mpca mn river and ww facilities
TRANSCRIPT
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Wastewater Facilities,
Phosphorusand
the Minnesota River
Wendy Turri
Municipal Wastewater Manager
Minnesota Pollution Control Agency
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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?