Assessing Sample Processing and Sampling Uncertainty for

Chapter 5

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Assessing Sample Processing and Sampling Uncertainty for Energetic Residues on Military Training Ranges: Method 8330B Marianne E. Walsh,1,* Alan D. Hewitt,2 Thomas F. Jenkins,3 Charles A. Ramsey,4 Michael R. Walsh,1 Susan R. Bigl,1 Charles M. Collins,1 and Mark A. Chappell5 1U.S. Army Engineer Research and Development Center, Cold Regions Research and Engineering Laboratory (ERDC/CRREL), 72 Lyme Road, Hanover, NH 03755 2Deceased, formerly of ERDC/CRREL 3Retired, formerly of ERDC/CRREL 4Envirostat, Inc., PO Box 636, Fort Collins, CO 80522 5U.S. Army Engineer Research and Development Center, Environmental Laboratory, 3909 Halls Ferry Road, Vicksburg, MS 39180 *[email protected]

The standard analytical method to determine explosives in soils (EPA SW-846 Method 8330) was developed in the late 1980s to support efforts to remediate Army ammunition plants and depots where wastewater from munitions production was released onto the soil. Subsequently, the characterization of energetic residues on military training ranges required the development of field sampling and laboratory processing methods suitable for the unique nature of the explosives and propellants dispersed by live-firing exercises. The revised method is based on research at more than 50 training ranges and addresses the uncertainty due to the heterogeneity in the physical form and the spatial distribution of these potentially hazardous constituents. The revised method (8330B) provides guidance for sampling and processing of soil samples. Proper sampling involves collecting an adequate number of evenly spaced increments from throughout a decision unit to reduce uncertainty due to distributional heterogeneity and enough

© 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.

mass to reduce uncertainty due to compositional heterogeneity. Soil samples may be several kilograms, and the entire sample must be processed to maintain representativeness.


Introduction Energetic residues are deposited on military training ranges as irregular fibers (1) or pieces of propellants (2, 3) and as particles of solid explosives (4, 5). These energetic residue particles accumulate on the soil surface of firing points and where ordnance has partially detonated or ruptured. In addition, energetic residues are found in areas where unexploded ordnance (UXO) has been “blown-in-place” during a range clearance or training activity (6–9). Protocols used for initial investigations on military training ranges included the collection of discrete samples or a five- to seven-increment sample (10) that was subsampled in the field and only a small soil aliquot used for determination of energetic concentrations. The Environmental Security Technology Certification Program (ESTCP) Environmental Restoration ER-0628 program recognized that use of different sampling and sample-processing protocols would impact the data used to estimate mass loading of energetic residues on Department of Defense (DoD) training and testing ranges. This project examined the uncertainties associated with estimates of the mean concentration of energetics in soil obtained using commonly used strategies and compared them to a revised approach based on the unique nature of energetic residues. Sampling error was examined using soils collected from a firing point, an impact area, and a demolition area. This paper briefly describes the technology demonstrated during ER-0628 and summarizes some of the more important findings. A detailed description of the demonstration sites, sampling activities, experimental design, and data evaluation were published elsewhere (11). The objective is to reduce the uncertainty associated with estimating the mean concentration of energetic compounds within a decision unit by using appropriate sample collection and processing methods.

Experimental Design Field Sites Three training areas on Fort Richardson, Alaska were chosen based on the known presence of energetic residues at concentrations that would be detectable by the standard analytical method (SW846 8330). Method 8330 (12) uses high performance liquid chromatography and an ultraviolet detector that provides reporting limits around 0.04 mg/kg. The field sites were also selected to represent different types of training ranges: an impact area, a demolition training range, and a mortar firing point.

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Impact Area


The Eagle River Flats impact area is used for live-fire training with mortars and howitzers. Within the central impact area, we chose a location that contained residues from a partial detonation of a 120-mm mortar projectile. The projectile was filled with Composition B (60% RDX, 40% TNT) and solid chunks of the explosive filler were scattered over a 380-m2 area (5). We marked a 20 × 20-m area that encompassed the Comp B pieces and the crater. In addition to RDX and TNT, the analytes of interest included HMX that exists as an impurity in RDX, 2,4-DNT and 2,6-DNT that exist as an impurity in TNT, and 2-Am-DNT and 4-Am-DNT that are reduction products of TNT. The surface of the impact area was a mudflat composed of glacially derived silts and clays that are saturated for most of the year.

Demolition Range Demo Range III is used for heavy demolition training, most with C4 (91% RDX, 9% nonexplosive plasticizers). We chose a 30 × 30-m area that encompassed an area that we sampled the previous year and found RDX from the C4 demolition charges and other energetic residues (HMX, TNT and 2,4-DNT). The surface of this area was gravel; pieces of C4 were scattered throughout the 30 × 30-m area.

Firing Point Firing Point Fox is a mortar firing point where we had previously found 10 mg/kg of NG, an ingredient in double-base propellant, in an 800-m2 portion of the 4,422 m2 firing point (13). We established a 40 × 40-m area in the center of the firing point. The surface of the firing point was vegetated loess that was underlain with sand and gravel. In addition to firing of mortars, excess propellant was burned at the firing point. Field Sampling Strategies Three conventional sampling strategies, known as discrete, box and the wheel, were used. Discrete samples were collected within each decision unit and were 150 to 200 g of field-moist soil or sediment. The locations for the discrete samples at the demolition range and firing point were randomly selected from a table of random numbers or from the roll of a pair of dice. The discrete samples from the impact area were positioned systematically at 2-m intervals from a random starting point. For the box sampling design, five increments, each equal in mass to a discrete sample, were combined to form one bulk sample. The increments were collected at the center and at 5-m distances from the center, moving in the four cardinal directions (Figure 1a). In the wheel sampling design, seven increments, each equal in mass to a discrete sample, were combined to form one bulk sample, with increments from a location at the center and at six equally spaced locations on the perimeter of a circle with a 0.6-m radius (Figure 1b). Locations for the center 93



points of the box and wheel samples were from random locations selected based on the roll of a pair of dice, with the constraint that the increments be within the area marked for sampling. At the demolition range and firing point, 100 discrete, five box, and five wheel samples were collected. At the impact area, two sets of 100 discrete samples along with five box and five wheel samples.

Figure 1. The two conventional sampling designs used.

Method 8330B uses a field sampling strategy called multi-increment where 100 soil increments are collected at evenly spaced intervals throughout each decision unit to form one sample (Figure 2). We collected ten multi-increment samples from each decision unit. The starting point for each multi-increment sample was a random point near one corner of each decision unit. All samples were collected to a depth of 2.5 cm. The discrete, box and the wheel samples were collected with stainless steel scoops. The multi-increment samples were collected with a 3-cm diameter corer (14).

Field Processing and Subsampling of Soil Samples The conventional practice is to perform a mass reduction step in the field to minimize the mass of soil that is sent to an analytical lab. We examined the error introduced by this procedure. In the field, the box and wheel samples were thoroughly mixed in a stainless steel bowl and subsamples were transferred to 250-mL jars with a large spoon. At each field site, one of the box and one of the wheel samples were completely divided in the field into five or seven jars, respectively (Figure 3). These and all other samples were chilled to 4°C and shipped to our laboratory in Hanover, NH.

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Figure 2. Illustration of multi increment sampling designs for collecting two separate samples.

Figure 3. Study design to evaluate uncertainties associated with conventional sample splitting method.

Laboratory Processing of Soil Samples Laboratory Subsampling Prior to Processing Another conventional practice once soil samples arrive at an analytical laboratory is to remove a small portion of an undried field sample for analysis and then archive or dispose of the rest of the sample. We measured the uncertainty associated with this practice using samples from the box and wheel designs from each field site (Figure 3). The selected samples, which were in 250-mL jars, were stirred, and then triplicate 20-g subsamples were removed off the top of the unprocessed soil with a stainless steel spatula. The subsamples were air-dried then passed through a 10-mesh sieve. A 10.0-g portion of each less than 2-mm 95


fraction was combined with 20 mL of acetonitrile in 60-mL amber wide-mouth glass bottles with Teflon-lined lids. Any soil that remained after subsampling was returned to the original 250 mL jar that was sent from the field site and contained the rest the unprocessed sample.

Samples Solvent-Extracted without Subsampling


The bulk samples from the step above and all other discrete, box, and wheel samples were air-dried and passed through a 10-mesh sieve. Each

Assessing Sample Processing and Sampling Uncertainty for

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