Phase II Environmental Site Assessment and Sampling
Purpose and design
A Phase II ESA is an intrusive investigation designed to evaluate whether contamination is present and to characterize its extent. It is not a cleanup; it is a data-gathering step. Sampling plans should be driven by the conceptual site model (CSM) and the RECs identified in Phase I. The work plan should specify analytes, locations, depths, methods, and quality assurance/quality control.
Sampling approaches
Soil sampling uses borings or test pits; groundwater uses monitoring wells or temporary points. Sampling should target the likely source area and migration pathways, with background or upgradient locations for comparison. Field screening with a photoionization detector (PID) or flame ionization detector (FID) guides sample selection. Sample handling matters: preserve with appropriate methods (e.g., methanol for volatile organics in soil, or the appropriate preservative), cool to 4 degrees C, and respect holding times. Chain of custody must be documented.
Analytical and QA/QC
Laboratory methods are chosen by analyte: volatile organic compounds by purge-and-trap, semivolatile organics by extraction and GC/MS, metals by ICP or ICP-MS, and petroleum by methods such as 8015 or 8260. QA/QC includes blanks, duplicates, matrix spikes, and calibration. Data quality indicators include precision, accuracy, representativeness, comparability, and completeness.
Traps
Do not assume a Phase II confirms or rules out a REC; it may do either, or be inconclusive. A single sample is not characterization. Be careful about comparing results to the wrong screening levels; use the applicable regulatory standard and land use. Vapor intrusion sampling requires different methods and timing.
Rule of thumb
Sample where the contamination would be if the REC were real, and include a background location.