Chain of Custody Best Practices - Common Errors That Invalidate Environmental Samples

Broken chain of custody invalidates samples and forces re-mobilization. A single missing signature or incorrect temperature can void weeks of field work. Re-sampling costs $5,000 to $15,000 per mobilization, plus project delays that push deadlines and budgets.

Why Chain of Custody Matters

Chain of custody (COC) documents sample integrity from collection to analysis. Courts, regulators, and insurance companies require unbroken documentation to accept analytical results. A compromised COC means the data cannot support regulatory decisions or legal proceedings.

Environmental samples often contain trace concentrations of contaminants. Without proper custody protocols, questions arise about sample identity, handling, and potential contamination. The COC form provides the legal framework proving samples were collected, transported, and analyzed according to established protocols.

Common COC Errors That Invalidate Samples

Missing or Incomplete Signatures

Every person handling samples must sign and date the COC form. This includes the sampler, courier, and laboratory personnel. Missing signatures break the custody chain.

Field error: Forgetting to sign when handing samples to a courier or shipping company. Lab error: Laboratory staff accepting samples without signing the COC form.

Temperature Exceedances

Most environmental samples require cooling to 4°C ± 2°C during transport. Temperature logs must document continuous compliance from field collection through laboratory receipt.

Samples exceeding 6°C or falling below 2°C may be rejected. VOC samples are particularly sensitive - temperature exceedances can cause volatile compounds to partition out of solution, producing false negative results.

Incorrect Sample Identification

Sample IDs on containers must exactly match the COC form. Even minor discrepancies like “MW-1” versus “MW-01” can cause rejection.

Common mistakes:

• Transposed numbers: Writing “MW-12” instead of “MW-21”
• Inconsistent naming: Using different formats on bottles versus COC forms
• Missing depth intervals: Soil samples without proper depth designation

Improper Preservation and Holding Times

Different analytical methods require specific preservatives and holding times. VOC samples need hydrochloric acid preservation and 14-day holding times. Metals samples require nitric acid and 180-day holding times for dissolved metals, 6 months for total metals.

Samples collected without proper preservation or exceeding holding times produce unreliable results that regulators will not accept.

Proper COC Documentation

Required Information

Every COC form must include:

• Project name and number
• Sample collection date and time
• Sampler name and signature
• Sample matrix (soil, groundwater, surface water)
• Requested analyses
• Preservation method
• Number of containers per sample

Custody Transfer Procedures

Document every custody transfer with signatures, dates, and times. When shipping samples:

1. Sampler signs relinquishing custody to shipping company
2. Courier signs accepting custody for transport
3. Laboratory personnel sign upon sample receipt
4. Time and date each transfer

Use waterproof ink. Pencil entries are not acceptable for legal documentation.

Sample Packaging Requirements

Pack samples to prevent breakage and maintain temperature. Use sufficient ice to keep samples at 4°C ± 2°C throughout transport. Include temperature blanks - water-filled bottles that travel with samples to verify temperature compliance.

Seal coolers with custody tape across the opening. If tape is broken upon laboratory receipt, document the condition and investigate potential tampering.

Field Quality Control Samples

Equipment Blanks

Collect equipment blanks to demonstrate decontamination effectiveness. Fill sample containers with laboratory-supplied deionized water after equipment cleaning. Analyze equipment blanks for the same parameters as environmental samples.

Frequency: One equipment blank per day when using reusable sampling equipment.

Trip Blanks

Include trip blanks with VOC samples to detect cross-contamination during transport. Laboratories provide sealed VOC vials filled with preservative and deionized water. Trip blanks travel with samples but are never opened in the field.

Frequency: One trip blank per cooler containing VOC samples.

Field Duplicates

Collect field duplicates to assess sampling precision. Take duplicate samples from the same location using identical procedures. Analyze duplicates for all requested parameters.

Frequency: One field duplicate per 20 samples, or as specified in the sampling plan.

Field Blanks

Field blanks detect airborne contamination during sample collection. Expose laboratory-supplied deionized water to field conditions during sampling activities, then preserve and analyze like environmental samples.

Frequency: One field blank per sampling event in potentially contaminated areas.

What to Do When COC Problems Occur

If you discover COC errors after sample collection:

Minor documentation errors: Contact the laboratory immediately. Some issues like missing times or minor spelling errors can be corrected with proper documentation.

Temperature exceedances: Discuss with the laboratory and project manager. Samples may still be usable depending on the magnitude and duration of the exceedance and the analytical methods involved.

Missing samples or broken containers: Document the condition thoroughly with photographs. Determine if re-sampling is necessary based on project objectives and regulatory requirements.

Custody breaks: Investigate immediately. Document all known sample handling and contact all parties involved. The laboratory may still be able to analyze samples with appropriate data qualifiers.

Bottom Line

Proper chain of custody prevents costly re-sampling and project delays. Document every transfer, maintain sample temperature, and include appropriate QC samples. When problems occur, contact the laboratory immediately to determine if samples remain usable. For specific analytical requirements, see our guide on low-flow groundwater sampling and PFAS sampling best practices.