A Story about Copper: Water vs. Wastewater, Part 4

In June 2015, we expanded on earlier newsletter articles (June 2013 and 2014) addressing the extremely low limits for copper on many wastewater plant effluents. For more than seven years, we (FOX Engineering, specifically Winnie Gleason, PE) have been working with IDNR staff to enable the utilization of the Biotic Ligand Model by POTWs with very low copper NPDES limits.

The following article is an update to an ongoing effort to resolve this issue in a manner that both protects the aquatic environment and allows cities to discharge their “used” drinking water to the wastewater treatment plant.

We continue to identify cities that are expected to have difficulty complying with the more stringent copper limits on their recent or pending NPDES permits. For some cities, the excess copper is not from industrial customers, but is from the copper picked up by slightly corrosive water flowing through copper piping and from food – both naturally occurring and added as a micronutrient.

The EPA has acknowledged that the current hardness-based water quality criteria for copper do not reflect the effects of water chemistry on metals bioavailability. Excess copper in the aquatic environment can be toxic to fish by building up on the gills.

The Biotic Ligand Model (BLM) method has been endorsed as a means to more accurately determine the aquatic toxicity of copper in a given environment. Much of the copper in the aquatic environment is tied up in organic matter and is not bioavailable to aquatic life; thus the additional data usually provides documentation that the copper effluent is less toxic than the default values currently used for NPDES permitting.

The BLM is a predictive tool that is based on conceptual modeling and experimentation that dates back to the early 1980s and continues to evolve today. In 1999, this approach was presented to EPA’s Science Advisory Board; they concluded that the BLM can “significantly improve predictions of the acute toxicity of certain metals across an expanded range of water chemistry parameters …”

The BLM utilizes site specific data (alkalinity, dissolved organic carbon, calcium, magnesium, sodium, potassium, chlorides, sulfates, sulfide, copper, and pH), from the receiving stream to model the aquatic toxicity of copper for that stream.

In the fall of 2014, the IDNR sponsored a stakeholder’s meeting to discuss pursuit of the necessary rulemaking that would allow Publicly Owned Treatment Works (POTWs) to use the BLM for adjusting their NPDES discharge limits based on the BLM data.

Another stakeholder meeting was held in June 2015 to discuss the inclusion of the Biotic Ligand Model in the determination of copper criteria. A draft version of “Implementation Procedures for the Site-Specific Application of Copper Biotic Ligand Model (BLM)” was prepared by IDNR staff and sent to the governor’s office for approval in late 2015.

Following release from the Governor’s office, the document was sent in early 2016 to EPA for their review. Review comments were received and addressed by IDNR staff and several stakeholders and additional minor adjustments were incorporated into the document.

The proposal to allow use of the BLM is scheduled to be presented to the Environmental Protection Commission on September 20, 2016. This will be the official kick-off to the actual rule change process. Barring any unforeseen obstacles, utilization of this option to procure more realistic evaluation of copper toxicity in their effluent should be available for use within the next six months.

FOX Engineering stays on the leading edge of regulatory and technical issues related to water and wastewater engineering. We take pride in working closely with our clients and regulatory agencies to help ensure reasonable, thoughtful, and cost-effective solutions to real problems.

Stay tuned – we will continue to provide updates on the challenges of copper and other metals in the coming months.

FOX Engineering is an environmental engineering firm based in Ames, Iowa. We specialize in water and wastewater solutions for our diverse municipal and industrial clients. Our work varies in size and scope and can be found throughout the Midwest and beyond.