6.4 Quality Assurance/Quality Control
Laboratory SOPs for ISM sample processing and analysis should be requested and reviewed as part of the systematic planning process.To help ensure data quality, all field sampling, field processing, and laboratory sample processing activities should be supervised by personnel trained in ISM. Samples should be shipped to a certified laboratory following recommended protocols for the class of target analytes (e.g., 4°C for VOCs and SVOCs) to be analyzed. See Section 5.4.1 for ISM field implementation details. Laboratories should have well-trained analyst(s) that follow documented SOPs while processing, subsampling, and analyzing samples. Laboratory SOPs for ISM sample processing and analysis should be requested and reviewed as part of the systematic planning process. Chain-of-custody, laboratory notes, and completeness reports should accompany all data packages.
QC measures should be implemented both in the field and laboratory. When sample processing is initiated in the field to reduce the amount of sample shipped off site, replicate samples of the processed soil should be taken to establish the uncertainty introduced by this step (see Section 5.4.1). It should be noted that reducing the mass of the sample shipped to the lab will tend only to increase the FE. Depending on the contaminant, field blanks and/or equipment blanks also may be required. Field blanks often are necessary for VOCs and some SVOCs, particularly when a solvent is involved.
General laboratory QA principles apply to incremental sampling methodology samples.
The laboratory must have QA/QC procedures for documenting ISM method performance (i.e., precision, accuracy, method sensitivity), as well as QA/QC procedures for documenting matrix effect(s). At a minimum, these procedures may include the analysis of QA/QC samples such as a method blank, a matrix spike/matrix spike duplicate (MS/MSD), sample replicates, and a laboratory control sample (LCS) in each analytical batch as appropriate. All QA/QC samples should be subjected to the same analytical procedure as those used on actual samples, as applicable to the contaminant and analysis.
Laboratory replicates are recommended to assess the precision of the ISM subsampling processes. Generally, two or three replicate subsamples should be collected after all ISM processing is complete. These replicates should then be carried through the rest of the analytical process. The frequency of these replicates can vary from one replicate set per batch to one set per project depending on the project DQOs. Note that there is a difference between replicates collected during sample processing and replicates collected during the field sampling effort. ISM replicates collected from a DU provide information on the variance in the estimate of the mean without specifically separating out the contribution of laboratory sample processing from other sources of variance.
Two or more laboratory replicates are recommended to assess the precision of the ISM subsampling.
A clean sample matrix, when available, can be used to establish whether equipment used to process samples (e.g., pulverize, split, mix, etc.) has been adequately cleaned between field samples. Clean soil matrices are more likely to be available for organic analytes. For metallic analytes there are no known soil-like matrices that are nondetect at environmental levels of concern for all likely metals. Reagent water or fluoropolymer boiling chips have been used in some instances. A well-characterized soil sample that has low or nondetect concentrations of the critical metals contaminants for a site can also be used to assess equipment and process cleanliness.
The LCS is a known matrix spiked with compound(s) representative of the target analytes. It is used to document possible analyte loss and/or laboratory method performance. LCS control limits must be established by the laboratory for each ISM procedure and analysis performed and provided in the final laboratory report.
The MS/MSD is an aliquot of sample spiked with a known concentration of target analyte(s). The spiking occurs prior to sample preparation and analysis. An MS/MSD is used to document the bias of a method in a given sample matrix.
Currently, most LCSs and MS/MSDs are introduced after ISM sample processing since it is costly to add surrogate or target analyte spikes of sufficient concentration to a 1 kg or greater ISM sample. Large-scale LCSs consisting of a clean matrix spiked at the laboratory with the analytes of interest and run through most if not all of the incremental processing steps should be considered. The current state-of-the-art materials limit the ability to accurately assess all processing steps. The current materials costs are high when considering 1 kg soil and associated spiking quantities. Additionally, storage and disposal of large volumes of this type of LCS matrix are an issue. Costs are expected to decrease over time if market demand for the material increases. As the technical issues and cost of large spike quantities are addressed, spiking prior to ISM processes may be more common.
Monitoring the air-drying and sieving steps is problematic for SVOCs and/or VOCs. The deposition of the spiking solution onto the LCS might not result in a sample with spiking compounds bound in the same manner as the sample contaminants themselves. The association between low-boiling-point SVOCs and the clean soil or sand matrix might be significantly weaker than in weathered field samples. Thus, potential losses from a laboratory prepared control sample that is air-dried can be significantly higher than from a field sample. Theoretically, it is also possible that COCs are bound significantly to the matrix and will not be dissociated completely during the extraction/digestion step, but these same compounds will be easily extracted/digested in the LCS. However, if, for example, air-drying, sieving, and subsampling are the only ISM sample processing steps being performed, a “standard” (i.e., approximately 30 g) clean matrix spiked LCS carried through all of these steps would present the potential “worst-case” analyte loss to be evaluated for some analytes and the “best-case” analyte recovery to be evaluated for other analytes. The “best-case/worst-case” scenario for the LCS exists for discrete samples too. The typical sample size of an ISM sample is 1 kg. An LCS may not need to be the same size as the ISM sample; it may only require the same preparation and analysis process.
In summary, synthetically fortified soils may not produce the same strength of interactions between the contaminants and the soil particles. Several studies demonstrate that extraction rates for short-term fortified soils can be as much as 10 times higher than weathered “native” contaminants from the same soils (Grant et al. 1995). This phenomenon indicates that QC materials spiked at the laboratory or other commercial providers may overestimate contaminant losses during ISM sample processing steps. Reference materials from weathered “native” contaminated soils are more likely to match the loss rates for field samples. However, the number of contaminants covered and the true concentrations are unknown. Neither type of QC material meets all QA goals. The limitations of each should be considered when interpreting the data.
Similarly, due to the bulk mass spiking limitation, modifications may be necessary for MS/MSD analysis. If systematic planning DQOs allow, a small portion (e.g., 100 g) of the as-received ISM sample could be removed using an appropriate splitting or subsampling process (e.g., 2-D slabcake). Before beginning any sample processing, this portion would be spiked with a known concentration of target analytes and then carried through the complete ISM process. This process would increase the uncertainty of the original ISM sample results. For sites with a large degree of heterogeneity, it may be necessary to collect a duplicate ISM sample to use with this type of MS/MSD approach so as not to remove a portion of the primary ISM sample.
Processing for ISM samples collected for energetic contaminants include air-drying, sieving, and grinding preparation steps. The associated QA/QC samples for energetics should also be ground. Grinding a sample may generate heat (see Section 220.127.116.11). The size (mass) of a ground LCS must be decided to more closely replicate the heat generated in the matrix samples. A 500 g solid QC standard for energetics is commercially available (e.g., Environmental Resource Associates, Wibby Environmental). This material is often analyzed as an LCS on a per batch basis. The project-specific DQOs should be assessed during systematic planning to determine the appropriate analysis frequency. Additionally, nitrobenzene, 2-nitrotoluene, 3-nitrotoluene, and 4-nitrotoluene have low recoveries when the QC standard is air-dried at room temperatures. The DQO process needs to address whether the QC standard will be air-dried or only ground. There can be significant cost associated with a commercial QC standard. A separate QC standard is available for Tetryl (an energetics constituent) and should be considered if it is a target analyte. The frequency at which the QC standard needs to be processed and analyzed should be defined during the systematic planning process dependent on project-specific DQOs. With respect to energetics, additional guidance for laboratory QA/QC can be found as part of USEPA SW-846 Method 8330B and is available through the Environmental Data Quality Working Group (EDQW 2008) and DOD Quality Systems Manual for Environmental Laboratories (QSM) (DOD 2010). Prior to using a grinding step for an ISM project with compounds other than those listed in SW-846 Method 8330B, the associated QA/QC samples must be defined.
ISM samples collected for nonvolatile metals may also include drying, sieving, and grinding preparation steps. It is assumed that this process does not cause the loss of metal analytes; therefore, it may not be necessary to require a large-scale LCS through the entire process. The necessity for the metals LCS (large-scale or otherwise) should be defined during the systematic planning process dependent on project-specific DQOs. If metals contributions from the grinding apparatus are of concern (see Section 6.3.3), a method blank carried through the entire process should be performed.
Monitoring of the effectiveness of the grinding steps for metals, explosives, or other particulate-based analytes would be best demonstrated by adding these analytes in solid particulate form (e.g. metal salts) rather than the traditional liquid spike solutions used by laboratories. Demonstrating the ability to produce representative subsamples from heterogeneous samples would require the original QA/QC sample be intentionally heterogeneous and not the highly homogenized reference materials commonly available from providers.
Much of the focus of this QA/QC section is targeted on the “grinding” or “milling” portion of the ISM process, largely due to the paradigm shift of grinding from “traditional” sample preparation and analyses. Simply put, grinding or particle reduction is an invasive sample handling technique and, therefore, requires an additional level of QC. Please note that for most organic analytical methods using ISM, particle reduction by grinding or milling is not necessary. The primary purpose for grinding is reduction of the FE by reducing the particle size and eliminating nuggets that can be the cause for extreme heterogeneity. The following methods are known candidates for particle reduction, milling or grinding:
| Analyte group
||USEPA SW-846 method|
Studies are currently being performed by CRREL for evaluating sample processing for metals that may lead to revisions of USEPA SW-846 Method 3050B.
As previously stated, to establish whether the sample processing protocol is achieving the level of precision stated in the SAP, subsample replicates should be taken at a predetermined frequency. Typically, two or more post-processing subsample replicates are collected and analyzed with every batch of 20 samples, with a targeted RPD or RSD as determined during the project-specific systematic planning process. The milling step can be evaluated for analyte losses under USEPA SW-846 Method 8330B with the aforementioned QC standard. Additionally, a separate QC standard is available for Tetryl and should be considered if it is a target analyte. However, caution must be used when using this QC standard since several of the more volatile analytes are susceptible to vaporization losses during prolonged (>1 hour) air-drying exposure at room temperatures (24°C).
Where technically feasible and practical, it is recommended that QA/QC samples that can accurately measure recoveries of target analytes throughout the entire preparatory and analytical process be included with every sample batch of 20 samples as is the current standard practice with discrete samples. As noted, the grinding and air-drying/sieving processes are areas of concern. Because of the highly invasive nature of the grinding procedure involving great force and production of heat, this step leaves a reasonable potential to affect target analyte recoveries, both high and low. Although large analyte losses are not suspected for select energetic (Walsh and Lambert 2006) and inorganic (metal) compounds, to date, limited data are available to verify this hypothesis. Likewise, limited data are available regarding the possible analyte loss due to the air-drying/sieving procedure. Therefore, demonstration of analyte recovery should be performance based and demonstrated through acceptable QA/QC samples.The long-term goal for technical, method, and material development is to use QA/QC samples that can accurately measure the recoveries of all target analytes throughout the entire preparatory and analytical process with every batch of samples. This is possible for most nonvolatile and high-boiling-point SVOC analytes. The technical issues surrounding lower-boiling-point analytes have not been resolved as of 2010. As QC standards become commercially available for other analyte groups, they should be incorporated into the laboratory QA program for ISM samples. All information presented in this section should be taken into consideration.