Greetings, stormwater professionals:

Please see the E-mail below and forward this on to your stormwater colleagues in your state.

Here in Minnesota, we are finding that a number of our constructed stormwater ponds are phosphorus sources instead of sinks. What does it mean that one of our oldest, simplest, and best-understood (we thought) stormwater control measures is functioning in such an unexpected manner?

This will be the focus of presentations and a discussion on July 19th. We have invited regulators from USEPA and the MN Pollution Control Agency to participate in a panel discussion after a couple technical presentations.

The event is scheduled for Saint Anthony Falls Laboratory (SAFL). SAFL will have it available via the Web. Please sign up to attend using this very short survey form:

We will send you additional information using the E-mail address you provide via the survey form.

You can find more information on this topic at these Web sites:

Please note that the agenda times are in Central Daylight Time.


Randy Neprash, PE
Staff, Minnesota Cities Stormwater Coalition
Direct 651-604-4703
Cell: 651-271-5535


From: Neprash, Randy
Sent: Tuesday, July 10, 2018 11:59 AM
Subject: MCSC News – Event to discuss phosphorus in stormwater ponds – July 19th

Greetings, stormwater professionals:

MCSC is presenting a technical discussion on phosphorus in constructed stormwater ponds. We are doing this in partnership with the good folks at Saint Anthony Falls Laboratory.

Here are the event details:

Date: Thursday, July 19th

           Time: 9:00 AM to noon

           Place: Saint Anthony Falls Lab       2 Third Avenue SE, Minneapolis, MN 55414

           Cost: Free

We request that you use this short survey form to sign up to attend.


9:00 AM – Presentation by Dr. John Gulliver, SAFL, U of MN – “Pollution from Urban Stormwater Ponds”

9:30 AM – Presentation by Joe Bischoff, Wenck – “Limitations of Using Stormwater Ponds for Phosphorus Control”

10:00 AM – Panel discussion

10:50 AM – Break

11:00 – Tour of SAFL

There are a few things to note about this event:

  • This is not just a presentation of technical papers. We will have a panel discussion to talk about the real-world meanings of all this – for water quality and regulations. We have invited USEPA and MPCA to participate on the panel. You will have a chance to ask questions.
  • This is an exciting partnership between MCSC and SAFL. SAFL is one of the most remarkable water research facilities in the world. They do a significant amount of important and useful urban stormwater research. This is a chance to get a comprehensive tour of this amazing place.
  • This is an important current issue in urban stormwater. We are finding that a number of our constructed stormwater ponds are sources of phosphorus, rather than sinks. This is an opportunity to better understand this issue and discuss the impacts.
  • You can attend this event in-person or via the Web. SAFL does a great job of making presentations accessible through the Web.

Please be sure to use the survey form to sign up to attend. We will use the information you provide to get additional information and details about the event to you soon.



Pollution from Urban Stormwater Ponds

By John S. Gulliver


Stormwater ponds are primarily designed to remove solids and phosphorus before runoff reaches the receiving water body.  These ponds are ubiquitous in many urban landscapes, but are not given much consideration post-construction. High total phosphorus (TP) concentrations from pond grab sample data in Minnesota suggest that many urban stormwater ponds may be releasing phosphorus (P) to receiving water bodies, which we believe is due to high internal P loading. Laboratory incubations of intact sediment and water cores suggest that mobile-P concentrations (iron-bound P, loosely-bound P, and labile organic P) in pond sediments and sediment oxygen demand (Smax) are indicators of P release potential. Actual observed P release was negligible in the presence of dissolved oxygen (DO) above a concentration of 1 mg/L. However, field monitoring revealed that several shallow stormwater ponds in the Twin Cities Metro Area are so strongly stratified during the spring and summer months that they prevent diurnal mixing and reoxygenation of the water column from periodic storm events. This resulted in anoxic conditions (<1mg/L) at the sediment-water interface throughout much of the year, which would facilitate P release into the water column and downstream receiving water bodies.

Slides from recent presentation by Joe Bischoff – Jan. 9, 2018