1. Charge Question 1-1: Please comment on whether the assessment provides a clear and logical summary of EPA’s approach and analysis. Please provide specific suggestions for improving the assessment. Discussion Leader Duane Huggett

2. Overview The “Scope of Assessment for HHCB” and Conceptual Model for the Environmental Assessment” sections provide a very clear picture in terms of the key questions and assessment scenarios. – Figure 1.1 clearly summarizes EPA’s thought process and focus of the assessment. This assessment focuses on effluent discharges to aquatic systems and terrestrial inputs via WWTP sludge. Exposure to aquatic, sediment and soil organisms is expected. Measured environmental concentrations are compared to effect concentrations from toxicity studies for the derivation of a risk quotient (RQ). – Other data are presented (e.g. estrogenic activity, multidrug resistant transporter inhibition)

3. Comments Assessment should be considered as a screening level assessment and needs to be clearly stated in the document – Probabilistic assessment with uncertainty analysis needed for risk determination – Read Across Levels of risk/hazard used in the assessment need to be explained or justified – “Negligible” vs “Acceptable” Why were mammals and birds beyond the scope of this assessment? – Higher Log K ow value of 5.3 and BCF value of 1,584

4. Comments Degradation products (e.g. HHCB-lactone) were not discussed in the assessment. Should this assessment address this transformation product or others in any way? At the very least, it should be stated that the assessment of transformation products is out of scope. Details of the QA/QC of data sets (e.g. USGS monitoring data) should be explained. – Often detected in laboratory and field blanks Add information to the Appendix

5. Comments Other data (e.g. estrogenic activity) were provided, but a statement is needed as to its use and meaning towards this assessment Conceptual Model could be improved by accounting for manufacturing input (not considered [pg 27] yet accounts for 10% of used volume)