Turbidity TMDLs and associated TP reductions

1. Turbidity TMDLs and associated TP reductions Effluent limits unit Dec 2010

2. Turbidity TMDLs • Minnesota has been working on turbidity TMDLs for approximately the past decade • These TMDLs are grounded in substantial modeling efforts • Minnesota River has most extensive modeling • MPCA has both approved and draft turbidity TMDLs

3. Turbidity TMDLs in MN

4. TP is often associated with TSS • Phosphorus is often adsorbed to sediment particles • BMPs to reduce TSS will have multiple benefits: • Increase water clarity • Reduce loading of sediment bound parameters such as TP and total Hg

5. One parameter vs many • Nonpoint and point source stakeholders have emphasized that we need to consider multiple parameters in TMDLs • New upgrades and/or BMPs for each pollutants are not efficient • Funding for modeling is limited so we need to utilize existing modeling • The MPCA has made a commitment to the legislature, taxpayers, and regulated parties to implement watershed management

6. Minnesota River Basin • Existing TMDL for low dissolved oxygen TMDL • Requires TP reductions for 40 point sources • Requires that small mechanical facilities and ponds maintain existing load • Draft TMDL for turbidity (includes major tributaries) • Extensive modeling with TP outputs • Lake Pepin Eutrophication TMDL (on-hold) • TP allocation for Minnesota River Basin

7. Nutrient Impairment Turbidity Impairment

8. Fort Snelling Jordan Lake Pepin

9. MN River modeling • HSPF model; assist with completion of the Minnesota River turbidity TMDL • Five reduction scenarios with various BMPs were completed • Point sources were included in modeling with limits set close to WLA for lower Minnesota River low DO TMDL

10. MN river basin example • Draft Lake Pepin eutrophication TMDL requires 50% reduction of TP loads from the MN river at Fort Snelling • HSPF model outputs are for the MN R. at Jordan • 40 miles upstream of Fort Snelling • 2 large point sources between Jordan and Fort Snelling • Reductions needed to meet MN R. turbidity TMDL between scenario 4 and 5 of the HSPF model • At this point, we feel that the requirements of the low DO and turbidity TMDLs are sufficient to meet the draft allocations of the Lake Pepin TMDL

11. HSPF model output for the MN R turbidity TMDL

12. Example BMPs for MN R. • Increase in the area of pasture, Conservation Reserve, and perennial crop lands, • Increased adoption of conservation tillage, • Elimination of surface tile drain inlets, • Reduction in ravine erosion through use of drop structures on tile drain outlets, • Detention of the first inch of runoff from cropland near the source area, • Infiltration of the first inch of runoff from urban land in MS4 areas, • Reduction in sediment load from urban land outside MS4 boundaries, • Reduction in rates of bluff collapse, and • Rehabilitation of channels to reduce bed and bank erosion in the bluff reaches.

13. Non-point reductions required to meet reservoir TP targets • Many points sources have reduced TP loads in the past decade by 60-90 percent • Even if we put all point sources at the lake/reservoir standards, concentrations in lakes/reservoirs will exceed standards • Existing draft TMDLs for lakes/reservoirs with large watersheds • Balance of point and non-point reductions • Recognition of spatial and temporal dynamics of nutrient loads to reservoirs

14. Summary • Reduction of non-point TP is essential to meet targets of the Lake Pepin eutrophication TMDL • Modeling for the Minnesota River Basin demonstrates that TP targets for Lake Pepin can be achieved if turbidity targets are achieved • Modeling also meets proposed river nutrient standards • We feel that is a defensible method of estimating non-point reductions for WQBELs