February 18 Research Spotlight
Title: Detecting phosphorus release from stormwater ponds to guide management and design
Presented by: John Gulliver, PhD; Professor, Department of Civil, Environmental and Geo- Engineering, Engineering and St. Anthony Falls Laboratory, University of Minnesota and/or Jacques Finlay, PhD; Professor, Department of Ecology, Evolution and Behavior and St. Anthony Falls Laboratory, University of Minnesota
There is growing concern that aging stormwater retention ponds may become net sources of phosphorus (P) to receiving waters. Release of P previously deposited in sediments (i.e. internal loading) is a major contributor to eutrophication in lakes. Stormwater ponds often have high external P loading, and other characteristics that may increase the likelihood of internal loading as ponds age. However, stormwater ponds have received comparatively little research attention, even though they are widely used with the intended goal of permanent immobilization of phosphorus. The ability of these systems to retain phosphorus over their lifespan is essentially unknown. The proposed research will build understanding necessary to assess the capacity of stormwater ponds to retain or release phosphorus in Minnesota’s stormwater pond infrastructure. The projects aim to develop methods for rapid and efficient identification of pond phosphorus release, to guide management of existing ponds, and to reveal factors that underlie poor performance for P removal. The results of this project will be used to inform and improve pond maintenance, pond design and decision making around construction of new ponds, and to ultimately improve the water quality of our lakes, rivers and wetlands.
Title: Pond Treatment with Spent Lime to Control Phosphorus Release from Sediments
Presented by: Greg Wilson, Barr Engineering Company
Sedimentation ponds that accumulate particles and phosphorus in stormwater runoff are a standard and widely applied storm water best management practice. However, just as internal loading occurs in lakes during warm summer periods when the potential for oxygen depletion is greatest, aging ponds have the potential to release more phosphorus than is captured during summer months (Watershed Protection Techniques, Technical Note 102). Dredging is a potential, but expensive, option to improve pond performance, but phosphorus release may occur long before a pond is filled with sediment. Areal applications of alum and iron can control phosphorus release, but incur raw material production costs.
In cooperation with SPRWS, City of White Bear Lake, RWMWD, and VLAWMO staff, Barr Engineering proposes this study to evaluate the application of spent lime (amorphous calcium carbonate from drinking water treatment) to pond sediments to reduce phosphorus release during warm summer months. Spent lime can reduce phosphorus release by forming calcium phosphate and potentially by increasing the pH of the treated sediments to facilitate iron and aluminum phosphate binding. This study includes a laboratory and a field component and is intended to validate large-scale applications. The laboratory component includes the addition of spent lime at a range of doses to phosphorus rich pond sediment to determine optimal spent lime dosing. The field component involves the addition of spent lime to two ponds and monitoring to determine the magnitude of reduced phosphorus release, evaluate cost-effective methods for areal application and quantify the benefits of this water treatment byproduct.