Energetic Residue Observations for Operational ... - ACS Publications

Chapter 6

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Energetic Residue Observations for Operational Ranges J. L. Clausen* US Army Corps of Engineers, Engineer Research and Development Center, Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, NH 03257 *[email protected]

Over the past 20 years the US Army Corps of Engineers (USACE) Engineer Research and Development Center (ERDC) Cold Regions Research and Engineering Laboratory (CRREL), USACE – ERDC – Environmental Laboratory (EL), US Army Public Health Command, Defense Research Establishment Valcartier - Canada, and various contractors have been engaged in the assessment of operational military ranges in the US and Canada to understand the extent of energetic residues derived from training. Surface soil sampling conducted at over 30 military installations has been the primary means of assessing the ranges. In addition to surface soil sampling, other media types have been assessed to a lesser degree including subsurface soil, surface water (including snow), storm water runoff, vadose zone pore-water, and groundwater. The primary focus of previous assessments has been on Army ranges; however a number of Air Force and Navy ranges have been studied. Samples were collected at open burn/open detonatiom (OB/OD) areas, firing points, and impact areas. Ranges were further subdivided depending on the type of weapon system being trained with, such as artillery, mortar, rocket, bombs, grenade, and small arms. The research has led to the identification of several energetic compounds typically present on operational ranges including 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), perchlorate, dinitrotoluene (DNT), nitroglycerin (NG), © 2011 American Chemical Society

try of Explosives and Propellant Compounds in Soils and Marine Systems: Distributed Source Characterization and Remedial Technolo ACS Symposium Series; American Chemical Society: Washington, DC, 2011.

pentaerythritol tetranite (PETN) and associated transformation products of TNT.


Introduction Military testing and training ranges are vital for preparing military troops for combat and maintaining readiness. In the late 1990s, energetic residues in soil and groundwater were found at Camp Edwards, MA. One of the questions raised was whether the presence of the energetic compounds at Camp Edwards was the norm or an atypical occurrence. The question is important because the Army, Navy and Air Force use munitions on an annual basis that collectively contain millions of pounds of RDX, HMX, TNT, and perchlorate (1). Prior to the 1990s, the assumption based on physical and chemical models was that greater than 99.999% of the energetic material used in munitions was consumed in the firing or detonation process. Sudies over the past two decades at military ranges demonstrate the presence of energetic compounds in surface soils (2–11). Further, these studies confirmed that under ideal conditions a large percentage of the energetic material is consumed during detonation. However, these studies also demonstrated field conditions are not always ideal and consequently not all munitions undergo a high-order detonation, thereby consuming the explosive material. In fact, a percentage of munitions undergo a partial detonation or loworder detonation, whereby only a portion of the energetic material is consumed in the detonation reaction. The remainder of the energetic material is scattered in the environment as particulate residues (3, 12–14) in an extremely heterogeneous manner (15–18). The percentage of loworder detonations is dependent on the ordnance type as well as environmental and human factors during training. It is also recognized that undetonated ordnance items on military ranges, unexploded ordnance (UXO), can be sympathetically detonated when a high- order detonation occurs nearby. In addition, burning of excess propellant for artillery and mortar weapons systems is an inefficient combustion process resulting in a large amount of propellant residue deposited into the environment. Consequently, open burn/open detonation (OB/OD) sites can have some of the highest concentrations of propellant residues. Additionally, open detonation of UXO or training activities with high explosives can result in very high concentration of explosive compounds. The types of energetic compounds present on military ranges and their associated fate and transport properties are important to the Department of Defense (DoD) because DoD has responsibility for 1,400 sites across the US where munitions containing energetic compounds have been used (19). Energetic residues may be a persistent source of soil and groundwater contamination and thus their presence is a potential concern for the DoD (10). Consequently, over the past several decades CRREL has been involved with the study of energetic compounds to determine what constituents are present and the concentration levels for specific types of training ranges. To date, studies have been conducted at over 30 different military installations (Army, Air Force, and Navy) in the US 108



and Canada (Figure 1). These studies have involved assessments at both firing points and impact areas for bombing, artillery/mortar, anti-tank rocket, tank, rifle-grenade, grenade, small arms, and demolition ranges. Limited subsurface soil sampling has been conducted as well as vadose zone monitoring with tension lysimeters.

Figure 1. Training and test ranges studied in the US and Canada by CRREL.

Firing Points Military training involves the firing of weapon systems that utilize energetic materials, such as solid propellants, to propel a projectile toward the target. There are three classes of propellants; single-base, double-base, and triple-base. The typical propellant formulations include a double-base formulation with nitrocellulose (NC) and either nitroglycerin (NG), DNT, or triple-base with NC, nitroguanidine (NQ), and NG (Table I). Single-base propellant consists of NC with DNT in some formulations. Historically, NG and DNTs were not considered threats to groundwater because they were believed to be too unstable to leach significantly. However, the regulators overseeing the actives at Camp Edwards, MA continue to demonstrate a high level of concern regarding NG and the DNTs. This concern has persisted because these compounds have been detected in surface soils at small arms ranges, artillery and mortar, and anti-tank firing positions. Interest in the migration of NG and the DNTs also has increased because recent field studies have found higher concentrations than previously measured (3, 20, 21) and have described NG as being “mobile in soil environments” (22). Concentrations up to 242 mg/kg 109



have been reported in the Central Impact Area at Camp Edwards, MA and more than 1 mg/kg has been found on various other MMR (Massachusetts Military Reservation) training ranges. At Canadian Forces Base (CFB) Valcartier Arnhem, anti-tank rocket range surface soils had NG concentrations of nearly 2,000 mg/kg 5 m behind the rocket firing line and over 100 mg/kg 25 m behind the firing line (23). A rocket firing range at CFB Gagetown was described as having NG concentrations over 1% near the firing location (23). Another study reported NG in all composite, and in several discrete samples, collected near the target area of an anti-tank range (11). Other constituents possibly present in the environment are burn rate modifiers, binders, plasticizers, and stabilizers. Two of the stabilizers used in propellant formulations are energetic materials and these include ethyl centralite (diethyl diphenyl urea) and akardites (methyl diphenyl urea). One of the plasticizers, diethylene glycol dinitrate (DEGDN) is also an energetic compound. The primary energetic compounds, oxidizers, and energetic binders constitute the largest mass in the propellant (60 to 90 percent by weight) followed by 5 to 25 percent for the plasticizers and binders, with stabilizers and other compounds making less than 5 percent (24). Solid propellants used in rocket fuel may have an oxidizer, such as ammonium perchlorate, HMX, a metal, and binder. The exact propellant formulation is dependent upon the weapon system and ordnance being used. Single base propellants are used with many artillery, tank, and small-arms nunitions. Double-base is the predominant class used in most ordnance. Triple-base is used with some of the larger artillery and tank weapons systems. Most ordnance utilizes a primer and two of the energetic compounds commonly used are pentaerythritol tetranitrate (PETN) and diazodinitrophenol (DDNP). In general, the firing points can be separated by use of the following types of weapon systems utilized; artillery and mortar, anti-tank rocket, rifle- grenade, and small arms. Artillery and Mortar Artillery and mortar firing positions are located around the periphery of an impact area and can vary in size from less than an acre to several acres or more. The firing location is typically cleared of trees and small vegetation and depending on the level of training the soil can be highly disturbed. At artillery and mortar firing positions, two sources of propellant materials exist; residue generated from the firing of the weapon system and residue from the burning of excess propellant charges on the ground surface. Following training with artillery and mortar weapon systems, there is often a large quantity of unused propellant remaining resulting from the lack of need for the full propellant charge supplied. The general practice is to destroy this unused material in the field by piling up the material or laying it in a line on top of the soil and igniting it. Sometimes it may be collected and burned in a burning pan. The principal propellants used with artillery and mortar munitions are types M1, M2, and M3 which contain some mixture of NC, NG, or DNT. Nitrocellulose is the primary constituent, with 0 to 43 percent of NG by weight as the secondary constituent. 110


Table I. Propellant classes with common formulations


Propellant Type

Uses

Examples

Principal ingredients

Single base

Small arms to cannons

M1 M6 M10

NC, 2,4-DNT NC, 2,4-DNT NC, diphenylamine

Double base

Multiple applications

M2 M5 M8

NC, NG, ethyl centralite NC, NG, ethyl centralite NC, NG, diethyl phthalate

Triple base

Large caliber guns

M30 M31

NC, NG, NQ, ethyl centralite NC, NG, NQ, ethyl centralite

Composite

Rockets and missiles

Class 1.3

Ammonium perchlorate, Al, HTPBa

CMDBb

Rockets and missiles

Class 1.1

NC, NG, Ammonium perchlorate, Al, HMX, HTPB

a

HTPB – hydroxyl-terminated polybutadiene base

b

CMDB – composite modified double

Numerous characterization efforts conducted at a variety of ranges demonstrate that propellants are not completely consumed during live-fire training exercises and result in surface soil contamination (3, 10, 11, 25–34). The mass of residue deposited by artillery and mortar weapon system has been measured (20, 35–45) and this material can be significant (40, 45). Significant levels of propellant residues are also produced during open burning of excess propellant (44, 46). The levels observed were in excess of those resulting from fallout from the firing of the weapon system. The principal energetics introduced to the environment during artillery and mortar training are 2,4-DNT, 2,6-DNT, and NG. The levels of these compounds observed in surface soil range from concentrations near the analytical detection limit (using EPA Method 8330B) to thousands of mg/kg (Table II). The higher NG and DNT concentrations were observed at sites where excess propellant burning occurred. In general, the concentrations of NG and DNT observed at artillery and mortar firing points is less than that observed at anti-tank firing points. Nitroguanidine (NQ) is only used in triple-based propellants, which also contain NC and NG. The M30 propellant mixture for the 105-mm projectile is a triple-based propellant. This mixture is intended for firing the projectile over long distances. Many of the military ranges in the US have limited space, therefore NQ is not widely utilized. Although NQ presence has only been assessed at a small number of sites it has been detected in surface soil. The detections shown in Table II occurred at 2 of the 11 sites studied. These were the only two sites with triple-base propellant use.

111


Analyte

HMX

RDX

TNT

2,4-DNT

2,6-DNT

Tetryl

NG

NQ

Min

0.017

0.009

0.004

0.0007

0.04

10

0

880

Max

302

186

5,600

237,000

4,840

24

11,290,000

2,350

Mean

118

34

0.049

0.87

102

18

11

1,940

Median

133

43

88

6,691

370

17

135,393

1,861

Detections

21

9

155

415

62

5

89

27

# Samples

577

577

577

577

577

577

577

577

# Installations

11

11

11

11

11

11

11

11

112


Table II. Energetic residues (mg/kg) detected in surface soil at artillery and mortar firing points studied from 2000 to 2010 by CRREL

In Environmental Chemistry of Explosives and Propellant Compounds in Soils and Marine Systems: Distributed Source Characterization and Remedial Technologies; Chappell, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


Depending on the activities performed at the firing point, it is possible to have non-propellant material present. For example, Table II shows that RDX, HMX, TNT, and tetryl have been detected on occasion at firing points, suggesting that artillery and mortar firing was not the only activity to have occurred at these sites. In this particular example, all of the detections were observed at a single military installation suggesting the presence of explosives at the firing point is atypical. The HMX, RDX, and TNT detections occurred at a military installation where a “shoot and scoot” type of training activity occurred, i.e. non-fixed firing points. At these sites, firing occurs in the impact area and so there are both propellant residues from firing, and explosives from the detonation of ordnance. Tetryl (2,4,6-trinitro-phenylmethylnitramine) was used in some munitions but was discontinued in the 1950s. Tetryl is typically subject to rapid transformation in the environment. Thus, the presence of tetryl likely is limited to sites where training occurred prior to the 1960s and also in an arid environment. In addition to the extensive CRREL studies, more than 1,300 soil samples were collected and analyzed for propellants at artillery and mortar positions at Camp Edwards (47). More than 500 samples were analyzed for other energetic compounds as well. Overall, 2,4-DNT was detected in four percent of these samples, approximately four times more often than 2,6-DNT. The majority (twenty-nine) of the detections were in samples collected 0 to 0.3 m in depth. Overall, the soil findings at the artillery and mortar firing positions at Camp Edwards are consistent with the CRREL observations from the 11 other installations studied. The only extensive study of groundwater beneath artillery and mortar firing points in the US has been at Camp Edwards, MA. These studies did not reveal the presence of propellant compounds (NG and DNT) in the groundwater (48), which is consistent with their fate and transport properties, i.e. slowly dissolved, highly sorbed to soil, and rapid transformation. Nitroglycerin found in surface soil samples at an artillery/mortar firing position did not have a corresponding presence in shallow vadose zone water (20). Apparently, leaching from surfaces and edges of the propellant residue cause an initial burst of contaminant transport, which quickly ceases because of rentention of NG and DNT within the NC matrix (68, 69). Anti-Tank Anti-tank weapons systems consist of rockets fired in line-of-site to the target. Nitroglycerine and NC are the primary propellants for the anti-tank rockets and resiudes are found in surface soil at firing positions (6, 9–11, 21, 23, 29, 31, 49–51). As shown in Table III, NG surface soil concentrations are the highest of the energetic compounds observed. The deposition pattern consists of NG residue distributed up to 10 to 20 m in front of the firing position and up to 50 m behind (20, 52). The highest concentration of NG is found behind the firing position and can approach percent levels. At Camp Edwards, NG was the most widespread energetic compound detected (49, 50). Consistent with the CRREL studies NG was most prevalent at the firing positions at Camp Edwards and was likely deposited as ejected gasses 113



and particles from firing the rocket. The distribution of NG in soil (highest concentrations at or near the surface and decreasing with depth) at the firing points is consistent with the presumed airborne deposition of propellant compounds. Nitroglycerine was detected in 22 out of 215 samples collected between 0 to 0.8 meters in depth at Camp Edwards (49, 50), but in none of the six samples collected from greater than 0.8 meters (49, 50). Detected concentrations ranged from an estimated high of 130 mg/kg in a discrete sample collected at the surface, to an estimated 2.9 mg/kg in the composite sample collected from a back-blast grid at a former 90 mm rocket firing point (34, 49, 50). The presence of other chemical constituents may be associated with activities unrelated to anti-tank training. For example, some anti-tank ranges also are used for small arms training and DNT is contained in small arms propellant. This explains the occasional observation of DNT. Although not typical, RDX, HMX, and TNT may be found at the anti-tank firing point and may be associated with a misfire. Also, the LAW rocket uses a booster propellant charge, which contains RDX. The compounds HMX and TNT are the principal explosives used in antitank rockets . The mass of propellant deposited was determined for several different antitank weapon systems (36, 52) and found to be the highest of any type of firing position, with the exception of excess propellant bag burning at the artillery and mortar firing positions. Despite these high mass loading rates, a study of the antitank ranges at Camp Edwards, MA did not reveal the presence of NG or DNT in groundwater (47, 48, 53, 54).

Table III. Energetic residues (mg/kg) detected in surface soil at Anti-Tank firing points studied from 2000 to 2010 by CRREL HMX

RDX

TNT

Min

0.008

0.004

0.002

0.01

0.048

0.002

Max

1,920

262

778

4520

126

1,380,000

Mean

0.078

0.047

0.004

0.23

4.0

0.5

Median

61

75

22

884

20

15,900

Detections

63

12

36

12

13

297

# Samples

300

300

300

300

300

300

# Installations

3

3

3

3

3

3

Analytes

2,4-DNT

2,6-DNT

NG

Rifle-Grenade Consistent with their use, the propellants NG and 2,4-DNT are found in surface soils where rifle-grenades have been fired (Table IV). Nitroglycerin is the principal propellant in rifle-grenades. Typically, these types of ranges also include small arms training and these types of projectiles contain DNT in the propellant. The NG and DNT concentrations observed at rifle-grenade ranges are less than 114


found at other types of firing positions. RDX and TNT are constituents present in the rifle-grenade warhead so their presence, although unusual is possible.

Table IV. Energetic residues (mg/kg) detected in surface soil at Rifle-grenade firing points studied from 2000 to 2010 by CRREL RDX


Analyte

TNT

2,4-DNT

NG

Min

0.004

70

0.014

0.012

Max

0.004

78

58

36,400

Mean

0.004

74

0.021

3.6

Median

0.004

74

15

9,430

Detections

1

2

4

10

# Samples

20

20

20

20

# Installations

2

2

2

2

Small Arms Ranges The configuration of a small arms range consists of a firing position from which a soldier fires the weapon over the range floor toward a target. The small arms ranges are typically oriented around the periphery of an artillery/mortar impact area. In some configurations, targets are located in a line spanning the width of the range at a fixed distance with a primary backstop berm originally installed for safety purposes, but now also serving an environmental function by concentrating bullet residue. The berm, usually constructed with native soil material, can vary from a few meters up to 10 m in height. Sometimes a trough to collect surface water runoff is located at the base. Other configurations include targets at varying downrange distances, often with a small berm,

Energetic Residue Observations for Operational ... - ACS Publications

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