Sampling and Analysis
Sampling and Analysis
This domain tests defensible data: DQOs, sampling design, container/preservation/holding time, chain of custody, and QC. It covers air, water, soil, and waste, with SW-846 and 40 CFR Part 136 methods as common references.
Core rules
- Start with the data quality objectives (DQOs): decision, analyte list, detection/reporting limits, precision/accuracy, and sampling design. A sample without a decision is just cost.
- Chain of custody: unique sample ID, date/time, location, matrix, preservative, analyses, relinquished signatures. Document deviations.
- QC: trip blank (VOCs, water), field blank, equipment blank, duplicate, matrix spike/matrix spike duplicate, and method blank. Trip blanks travel unopened with VOC samples.
- Soil VOCs: collect quickly, minimize headspace, use the method-specific container (e.g., SW-846 5035 methanol or sodium bisulfate preservation), cool to 4°C, and meet holding time.
- Water: 40 CFR 136 methods; preserve and hold per method (e.g., HNO3 for metals, HCl for VOCs). Air: TO-15 canisters or TO-17 tubes; use flow controllers and field blanks. Waste: TCLP (SW-846 1311) leachate then analysis.
- Report results with units, dilution, detection limits, and QA qualifiers.
Worked example
You need benzene in groundwater at a 1 µg/L decision level. Collect a 40-mL VOC vial with HCl preservative, fill with no headspace, cool, and submit a trip blank. If the lab reports benzene at 0.8 µg/L in the sample and 0.2 µg/L in the trip blank, the trip blank shows possible contamination; the sample result may be biased high, so qualify or resample. Do not subtract the blank blindly without the project's data-validation rules.
Traps
A field blank is not a trip blank. Holding time starts at collection, not receipt. “ND” is meaningless without the reporting limit. TCLP is not total waste concentration. Do not preserve VOC vials with nitric acid.