The Composite Sample Trap
A property manager asks you to inspect a 1920s four-unit building for a pre-renovation assessment. Budget is tight, so he proposes that you 'just take one composite dust sample from all four units to save money' and 'skip the soil because there's no garden.' You know the building has bare soil along the foundation, a shared laundry room, and one unit occupied by a family with two children under six. You have time for a proper sampling design if you push back, but the manager is impatient and hints he'll hire someone cheaper if you 'overcomplicate' things.
1. Explain why the composite-across-units proposal is technically unsound and what sampling design you should propose instead.
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Compositing across separate dwelling units destroys the ability to attribute a result to a location. If a composite fails, you cannot tell which unit is the source, and you cannot clear or remediate a specific unit. Composite sampling is only appropriate for samples from the same homogeneous location type within the same decision unit, and even then only when the protocol permits it.
Better design:
- Treat each unit as a separate decision unit; sample representative locations (floors, sills, troughs) per unit.
- Prioritize the unit with children under six.
- Include the shared laundry room as a common area.
- Collect soil samples at the foundation drip line and any bare play areas.
- Document the rationale so the client understands the cost is tied to defensible decisions, not to sample count for its own sake.
2. How should you handle the manager's implied threat to hire someone cheaper?
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State plainly, in writing if needed, that your scope is driven by the standard of care and the regulatory framework, not by price competition. Explain the consequence of the shortcut: a composite that cannot support unit-specific decisions may fail to protect occupants and may not satisfy the requirements of the renovation or abatement program the client is trying to comply with.
If the client insists on a technically inadequate scope, decline to perform it under your name, or perform only the defensible portion and clearly limit the report. Do not let a fee threat push you into a design you would not defend in a deposition or an audit.