Department of Health Seal

TGM for the Implementation of the Hawai'i State Contingency Plan
Section 5.6
COLLECTION OF MULTI INCREMENT SAMPLES FOR VOC ANALYSIS

5.6 COLLECTION OF MULTI INCREMENT SAMPLES FOR VOC ANALYSIS

Testing of Multi Increment samples for volatile organic compounds (VOCs) is discussed in Section 4.2.8. Samples to be tested for VOCs are typically collected from cores that represent increments extracted from subsurface DU layers rather than exposed surface soils (see Section 3.4.4). Testing of samples from freshly exposed faces of excavations for VOCs might be required as part of a response to a recent spill or for remedial actions, however (see Section 3.4.5).

The collection of soil samples to be tested for VOCs is similar to that described for non-volatile contaminants, except that increments (or more likely subsamples of DU layer increments collected from cores) are placed in an extraction solution in the field. The collection of samples to be tested under this method should be discussed with the laboratory well in advance of field work. A sampling and analysis work plan should also be provided to HDOH for review prior to the commencement of field activities. The analytical laboratory should be consulted prior to sample collection to discuss sample containers, sample handling, preservative type and volume, shipping of samples in methanol, anticipated laboratory method detection limits, etc.

Method 5035 allows for samples to be extracted in the field by placement in a selection of solutions, based on desired detection limits, sample preservation method, and holding time limitations (USEPA, 2002h; refer also to MADEP, 2002, TRNCC, 2002 and CalEPA, 2004b). The guidance recommends that soil samples, or in the case of Multi Increment sampling methods soil increments, to be tested for VOCs should be placed in containers with pre-measured amounts of either methanol (most common) or reagent-grade (e.g., distilled) water. However, the use of reagent-grade water for preservation is not recommended by the HEER Office due to concerns regarding extraction efficiency and very short hold times (See Section 11.2). The volume of the solution (typically provided by the laboratory in pre-weighed amber bottles) is based on the anticipated mass of soil sample to be collected. Although individual increments are not typically weighed in the field, coring devices with calibrated sample collection volumes are generally utilized so reasonable estimates of total mass can be made. The total mass of soil placed in the solution should closely match what was planned for a particular DU/site investigation to help ensure the amount of methanol provided by the laboratory is adequate to keep the soil covered by methanol at all times.

Methanol is the most commonly used solution for field preservation of soil samples. This allows for a holding time of 14 days prior to analysis by the laboratory. The samples should ideally reach the laboratory within 48 hours in order to verify that methanol is not being lost from the sample container. Potential problems with the use of methanol include an increase in method detection levels due to the need to dilute the solution for analysis, as well as logistical issues related to obtaining, storing and shipping the flammable solution around the islands.

The use of water as an extraction solution is not recommended (See Section 11.2. This approach was included in the original, USEPA 5035 lab method in order to allow for lower detection limits of VOCs in soil in comparison to samples extracted into methanol (USEPA, 2002h). Improvements in laboratory methods since that time should provide methanol based reporting limits of 50 µg/kg for volatile chemicals, which is more than adequate for screening purposes. The water-based extraction is also significantly less effective in comparison to methanol according to laboratories contacted by the HEER Office. While the precision of the data in terms of the analytical method might be higher than for methanol, there is a strong possibility that the concentration of the VOC reported will under-represent the actual concentration in the sample collected. In addition, VOCs will be less tightly held in water than in methanol and can be lost when the sample bottle is opened repeatedly to add increments. A further disadvantage is that samples must either be tested within 48 hours or frozen to -7ºC by that time and then tested within seven days from the sample collection date. This limited holding time can pose additional problems for samples that must be shipped to the mainland for analysis.

The use of an acidic, sodium bisulfate solution as an alternative to water provides both an extended holding time (up to 14 days) and allows for similarly low detection levels. Reaction with organic matter, effervescence and loss of VOCs in calcareous soils, and other potential problems interfere with the use of this approach in the field, however. Both of these issues can be significant problems in Hawai‘i and the use of sodium bisulfate is generally limited (See Section 11.2; and Alternative Approaches, Subsection 5.6.3).

5.6.1 INCREMENT COLLECTION

A volume of methanol adequate to accommodate the estimated mass of increments to be collected for a Multi Increment sample is placed in the sample bottle prior to collection of the sample (Figure 5-36). A minimum 1:1 ratio of solution to soil is recommended (i.e., 1 milliliter of methanol to 1 gram of soil). The laboratory will typically provide sample jars with pre-measured amounts of the solution based on direction from the sampler regarding the approximate mass of soil to be added. Additional methanol may be required to ensure the sample mass is completely submerged. This should be discussed with the laboratory that will receive and analyze the samples.

To select the appropriately sized sample container, consideration should be given to the total volume of soil to be collected and preservative required. A minimum 300 g mass of soil should be collected to prepare a bulk Multi Increment sample (refer to Section 4.2.3). For example, 60 increments of 5 g each for a total of 300 g of soil (minimal mass recommended for Multi Increment samples) would require approximately 300 ml of preservative. Utilize a container that is large enough to accommodate additional preservative (if needed) and to prevent loss of preservative through splashing as soil increments are dropped into the container. This can normally be accomplished using one-liter, amber glass bottles pre-filled at the laboratory with 300 ml of methanol.

It is very important to remember that soil samples (increments) collected for VOC analysis need to be placed in methanol as soon as possible (i.e. within a minute or two) to prevent potential loss of volatiles due to volatilization and/or biodegradation. Good planning of the field sampling effort is essential to help ensure VOC samples are collected appropriately.

Figure 5-36. Subsampling DU Layer Increments from Borehole Cores with Methanol Preservation

Upper Left Photo: DU layers identified in core (depicted by arrows).

Upper Right Photo: Core increment subsampled by collection of 5 gram plugs at regular spacing to collect targeted increment subsample mass (inexpensive TerraCore™ sampler shown). Subsample plugs placed in jar with pre-measured volume of methanol intended to provide a 1:1 ratio of methanol to soil.
Lower Left photo: Total weight of subsample plugs collected from increment monitored to ensure consistency between boreholes, and that the target bulk Multi Increment sample mass is met.
Lower Right Photo: Use of sealable, 5-10g coring devices for collection and storage of individual increment subsamples when field use of methanol is not practical (Core N' One™ device shown). Increment subsamples (or actual increments) immediately frozen and shipped to laboratory for subsequent combination, extraction into methanol and testing.

5.6.2 SUBSURFACE DU LAYERS

Small coring devices, as described in Subsection 5.4.2, can be used to collect Multi Increment samples from subsurface boring cores to be tested for VOCs (HDOH, 2011i). Recall that each section of core extracted from a targeted DU layer represents an increment, as is the case for surface Multi Increment samples (see Section 4.2.7). Individual core increments extracted from borings will normally need to be subsampled prior to placement in a container due to their large mass (see Subsection 5.4.2).

Evenly spaced plugs of soil should be removed from the core increment and placed in the preservative solution (i.e. methanol) container specifically designated for that DU layer (Figure 5-36). The use of plugs rather than wedges helps to control the total mass of soil collected, and may result in less disruption of the soil core that could contribute to loss of volatiles. Subsamples from core increments from other borings installed into the same DU layer are progressively added to the container as the field investigation advances in order to prepare a final bulk Multi Increment sample for that layer.

The mass of soil removed (subsampled) from each individual core increment should be kept constant, assuming a constant DU layer thickness, and adequate to ensure that a minimum 300 g bulk Multi Increment sample is collected from the DU layer. As a default, the collection of 5-10 g plugs every 5-10 cm (2-4 inches) along a core increment is recommended (refer to HDOH, 2011i). This should be adjusted based on target mass of soil to be collected from a targeted DU layer. Maintain consistent plug spacing for subsampling of core increments collected from DU layers with varying thicknesses between borings (see HDOH, 2011i).

As noted in Subsection 5.6.1, when sampling VOCs in soils it is important to ensure that soil is placed in the preservation fluid (methanol) within a few minutes after collection to reduce losses due to volatilization and biodegradation. This can be especially challenging when collecting samples or subsamples from multiple subsurface borings and multiple DU layers per boring. Very close coordination is necessary between the drill crew and the sampling crew to coordinate appropriate timing and handling of each soil boring to minimize the time between soil extraction and subsampling into methanol. The timing of each soil boring collected by the drill crew should be carefully synchronized with the rate at which the sampling team can access and subsample the soil boring quickly. A well organized work station for processing the subsamples needs to be set up, all sample containers should be pre-labeled to save processing time, and adequate storage containers/coolers provided to accommodate samples collected. If a nearby indoor workstation is not available for use, then a field work station with tarps or covers for rain, sun, and/or wind protection will likely be needed. An adequate number of personnel are needed on the sampling team to ensure subsamples from all DU layers in the soil boring can be obtained and placed in methanol within minutes of each boring being obtained and opened for access.

Increments should be collected using tools that minimize the loss of volatile chemicals during sample collection (i.e. cause the least disaggregation of soil during collection) and allow the collection of at least a five-gram mass of soil. Syringe-type, core-shaped devices that can be pushed directly into the soil are preferable. Examples include the TerrCore™, Core N' One™ and Encore™ tools (see Figure 5-36). Plastic, inexpensive devices that cannot be sealed (e.g., disposable syringes with forward ends cut off, TerraCore™ device) are most suitable for sample collection when methanol can be used in the field. These types of devices can also be used for the collection of samples to be tested for nonvolatile chemicals.

Somewhat more costly but sealable, Core N' One™ or Encore™-type devices are commonly used to collect increments or increment subsamples for projects where the use of methanol in the field is not practical (see Subsection 5.6.3 below).

As depicted in Figure 5-36, the device is pushed into the soil, retracted, and the increment collected is immediately extruded into a container with a premeasured volume of preservative (e.g. methanol). Then end of device can be trimmed to make a scoop for subsampling of gravelly soils. This is repeated with each increment or increment subsample. Dedicated sampling devices should be used between different DU layers within a single borehole, but can be reused for subsampling of core increments in multiple DU boreholes for the same DU layer.

A single large jar with a pre-measured volume of methanol adequate for the entire targeted DU layer could in theory be used to prepare a bulk Multi Increment sample in the field (i.e., plugs from subsample increments combined from 30+ borings). However, this risks an expensive total loss of the sample should the jar be accidentally broken in the field or at the laboratory.

An alternative approach is to place subsample plugs for individual core increments into a smaller jar specific to each borehole (e.g., see HDOH, 2011i). Methanol from individual jars (aliquots) representing the same targeted DU layer can then be combined at the laboratory for testing. This approach can also allow for different vertical and lateral combinations of core increments to be evaluated in order to obtain a better resolution of the location of the core mass of contamination at depth, and help optimize remediation (see HDOH, 2011i).

Subsample replicates should be collected from 10% of the borings and compared to evaluate the precision of method used (refer to Section 4.2.8.2). This will involve the collection and combination of three separate sets of subsample plugs from the same boring for each of the targeted DU layers. The relative standard deviation of the replicate data sets should be compared and subsampling methods modified, as needed, to achieve acceptable precision. Increasing precision could require a decrease in plug spacing and/or an increase in the mass of subsamples collected from individual increments.

5.6.3 ALTERNATIVE APPROACHES

Because methanol is a hazardous material with flammability and toxicity concerns, shipping by air is highly restricted unless it is in accordance with specific rules. The U.S Department of Transportation and the Airline industry (International Air Transportation Association or IATA) regulations on air shipping of hazardous materials provide "Excepted" quantities of methanol that can be shipped by air without special packing materials or special training/certification of the shipper. The excepted quantity for air shipping of methanol is no more than 30 milliliters per inner container, and a maximum of 0.5 liter per cooler or package. There is no limitation on the number of separate coolers or packages that can be shipped as long as each one meets the "Excepted" quantity requirements (confer with airline used and applicable IATA regulations). Those that are shipping Excepted quantities still need to ensure that the package(s) are properly labeled, and they have knowledge regarding the samples and sampling methods used. Check with the shipper beforehand to ensure that containers are properly labeled and shipping requirements met. Restrictions could vary between islands and airlines. For shipping methanol above the Excepted quantities, a hazmat-trained shipper or packer should be utilized, or someone with equivalent training/certification and knowledge of applicable IATA regulations.

Wherever volumes of methanol greater than 30 milliliters per container presents problems for air shipping (especially for sites not on O`ahu) alternatives can be considered in consultation with the laboratory. For example, collect Multi Increment increments into the full recommended volume of methanol in the field. Agitate the sample and allow the solution to equilibrate over a twenty-four hour contact period. Decant at least 20ml of the solution into a standard 40ml VOA vile (check with laboratory on required volume). This alternative should only be conducted under a specific SOP provided by the laboratory and is included in the site investigation report. Ship the samples to the laboratory under the "Excepted" quantity category for methanol (in accordance with airline used, and applicable IATA regulations). Method 5035A also notes that sonification of samples at 40°C for 30 minutes can be carried out for samples with less than 24 hours contact, so if this option is available it could be used shorten methanol contact time required before subsampling and shipping samples by air (include this practice in SOP with laboratory, if used). Note that the remaining spent methanol mixture is classifiable as a listed hazardous waste and must be managed accordingly (F003, spent, non-halogenated solvents; Hawai‘i Administrative Rules §11-262-11). The spent mixture might also be classifiable as a hazardous waste due to ignitability. However, quantities of waste methanol generated will likely be minimal, in which case regulations for conditionally exempt small quantity generators found in Hawai‘i Administrative Rules §11-26—1-5 will apply (100 kg limit).

A potential limitation of the extraction of samples in methanol is an increase in method detection limits (MDLs). This could cause the MDLs to be above relevant HDOH EALs for certain targeted chemicals. Multi Increment soil samples for volatile analyses can be tested using Selected Ion Monitoring (SIM) laboratory methods to reduce method reporting limits to target action levels for samples preserved in methanol. The SIM methods target a small number of select compounds instead of a full standard VOC list, and typically allow an order-of-magnitude reduction in reporting limits in comparison to standard Method 8260 analysis.

Another alternative used in Hawai‘i due to methanol air shipping restrictions is to immediately freeze individual MI increments for shipping and have the increments combined in methanol at the laboratory prior to analysis (refer to USEPA, 2002h; also see Section 11.2). Individual increments for MI samples are collected in separate sampling devices that have vapor tight seals and are designed for zero headspace (e.g. Core N’ One™, EnCore™, or equivalent type sampler). The samples are either stored on ice between 2°C and 6°C and must be analyzed within 48 hours, or immediately frozen in the field to between -7°C and -15°C (or stored immediately on ice between 2°C and 6°C and frozen within 48 hours to between -7°C and -15°C) and must be analyzed within 14 days of sample collection (see Section 11.2). Note that to freeze samples in small cores with vapor-tight seals to temperatures between -7°C and -15°C (for temporary storage and shipping) use water ice with added salt (Hewitt, 1999), and document that suitable freezing temperatures are achieved. Dry ice may be another option, though sample temperatures could go below -20°C and compromise the integrity of the seals on the small air-tight cores. Consequently, if dry ice is utilized packing methods should be developed to keep the dry ice from direct contact with the samples and document that temperatures of the samples remain between -7°C and -15°C. Check with the shipper for procedures to ship dry ice, including the amount of dry ice that can be placed in a single cooler, package labeling, and requirements for the use of a vented cooler.

Although not ideal, the approach of freezing individual increments of MI samples for VOC analyses may be unavoidable for samples collected on islands other than O´ahu due to the logistical difficulties of obtaining, storing, and shipping methanol from other islands and the time required to ship samples to a laboratory on the mainland for testing. If problems persist, then the DQOs of the investigation should be reviewed and discussed with the HEER Office. High-quality (e.g., MIS) data with elevated detection limits are preferable to low-quality data (e.g., discrete soil samples) with lower detection limits. In most cases use of the laboratory detection limit as a screening level when the EALs cannot be met will be acceptable (refer to EHE guidance; HDOH 2016). If discrete soil samples are collected and tested then the data should be considered usable for qualitative, screening level purposes only (e.g., presence or absence). Decision making should be supported by the collection of soil gas sample data at the site (recommended for all sites impacted with potentially significant amounts of VOCs; refer to Section 7).