mpca mn river and ww facilities

7/29/2019 MPCA MN River and WW Facilities

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Wastewater Facilities,

Phosphorusand

the Minnesota River

Wendy Turri

Municipal Wastewater Manager

Minnesota Pollution Control Agency


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3/12

Background

Historically we have seen low dissolved oxygen in the lower 22

miles of the MN River during low flow. 1988 - low flow conditions, fish kill at Lake Pepin.

1992 MN River listed as an impaired water for low dissolved

oxygen during low flowconditions.

2004

EPA approves MN River

Low dissolved oxygen TMDL.


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River depth increases from ~ 3 ft to 10 ft in navigational channelFlow velocity in navigational channel decreasesAlgae sink to the bottom of the channel, receive limited/no sunlight,

die offBacteria use oxygen to consume decaying algae

Algae in MN River


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TMDL Study Results

River needs a 5 mg/L Dissolved Oxygen at low flow.

We need to reduce phosphorus amounts duringlow flows.

The phosphorus sources during low floware:

14.4%

0.2%

4.0%

65.1%

16.3%

Wastewater Facilities

(39 facilities are 91 % of this)

AgricultureStormwater

Other &natural

Directdischarges (non-compliant ISTS)


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Reducing Phosphorus from Wastewater Facilities

Issued a Wastewater Permit that required/allowed:1. 39 largest Wastewater Facilities to reduce by 51 % in

10 years.

2. Trading

-Trading is a reallocation of phosphorus from one wastewater plants toanother.-Each trade retires a % of Phosphorus (existing 10 % and new 20 %).

3. Plan for reduction at Smaller Wastewater Facilities.

4. Plan for addressing Unsewered Communities.


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Wastewater Permit Results

7 new wastewater facilities in MN Basin, all by tradingphosphorus credits.

Average of 19 trades per year.

ALL of the 13 unsewered are addressed.

All smaller wastewater facilities are doing:-Phosphorus monitoring and Phosphorus Management Plans-4 have upgraded and have capped phosphorus amounts

39 large wastewater facilities

are meeting their phosphorusreduction goals.


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River Results1980

August 12-17

2006

August 31

September 12

2012

August 3 - 24

Mean Flow (cfs) @Jordan on lowest DO day

741 1,010 1220

Mean Temp Con lowest DO day

23.4 22.4 27.8

DO (mg/L)lowest daily mean

4.2 5.3 5.1

TP (ug/L)Range observed at most

downstream station

140

200 145

202 85

110

Chl-a (ug/L)Range observed at most

downstream station

44 98 38.7 81.5 26.1 50.2


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Conclusions

No violations of the 5 mg/L oxygen standard.

Much lower phosphorus. Wastewater improvements have translated to

significant improvements in the water quality.

Able to maintain oxygen standard atlower flows than in the past.


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Questions?

mpca mn river and ww facilities

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