Ecological Evaluation Technical Guidance - State of New Jersey

7.2.1 Apparent Effects Threshold ApproachThe Apparent Effects Threshold (AET) is the contaminant concentration in soil orsediment above which a specific biological effect is always found (i.e., the highestconcentration in which no effect is observed in a given data set). Because thisapproach is based on the absence of biological effects and associated chemicalconcentrations, it is useful with contaminant mixtures. See Evaluation of theApparent Effects Threshold (AET) Approach for Assessing Sediment Quality(USEPA, 1989a) for further guidance. A simplified example is presented inFigure 7-3Assume five (5) sample locations, with chemical analyses and toxicity testing conducted at each locationFor each contaminant, order the results from all locations from highest to lowest concentrations:Station #Arsenic Concentration (mg/kg) Earthworm Toxicity (biomass reduction)2 1000 *1 300 *4 150 *5 60 NE3 30 NE* - Significant effect in toxicity testNE – No significant effectRemediation Goal (As) = AET = 60 mg/kg (the highest concentration above which there is always an effect)Figure 7-3. Simplified Example of Determining a Remediation Goal Using theApparent Effects Threshold (AET) Approach7.2.2 Sediment/Soil Effects Concentration ApproachThe Sediment/Soil Effects Concentration (SEC) is the concentration of anindividual contaminant in soil or sediment below which toxicity is rarelyobserved. It is the concentration associated with an effect, and above thisconcentration, toxicity is frequently observed. See Calculation and Evaluation ofSediment Effect Concentrations for the Amphipod Hyalella Azteca and the MidgeChironomus Riparius (USEPA, 1996) for further guidance.8.0 UncertaintySeveral sources of uncertainty are associated with ecological risk estimates. Theseinclude initial selection of COPECs based on the sampling data, estimates of toxicity toecological receptors based on limited laboratory data (usually on other species), anduncertainties in exposure and effects assessment. As part of the final steps in estimatingpotential ecological risks associated with a site, the magnitude of uncertainties associatedwith the risk estimation should be discussed.Uncertainty in risk estimation has both qualitative and quantitative components.Qualitative uncertainty analyses are recommended by guidance (USEPA, 1988) andcontribute to the confidence with which risk assessment conclusions can be drawn andEcological Evaluation Technical Guidance Document 82Version 1.2 8/29/12