Soil Sampling Techniques for Environmental Site Assessments

When This Guide Applies

This guide covers soil sampling procedures for Phase II Environmental Site Assessments (ESAs) and environmental site investigations. It focuses on the practical field techniques you need to collect representative soil samples for laboratory analysis.

We assume you already have a work plan that defines your boring locations, sample depths, and analytical parameters. If you are designing a sampling plan, start with the contaminants of concern from your Phase I ESA and build your conceptual site model before selecting sampling methods.

This guide does not cover geotechnical soil sampling, agricultural soil testing, or PFAS-specific soil sampling (see our PFAS Sampling Best Practices guide for that).

Drilling and Sampling Methods

Direct Push (Geoprobe)

Direct push technology - commonly called “Geoprobe” after the dominant equipment manufacturer - is the standard method for most environmental soil investigations. A track- or truck-mounted rig uses hydraulic percussion to drive sampling tools into the ground without removing cuttings. This is the method you will use for the majority of Phase II ESAs and site investigations.

How it works: A sampling tool (usually a Macro-Core or dual-tube sampler) is driven to the target depth. The tool is retrieved with a soil core inside an acetate or clear PVC liner, typically in 4-foot runs. You split the liner lengthwise, log the soil, screen with a PID, and collect your samples from the appropriate intervals.

Best for:

• Phase II ESAs and site investigations requiring multiple borings
• Depths beyond hand auger range (roughly 10-100+ feet depending on geology)
• Continuous core recovery for detailed lithologic logging
• Sites where you need both soil and groundwater samples from the same boring

Limitations:

• Cannot penetrate bedrock, dense glacial till with cobbles, or thick gravel layers
• Requires a drilling subcontractor and equipment mobilization
• Needs adequate site access for the rig (minimum roughly 8-foot wide path for tracked units)
• Not practical for 1-2 shallow borings where a hand auger would suffice

Working with the core: When the core comes up, split the liner lengthwise to expose the soil. Examine both the outside and inside of the core - the outside surface does not always give a clear picture of what is in the core because it contacts the liner wall during advancement. Cut sections as needed to examine specific intervals more closely. For VOC sample collection, work quickly once the soil is exposed - collect your VOC samples from freshly cut surfaces before the core has time to off-gas.

Dual-tube versus single-tube: Dual-tube systems keep the borehole cased during sampling, preventing cross-contamination between soil zones. Use dual-tube when sampling through known contaminated intervals to reach deeper clean zones. Single-tube (Macro-Core) systems are simpler and faster but leave the borehole open as you advance. Clear acetate liners let you see soil color changes and staining through the liner before opening, which helps with field decisions about where to collect samples.

Hand Auger

A hand auger is a manually operated boring tool with a helical flight that you twist into the ground to bring up soil. Simple, portable, and cheap.

How it works: You twist the auger into the ground, pull it up when the flight is full, and empty the cuttings. Repeat until you reach your target depth. Extension rods let you reach deeper, but the work gets significantly harder below about 8-10 feet.

Best for:

• Limited access locations where a rig cannot reach (inside buildings, fenced yards, steep slopes)
• Shallow investigations (less than 10-15 feet) in soft, cohesive soils
• Small-scope projects with only a few sample points
• Confirmation sampling where you need one or two quick borings
• Utility clearance before machine drilling - if you have any doubt about underground utilities at a boring location, hand auger the first few feet to verify you are clear before bringing in the Geoprobe

Most firms default to Geoprobe for nearly all Phase II work. Hand augers are the fallback when access or budget constraints rule out a rig, not the first choice.

Limitations:

• Extremely difficult in dense clay, dry sand, gravel, or any soil with significant rock fragments
• Very slow below 8-10 feet
• Core recovery is poor compared to direct push - you are retrieving disturbed cuttings, not intact core
• Limited ability to log soil stratigraphy accurately due to mixing in the flight

Practical notes:

• In cohesive soils (silty clay, clay), a hand auger can be surprisingly effective down to 10 feet or more.
• In sandy or non-cohesive soils, the sample falls off the flight as you pull it up. Adding water helps retain soil on the flight, but be aware that adding water affects some analyses.
• When collecting discrete depth samples, auger to your target depth, pull the auger up, then push a clean stainless steel hand auger or dedicated sampler to the bottom of the hole to collect undisturbed soil from the target interval.

Hollow-Stem Auger (HSA)

Hollow-stem auger drilling uses a conventional drill rig to advance a hollow-stemmed auger into the ground. A split-spoon sampler or Shelby tube is lowered through the hollow center to collect soil samples at discrete intervals.

In environmental work, HSA is used most commonly for installing permanent monitoring wells, often in conjunction with direct push soil sampling performed during the same mobilization. The typical workflow is to collect soil cores with the Geoprobe, then switch to the HSA rig to install wells at selected locations.

How it works: The rig rotates the auger flights to bore through the soil. At the target depth, the driller stops rotation, and a split-spoon or other sampler is lowered through the hollow stem and driven into undisturbed soil below the auger bit. The sampler is retrieved with an intact soil sample.

Best for:

• Installing permanent monitoring wells (the hollow stem acts as temporary casing)
• Sampling in dense tills, stiff clays, or partially weathered bedrock where direct push cannot penetrate
• Sites requiring Standard Penetration Test (SPT) blow counts for geotechnical data alongside environmental samples
• Deep investigations (100+ feet) where direct push runs out of push capacity

Limitations:

• Generates drill cuttings (investigation-derived waste) that must be managed
• Slower and more expensive than direct push for routine soil sampling
• Potential for cross-contamination as cuttings travel up the auger flights
• Requires a larger rig with more site access than a Geoprobe

HSA becomes the primary soil sampling method only when the site geology causes Geoprobe refusal (dense till, cobbles, shallow bedrock) or when the investigation depth exceeds the practical range of the available direct push rig.

Sample Collection by Analyte Group

How you handle a soil sample in the field depends entirely on what the lab is analyzing it for. The wrong container, preservation, or handling technique can invalidate the result.

Coordinate with your lab before mobilizing. Container types, quantities, and preservation requirements vary between laboratories and analytical methods. Your lab will provide a sample container list or kit based on the analytical program in your work plan. Do not assume the containers described below are universal - always confirm with your lab.

In practice, the container set is often simpler than it sounds. For Ohio VAP sites, a typical sample point might include a Terracore or EnCore 5035 kit for VOCs (four 40-mL vials with various preservatives plus a dry weight jar) and two 4-oz glass jars for everything else (SVOCs, metals, TPH, pesticides, PCBs - the lab splits the soil between analyses). For BUSTR sites and most non-VAP work, it is often just two 4-oz jars per sample. The specific containers and quantities depend on the analytical program and the lab, so the details below are general guidance, not prescriptive.

Volatile Organic Compounds (VOCs)

VOC soil sampling requires minimizing the time that soil is exposed to the atmosphere, because volatile compounds begin evaporating the moment the soil surface is disturbed. How you collect VOC samples depends on whether your project uses EPA Method 5035 collection kits.

With Method 5035 kits (EnCore or Terracore samplers):

This is the more rigorous approach, commonly required for Ohio VAP sites. A typical 5035 kit includes four 40-mL vials: two with sodium bisulfate preservative (low-concentration), one with methanol (high-concentration), and one with no preservative (for dry weight determination). The exact kit contents vary by lab, so confirm with your laboratory before mobilizing.

1. Expose fresh soil at the target interval. Work quickly.
2. Using the Terracore or EnCore sampler, push the sampler directly into the freshly exposed soil face to collect approximately 5 grams.
3. Immediately transfer the soil into the pre-preserved vials per the kit instructions. Cap immediately.
4. Label and place on ice in the cooler.

Without Method 5035 kits:

For many BUSTR sites and non-VAP investigations, VOC soil samples are collected in a 4-oz glass jar with no preservative. This is simpler but less rigorous than the 5035 approach.

1. Expose fresh soil at the target interval. Work quickly.
2. Fill the jar to the top with minimal headspace.
3. Label and place on ice.

Critical rules for VOC soil samples (regardless of method):

• Never composite VOC samples. Always collect as discrete samples.
• Never homogenize or mix soil before collecting VOCs.
• Collect VOC samples first - before handling the core for other analytes.
• Time from soil exposure to sealing the container should be minutes, not longer.
• Holding time is 48 hours to the lab for unpreserved samples. Field-preserved samples (5035 vials with preservative) have a 14-day holding time.
• Screen the soil interval with a PID before collecting, but collect the VOC sample from an undisturbed adjacent portion of the same interval - not from soil you already broke apart to screen.
• Some soils with carbonate minerals will fizz on contact with sodium bisulfate. If this happens, note it in your field records and coordinate with the lab.

Semivolatile Organic Compounds (SVOCs) and PAHs

SVOCs and PAHs (polycyclic aromatic hydrocarbons) are less volatile than VOCs, so sample handling is less time-critical. PAHs are a subset of the SVOC analytical group.

Collection procedure:

1. Collect soil from the target interval into a 4-oz wide-mouth glass jar with a PTFE-lined lid.
2. Fill the jar to the top with minimal headspace.
3. Label and place on ice.

Key points:

• SVOCs can be composited if your work plan allows it, but discrete samples are preferred for site characterization.
• When compositing, mix equal portions of soil from each interval in a decontaminated stainless steel bowl, homogenize thoroughly, and fill the jar from the mixed material.
• Do not composite across obviously different soil types (for example, do not mix fill material with native clay).
• Holding time is typically 14 days to extraction for most SVOCs.
• Screen compositing locations with a PID. If any interval shows elevated PID readings, collect it as a discrete sample instead of including it in the composite.

Metals

All soil metals analyses report total concentrations. The total versus dissolved distinction applies only to water samples, not soil. In groundwater, dissolved metals are field-filtered through a 0.45-micron filter to remove suspended particulates before analysis. For soil, the lab digests the entire sample and reports total metal concentrations.

Collection procedure:

1. Collect soil from the target interval into a 4-oz or 8-oz wide-mouth glass or HDPE jar.
2. Remove any obvious rocks, debris, or root material that is not representative of the soil matrix.
3. Fill the jar to the top with minimal headspace.
4. Label and place on ice.

Key points:

• Metals can be composited if your work plan allows it.
• Avoid contact with metal sampling equipment if possible when collecting for metals analysis. Use disposable plastic scoops, wooden tongue depressors, or dedicated stainless steel tools.
• If collecting for both metals and organics from the same interval, collect the organics sample first to avoid cross-contamination from metal tools.
• Holding time is 180 days (6 months) for most metals, which is generous.
• For hexavalent chromium (Cr6+), the holding time is only 30 days and the sample requires specific preservation. Check with your lab.

Pesticides and PCBs

Collection procedure: Same as SVOCs - 8-oz glass jar with PTFE-lined lid, on ice.

Key points:

• Pesticides and PCBs are analyzed by EPA Method 8081/8082 (or equivalent).
• These compounds bind strongly to soil particles and are not volatile, so handling is similar to SVOCs.
• Can be composited under the same conditions as SVOCs.
• Holding time is 14 days to extraction.

PID Screening

A photoionization detector (PID) is your primary field screening tool for volatile contamination. Use it on every boring. Common field models include the MiniRAE 3000 and RKI instruments, both calibrated with isobutylene.

Screening procedure:

1. As each core run comes up, split the liner and immediately note any visible staining, odor, or discoloration.
2. Place a small amount of soil from each interval into a resealable plastic bag (Ziploc-style). Break the soil into small pieces.
3. Seal the bag and let it sit for a few minutes to allow headspace vapors to accumulate.
4. Insert the PID probe into the bag, break the seal minimally, and record the peak reading.
5. Record the reading in your field notes alongside the depth interval.

Using PID results:

• PID readings help you decide where to collect samples. Elevated readings may indicate contamination, but a PID alone does not tell you what compound is present.
• Compare readings across intervals to identify zones of highest contamination.
• PID readings of zero do not mean the soil is clean - the PID only detects certain compounds, and many contaminants (metals, pesticides, most SVOCs) do not produce a PID response.
• Note your PID model and lamp energy (typically 10.6 eV) in your field records. This matters for data interpretation because different lamp energies ionize different compound groups.
• Calibrate your PID before each day of fieldwork using isobutylene (100 ppm standard is typical). Record the calibration standard concentration, pre-calibration reading, post-calibration reading, and instrument serial number.

Soil Logging

Log every boring. Even if the work plan only calls for chemical sampling at specific intervals, a complete lithologic log is essential for understanding subsurface conditions and building your conceptual site model.

What to record at each interval:

• Depth interval (top and bottom of the observation, typically in 1-foot increments for continuous core)
• Unified Soil Classification System (USCS) group symbol (CL, SM, SP, etc.)
• Color using Munsell notation (for example, 10YR 4/3 - brown) or descriptive color
• Moisture content (dry, moist, wet, saturated)
• Consistency/density (for cohesive soils: very soft through hard; for granular soils: very loose through very dense)
• Grain size observations (percentage of sand, silt, clay; presence of gravel or cobbles)
• Odor (none, slight petroleum, strong solvent, etc.)
• Staining or discoloration
• PID reading for that interval
• Recovery (if the sampler advanced 4 feet but only recovered 2 feet of core, note 50% recovery and which portion is missing)
• Depth where water was first encountered
• Sample collection times and depths
• Any other notable features: fill material, debris, root zone, perched water, sheen on water

On subjectivity in soil classification: Logging has an inherently subjective component. Is it a clayey silt or a silty clay? Reasonable geologists will disagree, and the answer often depends on who is holding the core. The important thing is consistency - the same person logging the same material should call it the same thing across all borings on a given project. If you are logging alongside another geologist, agree on terminology before you start.

Practical tips:

• Note the depth to water if you encounter it. This is critical for the conceptual site model.
• Photograph the cores before disturbing them for sample collection. A ruler or tape alongside the core for scale is helpful.

Decontamination

Decontaminate all reusable sampling equipment between each boring location to prevent cross-contamination.

Standard decon procedure:

1. Alconox (or equivalent laboratory-grade detergent) and water wash - scrub all soil contact surfaces
2. Tap water rinse
3. Deionized (DI) water rinse
4. Air dry or pat dry with clean paper towels

Some project work plans may require a solvent rinse (methanol or hexane) for sensitive analytes. This is less common now, but check your work plan before mobilizing.

What needs decon:

• Hand auger flights and extensions
• Stainless steel trowels, scoops, and mixing bowls
• Split-spoon samplers (if reusable)
• Water level meters and PID probes (wipe down between wells)
• Any other reusable equipment that contacts the sample

What does not need decon:

• Disposable equipment: En Core samplers, acetate liners, disposable scoops, nitrile gloves
• Geoprobe drive rods (these do not contact the sample - the liner does)

Practical notes:

• Set up your decon station before you start drilling. You do not want to be washing equipment in a bucket while the driller waits.
• Carry enough DI water for the entire day. Running out mid-day is a common and avoidable problem.
• In cold weather, keep your Alconox solution warm or it will not lather. Some field crews use a small bucket heater.

Quality Control Samples

Your work plan should specify the QC sample frequency. Common field QC samples include:

Field duplicate: A second sample collected from the same interval, placed in a separate container, and submitted to the lab under a different sample ID. Typically collected at a frequency of 1 per 20 samples or 1 per day, whichever is more frequent. The lab does not know it is a duplicate.

Equipment blank (rinsate blank): After decontaminating your reusable equipment, pour DI water over the clean equipment surfaces and collect the rinsate in a sample container. Submit to the lab to verify your decon procedure is effective. Some programs require these; others do not.

Trip blank: A set of sealed, lab-prepared VOA vials containing reagent-grade water that travel with your VOC samples in the cooler. Trip blanks are opened only at the lab. They verify that no contamination was introduced during shipping and handling. Trip blanks are required for all VOC shipments.

Matrix spike/matrix spike duplicate (MS/MSD): Extra sample volume collected from one location for the lab to use in spiking analyses. Your lab will tell you how much additional volume they need. Typically required at 1 per 20 samples.

Chain of Custody

Every sample shipment needs a completed chain of custody (COC) form. The COC is the legal record of who possessed the samples at every step from collection to analysis.

What goes on the COC:

• Project name and number
• Sampler’s name and signature
• Sample ID, date, time of collection
• Matrix (soil for all samples discussed here)
• Number of containers per sample
• Requested analyses with method numbers
• Preservation (on ice, preservative type, or none)
• Turnaround time requested
• Any special instructions to the lab

Practical notes:

• Fill out the COC in the field as you collect samples, not at the end of the day from memory.
• Keep a copy for your records before sealing the cooler.
• Custody seals go on the cooler - across the lid opening so the lab can verify the cooler was not opened in transit.
• Ship samples on ice (not dry ice, unless specifically required by the method). Target 4 degrees Celsius.
• If you are shipping overnight, package the cooler so it will not leak. Double-bag the ice. The carriers will reject leaking packages.

Common Mistakes

1. Collecting VOC samples last. VOCs should always be the first samples collected from a freshly exposed interval. Handling the soil for other analytes first causes volatile loss.

2. Compositing when the work plan says discrete. Read your work plan carefully. If it specifies discrete samples, do not composite to save on laboratory costs without getting approval from the project manager and the regulatory program.

3. Not screening with the PID. Even if your analytical program does not include VOCs, PID screening provides real-time field data that helps with decision-making. Skipping it means you are working blind.

4. Insufficient decon between borings. Rinsing with a garden hose is not decontamination. Follow the full Alconox-rinse-DI sequence, especially when moving from a contaminated boring to a potentially clean one.

5. Poor soil logging. A soil log that says “brown clay” for every interval is useless. Note changes in color, moisture, grain size, and consistency. The log is often more valuable than the analytical data for understanding how contaminants move at the site.

6. Not recording PID calibration. If you cannot prove your PID was calibrated at the start of the day, the screening data has limited defensibility. Record the calibration standard, pre-calibration reading, post-calibration reading, and instrument serial number.

7. Running out of supplies. Count your sample containers, En Core samplers, labels, COC forms, and ice before leaving for the field. Coming back for supplies costs time and money.

8. Forgetting the moisture content jar for VOC samples. The lab needs a separate moisture content sample to report VOC results on a dry-weight basis. If you forget this, the lab cannot report results properly.