The guidelines in this document describe the Minnesota Pollution Control Agency's (MPCA) recommended review criteria for wastewater treatment facilities that:
- need to perform system maintenance,
- do not have system reliability (duplicate treatment units), and
- request approval to bypass untreated or partially treated domestic wastewater.
These guidelines have been developed to serve as recommended minimum requirements for public health and receiving-water protection to the maximum extent possible. The guidelines are not intended to be acceptable criteria for allowable bypassing of inadequately treated wastewater. Where practical, sufficient treatment of the wastewater should be implemented to maintain compliance with permit limitations.
A bypass is a diversion of a waste stream from any portion of the treatment facility. In general, the National Pollutant Discharge Elimination System (NPDES) permit prohibits bypasses except as follows (Part II, A.1.):
Bypass not causing exceedance of permit effluent limitations. The Permittee may allow a bypass to occur if the bypass will not cause the exceedance of an effluent limit, but only if the bypass is necessary for essential maintenance to ensure efficient operation of the facility. The Permittee shall submit notice of the need for the bypass at least ten days before the date of the bypass or as soon as possible under the circumstances.
Bypass causing exceedance of permit effluent limitations. A bypass that causes an exceedance of an effluent limit, whether anticipated or unanticipated, is prohibited except under the following conditions:
- The bypass is unavoidable to prevent loss of life, personal injury, or severe property damage. For the purposes of this paragraph, "severe property damage" means substantial damage to property of the Permittee or of others; damage to the wastewater treatment facilities that may cause them to become inoperable; or substantial and permanent loss of natural resources that can reasonably be expected to occur in the absence of a bypass. "Severe property damage" does not mean economic loss as a result of a delay in production.
- There is no feasible alternative to the bypass, such as the use of auxiliary treatment facilities, retention of untreated wastes, or performance of maintenance during normal periods of equipment downtime. This condition is not satisfied if adequate back-up equipment should have been installed in the exercise of reasonable engineering judgment to prevent a bypass which occurred during normal periods of equipment downtime or preventative maintenance.
- In the case of an anticipated bypass, the Permittee has notified the Commissioner at least ten days in advance of the bypass or as soon as possible under the circumstances, and the Commissioner has approved the bypass. The Commissioner shall approve the bypass if the Commissioner finds that the conditions set forth in (1) and (2) above are met. The Permittee shall provide the Commissioner such information as the Commissioner requires to make a decision on the bypass.
- In the case of an unanticipated bypass, the Permittee has notified the Agency within 24 hours of the bypass. The Permittee shall provide in writing the reasons for an unanticipated bypass.
In addition, the Permittee is responsible for maintaining adequate safeguards to prevent the discharge of untreated or inadequately treated wastes at all times. The Permittee is responsible for insuring system reliability by means of alternate power sources, back-up systems, storage of inadequately treated effluent, or other appropriate methods of maintaining system reliability.
For more background information regarding recommended system design, bypassing, and system reliability refer to the MPCA Reliability Guidelines for Mechanical Wastewater Treatment Plants.
Minimum requirements for implementing bypass
In general, the following are minimum requirements for implementing scheduled maintenance bypassing where permit effluent limits may be exceeded:
- Existing or temporary wastewater treatment facilities should be used to the maximum extent practical to ensure compliance with permitted effluent discharge limits.
- Submit a written request for a scheduled maintenance bypass by January 1 for a bypass period of April through May (high receiving water flow period). Scheduled maintenance should be performed under high flow conditions to minimize receiving water impact. MPCA Assessment and Planning will review the request and determine if the proposed bypass is acceptable based on the receiving water quality. Allow MPCA up to 90 days to review scheduled maintenance bypass requests. The written request should include a plan which includes dates for the bypass, reasons for the bypass, alternative treatment options with estimated costs, the anticipated duration and quantity of the bypass, and the anticipated impacts to the facility effluent and receiving stream. The bypass should occur under low plant flow conditions and be as short as possible. Additional effluent sampling will be required.
- Provide a minimum of primary treatment for the removal of floatable and settleable solids as well as any permit-required disinfection for maintenance bypassing performed from April through May.
- Provide primary treatment, secondary treatment, secondary clarification and permit-required disinfection for maintenance bypassing performed from June through March.
- Every effort must be made to bring the facility back into compliance as soon as the maintenance is complete, which includes reseeding biological treatment units.
- If maintenance bypassing becomes a repetitive problem for the facility, the permittee should implement a plan to correct the duration and frequency of the bypassing.
- Permit violations resulting from unauthorized maintenance bypassing will result in enforcement action/penalties.
- If wastewater treatment facility maintenance results in significant construction or process modification, plans must be submitted to the MPCA for review. Plans must be signed by an engineer registered in the state of Minnesota.
- All submittals or questions regarding scheduled maintenance bypassing should be directed to MPCA Municipal Section Enforcement personnel.
For assistance or further information regarding scheduled maintenance bypassing, call the Customer Assistance Center at 651-297-2274 or 800-646-6247.