Implementing river nutrient standards

1. Implementing river nutrient standards Dennis Wasley and Steve Weiss

2. Overview • How effluent limits are set • River nutrient standards • Summer average • Long-term average • Response variables • Non-point sources are very important • Streamflow • Examples

3. Effluent limits 101 • Establish background concentration of stream • Calculate load from facility • Determine if load from facility drives concentration in stream above standard during a critical condition • Dilution is the solution

4. Effluent limits 101 (RNS standards) • Establish background concentration of stream • Background concentration is dynamic for TP over summer period • Calculate load from facility • Standard applies during wet and dry times • Determine if load from facility drives concentration in stream above standard during a critical condition • Requires extensive concentration and flow data for stream • Dilution is the Solution • High flows do not always offer dilution

5. There is more than 1 way to meet 150 ug/L (ug/L) High flow Low flow

6. Single flow vs all flow (ug/L) 122Q10

7. Source contributions

8. Flow considerations • Very difficult to pick one flow to set limits on that would protect long-term summer average • High flows can be very high in TP • Important for downstream resources • Zero flows can occur in headwaters and western streams • How far downstream does effluent travel during low flows • Impact of zero flows on long-term average?

9. Examples

10. Bigfork River (meets RNS) High flow Low flow

11. Bigfork River (daily loads)

12. Bigfork River • Very minimal point sources • Non-point only exceeds standard at highest flows • This is expected and complies with RNS • Downstream impairment in Lake of the Woods (LOW) • Existing limits in Bigfork watershed will be adopted by LOW TMDL • Boise Cascade, North Kooch larger point sources • Complicated lake

13. Cottonwood River • TP exceeds RNS at watershed outlet • Response data is very limited • Downstream rivers do exceed both TP and response variable • Extensive non-point sources in cottonwood and downstream watersheds

18. Point source locations in Cottonwood Minnesota R. at Jordan Cottonwood at New Ulm Minnesota R. Mankato

19. HSPF modeled TP for the Minnesota River downstream of Mankato

21. Cottonwood: proposal • Very minimal point sources • No point source signature during low flow • Non-point drives impairment • Clearly exceed standards above median flow • Focus on non-point and set point source limits to protect MN River • Minnesota needs considerable non-point reductions and some point source reductions • Balanced approach to point sources in Minnesota R watershed

22. South Fork Crow River • Large point and non-point contributions • Recent point source reductions • Clearly exceeds TP and response variables of RNS • Restrictive WWTP limits and considerable non-point reductions will be needed to meet RNS

23. SF Crow River (high TP at all flows)

25. SF Crow loads

26. SF Crow • Considerable non-point reductions needed • Very difficult to drive concentration at moderate to high flows below 0.150 mg/L • Non-point trading options • Existing point sources overwhelm background at moderate to low flows • Could assume 0.075 – 0.10 mg/L based on other watersheds • Tremendous algal production at low flows • Low flow is really low flow in SF Crow?

27. Use available data to determine status of receiving reach and impact of point source on that reach (reasonable potential) Immediate stream exceeds TP standard No data at receiving reach Focus on downstream CWLSS or representative reach Limited response data or acceptable response data in immediate reach Response variables exceeded in immediate stream: Set limits to meet TP standard in immediate stream reach River meets TP standard Collect more data at receiving reach, Set TP limits based on downstream response Existing Facilities: Evaluate if existing design limits are sufficient to protect downstream waters (e.g. St. Cloud WWTP) Expanded/New Facilities:Design plant to meet RNS and applicable nondegradation requirements. Protect downstream waters. One permit cycle TP and response variables exceed standards in immediate reach Response variables do not exceed standards in immediate reach Maintain TP limits to protect downstream resources

28. Headwaters / small rivers • If good data for TP, response and flow • Proceed with same process as outlined in examples • Limited data at immediate reach • Set limits for downstream impairments • Require additional monitoring for immediate reach • Flow • TP • Response varibles

29. Stream description Suspended algae Periphyton Headwater stream Very limited Common dependent on habitat (1-2 order) Large stream Limited? Common dependent on habitat (HUC 10 ) Need more data River Common Present dependent on habitat (HUC 8) Large River Abundant Limited in main channel (6-8 order)

30. SF Crow River 10X sampling sites

31. Other considerations • Seasonal relief (no downstream lakes) • State rule for October-March/April • RNS limit for April/May-September • Pond discharges • Adjust discharge window in watersheds where restrictive limits are needed • Maintain limits in watersheds where meet RNS or non-point is the major source reduction needed

32. Summary • Set limits on downstream reach with adequate data to make calculations • MPCA wants to be right the first time • Watershed approach, TMDLs and additional monitoring will refine original limit calculations • Non-point reduction considerations are critical to our approach • This is especially true during moderate to high flows

33. Point Source Primary Load Source Non Point Source Moderate Resource Restored Ex. Rum River Moderate Restoration dependent on np reductions Ex. Cottonwood Small Necessary Load Reduction Restrictive significant wq improvement Ex. Headwater stream with large point source (likely no immediate response) Moderate  Restrictive If necessary np reductions approach max feasible level, ps limits approach very restrictive. Ex. SF Crow Large wq = water quality np = non point source Limit Range Comment Examples