Scoping a Phase II

The scope is where a Phase II succeeds or fails, and it is set before anyone mobilizes a drill rig. A good scope translates each REC from the Phase I into testable questions, then places sampling points where those questions get answered.

The conceptual site model

Every defensible scope rests on a conceptual site model: what substance was likely released, from what source, into what medium, and where it would have gone. A former dry cleaner suggests chlorinated solvents near the machine location and the sanitary sewer lateral, with a dissolved plume moving down-gradient. A fuel UST suggests petroleum in soil at the tank pit and dispenser island. The model tells you where to drill and what to analyze for; sampling without it is guessing at intervals.

What the plan specifies

• Locations and depths: borings at the suspected source, points to check lateral and vertical extent, wells placed down-gradient where groundwater is the question.
• Media: soil, groundwater, soil vapor, or some combination. Vapor matters when buildings sit over volatile contamination.
• Analytes: the laboratory methods matched to the suspected release. Analyzing for everything everywhere is a budget decision, not a technical one.
• Screening criteria: which regulatory levels results will be compared against, decided up front, not after the data arrives.

Questions to ask before approving a scope

Does every REC from the Phase I map to at least one sampling location? Is anything being sampled that no REC supports? If groundwater flow direction is unknown, how were well locations chosen? And what happens if the first round finds contamination: is a contingency for step-out sampling priced, or does that become a change order?