1. Session 3- Water Quality Thresholds Ecosystems 1

2. Process for Establishing Thresholds Concentration monitoring and Biological effects data High Low High Further studies 2nd tier thresholds High Priority High Low No further study req’d Further studies 2nd tier thresholds Further studies 2nd tier thresholds

3. Detemining Impairments – Assessment Tools Tools Exist: Limitation is Data –NOECs, NOELs,Water Quality Criteria –Transport/Fate/Exposure Models –Uniqueness of endpoints??

4. Threshold Specificity By Use/Habitat Ideally, yes. Expensive undertaking CECs unique? –Site Specific Objectives –Flexibility within Guidance (Bacteria, Oxygen) –Safety Factors & Expert Judgment

5. Spatial-Temporal Scales Temporal scale issues more important than spatial scales Temporal – time versus life history cycle of chemical Mode of Action Tie to source timescale (wet weather)

6. Uncertainty Uncertainty for CECs relatively high Use larger safety factors –Apply strategy from human health risk assessment –Relate to extent of data available –Relate to consequence of being wrong Reiterate choice of compounds for threshold development every x years