Because the whole effluent toxicity critical dilution limit for the Waco Metropolitan Area Regional Sewerage System’s National Pollution Discharge Elimination System permit is 50%, a NOEC of 50% dilution level indicated that the MTP was likely operating normally during this study. STS effluent was most hazardous to D. magna, as an eightfold difference in mortality and growth NOECs was observed among the STS system and MTP and ATS effluents (Fig. 3). Based on whole effluent
toxicity to D. magna survival, growth and reproduction, water quality of effluent discharges were observed to be MTP P ATS > STS.