a composite

k = number of replicate analyses done

on the composite.

In Table 13 we show values of CT for various

combinations of CS, CA, n and k. The values chosen for CS and CA are typical of those found here

for field or laboratory analyses of TNT. There

would be nothing to prevent using larger values

of n, but there is no benefit in using larger values

36
of k given the relationship of CS to CA. If desired,

plots of CT vs. n could be formed for various

values of CS, CA and k. We should also remember

that the values of CT are for a single composite.

Uncertainty in a mean of several composites

would be reduced by 

1 N where N is the number of composites averaged.

Table 13 very obviously shows that improved

reliability of concentration estimates can only be

realized by reducing the magnitude of CS relative

to CA. On-site analysis is just as reliable as laboratory analysis for TNT in surface soils, and the

analysis step doesn’t contribute much error anyway. When we look at the cost estimates (Table

13) for on-site vs. laboratory analysis and combine that with the fast turnaround of on-site analysis, the advantages of field analysis are clear. In

arriving at the cost of on-site analyses, all materials and their disposal were included along with

capital equipment costs and labor. An allowance

was also made for 10% of the samples to be sent

for laboratory analysis. Clearly, the cost of

compositing is relatively small compared to the

benefits. Unless CS is much lower than found for

the sites studied so far, there is no justification for

performing replicate analyses of composites.

The approach to a new site should involve a

preliminary field survey to obtain information on

the magnitude of both short- and long-range heterogeneity. From these results, a flexible sampling

plan would evolve with the understanding that it

was subject to modifications (if necessary) as results accumulate. It is our intention to conduct

one or more such studies (demonstration projects)

as the next phase of this research.

LITERATURE CITED

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Table 13. Dependence of total percent relative standard deviation (CT) on

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Number of Number of Percent relative

samples replicate standard deviations

composited analyses Sampling Analysis Total Cost of procedure ($)

(n) (k) (CS) (CA) (CT) On-site Lab

1 1 50 10 51.0 81 337

4 1 50 10 26.9 86 342

7 1 50 10 21.4 90 347

7 2 50 10 20.2 166 680

1 1 100 10 100.5 81 337

4 1 100 10 51.0 86 342

7 1 100 10 39.1 90 347

7 2 100 10 38.5 166 680

1 1 150 10 150 81 337

7 1 150 10 57.6 90 347

7 2 150 10 57.1 166 680

1 1 100 5 100 81 337

7 1 100 5 38.1 90 347

7 2 100 5 38.0 166 680

1 1 50 20 53.9 81 337

7 1 50 20 27.5 90 347

7 2 50 20 23.6 166 680

7 1 100 20 42.8 90 347

7 2 100 20 40.4 166 680

37
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August 1996

Assessment of Sampling Error Associated with Collection and

Analysis of Soil Samples at Explosives-Contaminated Sites

Thomas F. Jenkins, Clarence L. Grant, Gurdarshan S. Brar,

Philip G. Thorne, Thomas A. Ranney and Patricia W. Schumacher

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road Special Report 96-15

Hanover, New Hampshire 03755-1290

U.S. Army Environmental Center

Aberdeen Proving Ground, Maryland 21010-5401 SFIM-AEC-ET-CR-96157

Approved for public release; distribution is unlimited.

Available from NTIS, Springfield, Virginia 22161

Ammonium picrate DNT Heterogeneity Soil 47

Analytical error Explosives On-site analysis TNT

Colorimetric methods Field screening Sampling error

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

This study is an assessment of short-range heterogeneity in contaminant concentrations within surface soils at

explosives-contaminated sites. Intensive sampling was conducted over short distances. Discrete and composite

samples were analyzed by both on-site colorimetric methods and standard laboratory protocols. Three locations

were sampled at each of three installations and the results used to estimate the relative contributions of analytical

error and sampling error to the total uncertainty. The major contaminant at seven of the nine sampling locations

was TNT; results from the on-site colorimetric method were in excellent agreement with laboratory results using

SW846 Method 8330. DNT and ammonium picrate were the contaminants present at the highest concentration in

the other two locations. For four sampling locations, short-range concentration variations were modest and

analyte distribution was sufficiently Gaussian to apply normal distribution statistics to fractionate the total error

variances. For these four locations, analysis standard deviations were always much lower than the sampling

standard deviations; total error was dominated by sampling error, whether characterization was done using onsite or laboratory analysis. The other five sampling locations had enormous short-range heterogeneity and

sampling error overwhelmed analytical error. To improve the quality of site characterization data, emphasis

should be placed on reducing sampling error by the use of composite sampling strategies. Characterization of

explosives-contaminated sites using composite sampling, in-field sample homogenization, and on-site analysis is

an efficient method of producing data that are accurate and precise, and also representative of the area.

For conversion of SI units to non-SI units of measurement consult ASTM Standard E380-93, Standard Practice for Use of the

International System of Units, published by the American Society for Testing and Materials, 1916 Race St., Philadelphia, Pa.

19103.