A Story about Copper: Water vs. Wastewater, Part 2

A year ago, we described a situation in New Hampton where the copper in the city’s drinking water, which is well below the recommended drinking water limit, will cause the wastewater effluent to violate its discharge permit. Now, as DNR is steadily re-issuing NPDES permits, it appears that New Hampton is not alone; a number of other cities will face a similar situation.

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. Click on the following link to access Part 1 of this series: www.foxeng.com/news/story-about-copper-water-vs-wastewater-part-1 *

Background

We were aware of the impending copper problem in New Hampton because we had been working with the city to permit a new industrial customer and requested a preliminary wasteload allocation from IDNR. New Hampton discharges to a very small stream, which offers little or no dilution or mixing of the effluent – the effluent limits essentially represent the stream standards that have been determined to be harmful to aquatic life. The bottom line is that the copper concentration in the drinking water will cause a violation of the NPDES stream standards.

Who does this affect?

IDNR staff initially indicated that the situation in New Hampton was an anomaly of worst case scenarios. However, as more NPDES permits have been issued, it has become clear that other cities will be impacted by the very stringent copper limit. Municipalities that discharge to a small stream and do not soften their water are possible candidates for a permit where the copper limit cannot reasonably be met.

FOX is working with a number of cities that are currently or will be impacted by an NPDES copper limit that is not realistically achievable. It is critical to evaluate your draft NPDES permit renewal to determine if a compliance schedule should be requested before the permit is final. A compliance schedule will provide time to evaluate available options to ensure wastewater discharge will not violate limits.

What are the options?

There are a few reasonable, realistic options to develop less stringent metal limits. Included are:

  • Additional sampling
  • Source reduction
  • Relocation of effluent outfall
  • Implement site specific conditions such as the biotic ligand model

What do we know about the biotic ligand model (BLM)?

This is a tool used to evaluate the bioavailability of copper in water and the affinity of these metals to accumulate on the gills of aquatic organisms. The BLM utilizes site specific data to model and estimate the actual toxicity of copper to aquatic life in a particular stream.

The BLM is being considered for use in other states and may be the least-cost means of solving this problem. State rulemaking and EPA approval would be required to utilize the BLM to revise effluent limits in Iowa.

Last year, FOX prepared for the city of New Hampton a plan of study to be evaluated by IDNR and EPA. The plan included the initial stages and details of sampling required to utilize the model. IDNR staff indicated they were willing to use this situation as a test case. We anticipated a twofold result – solve the city’s copper dilemma and set the stage for other communities to deal with these more stringent effluent limits.

December 2013, IDNR staff held stakeholder meetings to determine level of interest in pursuing state-wide acceptance of and rulemaking to adopt the BLM as an option for calculating acceptable discharge limits for copper. At that time, we recommended that New Hampton put a “hold” on their individual pursuit of rulemaking for site specific considerations and wait to see if the state-wide effort would achieve the desired result.

IDNR has formed a Technical Advisory Committee tasked with developing a detailed plan for moving this effort forward. The first meeting is scheduled for June 24, 2014 in Des Moines. Winnie Gleason, P.E., was asked to join the committee. Please contact her prior to the meeting date if you have any questions or suggestions for the committee. We will provide updates in the FOX newsletter or you can contact us anytime for the most up-to-date information on this issue.

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 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.