marianne e. walsh and michael r. walsh charles a. ramsey

Marianne E. Walsh and Michael R. Walsh

Charles A. Ramsey

• Live-fire of high explosive ordnance onto repeatedly-used training ranges

• Potential accumulation of energetic residues

• Source for groundwater contamination and off-site migration

Nitramines: RDX, HMX

Nitroaromatics: TNT

Comp B (RDX/TNT)

Nuggets of C4 (RDX)

105-mm Howitzer

Fibers 0.4 to 7.5 mm long containing 2,4-DNT

Anti-tank Rocket (AT-4)

38% of propellant residue mass is NG

NO 2

CH 3

NO 2

HC-O-NO2

H2C-O-NO2

H2C-O-NO2

2,4-Dinitrotoluene (2,4-DNT)

Nitroglycerin (NG)

• The sampling procedure must minimize the error due to the heterogeneous sizes, compositional variability, and spatial distribution of the energetic particles.

• Samples must have sufficient mass to include all constituents in the same proportions as the soil surface

• Multi-increment samples composed of a minimum of 50 soil aliquots.

How Much Mass is Enough?

http://www.epa.gov/osw/hazard/testmethods/sw846/new_meth.htm#8330B

At the analytical lab, a small mass of soil is used to estimate the mean concentration in the field sample that is likely to be a kilogram or more, which in turn ideally represents the mean concentration at the field site.

Decisions are made about tons of soil based on a concentration estimate from a few grams of soil.

Air-dry Sieve using 2-mm mesh Particle size reduction

Grind for the appropriate amount of time without heating the sample

Subsample Many increments (>30) through the thickness of the

sample

Solvent extraction with acetonitrile Analysis using HPLC-UV

• Drying arrests microbial activity and enhances further processing prior to subsampling

• Oven drying not acceptable due to thermal degradation and/or sublimation of semi-volatile analytes

• Analyte concentrations in field-contaminated air-dried soils are stable at room-temperature.

Soil Initial

Processing

Date 1st

Analyzed

1st Conc.

Estimates*

(mg/kg)

2005 Results*†

mg/kg

Milan AAP 10 Mesh sieve

1999 RDX 23 ± 10

HMX 4 ± 1

RDX 29 ± 0.3

HMX 6.6 ± 0.1

Volunteer

AAP

Manual grind,

30 mesh sieve 1995

TNT 10.5 ± 0.3

DNT 1.4 ± 0.04

TNT 10.2 ± 0.3

DNT 2.7 ± 0.08

Fort Lewis

Hand

Grenade

Range

None 2001

Co-located sample

RDX 3.8 ± 1.8

HMX 1.0 ± 0.24

TNT 1.4 ± 0.88

Co-located sample

RDX 3.8 ± 0.08

HMX 0.95 ± 0.01

TNT 0.96 ± 0.05

* n ≥ 3 † Samples mechanically ground

• EPA SW-846 Method 8330 specified a 2-g subsample of a soil sample that has been manually ground with a mortar and pestle to pass through a #30-mesh (0.595 mm) sieve.

• Is this sieve size appropriate for training range soils?

Size Fraction Soil RDX TNT

>2 mm (#10-mesh) 257 g (21%) 6.2 µg (0.3%) 58 µg (0.8%)

>0.595 mm and < 2 mm 243 g (20%) 1,540 µg (66%) 5130 µg (74%)

<0.595 mm (#30-mesh) 713 g (59%) 786 µg (34%) 1,780 (26%)

>2 mm 188 g (17%) 4.3 µg (1.1%) 67 µg (5.6%)

>0.595 mm and < 2 mm 212 g (19%) 151 µg (40%) 708 µg (59%)

<0.595 mm 711 g (64%) 224 µg (59%) 420 µg (35%)

>2 mm 239 (14%) 7.2 µg (0.2%) 23 µg (1.8%)

>0.595 mm and < 2 mm 302 (18%) 2,050 µg (49%) 1,024 µg (77%)

<0.595 mm 1,183 (69%) 2,110 µg (51%) 275 µg (21%)

Size Fractionation of Three Soils from a Hand Grenade Range

Mass in Fraction (% of Total Mass)

Size Fraction Soil 2,4-DNT

>2 mm 1,870 g (44%) <d (0%)

>0.595 mm and < 2 mm 800 g (19%) 1,510 µg (69%)

<0.595 mm 1,610 g (38%) 680 µg (31%)

>2 mm 1,260 g (43%) <d (0%)

>0.595 mm and < 2 mm 500 g (17%) 1,650 µg (73%)

<0.595 mm 1,160 g (40%) 600 µg (27%)

>2 mm 1,600 g (43%) <d (0%)

>0.595 mm and < 2 mm 610 g (17%) 780 µg (61%)

<0.595 mm 1,470 g (40%) 500 µg (39%)

Size Fractionation of Three Soils from a 105-mm Firing Point

Mass in Fraction (% of Total Mass)

RDX Conc. (mg/kg) TNT Conc. (mg/kg)

Subsample 2-g 50-g 2-g 50-g

1 2.36 1.68 0.39 0.25

2 0.98 1.77 0.48 1.81

3 4.26 1.46 0.37 0.37

4 2.08 3.80 0.41 1.48

5 2.85 7.83 28.6 7.93

6 1.65 1.81 0.48 0.56

7 1.24 2.35 0.45 0.35

8 2.30 2.51 0.68 0.75

9 1.23 2.08 0.77 0.56

10 8.49 1.98 1.08 0.35

11 2.28 1.68 0.77 0.62

12 2.62 13.0 0.47 5.62

Particle Size Reduction by Machine Grinding on a Puck Mill

• The multi-increment sample will contain very few energetic particles or propellant fibers compared to the total soil matrix.

• Grinding reduces the particle size of the course soil to the texture of flour (<75 μm) and vastly increases the number of particles.

RDX Conc. (mg/kg) TNT Conc. (mg/kg)

Subsample Not Ground Ground Not Ground Ground

1 1.68 4.75 0.25 2.03

2 1.77 4.71 1.81 2.04

3 1.46 4.80 0.37 2.00

4 3.80 4.73 1.48 2.03

5 7.83 4.67 7.93 1.97

6 1.81 4.66 0.56 2.00

7 2.35 4.62 0.35 1.90

8 2.51 4.62 0.75 2.02

9 2.08 4.64 0.56 1.97

10 1.98 4.69 0.35 1.98

11 1.68 4.66 0.62 1.90

12 13.0 4.60 5.62 1.91

*50-g subsamples.

Subsampling Variance following Grinding for 60 s of Training Range Soils

Concentration (mg/kg)

Training Range Analyte Lab Rep 1 Lab Rep 2 Lap Rep 3 RSD

Hand Grenade

(10-g subsamples)

HMX 1.68 1.66 1.61 2.1%

RDX 10.9 10.6 10.4 2.4%

TNT 1.32 1.28 1.18 5.6%

Anti-Tank

(10-g subsamples)

HMX 410 382 404 3.7%

TNT 5.02 4.68 4.98 3.8%

NG 0.57 0.45 0.83 32%

Artillery/Mortar Impact

Area

(10-g subsamples)

HMX 1.49 1.44 1.48 1.8%

RDX 12.8 12.5 13.0 2.0%

TNT 4.78 4.86 4.80 0.86%

105-mm Firing Point

(60-g subsamples)

2,4-DNT 0.35 0.41 0.66 35%

2,4-DNT 1.1 0.61 2.34 66%

Fibers 9% DNT

1 m

m

120-mm Mortar

Flakes 36% NG

Rings or fragments 10% NG

Nitrocellulose propellant is fibrous and does not disaggregate like crystalline explosives. Soils must be ground for five 60-s cycles

Slide courtesy of Larry Penfold, TestAmerica

Subsampling and Solvent Extraction of Machine-Ground Soils Containing Energetics

Sonic Bath

Shaker Table

Yes, if the sample is processed correctly!

Concentration (mg/kg) Soil from a Demolition Training Range Mass (g) Extracted HMX RDX 2,4-DNT 10 g (Rep 1) 1.98 11.7 4.6 10 g (Rep 2) 2.00 11.6 4.9 10 g (Rep 3) 1.98 11.8 5.2 1770 g (Rest of sample) 2.02 11.9 4.8 Soil from an Artillery Impact Area Mass (g) Extracted HMX RDX TNT 10 g (Rep 1) 2.72 14.1 1.60 10 g (Rep 2) 2.72 14.1 1.60 10 g (Rep 3) 2.60 13.9 1.63 1300 g (Rest of sample) 2.76 14.3 1.56

Air-drying Isolate high concentration samples to prevent cross contamination

Sieving Use appropriate mesh size

No Splitting Process entire sample

Particle size reduction Grind for the appropriate amount of time without heating the sample

Subsampling Take many increments (>30) through the thickness of the sample

Solvent extraction Shaker table extraction is an acceptable alternative to the sonic bath extraction Some soils (clays) may require extended (>18 hrs) extraction time

Lab Analytical Methods

•Method 8330 (Nitroaromatics and Nitramines by High Performance Liquid Chromatography (HPLC))

- UV Detector (update of method will incorporate MS) - Detection limits around 0.05 mg/kg •Method 8095 (Nitroaromatics and Nitramines by Gas

Chromatograph(GC)) - Electron Capture Detector - Detection limits less than 0.010 mg/kg for TNT and RDX

Sample processing is the same for both methods.

HPLC-UV Instrumentation

Column: Waters Nova-Pak C8

60Å 4µm

3.9 X 150mm

Eluent: 1.4 mL/min

15:85 2-Propanol:Water

28°C

Detector:

ThermoSeparations Products

Spectra System UV2000

Dual Wavelength

254 nm and 210 nm

Chromatogram (HPLC-UV) Calibration Standard

HPLC-UV Chromatograms from a Multi-increment Sample†: Duplicate 10-g Subsamples

†Sample Mass: 1860 g

HMX 2.1 mg/kg

RDX 10 mg/kg

TNT 2.7 mg/kg

HMX 2.0 mg/kg

RDX 10 mg/kg

TNT 2.6 mg/kg

HMX

RDX

TNT HMX

RDX

TNT

Peak heights for HMX, RDX, and TNT are almost identical in the two chromatograms

Chromatogram (GC-µECD) Calibration Standard

0

1000

2000

3000

4000

5000

6000

0 2 4 6 8 10 12 14

Sig

nal

(Hz)

Time (min)

NB

NG

1,3

-DN

B2

,6-D

NT

2,4

-DN

T

TN

BT

NT

PE

TN

RD

X

4-A

m-D

NT 2

-Am

-DN

T

Tetr

yl

HM

X

NT

s

100 µg/L Standard

3,5

-DN

A

Chromatogram (GC-µECD) 81-mm Mortar Impact Area

500

1,000

1,500

2,000

2,500

5 10 15

Time (min)

Sig

nal (H

z)

RD

X (

95 µ

g/k

g)

HM

X (

620 µ

g/k

g)

HPLC-UV More rugged

Better reproducibility (smaller analytical error)

GC-ECD Lower detection limits for most analytes

Determination of nitramines and nitrate esters requires

constant injector maintenance

Appropriate for soils with explosives concentrations

ranging from 1 to 100 µg/kg

Good method for confirmation, but not rugged

•The entire sample received by an analytical lab must be processed (not just a small portion off the top).

•Field sampling and laboratory subsampling error cannot be ignored.

•Appropriate analytical method must be used. Standard methods for semi-volatiles ARE NOT appropriate for explosives and propellants.

•New methods and procedures need to be verified using field soils.

Tons of Soil 3 mg/kg RDX

Kilograms of Soil 3 mg/kg RDX

10 g of soil 3 mg/kg RDX

100 µL of solvent analyzed

Solvent Extraction 0.03 mg RDX