The Need for Field Validation

The Need for Field Validation

Field validation projects would help USACE to understand whether

predictions of fate and transport models, bioaccumulation models, and toxicity

tests are relevant to field conditions. Uncertainties could be reduced through a

series of small, strongly focused field validation efforts that target dominant

elements of the dredged material evaluation process (e.g., use and reliability of

chronic sublethal bioassays, bioaccumulation and trophic transfer modeling,

population modeling). Such field validation could be performed in conjunction

with population modeling efforts to improve understanding of any dredged

material impacts and to test model predictions.

It would also be useful to learn from past USACE experience by reviewing a

carefully selected subset of toxicity and bioaccumulation bioassay data. For

example, data submitted in support of permit applications could provide a useful

starting point for evaluating the potential for trophic transfer of nonpolar organic

contaminants. Trophic transfer can be evaluated by using sediment concentration

data and sediment characteristics information (e.g., organic carbon content) in a

trophic transfer model such as Gobas (1993) or FGETS (Barber, Surez, and

Lassiter 1988 and 1991). Predicted concentrations from the model(s) can be used

to evaluate whether the potential for trophic transfer occurs at sites for which

disposal was deemed acceptable. Toxicity testing results could be analyzed to

validate the Σ PAH model (Swartz et al. 1995). Results from such data analyses

could benefit the development of bioassay interpretation guidance for USACE

field staff.

A well-conceived plan coordinating data analysis, modeling, and field

monitoring efforts is needed to ensure that principal sources of uncertainty in the

dredged material tiered evaluation are reduced.

Chapter 6 Preliminary Ranking and Recommendations