3.3 Environmental Sampling Protocols & Chain of Custody

Introduction to Environmental Sampling

Environmental sampling is the process of collecting representative portions of air, soil, or water from a site to determine the precise identity and concentration of hazardous substances. Unlike direct-reading instruments that provide immediate but often non-specific results in the field, environmental samples are sent to an analytical laboratory for rigorous quantitative analysis. Strict adherence to sampling protocols and documentation procedures is paramount to ensure the data is accurate, reliable, and legally defensible.

Air Sampling Methodologies

Air sampling is conducted to evaluate worker exposure to airborne contaminants and to characterize emissions from the site.

Active vs. Passive Sampling

• Active Sampling: Involves the use of a mechanical pump to draw a known volume of air through a collection medium over a specific period. This is the most common method for compliance monitoring.
• Passive Sampling: Relies on the natural diffusion of gases or vapors onto a collection medium (like a dosimeter badge) without the use of a pump. It is simpler but generally less precise for short-term exposure assessment.

Collection Media

• Sorbent Tubes: Small glass tubes filled with a solid adsorbent material (e.g., activated charcoal or silica gel). A pump draws air through the tube, trapping gases and vapors. The tube is later desorbed in the lab for analysis.
• Impinger Trains: Used for collecting highly reactive or water-soluble gases. Air is bubbled through a series of glass vials containing a liquid absorbing solution, which captures the contaminant.
• Particulate Filters: Used to collect dusts, fumes, and mists. Air is pulled through a filter cassette (e.g., PVC or mixed cellulose ester), and the trapped particulate mass is analyzed gravimetrically or chemically.

Personal vs. Area Sampling

• Personal Air Sampling Pumps: Small pumps worn by a worker, with the collection medium placed in their breathing zone (a 10-inch radius around the nose and mouth). This measures individual exposure levels compared to OSHA Permissible Exposure Limits (PELs).
• Area Monitors: Pumps placed in stationary locations around the site to measure ambient background levels or perimeter concentrations, rather than individual worker exposure.

Soil and Sediment Sampling

Soil sampling is critical for delineating the extent of contamination in the ground.

Sampling Tools

• Split-Spoon Sampler: A heavy steel tube driven into the ground by a drill rig. The tube splits in half lengthwise to allow retrieval of an intact, relatively undisturbed soil core from specific depths.
• Hand Auger: A manually operated tool used to collect disturbed soil samples from shallow depths (typically less than 10 feet). It resembles a large corkscrew.
• Trier: A long, narrow tube with a slot cut along its length, used for sampling sticky soils or sediments.
• Coliwasa (Composite Liquid Waste Sampler): While primarily for liquids, modified versions are sometimes used for sludges. It is a long glass or plastic tube with a stopper mechanism at the bottom, allowing sampling at various depths in a container or lagoon.

Grab vs. Composite Samples

• Grab Sample: A single sample collected from a specific location and depth at a single point in time. It represents the conditions at that exact spot.
• Composite Sample: A mixture of several grab samples collected from different locations or times, combined into a single container. This provides an average concentration over the sampled area or time period, reducing analytical costs but masking localized "hot spots."

Surface Water and Groundwater Sampling

Water sampling assesses the migration of contaminants through aquatic systems.

Sampling Techniques

• Bailers: Simple, hollow tubes with a check valve at the bottom. They are lowered into a monitoring well to retrieve a water sample. While cheap and easy to use, they can cause excessive agitation, potentially stripping volatile organic compounds (VOCs) from the sample.
• Peristaltic Pumps: Suction-lift pumps that draw water up through tubing. They are useful for shallow wells or surface water but are generally limited to depths of about 25 feet.
• Low-Flow Purging: A precise methodology used in groundwater monitoring. A submersible pump extracts water at a very low rate (e.g., 100-500 mL/min) to minimize drawdown and turbulence, ensuring a highly representative sample of the surrounding formation water, especially for VOCs.

Decontamination and Sample Preservation

Decontamination of Equipment

To prevent cross-contamination between sampling locations, all non-disposable sampling equipment (augers, bailers, pumps) must be rigorously decontaminated. This typically involves a multi-step process: an initial wash with a non-phosphate detergent (like Alconox), a tap water rinse, a deionized water rinse, an acid or solvent rinse (if necessary for specific contaminants), and a final deionized water rinse.

Sample Preservation and Holding Times

Once collected, samples must be preserved to prevent chemical or biological degradation before reaching the laboratory.

• Thermal Preservation: Almost all samples must be immediately placed in a cooler and maintained on ice at a temperature of 4°C (±2°C).
• Chemical Preservatives: Specific chemicals are added to the sample containers depending on the analyte.
  • HNO3 (Nitric Acid): Used to preserve samples for metals analysis (lowers pH to <2).
  • H2SO4 (Sulfuric Acid): Used for ammonia or nutrient analysis.
  • NaOH (Sodium Hydroxide): Used to preserve cyanide samples (raises pH to >12).
• Holding Times: Every analytical method specifies a maximum holding time—the legal limit on how long a sample can be kept before it must be analyzed. Exceeding the holding time invalidates the data.

Chain of Custody (COC) Documentation

The Chain of Custody is a legally binding document that traces the lifecycle of a sample from the exact moment of collection through analysis and final disposal. Its purpose is to prove that the sample was not tampered with and is exactly what it claims to be.

COC Procedural Workflow

1. Field Collection: The sampler logs the Sample ID, date, exact time of collection, sampling location, matrix (e.g., soil, water), and their own name directly onto the COC form.
2. Custody Seals: The sample cooler or individual containers are sealed with tamper-evident custody seals. If the seal is broken by an unauthorized party, the integrity of the sample is compromised.
3. Transfer Signatures: Every time the samples change hands (e.g., from the sampler to a courier, from the courier to the laboratory receiving department), both the person relinquishing the samples and the person receiving them must sign, date, and record the time on the COC form.

Sample Matrix and Preservation Guidelines