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3.d.3 Nitrogen Mitigation Memo to MPCABQ L__.TQN 8 M EE N K, Consulting Engineers & Surveyors " 12224 Nicollet Avenue • Burnsville, MN 55337 Phone (952) 890-0509 • Fax (952) 890-8065 www.bolton-menk.com MEMORANDUM Date: July 7, 2016 To: Kaitlin Jamieson, Minnesota Pollution Control Agency From: Seth Peterson, P.E. Ryan Goodman, P.E. Subject: Scandia — Bliss Collector WWTF Nitrogen Mitigation I N G® Introduction This memo has been written in response to a June 9, 2016 letter from the Minnesota Pollution Control Agency (MPGA) regarding the Compliance Evaluation Inspection of the Scandia Bliss Wastewater Treatment Facility on May 24, 2016. The purpose of this memo is to address the concerns regarding the Nitrogen Mitigation Plan. The City submitted a Nitrogen Mitigation Plan that was incomplete and lacked the necessary detail showing that the system consistently removes nitrogen to less than 10 mg/L. Details regarding the plan follow. System Evaluation/Compliance Inspection Action In the June 9, 2016, Compliance Evaluation Inspection on the Scandia Bliss WWTF several deficiencies are noted by the MPCA: 1. Daily Maximum flow exceedance above permit limit 2. Late and/or not submitted Discharge Monitoring Reports (DRM's) 3. Original records of sample time and analysis for sampling and monitoring and verification of instrument calibration were not maintained 4. No verification for pump calibration and maintenance The City will respond to these comments in a separate letter. DESIGNING FOR A BETTER TOMORROW Bolton & Menk is an equal opportunity employer ()J ON 0�' � Attached to this memo is a memo Bolton & Menk Inc., brought to the City on June 23, 2016 to discuss possible nitrogen mitigation measures. The information in the attached memo is to serve as the basis for the Nitrogen Mitigation Plan for the City. The purpose of the Nitrogen Mitigation Plan is to summarize the treatment systems ability to consistently achieve nitrate -nitrogen removal to meet the Minnesota Department of Health's (MDG) drinking water standard of 10 mg/L, and include what is necessary to maintain compliance with the MDH 10 mg/L standard. Based on the existing data, one of the downgradient monitoring wells has elevated nitrate - nitrogen levels that exceed 10 mg/L. This indicates that the system does not consistently achieve nitrate -nitrogen removal to less than 10 mg/L. Therefore, future nitrogen treatment is necessary. In the attached memo, two different treatment methods are presented that would help reduce the nitrogen level entering the groundwater. Either a denitrification only system or a nitrification/denitrification system would be installed to reduce the Total Nitrogen leaving the system. In order to achieve compliance with the Minnesota Department of Health's (MDH) drinking water standard, the City of Scandia will need to improve the Bliss Drainfield by adding nitrogen removal measures in the future. Along with the memo provided by Bolton & Menk, Inc., operational options to help reduce the nitrogen level will also be evaluated. These include monitoring the influent and flow control to best optimize the system for nitrogen removal. Groundwater nitrate -nitrogen levels and influent nitrate -nitrogen levels will need to be monitored and recorded. An investigation will need to be conducted to see if more land is required for a nitrogen removal system. Conclusion Overall, the system is in good condition. The information in the attached memo shows that Bliss WWTF cannot consistently achieve nitrate -nitrogen levels less than 10 mg/L in the downstream monitoring wells. The City will look at operational changes and modifications to the system to see if performance of the system can be enhanced. However, if these changes/modifications do not result in better performance the City will need to look at additions to the system that will remove nitrogen to comply with the MPCA permit. Several proprietary systems will be evaluated along with operational options to find one that best suits the Bliss WWTF and will consistently achieve nitrate -nitrogen levels below 10 mg/L. DESIGNING FOR A BETTER TOMORROW Bolton & Menk is an equal opportunity employer.