10-21-2004 Council Work SessionA

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Executive Summary The Minnehaha Creek Wiatrihed District (MCWD) 2003 Hydrologic Data Report indicates that the current Stubbs Bay water qa-.Kty would only support restricted use, based on the average total phosphorus concentration. Based on the average chloroph> 11-a concentration, Stubbs Bay should be subject u» nuisance algal blooms 50 percent or more of the time. In 2002, MCWD Managers authorized an investigation of Stubbs Bay after the City of Orono expressed concerns about its water quality. A diagnostic report, intended to evaluate the total phosphorus loadings to Stubbs Bay, was completed in 2004. As a follow-up to the diagnostic study, this report has been prepared to discuss the feasibility analysis for controlling phosphorus loads and improving water quality in Stubbs Bay. fliis report is intended to: • Summarize conclusions from previous studies that discuss watershed and internal pho.sphorus loadings and the resultant water quality of Stubbs Bay • Update the water quality response modeling for the planned (2020), full development land uses and use it as a benchmark for evaluating expected water quality improvements • Preseivt the results of this feasibility analysis to consider and evaluate the expected cost, feasibility and benefits of several water quality improvement options • Provide recommendations for further evaluation and/or implementation of specific water quality improvement options Based on the projected 2020 land uses, conversion of undeveloped and agricultural property will increase the residential land use percentage to approximately 80 percent of the upland area. Roadways will represent another 7 percent of the projected land use. Comparing the two land use coverages rev eals that approximately 983 acres (56% of the watershed area) will be developed or redeveloped by 2020. Of this area, approximately 314 acres have soils that should be appropriate for infiltration practices. Fach of the in-lake improvement options- in-lake alum application, hvpolimnctic aeration, diffused aeration and artificial circulation are expected to improve the water quality in Stubbs Bay to approximately the sanv* level. However, the annualized cost per unit decrease in total phosphorus concentration is at least twice as high for hypolimnctic aeration, compared to the other optior^, while the cost of artificial circulation is approximately two-thirds of the cost for an in-lake alum P U3V27\f ImDiaU Stubbs Hiy Feasibility Study doc