Soil Sampling Procedures

The procedures described here generally apply to any type of soil sampling. Any departures from the procedures contained in the SAP should be documented and justified.

4.7.1. Preparation

Thorough preparation is the key to a successful project. Before beginning any sampling program, personnel should complete the following:

 Review the SAP and HASP to identify special equipment and procedures

 Obtain the required equipment. A sample list of soil sampling equipment is provided at the end of this chapter

 Inspect the site to ensure that present conditions are the same as indicated in the

SAP and that all designated sample locations are accessible

 Prepare decontamination facilities for personnel and equipment as required by the HASP.

Refer to Chapter 3 for a complete discussion of sampling preparation requirements applicable to all types of sampling programs.

4.7.2. Sample Collection

Field sampling personnel should be familiar with all of the technical issues and documentation provided in the SAP. The following sampling procedures can be used when there are no special conditions present or special requirements speci-fied by the SAP. Refer to Chapter 3 for a com-plete discussion of sample collection require-ments applicable to all types of sampling pro-grams.

4.7.2.1. Surface Samples

The simplest and most direct method for collect-ing surface soil samples is with a spade and scoop. The accuracy and representative nature of these samples depends on the care and precision demonstrated by the sampler. A flat, pointed trowel can be used to cut a block of soil 2 inches deep. Chrome plated tools, common with garden implements such as potting trowels, should be avoided.

Sampling Procedures

1. Clear the area to be sampled of any surface debris such as twigs, rocks, and litter. Cut grass down to the level of the soil and re-move.

2. Define a sample area such that a 2-inch deep soil sample will provide enough material for all required sample containers.

3. Dig a trench at least 2 inches deep around the sample block using a clean spade.

4. Cut the sample loose from the ground using a pre-cleaned stainless steel trowel. Place the soil in a clean stainless steel bowl.

5. Remove all roots and other debris. Describe the amount and kind of material removed in the FLB/FN.

6. If instructed by the SAP, sieve the sample as described in Section 4.7.4.2.

7. Fill the sample container(s).

4.7.2.2. Subsurface Samples

Handheld augers and thin-walled tube samplers can be used separately or in combination to col-lect subsurface samples. Where rocky soils do not limit the use of tube samplers, a combination of augers to remove soil material to the depth of interest and tube samplers for actual sample collection allows the most precise control of sample collection. Depths of up to 2 meters can be readily sampled, and depths of up to 6 meters can be achieved where conditions are favorable.

A drill rig should be used to gain access where deeper samples are required or where soil condi-tions preclude the use of augers. Tables 5-1 and 5-2 summarize the applications and limitations of different types of augers and tube samplers for sampling under different soil conditions. Section 4.6.2.1 describes procedures for using augers.

Section 4.6.4.5 discusses the selection and use of various types of thin-walled tube samplers.

4.7.2.3. VOCs

EnCore™ samplers can be used to collect soil samples for VOC testing. Separate procedures are provided below for collecting samples with high and low concentrations of VOCs.

Note: The EnCore™ sampler has not been thoroughly evaluated by EPA as a sample storage device. While preliminary results indicate that storage in the EnCore™

device may be appropriate for up to 48 hours, samples collected in this device should be transferred to the soil samplevials as soon as possible, or analyzed within 48 hours.

When sampling for VOCs, soil samples should be taken from auger cuttings only if soil conditions make collection of undisturbed cores impossible.

New techniques, such as direct-push technologies with the ability to continuously measure vadose zone VOC concentrations in the soil gas, are

useful for defining the boring depth where dis-crete soil samples should be collected for labora-tory analysis. Soil recovery probes with dedicat-ed or reusable liners (see Table 4-2) will minim-ize contact of the sample with the atmosphere.

Sampling Procedures

Low-Concentration VOC Soil Samples Steps 1 – 5 are performed prior to transporting VOC vials to the field for sample collection.

1. Add approximately 1 gram of sodium bisul-fate to each vial. If samples that are markedly smaller or larger than 5 grams are to be col-lected, adjust the amount of preservative to correspond to approximately 0.2 grams of preservative for each gram of sample.

Enough sodium bisulfate should be present to ensure a sample pH of 2.

2. Add 5 milliliters of organic-free reagent water to each vial. The water and the preservative will form an acid solution that will reduce or eliminate the majority of the biological activi-ty in the sample, thereby preventing biode-gradation of the VOAs.

3. Seal the vial with the screw cap and septum seal. If double-ended, fritted vials are used, seal both ends as recommended by the manu-facturer.

4. Affix a label to each vial to eliminate the need to label the vials in the field. This will ensure that the tare weight of the vial includes the bel. The weight of markings added to the la-bel in the field is negligible.

5. Weigh the prepared vial to the nearest 0.01 gram, record the tare weight, and write it on the label.

6. Using an EnCore™ Sampler, collect approx-imately 5 grams of sample as soon as possible after the surface of the soil or other solid ma-terial has been exposed to the atmosphere- generally within a few minutes at most. Care-fully wipe the exterior of the sample collec-tion device with a clean cloth or towel.

7. Add about 5 grams (2 – 3 centimeters) of soil from the EnCore™ Sampler to the sample vi-al containing the preservative solution. Quick-ly brush any soil off the vial threads, and im-mediately seal the vial with the septum and screw cap. Store samples on ice at ≤ 6°C.

Note: When samples are known or suspected to contain high levels of carbonates, a test sample should be collected, added to a vial, and checked for effervescence. If a rapid or vigorous reaction occurs, discard the sample and collect low-concentration samples in vials that do not contain the preservative solution.

8. When practical, use a portable balance to weigh the sealed vial containing the sample to ensure that 5.0 ± 0.5 grams of sample were added. The balance should be calibrated in the field using an appropriate weight for the sample containers. Record the weight of the sealed vial containing the sample to the near-est 0.01 gram.

High-Concentration VOC Soil Samples 1. Add 10 milliliters of methanol to each vial.

2. Seal the vial with the screw cap and septum seal.

3. Affix a label to each vial to eliminate the need to label the vials in the field. This will ensure that the tare weight of the vial includes the bel. The weight of markings added to the la-bel in the field is negligible.

4. Weigh the prepared vial to the nearest 0.01 gram, record the tare weight, and write it on the label.

Note: Vials containing methanol should be weighed a second time on the day that they are to be used. Vials found to have lost methanol (reduction in weight of > 0.01 gram) should not be used for sample collection.

5. Using an EnCore™ Sampler, collect approx-imately 5 grams of sample as soon as possible after the surface of the soil or other solid ma-terial has been exposed to the atmosphere- generally within a few minutes at most. Care-fully wipe the exterior of the sample collec-tion device with a clean cloth or towel.

6. Add about 5 grams (2 – 3 centimeters) of soil from the EnCore™ Sampler to the sample vi-al containing the preservative solution.

Quickly brush any soil off the vial threads, and immediately seal the vial with the septum and screw-cap. Store samples on ice at ≤ 6°C.

7. When practical, use a portable balance to weigh the sealed vial containing the sample to ensure that 5.0 ± 0.5 grams of sample were added. The balance should be calibrated in the field using an appropriate weight for the sample containers. Record the weight of the sealed vial containing the sample to the near-est 0.01 gram.

4.7.2.4. Other Parameters

Collect approximately one liter of soil for each sample, and follow procedures for sampling handling and preparation (see Section 4.7.4).

Record the depth from the surface to the top and the bottom of the core, soil color, type, and other attributes in the FLB/FN. If the sample consists of two different types of soil (e.g., sand and clay, or different color layers), split the core as re-quired so that only one soil type is present in the sample; record the depth of the change of soil types in the FLB/FN.

Following sample preparation and handling, cap sample bottles tightly, affix labels, and place the bottles in resealable plastic bags. The chemical preservation of soils generally is not required.

However, samples should be cooled to ≤ 6°C as soon as possible.

4.7.3. Composite Sampling

Compositing is the process of physically combin-ing and homogenizcombin-ing several individual soil aliquots. Compositing provides for an average concentration of contaminants over a certain number of sampling points, which reduces both the number of required laboratory analyses and the sample variability. Compositing always should be implemented with caution. Composite samples should be collected only after full justifi-cation and documentation of rationale in the sampling plan. Composite sample collection

techniques should not be used if justified solely on the basis of reducing sample testing costs.

The method of compositing the sample should be documented and uniform to ensure future data comparability.

4.7.3.1. Composite Sampling Techniques If composite samples are collected, the first step is to collect a soil sample from the sampling location specified in the sampling plan using the documented procedure. Any variation from the stated procedure or SAP must be recorded. Com-posite samples may be collected on the basis of biased sampling or a variety of statistical sam-pling techniques. Biased samsam-pling is used when visual, odor, or volatile organic detection is found. A portion of the material is collected and combined with other positive areas. Two statis-tical sampling techniques that can be used for composite sampling are described below.

4.7.3.1.1. Random Sampling

Random sampling is the arbitrary collection of samples within defined boundaries of the area of concern. Random sample locations should be chosen with a random selection procedure (e.g., using a random number table). Each sampling point must be selected independently, so that all locations within the area of concern have an equal chance of being selected. Randomization is necessary to support probability or confidence statements about the sampling results. The key to interpreting these probability statements is the assumption that the site is homogeneous with respect to the parameters being monitored. The random sampling technique will not adequately characterize the true conditions of a heterogene-ous site.

The following example illustrates how random soil sampling has been used to verify the achievement of soil remediation objectives:

Random Sampling Example. Approximately 300 tons of diesel contaminated soils were exca-vated from a railroad fueling operation and thinly spread over approximately one half acre to allow for biodegradation. A single composite soil

sample was to be collected quarterly for total petroleum hydrocarbons to monitor remedial progress. The composite sample was to be pre-pared from 6 discrete soil samples. To collect the 6 soil samples from random locations across the half-acre area, a grid consisting of 40 equally sized squares was placed on a site map showing the area. Each square was numbered from 1 – 40, and a random number generator was used to pick locations from the grid. The sampling team then collected discrete soil samples from each of the six locations and prepared a single composite sample for laboratory analysis.

4.7.3.1.2. Stratified Random Sampling Stratified random sampling often relies on histor-ical information and prior analythistor-ical results (or screening data) to divide the sampling area into smaller areas called strata. Each stratum is more homogeneous than the site as a whole. Strata can be defined based on various factors, including sampling depth, contaminant concentration le-vels, and contaminant source areas. Stratified random sampling imparts some control upon the sampling scheme but still allows for random sampling within each stratum. Different sam-pling approaches may be selected to address the different strata at the site. Stratified random sampling is a useful and flexible design for esti-mating the pollutant concentration within each depth interval or area of concern.

4.7.3.2. Sample Compositing Procedures In most cases of sample compositing, equal amounts of material are collected and mixed in the sample container. Protocols for combining the sample are based on site conditions, the para-meters being measured, the regulatory limit, and DQOs. The rationale for the use of glass, stain-less steel, or polyethylene equipment for combin-ing samples, and the rationale for combincombin-ing the soil in equal amounts, proportional amounts, or other amounts should be documented.

Specify the method for selecting the composite aliquots and the compositing factor in the sam-pling plan. The compositing factor is the number of aliquots to be composited into one sample

(e.g., 3 – 1, 10 – 1). Determine this factor by evaluating the detection limits for parameters of interest and comparing them with the selected action level for that parameter. Compositing also requires that each discrete aliquot be the same in terms of volume or weight and that the aliquots be thoroughly homogenized. Because composit-ing dilutes high-concentration aliquots, the appli-cable detection limits should be reduced accor-dingly. If the composite value is to be compared to a selected action level, then the action level should be divided by the number of aliquots that make up the composite to determine the appropri-ate detection limit (e.g., if the action level for a particular substance is 50 parts per billion (ppb), an action level of 10 ppb should be used when analyzing a 5-aliquot composite). The detection level need not be reduced if the composite area is assumed to be homogeneous in concentration (e.g., stack emission plume deposits of particulate con-tamination across an area, or roadside spraying of waste oils).

In an example situation of a soil sampling pro-gram designed to detect petroleum products in an area of homogenous concentration, an appropriate sample compositing technique would be to use an adequately sized resealable freezer storage bag.

Sampling personnel would collect a minimum of three equally sized samples (10 is preferred) from designated sample locations and place those samples in the sample bag. Personnel would then close and secure the bag using care to eliminate trapped air and combine the samples by tumbling and kneading until fully mixed.

Soil samples should be homogenized after com-positing is complete to ensure soil uniformity.

Note: Do not composite or mix soil samples that are to be tested for volatile organics.

4.7.4. Sample Handling and Preparation Proper sample handling and preparation ensures that each sample container is filled with soil that represents the entire sample and that large rock fragments are either removed or included in each container in an amount proportional to their presence in the soil, as specified by the SAP.

Techniques for sample handling and preparation are provided in the subsections below.

4.7.4.1. Soil Homogenization

Homogenization is the mixing or blending of a soil sample to provide uniform distribution of conta-minants. Ideally, proper homogenization ensures that portions of the containerized samples are equal or identical in composition and representa-tive of the total soil sample collected. Incomplete homogenization will increase sampling error.

Samples to be composited or split should be ho-mogenized after all aliquots have been combined.

Manually homogenize samples using a stainless steel spoon or scoop and a stainless steel bucket, or use a disposable scoop and pan.

Note: Do not homogenize soil samples that are to be tested for volatile organics.

4.7.4.2. Sieving

Sieving eliminates large rock fragments. Under some EPA protocols, only fine soil material should be analyzed; see Figure 4-5 for an illustra-tion of sieves.

Note: Do not sieve soil samples that are to be tested for volatile organics.

Instructions for sieving are as follows:

1. Break up soil aggregates and pull apart any vegetation and root mat, if present. Weigh the non-soil vegetation fraction, and archive or discard, as required by the SAP.

2. Remove and weigh large rocks. Archive for possible analysis.

Figure 4-5. Sieves

3. Crush the entire soil sample with a rolling pin, stainless steel spoon, or similar tool. Mix tho-roughly with a stainless steel spoon.

4. For samples of surface soil, sieve through a clean 0-mesh (No. 1, 2 mm) screen. Use a 3/8-inch standard sieve (9.5 mm) to screen samples that will be tested to determine whether the soil should be classified as ha-zardous waste under RCRA. Use a disposa-ble stainless steel screen for samples to be analyzed for semivolatile organic contamina-tion. Use Teflon® screens for samples to be analyzed for metal contamination.

5. If the soil is too wet or too cohesive to pass through the sieve, note that the required siev-ing was not done in the FLB/FN, and enter this notation on the Field Sampling Form. In-form the Sampling Program Manager that the sample could not be sieved.

6. Spread out the screened sample, mark off quarters, and take samples from each quarter in a consecutive manner until appropriate sample volume is collected. If specified, arc-hive the remaining sample for future analysis.

7. Before shipping the samples to the laboratory, shake each sample container to mix thorough-ly.

4.7.4.3. Splitting Samples

Many times samples are split between representa-tives of the property owner or between state or federal enforcement agencies so results may be independently verified. Soil samples split be-tween laboratories are typically performed to evaluate laboratory quality. Soil samples should be split from a single sampling event following homogenization and sieving. Specific procedures for splitting samples for VOC, semivolatile or-ganic, and metal analyses are described below.

 Splitting Samples for VOC Analysis. To split samples for VOC analysis, collect two core samples from adjacent locations.

Alternatively, split a soil core longitudinally with a clean knife and place half of the core into each sample container, minimizing air

contact as much as possible. The method of splitting the sample may greatly affect the results. Documentation and execution of the splitting technique should be uniform to ensure data comparability.

 Splitting Samples for Semivolatile Organic Chemical (SVOC) and Metal Analyses. To split samples for semivolatile and metal

analyses, place the soil in a clean stainless steel

analyses, place the soil in a clean stainless steel