Guidance for Issuing NPDES Permits for Discharge to Impaired Waters: New and Existing/Expanding Facilities
In a decision issued on May 17, 2007, the Minnesota Supreme Court upheld the Annandale and Maple Lake NPDES (National Pollutant Discharge Elimination System) permit for construction of a joint wastewater treatment facility with a discharge upstream of impaired waters in advance of an approved TMDL. In the majority opinion of the court, the permit represented a reasonable interpretation of the Clean Water Act (CWA) by allowing a reduction of phosphorus discharged at one facility to make up an increase of phosphorus discharged at another facility in the same watershed. Based on this ruling, the MPCA developed guidance for issuing permits to facilities intending to discharge to impaired waters. The guidance applies to phosphorus as well as other pollutant discharges for which a downstream impairment exists.
Federal regulations
Federal Regulations 40 C.F.R 122.4(i) and 40 C.F.R 122.44(d)1 have the primary purpose of ensuring that impaired waters are not further degraded before a TMDL is complete.
Enacted in the early 1980s, these regulations fulfill the Clean Water Act objective to restore and maintain the chemical, physical, and biological integrity of the nation’s waters. 40 C.F.R. § 122.4(i) prohibits the net increase of any pollutant that will cause or contribute to a numeric or narrative water quality standard violation. 40 C.F.R. § 122.44(d) requires effluent limits in permits to ensure discharges do not cause, have a reasonable potential to cause, or contribute to the violation of a numeric or narrative water quality standard.
Affected facilities
New facilities proposing a discharge of a pollutant for which a downstream impairment exists may be affected by 40 CFR § 122.4(i). Facilities are affected:
- If the proposed discharge contains a pollutant of concern that would impact an identified impairment, and
- If no approved TMDL is in place for the pollutant of concern.
If an approved TMDL is in place for the pollutant of concern, the facility must meet the conditions of the TMDL.
Existing facilities determined to have reasonable potential to cause or contribute to an immediate or downstream impairment and expanding facilities proposing additional discharge to or upstream of an impaired surface water may be affected by 40 CFR § 122.44(d)1. Facilities are affected:
- If the proposed discharge contains a pollutant of concern that would cause or contribute to an identified impairment, and
- If no approved TMDL is in place for the pollutant of concern.
If an approved TMDL is in place for the pollutant of concern, the facility must meet the conditions of the TMDL.
Consistent with 40 CFR § 122.44(d) all facilities with reasonable potential to cause or contribute are required to have water-quality-based effluent limits (WQBELs) in their NPDES permits. Upon permit reissuance, even if a TMDL is not yet complete, the NPDES permit must include a WQBEL and, if appropriate, a schedule of compliance to achieve the WQBEL, as soon as possible. WQBELs developed in advance of a TMDL should consider available draft TMDL waste load allocations. If a schedule of compliance is included, the permit must also include interim limits to assure that the existing discharge does not further contribute to the downstream impairment.
Potential impacts of new and expanding discharges on downstream impaired waters will be considered on a case-by-case basis. Some of the factors that will be considered include:
- Whether the discharge is at a concentration greater than the applicable numeric standard.
- Whether the discharge upstream of the impaired water at a concentration greater than the applicable standard is determined, through modeling or other means, to have a measurable effect on the downstream conditions.
- Whether the pollutant from the discharge is delivered to the downstream impaired water at a concentration greater than the standard.
Discharge alternatives
To meet the requirements of Federal Regulation 40 CFR § 122.4(i), affected facilities have the following options:
- Eliminate all surface water discharge by using land treatment options such as spray irrigation, rapid infiltration basin, or soil treatment systems.
- Implement pollution prevention actions or treatment to eliminate the source of the pollutant.
- Discharge to a permitted wastewater treatment facility that has capacity to treat the pollutant in question, ensuring that the facility does not exceed current mass allocations.
- Participate in pre-TMDL trading by purchasing pollutant load from another facility.
To meet the requirements of Federal Regulation 40 CFR § 122.44(d)1, affected facilities have the following options:
- Provide treatment to meet the applicable WQBEL. If a schedule of compliance is determined to be appropriate, make interim reductions in pollutant load and/or concentration such that ultimate compliance with the WQBEL is attained as soon as possible.
- Eliminate some or all surface water discharge by using land treatment options such as spray irrigation, rapid infiltration basin, or soil treatment systems.
- Initiate pollution prevention actions to reduce source pollutant to meet the mass limit.
- Discharge to a permitted wastewater treatment facility that has available phosphorus capacity.
- Participate in pre-TMDL trading by purchasing the needed pollutant load from another facility.
For more information
Municipal Division
Lisa Thorvig , Director
520 Lafayette Road N
St. Paul, MN 55155
lisa.thorvig@state.mn.us
Wendy Turri, Wastewater Manager
18 Wood Lake Drive SE
Rochester, MN 55904
wendy.turri@state.mn.us
Industrial Division
Jeff Smith, Director
520 Lafayette Road N
St. Paul, MN 55155
jeff.smith@state.mn.us
Jeff Stollenwerk (acting) Permitting Manager
520 Lafayette Road N
St. Paul, MN 55155
jeff.stollenwerk@state.mn.us
Environmental Analysis and Outcomes
Mike Sandusky, Director
520 Lafayette Road N
St. Paul, MN 55155
mike.sandusky@state.mn.us
Shannon Lotthammer, Assessment Manager
520 Lafayette Road N
St. Paul, MN 55155
shannon.lotthammer@state.mn.us
