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◊ Gas Chromatography
◊ Graphite Furnace Atomic Absorption Spectrometry
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◊ Explosives
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◊ Magnetics for Environmental Applications
◊ Passive Diffusion Bag (PDB) Samplers
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Explosives Overview of Environmental Issues Associated with Residues of Energetic Materials
It has been estimated that there are thousands of explosives-contaminated sites within the United States, and even a greater number in Europe and the Soviet Union (Major et al., 1997). The sources of this contamination are wastes produced from synthesis of explosive chemicals; load, assemble, and pack operations of finished munitions; residues deposited during munitions testing and training; residues from ordnance demilitarization; and disposal of out-of-date and off-specification material (Yinon, 1999; Jenkins and Walsh, 1987; Major et al., 1991; Cragin et al., 1985; Selim and Iskandar, 1994; Fellows et al., 1992; EPA Handbook # EPA/625/R-93/013, 1993). These activities have led to soil contamination at ammunition plants, depots, and testing and training ranges (Figure 1-1). Contaminated soils have, in some cases, been the source of groundwater contamination in aquifers beneath these facilities. Nevertheless, the need to maintain our military in a state of combat readiness requires that production, testing, and training with energetic materials continues.
The task of identifying the extent of contamination at these facilities becomes complicated when the contaminants are energetic materials. Energetic materials behave differently than most other organic contaminants and pose an immediate safety hazard when present in large quantities or within unexploded ordnance (UXO). Energetic materials include chemicals that are used by the military as propellants, explosives, and pyrotechnics (PEP). By far, the energetic compounds produced and used for the Department of Defense (DoD) in the greatest quantities are secondary explosives. To assess the extent of explosive contamination, it is necessary to detect and identify explosives and their degradation products in soil and groundwater. This module presents information on the various technologies available to assist in this characterization. Explosives are classified as “primary” or “secondary” based on their susceptibility to initiation. Primary explosives, which include lead azide, lead styphnate, and mercury fulminate, are highly susceptible to ignition (easily detonated by heat, spark, impact or friction) and are often referred to as initiating explosives, because they can be used to initiate the detonation of secondary explosives. Secondary explosives are used in much greater quantities within military munitions than primary explosives and are more prevalent at military facilities. Secondary explosives include 2,4,6-trinitrotoluene (TNT), 1,3,5-hexahydro-1,3,5-trinitrotriazine (RDX), octrahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 2,4,6-trinitro-phenylmethylnitramine (tetryl), and ammonium picrate (AP). Since these compounds are formulated to detonate under specific circumstances, secondary explosives are often used as main charges or boosting explosives. Secondary explosives fall into two main categories: (1) melt-cast explosives, based primarily on TNT, and (2) plastic-bonded explosives (PBX), which consist of a polymer matrix filled with a crystalline explosive such as RDX. Secondary explosives can also be classified according to their chemical structure. For example, TNT and picric acid/ammonium picrate are classified as nitroaromatics, whereas RDX and HMX are nitramines. Other energetic materials sometimes found at military facilities include 2,4-dinitrotoluene (2,4-DNT), nitroglycerin (NG), pentaerythritol tetranitrate (PETN), nitroguanidine (NQ), and nitrocellulose (NC). NC, NG, and 2,4-DNT are used in several different types of artillery, mortar, and rocket propellants. PETN is the major component of detonation cord often used during demolition activities. This module focuses on the characterization of secondary explosive compounds in soil and groundwater, since they represent the largest potential concern to the environment. Pertinent information specific to the safe and effective sampling and analysis of explosive compounds such as TNT, RDX and HMX is included in this module. TNT and RDX constitute the largest quantity of secondary explosives used in military applications, since they are major ingredients in nearly every munition formulation (Table 1.1; Walsh et al., 1993). While some energetic chemicals, such as tetryl, are no longer used in current munitions, residues from their manufacture and use remain at contaminated sites. In addition to the chemicals added to explosive formulations, residues contain compounds such as production impurities or decomposition by-products. For example, military grade TNT often contains a number of impurities, including 2,4-DNT and other isomers of dinitrotoluene and trinitrotoluene (Leggett et al., 1977). In addition, TNT is susceptible to photo and microbial degradation from which a variety of transformation products have been identified (Walsh et al., 1995). The major impurity in production grade RDX is HMX, which can be present at concentrations as high as 12% (U.S. Dept. of Army, 1994). Characterization procedures (i.e., sampling design, sample collection, subsampling, and analysis protocols) must be robust enough to address all these explosives. In addition, the conceptual site model (CSM) must address all of the pertinent information when developing an environmental assessment work plan. Procedural guidance for this aspect of a site investigation is addressed in the EM 1110-1-1200 (U.S. Army Corps of Engineers, 2003). Abbreviations
Table 1.1. Common Composite Explosives
References
Physical and Chemical Properties of Organic Energetic Compounds
The organic chemicals used as components of explosives and propellants have physical and chemical properties that differ somewhat from those normally encountered at hazardous waste sites. These properties affect the mobility of these chemicals in the environment and the analytical methods that we use to measure them in environmental samples. This section provides physical and chemical properties of the important organic energetic compounds (Burrows et al., 1989) and provides a short discussion of the impact these properties have on specific analytical protocols developed for their analysis. Types of Organic Energetic Materials There are three main categories of organic energetic materials: nitroaromatics, nitramines, and nitrate esters. All of these compounds contain the NO2 functional group. For nitroaromatics, the NO2 groups are bonded to carbon atoms on an aromatic ring. For nitramines, the NO2 group is bonded to a nitrogen atom that is present within an alicyclic ring. For nitrate esters, the NO2 group is bonded to an oxygen atom attached to an aliphatic carbon. The most commonly used nitroaromatic compounds in energetic materials are TNT (Figure 2-1), picric acid/ammonium picrate, tetryl, and 2,4-DNT. Other nitroaromatic compounds that are present as impurities, or are formed as photochemical or microbiological transformation products, include 1,3,5-trinitrobenzene (TNB), 1,3-dinitrobenzene (DNB), 2,6-ditrotoluene (2,6-DNT), 2-amino-4,6-dinitrotoluene (2ADNT), 4-amino-2,6-dinitrotoluene (4ADNT), and other isomers of TNT and DNT. Tetryl was used as an explosive prior to the 1970s and can still be found at some installations. Tetryl is both a nitroaromatic and a nitramine, having both types of functional groups present in the molecule. The major nitramine compounds used in energetic materials are RDX (Figure 2-1) and HMX. There are two impurities that are formed in the synthesis of these compounds: TAX (hexahydro-1-acetyl-3,5-dinitro-1,3,5-triazine) formed in the synthesis of RDX, and SEX (octahydro-1-acetyl-3,5,7-trinitro-1,3,5,7- tetrazocine) formed in the synthesis of HMX. TAX and SEX may be found in wastes at the facility where RDX and HMX are synthesized (Holston Army Ammunition Plant), but they are not routinely found either at load, assemble, and pack installations or at ranges.
The most commonly used nitrate esters include NC, NG (Figure 2-1), NQ, and PETN. Melting Points Except for NG, the melting points of these energetic compounds are higher than can be experienced in the environment (Table 2.1). Thus when found at high concentrations, energetic materials will be present in the environment as solids. At ammunition plants, concentrations of energetic substances higher than 50% by weight have been found in sediment at the bottom of disposal lagoons. At burning grounds, slabs of crystalline material weighing many pounds have been found in the subsurface. On training ranges, chunks of explosive are found near rounds and bombs that have undergone low-order (partial) detonations. NG, which is a liquid at environmental temperatures, is used in double- and triple-based propellants imbibed within a nitrocellulose (polymer) matrix. Thus, even NG is generally found dispersed in the environment within a solid material, except for NG production facilities where subsurface pools of NG have been found. Even at lower concentrations, energetic compounds are often present in soils as discrete particles. This has a large impact on the nature of the distribution of these substances at contaminated sites and this will be discussed in greater detail later. It also has a large effect on the nature of the distribution within samples shipped to the laboratory for analysis. Segregation of fine particles can occur during shipping to the laboratory, and it is important to homogenize the entire sample and use proper subsampling techniques prior to removal of a subsample for extraction and analysis. Boiling Point and Vapor Pressure Many of the energetic compounds decompose or explode before they boil (Table 2.1). The fact that these compounds are thermally labile was the major reason that the initial development of methods for their determination in environmental samples was based on high performance liquid chromatography (HPLC) rather than gas chromatography (GC). The vapor pressures of the most important energetic materials are all less than 1E-04 torr (mm of mercury) at room temperature. Thus, evaporative losses during sample processing are minimal. For most analytical protocols for these compounds in soil, the samples are air dried prior to homogenization. Experiments indicate that as the soils dry, they become more sorptive, inhibiting volatilization (Jenkins et al., 1999). Volatile losses during air-drying have been shown to be insignificant (Walsh et al., 1999). Solubility and octanol/Water Partition Coefficient The solubility of energetic compounds in water varies greatly from ammonium picrate (AP), which is about 10,000 mg/L, to PETN and HMX, with solubilities of about 2 and 5 mg/L, respectively (Table 2.1). NC is a water-insoluble polymer; therefore, it does not migrate as a dissolved constituent. Octanol/water partition coefficients (Kow) are used to assess the hydrophobicity of various organic compounds. For many organic compounds, like polychlorinated biphenyls (PCBs) and polynuclear aromatic hydrocarbons (PAHs), their low water solubilities are due to their hydrophobic nature as quantified by high Kow values (10E4 and greater). This is not the case for HMX and other energetics, however. For example, HMX has a water solubility of about 5 mg/L, but a Kow value of 1. Thus it is not hydrophobicity, but rather its high crystal energy that makes HMX relatively insoluble in water. Once dissolved though, many organic energetic compounds do not sorb strongly to soils and hence they are quite mobile in the environment relative to more hydrophobic organic compounds. This property has led to transport of RDX and HMX through vadose zone soils to groundwater at a number of DoD installations. The solubility of organic energetic compounds in organic solvents differs somewhat from more hydrophobic organics. The best solvents for these energetic compounds are generally quite polar. Acetone, acetonitrile, and methanol are generally used for preparation of standards and spiking solutions for on-site and laboratory methods. The solubility of HMX and RDX is considerably lower in methanol than in acetone or acetonitrile. Acetonitrile has been shown to be an effective extractant for these compounds in water when the compounds are salted out (Leggett et al., 1990), and acetonitrile is transparent in the UV at wavelengths generally used for HPLC analysis. For hydrophobic compounds, extraction with nonpolar organic solvents provides an excellent means of extraction and preconcentration for water samples. For HMX and RDX, though, extraction of a 400-mL sample with 20-mL of methylene chloride resulted in only a 24% recovery of HMX and a 60% recovery of RDX (Leggett et al., 1990). Using salting out extraction with acetonitrile, however, recovery was 96% and 94% of these two compounds, respectively (Leggett et al., 1990). These properties also affect the types of solid phase sorbents that can be used for preconcentration of organic energetic compounds from water. For hydrophobic compounds, octadecylsilane-based sorbents (C18) are often used for extraction and preconcentration. While this material probably works reasonably well for nitroaromatics, the retention capacity for RDX and HMX is poor. Much greater retention capacities have been found for solid sorbents composed of a divinylbenzene n-vinylpyrrolidone copolymer. Solid phase extraction of water samples using these resins has proven to be dependable. Stability in Soil The stability of several of these organic energetic compounds in soil has been studied. Typically, the stability reported refers to half-life (in days) of the compound once it is in equilibrium between soil surfaces and pore water. This does not relate to compounds present as solid particles at the soil surface that are sometimes found at DoD training ranges. For nitramines, such as RDX and HMX, the half-life is generally hundreds of days, but for nitroaromatics and nitrate esters, the half-life is much shorter (Grant et al., 1993; Miyares and Jenkins, 2000). References
Table 2.1. Physical and Chemical Properties of Nitroaromatics and Nitramines (Walsh et al., 1995).
DoD Installations with Potential Contamination with Energetic Compounds
Introduction The Department of Defense (DoD) historically manufactured energetic compounds for propellants, explosives, and pyrotechnics (PEP) on U.S. Government installations that were operated under contract to private industry. These government-owned, contractor-operated (GOCO) installations synthesized the energetic compounds, purified them to acceptable levels, and manufactured the finished products including loading them into propellant bags, artillery and mortar shells, rockets, and bombs. Often, different installations did the synthesis and the final manufacturing operations; the latter are referred to as load, assemble, and pack (LAP) facilities. Wastes from these LAP manufacturing operations account for the largest source of environmental contamination with energetic compounds. This is understandable when you consider that these compounds are inherently very dangerous and any residues on equipment and spillage produced a highly dangerous situation that often was mitigated by washing with large volumes of water. One estimate was that wastewater from full-scale operation of a single load line at a LAP facility produced up to one-half million gallons of wastewater per day (Walsh et al., 1973). The total mass of contamination generated from one installation was estimated at 7,300 kg of RDX and 26,410 kg of TNT (Spaulding and Fulton, 1988). Wastewater from manufacturing operations is currently collected in holding tanks and treated using carbon adsorption columns. In the past, however, wastewater was often transported through pipes or ditches to unlined disposal ponds where particulates settled forming a sludge in which the explosive concentration could range into percent levels. Areas in the transport system where there were leaks in pipes or low spots in ditches also resulted in accumulation and subsequently high concentrations of residues in soils. In addition, synthesized material that was found to be below specification was often disposed at burning areas where this operation was often conducted directly on the soil. Heat from the burning process sometimes resulted in melting of the energetic material, which penetrated below the surface at burning grounds and resolidified sometimes leading to pure material in the shallow subsurface (Figure 3-1). Disposal operations were also conducted at DoD depots where out-of-date munitions were destroyed, often by either open burning or open detonation (OB/OD). Sometimes these operations resulted in deposition of residues of energetic materials as well.
The use of finished munitions at DoD testing and training ranges has also resulted in the deposition of residues of energetic compounds. The mass of residues deposited at these facilities is much lower than at manufacturing operations, but the dissolution and leaching of these residues has resulted in the suspension of training at one DoD facility. Manufacturing Operations Synthesis of TNT and 2,4-DNT in the United States was conducted at a number of ammunition plants, mostly located in the South and Midwest. In the past, TNT production involved a step-wise nitration of toluene with a mixture of nitric, sulfuric, and fuming sulfuric (oleum) acids. This crude TNT mixture underwent a two-step purification: the initial wash with warm water and soda ash (sodium carbonate) generated a highly acidic wastewater referred to as “yellow water”, and the second wash with cold water and sellite (sodium sulfite) generated an alkaline wastewater referred to as “red water”. Wastewater generated from these operations included the unsymmetrical isomers of trinitrotoluene, the various isomers of dinitrotoluene, trinitrotoluene, dinitrobenzene, and di- and trinitroxylene. For many years red water was reused by the dye industry until environmental regulations precluded this reuse. Because no satisfactory treatment alternative for this wastewater has been developed, the synthesis of TNT and 2,4-DNT in the United States was suspended in 1977 and no TNT or 2,4-DNT has been produced domestically ever since. Currently, all TNT used by the DoD is purchased from foreign sources. Residues resulting from the disposal of wastewater appear to be minor, however, in comparison to those produced from load, assemble, and pack operations. RDX and HMX are synthesized in the United States at Holston Army Ammunition Plant (AAP) in Kingsport, Tennessee. The major impurities in the production of RDX and HMX are hexahydro-1-(N)-acetyl-3,5-dinitro-1,3,5-triazine (TAX) and octahydro-1-(N)-acetyl-3,5,7-trinitro-1,3,5,7-tetrozocine (SEX), respectively. Purification procedures remove these compounds to barely detectable concentrations in the final products. Deposition of residues of the RDX, HMX, TAX, and SEX from these operations appears to be small and limited to this one installation. The synthesis of the nitrate esters such as NC, NG, PETN, and NQ has also been conducted at several ammunition plants. Generally these compounds were manufactured at different ammunition plants from those manufacturing munitions containing TNT and RDX. Some localized contamination at these facilities may be present, and the residues appear more of a safety hazard than an environmental concern. Much less work has been conducted at these facilities than at facilities where munitions containing TNT and RDX were manufactured. Load, Assemble, and Pack (LAP) Operations By far the largest mass of residues of explosives resulted from LAP operations at ammunition plants. Wastewater from the assembly of TNT- and Composition B-containing munitions is called “pink water” (because it turns pink to red in the sunlight) and contains a variety of explosives-related chemicals of which TNT and RDX predominate, in both the particulate and dissolved form. Currently these wastewaters are treated using carbon adsorption, but in the past they were disposed in unlined ponds. At a number of installations, groundwater plumes of RDX, in particular, are located below these ponds and migration of RDX has sometimes extended for miles down gradient (Spaulding and Fulton, 1988). Because TNT is sorbed to a greater extent by soils than RDX, TNT plumes are generally much smaller in size and the migration in groundwater is much slower. DoD Testing and Training Ranges The sampling of ranges for explosives residues is a fairly recent activity, with the first information published by Racine et al. in 1992, although some earlier work by the U.S. Army Environmental Hygiene Agency (now U.S. Army Center for Health Promotion and Preventive Medicine, USACHPPM) was conducted for water and sediments. Walsh et al. (2001) have summarized the early work in this area. There are a number of different types of ranges that differ significantly in the types and concentrations of residues present in the soil. These include various types of Army ranges such as artillery and mortar ranges, hand-grenade ranges, 40-mm grenade ranges, demolition ranges, antitank-rocket ranges, and tank-firing ranges (often called multipurpose ranges), and Air Force ranges such as bombing ranges, rocket ranges, C-130 firing ranges, and demolition ranges. Very little information is available for Navy ranges. Antitank-rocket ranges were the first type of range in which extensive characterization was conducted (Jenkins et al., 1997, 1998; Thiboutot et al., 1998; Pennington et al., 2002). These studies indicated that down-range HMX was the major contaminant (1 to >100 ppm) present with TNT present at concentrations about 1/100 of HMX. Contamination is largely present near the target and is due to LAW rockets (containing octol) that ruptured but did not detonate. The concentrations of residues of explosives at artillery and mortar ranges are generally very low or below detection limits of the current methods except in areas next to targets or near rounds that underwent low-order (partial) detonations (Jenkins et al., 2001; Pennington et al., 2002; Ampleman et al., 2003). In the latter areas, concentration in soil can be in the percent level with chunk explosives sometimes visible at the surface (Pennington et al. 2003) (Figure 3-2). The major residues at these sites are TNT and RDX from TNT- and Composition B-containing munitions.
The residues present at hand-grenade ranges are largely due to training with M67 grenades containing Composition B (Jenkins et al., 2001). The major sources of residues at these ranges are hand grenades that undergo low-order (partial) detonations and unexploded grenades that are destroyed by EOD personnel using C4. Concentrations of TNT, RDX, and HMX have been detected at these ranges as high as the low ppm range. Firing points for LAW rockets and various types of artillery and mortars have been investigated. The major residues are a function of the type of propellant used for the various weapon systems. For example, 2,4-DNT was found to be present in soil where 105-mm howitzers were fired (Jenkins et al., 2001; Walsh et al., 2003) because these propellants are single-based in which 2,4-DNT is used as a plasticizer with nitrocellulose. At the firing points on LAW-rocket training ranges, NG is the analyte found due to its use in the double-based propellant used for these rockets. NG is also the major residue found at 155-mm howitzer firing points because of its presence in the triple-based propellant used for this weapon system. Generally these residues from propellants are present in the ppb range except behind the firing line for LAW rockets where the NG concentration can be much higher (1 to >100 ppm) due to the back blast produced when these shoulder-fired weapons are used. Air Force ranges have been studied to a much lesser degree than Army ranges. Training rounds that do not contain secondary explosives are used for many ranges and the levels of residues at these ranges are very low. One Canadian bombing range where live bombs are dropped has been studied and the major contaminant found in the soil was TNT in the ppm range (Ampleman, personal communication). This is consistent with the use of tritonal as the major explosive in Air Force bombs. Partial detonation of Air Force bombs has been observed at two ranges and this leads to very highly localized concentrations of TNT (Pennington et al., 2002; Ampleman, personal communication). Tritonal contains TNT and aluminum. Another potential source of contamination at Air Force ranges is rocket propellant, but research is lacking to assess the magnitude of this problem. Disposal Operations Numerous energetic compounds have been detected in soil samples collected on demolition ranges used for the OB/OD of UXOs and perhaps obsolete munitions (Hewitt et al., in prep). On a demolition range where there was evidence of recent activity, energetic residues in the 1 to 100 mg/kg range were detected for RDX, HMX, NG, 2,4-DNT, and TNT. However, TNB, 2-ADNT and 4-ADNT were also detected at lower concentrations (<1 ppm). Many of these same energetic compounds were found at similar concentrations in surface samples obtained from the demolition range at Camp Edwards Massachusetts Military Reservation (Jay Clausen, personal communication). These high concentrations and wide variety of energetic residues are consistent with residues detected after blow-in-place operations (Hewitt et al., 2003). References
Safety Safety Inspection and Clearance The first steps when planning a sampling campaign on a site potentially contaminated with explosives are to review all the historical information available and to perform a visual inspection of the area of concern. Sampling activities should only occur after performing these two initial tasks and obtaining the appropriate safety clearance for the sampling site. For example, many military firing ranges contain a significant amount of unexploded ordnance (UXO) on and below the surface. Prior to any sampling event for this type of site, clearance must be provided by explosive ordnance disposal (EOD) personnel who have the proper expertise and equipment (Figure 4.1). Once surface clearance has been performed (flagging area where UXO are suspected), care must still be taken, because highly contaminated soils (in excess of 10%) can propagate a detonation (Kristoff et al., 1987). Exposure of secondary explosives to heat, shock, impact, friction, and electrostatic charge can lead to violent reactions, including detonation, deflagration, and burning.
Surface and Subsurface Sampling At sites contaminated with explosives, sampling should first be carried out in the area that is suspected of having the highest concentration of energetic residues (Sisk, 1992). Moreover, only surface soil samples (0-5 cm) should be taken and no drilling should take place. If shallow-depth subsurface sampling is necessary, this task should be performed with extreme caution. This is a good example of where the field analytical methods can be very helpful. These tests can be performed rapidly, on-site to provide immediate information with respect to any potential risks. Both the colorimetric methods and immunoassay methods could be used to screen soil, however, since the colorimetric is less selective and has a greater dynamic working range it is better suited for this task (Crockett et al., 1994). Screening protocols that can be used with two commercially available colorimetric kits are presented in the screening technique section of this module (Jenkins et al., 1996; Hewitt et al., 2001). On-site colorimetric screening results can also inform the analyst of the need to dilute sample extracts in order to fall within the analytical range of the laboratory analysis method. When energetic residue levels exceed 10% by weight of the sample, additional safety precautions must be implemented. The most important safety precaution is to minimize exposure, which involves reducing the number of workers exposed to the hazardous situation and limiting the duration of exposure on site. To reduce the hazard during the sample collection activity all mechanical operations should be carried out on materials that have been moistened with water. Water desensitizes the explosive to phlegmatizing by reducing potential to generate heat or friction while manipulating the sample. If operations involving mechanical shovelling are required, remotely controlled operations offer the best protection. When robotics are not available, armoured safety glass must be installed in the operator compartment, and operations should only be permitted after removing the soil layer that is contaminated above the safety level. Moreover, machinery used to acquire samples with high levels of energetic materials should have sealed bearings and shielded electrical junction boxes. This equipment should also be decontaminated frequently to prevent the build-up of explosives residues. Additionally, ungrounded plastic equipment and screw-top bottles should not be used for sample collection and storage of highly contaminated soil samples. On military firing ranges, safety clearances can be performed at three different levels. Level-one clearance consists of identifying and/or removing surface UXOs. Level-two clearance consists of identifying and/or removing surface UXOs and screening the top 30-45 cm of soil for metal objects (i.e., potential UXOs) with the help of a hand-held magnetic detector. Level-three clearance involves completely clearing the area of the site of UXOs in the area where work is to be performed. This high-level clearance ensures the greatest safety and also allows the drilling of wells directly on the site. However, this operation is not generally economical and/or physically feasible. Therefore, often a level-two clearance that is capable of detecting metallic objects to profile depths of 1-2 m is obtained with the help of the proper equipment such as an electromagneto-meter. Monitoring wells can also be installed on a site that has been cleared with the level-two procedure, provided down-hole geophysical monitoring is conducted. Lastly, an EOD technician must be present at all times during the sampling operation to ensure that proper procedures are followed. Shipping Requirements Shipping of soils containing reactive levels of explosives using normal shipping procedures is prohibited. It has been determined that soils containing more than 12% (120,000 mg/kg) secondary explosive by weight can propagate a detonation (EPA 1993). To incorporate a small safety factor, a value of 10% is used in this regard. It should be noted that concentrations as high as 120,000 mg/kg of explosives residues are rarely encountered, and often a visual inspection will identify the presence of pure crystalline materials. These high levels have been found at old explosive production sites where production waste was dumped directly on the ground, in former lagoons used to contain wastewater at production facilities, around partially detonated munitions, and in areas where open burning / open detonation (OB/OD) of off-spec material and UXOs has been performed. If screening of soil samples indicates that energetic materials are above the 10% limit, the contaminated material should be blended with background soil. This dilution is not a remedial action by itself, but a safety measure that will allow the safe handling, storing, and shipping of samples. Blending should be carried out precisely to calculate the initial concentration that was present in the sample. If the soil were not diluted, the transport of the samples would require the same safety waiver (manifested as a hazardous material and shipped according to DOT requirements for explosives) as that required for transporting pure secondary explosive material (AEC 1994). References
Potential Applicable Criteria for Explosives In addition to the hazards associated with the detonation of energetic compounds, there are toxicological considerations. Some of the secondary explosives are considered carcinogenic and mutagenic. The toxicity of explosive chemicals has been studied extensively by the U.S. Army Biomedical Research and Development Laboratory, and summaries of these investigations have been published (Rosenblatt, 1986; Burrows et al., 1989). For an indication of the toxicity of explosives on human health, Table 5.1 presents drinking water criteria for seven energetic compounds at a lifetime exposure cancer risk level of 10‑6. For energetic compounds in soils the threshold levels are often evaluated on a site-by-site basis, depending on factors such as the proximity of the contaminated soils to other locations and the use of surrounding groundwater. Future use of the site is also taken into account. Risk based concentrations (Table 5.2), however, are available from the Environmental Protection Agency Region 3 to help provide guidance.
Other sources of information concerning drinking water standards and risk-based criteria can be found at the following sites:
References
Selecting an Appropriate Sampling Scheme Technical Project (or Systematic) Planning The investigation of any potentially contaminated site requires the development and implementation of a study plan that states the objectives of the work to be performed. Three of the issues that this study plan must address are the contaminants of interest, area(s) potentially contaminated, and the receptor(s) of concern. The area of interest could be an entire site or several defined areas (separate strata or populations) within a site. The receptors are plants, animals, or humans and the potential pathways of contaminant exposure: ingestion, inhalation, or dermal should be considered. Other issues that should be taken under consideration during the development of the study plan are site specific parameters such as the mode of contamination, the physical and chemical properties of the major potential contaminants that effect their fate and transport, and the geology and the hydro-geology of the site. The conceptual site model (CSM) is the day-to-day working tool that integrates all this information, along with knowledge about contaminant release and migration mechanisms, into a representation of the different contaminant populations likely present on a site. Distinctly different populations or strata can be created when distinctly different physical mechanisms of release or transport produce different contaminant distributions. At the level of project decisions, different populations often have different decision outcomes (e.g., soil areas needing no further action versus areas needing removal or treatment; choosing between one treatment/disposal option versus another). Project decision about characterization and cleanup can be much more cost-effective when different populations are reliably and clearly identified and delineated by the CSM. Collecting “representative data” often requires a two-stage process. If the preliminary CSM is uncertain about what populations are present and where, then data should be gathered to develop the CSM until it is complete enough to distinguish different decision-based populations or strata. Only then can a sampling design be developed that is appropriate to characterize those populations to estimate the characteristics of interest to the decision process (such as the population's variability and its mean). Within the context of an adaptive/dynamic sampling strategy, maturation of the CSM can proceed efficiently in real-time, as each cycle of data collection adds information that guides subsequent data collection events without needing multiple mobilizations. Real-time detection, delineation, and characterization of decision-based populations ensure that data will be representative of the intended decisions. Additional guidance on the information necessary to develop a study plan for a potentially contaminated site can be found in the “Conceptual site models for ordnance and explosives (OE) and hazardous, toxic, and radioactive waste (HTRW) projects” (U.S. Army Corps of Engineers, 2003). Once this information has been obtained, an appropriate sampling strategy can be selected to satisfy the project's decision-making objectives. Sampling Design The site should initially be divided into areas based on known or suspicion of contamination. These areas will likely require further segregation into areas (or strata) based on similar characteristics or the evaluation criteria of the data user. Once determined, the objective is to understand what information is needed about that population; how it will be represented by physical site samples; and what type of data can be obtained to evaluate site conditions from a spectrum of chemical analyses. When the objective is to estimate the statistical properties (such as the variability and mean) for a site or for a stratum within a site that is comprised of a single decision-based population, either an equiprobable (i.e., simple random) sampling or a systematic sampling design can be used. However, neither of these sampling schemes should be used if the CSM predicts that the area of interest contains substrata that are expected to have very different concentrations of the contaminants (i.e., different populations). For example, it would not be appropriate to include within a single stratum a drainage ditch or lagoon that was used to transfer or retain the contaminant of interest with areas where there is no previous history of contaminant exposure. Likewise, areas on military training ranges with fixed targets should be identified as separate strata from areas where there is no history of target placement (Figure 6.1). Failure to employ a properly stratified sampling scheme underestimates the influence of areas of potentially higher contamination or completely misses them altogether. Indeed, the chances of missing locations of elevated contamination increases proportionally with size discrepancy between the stratum and the substratum within that area that has higher contaminant levels. As more strata are identified within an area, the more segregated the contaminant populations become, and, subsequently, the sampling scheme changes from one that is based on probability to authoritative. Coupling an authoritative (i.e., judgmental) sampling scheme with sufficient knowledge of the mode of contamination often is very useful when the objective is to rank potential source strengths. Once the source strengths (mass loading) for different strata have been determined, predictive models can be used to predict the exposure level for a given receptor.
Once the different strata have been identified, either a simple random or systematic sampling scheme can be used for the sample collection process. A systematic design (location of sample collection is predetermined) is used when assessing if spatial patterns exist (gradients in concentration) or for establishing if there are trends. A simple random sampling design provides a statistically unbiased approach because every unit has an equiprobable chance of being collected. The number of samples that should be collected in a chosen stratum should be determined empirically. Therefore, as part of the sampling plan a predetermined number of field-sample replicates should be obtained to assess if the uncertainty among the concentration estimates is within a range that is acceptable to the project's decision-making objectives. Likewise the number of increments collected to build a composite sample should be empirically determined for a given stratum. Our experience has been that the distribution of discrete samples for energetic compounds is never sufficiently normal to justify the use of normal distribution statistics. However, multi-increment composite samples are often distributed normally if a sufficient number of increments are collected for each composite. Generally, 30 increments are adequate in this regard. The module on collecting a representative soil sample further addresses the strategies that can be used to collect soil samples that support project decisions. References
Collecting a Representative Soil Sample
Sample Depth The unusual nature of energetic compounds as contaminants should be taken into consideration prior to developing a field-sampling plan. Explosives are solids at ambient temperature, and they are often dispersed as various sized and shaped particles that slowly dissolve in precipitation because they are sparingly soluble and are only wetted on a periodic basis. They also possess low vapor pressures and hence do not volatilize to any extent (Table 2.1). Their distribution is typically very heterogeneous, and they are only transported through soil after they are dissolved in water. Hence, the highest levels of explosive contamination are most likely to occur on or near the soil surface, unless the soil has been moved or filled, even at sites that have remained dormant for many years. We recommend that when the explosives residues are dispersed as particles (i.e., impact ranges, demolition range, firing points) the sampling depth should be limited to the near surface (0-5 cm). The more common 0- to 15-cm sampling depth, however, may be appropriate for locations where explosive residues are in a dissolved state when they are introduced into the environment. Nevertheless, the spatial distribution of residues will vary, depending upon the manner in which the contamination occurred, the specific target compound, and the nature of the soil matrix. For these reasons, subsurface soil sampling may be necessary to delineate the transport pathway or the contamination plume. Discrete vs. Composite Sampling The major objective of any sampling plan is to obtain samples that are representative of the property or characteristic used as the basis of project decision-making. For some decisions, the desired property of interest is an estimate of the mean over a given area, or for a single distinct population or stratum. For other decisions, the extent of contamination may be desired, requiring a data set that shows that the boundaries of contamination have been located. In other cases, data is used to guide decisions about cleanup strategies or disposal options, requiring data sets that estimate the volumes of contaminated material categorized by concentration and other matrix characteristics determining migration potential or cost-effective treatment options. Different decision goals require data sets with different representativeness. During systematic project planning, the spatial, temporal, and other scales relevant to individual project decisions are clarified. During sampling-plan development, the scales of data collection are designed to match the scales of decision-making. The goals of data collection are used to decide the scales (such as scales of space, particle size, and occasionally, time) over which the impact of contaminant variability must be controlled to provide meaningful information to the decision-making process. For extremely heterogeneous matrices (such as soils contaminated by explosives residues) matching the scale of data collection to the scale of decision-making requires careful planning that considers all steps in the sample collection, handling and processing chain. Variables that impact the representativeness of analytical results, such as the sample volume and orientation, homogenization procedures, subsample volume, and particle size must be controlled when dealing with matrices that are heterogeneous at both macro and micro scales. This implies that the concentration determined for the sample will provide a valid estimate of the average concentration for the specified area of concern. Therefore, it is imperative that the area of concern be defined prior to designing a sampling plan. Two typical scenarios are the identification of a suspected surface hot spot and establishing the average surface concentration of explosives residues over a specified area. In the past, sampling plans for each of these cases were written for the collection of discrete samples at a specified number of sampling locations. However, several studies have shown the futility of this practice, due to extreme short-range spatial variability that often exists for explosives in surface soils (Walsh et al., 1993; Jenkins et al., 1996a; Jenkins et al., 1997a; Jenkins et al., 1997b; Thiboutot et al., 1997; Jenkins et al., 1997c) (Figure 7.1).
As a consequence, multi-increment composite sampling is strongly recommended when characterizing the ground surface at a site potentially contaminated with explosives or propellants. In a small area (1 m x 1 m), multiple units (10 or more, each of the same approximate amount) should be systematically or randomly collected and placed into a single container. For larger areas, systematic gridding is useful for establishing sampling nodes, at which an area of between 3- and 10-m diameter could be systematically or randomly sampled by obtaining 30 or more individual increments (Figure 7.2). Another approach that can be used if the area of concern isn't too large (100 x 100 m) is the collection of a large composite sample by obtaining the increments at established grid nodes (intervals) or at random intervals while walking around the entire site. Consult “Statistical Method for Environmental Pollution Monitoring” (Gilbert, 1987) for selecting the appropriate sampling design, i.e., grid spacing, to meet decision confidence goals for various project decisions.
Subsurface Sampling With the exception of coupling soil profile sampling with the installation of groundwater sampling points, subsurface (vadose zone) sampling should only occur after the identification of a surface hot spot (including disposal lagoons, unlined burning pits). Beneath a hot spot it is recommended that a continuous vertical profile be collected over the first meter, with the profile broken into several (5 or more) increments, and each increment individually processed for analysis. Beneath 1 m, samples can be collected at larger intervals. Sample Size For each sample, a minimum of 500 g of soil should be collected and stored at a low temperature (typically less than 4 °C) until being processed for analysis. One exception is when performing profile sampling. In this case, the dimensions of the drilling equipment and the interval of concern may limit the sample size. The surface interface of training ranges is particularly important because both propellant and secondary explosives residues are distributed as particles during projectile firing and ordnance detonation. In some cases this means that leaf litter, moss, and grasses should be considered as part of the sample. These various forms of vegetation have traditionally been scraped away prior to the collection of a soil sample when performing environmental investigations. Sampling Tools and Supplies Typically, soil samples can be collected using either metal or rigid plastic tools. One exception is when energetic residues exceed 12% w/w of the medium being sampled. In these infrequent situations special sampling protocols, equipment, and storage vessels are recommended to help insure sampler safety. The collection tool used often depends on the cohesiveness, coarseness, and moisture content of the soil, and the vegetative surface cover. In general, when sampling a sandy soil with sparse vegetation, hand-held metal or plastic scoops work well. For more consolidated soils with a vegetated surface, a tool similar to a bulb planter works well. When shallow depth sampling is necessary, a metal corer (stainless steel hand corer) that is manually pushed or driven into the ground can be used. Generally, mechanically driven sampling equipment will be necessary when sampling at depths greater than a meter. All of the equipment that comes into contact with the soil should be carefully wiped with a clean paper towel to remove soil, rinsed with water and then with acetone, and air-dried between sampling locations. Clean polyethylene plastic bags or glass jars should be used as containers while collecting soil samples in the field and for storage prior to and after subsampling. Immediately after collection the samples should be cooled and stored in the dark (e.g., in ice coolers). Sampling Areas where Chunks of Energetic Residues are Present When “chunks” of energetic residues are visibly present the subsequent samples collected to assess the surface soil concentrations should be specially marked. Furthermore these samples should be collected with separate sampling equipment and stored in separate shipping containers than all other samples. Taking these measures will help to prevent cross contamination between sample during field operations and transport. Most importantly, these samples should be marked to alert laboratory personnel that they should remain isolated from the other field samples throughout the entire preparation protocol. References
Groundwater Sampling
Introduction Over the last decade, groundwater-sampling techniques have been the topic of intense scrutiny with respect to representativeness and the effect of various methods and equipment on sample quality. The reason for this concern is the growing awareness that contamination can be strongly localized to certain discrete stratigraphic layers. When this kind of heterogeneity is present, the placement and length of the well screen and the degree of mixing (e.g., through purging) across different layers is a strong determinant of the contaminant concentrations in the groundwater sample. The misleading data that is produced when sampling-related variables are uncontrolled easily creates inaccurate CSMs and faulty decisions about exposure and remedial design. In general, the intended decision should guide the design of sampling procedures so that the data produced are representative of the decision. For example, sample collection for data representative of a drinking water scenario would properly mirror the mixing that occurs in a drinking water well, but sample collection geared to developing an accurate CSM to support source detection and remedial design would avoid that mixing. Currently, a low-flow purging and sampling protocol, with minimal drawdown and dedicated pumps (Puls and Barcelona, 1996; EPA Region 1, 1996; Nielsen and Nielsen, 2002; ASTM, 2003), is commonly used. In addition, more emphasis is being placed upon discrete-interval sampling (profiling contamination with depth in a well) and using shorter screens in monitoring wells. The need to purge a well prior to sampling is another issue that is currently being debated. This section presents general information about several different types of groundwater samplers without specifying equipment-unique sampling protocols. In general, when the principle objective is to establish the presence or absence of explosives, sampling can be performed using a variety of fairly simple techniques. Because the most important factor in this instance is cross contamination between sampling points, it is advisable to use dedicated or disposable devices. When groundwater sampling is being used to monitor spatial and temporal trends within a contaminant plume, the sampling protocol needs to enhance the ability of the samples to represent the local concentrations in the formation. Under these circumstances, a much more stringent protocol, which is consistent with both the project decision goals and equipment to be used, needs to be specified. Considerations When Sampling Explosives Because of the physical properties of explosives, they do not readily volatilize from solution or dissociate in solution (i.e., form charged species). They are also relatively hydrophilic and thus do not tend to sorb or partition into organic matter. Thus, we would expect that these analytes would not have a great affinity for other solid phase materials, particulates, or colloids. Therefore, high turbidity in samples, mobilization of colloids during sampling, and colloidal transport in groundwater are not significant issues when sampling for explosives. Because of the tendency of explosives to stay in solution, obtaining sample results representative of the total environmental loading is less problematic than for metals and other organics such as volatile organic compounds (VOCs) and highly hydrophobic compounds (e.g., polycyclic aromatic hydrocarbons). Thus, it may be possible to use less stringent sampling methods than the currently accepted low-flow sampling protocol when sampling exclusively for explosives, depending upon the analytical requirements, site conditions, and regulatory guidelines and requirements. Despite the conservative behavior of most explosives in solution, there is evidence that substantial quantities of production by-products (e.g., nitrotoluenes and nitrobenzene) are sorbed by most polymers used in sampling (e.g., polyethylene and polypropylene), and that Teflon fluoropolymers are the least sorptive (tubing) materials tested (Parker and Ranney, 1997). While there is not a lot of data on the sorption of explosives by polymers per se, it has been shown that sorption is minimal for less sorptive materials such as rigid polyvinyl chloride (PVC) and polytetrafluoroethylene (Parker and Ranney, 1994). Therefore, more sorptive materials should be given time to equilibrate with the groundwater to reduce losses due to sorption. For tubing, some equilibration occurs normally during the purging process; the time required for equilibration will depend upon the analyte, tubing material, length of tubing, and flow rate (Parker and Ranney, 1998). Thief-Type Samplers
Typically, grab- or thief-type samplers are easy to use, allow quick and relatively inexpensive sampling, and can be used to sample deeper wells and a variety of analytes. Older thief-type devices used for groundwater sampling include bailers and syringe samplers. Although commonly used, bailers typically require that the well be purged, and they have been shown to agitate the water in the well, aerate samples during sample collection and transfer, and undergo depressurization when raised from deep wells (thereby affecting the chemistry of some samples). Therefore, these older devices are reported to be best suited for sampling contaminants, such as explosives, that are not volatile and are not readily oxidized and subject to precipitation reactions. Newly developed thief-type devices have been designed to sample discrete levels within a well and may not require the well to be purged. These devices include the HydraSleeve (GeoInsight) (Figure 8.1) and Kabis (SIBAK Industries Ltd., Inc) samplers. The HydraSleeve sampler consists of a flexible polyethylene sleeve with a polyethylene check ball at the top. The device is left in the well overnight to equilibrate and then filled by being moved up and down several times. This device has been shown to recover concentrations of explosives from a standpipe that are representative of the dissolved, uniform concentration present in the test standpipe (Parker and Clark, 2002). This device has recently been redesigned so that it can be filled in a single pull, which should greatly reduce any disturbance of the well by the device during sampling. The Kabis sampler is a bullet-shaped, stainless-steel device that holds a sample bottle. The inlet and exhaust ports are designed to prevent the device from filling as it is lowered into the well. Once it remains stationary for a few seconds, the device fills and the sample container(s) is rinsed several times with well water prior to collecting the final sample. Although Parker and Clark (2002) found that they could recover representative concentrations of explosives from a test standpipe with this device, Einfeld and Koglin (2000) found that this device either entrained contaminants or collected a partial sample as it was lowered through the water column. Pressurized thief-type samplers use positive pressure while the device is raised and lowered to achieve discrete level sampling. Reported advantages include being able to: 1) sample a broad variety of analytes; 2) profile concentrations gradients with depth; 3) sample deeper wells; 4) sample with little or no purging; and 5) recover a sample that is under the same pressure and redox conditions that exist in the well. Commercially available devices include the Discrete Interval Sampler (Solinst Canada Ltd.) and the Pneumo-Bailer (Best Environmental Subsurface Sampling Technologies, Inc.). In a lab study, both devices were shown to recover concentrations of explosives representative of the uniform concentrations present in the test container (Parker and Clark, 2002). Discrete-Interval Pump Samplers The Easy-Pump™ Direct Purge and Sample System (Voss Technologies, Inc.) isolates the water column above the screened interval with an inflatable bladder and then pumps water from the screened interval into the water column above the well screen, thereby eliminating the cost of disposal of purge water. We are unaware of any studies that have evaluated this system for use in the collection of samples for explosives analyses. The multi-level sampler (Solinst Canada, Ltd.), also known as the continuous multi-channel tubing (CMT) system, consists of a length of multi-channel tubing with up to seven sampling ports that can be positioned at various depths within the well screen (Einarson and Cherry, 2002). Typically, the individual channels are sampled using a peristaltic pump, although a 3/8-inch bladder pump (Solinst Canada, Ltd.) has recently been developed. For deeper wells, small-diameter bailers, inertial lift pumps, and small-diameter canister samplers have also been used. Although neither of these systems has been evaluated for sampling explosives, presumably both could be used for sampling explosives. Low-Flow Sampling The purge parameters commonly used with low-flow sampling are temperature, conductivity, and dissolved oxygen to determine when concentrations have stabilized and purging is no longer required. Moreover, while purging groundwater the flow rate should be controlled so as to limit a water level draw down. When the sampling depth is less than 25-ft (7.6 m), a suction lift pump can be used, while a submersible pump is recommended for greater depths. Measurements are taken at time intervals (3 to 5 min.) or after successive half-well volumes. When the appropriate parameter(s) has stabilized (agrees within 10% of each other for three consecutive measurements) and sufficient water has been purged from the well, a groundwater sample can be collected. The positioning of sample inlet (collection point), water quality stabilisation parameters, and flow rate should be recorded for each sampling event. Moreover, the sampling team should strive to match each of these parameters during all subsequent sampling events. Passive Diffusion Samplers With passive diffusion devices, contaminants permeate a polymeric membrane into a chamber initially filled with distilled or deionized water. Diffusion continues until equilibrium is reached. Because no water is drawn into the well via pumping, water is not pulled from other parts of the formation. These devices have been used to profile contamination in a well with depth and can be used to collect samples in formations with low permeability (Robin and Gillham, 1987). Under a hydrological regime where vertical flow inside the well in insignificant, mixing of water between different depth zones is avoided. For some contaminants, stratification of concentrations with depth can be severe. Uncontrolled mixing between stratified zones can introduce large variability into data. Since depth-discrete samplers avoid mixing between high and low concentration zones, the analytical data are representative of contaminant concentrations in the immediate vicinity of the sampler. A vertical string of samplers down a well preserves information about vertical stratification in the well. This information can be critical to support development of an accurate CSM that guides correct decisions about contaminant fate, migration, and treatment. Currently, two types of diffusion samplers are commercially available: the passive diffusion bag (PDB) sampler (marketed by Columbia Analytical and Eon Products) and the Multilevel Sampler (MLS) (sold in the U.S. by Johnson Well Screens, Inc.). The PDB sampler consists of a polyethylene bag and was developed for sampling VOCs (Vroblesky and Hyde, 1997; Vroblesky, 2001). This sampler should not be used for sampling explosives (Parker and Clark, 2002). The DMLS consists of a PVC rod that contains 20-mL polyethylene cells with dialysis membrane covered end caps. The DMLS has been used to sample anions, dissolved gases, and VOCs (Ronen et al., 1986; Magaritz et al., 1989; Kaplan et al., 1991) but has not been tested for sampling explosives. However, the small sample volume collected with this device limits its use for explosives. Sample Collection, Handling, and Storage Groundwater containing explosives should be collected in amber glass bottles to prevent photodegradation. For low concentrations (ppb levels), a 1-liter bottle is required. The sample does not need to be filtered but should be acidified to a pH of 2 using sodium bisulfate (Jenkins et al., 1995) and kept cold (4°C). Because of the relatively low solubility of explosives in water, there are no special safety concerns associated with shipping groundwater samples containing explosives. References
Sample Preservation Soil/Sediment Samples For soil samples, Method 8330 specifies a maximum pre-extraction holding time (MHT) of seven days in the dark at 4 °C for nitramines and nitroaromatics. However, studies have shown that nitramines are stable over an eight-week period when held at 4 °C in the dark, and that nitroaromatics are stable for the same period when frozen (Grant et al., 1993a; Jenkins et al., 1994). In the field, soil or sediment samples should be placed in a cooler packed with ice or with another refrigerant soon after collected. Once the laboratory receives them, the samples should either be frozen or immediately spread out on clean surface to air dry. Once air-dried the need to refrigerate no longer is critical for short periods (days to weeks), however, long-term storage at 4 °C or lower, is recommended. Following extraction with acetonitrile, the analytes are stable if held in a vapor tight container. Refrigeration of extracts in amber glass bottles with Teflon lined septa is recommended for long-term storage of sample extracts. Water Samples For water samples, Method 8330 specifies a maximum pre-extraction holding (MHT) time of seven days in the dark at 4 °C for nitramines and nitroaromatics. Studies have evaluated the pre-extraction holding times for nitroaromatic and nitramine explosives (Maskarinec et al., 1991; Grant et al., 1993b) and the preservation of water samples (Jenkins et al., 1995). The first two studies demonstrated that MHT of 50 days could be used for both nitramines and nitroaromatics in many types of water samples when refrigerated at 4 °C. However, water with active microbial populations (such as surface water) showed significant losses of TNB and TNT within a day or two, when refrigerated at 4 °C. The preservation study concluded that the MHT for water samples containing nitroaromatics such as TNT, TNB, and tetryl can be extended to at least 28 days by acidification to pH 2 using NaHSO4 (e.g., 1.2 g / 1 L). Furthermore, the acidification did not affect the stability of nitramines that were already stable over a period of 50 days, with or without preservation. Therefore, all water samples should be acidified to pH 2 (or less) soon after collection. In the field this can be accomplished by adding the appropriate amount (weight) of NaHSO4 to the water sample. Once acidified, they should be stored in the dark a | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
