Text description of " Research on Pond Remediation Technology" poster

John Gulliver, Civil Environmental and Geo-Engineering, University of Minnesota

Jacques Finlay, Ecology, Evolution and Behavior, University of Minnesota

Poornima Natarajan, St. Anthony Falls Laboratory, University of Minnesota

Ben Janke, St. Anthony Falls Laboratory, University of Minnesota

Bill Herb, St. Anthony Falls Laboratory, University of Minnesota

Joe Bishoff, Barr Engineering

Bill Selbig, United States Geological Service

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Introduction

Phosphorus is the limiting nutrient in freshwater bodies. When phosphorus is added to a water body it will cause algae blooms, resulting in blue green algae which can release toxic chemicals. roughly 40% of the lakes aross the US are impaired due to excess phosphorus and the resulting eutrophication. We discoevered in 2016 that stormwater ponds are not well-mixed, but are stratified due to the high level of sheltering from the wind. The result is that many ponds have low dissolved oxygen levels near the bottom, with internal phosphorus loading from the sediments. We are now working on remediation technologies for ponds that have high internal phosphorus loading to avoid phosphorus export to receiving water bodies.

Research Questions

What is the most effective means of reducing phosphorus export from stormwater ponds?
Which is the most cost-effective remediation method?
What recommendations can we make?

Photo of pond covered in algae

Methods

We started the investigation with a computer model that was a revision of the MinLake model developed by Prof. Heinz Stefan and students over many years. We converted it to the MinPond model by adding extreme sheltering and floating plant cover to the model, as shown in Figure 1. The result is a model that can have stratification of the pond in the vertical direction with temperature, chloride, dissolved oxygen, etc. Then we placed various remediation techniques into the model: alum treatment, iron filings treatment, aeration, sheltering removal, watershed treatments, etc., and computed the cost of each treatment on six ponds.

Image of Figure 1. Schematic representing the variable present in MinPond

We also tried some of the remediation techniques in the field on stormwater ponds, by measuring pond parameters before and after each treatment, including sediment characteristics.

Photo of kayaks in pond

Photo of device in algae covered pond

Photo of soil/water samples

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Results

MinPond results are summarized in Table 1. Not shown are sheltering removal, intelligent water level control and pond lining, which had only minor effects. Dredging and aeration are variable and under field investigation.

We have tested the following remediation techniques on 17 ponds: 3 iron treatment, 4 alum treatment, 5 dredged, and 4 with aeation (currently in progress). Sample results are shown in Figure 2 (alum), Figure 3 (iron), and Figure 4 (dredging) for the ability to reduce phosphorus release from the sediments.

Table 1. Summary of pond TP export reductions and the associated annual costs over 10 years of simulated phosphorus export.

Figure 2. Anoxic sediment release of phosphorus before and after treatment with alum in two ponds.

Figure 3. Anoxic sediment release of phosphorus before and after treatment with iron filings.

Figure 4. Anoxic sediments phosphorus release before and after treatment by dredging in five ponds.

The research indicates that alum treatment works the best, and is still working after 5 years; iron treatment works as well, but only for approximately 5 years, and dredging sometimes partially works and sometimes does not work, depending on the specifics of the pond depth and sediment.

Discussion

We found that eliminating trees around ponds, installing and operating intelligent water level control and lining ponds did not have a substantial effect upon phosphorus export from stormwater ponds. Iron filings placement on pond sediments is effective for about five years, but alum treatments are effective for more than five years. Both remediation technologies are cost-effective. An intensive street sweeping program, designed to reduce inflow to ponds by 25%, is the most cost-effective means of reducing phosphorus export. The combination of alum treatment and intensive street sweeping will be a powerful combination designed to reduce phosphorus export from stormwater ponds. We are currently investigating aeration/mixing techniques as a viable remediation technique for phond phosphorus export.

Acknowledgments

Supporters of this research were the Minnesota Stormwater Research Council and the Minnesota Department of Transportaion based upon recommendations from the Local Road Research Board. We thank all the individuals who advised and reviewed the projects, the cities that allowed access to their ponds, and the many staff and students who worked on both projects.

Sources

Herb, W., P. Natarajan, B.D. Janke, J.S. Gulliver and J.C. Finlay, (2026). Wet Pond Modeling for Contaminant Retention and Maintenance, MnDOT Report, In preparation.
Effectiveness of Remediation Techniques on Pond Phosphorus Release Rates, (2024-2027). Funded by the Minnesota Stormwater Research Council.
Taguchi, V.J., Olsen, T., Natarajan, P., Janke, B.D., Gulliver, J.S., Finlay, J.C. and Stefan, H.G. (2020). Internal Loading in Stormwater Ponds as a Phosphorus Source to Downstream Waters, Limnology and Oceanography Letters, 5(4), 322-330.

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