Critical Evaluation of a Potential Wastewater Limit for Aluminum, 2003 Environmental Conference Proceedings

This paper presents a case study of how a weight-of-evidence approach may be used to suggest effluent limits for aluminum are not necessary to protect water quality from a pulp mill discharge to Leaf River, MS. First, the National AWQC for aluminum (and, hence, the state WQS) is overly conservative for protection of aquatic life, and may warrant adjustment/recalculation owing to scientific uncertainties, and lack of fish species in Leaf River which are critical to criteria calculations. Second, whole effluent toxicity (WET) tests conducted for LRPO have consistently passed discharge permit requirements. This result is consistent with extensive field studies which suggest that Leaf River aquatic communities are not impaired by LRPO effluent discharge. Furthermore, concentrations of aluminum in Leaf River are naturally elevated, and empirical data demonstrate that LRPO discharge has no statistically significant effect on downstream aluminum concentrations. Our evaluation of aluminum toxicity in site waters highlighted both the lack of aluminum toxicity and the complexity of aluminum chemistry. Several regulatory mechanisms were explored as a means of avoiding a NPDES permit limit for aluminum. MDEQ was persuaded that aluminum in effluent does not present a threat to the river’s water quality but still believed that a permit limit was necessary. The NPDES permit limit was based on a no net addition of aluminum relative to upstream waters including accounting for statistical variation in water quality. LRPO was able to modify the calculation used to derive the permit limit to accurately account for population variation and yielding a permit limit that was accepted to both parties.