Greetings, stormwater professionals:

This item is of interest to anyone who has one or more constructed ponds in your city.

Our event on Phosphorus Release in Stormwater Ponds went very well. This was a joint presentation by the Minnesota Cities Stormwater Coalition and Saint Anthony Falls Laboratory.

Here in Minnesota, we have recently found that a number of our constructed stormwater ponds are releasing and discharging significant amounts of phosphorus from sediments. This is the reverse of the expected net phosphorus retention that we expect. This raises a number of important questions. We thought these could be best addressed through an event that involved a couple research presentations and a panel discussion with researchers, local implementers, and state/federal regulators. Our panelists were:

Dr. John Gulliver, U of MN, SAFL

Eric Macbeth, City of Eagan

Dr. Claire Bleser, Riley-Purgatory-Bluff Creek Watershed District

Mike Findorff, Minnesota Pollution Control Agency

Ken Pantuck, EPA Region 3 (remote)

Elizabeth Ottinger, EPA Region 3 (remote)


The two presentations in the first part of the program are especially impressive and useful. The U of MN folks looked at 80 ponds and found that 32 of them have higher P concentrations than should be expected. Similar problems were found in the Shingle Creek Watershed (67 sq. mi., fully urbanized, just north and west of Minneapolis). Almost $17 million has been spent in this watershed since 2005 for water quality improvements, but they are finding higher concentrations of dissolved P (most bioavailable) now than they did in the early 2000’s (see chart below). This problem with P release in stormwater ponds may be the best explanation for this lack of progress. The presenters were:

Dr. John Gulliver – University of Minnesota, St. Anthony Falls Lab

Joe Bischoff – Wenck Associates, Inc.


You can access the video/audio for the entire event here. Please see the end of this message for details.

Phosphorus Release in Stormwater Ponds                     Thursday, July 19, 2018
Play recording (2 hr 11 min)                                          (This recording does not require a password.)

When you click on “Play recording” above, the event should open up in the Webex player on your computer. You  may need to have your IT staff help you install some software. Please let me know if you have problems accessing this. The audio starts at 1:18 into the recording. It is silent until then.

I came away for this more convinced that this is a legitimate issue that deserves serious attention. I think the next best step is convene a relatively small group to identify and list the set of questions that should be addressed. Once we have this list, we can:

  • Put the questions into useful, related groups
  • Determine which questions should be addressed first, which questions must be addressed sequentially, and which questions can be addressed simultaneously
  • Begin to discuss how to get answers
  • Begin to determine the best and most appropriate next steps.

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Please forward this E-mail message to your colleagues who would find it interesting and/or valuable.



Randy Neprash, PE

Vice-Chair, National Municipal Stormwater Alliance

Staff, Minnesota Cities Stormwater Coalition

Land: 651-604-4703

Cell: 651-271-5535






Here is some information to view the event most efficiently:


  1. The audio starts at 1:18 into the recording. It is silent until then.


  1. My intro – 00:01:18 to 00:14:00


  1. Dr. John Gulliver’s presentation – 00:14:00 to 00:46:15


    1. Gulliver’s summary – 00:39:25 to 00:42:02 (see below for slide)


  1. Joe Bischoff’s presentation – 00:46:30 to 1:19:50


    1. Bischoff’s summary – 01:18:15 to 01:19:30 (see below for slide)


  1. Q & A and panel discussion – 01:19:50 to 02:11:35



Graphics (also attached as files)



Gulliver’s summary slide



Bischoff’s summary slide