Site Characterization and Analysis
Purpose and sequence
Site characterization answers three questions: what contaminants are present, where they are, and how they can hurt workers. The sequence is off-site information review (records, historical use, prior reports), then on-site survey (walkover, interviews, visual evidence), then sampling and monitoring to confirm. Off-site review comes first because it shapes the sampling plan and the initial PPE and monitoring decisions.
Concepts to know
- Hazard identification categories: chemical, physical (noise, heat, slips), biological, radiological, and safety hazards.
- Exposure pathways: inhalation, dermal contact, ingestion, injection. Inhalation and dermal are the dominant concerns at waste sites.
- Contaminant behavior: volatile organics move to the vapor phase (vapor intrusion, confined spaces); dense non-aqueous phase liquids (DNAPLs) sink; lighter fractions float. Soil type affects migration.
- Background vs. site-related contamination - do not attribute naturally occurring metals to the site.
- Real-time instruments vs. laboratory analysis: field instruments screen; lab methods confirm and quantify.
Traps in questions
- Skipping the records review and going straight to sampling - questions reward the documented sequence.
- Treating a field screening reading as a definitive concentration; it is a screening value used to trigger action levels.
- Ignoring physical hazards (heat stress, noise, traffic) because the site is "chemical."
- Assuming an odor means high concentration or that no odor means safe - odor is not a reliable exposure indicator.
Worked rule of thumb
If a question describes a site with unknown drums and no records, the correct first step is a records/historical review plus a preliminary walkover with conservative PPE and monitoring - not immediate intrusive sampling. Characterize before you disturb.