A site-specific chronic water quality criterion was developed for copper at a municipal wastewater treatment facility in Michigan using the water-effect ratio (WER) procedure. Acute WERs using Daphnia magna were determined using three measured flow conditions and one pre-determined flow condition which represented a very low flow occurrence. Acute total recoverable WERs ranged from 11.2 to 31.4 with the hWERs (highest WERs – accounts for upstream dilution) ranging from 70.9 to 99.3. A final WER of 10.3 was used to derive the site-specific chronic for copper.
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