Sedimentation ponds that accumulate particles and phosphorus in stormwater runoff are a standard and widely applied stormwater 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. Aerial 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 aerial application and quantify the benefits of this water treatment byproduct.