Reading Phase II results

ASTM E1903-19 sets an order for reading Phase II results. First the Phase II Assessor checks whether the conceptual model holds, by testing its assumptions and then the quality of the chemical data; only once data quality is acceptable may the results be interpreted against the user's objectives (E1903-19, 6.4.6, 7.7 to 8.1).

Does the conceptual model hold?

The data must be weighed systematically against the model and the question being asked, to decide whether site conditions are soundly and sufficiently understood; if the whole body of data bears out the model's predictions about entry locations, routes of migration and where analytes now occur, the model is validated (E1903-19, 7.7). The analysis asks whether a release occurred and whether what is present is understood well enough for the objective, or more rounds are warranted; the Phase II Assessor should call the investigation adequate only when the results fit the updated model (E1903-19, 7.7).

A round can end three ways:

Validated. The results agree with the model's assumptions and support sound conclusions about whether target analytes are present; sufficient investigation has then been shown (E1903-19, 6.4.6.1).
Revised. The results do not fit, or support no sound conclusion. It must then be decided whether a revised model consistent with the data can meet the objectives, as first written or revised; if so, it may be considered validated (E1903-19, 6.4.6.2).
Not validated. No model that can be stated fits the results, and no sound conclusion can be drawn. The user and the Phase II Assessor may confer on whether to investigate further toward a model that can be validated (E1903-19, 6.4.6.3).

First check: the assumptions

The first task asks whether the right media were sampled at the right place, depth and time, meaning where and when the highest concentrations would be if a release had happened (E1903-19, 7.7.1). A model usually starts from assumptions about the subsurface, such as groundwater flow direction, depth to the water table and relative permeability, and about the release, such as its form and volume (E1903-19, 7.7.1.1). After each round the Phase II Assessor must test those assumptions against the conditions actually met; where one failed, the investigation may have missed its purpose and more rounds may be warranted (E1903-19, 7.7.1.1). Any further round should begin with the Phase II Assessor and the user revisiting the question and the cost and likely effectiveness of more work (E1903-19, 7.7.1.2).

Second check: the chemical data

The second task is whether the chemical testing data meet the QA/QC plan (E1903-19, 7.7.2). A detected analyte must be confirmed as coming from the site, not from sampling, handling or testing artifacts, and a reported absence must be judged in light of the detection limits reached and the surrogate recoveries, if any; once data quality is found acceptable, interpretation may begin (E1903-19, 7.7.2). The assessor should require laboratory disclosure of problems or unusual testing events and should pass that information to the user in reports (E1903-19, 4.2.1.3).

Interpreting the results

Results should be read for their significance to the objectives, and also for signs of other sources, or higher concentrations, at the site that were not specifically assessed (E1903-19, 8.1).

Naturally occurring analytes. When a detected analyte, such as a heavy metal or total petroleum hydrocarbons, may be natural in a setting like the property's, the Phase II Assessor must consider whether it is at background concentration, reflects diffuse anthropogenic contamination, or comes from a release (E1903-19, 8.1.1). Background concentration comes from a nearby reference location and excludes contributions attributable to the investigated area; diffuse anthropogenic contamination comes from broad activities, such as agriculture, urban runoff and atmospheric deposition, that are harder to single out than one site's release (E1903-19, 3.1.2, 3.1.15). An objective may still call for investigating substances that are natural or were applied on purpose, such as pesticides (E1903-19, 7.1).
Criteria. The standard sets no level at which a target analyte becomes a concern; users may apply regulatory criteria, liability principles or objectives of their own (E1903-19, 4.1.2.2). Where analytes are confirmed present, the Phase II Assessor may, as the objectives call for, compare them with numerical criteria, regulatory ones where relevant, or other criteria from the user's needs or a contract (E1903-19, 8.1.2). In doing so, the results must be checked against the model for whether they represent site conditions, including, where needed, the highest concentration present; setting aside analytes from a release because they fall below the criteria is not justified unless data representing the highest concentration have been considered (E1903-19, 8.1.2).
Nondetects. When Section 7's QA/QC procedures were followed and testing found no target analytes exceeding laboratory reporting limits appropriate for the objectives, the assessor may conclude that the evidence gives no reasonable grounds to believe those analytes are present (E1903-19, 8.1.3).
Presence is not extent. Presence, as the standard defines it, does not mean the full extent of an analyte is known (E1903-19, 3.1.35).

Uncertainty and how long data last

No Phase II removes all uncertainty. Any sample may or may not represent a larger population, and professional judgment leaves some uncertainty however objectively it is used; more assessment may reduce it (E1903-19, 4.2.1). Some conditions make detection especially hard, such as complex geology, substances whose behavior is poorly understood, patchy or shifting distributions, obstructions created by utilities or other constructed features, and technological limits on assessment (E1903-19, 4.2.1.1). Missing information about past uses or earlier assessments can also weaken a Phase II (E1903-19, 4.2.1.2).

Data generally show conditions only as they were when collected, and conditions can change, so their usefulness may have a limited life (E1903-19, 4.2.4). Where Phase II data are the kind a Phase I uses, the Phase I standards' time limits apply; otherwise the Phase II Assessor should judge whether older data suit a new use, or face limits under other laws or regulatory policies (E1903-19, 4.2.4).

This page is general reference for environmental professionals. It does not assess any property. ASTM E1903-19 is the standard and is not reproduced here; the judgment of the Phase II Assessor on the facts governs.